GB667659A - Improvements in production of nickel - Google Patents

Abstract

In a method of refining nickel electrolytically with a sulphate-chloride electrolyte, in which metals such as iron, copper, lead, arsenic and cobalt present in solution are removed and nickel cathodes are obtained from the purified electrolyte, a portion of the purified electrolyte is withdrawn from the main stream and is subjected to electrolysis to liberate chromium and sulphuric acid, the chrome being used to precipitate the cobalt with or without one or more of the other metals in the main stream of electrolyte, and the acid being used to extract nickel from at least one of the metal precipitates, the resulting solution of nickel sulphate being returned to the system, so that the composition of the main stream <PICT:0667659/III/1> of electrolyte is maintained constant as regards the chlorides and sulphates. In the flow sheet shown, there are three cells 10, 12, 14 provided with cathode starting sheets in cathode compartments having canvas filtering bags, and with impure nickel anodes in the anode compartments. The electrolyte is a mixed sulphate-chloride electrolyte which is conducted through a line 16 to a tank 18 where it is subjected to aeration whereby iron and some of the other metals are precipitated. The resulting slurry is passed through line 20 to a filter press 22. The filter cake containing the precipitated iron is treated in a tank 26 with mineral acid to convert nickel present (and also some iron and other metals) to a soluble salt of the acid. The solution thus formed is conducted through a line 28 to line 16, providing an opportunity for re-treating any iron in the solution. The filtrate from the filter press 22 passes through a line 30 to a copper-concentration tank 32 where the electrolyte is treated with gas-reduced nickel powder causing copper to be thrown out of solution as cement-copper. The slurry is passed to a filter press 36, the filter cake being withdrawn and treated to remove the copper. The filtrate is passed through a line 38 into a cobalt precipitation tank 40, where the electrolyte is treated with chlorine to oxidize and hence precipitate the cobalt and any lead and arsenic not yet removed. Some nickel is also precipitated. The slurry is passed to a filter press 44, the filter cake being treated with mineral acid in a nickel-extraction tank 46. The nickel in the form of a soluble salt is passed back to the system through a line 48. Cobalt residues in the tank 46 are recovered. The filtrate from the filter press 44 is divided into two portions, one portion passing into the cathode compartments of the cells 10, 12, 14 when it is subjected to electrolysis to form nickel cathodes substantially free from cobalt. The other portion of the filtrate passes through a line 58 to an electrolytic cell 60 where chlorine and sulphuric acid are formed, and nickel is deposited on cathode starting sheets. Chlorine from the cell is passed through line 62 to the iron-precipitation tank 18 and the cobalt-precipitation tank 40. Sulphuric acid from the cell 60 is passed through line 68 to nickel-extraction tanks 26 and 46 and to copper-concentration tank 32. Some of the chlorine produced in the cell 60 may be combined with hydrogen to form hydrochloric acid and re-introduced into the system, for example, to extract nickel from at least one of the metal impurities.