Process for the separation of nickel from solutions containing cobalt and nickel salts

摘要

Nickel is separated from an aqueous solution containing a mixture of cobalt and nickel salts by first precipitating the nickel by adding a metal more electronegative than nickel, for example iron, and also one or more metalloidic compounds formed between sulphur, selenium or tellurium on the one hand, and antimony or arsenic on the other. The separated nickel is then redissolved and the metalloidic compounds regenerated for further use. Copper may also be added in the first stage of the PICT:0853323/III/1 process, either as a soluble salt, the amount of copper added being 0.3-2% by weight of the nickel, or as the sulphide, the copper being 10-25% by weight of the nickel. The first stage may be carried out at 50-100 DEG C. and at a pH of approximately 2.5. Suitable metalloidic compounds include arsenic and antimony sulphides, which may be naturally occurring, such as realgars, orpiments, and stibnites and may be employed in an amount 1-2 times by weight of the nickel present in the solution. Between 1 and 5 times the theoretically required amount of metal more electronegative than nickel may be employed, preferably between 1.1 and 1.3 times, and is preferably in a finely divided state. In an example, a solution of nickel and cobalt sulphate or chloride is heated to above 50 DEG C. with agitation, and copper is added, either as a soluble salt or as the sulphide, which may be added with the metalloidic compound. Arsenic trisulphide and iron are then added, preferably simultaneously, and the pH is maintained at about 2.5 by acid addition, for example hydrochloric acid. The suspended solids are then removed and washed. The cobalt-containing mother liquor remaining is practically free of nickel and copper. The solids are then treated to regenerate the arsenic trisulphide, for example by suspending in water and passing in chlorine until the nickel is substantially completely dissolved, removing the residue, acidifying and adding a sulphide, for example iron sulphide or preferably hydrogen sulphide, to precipitate arsenic and copper sulphides. This precipitate may be freed of copper by dissolving the arsenic sulphide in sodium sulphide solution and acidifying to reprecipitate. The filtrate obtained after the arsenic and copper sulphides have been precipitated is treated to eliminate cobalt and iron by oxidising with chlorine and precipitating ferric hydroxide by adding calcium carbonate to a pH of 3.0-3.5, and precipitating cobalt hydroxide, contaminated with a little nickel which may be recycled to the first stage of the process, by the simultaneous action of chlorine and sodium hydroxide as in Specification 795,410. The cobalt-containing mother liquor obtained after removing the suspended solids in the initial stage of the process may be freed from iron by precipitation as the hydroxide as indicated above. The accompanying flow sheets illustrates the process of the invention.