Ambient pressure hydrometallurgical conversion of arsenic trioxide to crystalline scorodite

摘要

Arsenic trioxide is a common by-product of the non-ferrous smelting industry. Due to a lack of demand most of it has to be disposed of. However, this can only be done temporarily due to its extremely toxic nature which poses a serious threat to the environment. Hence, an environmentally safe way of stabilizing and disposing of this product is needed. In this paper, a novel process for the ambient pressure conversion of arsenic trioxide (As_2O_3) to stable crystalline scorodite (FeAsO_4 centre dot 2H_2O) is discussed. The process consists of three stages: dissolution of arsenic trioxide in acidic water (95 deg C); oxidation of As(III) to As(V) using near stochiometric amounts of hydrogen peroxide; and precipitation of crystalline scorodite (FeAsO_4 centre dot 2H_2O) with addition of ferric iron (1.2 molar units Fe per molar unit As) in a sulphate medium at 95 deg C.