GB782185A - Improvements in or relating to hydrometallurgical production of metallic powders - Google Patents

Abstract

Solutions containing salts of an inorganic acid and at least one of the metals Co, Cu and Ni are treated with a reducing gas at elevated temperature and pressure in two stages to precipitate metal, the first nucleation stage consisting of inducing the precipitation of a fine seed powder at an acidic hydrogen ion concentration below that at the limiting free acid concentration at which reduction of the desired metal ceases, this fine seed powder being used in a second densification stage in a solution of salts in which the hydrogen ion concentration is adjusted to a value at which reduction proceeds readily by deposition on the seed powder, sufficient neutralizing agent being provided in this stage to prevent the acid liberated during reduction from increasing the acid concentration until the reduction is sufficiently complete. The whole of a solution may be treated in this manner being subjected to nucleation, adjustment and densification successively or a small portion of the solution may be nucleated and then added to the already adjusted main body of solution for densification or a body of solution which has been subjected to a partial reduction in a densification step may be separated from the precipitated metal, adjusted to conditions suitable for production of seed, and reduced to form seed powder which is then recycled to a fresh body of solution for the densification reduction. In the production of powder from a solution of NiSo4 the nucleation is initiated at an acid concentration between that at pH 6.7 and that at 5.0 per cent free acid, the solution is treated with ammonia to produce a basic pH and to convert the Ni to an ammine and then subjected to densification reduction, ammonia being added so that the terminal sulphuric acid concentration is between those at pH 1.5 and 5.0 per cent free acid.