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UNITED STATES MINERAL RESOURCES 



from the combustion of coal. Additional potential 

 sources of recovery exist in the processing of cop- 

 per and lead ores and possibly in the processing of 

 ores of other metals, including tin, tungsten, molyb- 

 denum, and arsenic. 



The major resource problem therefore involves 

 not so much the geologic occurrences of the three 

 metals as the fate of the three metals during the 

 processing of the ores for their major components. 



From the scattered data on occurrence, apparently 

 relatively little of the gallium, germanium, and in- 

 dium potentially recoverable is now being obtained. 

 Estimates of the germanium content of zinc ores, 

 for example, suggest that potential resources are 

 adequate to support a several-fold increase in annual 

 production and the additional potential resources in 

 coal would permit further expansion of production. 

 Potential for recovery of additional gallium is also 

 quite large, and the potential for indium is appre- 

 ciable. 



EXPLOITATION 



Gallium, germanium, and indium have had similar 

 histories. About half a century elapsed between the 

 time they were first identified and the time that 

 first commercial uses for them were developed. The 

 growth in specific uses of the elements was un- 

 doubtedly retarded by the lack of natural sources 

 of ores containing appreciable concentrations and 

 by the relative difficulty of refining each of them 

 from dispersed sources. Systematic study of their 

 physical and chemical properties and investigation 

 of their compounds and alloys are still progressing; 

 thus, additional new uses will undoubtedly be found. 



Recovery of indium on a semicommercial scale 

 began in the 1920's for use as a precious-metal alloy- 

 ing agent to enhance brightness and retard tarnish. 

 Additional uses developed in special bearing-metal 

 alloys in the 1940's, but until the development of 

 uses in semiconductor devices about 1952 the de- 

 mand was not particularly steady. Similarly, germa- 

 nium was not recovered in significant quantities 

 until the early 1940's, when its use in electronic 

 rectifiers led to initial commercial-scale production. 

 With the development of transistors, beginning 

 about 1948, germanium consumption increased 

 greatly, and it continued to increase steadily through 

 1960, when there was a sharp decline in consumption 

 because of competition from silicon and because of 

 improvements in fabricating techniques. Gallium 

 production began in 1943 with most of the few kilo- 

 grams produced being used in research. With the 

 development of semiconductor devices, production 

 grew in the late 1940's and early 1950's to about 90 



kg (kilograms) a year and has apparently stayed at 

 about that level since then, with 1968 production 

 estimated to be in the range of 100-300 kg. The 

 present commercial production of each of the three 

 elements is substantially smaller than might be 

 achieved if there were larger markets. Recovery and 

 refining are expensive; therefore, only the amounts 

 that can be marketed are processed. The amounts re- 

 covered are obtained from several different interme- 

 diate products in the processing of ores of other 

 metals. These starting materials in the recovery of 

 the three metals generally represent the highest con- 

 centrations of gallium, germanium, or indium that 

 can be obtained at some point in the production line 

 where a separation can be made conveniently. 



The principal products in which appreciable gal- 

 lium, germanium, and indium are concentrated are 

 recovered by roasting zinc sulfide ores to produce 

 crude zinc oxide and by further roasting this with 

 salt to separate the volatile chlorides of germanium, 

 gallium, cadmium, and indium from the zinc. These 

 chlorides are collected by electrostatic precipitation 

 and purified by complex distillation, chemical treat- 

 ment, and electrolytic separation. 



In addition, the drosses, slags, and anode slimes 

 in other smelting and refining processes can be used 

 as starting materials, especially the materials that 

 are associated with the recovery from zinc of other 

 byproduct metals such as cadmium, lead, and tin. 

 Gallium is also recovered from the leaching solutions 

 used to make alumina from bauxite. At some stage 

 in the caustic leaching cycle the solution builds up 

 an equilibrium concentration of gallium (about 0.1 

 g per liter) which can be recovered by precipitation 

 with carbon dioxide, filtration, and complex separa- 

 tion followed by electrolysis. 



The complex chemical and physical processes used 

 to separate and concentrate these metals have been 

 developed primarily to operate on specific starting 

 materials available to individual companies. For the 

 most part, these starting materials are selected be- 

 cause they have the highest initial concentration of 

 one or more potentially salable byproducts and be- 

 cause the particular starting materials can be con- 

 veniently acquired. Very few data are published on 

 the trace-metals content of potential interest for 

 other possible off-products at various stages of 

 smelting and refining. 



Judging from geochemical data on their germa- 

 nium and indium contents, some copper ores, espe- 

 cially those containing enargite, bornite, tennantite, 

 and tetrahedrite, would seem to be of particular in- 

 terest as sources of these metals. The distribution of 

 such trace metals in various stages of concentrating, 



