To understand the mechanics of the petrodollar, we have to look past the diplomacy and into the cold math of international trade and monetary policy. This system essentially functions as a global “tax” on energy consumers that subsidizes the American capital market.

The Economic Model: The Triffin Dilemma and Petrodollar Recycling

The petrodollar system is a practical solution to the Triffin Dilemma, which suggests that a country whose currency is used as a global reserve must be willing to run large trade deficits to provide the world with the liquidity it needs.

The “Recycle” Equation

The flow of petrodollars can be modeled as a closed-loop system. When an oil-importing nation (Nation A) buys oil from an OPEC member (Nation B), the transaction follows this fundamental identity:

GNDI = C + I + G + (X – M) + NIA

Where:

$GNDI$ : Gross National Disposable Income
$X – M$ : Trade Balance (Exports – Imports)
$NIA$ : Net Income from Abroad (Petrodollar reinvestments)

In this model, the Capital Account Surplus of the U.S. must offset the Current Account Deficit. The “Petrodollar Recycle” ensures that the surplus revenue from Nation B flows back into U.S. assets (Treasuries, Real Estate, Stocks), effectively financing the U.S. deficit.

Quantitative Comparison: Petrodollar vs. Traditional Trade

The table below illustrates how the petrodollar system differs from a standard bilateral trade agreement between two nations using their own local currencies.

Feature	Standard Bilateral Trade	Petrodollar System
Currency Risk	Both nations face exchange rate volatility.	Risk is borne by the importer; the U.S. is insulated.
Reserve Demand	Moderate; based on trade volume.	Extreme; mandatory for energy security.
Interest Rates	Determined by local central bank policy.	Suppressed; high demand for U.S. debt lowers yields.
Sanction Power	Limited to direct trade.	Total; exclusion from the dollar system halts oil imports.

Modelling the “Exorbitant Privilege”

The economic “privilege” mentioned earlier can be expressed through the Seigniorage value. For the U.S., the cost of producing a dollar is negligible, but its value is tied to the energy output of the world.

If we look at the demand for dollars (

L

), it is a function of global oil prices (

P_o

) and the volume of oil traded (

Q_o

L_d \approx f(P_o \cdot Q_o) + \sum (Reserves)

Because

P_o

is denominated in USD, any increase in oil prices actually strengthens the demand for the dollar, creating a paradoxical “energy-backed” stability for the currency.

Impact on Global Trade Balances

The petrodollar creates a unique “Balance of Payments” (BoP) structure. Below is a simplified representation of how funds move when oil is purchased by a third party (e.g., India) from an oil producer (e.g., UAE).

The Trade Flow Model

Demand Generation: India must sell goods/services to the world to acquire USD.
Transaction: India pays UAE in USD for oil.
Recycling: UAE has more USD than it can spend locally; it “recycles” these by purchasing U.S. Treasury Bonds.
U.S. Benefit: The U.S. government uses the proceeds from these bond sales to fund domestic infrastructure or military spending at low interest rates.

Summary of Economic Significance

The petrodollar isn’t just a medium of exchange; it is a synthetic demand generator. By anchoring the world’s most essential commodity to a single currency, the U.S. ensures that its debt remains the world’s most “liquid” asset. However, as nations move toward bilateral clearing houses (using local currencies for trade), the

L_d

equation starts to weaken, potentially leading to higher domestic inflation and interest rates for the U.S. economy.

Now let us insert more content to the same blog post from various other sources.

First I will show you how to add content via image/PDF.

RI 9419

REPORT OF INVESTIGATIONS/1992

PLEASE DO NOT REMOVE FROM LIBRARY

LIBRARY SPOKANE RESEARCH CENTER RECEIVED

AUG 7 1992

US BUREAU OF MINES E. 315 MONTGOMERY AVE. SPOKANE, WA 99207

Gallium and Germanium Recovery From Domestic Sources

By D. D. Harbuck

UNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF MINES

Mission: As the Nation’s principal conservation agency, the Department of the Interior has responsibility for most of our nationally-owned public lands and natural and cultural resources. This includes fostering wise use of our land and water resources, protecting our fish and wildlife, preserving the environmental and cultural values of our national parks and historical places, and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also promotes the goals of the Take Pride in America campaign by encouraging stewardship and citizen responsibility for the public lands and promoting citizen participation in their care. The Department also has a major responsibility for American Indian reservation communities and for people who live in Island Territories under U.S. Administration.

Report of Investigations 9419

Gallium and Germanium Recovery From Domestic Sources

By D. D. Harbuck

UNITED STATES DEPARTMENT OF THE INTERIOR Manuel Lujan, Jr., Secretary

BUREAU OF MINES T S Ary, Director

Library of Congress Cataloging in Publication Data:

Harbuck, D. D. (Donna D.)

Gallium and germanium recovery from domestic sources / by D.D. Harbuck.

p. cm. — (Report of investigations; 9419)

Includes bibliographical references (p. 25).

Supt. of Docs. no.: I 28.22:9419.

Gallium—Metallurgy. 2. Germanium—Metallurgy. 3. Leaching. 4. Solvent extraction. I. Title. II. Series: Report of investigations (United States. Bureau of Mines); 9419.

TN23.U43 [TN799.G3] 622 s—dc20 [669′.79] 92-6230 CIP

Page

Abstract 1

Introduction 2

Identifying domestic sources 2

Leaching of zinc residue 3

Background 3

Statistical determination of significant variables 3

Batch testing of significant variables 3

Improving germanium extraction from zinc residues 6

Germanium insolubility during roasting 6

Germanium insolubility during leaching 7

Methods for overcoming germanium insolubility 9

Leaching of germanium-gallium ore 10

Background 10

Results and discussion 10

Germanium extraction 11

Two-stage countercurrent leaching 11

Increasing germanium extraction 13

Gallium and germanium solvent extraction from $\mathrm{H}_2\mathrm{SO}_4$ solutions 14

Gallium solvent-extraction background 14

Germanium solvent-extraction background 14

Solution preparation and analysis 15

Initial solvent-extraction testing 15

Gallium solvent extraction 15

Iron versus gallium loading 15

OPAP and DEHPA 16

Rate and equilibrium analysis 17

Gallium loading 17

Gallium stripping 17

Ferric stripping 17

Continuous solvent extraction of gallium 17

System design 17

System operation 18

Strip liquor purification 18

Germanium solvent extraction 18

Effect of copper and iron 19

Synergism 20

Effect of acid concentration 20

Germanium stripping 20

Germanium rate and equilibrium analysis 21

Germanium loading 21

Germanium stripping 21

Iron scrubbing 21

Continuous solvent extraction of germanium 22

System design 22

System operation 22

Gallium and germanium coextraction 23

Experimental results 23

Industrial application 24

Summary 24

References 25

ILLUSTRATIONS

Stages of zinc processing … 3
Effect of percent solids on metal extraction from zinc residue … 4
Effect of H₂SO₄ addition on metal extraction from zinc residue … 4
Effect of leach time on metal extraction from zinc residue … 4
Effect of temperature on metal extraction from zinc residue … 4
Effect of adding SO₂ to H₂SO₄ leach on gallium and germanium extraction from zinc residue … 5
Effect of H₂SO₄ molarity on gallium and germanium extraction from zinc residue … 5
Solubility of GeO₂ in H₂SO₄ … 5
XRD printouts of ZnO-GeO₂ mixtures at 650°, 800°, and 950° C … 6
XRD printouts of ZnO-SiO₂ mixtures at 900°, 1,000°, and 1,100° C … 7
Shift of 2θ quartz angle with increasing amounts of GeO₂ … 7
SEM photograph of SiO₂-GeO₂ solid solution … 8
Effect of HF concentration on germanium extraction from H₂SO₄-leached residue … 10
Effect of H₂SO₄ concentration on metal extraction from gallium-germanium ore … 11
Effect of leach temperature on metal extraction from gallium-germanium ore … 12
Effect of leach time at various acid concentrations on metal extraction from gallium-germanium ore … 12
Proposed two-stage leach system … 13
Photomicrographs of gallium-germanium ore … 13
Gallium and iron extraction from reduced and reoxidized solutions … 16
Effect of pH on gallium extraction using the solvents OPAP and DEHPA … 16
Gallium equilibrium loading and stripping on 0.3M OPAP … 17
McCabe-Thiele analysis loading 0.32-g/L-Ga aqueous on 0.3M OPAP … 17
McCabe-Thiele analysis stripping 0.32-g/L-Ga loaded organic using 1.5M H₂SO₄ … 18
McCabe-Thiele analysis stripping ferric iron with 50 pct H₃PO₄ … 18
Germanium equilibrium loading and stripping on 0.2M OPAP-30 pct LIX 63 … 21
McCabe-Thiele analysis of germanium-loading isotherm, 40-g/L-H₂SO₄ solution … 21
McCabe-Thiele analysis of germanium-loading isotherm, 60-g/L-H₂SO₄ solution … 22
McCabe-Thiele analysis stripping 0.3- or 0.6-g/L-Ge loaded organic using 75° C H₂O … 22
McCabe-Thiele analysis stripping iron with 3M H₂SO₄ … 22
Effect of multiple contacts in the coextraction of germanium and gallium from zinc processing liquors … 24

TABLES

Analyses of potential gallium and germanium ores … 2
Elemental analyses of studied materials … 2
Results of statistically designed experiments … 3
2θ angles for SiO₂ under various conditions … 7
Typical analyses of leach solutions … 8
Selectivity of silica gel for germanium … 8
Effect of ZnSiO₄ addition on gallium and germanium extraction … 8
Effect of silica on germanium extraction … 9
Effect of “weak acid” leach pH on subsequent germanium extraction from final zinc residue … 9
Effect of acid concentration on metal extraction in two-stage leach … 12
Effect of acid concentration on metal extraction in two-stage leach with varying percent solids … 13
HF leaching of residue … 14
Concentration of metals in leach filtrates … 15
Solvent-extraction results testing various extractants … 15
Solvent extraction of gallium and zinc from reduced leach solutions … 16
Testing various organics for germanium selectivity … 19
Germanium extraction with various organic combinations … 19
Effect of copper and iron on germanium extraction … 20

iii

TABLES—Continued

Synergistic effect of OPAP-LIX 63 mixture 20
Effect of solution acidity on germanium extraction 20
Germanium stripping results testing various reagents 20
Effect of increasing water temperature on germanium stripping 21
Effect of recycling OPAP-LIX 63 extractant 23
Coextraction of gallium and germanium 23
Coextraction of gallium and germanium from zinc process solution 24

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

°C	degree Celsius	min	minute
cm³/min	cubic centimeter per minute	mL	milliliter
deg	degree	mm	millimeter
g/L	gram per liter	μm	micrometer
h	hour	mol/L	mole per liter
L	liter	mol pct	mole percent
(lb/min)/st	pound per minute per standard (short) ton	pct	percent
lb/st	pound per standard (short) ton	vol pct	volume percent
M	molarity	wt pct	weight percent

GALLIUM AND GERMANIUM RECOVERY FROM DOMESTIC SOURCES

By D. D. Harbuck¹

ABSTRACT

To decrease reliance on foreign sources for the strategic and critical metals gallium and germanium, the U.S. Bureau of Mines identified and developed processing technology for two domestic sources of these metals: a Tennessee zinc residue and a Utah ore. Sulfuric acid (H₂SO₄) solutions were used to solubilize gallium and germanium in both sources. Statistically designed experiments showed that the most important parameter for high metal extraction from zinc residue was the H₂SO₄ concentration. At a concentration of 2.9M H₂SO₄, 95 pct of the gallium was extracted, and at a concentration of 0.6M H₂SO₄, 73 pct of the germanium was extracted. Controlled H₂SO₄ concentration was also the key for high metal extractions (97 pct Ga, 87 pct Ge) from the Utah ore. Such control was achieved using a two-stage countercurrent leach circuit. Testing showed that the insoluble germanium in both the residue and ore was tied up with silica. Several methods for overcoming this problem are given. To recover gallium and germanium from the leach solutions, the solvent extractants octylphenyl acid phosphate (OPAP) (for gallium) and LIX 63-OPAP (for germanium) were identified. These extractants were tested in separate, continuous, solvent-extraction circuits yielding a gallium recovery of 94 pct and a germanium recovery of more than 90 pct.

¹Supervisory chemical engineer, Salt Lake City Research Center, U.S. Bureau of Mines, Salt Lake City, UT.

INTRODUCTION

Gallium and germanium are assuming an increasingly important role in U.S. industry owing to their technological and strategic applications. The demand for these metals is expected to increase significantly during the next 10 years (1-2).² More than 95 pct of the gallium consumed in the United States is used in gallium arsenide devices, which have extensive electronic applications. These devices include light-emitting diodes, laser diodes, fiber optics, and semiconductors (3). Gallium arsenide superconductors, which enhance the speed of electron transfer, are potentially 25 times faster than conventional silicon devices (4-5). Because of the speed factor and its impermeability to high doses of radiation (6), gallium arsenide is finding increasing use in military radar systems and supercomputers.

The major uses for germanium are infrared optics, fiber-optics systems, detectors, and semiconductor devices, including transistors, diodes, and rectifiers (2). Infrared and fiber-optics systems have become useful in a wide variety of applications, including night vision, target acquisition, fire control, communication, surveillance, navigation, reconnaissance, tactical offense, strategic defense, and heat and/or infrared search and track (2). In most cases,

substitution for germanium cannot be made without a substantial loss in performance (2).

