GALLIUM, GERMANIUM, AND INDIUM 



241 



smelting, and refining have not been described in 

 detail. 



RELATION TO OTHER COPRODUCTS OR BYPRODUCTS 



The interrelationship of these minor byproduct 

 metals to other byproduct or coproduct metals is of 

 particular interest. For example, the refining of cad- 

 mium from zinc plant residues offers an additional 

 stage of processing in which germanium and indium 

 may be volatilized and partly separated from other 

 metals into an enriched product. Similarly, in the 

 re-treatment of lead-bearing wastes in the refining 

 of zinc, several metals, such as tin, bismuth, and 

 indium, are concentrated in the dross skimmed from 

 lead bullion. Recovery of these minor constituents 

 and further separation account for most of the 

 Canadian production of indium. 



The economic viability of production of these 

 minor metals from a particular source is not easily 

 determinable. With limited markets, the search for 

 additional sources has not been intensive. The re- 

 covery and separation methods have not yet been 

 simplified to the extent that any one technique 

 could be incorporated as a step in a continuous 

 smelting or refining process. 



ENVIRONMENTAL RELATIONSHIP 



Both gallium and germanium, in limited amounts, 

 are apparently taken up by plants. A germanium 

 concentration of 10 ppm (parts per million) in the 

 ash is reported to be the toxic limit for plants under 

 experimental conditions. There are no reported oc- 

 currences of natural concentrations of germanium in 

 soils above toxic limits. No toxicity in plants has 

 been established for gallium or indium. Gallium is 

 reported to be found in concentrations of 0.1-0.2 

 ppm in plant ash and has been detected in vegetable 

 foodstuff and hens' eggs. No adverse environmental 



factors have been directly attributed to any of the 

 three elements, although indium and its compounds 

 have toxic properties to humans if ingested in large 

 quantities, and massive ingestion of gallium com- 

 pounds is also toxic. 



GEOLOGIC ENVIRONMENT 

 GEOCHEMISTRY 



All three elements are among the "dispersed" 

 elements that tend not to form distinct minerals 

 of their own, but to proxy for other major elements 

 in most rocks and minerals. 



Gallium is closely coordinated geochemically with 

 aluminum, with which it is associated. Its ionic 

 radius is 0.70 A in sixfold coordination (valence 

 +3), permitting relatively easy substitution for 

 aluminum (ionic radius 0.61 A). This association 

 accounts for the thorough dispersal of gallium as a 

 trace constituent in most igneous and sedimentary 

 rocks, as shown in table 47. It also accounts for the 

 relatively higher concentration of gallium in bauxite 

 and other aluminous rocks. Gallium is also concen- 

 trated in sulfide minerals, especially the zinc sulfide 

 minerals sphalerite (ZnS) and wurtzite ( [Zn,Fe] S) , 

 in which concentrations of as much as 0.5 percent 

 gallium have been reported. The concentration of 

 gallium is reported to be higher in sulfide minerals 

 formed at lower temperatures. Gallium is apparently 

 absorbed by the organic matter in some plants and 

 becomes concentrated in coal beds. 



Germanium is closely coordinated with silicon and 

 tin, and it can proxy for these elements in the 

 crystal lattices of appropriate minerals. Germanium 

 is distributed rather uniformly among the silicate 

 minerals of most rocks. It is notably concentrated 

 in topaz (as much as 700 ppm) and, to a lesser 

 extent, in cassiterite, garnet, and micas from rocks 

 rich in fluorine, such as some granite pegmatites 



Table 47. — Gallium, germanium, and indium contents of various materials 



[Crust and rocks, parts per million: waters, parts per billion] 



Gallium Germanium 



Material — 



Usual range Average Usual range Average 



Continental crust 18 1.5 



Igneous rocks: 



Ultramafic 1-5 2 0.7- 1.5 1 



Basaltic 9-20 15 .8- 3.2 1.3 



Intermediate 10-23 16 1.2- 6 1.6 



Silicic 14-30 19 .6- 4.7 1.6 



Alkalic 18-70 40 .9- 3.5 1.4 



Sedimentary rocks: 



Limestones 4 0- .8 .4 



Sandstones 3-20 8 0- 3.5 .8(7) 



Shales and clays 7—50 20 0- 3.9 2.2 



Bauxites 20-100 60 1.0- 3.6 2 



Coal 7 1 -150 5.6 



Waters ; 



Ground water 0- 24 .3(7) 



Hot springs .4- 44 10 



Rivers .03- .11 .05 



Sea water .06 



