Extra‐High‐Purity Nickel Powder from Nickel Sulfate Solution by Hydrogen Reduction

Abstract

The method described for the preparation of extra‐high‐purity nickel powder is based on the reduction of nickel sulfate solution by hydrogen under pressure in an autoclave. To obtain the required purity, the nickel sulfate solution must first be thoroughly purified from the elements that are more electropositive than nickel in the Nernst electromotive series and from the elements, the salts of which are susceptible to hydrolysis above a pH of 4. The methods employed for removing the traces of impurities include cementation of the copper, hydrolysis of the iron salts, and chemical precipitation of the cobalt. Unlike commercial practice of the hydrogen reduction process, the reduction of the purified nickel sulfate solution is carried out without a ferrous salt catalyst. To initiate the reduction reaction, a small amount of ammonium carbonate is introduced into the system. Reduction is carried out at a temperature of 350°F under a hydrogen pressure of 350 psi. The ammonium carbonate presumably promotes the formation of a fine suspension of solid basic nickel carbonate which then plays the role of a catalyst and provides the nuclei on which the nickel precipitates. In this way, contamination by the foreign elements originating from the catalysts normally used is avoided. Final “polishing” of the nickel powder is done using a wet hydrogen treatment at a temperature of 800°F to remove traces of carbon from the nickel powder, and a dry hydrogen heat treatment at 800°F to remove oxygen. The purity and some of the properties of the nickel powder produced are given.