Although gallium and germanium are often together in nature, they are generally not found in concentrated forms. While trace amounts of gallium and germanium are identified in many minerals, they are not usually economically recoverable. Presently, gallium and germanium are produced almost exclusively as byproducts of the aluminum and zinc industries. Currently, more than 90 pct of the gallium and 50 pct of the germanium used in the United States is imported. A major focal point of this U.S. Bureau of Mines study was to identify potential domestic sources of gallium and germanium and to develop the necessary leaching and solvent extraction technology to recover these important metals. This work was done in support of the Bureau’s program to decrease U.S. reliance on foreign sources for critical and strategic metals, such as gallium and germanium.

This report is divided into six sections: (1) identification of domestic sources, (2) leaching of a zinc residue, (3) leaching of a gallium-germanium ore, (4) gallium solvent extraction, (5) germanium solvent extraction, and (6) germanium and gallium coextraction.

IDENTIFYING DOMESTIC SOURCES

To decrease the U.S. dependence on foreign sources, more than 50 potential gallium and germanium ores and several residue byproducts were examined using inductively coupled plasma spectrophotometry (ICP), neutron activation analysis (NAA), and atomic absorption spectroscopy (AA). The results of this search are summarized in table 1.

Table 1.—Analyses of potential gallium and germanium ores, percent

	Ga	Ge
Ore:
Southern Utah	0.04	0.09
Central Utah	.01	.01
48 various locations	0	0
Residue:
Zn—Tennessee	.32	.46
Zn—Missouri	.03	.03
Al	.02	.02

As seen, only one ore and one residue showed any significant amount of gallium or germanium. From

estimated reserves of these materials, each source has enough gallium and germanium to potentially supply the annual needs of the United States for many years; therefore, both of these sources were chosen for further study. Table 2 provides more detailed analyses of these two materials.

Table 2.—Elemental analyses of studied materials, percent

Element	Tennessee Zn residue	Southern Utah ore
Al	0.59	0.47
As	<.02	.79
Ca	4.13	2.2
Cd	.19	.01
Cu	1.05	.86
Fe	11.90	20.2
Ga	.32	.036
Ge	.46	.089
Pb	5.60	.94
S (free)	11.70	NA
Si	4.90	9.1
Zn	19.20	.44

NA Not available.

²Italic numbers in parentheses refer to items in the list of references at the end of this report.

X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that the zinc residue contained zinc sulfide (ZnS), calcium sulfate (CaSO₄), lead sulfate (PbSO₄), silica (SiO₂), iron sulfide (FeS), zinc ferrate (ZnFe₂O₄), and free sulfur, while the ore was goethite (FeOOH), jarosite KFe₂(SO₄)₂(OH)₆, and SiO₂. In both samples, the concentrations of gallium and germanium were so low and the particle sizes were so fine that SEM could not detect discrete germanium- or gallium-bearing minerals.

LEACHING OF ZINC RESIDUE

BACKGROUND

The Tennessee residue used in this study is the end product of the zinc process depicted in figure 1. There are four major operations in the process: (1) roasting of ZnS to calcine (ZnO); (2) “neutral” leaching of approximately 70 pct of the calcine in a pH 4.5 sulfuric acid (H₂SO₄) solution for 5 to 6 h to form a zinc sulfate (ZnSO₄) solution, which is further purified and sent to zinc electrowinning; (3) “weak acid” H₂SO₄ leaching at pH 1.5, 60° C, 2 to 3 h, of the “neutral” leach residue to dissolve the remaining zinc; and (4) neutralization to pH 4.5 of “weak acid” leach solution to precipitate impurities (this precipitate becomes zinc residue) from the ZnSO₄ solution before it proceeds to further purification and zinc electrowinning.

During roasting, sulfur dioxide (SO₂) gas is trapped and converted to H₂SO₄. Because of the large amount of low-cost H₂SO₄ produced, it is the preferred acid for leaching gallium and germanium from zinc residue. Specific leach tests are described below.

STATISTICAL DETERMINATION OF SIGNIFICANT VARIABLES

To quickly identify the significant leach variables necessary for high gallium and germanium extraction from zinc residue, two factorially designed statistical tests (7-8) were set up to study the main and interactive effects of

Figure 1.—Stages of zinc processing.

H₂SO₄ and SO₂ addition, leach time, percent solids, and preleach roast temperature. The following ranges of conditions were tested: 400 to 2,000 lb/st H₂SO₄, 0 to 25 cm³/min SO₂, 30 to 270 min leach time, 5 to 30 pct solids, and 300° to 900° C preleach roast temperature. Batch agitation leach tests, under various experimental conditions, were performed using standard laboratory hotplates, thermocouples, stirring devices, and glassware.

The major findings of these statistically designed tests are presented in table 3. The minimum significant factor (MIN) is the amount that an effect must exceed to be considered statistically significant. Negative numbers demonstrate that metal extraction decreased as the level of the corresponding variable increased. A complete discussion of the statistical analysis of factorial experiments can be found in many references (7-8).

Table 3.—Results of statistically designed experiments

Variable	Ga		Ge
	Effect	MIN	Effect	MIN
Roast temperature	-29.1	2.2	-4.1	2.2
Leach time	6	4.5	2.6	3.7
SO₂ addition	6.2	2.2	5.8	2.2
H₂SO₄ addition	69.3	4.5	12.2	3.7
Percent solids	3.3	4.5	-28.3	3.7
H₂SO₄ + pct solids	-7.4	4.5	-30.2	3.7
H₂SO₄ + leach time	13.3	4.5	2.6	3.7

MIN Minimum significant factor.

The results in table 3 indicate that the most important variables for high gallium and germanium extractions, respectively, were high H₂SO₄ addition and the interactive effect between H₂SO₄ addition and percent solids. This interactive relationship will be discussed in more detail later. Increasing the preleach roast temperature was detrimental to both gallium and germanium extraction; therefore, zinc residue was not roasted in further tests.

BATCH TESTING OF SIGNIFICANT VARIABLES

To better understand the effects of leach time, H₂SO₄ and SO₂ addition, and percent solids on gallium and germanium extraction, additional batch tests were performed to augment the statistical data obtained. Plots of metal (gallium, germanium, zinc, and iron) extraction versus

percent solids, $\mathrm{H}_2\mathrm{SO}_4$ addition, and leach time are presented in figures 2, 3, and 4, respectively. Main effects predicted by the statistical test are clearly confirmed. The dramatic decrease in germanium extraction with increasing percent solids is very apparent, as is the rise in gallium extraction as $\mathrm{H}_2\mathrm{SO}_4$ addition is increased. Leach time response is flat over the range studied.

Figure 2.—Effect of percent solids on metal extraction from zinc residue (2,000 lb/st $\mathrm{H}_2\mathrm{SO}_4$ , 4.5 h, $80^{\circ}$ C).

Figure 3.—Effect of $\mathrm{H}_2\mathrm{SO}_4$ addition on metal extraction from zinc residue (4.5 h, $80^{\circ}$ C, 10 pct solids).

Experiments in the statistical designs were performed at $80^{\circ}$ C. This temperature was verified using the following test conditions: 10 pct solids, 2,000 lb/st $\mathrm{H}_2\mathrm{SO}_4$ , and a 4.5-h leach time. From the plot of metal extraction versus leach temperature presented in figure 5, it is clear that $80^{\circ}$ C is a valid operating temperature.

The effect of $\mathrm{SO}_2$ addition is shown in figure 6. In these tests, residue was leached for $4\,\mathrm{h}$ at $80^{\circ}$ C, 20 pct solids, with 200 to 1,600 lb/st $\mathrm{H}_2\mathrm{SO}_4$ . In one-half of the tests, $\mathrm{SO}_2$ was added at a constant flow rate of 2.9 (lb/min)/st $\mathrm{SO}_2$ . Approximately 90 pct of the gallium and 55 pct of the germanium were extracted when using

Figure 4.—Effect of leach time on metal extraction from zinc residue (2,000 lb/st $\mathrm{H}_2\mathrm{SO}_4$ , $80^{\circ}$ C, 10 pct solids).

Figure 5.—Effect of temperature on metal extraction from zinc residue (2,000 lb/st $\mathrm{H}_2\mathrm{SO}_4$ , 4.5 h, 10 pct solids).

either 1,600 lb/st H₂SO₄ alone or 800 lb/st H₂SO₄ in combination with the SO₂. Assuming that SO₂ converted to sulfurous acid, 800 lb/st sulfurous acid was added at these conditions, bringing the total acid content to approximately 1,600 lb/st. Therefore, any advantage gained by adding SO₂ could be achieved simply by increasing the amount of H₂SO₄. Because H₂SO₄ is less expensive and poses less of a negative environmental impact, its use is preferred to SO₂.

Perhaps the interactive effect between percent solids and H₂SO₄ addition can best be related as H₂SO₄ concentration. When data from various tests were plotted as extraction versus acid molarity (fig. 7), it is seen that as acid concentration increased, germanium extraction proceeded through a peak, then decreased significantly. Pugh (9) in studying the germanium dioxide (GeO₂)-H₂SO₄ system (fig. 8), found that as H₂SO₄ concentration increased, germanium concentration in solution decreased. He concluded that germanium sulfate is incapable of existence, a conclusion that has been substantiated through the years (10). Therefore, germanium must be precipitating from concentrated sulfate solutions as GeO₂. This explanation matches the data obtained in this study. Although H₂SO₄ is needed to solubilize germanium in zinc residue, too much acid will precipitate germanium from solution.

Figure 7 reveals that a gallium extraction of 95 pct was attained at 2.9M H₂SO₄, while germanium extraction reached a peak of 73 pct at 0.6M H₂SO₄. Conditions for

Figure 6.—Effect of adding SO₂ to H₂SO₄, leach on gallium and germanium extraction from zinc residue (4 h, 80° C, 20 pct solids).

simultaneously high gallium and germanium extraction were 10 pct solids, 2,000 lb/st H₂SO₄, 4 h, and 80° C, yielding 89 pct Ga and 70 pct Ge extraction.

The problem remained that a large percentage of the germanium could not be extracted with H₂SO₄, even at appropriate acid conditions. To effect total germanium extraction, further experimental work was required and is presented in the following section.

Figure 7.—Effect of H₂SO₄ molarity on gallium and germanium extraction from zinc residue (4 h, 80° C).

Figure 8.—Solubility of GeO₂ in H₂SO₄.

IMPROVING GERMANIUM EXTRACTION FROM ZINC RESIDUES

A key to increasing germanium extraction is to identify the mineralogical form of germanium in the zinc residue. Unfortunately, as explained previously, this is very difficult to do. Another option would be to track germanium through the stages of the zinc process and theorize the changes it undergoes in each step. From figure 1, it would appear that germanium insolubility could occur either during the roasting or leaching procedures. Both of these possibilities are explored below.

Germanium Insolubility During Roasting

In hydrometallurgical zinc processing, zinc concentrates containing ZnS with minor amounts of iron, copper, lead, silica, gallium, and germanium are roasted at $900^{\circ}$ to $1,100^{\circ}$ C to convert sulfides to oxides. There is no unanimous opinion concerning the form of germanium in sphalerite. Researchers have suggested that germanium is present as the disulfide $\mathrm{GeS}_2$ (11) or the monosulfide (12). One work maintains that a small amount of germanium metal can form a solid solution with ZnS (13). In any case, roasting the germanium compound most certainly converts it to $\mathrm{GeO}_2$ .

During the roast, it is proposed that $\mathrm{GeO_2}$ reacts with both $\mathrm{ZnO}$ and $\mathrm{SiO_2}$ according to reactions A and B, while $\mathrm{ZnO}$ combines with $\mathrm{SiO_2}$ to form zinc silicate $(\mathrm{Zn_2SiO_4})$ , reaction C. $\mathrm{GeO_2} + 2\mathrm{ZnO} \rightarrow \mathrm{Zn_2GeO_4}. \tag{A}$ $\mathrm{GeO_2} + \mathrm{SiO_2} \rightarrow \text{solid solution}. \tag{B}$ $2\mathrm{ZnO} + \mathrm{SiO_2} \rightarrow \mathrm{Zn_2SiO_4}. \tag{C}$

Umetsu and Tozawa (14) recently observed the formation of zinc germanium oxide $(\mathrm{Zn_2GeO_4})$ in a $\mathrm{ZnS – GeO_2}$ roast. In the current study, stoichiometric amounts of $\mathrm{GeO_2}$ and $\mathrm{ZnO}$ were uniformly mixed and then roasted at $650^{\circ}\mathrm{C}$ for $12\mathrm{h}$ . This procedure was repeated for roasts at $800^{\circ}$ and $950^{\circ}\mathrm{C}$ . An examination of the reaction products using XRD revealed the beginning formation of $\mathrm{Zn_2GeO_4}$ at $800^{\circ}\mathrm{C}$ (fig. 9). By $950^{\circ}\mathrm{C}$ , a substantial amount of this compound was present.

A similar technique was used to verify reaction C. Stoichiometric amounts of $\mathrm{SiO_2}$ and $\mathrm{ZnO}$ were uniformly mixed and roasted at $900^{\circ}$ , $1,000^{\circ}$ , and $1,100^{\circ}$ C for $10\mathrm{h}$ . XRD analyses revealed that $\mathrm{Zn_2SiO_4}$ began to form at $1,000^{\circ}$ C, and by $1,100^{\circ}$ C, a substantial amount was present (fig. 10).

In contrast, when $\mathrm{SiO_2}$ and $\mathrm{GeO_2}$ were heated together, a separate compound did not form. It is theorized that

$\mathrm{GeO_2}$ substituted into the $\mathrm{SiO_2}$ lattice to form a solid solution. Miller, Dachille, Shafer, and Roy (15) showed that up to 31 mol pct $\mathrm{GeO_2}$ is soluble in $\alpha\text{-SiO}_2$ . They also demonstrated that as the amount of $\mathrm{GeO_2}$ going into solution with $\mathrm{SiO_2}$ increases, the 2θ angles that correspond to the XRD peaks of $\mathrm{SiO_2}$ shift downward. This phenomenon is better understood when the experimental results are plotted as in figure 11. A major XRD peak for $\mathrm{SiO_2}$ occurs at a 2θ angle of approximately $50.2^{\circ}$ . As shown in figure 11, when 31 mol pct $\mathrm{GeO_2}$ is in solid solution with $\mathrm{SiO_2}$ , the 2θ angle shifts down to around $50^{\circ}$ .

