Removal of arsenic from arsenate complex contained in secondary zinc oxide

A promising process, including selective arsenic extraction, oxidation and lime precipitation, was proposed to treat arsenate bearing secondary zinc oxide, which was a smelting dust generated from fuming furnace. With a mixed solution of 50 g/L NaOH and 50 g/L Na2S·9H2O at L/S ratio of 3:1, more than 73% As was extracted at 80 °C in 1 h, while the leaching of Pb and Zn was below 1%, respectively. Each residual contained 1.68% As, which was supposed to exist as inclusions. To minimize the loss of metal values, lead and zinc dissolved in the leach solution were further recovered by adjusting the pH of solution to 12, which avoided the formation of lead and zinc arsenate in lime precipitation. More than 99.8% As was precipitated as crystallized Ca5(AsO4)3OH, leaving 3 mg/L As in the final liquor, which was recycled with additional NaOH and Na2S·9H2O to leaching step.