Removal of arsenic from Waelz zinc oxide using a mixed NaOH-Na2S leach

Arsenic was selectively leached from Waelz zinc oxide with a mixed NaOH + Na2S solution followed by hydrogen peroxide oxidation and lime precipitation. The effects of temperature, L/S ratio, leaching time and reagent concentration on the leaching of arsenic were investigated. With the mixed solution of 25 g/L NaOH and 25 g/L Na2S center dot 9H(2)O and L/S ratio of 4:1, more than 90% As was extracted at 30 degrees C in 3 h, while the concentrations of lead and zinc in the leach solution were below 0.005 and 0.02 g/L, respectively. After recycling the leach solution and doubling the concentration of arsenic, the leach solution was treated by hydrogen peroxide oxidation followed by lime precipitation which removed 99.86% As, leaving 2 mg/L As in the solution. The filtrate was recycled with additional NaOH and Na2S center dot 9H(2)O and the precipitate of calcium arsenate was solidified with cement and treated in landfill. (C) 2011 Elsevier B.V. All rights reserved.