A STUDY OF A NICKEL-HYDROXIDE SULFATE PRECIPITATE OBTAINED DURING HYDROGEN REDUCTION OF NICKEL-HYDROXIDE SLURRIES

A nickel sulphate hydroxide precipitate that is insoluble in sulphuric acid medium at pH 2.0 was detected during hydrogen reduction experime nts on nickel slurries. This precipitate always appeared when a slurry , obtained by neutralising nickel sulphate by addition of sodium hydro xide, was being reduced by hydrogen gas at an elevated temperature, 16 0 degrees C, and a total pressure of 21 bar, the hydrogen partial pres sure being 15 bar, The properties of this precipitate were studied. Th is secondary precipitate proved to be stable for months when suspended in sulphuric acid at pH 2.0. When a similar slurry made by adding nic kel sulphate to sodium hydroxide (only the addition order of solutions changed) was reduced under the same conditions, no such 'insoluble' p recipitate occurred. The stable secondary precipitate was found to dis appear by further hydrogen reduction and it also dissolved at a temper ature of 80 degrees C at pH 4.