Arsenides, roasting

Treatment of Arsenical Ores.—Nickel is also obtained on a small scale from its arsenical ores. These are roasted to remove part of the arsenic and sulphur, smelted with silica and coke to remove iron in the slag, and the crude nickel arsenide thus obtained roasted in a reverberatory furnace to oxidise more iron and remove more arsenic. The last two operations are repeated until the product is sufficiently... 

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. 

Roasting [5.1,5.2,5.8,5.9]. This process can be applied to scheelite and wolfhunite. Treatment of ore concentrates at 660 to 1000 °C in air in rotary furnaces has been proposed to reduce the content of sulfides and/or arsenides by volatilization as sulfur dioxide and AS2O3, respectively. The addition of powdered coke leads to the evaporation of tin as SnO (900-1000 °C). If CO-CO2 or water vapor is added to the roasting atmosphere, arsenic and antimony volatilize. 

Copper is widely distributed in Nature as metal, in sulfides, arsenides, chlorides, and carbonates. It is extracted by oxidative roasting and smelting,... 

Like cobalt, nickel occurs as sulfide and arsenide minerals, e.g. pentlandite, (Ni,Fe)9Sg. Roasting such ores in air gives nickel oxide which is then reduced to the metal using carbon. The metal is refined electrolytically or by conversion to Ni(CO)4 followed by thermal decomposition (eq. 21.4). This is the Mondprocess, which is based on the fact that Ni forms a carbonyl derivative more readily than any other metal. 

Cobalt(II) arsenate is synonymous with cobalt arsenic oxide, Co3(As04)2. a production method given by Riffault et al. (1874) involves a sulpho-arsenide of cobalt being mixed with sand and twice its weight of potassa and fused . The product is ground and the process repeated with the addition of more potassa. The pure arsenide formed is then powdered and roasted. 

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