Mechanism of removal of toxic arsenic (As) from zinc sulfate solution by ultrasonic enhanced neutralization with zinc roasting dust

Abstract

Arsenic in zinc sulfate solution greatly hinders the zinc hydrometallurgy process, and the treatment of arsenic residue with lime also generates large cost due to the large amount of residue. Herein, a new process of neutralization by zinc roasting dust (ZRD) and ultrasound (US) field enhancement of arsenic removal was proposed. The process includes the following steps:one-stage neutralization, KMnO4 oxidation and two-stage neutralization to remove arsenic. The process has the advantages of a good arsenic removal effect, no introduction of new impurities, and less residue. The effects of the ZRD dosage, temperature and US power on arsenic removal were investigated. The optimal conditions were 12 g/L, 70 ℃ and 300 W, respectively, and the arsenic removal rate reached 99.3%. The X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM-EDS) were utilized to analyze the raw materials and residue. The results showed that, compared with conventional conditions, US strengthening treatment led to more complete reaction of ZRD. The arsenic removal residue after US treatment mainly existed in the form of ZnFe2O4, Fe3O4 and ZnS, which exhibited low reactivity. Ultrasound could effectively destroy the wrapper on the surface of ZRD, and enhance the liquid–solid reaction, which reduced the amount of residue and improved the arsenic removal efficiency. Interestingly, we found that ultrasound could enhance arsenic removal by increasing the ligand exchange between arsenate and sulfate. Compared with the lime and conventional ZRD neutralization, the wet residue weight after US treatment was reduced by 46.8% and 16.3%, respectively.