GB1067007A - Method of leaching high grade nickel matte - Google Patents

Abstract

In the leaching of nickel and associated non-ferrous metals, i.e. Co and Cu from high-grade nickel matte which contains also S, Fe, one or more of the precious metals Pd, Pt, Ag and Au and at least one of the metalloid elements As and Sb to ensure minimum dissolution of As and Sb, a slurry of the finely-ground matte is formed in aqueous H2SO4 the total sulphur content of the slurry being at least the stoichiometric amount required to combine with the non-ferrous metals content of the slurry as sulphates; the slurry is subjected to a first leach at a temperature above 250 DEG F. (preferably 275 DEG to 300 DEG F.) and under a partial pressure of O2 above 10 p.s.i., this first leach being terminated at a slurry pH of 3.5 to 5.5 (preferably 4.5 to 5.0); the solution is separated from undissolved residue which is subjected to a second leach at a temperature above 250 DEG F. and under a partial pressure of O2 above 10 p.s.i., this leach being continued until substantially all the Ni, Co and Cu is extracted; the second leach solution is separated from undissolved residue and is treated together with the first leach solution to remove Cu and Fe and the purified leach solutions are treated for the recovery of Ni and Co. The undissolved residue from the second leach may be passed to a precious metals recovery operation and the first leach solution may be passed directly to the Ni and Co recovery steps without treatment for Cu and Fe removal. Cu may be removed from the leach solution by treatment with H2S and Fe and residual As precipitated by adjustment of the solution pH to 4.5 to 5 by addition of ammonia. The second leach solution may be treated to remove residual As by addition of Fe in an amount in excess of ten times the As content of the solution. The Ni and Co are obtained by known H2 reduction techniques after adjustment of the solution with ammonia and ammonium sulphate and the previous metals may be recovered from the undissolved residue by conventional processes such as cyanidation.