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

Ultrasonication has macroscopic and microscopic effects on the removal of arsenic from zinc sulfate solution by zinc roasting dust. From a macro perspective, conventional reactions can lead to agglomeration and a wrapping layer, slowing the occurrence of the reaction. Under the action of ultrasound, the strong jet generated by ultrasonic cavitation can physically peel off the inclusions deposited on the surface of zinc roasting dust in the reaction process, exposing a new reaction layer. Meanwhile, strong jets can accelerate solution flow and promote liquid–solid reactions. From a microscopic perspective, ultrasound can enhance the ligand exchange between sulfate and arsenate on the surface of iron hydroxide colloids, thereby enhancing the arsenic removal effect of zinc sulfate solution. [Display omitted] •Removal of arsenic from zinc sulfate solution by ZRD instead of lime as neutralizer.•The use of ZRD can reduce the amount of wet residue by 46.77%•Ultrasonic enhancement can increase arsenic removal rate to 99.28%•Ultrasonic can open the wrapper and reduce the amount of arsenic removal residue.•Ultrasound can promote ligand exchange between arsenate and sulfate. 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 d