Separation of arsenic and tin from Cu–As alloy based on phase transformation in a vacuum to form Cu–Fe–S compounds

Abstract

Cu–As alloy is viewed as one kind of secondary copper resources. It is difficult to simultaneously recover copper and remove arsenic using conventional processes. To separate arsenic and tin from Cu–As alloy (mainly Cu3As), an innovative methodology that uses vacuum distillation in the presence of pyrite to form new phase is proposed herein. The constituents, phases and morphology of the sample before and after vacuum distillation were investigated by chemical analysis, X-ray diffraction (XRD) analysis and electron probe microanalysis (EPMA) to interpret separation performances and volatilization mechanisms of arsenic and tin. Chemical analysis results showed that it is difficult to separate arsenic from Cu-As alloy by direct vacuum distillation, but arsenic and tin were effectively separated after introducing pyrite. The effects of several factors, such as temperature, pyrite dosage and distillation time, on separation performances of arsenic and tin were examined. Volatilization ratios of copper, arsenic and tin reached 0.84%, 96.29% and 88.70%, respectively. Results of XRD analysis and EPMA revealed that arsenic had strong affinity to copper in Cu-As alloy, which inhibited free volatilization of arsenic. After introduction of pyrite, formation of copper sulfides, such as mainly Cu5.433Fe1.087S4, Cu1.96S and Cu9S5, destroyed the alloy structure, which made elemental arsenic volatilize. Excessive sulfur also interacted with elemental arsenic to form mainly As4S3 that is also easily volatilized. Nevertheless, tin was only separated in the form of SnS. It is a promising method to achieve cleaner utilization of Cu-As alloy and effective control of arsenic pollution.