Nickel recovery from spent Raneynickel catalyst through dilute sulfuric acid leaching and soda ash precipitation

Pharmaceutical industry makes extensive use of Raneynickel catalyst for various organic drug intermediates/end products. Spent catalysts contain environmentally critical and economically valuable metals. In the present study, a simple hydrometallurgical process using dilute sulfuric acid leaching was described for the recovery of nickel from spent Raneynickel catalyst. Recovery of nickel varied with acid concentration and time, whereas temperature had negligible effect. Increase of S/L ratio to 30% (w/v) showed marginal effect on nickel (90%) recovery, whereas Al recovery decreased drastically to similar to 20%. Under the optimum conditions of leaching viz: 12vol.% H2SO4, 30 degrees C, 20% solid to liquid (S/L) ratio and 120min reaction time, it was possible to recover 98.6% Ni along with 39.2% Al. Leach liquor [pH 0.7] containing 85.0g/L Ni and 3.25 g/L Al was adjusted to pH 5.4 with 30wt.% alkali for quantitative aluminum removal. Nickel loss was about 2% during this Al removal step. Nickel from the purified leach liquor was recovered as nickel carbonate by adding required amount of Na2CO3. The purity of NiCO3 product was found to be 100% with a Ni content of 48.6%. Na2SO4 was recovered as a by-product with a purity of 99%. Complete process is presented. (C) 2009 Elsevier B.V. All rights reserved.