Metal oxides sulphation roasting

Preparation. Industrially, cobalt is normally produced as a by-product from the production of copper, nickel and lead. The ore is roasted to form a mixture of metals and metal oxides. Treatment with sulphuric acid leaves metallic copper as a residue and dissolves out iron, cobalt and nickel as the sulphates. Iron is separated by precipitation with lime (CaO) while cobalt is produced as the hydroxide by precipitation with sodium hypochlorite. The trihydroxide Co(OH)3 is heated to form the oxide and then reduced with carbon (as charcoal) to form cobalt metal. 

After filtration, addition of sodium sulphide to the clear solution effects the precipitation of the three metals, cobalt, nickel, and manganese, as sulphides. Digestion with the calculated quantity of ferric chloride oxidises the manganese sulphide to sulphate, which passes into solution. The residue consists of cobalt and nickel sulphides, which are washed and converted into their soluble sulphates by roasting. The sulphates are extracted with water, and converted into chlorides by addition of calcium chloride solution. Their separation is effected g.s follows The requisite fraction of the chloride solution is precipitated with milk of lime, and the insoluble hydroxides of nickel and cobalt thus obtained are oxidised to the black hydroxides by treatment with chlorine. The. washed precipitate is then introduced into the remainder of the chloride solution, and the whole is well stirred and heated, when the black hydrated oxide of nickel passes, into solution, displacing tlm Remainder of. the cobalt from the solution, into. the precipitate.. The final product is thus a suspension of hydrated peroxide.of cobalt,in p. solution of nickel chloride, from which idle cobalt precipitate is removed by filtration, washed, and ignited, to the black oxide. 

The Ziervogel process can be worked with argentiferous copper mattes free from lead, arsenic, antimony, and bismuth. By roasting the matte in an oxidizing atmosphere, the iron is converted into sulphate. About 700° C. this substance is decomposed, the copper being converted into sulphate. At 840° to 850° C. the copper salt is converted into cupric oxide,8 and silver sulphate simultaneously formed. At this point the roasting is stopped, the silver sulphate is extracted with hot water, and the silver precipitated by means of metallic copper. These mattes are now usually worked for copper, and the silver separated electrolytically. 

The metal itself does not occur naturally and is extracted from its ores using long established but ever improving technologies. Crude ore is first roasted in large batches until part of it has been converted to lead oxide and lead sulphate. The air supply is then turned off and the temperature... 

As far as the roasting of galena is concerned it may be remarked that the above is not a complete discussion, because alternative products such ts lead sulphate and metallic lead need to be considered. By utilizing the known free energies of these substances it may be established by similar reasoning that the main products of reaction at 800 K are lead oxide and lead sulphate. 

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