Experimental Study on the Recovery of Arsenic and Iron from Arsenic–Iron Precipitate by Carbon Thermal Magnetization Reduction

Abstract

Arsenic–iron precipitate was treated using a carbon thermal magnetization reduction method in order to recover arsenic and iron. Arsenic–iron precipitate mixed with coke powder was roasted at a low temperature; arsenic was recovered in the form of As2O3, and iron was recovered in the form of Fe3O4. The volatilization rate of arsenic was 97.45%, and the content of arsenic in the precipitate was decreased to 0.60%. Iron and arsenic were recovered in the form of Fe3O4 and As2O3 with a purity of 99.91 wt.% under the conditions of a roasting temperature of 650 °C, coke powder addition of 25 wt.%, a roasting time of 180 min, and an argon flow rate of 10 L/min. The volatilization of arsenic was controlled by a chemical controlling step at 20–100 min, and this was switched to a diffusion controlling step at 120–180 min by kinetic experiments. The reaction mechanism of arsenic and iron under carbon thermal magnetization reduction was as follows: in the early stage of the reaction, a large amount of FeAsO4 was decomposed into As2O3 and Fe3O4; in the middle and late stages of the reaction, FeAsO4 was continuously decomposed and reduced, and the content of Fe3O4 was continuously increased until all iron was magnetized to generate Fe3O4, and the decomposed As2O3 volatilized into dust. Arsenic reacted with CaO to generate Ca3(AsO4)2, and this may be the reason why arsenic could not be removed completely.