To verify the possibility of $\mathrm{SiO_2 – GeO_2}$ solid solution, $\mathrm{SiO_2}$ and $\mathrm{GeO_2}$ (30 mol pct) powders were mixed and then roasted at $650^{\circ}\mathrm{C}$ for $12\mathrm{h}$ . This procedure was repeated for roasts at $800^{\circ}$ , $950^{\circ}$ , and $1,100^{\circ}\mathrm{C}$ . Examining the products using XRD revealed that there were four prominent

Figure 9.—XRD printouts of $\mathrm{ZnO – GeO_2}$ mixtures at $650^{\circ}$ , $800^{\circ}$ , and $950^{\circ}$ C.

Figure 10.—XRD printouts of ZnO-SiO₂ mixtures at 900°, 1,000°, and 1,100° C.

2θ angles for SiO₂. Table 4 lists the angles obtained for each product. As the temperature of the mixtures increased, the SiO₂ 2θ angles shifted downward. Table 4 also reveals that as SiO₂ was heated, the 2θ angles naturally shifted downward. However, the shift seen with the SiO₂-GeO₂ mixture was much greater than with SiO₂ alone.

An even more dramatic proof of the existence of a SiO₂-GeO₂ solid solution was seen using SEM. Figure 12 is a photomicrograph of the SiO₂-GeO₂ mixture that was heated at 1,100° C. The dark, flat plates are SiO₂; the white botryoidal particles are GeO₂. A close look at the center area shows particles combined into a solid solution.

Figure 11.—Shift of 2θ quartz angle with increasing amounts of GeO₂.

Table 4.—2θ angles for SiO₂ under various conditions, degrees (Four most prominent X-ray diffraction peaks)

Compound and test temperature, °C	1	2	3	4
SiO₂:
25	26.710	50.155	59.965	20.925
1,100	26.650	50.108	59.965	20.875
SiO₂ with 30 mol pct GeO₂:
650	26.688	50.153	59.983	20.920
800	26.690	50.143	59.963	20.920
950	26.618	50.090	59.898	20.855
1,100	26.600	50.063	59.883	20.833

Any SiO₂-GeO₂ solid solution formed during roasting would be very refractory. It would pass unaffected through the leaching and neutralization steps of zinc processing and be carried along to the residue; thus, part of the germanium in the residue would not be solubilized during H₂SO₄ leaching.

Germanium Insolubility During Leaching

In the two-stage leach of the zinc process (see fig. 1), calcine is reacted in H₂SO₄ solutions to dissolve ZnO. Typical analyses for the “neutral” and “weak acid” leaches of the zinc process are given in table 5. As seen, most impurities, including germanium, are solubilized in the “weak acid” leach, indicating the dissolution of Zn₂GeO₄ at these conditions. (Zangieve, Kaloev, Bashkov, Burtakova, and Kubaloun (16) also conducted research verifying the solubility of Zn₂GeO₄ in H₂SO₄.) A small fraction of the calcine is not solubilized in either stage of the zinc leach process. This material is referred to as “gangue.”

Table 5.—Typical analyses of leach solutions, grams per liter

	Neutral leach	Weak acid leach
Cd	1.2	1.4
Cu	<.5	1.7
Fe	<.2	4.3
Ga	0	.13
Ge	.01	.29
Zn	200	163

The dissolution of $\mathrm{Zn_2SiO_4}$ was studied using the two-step leach process on commercially prepared material. Approximately 20 pct of the $\mathrm{Zn_2SiO_4}$ dissolved in the “neutral” leach, while 97 pct of the remaining $\mathrm{Zn_2SiO_4}$ was solubilized in the pH 1.5 “weak acid” leach. Matthew and Elsner extensively studied the leaching of zinc silicate ores with $\mathrm{H_2SO_4}$ (17-18). They discovered that $\mathrm{Zn_2SiO_4}$ dissolves to form $\mathrm{Si(OH)_4}$ and $\mathrm{ZnSO_4}$ according to reaction D at a pH of approximately 1.5 to 2. $\mathrm{Zn_2SiO_4} + 2\mathrm{H_2SO_4} \rightarrow 2\mathrm{ZnSO_4} + \mathrm{Si(OH)_4}. \tag{D}$

The $\mathrm{Si(OH)_4}$ subsequently polymerizes to produce polysilicic acid. With continued polymerization, the polymers attain colloidal dimensions. The stability of colloidal silica particles is dependent on such factors as pH, temperature, concentration, and ionic strength. Unstable colloidal particles aggregate to form silica gel.

It is postulated that in the “weak acid” leach, where both solubilized germanium and silica gel are present, a portion of the germanium becomes tied up with silica gel. Gruzdev and Vydrin (19) documented the affinity germanium has for silica. Miller, Dachille, Shafer, and Roy (15)

Figure 12.—SEM photograph of $\mathrm{SiO_2 – GeO_2}$ solid solution. $(\mathrm{A} = \mathrm{SiO}_2, \mathrm{B} = \mathrm{GeO}_2, \mathrm{scale} = 50\ \mu\mathrm{m})$

demonstrated how easily $\mathrm{GeO_2}$ substitutes into the silica lattice, and Caletka and Kotas (20) observed that silica gel selectively adsorbs germanium from acidic solutions. In the present investigation, commercially prepared -3 mm silica gel was contacted with a pH 1.5 $\mathrm{H_2SO_4}$ leach solution containing 0.44 g/L Ge as well as calcium, cadmium, copper, iron, zinc, and gallium. As seen in table 6, the silica gel selectively removed germanium from solution.

Table 6.—Selectivity of silica gel for germanium

Element	Removal by silica gel, pct
Ca	6.7
Cd	9.3
Cu	7.5
Fe	8.6
Ga	0
Ge	61.5
Zn	8.3

The hypothesis that germanium becomes tied up with silica in the “weak acid” leach was further verified by adding varying amounts of $\mathrm{Zn_2SiO_4}$ to zinc calcine and leaching the mixture in the two-stage zinc leaching process. Less than 2 pct of the germanium was solubilized in the “neutral” leach. The slurry from the “weak acid” leach was filtered, and the solids were then leached five separate times in 20-pct- $\mathrm{H_2SO_4}$ solutions (this procedure will subsequently be referred to as “intensive” leach) to ensure that all the soluble germanium was removed. Table 7 shows that as the amount of added $\mathrm{Zn_2SiO_4}$ increased, the amount of soluble germanium in the “weak acid” leach residue decreased. When enough $\mathrm{Zn_2SiO_4}$ was added to correspond to 10-wt-pct $\mathrm{SiO_2}$ in the calcine, germanium extraction from the “weak acid” leach residue decreased to less than 38 pct. Gallium extractions are included to emphasize that only the germanium was rendered insoluble.

Table 7.—Effect of $\mathrm{ZnSiO_4}$ addition on gallium and germanium extraction, percent

Zn calcine + Zn_{2}SiO_{4}, wt pct SiO_{2}	Ga	Ge
0.6 (calcine as received)	97	82
1	97	76
3	96	56
5	96	55
10	97	<38

These results suggest that $\mathrm{Zn_2SiO_4}$ dissolved to form silica gel, which removed germanium from solution. As additional evidence, the 10-wt-pct $\mathrm{SiO_2}$ residue remaining after the “intensive” leach was completed was examined with both a standard laboratory microscope and a cross-polarized light microscope. Because silica gel is isotropic,

it is not visible in cross-polarized light. The residue could easily be seen using the standard microscope; however, under cross-polarized light, most of the residue was not visible, indicating the presence of silica gel.

This same residue was also examined using XRD. Because XRD is a technique used to identify crystalline solids, silica gel, being amorphous, should produce no XRD pattern. The XRD background pattern of the residue from the zinc calcine- $\mathrm{Zn_2SiO_4}$ mixture drifted upward, and the compound peak heights were substantially diminished compared with the XRD pattern of the residue produced without the addition of $\mathrm{Zn_2SiO_4}$ . This phenomenon indicates that the residue produced with $\mathrm{Zn_2SiO_4}$ addition was less crystalline than the residue produced without $\mathrm{Zn_2SiO_2}$ addition, further supporting the hypothesis that silica gel was formed.

In the zinc process, after the “weak acid” leach is completed, calcine is added to the slurry to precipitate impurities and raise the pH to approximately 5. The germanium in solution, which is not bound to silica gel, is precipitated with the other solubilized impurities. Testing showed that this precipitated germanium was readily soluble in $\mathrm{H}_2\mathrm{SO}_4$ solutions. The germanium that is bound to silica gel proceeds through this precipitation step unaffected and is carried along in the precipitate-gangue mixture.

In summary, using current leach practice, approximately 20 to 30 pct of the germanium reporting to the zinc residue is tied up with silica gel. Even under “intensive” $\mathrm{H}_2\mathrm{SO}_4$ leaching conditions, this germanium will not be solubilized.

In light of these results, of the two hypotheses presented on how germanium could become insoluble during zinc processing, the formation of silica gel is the most probable. With either theory, it is apparent that silica in the zinc concentrates is the problem. Possible solutions to this problem are presented in the next section.

Methods for Overcoming Germanium Insolubility

Potential alternatives for increasing germanium extraction from zinc residue were investigated. Methods tested, together with research results, included the following:

Lower the silica content of zinc concentrates before they enter the roaster. If less silica is present, then less $\mathrm{Zn_2SiO_4}$ or $\mathrm{SiO_2 – GeO_2}$ solid solution will form, and more of the germanium will be recoverable from subsequent process residues. Silica removal was explored using a Bureau column flotation system (21). ZnS concentrates containing 0.6 pct $\mathrm{SiO_2}$ (obtained using traditional flotation cells) were reprocessed using column flotation to obtain concentrates containing 0.19 and 0.27 pct $\mathrm{SiO_2}$ . More than 96 pct of the zinc was recovered and more than 70 pct of the calcium and magnesium were eliminated. The “clean” concentrates were then roasted at $1,000^{\circ}\mathrm{C}$ . The calcines

produced were leached by two-stage zinc process leaching methods. The residues from these leaches were then “intensively” leached to remove all soluble germanium. As seen in table 8, decreasing the $\mathrm{SiO}_2$ content in the concentrates prior to roasting increased the amount of germanium that could be extracted from the subsequent zinc residues.

Table 8.—Effect of silica on germanium extraction

SiO2, pct	Ge extraction, pct
0.19	98.2
0.27	96.8
0.60	82.0

Lower the temperature of the roast. As shown in figure 10 and table 4, at lower roast temperatures, less $\mathrm{Zn_2SiO_4}$ and $\mathrm{SiO_2 – GeO_2}$ solid solutions were formed. If less $\mathrm{Zn_2SiO_4}$ is present, less silica gel will form to insolubilize germanium. If less solid solution forms, more germanium can proceed through the zinc process in a soluble state. However, it must be remembered that the primary purpose of a high roast temperature is to oxidize ZnS to recover zinc. Lower temperatures could harm zinc extraction. Therefore, this alternative for increasing germanium extraction might not be acceptable to the zinc industry.
Leach the insoluble germanium in the residue with hydrofluoric acid (HF). It is well known that HF dissolves $\mathrm{SiO}_2$ . Since the germanium is tied up with $\mathrm{SiO}_2$ , leaching the final residue with HF will free the germanium. Figure 13 shows germanium extraction versus HF addition for zinc residue that had previously been leached with $\mathrm{H}_2\mathrm{SO}_4$ . As seen, leaching the $\mathrm{H}_2\mathrm{SO}_4$ -leached residue with $500\mathrm{lb / st}$ HF for $2\mathrm{h}$ at $80^{\circ}\mathrm{C}$ and 10 pct solids extracted 93 pct of the remaining germanium, bringing the total germanium extraction from approximately 70 to 98 pct.
Modify the two-stage zinc leaching procedure. Testing showed that silica gel formation in the “weak acid” leach was affected by solution pH. Table 9 demonstrates that as the pH of the “weak acid” leach decreased from 1.5 to 0, germanium extraction during subsequent leaching of the final zinc residue increased from 70 to 96 pct.

Table 9.—Effect of “weak acid” leach pH on subsequent germanium extraction from final zinc residue

pH	Ge extraction, pct
1.5	70
1.0	85
0.5	84
0.0	96

LEACHING OF GERMANIUM-GALLIUM ORE

BACKGROUND

The Apex Mine near St. George, UT, is the only ore body in the world that has been mined primarily for germanium and gallium within the last 20 years. From 1880 to 1945, copper was extracted from this unique property leaving behind unmined iron-rich minerals containing germanium and gallium. Geological studies of the site (22-23) have revealed that germanium is concentrated mainly in goethite, while gallium is found chiefly in jarosite. It is postulated that at some geological time, germanium and gallium substituted for iron in these minerals. Therefore, to extract germanium and gallium from the ore, it is necessary to solubilize the iron compounds.

Musto Explorations LTD, former owner of the mine, employed a three-stage countercurrent process using $\mathrm{H}_2\mathrm{SO}_4$ and $\mathrm{SO}_2$ to leach approximately 80 pct of the germanium and 90 pct of the gallium from the ore (24). Researchers commissioned by Musto (25) determined that a reducing agent, such as $\mathrm{SO}_2$ , must be present along with $\mathrm{H}_2\mathrm{SO}_4$ to attack goethite according to reaction E. Jarosite could be attacked by $\mathrm{SO}_2$ alone according to reaction F.

