Heavy metals in the environment. II: A hydrochloric acid leaching process for the recovery of nickel value from a spent catalyst

A hydrochloric acid leaching process for the recovery of nickel, as nickel oxide, from low-grade spent catalyst analysing 17.7% Ni was studied. The effects of acid concentration, temperature, etc., on the extraction of Ni in chloride solution are first reported. Two different methods were examined for the separation of impurities from nickel chloride solution. In the first method, Ni was precipitated as solid nickel chloride by saturating the solution with hydrogen chloride gas. The effects of repeated leach /precipitation cycles were also investigated and it was found that the purity of the precipitated nickel chloride decreased as the number of cycles increased. Further purification was achieved by washing and anion exchange treatment. In the second method, nickel chloride solution was purified by removing impurities such as copper by cementation and iron and aluminum by oxidation/pH adjustment process. The preparation of nickel oxide from both methods was carried out by first precipitating nickel hydroxide, followed by calcination, to give an oxide with a purity suitable for the smelting process.