The ambient pressure precipitation of crystalline scorodite (FeAsO(4).2H(2)O) from sulphate solutions

Arsenic extraction and immobilization from hydrometallurgical solutions and effluents is usually achieved by ferric arsenate precipitation. An alternative vehicle is proposed in the form of crystalline ferric arsenate, or the mineral scorodite (FeAsO;The precipitation of scorodite from sulphate-based effluents at ambient pressure (95;Test work using NaOH showed that amorphous ferric arsenate precipitation was avoided even at very high supersaturation levels (;The slow addition of ferric ions to sulphate solutions containing arsenic was also found to precipitate scorodite. Decreasing pH values resulted in faster Fe(III) addition rates, and below the induction pH (pH;The scorodite samples produced in this work exhibit slightly higher solubilities (0.7 ppm (As) at pH = 5 versus 0.1 ppm (As)) compared to scorodite produced from chloride and nitrate solutions. (Abstract shortened by UMI.).