Cobalt, arsenic volatilization

Figure 4 Influence of cobalt added to a culture medium in the presence of Penicillium sp. on arsenic volatilization. Standard error of mean was calculated based on five replicates incubated for 7 days (From Ref. 57.)...

Space will not be devoted here to emphasis of the vast technological importance of iron and the steels nor to the discussion of ferrous metallurgy. However, typical processes for obtaining cobalt and nickel from natural sources are outlined in Table 24-1. The process for cobalt is somewhat oversimplified, for cobalt ores often contain, in addition to iron and arsenic, nickel, silver, or copper, which must also be removed. Note that nickel is conveniently purified by conversion to its volatile carbonyl, Ni(CO)4, unstable at high temperatures Mond process). 

Cobalt sulfide and arsenide ores are often found mixed with those of nickel and copper. The mixed ore is roasted with Na2C03 and KNO3, which removes part of the sulfur and arsenic as volatile species. The residue contains the metal oxides, as well as sulfate and arsenate, and the latter are removed by leaching with water. The metal oxide mixture is then dissolved in hot HCl or H2SO4, and the individual metal oxides are fractionally precipitated using Ca(OH)2 and NaOCl. This process gives the mixed valent oxide C03O4, which is then reduced to the metal by treatment with charcoal. 

The mechanically dressed ore is first roasted in order to remove sulphur, arsenic, and other volatile ingredients, and then heated in a reverberatory furnace with sodium carbonate or sodium sulphate. The product is extracted with %varm dilute sulphuric acid, whereupon the uranium passes into solution, whilst the radium remains in the residue witlr calcium, barium, and lead. Tliis residue, which is the starting material for tlie extraction of radium, also contains silica and small quantities of copper, bismutli, arsenic, antimony, iron, aluminium, manganese, zinc, nickel, cobalt, thallium, vanadium, columbium, tantalum, and rare earths. 

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