Recovery of nickel and other metals from nickel alloy scrap

Abstract

A pilot plant procedure to treat alloy scrap containing 30–60% nickel, 0.5–15% chromium and < 0.1% cobalt to recover nickel and other metals is described. Alloy scrap was melted in an electric furnace and cast into anodes for electrolysis in a diaphragm cell operating with a recycled chloride electrolyte. Effective electrolytic conditions were 200–250 A m⁻², 60–65°C, a 4.0–4.5 pH catholyte solution containing 60–65 g l⁻¹ nickel, and a 2.0–3.0 pH anolyte solution. Purified catholyte was prepared by removing chromium hydroxide which was precipitated by adding Na₂CO₃ or NiCO₃ solution to pH 4.2–4.6. Iron was eliminated with chlorine gas by vigorously aerating the solution to oxidize the iron and precipitate ferric hydroxide at pH 4.8–5.0. Cobaltic hydroxide was also precipitated along with iron. Activated carbon and anion exchange resin were used to remove trace amounts of copper, chromium, zinc and organic matter. After pH adjustment, the remaining purified solution was used for electrolysis in the cathode compartment where nickel was recovered. Some problems in the melting step and the control of technical conditions are discussed.