Figure 13.—Effect of HF concentration on germanium extraction from $\mathrm{H}_2\mathrm{SO}_4$ -leached residue (2 h, $80^{\circ}$ C, 10 pct solids). $2 \mathrm{FeOOH} + \mathrm{SO}_2 + \mathrm{H}_2\mathrm{SO}_4 \rightarrow 2 \mathrm{FeSO}_4 + 2 \mathrm{H}_2\mathrm{O}. \tag{E}$ $\begin{array}{l} 2 \mathrm{KFe}_3(\mathrm{SO}_4)_2(\mathrm{OH})_6 + 3 \mathrm{SO}_2 \rightarrow 6 \mathrm{FeSO}_4 + \mathrm{K}_2\mathrm{SO}_4 \\ + 6 \mathrm{H}_2\mathrm{O}. \tag{F} \end{array}$

Jiang, Lee, Singh, Singh, and Torma (26) in their $\mathrm{H}_2\mathrm{SO}_4$ leaching studies of this ore also maintained that a reducing agent was needed for high germanium and gallium extractions. These researchers were able to leach approximately 95 pct of the gallium, but only up to 65 pct of the germanium.

Research reported in the previous section on $\mathrm{H}_2\mathrm{SO}_4$ leaching of germanium and gallium from zinc residues showed that although the addition of $\mathrm{SO}_2$ increased extraction, the same effect could be achieved with increased $\mathrm{H}_2\mathrm{SO}_4$ concentration. Because germanium and gallium in both zinc residues and Apex ore are tied up in iron compounds, it was felt the previous research could be applicable to this ore.

According to reactions G and H, goethite and jarosite can be attacked with $\mathrm{H}_2\mathrm{SO}_4$ alone. $2 \mathrm{FeOOH} + 3 \mathrm{H}_2\mathrm{SO}_4 \rightarrow \mathrm{Fe}_2(\mathrm{SO}_4)_3 + 4 \mathrm{H}_2\mathrm{O}. \tag{G}$ $\begin{array}{l} 2 \mathrm{KFe}_3(\mathrm{SO}_4)_2(\mathrm{OH})_6 + 6 \mathrm{H}_2\mathrm{SO}_4 \rightarrow 3 \mathrm{Fe}_2(\mathrm{SO}_4)_3 + 12 \mathrm{H}_2\mathrm{O} \\ + \mathrm{K}_2\mathrm{SO}_4. \tag{H} \end{array}$

Comparing reaction E with G and F with H, it is seen that the addition of $\mathrm{SO}_2$ reduces the total moles of leaching reagents needed to attack the iron compounds. However, because $\mathrm{SO}_2$ is approximately six times more expensive than $\mathrm{H}_2\mathrm{SO}_4$ , the cost of reagents would be considerably less, and the overall leaching process would be simplified if only $\mathrm{H}_2\mathrm{SO}_4$ were used. In addition, $\mathrm{SO}_2$ is difficult to handle and environmentally hazardous. Therefore, it was the goal of this research to study the extraction of germanium and gallium from Apex ore using only $\mathrm{H}_2\mathrm{SO}_4$ and eliminate the use of $\mathrm{SO}_2$ .

RESULTS AND DISCUSSION

$\mathrm{H}_2\mathrm{SO}_4$ leaching of Apex ore was initially tested at 20 pct solids for $2\,\mathrm{h}$ at $80^{\circ}\mathrm{C}$ . Figure 14 shows the effect of increasing the initial solution $\mathrm{H}_2\mathrm{SO}_4$ concentration on germanium, gallium, and iron extraction. Since geological studies maintain that germanium and gallium are uniformly distributed in the iron lattices (22), and since goethite and jarosite are both ferric iron minerals, it was expected that the three extraction curves would follow each other

11 Figure 14.—Effect of $\mathsf{H}_2\mathsf{SO}_4$ concentration on metal extraction from gallium-germanium ore (2 h, $80^{\circ}$ C, 20 pct solids).

fairly closely. As seen, gallium and iron extractions increased to more than 95 pct as the $\mathrm{H}_2\mathrm{SO}_4$ concentration increased, indicating the relatively high solubility of these metals. Germanium extraction, however, reached a peak of 71 pct using $5M\mathrm{H}_2\mathrm{SO}_4$ . Above this point, germanium extraction decreased with increasing $\mathrm{H}_2\mathrm{SO}_4$ concentration, indicating the precipitation of solubilized germanium from the leach solution. This initial testing showed that while high gallium extraction from Apex ore was easily attainable by increasing the $\mathrm{H}_2\mathrm{SO}_4$ concentration in the leach liquor, germanium extraction warranted further investigation.

Germanium Extraction

From figure 14, it is apparent that in the leaching of Apex ore, germanium solubility decreased substantially in highly concentrated $\mathrm{H}_2\mathrm{SO}_4$ solutions. This same behavior was observed and explained previously for the leaching of germanium from zinc processing residues (see the “Batch Testing of Significant Variables” section). It is believed that the same mechanism applies here. When Apex ore is leached, $\mathrm{H}_2\mathrm{SO}_4$ attacks the goethite and frees the germanium. However, during the leach (and before complete dissolution of germanium from the ore) as the $\mathrm{H}_2\mathrm{SO}_4$ concentration becomes too high, part of the solubilized germanium precipitates as $\mathrm{GeO}_2$ .

To avoid germanium precipitation during the leaching of Apex ore, the amount of $\mathrm{H}_2\mathrm{SO}_4$ in the leach solution must be controlled. If too much acid is added, germanium will begin precipitating from solution before the dissolution of germanium from the ore is complete. If not enough acid is added, germanium will not be freed from the goethite lattice. In either case, the end result is low germanium extraction.

To obtain high germanium extraction at the lowest possible $\mathrm{H}_2\mathrm{SO}_4$ concentration, other variables such as leach temperature and time were examined. The effect of increasing leach temperature from $25^{\circ}$ to $100^{\circ}\mathrm{C}$ is shown in figure 15 for tests performed for $2\mathrm{h}$ with a $2.2M\text{-}\mathrm{H}_2\mathrm{SO}_4$ solution. As seen, the highest germanium extractions were obtained at temperatures of $90^{\circ}$ to $95^{\circ}\mathrm{C}$ .

Time tests were conducted at $90^{\circ}\mathrm{C}$ and 20 pct solids at three different acid concentrations: $2.6M$ , $5.3M$ , and $8.0M$ . The corresponding germanium and iron extraction curves are shown in figure 16. The highest germanium extraction of 85 pct was attained after $80\mathrm{h}$ using the $2.6M\text{-}\mathrm{H}_2\mathrm{SO}_4$ leach solution. For comparison, germanium extractions with the $5.3M-$ and $8.0M\text{-}\mathrm{H}_2\mathrm{SO}_4$ leach solutions decreased to 78 and 37 pct, respectively, after $72\mathrm{h}$ . More importantly, because germanium extraction continued to follow iron extraction in the $2.6M\text{-}\mathrm{H}_2\mathrm{SO}_4$ test, it is clear that germanium was not precipitating from solution, as it clearly was in the $5.3M-$ and $8.0M\text{-}\mathrm{H}_2\mathrm{SO}_4$ tests. Thus, the use of lower $\mathrm{H}_2\mathrm{SO}_4$ concentrations over longer leach times increased germanium extraction to 85 pct, a level 5 pct higher than that obtained in the system using both $\mathrm{H}_2\mathrm{SO}_4$ and $\mathrm{SO}_2$ (24).

Two-Stage Countercurrent Leaching

Based on these results, a two-stage countercurrent leach system, as shown in figure 17, was proposed for extracting high amounts of both germanium and gallium from Apex ore.

In stage A, used acid from stage B contacts fresh ore for a relatively long leach time (at least $20\mathrm{h}$ ) to extract high amounts of germanium. In stage B, fresh acid contacts previously leached ore for a shorter period of time (approximately one-third the time of stage A) to extract relatively high amounts of gallium. The acid concentration in stage B must be sufficiently high to extract most of the gallium. However, because of the countercurrent action, the acid concentration can be considerably less than shown in figure 14, i.e., $8M\mathrm{H}_2\mathrm{SO}_4$ . Since most of the germanium would be solubilized in stage A, a high acid concentration in stage B would not adversely affect germanium extraction.

This system was tested using a leach time of $20\mathrm{h}$ in stage A and $6\mathrm{h}$ in stage B with a temperature of $90^{\circ}\mathrm{C}$ and 20 pct solids in each stage. The pulp density in

Figure 15.—Effect of leach temperature on metal extraction from gallium-germanium ore $(2.2M\ \mathrm{H_2SO_4},\ 2\ \mathrm{h})$ .

stage B was based on the actual weight of dry solids remaining after the stage A leach. Varying amounts of $\mathrm{H_2SO_4}$ were added to determine the optimal amount of acid needed for both high gallium and germanium extractions. The results shown in table 10 indicate that germanium extraction remained fairly constant as the initial acid concentration in stage A decreased from $3.2M$ to $1.9M$ . However, when the initial acid concentration in stage B decreased from $4.9M$ to $2.9M$ , gallium extraction dropped from 97 to 70 pct. Table 10 also lists the total amount of acid used on a pound-per-standard-ton basis. At 20 pct solids, at least $2,000\ \mathrm{lb/st\ H_2SO_4}$ was required for both high gallium and germanium extraction.

Table 10.—Effect of acid concentration on metal extraction in two-stage leach (Stages A and B = 20 pct solids)

Added H₂SO₄, lb/st	Initial molarity, M		Total extraction, pct
	Stage A	Stage B	Ga	Ge
2,200	3.2	4.9	97	87
2,000	2.9	4.4	96	85
1,800	2.6	3.8	91	86
1,600	2.3	3.4	85	87
1,400	1.9	2.9	70	85

Figure 16.—Effect of leach time at various acid concentrations on metal extraction from gallium-germanium ore $(90^{\circ}\ \mathrm{C},\ 20\ \mathrm{pct}$ solids).

Increasing pulp density of the leach slurry was studied as a method to use acid more efficiently (less $\mathrm{H_2SO_4}$ to maintain the same acid concentration). Table 11 shows the effect on metal extraction when the initial percent

solids in stages A and B were 25 and 30 pct, respectively. Increasing the pulp density of the two-stage leach did not significantly reduce the amount of acid needed (per ton of ore) to leach high amounts of gallium and germanium. However, increasing the pulp density did significantly increase the iron concentration in solution from an average of 55 g/L (with 20 pct solids) to 90 g/L Fe (with 30 pct solids), approaching iron saturation. To avoid this problem, the two-stage, 20-pct-solids leach is recommended. It should be realized that these tests show trends on a laboratory scale. To use the information on an industrial level, pilot-plant studies must be performed.

Table 11.—Effect of acid concentration on metal extraction in two-stage leach with varying percent solids (Stage A = 25 pct solids, stage B = 30 pct solids)

Added H₂SO₄, lb/st	Initial molarity, M		Total extraction, pct
	Stage A	Stage B	Ga	Ge
1,500	2.9	6.0	91	81
1,300	2.5	5.0	67	79
1,100	2.0	4.2	57	77

Increasing Germanium Extraction

The highest germanium extraction attained, even under optimum two-stage leaching conditions, was 87 pct (see table 10). A key to increasing germanium extraction is understanding the mineralogy of the ore. In this study, microprobe studies were performed on the ore before and after leaching. Individual grains of the original and leached ore (residue) were scanned with the electron beam and analyzed for germanium, iron, and silicon. Figure 18 shows photomicrographs of germanium, iron, and silicon in the ore. As seen, although most of the germanium is with the iron, as predicted by geologists, a significant amount (approximately 10 to 20 pct) is also associated with silicon. Similar analyses of the residue showed the germanium was no longer associated with iron, but was found in solid solution in individual quartz (silica) grains. This information suggests that 10 to 15 pct of the germanium in Apex ore is tied up with silica and cannot be leached with H₂SO₄.

Figure 17.—Proposed two-stage leach system.

Figure 18.—Photomicrographs of gallium-germanium ore (X 300). White dots indicate germanium (top), iron (middle), and silicon (bottom).

Gruzdev and Vydrin (19) documented the affinity germanium has for silica. Miller, Dachille, Shafer, and Roy (15) demonstrated how GeO₂ can substitute into the four-fold coordinated structures of silica. Therefore, it is theorized that in the formation of this deposit, some germanium substituted into silica grains. This theory was further verified by leaching the residue in an HF solution. Since HF attacks silica, leaching with HF should destroy the silica and solubilize the germanium. Table 12 shows that as the HF concentration in the leach solution increased, germanium solubility increased, resulting in a total of 99 pct of the germanium in Apex ore being extracted.

Because of the higher reagent cost and related environmental and safety problems associated with HF, recovering the remaining 10 to 15 pct Ge with HF would probably not be an economical option.

HF, pct	Total Ge extraction, pct^{1}
0	85.0
1	87.7
5	92.3
10	93.1
20	98
30	99.1
^{1}After H₂SO₄ leach.

GALLIUM AND GERMANIUM SOLVENT EXTRACTION FROM H₂SO₄ SOLUTIONS

Leaching tests described in the previous research were performed to solubilize gallium and germanium. The next step toward metal recovery was the selective removal of these elements from solution. Traditional methods, such as chemical precipitation, are effective in some applications; however, these processes usually require many high-cost, complicated, and time-consuming steps (27). Other techniques, such as the use of resins, are being explored, but low loading capacity as well as high cost and strict separation conditions have limited their usefulness (28). The preferred method of gallium and germanium recovery from solutions is solvent extraction. Therefore, it was the goal of this research to identify or develop solvent extractants capable of recovering gallium and germanium from H₂SO₄ solutions.

