The Preparation of Pure Electrolytic Nickel

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Abstract
The electrochemical methods for removing traces of copper and cobalt from nickel sulfate solutions were further investigated. When two or more metals are present in solution, it is difficult to predict which one will preferably deposit on the cathode, owing to many conflicting factors. By carefully selecting and controlling such factors as temperature, current density, hydrogen ion concentration, and cathode polarization film thickness, one metal may be deposited in preference to others even when such metal is present in solution in relatively small concentrations. The cathode polarization film thickness can easily be varied by employing a rotating cathode, operated at speeds of from 1,000 to 6,000 r.p.m. or a rapidly circulated catholyte. The concentration polarization effect at the cathode can be almost entirely eliminated by means of the high speed rotating cathode or by a rapidly circulated catholyte. Copper was removed almost quantitatively from solutions containing as little as 0.001 per cent copper. Copper was readily recovered from tails waters containing 0.01 per cent copper and 0.02 per cent iron, which latter, under ordinary conditions, prevents deposition of copper. From a solution containing both nickel and cobalt, in the ratio 100: 1, a nickel‐cobalt alloy deposit was obtained, containing over 40 per cent cobalt. The commercial possibilities of a highspeed rotating cathode or of a vigorously circulated catholyte are discussed, and commercial adaptation of the method is briefly outlined. The nickel metal obtained is free from cobalt and iron, and contains only a trace of copper, less than can be determined chemically. A simple laboratory scheme of continuously circulating the electrolyte in a 6‐liter cell is described and illustrated.

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