Valuable Metal Recovery from Nickel Sulfide Flotation Tailings via Chloride-Based Acid Leaching

The current study proposes an efficient approach for the recovery of nickel and other valuable metals from nickel sulfide flotation tailings. In the study, magnesium chloride, sodium chloride, and ferric chloride were investigated as reactants in an acidic medium to improve metal extraction. The effect of leaching time, leaching temperature, H2SO4 concentration, reactant concentration, and the feed sample particle size on recovery of metals was correspondingly examined using the central composite design and response surface methodology optimization technique. The preliminary leaching studies indicated that HNO3 acid yielded the best recoveries for nickel under the same leaching conditions as HCl and H2SO4, however, H2SO4 was selected considering industrial and economic potential. The addition of ferric chloride as an oxidative significantly improved leaching as well as the leaching temperature. Optimization tests were performed using response surface methodology and under the optimum conditions, 98.9% nickel and 99.1% copper was effectively leached from the flotation tailings into solution. Economic evaluation of the chloride-acid leach approach also proved that the cost of using ferric chloride can be profitable. The kinetics was studied using nickel and copper as a baseline and it was established that the dissolutions of these metals were internal diffusion controlled with apparent activation energies of 19.63 kJ/mol and 15.98 kJ/mol for nickel and copper, correspondingly.