GALLIUM SOLVENT-EXTRACTION BACKGROUND

A literature survey revealed that most of the research previously conducted on gallium solvent extraction concerned the recovery of gallium from basic sodium aluminate solutions produced in the Bayer process. U.S. patents such as 4,468,374; 4,135,917; 3,988,150; and 3,899,422 discuss these efforts.

Sheka, Chaus, and Mityureva (29) reviewed the extraction of gallium from hydrochloric acid (HCl) solutions with different organic extractants including ethers; ketones; esters; higher alcohols; and primary, secondary, and tertiary amines. Among these organic extractants, isopropyl ether and tri-n-butylphosphate (TBP) have received the most attention. Although processes employing isopropyl ether and TBP profess to selectively separate gallium, they require highly concentrated HCl solutions (7 to 9M), which shorten the life of the extractant (30-31).

Gallium solvent extraction from H₂SO₄ solutions using methyl isobutyl ketone (MIBK) has been researched, but this process extracted less than 0.5 pct of the gallium (32). Katsura and Abe (33) patented a process using versatic acid as the organic extractant in removing gallium from H₂SO₄ solutions. However, to obtain high gallium extractions, a pH of more than 3.5 was needed. To neutralize solutions to such a pH requires costly and time-consuming measures.

It has been reported that in an H₂SO₄ system di(2-ethylhexyl) phosphoric acid (DEHPA) can be used to extract gallium (25-26), but commercial production has not been attained. Musto Explorations (28), in St. George, UT, tried extracting gallium from an H₂SO₄ leach filtrate of Apex Mine ore using DEHPA; however, processing problems prevented the operation from becoming economically viable. A major obstacle in using DEHPA is that the pH of the leach filtrates, which ranges from 0 to 0.5, must be raised by neutralization to a range of 2 to 3 for high gallium extraction. Neutralization increases the cost and time required for processing.

GERMANIUM SOLVENT-EXTRACTION BACKGROUND

Various solvents, including carbon tetrachloride, chloroform, TBP, long-chain amines, alkylphosphoric acids, phosphinic acid, oxime, hydroxamic acids, and alkylpyrocatechol, have been proposed for the solvent extraction of germanium (34-35). Of these, only Kelex 100 (36) (beta-dodecenyl 7-alkenyl-8-hydroxyquinoline) and LIX 63 (37) (19-hydroxyhexatriaconta-9,28 diene-18 oxime) have been mildly successful in extracting germanium from H₂SO₄ solutions. Kelex 100 effectively loads germanium from

acidic solutions; however, the rate of aqueous and organic disengagement is slow, and a harsh caustic is needed to strip germanium from the organic. LIX 63 is only effective with solutions containing high amounts of acid (more than 100 g/L), and again, strong caustic is needed to strip germanium from the organic. More importantly, patents for germanium solvent-extraction technology using these two solvents are owned by foreign companies that have been reluctant to lease the know-how to U.S. firms. It is clear that other extractants need to be found.

It was the goal of this research to identify effective solvent extractants for recovering gallium and germanium from H₂SO₄, leach solutions and to test the extractants in continuous, solvent-extraction circuits.

SOLUTION PREPARATION AND ANALYSIS

Four solutions were tested in this work: (1) synthetic solution A, produced by dissolving 99.99 pct pure GeO₂ in water and then adding H₂SO₄; (2 and 3) filtrates B and C, obtained by H₂SO₄ leaching of zinc residue at different conditions; and (4) filtrate D, produced by H₂SO₄ leaching of the Utah germanium-gallium ore. Table 13 shows the concentration of metals in each solution as determined by ICP and AA. Radioisotope tracers were used in this research for determining germanium extraction from these solutions.

Table 13.—Concentration of metals in leach filtrates, grams per liter

Element	Synthetic solution A	Zn residue filtrate		Apex ore filtrate D
		B	C
As	0	<0.1	<0.1	2.3
Cd	0	.24	.17	<.1
Cu	0	2.10	1.06	3.5
Fe	0	18	11	81
Ga	0	.55	.32	.12
Ge	.24	.64	.32	.30
Zn	0	19	12	1.8

INITIAL SOLVENT-EXTRACTION TESTING

Nine different organic extractants were initially tested to determine their selectivity for extracting gallium and germanium from leach filtrate B: bis 2,4,4-trimethylpentyl phosphinic acid (Cyanex 272), DEHPA plus isodecanol (IDA), Kelex 100, LIX 63 plus IDA, octylphenyl acid phosphate (OPAP) plus IDA, 2-ethylhexyl phosphonic acid (PC88A), TBP, tri-octylphosphine oxide (TOPO) plus IDA, and tri-n-octylamine. Single-contact batch tests were conducted in separatory funnels on a wrist-action shaker for 30 min using aqueous-to-organic (A-O) volume ratios of 1:1 with kerosene as the diluent.

Table 14 shows that 0.3M OPAP plus 10 vol pct IDA in kerosene (this combination will subsequently be referred to as “OPAP”) extracted the most gallium, while Kelex 100 extracted the most germanium. As explained previously, the use of Kelex 100 for germanium extraction is patented; however, the use of OPAP for gallium extraction is new and was, therefore, examined in more detail. Further testing for germanium solvent extraction is presented later.

Table 14.—Solvent-extraction results (percent) testing various extractants

Organic extractant^{1}	Cd	Cu	Fe	Ga	Ge	Zn
Cyanex 272	1.2	0.7	7	5.6	1.6	0.8
DEHPA plus IDA	.5	1.1	21	0	.4	.6
Kelex 100	0	49	10	0	84	0
LIX 63 plus IDA	1.8	2	2.3	6	4	2.9
0.3M OPAP plus IDA	3.3	4	49.0	43.0	.4	3.9
PC88A	0	0	26	0	1.6	0
TBP	0	0	0	0	0	0
0.125M TOPO plus IDA	4.9	5	10	0	8	6.2
Tri-n-octylamine	0	0	0	0	0	0

¹10 vol pct except as noted.

GALLIUM SOLVENT EXTRACTION

In addition to OPAP, DEHPA was also included in a more detailed study for gallium extraction from H₂SO₄ solution. Although preliminary results using DEHPA were not encouraging, its use was not eliminated at this point because other researchers had found it to be successful in recovering gallium (25-26). In addition, DEHPA and OPAP are both organophosphate extractants with similar structures (38). The commercially prepared OPAP used in this study was obtained from Albright Wilsons Americas, and is reportedly a 60:40 mixture of monomer and dimer OPAP.

Iron Versus Gallium Loading

Zekel, Nosovshii, Rexnik, and Shpirt (30) found that when gallium was extracted from HCl solutions using TBP, any oxidized iron (ferric) in solution loaded preferentially to gallium. However, when iron was in the reduced state (ferrous), it did not load onto TBP. Tests using 0.3M OPAP showed that when solvent extraction was conducted immediately after the iron in the filtrate was reduced with metallic iron, reaction I, gallium extraction was high, and iron extraction was low. $2 \mathrm{Fe}^{+++} + \mathrm{Fe}^{2+} \rightarrow 3 \mathrm{Fe}^{++}. \tag{I}$

However, when the solution was allowed to oxidize, the opposite occurred. It was theorized that ferric iron inhibits gallium loading onto OPAP, whereas with ferrous iron,

this problem does not exist. This assumption was verified by repeatedly contacting OPAP with reduced and oxidized leach solutions. Figure 19 shows that with a reduced solution, only small amounts of iron were loaded onto the OPAP, and gallium extraction remained high. When the solution was reoxidized, considerable amounts of iron loaded onto the OPAP on each contact, corresponding to decreased gallium loading; therefore, metallic iron was added to all filtrates to convert the ferric to ferrous iron to ensure high gallium loading onto OPAP.

An added advantage of reducing the solutions with iron is that copper is cemented out in the process, eliminating the need for copper removal at some later stage in the operation.

OPAP and DEHPA

Solvent extraction tests using OPAP and 10 vol pct DEHPA in kerosene were conducted using reduced leach filtrate C. Table 15 shows that one 30-min contact of filtrate with OPAP at an A-O ratio of 1:1 extracted 96 pct of the gallium and only 1 pct of the zinc. DEHPA alone extracted only 23 pct of the gallium in one contact. When the pH of the filtrate was increased by neutralization with sodium hydroxide (NaOH), gallium extraction using DEHPA increased. At pH 2.3, 81 pct of the gallium and 34 pct of the zinc were extracted after two contacts at an A-O ratio of 1:1; however, at pH 3.3, 68 pct of the gallium and 16 pct of the zinc were precipitated from solution.

Table 15.—Solvent extraction of gallium and zinc from reduced leach solutions, percent

Number of contacts	OPAP, pH 0.5		DEHPA
	Ga	Zn	pH 0.5		pH 1.1		pH 2.3		pH 3.3
			Ga	Zn	Ga	Zn	Ga	Zn	Ga	Zn
0 …	0.0	0	0	0	0	0	0	0	168	116
1 …	96	1	23	7	32	2	62	18	90	37
2 …	99.9	0	32	11	NA	NA	81	34	NA	NA

NA Not available. ¹Precipitated.

Figure 20 demonstrates the effect of pH on gallium solvent extraction with OPAP. As seen, OPAP extracted more than 98 pct of the gallium even at a pH as low as 0 (corresponding to approximately $40\mathrm{g / L}$ $\mathrm{H}_2\mathrm{SO}_4$ ). As the pH dropped below 0, gallium extraction decreased dramatically. DEHPA, however, needed a pH of 2 to 3 to extract gallium. Therefore, the distinct advantage of OPAP is that the leach filtrate needs no neutralization and can be used as received. Because OPAP gave such excellent results, it was studied in more detail.

Figure 19.—Gallium and iron extraction from reduced and reoxidized solutions.

Figure 20.—Effect of pH on gallium extraction using the solvents OPAP and DEHPA.

Rate and Equilibrium Analysis

Rate and equilibrium analyses were conducted using OPAP to better understand its gallium loading and stripping properties.

Gallium Loading

Figure 21 shows that a contact time of 10 min was sufficient for gallium equilibrium loading onto OPAP. A McCabe-Thiele analysis of the gallium-loading isotherm for a 0.3M-OPAP organic and a 0.32-g/L-Ga filtrate showed that a loaded solvent containing 0.32 g/L Ga could be produced at an A-O ratio of 1:1 with four theoretical stages of mixing and separating (fig. 22).

Gallium Stripping

Batch solvent extraction tests conducted on a wrist-action shaker showed that gallium could be stripped from OPAP using 1 to 3M-H₂SO₄ solutions. Figure 21 reveals that stripping with a 1.5M-H₂SO₄ solution removed 98 pct of the gallium in 10 min. A McCabe-Thiele analysis of the equilibrium stripping isotherm for a 1.5M-H₂SO₄ strip solution and a 0.3M-OPAP organic containing 0.32 g/L Ga indicated that a strip liquor containing 1.3 g/L Ga could be produced at an A-O ratio of 1:4 with four theoretical stages (fig. 23).

Ferric Stripping

Even when extracting freshly reduced solution, a small amount of ferric iron was present and loaded onto the OPAP. An H₂SO₄ strip alone could not remove this ferric. Tests showed that a 50-pct-phosphoric acid (H₃PO₄), 50-pct-H₂O solution stripped 92 pct of the ferric from OPAP within 5 min. When the OPAP was reused, it extracted gallium nearly as well as fresh extractant. A McCabe-Thiele analysis (fig. 24) of the iron-stripping isotherm for a 50-pct-H₃PO₄ solution and a 0.3M-OPAP organic containing 0.53 g/L Fe showed that iron on the OPAP can be reduced from 0.53 to 0.02 g/L at an A-O ratio of 1:4 in three theoretical stages.

Continuous Solvent Extraction of Gallium

With this background information, it was possible to operate a continuous, gallium solvent-extraction circuit using OPAP for gallium loading and H₂SO₄ and H₃PO₄ for gallium and iron stripping.

System Design

A continuous system was constructed consisting of mixer-settlers arranged so that the organic was fed at the top of the operation and cascaded down through the setup. The mixer-settlers were divided into three sections. Gallium was loaded in the highest section and stripped in the middle section. The lowest section was for ferric iron stripping. Mixer-settlers could be added or removed from each section as needed. Pumps and flowmeters made it possible to adjust the aqueous flows so proper A-O ratios and retention times could be maintained. To ensure that the iron in solution remained in the reduced state, an upflow column containing iron metal was inserted before the first mixer-settler. All solution entering the system passed through this iron reducer.

Figure 21.—Gallium equilibrium loading and stripping on 0.3M OPAP.

Figure 22.—McCabe-Thiele analysis loading 0.32-g/L-Ga aqueous on 0.3M OPAP. (A/O = aqueous-to-organic ratio)

18 Figure 23.—McCabe-Thiele analysis stripping 0.32-g/L-Ga loaded organic using 1.5M H₂SO₄. (A/O = aqueous-to-organic ratio)

Figure 24.—McCabe-Thiele analysis stripping ferric iron with 50 pct H₃PO₄. (Additional data point x = 0.68, y = 7.09; A/O = aqueous-to-organic ratio)

System Operation

The system was operated for maximum gallium recovery using conditions determined by the McCabe-Thiele analyses for leach filtrate C and for an organic containing 0.3M OPAP (figs. 21 through 24). The gallium-loading section contained four mixer-settlers and was operated at an A-O ratio of 1:1. Gallium stripping with 1.5M H₂SO₄ was conducted in four mixer-settlers at an A-O ratio of 1:4. A two-stage iron strip with 50 pct H₃PO₄ and an A-O ratio of 1:4 was used to keep ferric iron concentration on the OPAP below 0.5 g/L, thus allowing OPAP to function efficiently as it was recycled. Twelve liters of reduced leach filtrate containing 0.32 g/L Ga and 20 g/L Fe were pumped through the system in 32.4 h. Organic and aqueous flow rates were set to maintain a retention time of at least 10 min in each mixer of the loading section.

