Aqueous Recovery of Zinc and Lead from Coal Fly Ashes of a Colombian Thermoelectric Plant

A hydrometallurgical treatment under ambient conditions was proposed in order to eliminate and recover the lead and zinc contained in a sample of thermal coal fly ash used to produce energy. By using leaching solutions with conventional inorganic acids (HCl, HNO3, and H2SO4), ferric chloride, and sodium citrate, more than 90% zinc and approximately 40% lead were obtained. The most favorable leaching conditions were set at 0,5 M, with a pH value of 8 for citrate. Two leaching stages were necessary to optimize metal recovery: the first with nitric acid for zinc extraction and the second one with citrate for the lead. The sulfur phases of the metals limited a complete metal extraction.