GB761129A - Method of separating metal values from ammoniacal solutions - Google Patents

Abstract

In the recovery of nickel and/or cobalt from an ammonical solution containing free ammonia, dissolved nickel and cobalt and dissolved values of at least one other metal the sulphide of which is of lower solubility in the ammoniacal solution than nickel sulphide, especially copper, the solution is provided with at least one sulphur compound of the group consisting of polythionates having more than two sulphur atoms and thiosulphates in an amount sufficient to provide sulphur atoms to combine with the values of other metal or metals and the solution is heated for a period of time to reduce the free ammonia content and to convert the said other metals to and precipitate them as, sulphides, which are separated, after which the purified nickel and cobalt solution may be treated for the recovery of nickel and cobalt by conventional means, e.g. by treating the solution with sulphuric acid to recover nickel and/or cobalt ammonium sulphates or by treatment with hydrogen at elevated temperature and pressure to recover the metals. The initial ammoniacal solution may be obtained by an oxidative leaching of mineral sulphides with strong aqueous ammonia, as in Specification 670.184, whereby in general the necessary polythionate or thiosulphate ions are formed in situ, or if necessary, can be added in the form of ammonium trithionate or thiosulphate. The initial leaching to obtain the ammoniacal solution is preferably conducted by passing mineral sulphides and leach solutions in counter current in a plurality of stages, the pregnant leach solution being discharged from and the fresh mineral sulphides being charged to the first stage of the series; fresh ammonia solution may be charged to any of the leaching stages. According to an example a nickel, copper, cobalt sulphide concentrate containing 11 per cent nickel and 2 per cent copper was leached in successive stages with aqueous ammonia at 60 to 90 DEG C. with an oxygen partial pressure of 1.75 kg. per cm2 and a total pressure of 5.5 to 7 kg. per cm2. The leach solution contained about 90 gms of nickel and 20 of copper per litre. The partially leached solids from the first leaching stage were passed to the second and successive leaching stages and the pregnant leach solution from the first stage, rich in thiosulphate and polythionate ions, was passed to a heating stage where is was heated to 95 to 100 DEG C. thus removing the ammonia (which was recovered and returned to the leaching stage) and reducing the copper content to 0.5 to 1.5 grams per litre. No nickel or cobalt was precipitated. The precipitated copper sulphide was separated and the residual solution passed to a stripping stage to precipitate the remainder of the copper as sulphide by adding a further thiosulphate or polythionate or hydrogen sulphfiide, or alternatively by adding sulphide concentarte of the type employed in the leaching stage e.g. pyrrhotite, which is oxidized to provide the necessary polythionate or thiosulphate ions for example by heating at 88 to 100 DEG C. for thirty minutes. The undissolved concentrates and precipitated copper sulphide were returned to the leaching stage and the copper free solution was passed to a nickel and/or cobalt recovery step. ... Reference has been directed by the Comptroller to Specification 722,373.