Operation of the system at these conditions resulted in a raffinate containing 0.02 g/L Ga and 20 g/L Fe. Organic loadings averaged, in grams per liter, 0.31 Ga and 0.36 Fe. The H₂SO₄ strip liquor averaged, in grams per liter, 1.07 Ga and 0.74 Fe. Gallium extraction from the leach filtrate averaged 95 pct; gallium recovery from the organic with the H₂SO₄ strip liquor averaged 94 pct. Operating the continuous system at these conditions concentrated the gallium by a factor of 3.3 (0.32 to 1.07 g/L). The rate of organic loss was 13.3 mL of organic extractant per liter of leach filtrate processed. The test was continued for an additional 20 h (7.9 L) with the H₃PO₄ strip removed. This was done to see how necessary this step was to the success of the operation. The gallium extraction dropped from 94 to 84 pct, while the iron concentration on the organic steadily increased from 0.4 to 0.79 g/L; thus, a H₃PO₄ strip was needed to maintain high gallium recovery.

Strip Liquor Purification

Although gallium recovery was high in the continuous system, the strip liquor contained too much iron to effectively precipitate a high-gallium product. Batch tests showed that by repeating the OPAP loading and stripping three times, 99.9 pct of the remaining iron was removed. When the liquor from the third and final strip was neutralized with ammonium hydroxide (NH₄OH), a product containing 40 pct Ga was precipitated. Such a product can be incorporated into traditional gallium purification systems.

GERMANIUM SOLVENT EXTRACTION

In a further effort to identify a germanium solvent extractant, 29 organic extractants, other than those listed in table 14, were tested for germanium selectivity using solution A spiked with either 100 or 10 g/L H₂SO₄. In each test, 10 vol pct of liquid extractant was mixed with 90 vol pct kerosene. Where the extractant was a solid, the final concentration of the extractant in kerosene was 0.3M. Single-contact batch tests were conducted in separatory funnels on a wrist-action shaker for 30 min using A-O volume ratios of 1:1. The results in table 16 show that only Cyanex 301 (bis (2,4,4-trimethylpentyl) dithiophosphinic acid) extracted high amounts of germanium.

Table 16.—Testing various organics for germanium selectivity, extraction in percent

Organic extractant	H_{2}SO_{4}, g/L		Organic extractant	H_{2}SO_{4}, g/L
	100	10		100	10
Adogen 283	1	0	JMT	9	7
Adogen 364	2	5	LIX 64N	2	2
Adogen 381	0	2	LIX 622	1	2
Adogen 464	9	11	LIX 860	1	1
Alamine 304	1	2	LIX 84	1	1
Alamine 308	0	2	LIX 984	0	3
Alamine 310	1	2	M-5640	0	0
Alamine 336	0	2	MEHPA	0	0
Aliquat 336	0	0	NeodecanoicPrine	0	0
Amberlite LA2	1	2	Octyl-oxime	1	0
BC-150	0	0	P-5050	0	0
Cyanex 301	89	65	P-5100	1	0
Cyanex 302	0	0	Tri-octylamine	0	3
Cyanex 923	1	1	Versatic acid	0	0
Cyanex 925	5	0

The selectivity of Cyanex 301 for germanium was then tested using filtrate B, an actual leach solution containing 60 g/L H₂SO₄. As before, an A-O ratio of 1:1 and contact time of 30 min were used. Cyanex 301 extracted more than 80 pct of the germanium, but it also extracted 98 pct of the copper, 99 pct of the zinc, and more than 30 pct of the cadmium. Because Cyanex 301 was so nonselective for germanium, other possible extractants were sought.

Often when two extractants are mixed, a synergistic effect occurs whereby the combination of extractants is capable of extracting more of a metal than either organic alone. This was shown by Demopoulos and Gevfert for extracting ferric iron (39) and by De Schepper, Commemant, and Van Peteghem (40) for increasing germanium extraction by mixing Kelex 100 and LIX 26. In the current study, various extractants were grouped by twos and mixed with kerosene as the diluent. Each combination was then contacted with leach filtrate B for 30 min at an A-O ratio of 1:1. Select results in table 17 show that one combination, 0.3M OPAP and 10 pct LIX 63, extracted more than 40 pct of the germanium. Table 17 also shows the results when filtrate B was contacted with OPAP and LIX 63 alone. These results indicate that the OPAP-LIX 63 mixture had a synergistic effect on germanium extraction; therefore, work on this combination was expanded.

Effect of Copper and Iron

Because germanium extraction from an actual leach solution averaged only 40 pct when using the OPAP-LIX 63 mixture, methods to increase extraction were examined. LIX 63 was originally developed as a copper extractant (41) and OPAP is known to extract ferric iron (see the “Iron Versus Gallium Loading” section); therefore, a series of tests was performed to determine the effect of aqueous copper and iron on germanium extraction when using the 0.3M-OPAP-10-pct-LIX 63 mixture. Table 18 shows that the highest germanium extraction was possible when the leach solution was free of copper and the iron was in the reduced state. These objectives can be accomplished by contacting the leach solution with metallic iron as shown in reactions I and J. $2 \mathrm{Fe}^{+++} + \mathrm{Fe}^{2+} \rightarrow 3 \mathrm{Fe}^{++}. \tag{I}$ $\mathrm{Cu}^{++} + \mathrm{Fe} \rightarrow \mathrm{Cu} + \mathrm{Fe}^{++}. \tag{J}$

All further tests were performed using solutions contacted with metallic iron.

Table 17.—Germanium extraction with various organic combinations

Organic	Ge extraction, pct
10 pct DEHPA with—
10 pct Adogen	8
10 pct JMT	9
10 pct LIX 64N	6
10 pct LIX 63	4
0.3M OPAP	0
0.3M OPAP with—
10 pct Cyanex 272	0
10 pct DEHPA	0
10 pct Kelex 100	85
10 pct LIX 63	49
10 pct TOPO	0

Table 18.—Effect of copper and iron on germanium extraction

	Ge extraction, pct
With Cu and—
Fe⁺⁺	72
Fe⁺⁺⁺	41
Without Cu:
Fe⁺⁺	76
Fe⁺⁺⁺	32

Synergism

Table 19 more clearly shows the synergistic effect obtained when various OPAP-LIX 63 combinations were used for germanium extraction. Filtrate C with 60 g/L free acid was used in these tests. As before, A-O ratios of 1:1 were used, and kerosene was the diluent. An organic with 10 pct LIX 63 extracted only 8.7 pct of the germanium; however, with a 0.3M-OPAP-10-pct-LIX 63 combination, germanium extraction increased to 57 pct. As another example, germanium extraction increased from 30 to 83 pct with the 0.2M-OPAP-30-pct-LIX 63 combination as compared with the 30-pct-LIX 63 organic.

Table 19.—Synergistic effect of OPAP-LIX 63 mixture; extraction in percent

Extractant	Ga	Ge
0.3M OPAP	77.7	0
10 pct LIX 63	0	8.7
10 pct LIX 63 and 0.3M OPAP	61.0	57.0
20 pct LIX 63	NA	21.0
20 pct LIX 63 and 0.3M OPAP	NA	80.5
30 pct LIX 63	0	30
30 pct LIX 63 and 0.2M OPAP	8	83

NA Not available.

Table 19 also demonstrates that the concentrations of LIX 63 and OPAP are important variables in obtaining high germanium extraction. By increasing the LIX 63 concentration from 10 to 20 pct in the 0.3M-OPAP organic, germanium extraction increased 23.5 pct.

An interesting phenomenon was observed in the data reported in table 19. The OPAP-LIX 63 mixture had the ability to coextract gallium along with germanium. A literature survey revealed that such a process has not previously been reported. Coextraction was pursued on a limited scale with some pertinent results given in a later section.

Effect of Acid Concentration

Table 20 shows the importance of solution acidity for germanium extraction with the OPAP-LIX 63 combination. As seen, germanium extraction increased with increasing free acid for both OPAP-LIX 63 combinations.

Table 20.—Effect of solution acidity on germanium extraction, percent

Free acid concentration, g/L	30 pct LIX 63-0.2M OPAP	20 pct LIX 63-0.3M OPAP
22.5	71.2	64.7
32.5	75.7	71.8
42.5	78.6	75.9
52.5	81.4	79.6
62.5	84.8	81.9

Germanium Stripping

Once the organic was loaded with germanium, a proper stripping agent was needed to make solvent extraction complete. Several possible reagents were tested to strip germanium from a loaded OPAP-LIX 63 organic mixture. Table 21 shows the results obtained using contact times of 1 h and A-0 ratios of 1:1 to treat a loaded 0.3M-OPAP-10-pct-LIX 63 organic solvent.

Table 21.—Germanium stripping results (percent) testing various reagents

Reagent	Ge stripped
Distilled water	41.9
1 g/L FeSO₄	38.5
10 pct HCl	19.5
1.0M H₃PO₄	35.9
1.5M H₂SO₄	28.4
1.0M Na₂CO₃	12.0
0.5M NaOH	63.6
1.0M Na₂SO₄	40.2

As anticipated, NaOH stripped a high percentage of the germanium; however, germanium stripping using distilled water was also surprisingly high. Because water is inexpensive and easy to handle, it was tested further. In particular, table 22 shows that increasing water temperature from 25° to 75° C increased germanium stripping from 41.9 to 73.9 pct.

With this background information, a study of continuous germanium solvent extraction was proposed using OPAP-LIX 63 for loading and hot water for stripping. For such an investigation, it was necessary to perform basic rate and equilibrium tests.

Table 22.—Effect of increasing water temperature on germanium stripping

Temperature, °C	Ge stripped, pct
25	41.9
60	64.6
75	73.9

Germanium Rate and Equilibrium Analysis

Rate and equilibrium analyses were conducted using a 0.2M-OPAP-30-pct-LIX 63 mixture for loading and 75° C water for stripping. Two samples of filtrate D were tested: one with the free acid adjusted to 40 g/L, the other with the free acid adjusted to 60 g/L. These tests were used to determine the number of loading and stripping stages as well as the retention time needed in a continuous, solvent-extraction operation.

Germanium Loading

Figure 25 shows equilibrium loading data obtained after one contact of aqueous with organic. A contact time of 20 min was deemed sufficient for loading germanium onto the extractant for a multicontact system.

Figure 26 shows a McCabe-Thiele analysis of the germanium-loading isotherm for a filtrate with 40 g/L free acid. As seen, a loaded solvent containing 0.3 g/L Ge could theoretically be produced at an A-O ratio of 1:1 using four mixer-settlers. When the 60-g/L-free acid

Figure 25.—Germanium equilibrium loading and stripping on 0.2M OPAP-30 pct LIX 63.

filtrate was tested, the McCabe-Thiele analysis of the germanium-loading isotherm (fig. 27) revealed that a loaded organic containing 0.6 g/L Ge could be obtained at an A-O ratio of 2:1 using four theoretical stages. Therefore, by increasing the free acid concentration in solution from 40 to 60 g/L, germanium concentration on the loaded organic would double.

Germanium Stripping

Stripping germanium from a loaded organic containing 0.3 g/L Ge with 75° C water reached equilibrium after a contact time of approximately 20 min, as seen in figure 25. A McCabe-Thiele analysis of the equilibrium stripping isotherm (fig. 28) indicated that an organic containing 0.3 g/L Ge could be stripped in three stages at an A-O ratio of 1:1 to produce a strip liquor containing 0.3 g/L Ge, while an organic containing 0.6 g/L Ge could be stripped in three stages at an A-O ratio of 1:1 to produce a strip liquor containing 0.6 g/L Ge.

Iron Scrubbing

Analysis of the organic after germanium loading and stripping revealed that up to 8 g/L Fe was present, even when the iron in the filtrate was maintained in the ferrous state. If the 8-g/L-Fe organic were recycled, this much iron would hinder germanium loading. To avoid this problem, iron scrubbing was studied. Rate and equilibrium

Figure 26.—McCabe-Thiele analysis of germanium-loading isotherm, 40-g/L-H₂SO₄ solution. (A/O = aqueous-to-organic ratio)

analyses for iron scrubbing were conducted using a loaded organic containing 7 g/L Fe and a 3M-H₂SO₄ scrub liquor. McCabe-Thiele analyses of the iron-scrubbing isotherm (fig. 29) showed that iron on the organic could be reduced from 7 to 2.4 g/L at an A-O ratio of 1:1 in two stages.

Figure 27.—McCabe-Thiele analysis of germanium-loading isotherm, 60-g/L-H₂SO₄ solution. (A/O = aqueous-to-organic ratio)

Figure 28.—McCabe-Thiele analysis stripping 0.3- or 0.6-g/L-Ge loaded organic using 75° C H₂O. (A/O = aqueous-to-organic ratio)

Continuous Solvent Extraction of Germanium

With this background information, it was possible to operate a continuous germanium solvent-extraction circuit using the OPAP-LIX 63 organic mixture for germanium loading, hot water for germanium stripping, and H₂SO₄ for iron scrubbing.

System Design

The continuous solvent-extraction circuit used for testing gallium solvent extraction was also used for testing germanium solvent extraction. For this work, the mixers-settlers were divided into three sections: germanium loading with four mixer-settlers, germanium stripping with four mixer-settlers, and iron scrubbing with two mixer-settlers. As before, to ensure that the iron in solution remained in the reduced state, an up-flow column containing metallic iron was inserted so that all solution entering the system passed through this column. The germanium-stripping stage was maintained at 75° C by circulating hot water through specially designed glass tubing placed in each settler.

System Operation

The continuous system was operated according to conditions determined by the McCabe-Thiele analyses for 0.2M-OPAP-30-pct-LIX 63 extractant combination.

