HEAVY-METALS IN THE ENVIRONMENT .6. RECOVERY OF COBALT VALUES FROM SPENT COBALT MANGANESE BROMIDE OXIDATION CATALYSTS/

Cobalt is recovered from a series of spent cobalt/manganese bromide ox idation catalysts containing 27-31% Co, 25-33% Mn, 0-14% Fe together w ith Cr, Cu and Ni. While ammoniacal leaching in the presence of reduci ng agents can be used to extract cobalt, the process has to be separat ely optimized for each sample. Leaching with 4 M HCl at 80 degrees C f or 4 hours, however, proved successful for all the catalysts. A method of successive neutralization is used for the separation of cobalt fro m the acid solutions. Addition of solid NaOH to pH 2 removes Fe and Cr as hydroxide, while addition of ammonia to pH 10 precipitates mangane se oxide from an aerated solution leaving Co as a Co-III hexammine com plex. Cobalt can be recovered from this solution by chemical or electr ochemical processes. After crystallization the complex is converted to anhydrous cobalt chloride by heating it to 320 degrees C or to Co2O3 by roasting it in air at 500 degrees C. Either of these materials may be readily converted into other cobalt chemicals. Alternatively, fluid ized bed cell electrolysis of the Co-III complex solution yields cobal t with purity > 99.5%.