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The operation parameters and results of each test, along with any variables tested, are given below.

Testing Leach Filtrate D Containing 40 g/L H₂SO₄

In these tests, germanium loading was operated at an A-O ratio of 1:1, as determined by the McCabe-Thiele analysis shown in figure 26. Germanium stripping with 75° C water was conducted at an A-O ratio of 1:1, as was the iron scrubbing with 3M H₂SO₄. Organic and aqueous flow rates were set to maintain a retention time of at least 20 min in each stage of the loading and stripping sections. In the first 30 h, the organic extractant was not recycled. Under these conditions, an average of 91 pct of the germanium loaded onto the extractant and 67 pct of this germanium was stripped from the organic extractant. When the organic was recycled, germanium loading stayed consistent at 88 pct, while germanium stripping increased to 77 pct.

The results using a 40-g/L-H₂SO₄ filtrate were encouraging; however, even under optimum conditions, the final strip liquor would have the same germanium concentration as the initial leach filtrate. One method of increasing the germanium concentration of the strip liquor would be to recycle the aqueous solution to load the organic to capacity and to recycle the aqueous during the stripping cycle to improve concentration ratios. In some operations, up to 90 pct of the aqueous is recycled. However, recycling increases operating costs and decreases the output rate. A better alternative would be to increase solution acidity so higher amounts of metal initially load onto the organic.

Testing Leach Filtrate D Containing 60 g/L H₂SO₄

In these tests, all conditions remained the same as described for the 40-g/L-H₂SO₄ solution tests except germanium loading was operated at an A-O ratio of 2:1, as shown in figure 27. In the first 20 h, the organic extractant was not recycled. Under these conditions, an average of 92 pct of the germanium loaded onto the extractant and 66 pct of this germanium was stripped from the organic extractant. These results are similar to those obtained using the 40-g/L-H₂SO₄ filtrate, but the highest germanium concentration in the strip liquor was 0.54 g/L, as opposed to a high of 0.24 g/L for the 40-g/L-H₂SO₄ solution.

The system was then operated for 24 h with the organic being recycled. Table 23 shows that germanium extraction remained relatively high at 85 to 90 pct, and the iron level remained consistently around 2.6 g/L. The fact that the amount of germanium stripped increased with each recycle indicates that an equilibrium amount of germanium remained on the organic, but did not affect subsequent germanium loading or stripping when the organic was recycled.

Table 23.—Effect of recycling OPAP-LIX 63 extractant

Condition	Ge		Fe load-ing, g/L
	Loading, pct	Stripping, pct
1st recycle	85	71	2.6
2d recycle	85	79	2.8
3d recycle	90	99	2.6

GALLIUM AND GERMANIUM COEXTRACTION

There is currently no available technology for the simultaneous solvent extraction and selective recovery of germanium and gallium from acidic solutions. This is significant because germanium and gallium often occur together in nature and can be leached using the same reagents. By extracting both metals at the same time, many processing steps could be eliminated.

EXPERIMENTAL RESULTS

Germanium and gallium coextraction was tested using OPAP-LIX 63 combinations in conjunction with filtrate B at A-O ratios of 1:1 and contact times of 1 h. The results in table 24 show that if the acid concentration of the aqueous and the strength of the extractant were properly controlled, appreciable amounts of both gallium and germanium could be extracted simultaneously.

Stripping the loaded organic with 75° C water at an A-O ratio of 1:1 removed 96 pct of the germanium. A subsequent strip of the organic with 3M H₂SO₄ removed more than 95 pct of the gallium. More importantly, less than 1 pct of each metal contaminated the other.

Table 24.—Coextraction of gallium and germanium (Solution free of Cu and Fe⁺)

Organic	Free acid, g/L	Extraction, pct
		Ga	Ge
0.3M OPAP and 10 pct LIX 63	40	58	55
Do.	60	57	61
Do.	80	28	69
Do.	100	26	77
0.2M OPAP and 30 pct LIX 63	30	21	80
Do.	50	16	82
Do.	60	8	83

INDUSTRIAL APPLICATION

During the processing of certain zinc concentrates, germanium and gallium are solubilized in a pH 1.5 H₂SO₄, and approximately 0.13 g/L Ga and 0.29 g/L Ge. Coextraction using the 0.2M-OPAP-30-pct-LIX 63 mixture was tested on such a solution with the results shown in table 25. With just one contact of aqueous with organic, 60 pct of the gallium and 84 pct of the germanium were extracted. High germanium extraction from a pH 1.5 solution is quite significant. Table 25 also shows that when increasing amounts of H₂SO₄ were added to the solution, germanium extraction increased, while gallium extraction decreased.

Table 25.—Coextraction of gallium and germanium from zinc process solution, percent

you can edit everything	Ga	Ge
1.5	60	84
11.5	36	90
50.5	18	92

Results of multiple contacts of aqueous with organic are shown in figure 30. As seen, germanium and gallium continued to load without crowding one another off the organic. These results imply that an OPAP-LIX mixture

Figure 30.—Effect of multiple contacts in the coextraction of germanium and gallium from zinc processing liquors.

could be used to recover gallium and germanium during zinc processing, before these metals report to the waste residue. Such technology would greatly increase the supply of these critical metals.

SUMMARY

To decrease U.S. reliance on foreign sources of the strategic metals gallium and germanium, the Bureau has identified two potentially significant domestic supplies of these metals: a Tennessee zinc residue and a Utah ore. Leaching and solvent extraction techniques were studied for gallium and germanium recovery from both of these sources with the significant results summarized below:

For extracting high amounts of gallium and germanium from zinc residue, the following observations were noted:

The most important operational parameter was shown to be the H₂SO₄ concentration.
Conditions for simultaneously high gallium and germanium extraction were 10 pct solids, 2,000 lb/st H₂SO₄, 4.5 h, and 80° C, yielding 89 pct Ga and 70 pct Ge extraction.
Gallium extraction at ideal conditions approached 95 pct; however, germanium extraction of only 73 pct was achievable.
It was postulated that germanium insolubility occurred during the leaching stages of zinc processing via the following mechanism: Minor amounts of Zn₂SiO₄ dissolve during calcine leaching to form silica gel and ZnSO₄. Silica gel selectively adsorbs germanium from solution, thus rendering it insoluble in H₂SO₄ leaches. Several potential alternatives exist to avoid this problem:

a. Remove silica from the concentrates by column flotation. b. Perform ZnS roasting at a lower temperature to avoid formation of Zn₂SiO₄. c. Leach the insoluble germanium with HF acid. d. Decrease the pH of the “weak acid” leach to avoid losing germanium in silica gel formation.

Each of these methods increased germanium extraction from zinc residue to more than 96 pct.

In leaching the Utah gallium and germanium ore, it was shown that H₂SO₄ alone could extract gallium and germanium without the use of a reducing agent such as

SO₂. Leaching studies showed that as the H₂SO₄ concentration increased, gallium extraction increased to more than 95 pct, while germanium extraction reached a peak of 71 pct before decreasing to less than 50 pct. It was hypothesized that at high acid concentrations, germanium precipitated from solution as GeO₂.

For optimum gallium and germanium extraction, a two-stage countercurrent leach system was devised to adequately control the solution acidity. At operating conditions of 2,000 lb/st H₂SO₄, 20 pct solids, and 90° C, 96 pct of the gallium and 85 pct of the germanium in the ore were extracted. Microprobe studies showed that approximately 10 to 15 pct of the germanium in Apex ore is in solid solution with silica and cannot be leached with H₂SO₄ or SO₂.

Gallium solvent extraction from H₂SO₄ filtrates was studied with the following conclusions being made:

Solvent extraction with the organophosphate OPAP proved very successful for recovering more than 98 pct of the gallium from solutions with acid content as high as 40 g/L (approximately pH 0).
Gallium extraction using OPAP was hindered when ferric iron was present in solution. Therefore, the iron in the filtrate was maintained in a reduced state by contacting the solution with metallic iron.
Continuous gallium solvent extraction using a leach solution containing 0.32 g/L Ga and an organic containing 0.3M OPAP effectively loaded 95 pct of the gallium onto the organic. Stripping the organic with a 1.5M·H₂SO₄ solution recovered 94 pct of the gallium.
A 50-pct·H₂PO₄ strip effectively reduced the amount of ferric iron remaining on the OPAP to less than 0.5 g/L, thus enabling the continuous system to maintain high gallium recoveries.

The investigation of germanium solvent extraction from H₂SO₄ solutions yielded the following results:

Of the 60 potential extractants and combinations of extractants screened, the organic mixture of OPAP-LIX 63 was found to synergistically extract more than 40 pct of the germanium after one contact with actual leach solution.
Germanium extraction increased to more than 80 pct when copper was removed from solution and iron was reduced to the ferrous state by contacting the leach solutions with metallic iron.
Germanium was effectively stripped from the loaded organic using only 75° C water. Residual iron on the organic was reduced to acceptable levels using H₂SO₄ scrub solutions.
A continuous germanium solvent-extraction circuit using OPAP-LIX 63 for germanium loading, 75° C water for germanium stripping, and H₂SO₄ for iron scrubbing extracted more than 90 pct of the germanium from leach solutions.

Research showed that the OPAP-LIX 63 organic combination was capable of extracting both gallium and germanium from H₂SO₄ solutions if the acid concentration of the aqueous and the strength of the extractant were properly controlled. More importantly, selective stripping with 75° C water stripped 96 pct of the germanium, while 3M H₂SO₄ removed 95 pct of the gallium.

REFERENCES³

Petkof, B. Gallium. Ch. in Mineral Facts and Problems, 1985 Edition. BuMines B 675, 1985, pp. 291-296.
Llewellyn, T. O. Germanium. Sec. in BuMines Mineral Commodity Summaries 1989, pp. 62-63.
Kramer, D. Gallium. Sec. in BuMines Mineral Commodity Summaries 1989, pp. 56-57.
Wall Street Journal. Silicon Successor? May 29, 1987, p. 1.
Brody, H. Ultrafast Chips at the Gate. High Technol., v. 6, No. 3, 1986, pp. 28-35.
Electronics. GaAs-on-Silicon Wafers Are Set To Go Commercial. Oct. 15, 1987, pp. 47-48.
Murphy, T. D. Design and Analysis of Industrial Experiments. Chem. Eng., v. 84, No. 12, 1977, pp. 168-182.
E. I. du Pont de Nemours & Co., Inc. (Wilmington, DE). Strategy of Experimentation. 1975, 70 pp.
Pugh, W. The Solubility of Germanium Dioxide in Acids and Alkalis. J. Chem. Soc., v. 51, No. 6, 1929, pp. 1537-1541.
JCPDS International Centre for Diffraction Data (Swarthmore, PA). Powder Diffraction File. 1989, p. 246.
Brewer, F. M., J. O. Cox, and D. F. Morris. The Occurrence of Germanium in Blende. Geochim. et Cosmochim. Acta, v. 8, No. 3, 1955, p. 131.
Malevskiy, A. Y. Form of Germanium in Sphalerite. Ch. in Geochemistry of Germanium, ed. by J. Weber. Hutchinson and Ross, 1973, pp. 371-373.
Warren, H. V., and R. M. Thompson. Sphalerites From Western Canada. Econ. Geol., v. 40, No. 5, 1945, p. 309.
Umetsu, Y., and K. Tozawa. Study on Behavior of Germanium in Electrolytic Zinc Production Process. Metall. Rev. MMIJ, v. 4, No. 1, 1987, pp. 66-81.
Miller, W. S., F. Dachille, E. C. Shafer, and R. Roy. The System GeO₂-SiO₂. Ch. in Geochemistry of Germanium, ed. by J. Weber. Hutchinson and Ross, 1973, pp. 11-19.
Zangieve, Z. G., N. I. Kaloev, B. I. Bashkov, V. E. Burtakova, and L. M. Kubaloun. (Solubility of Zinc Germanate in Sulfuric Acid). Zh. Neorg. Khim, v. 28, No. 10, 1983, pp. 2631-2633.
Matthew, I. G., and D. Elsner. The Hydrometallurgical Treatment of Zinc Silicate Ores. Metall. Trans. B, v. 8B, No. 1, 1977, pp. 73-84.
The Processing of Zinc Silicate Ores—A Review. Metall. Trans. B, v. 8B, No. 1, 1977, pp. 85-91.

³A title enclosed in parentheses is a translation from the language in which the work was published.

Grusdev, V. S., and V. M. Vydrin. Geochemical Features of Germanium in the Hydrothermal Process. Dokl. Acad. Sci. USSR Earth Sci. Sect. (Engl. Transl.), v. 175, No. 2, 1967, pp. 188-190.
Caletka, R., and P. Kotas. Separation of Germanium From Some Elements by Adsorption on Silica Gel. J. Radioanal. Chem., v. 21, No. 2, 1974, pp. 349-353.
Foot, D. G., Jr., J. D. McKay, and J. L. Huiatt. Column Flotation of Chromite and Fluorite Ores. Can. Metall. Q., v. 25, No. 1, pp. 15-21, 1986.
Bernstein, L. R. Geology and Mineralogy of the Apex Germanium-Gallium Mine, Washington County, Utah. U.S. Geol. Surv. Bull. 1577, 1986, 9 pp.
Dutrizac, J. E., J. L. Jambor, and T. T. Chen. Host Minerals for the Gallium-Germanium Ores of the Apex Mine, Utah. Econ. Geol., v. 81, No. 4, 1986, pp. 946-950.
Olsen, T. M., D. E. Voelker, and R. A. Smith. Gallium and Germanium Extraction From the Apex Mine Ore. Paper in Proceedings of Precious and Rare Metal Technologies (Albuquerque, NM, Apr. 6-8, 1988). NM Inst. Min. and Tech., Socorro, NM, 1989, pp. 531-545.
Swinkels, G. M., and J. E. Litz. The Apex Project: Development of a Primary Gallium and Germanium Producer. Soc. Min. Eng. AIME preprint 86-153, 1986, 4 pp.
Jiang, H., K. Lee, A. J. Singh, A. K. Singh, and A. E. Torma. Kinetics of Gallium and Germanium Extraction From a Complex Ore by $\mathrm{H}_2\mathrm{SO}_4$ – $\mathrm{Na}_2\mathrm{S}_2\mathrm{O}_3$ Leachants. Paper in Proceedings of Precious and Rare Metal Technologies (Albuquerque, NM, Apr. 6-8, 1988). NM Inst. Min. and Tech., Socorro, NM, 1989, pp. 547-565.
Davies, G. R., and G. T. Morgan. Determination of Germanium. Analyst (London), v. 63, No. 744, 1938, p. 388.
Boateng, D. A., D. L. Ball, and G. M. Swinkels. Recovery of Germanium From Aqueous Solutions. U.S. Pat. 4,525,332, June 25, 1985.
Sheka, I. A., I. S. Chaus, and T. T. Mityureva. Methods of Preparation of Gallium. Ch. in The Chemistry of Gallium. Elsevier, 1966, pp. 225-230.
Zekel, L. A., M. D. Nosovshii, A. M. Rexnik, and M. Y. Shpirt. Extracting Gallium From Discard Solution of Germanium Plants. Tsvetn. Met., v. 45, No. 5, 1972, p. 54.
Nagumo, T., and M. Murakoshi. Extraction of Gallium Using a Trialkyl Phosphate. U.S. Pat. 3,151,946, Oct. 6, 1964.
Rafaeloff, R. Separation of Gallium From Group III Elements, Germanium, Copper, Arsenic, and Iron. Anal. Chem., v. 43, No. 2, 1971, pp. 272-274.
Katsura, T., and H. Abe. Solvent Extraction of Indium and/or Gallium. U.S. Pat. 3,920,450, Nov. 18, 1975.
Bauer, H., and K. Burschkes. Organic Compounds of Germanium. Berlin, v. 65B, No. 1, 1932, p. 960.
Cote, G., and D. Bauer. Liquid-Liquid Extraction of Germanium With Oxime Derivatives. Hydrometallurgy, v. 5, No. 2-3, 1980, pp. 149-160.
Bauer, D., G. Cote, P. Fossi, and B. Marchon. Process for Selective Liquid-Liquid Extraction of Germanium. U.S. Pat. 4,389,379, June 21, 1983.
De Schepper, A., and A. Van Peteghem. Liquid-Liquid Extraction of Germanium From Aqueous Solution Using Hydroxy-Oximes. U.S. Pat. 3,883,634, May 13, 1975.
U.S. Department of Energy. Uraniferous Phosphate Resources and Technology and Economics of Uranium Recovery From Phosphate Resources, United States and the Free World. GJBX-110(79), 1979, p. 245.
Demopoulos, G. P., and D. L. Gevfert. Iron (III) Removal From Base-Metal Electrolyte Solutions by Solvent Extraction. Hydrometallurgy, v. 12, No. 3, 1984, p. 299.
De Schepper, A., M. Commement, and A. Van Peteghem. Process for Separating Germanium From an Aqueous Solution by Means of an Alphahydroxyoxime. U.S. Pat. 4,432,952, Feb. 21, 1984.
Ashbrook, A. W. Commercial Chelating Solvent Extraction Reagents: I. Purification and Isomer Separation of 2-hydroxyoximes. J. Chromatog., v. 105, No. 1, 1975, p. 141.

INT.BU.OF MINES,PGH.,PA 29562

USGPO: 1992–617-007/60061

Let us now in this same blogpost insert new content from chatGPT.

The mathematics of entity[“scientific_concept”,”Quantum Entanglement”,”quantum mechanics phenomenon”] starts with how quantum systems are represented.

1. Single quantum system

A quantum state is described by a vector in a complex vector space called a Hilbert space.

For a single qubit (like a spin-1/2 particle), the state is

|\psi\rangle = \alpha |0\rangle + \beta |1\rangle

where:

$|0\rangle$ and $|1\rangle$ are basis states
$\alpha, \beta \in \mathbb{C}$
normalization requires

|\alpha|^2 + |\beta|^2 = 1

These coefficients determine measurement probabilities.

2. Two-particle systems: tensor product

For two particles, we do not add spaces-we use the entity[“scientific_concept”,”Tensor Product”,”linear algebra operation for combined quantum states”].

If particle A has space

\mathcal{H}_A

and particle B has space

\mathcal{H}_B

, then the combined system is

\mathcal{H}_{AB} = \mathcal{H}_A \otimes \mathcal{H}_B

For two qubits, the basis becomes:

|00\rangle,\ |01\rangle,\ |10\rangle,\ |11\rangle

A general two-qubit state is

|\Psi\rangle = a|00\rangle + b|01\rangle + c|10\rangle + d|11\rangle

with

|a|^2+|b|^2+|c|^2+|d|^2 = 1

3. Separable vs entangled states

A state is separable if it can be written as

|\Psi\rangle = |\psi_A\rangle \otimes |\psi_B\rangle

Example:

\left(\frac{|0\rangle+|1\rangle}{\sqrt2}\right)\otimes |0\rangle

This is not entangled.

A state is entangled if it cannot be factorized this way.

4. Famous Bell state

The simplest entangled state is a entity[“scientific_concept”,”Bell State”,”maximally entangled two-qubit quantum state”]:

|\Phi^+\rangle = \frac{1}{\sqrt2}(|00\rangle + |11\rangle)

This means:

if the first particle is measured as 0, the second is also 0
if the first is 1, the second is also 1

But before measurement, neither particle has a definite individual value.

This correlation is stronger than classical probability allows.

5. Density matrix view

Sometimes we use the entity[“scientific_concept”,”Density Matrix”,”quantum state operator representation”]:

\rho = |\Psi\rangle\langle\Psi|

For the Bell state:

\rho = \frac12 \left( |00\rangle\langle00| + |00\rangle\langle11| + |11\rangle\langle00| + |11\rangle\langle11| \right)

The cross terms show genuine quantum coherence.

6. Reduced density matrix

To study one subsystem alone, we use the partial trace:

\rho_A = \mathrm{Tr}_B(\rho)

For the Bell state:

\rho_A = \frac12 \begin{pmatrix} 1 & 0 \\ 0 & 1 \end{pmatrix}

This means each particle alone looks completely random.

Only together do they show perfect order.

That is the signature of entanglement.

7. Entanglement entropy

A standard measure is the entity[“scientific_concept”,”Von Neumann Entropy”,”quantum information entropy measure”]:

S(\rho_A) = -\mathrm{Tr}(\rho_A \log \rho_A)

For a Bell state:

S = 1

which indicates maximal entanglement.

For separable pure states:

S = 0

8. Bell inequalities

Entanglement can violate entity[“scientific_concept”,”Bell’s Inequality”,”test distinguishing quantum correlations from classical hidden variables”], showing that no local hidden-variable theory can explain the correlations.

This is where the mathematics meets experimental physics.

Short intuition

Classically:

“particle A has value, particle B has value”

Quantum mechanically:

“only the whole system has a definite state”

That is the mathematical heart of entanglement.

In one sentence:

Entanglement is the failure of factorization of the joint quantum state in tensor-product Hilbert space.

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The economics of ethanol blending is a tug-of-war between agricultural support, environmental policy, and energy efficiency. In the U.S., this is driven primarily by the Renewable Fuel Standard (RFS), which mandates that a certain volume of renewable fuel be blended into the national transportation fuel supply.

Here is a breakdown of the economics using current 2024–2026 data and estimates.

1. The Price Gap: Ethanol vs. Gasoline

On a pure volume basis, ethanol is often cheaper than “neat” (unblended) gasoline. However, ethanol contains about 33% less energy per gallon than gasoline.

Component	Approx. Wholesale Price (per gallon)	Energy-Adjusted Price (per gallon)
Unleaded Gasoline	$2.15	$2.15
Ethanol	$1.85	$2.76

The Economic Reality:

Wholesale Benefit: Refiners often save money by blending ethanol because it is a cheap “octane booster.” Without ethanol, they would have to use more expensive petroleum-based aromatics to reach the 87-octane standard.
Consumer Trade-off: While the price at the pump might be $0.05 to$ 0.10 cheaper for an E10 blend (10% ethanol), you may see a 3–4% drop in fuel economy, meaning you pay slightly more per mile driven.

2. The “Corn-to-Fuel” Economy

In the U.S., roughly 35–40% of the corn crop is used for ethanol production. This creates a massive economic link between the energy and food sectors.

For Farmers: Ethanol provides a “price floor” for corn. By creating a consistent demand for billions of bushels, it stabilizes farm income.
For Consumers (Food): Because such a large portion of corn is diverted to fuel, it can lead to higher prices for livestock feed (beef, poultry, pork).
Example: If a drought hits and corn prices spike to $7.00/bushel, the cost of producing ethanol rises sharply. However, because refiners are mandated to blend it, they must buy it anyway, which can keep food prices high even when fuel demand is low.

3. Policy Incentives: The RIN Market

The “invisible” economy of ethanol blending runs on RINs (Renewable Identification Numbers). These are digital credits that represent one gallon of biofuel.

How it works: When a refiner blends a gallon of ethanol into gasoline, they “earn” a RIN.
The Mandate: If a refiner doesn’t blend enough ethanol to meet the government’s quota, they must buy RINs from other companies that did.
Economic Impact: In 2024–2025, RIN prices have fluctuated significantly. High RIN prices (e.g., $1.50 per credit) act as a hidden tax on independent refiners who don’t have their own blending facilities, potentially raising the final price of gasoline for consumers.

4. Infrastructure Costs

Moving to higher blends like E15 or E85 (85% ethanol) requires specialized infrastructure.

Gas Stations: Upgrading a single fuel dispenser and underground tank to be “ethanol-compatible” can cost a small business owner $50,000 to$ 200,000.
Subsidies: Programs like the Higher Blends Infrastructure Incentive Program (HBIIP) provide millions in federal grants to offset these costs, essentially using taxpayer dollars to lower the barrier for ethanol entry into the market.

Summary Table: Winners and Losers

Stakeholder	Economic Impact
Corn Farmers	Win: Guaranteed high-volume market for their crop.
Refiners	Mixed: Save on octane costs but pay for compliance (RINs).
Motorists	Mixed: Slightly lower pump price, but lower MPG and potential long-term engine wear on older cars.
Environment	Win: Reduction in greenhouse gas emissions (approx. 40% vs. gasoline).

Would you like to dive deeper into how RIN trading affects the stock prices of independent oil refiners?

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The Economic Model: The Triffin Dilemma and Petrodollar Recycling

The “Recycle” Equation

Quantitative Comparison: Petrodollar vs. Traditional Trade

Modelling the “Exorbitant Privilege”

Impact on Global Trade Balances

The Trade Flow Model

Summary of Economic Significance

Gallium and Germanium Recovery From Domestic Sources

Gallium and Germanium Recovery From Domestic Sources

CONTENTS

ILLUSTRATIONS

TABLES

TABLES—Continued

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

GALLIUM AND GERMANIUM RECOVERY FROM DOMESTIC SOURCES

ABSTRACT

INTRODUCTION

IDENTIFYING DOMESTIC SOURCES

LEACHING OF ZINC RESIDUE

BACKGROUND

STATISTICAL DETERMINATION OF SIGNIFICANT VARIABLES

BATCH TESTING OF SIGNIFICANT VARIABLES

IMPROVING GERMANIUM EXTRACTION FROM ZINC RESIDUES

Germanium Insolubility During Roasting

Germanium Insolubility During Leaching

Methods for Overcoming Germanium Insolubility

LEACHING OF GERMANIUM-GALLIUM ORE

BACKGROUND

RESULTS AND DISCUSSION

Germanium Extraction

Two-Stage Countercurrent Leaching

Increasing Germanium Extraction

GALLIUM AND GERMANIUM SOLVENT EXTRACTION FROM H₂SO₄ SOLUTIONS

GALLIUM SOLVENT-EXTRACTION BACKGROUND

GERMANIUM SOLVENT-EXTRACTION BACKGROUND

SOLUTION PREPARATION AND ANALYSIS

INITIAL SOLVENT-EXTRACTION TESTING

GALLIUM SOLVENT EXTRACTION

Iron Versus Gallium Loading

OPAP and DEHPA

Rate and Equilibrium Analysis

Gallium Loading

Gallium Stripping

Ferric Stripping

Continuous Solvent Extraction of Gallium

System Design

System Operation

Strip Liquor Purification

GERMANIUM SOLVENT EXTRACTION

Effect of Copper and Iron

Synergism

Effect of Acid Concentration

Germanium Stripping

Germanium Rate and Equilibrium Analysis

Germanium Loading

Germanium Stripping

Iron Scrubbing

Continuous Solvent Extraction of Germanium

System Design

System Operation

Testing Leach Filtrate D Containing 40 g/L H₂SO₄

Testing Leach Filtrate D Containing 60 g/L H₂SO₄

GALLIUM AND GERMANIUM COEXTRACTION

EXPERIMENTAL RESULTS

INDUSTRIAL APPLICATION

SUMMARY

REFERENCES³

1. Single quantum system

2. Two-particle systems: tensor product

3. Separable vs entangled states

4. Famous Bell state

5. Density matrix view

6. Reduced density matrix

7. Entanglement entropy

8. Bell inequalities

Short intuition

1. The Price Gap: Ethanol vs. Gasoline

2. The “Corn-to-Fuel” Economy

3. Policy Incentives: The RIN Market

4. Infrastructure Costs