Ultrasonic Enhanced Sodium Sulfide Removal of Arsenic from Zinc Sulfate Solution

The ZnSO 4 solution leached from zinc oxide dust requires arsenic removal prior to electrolysis. Traditional lime-ferric salt methods face issues like long reaction times, large As residue, and low efficiency. This study proposes an ultrasound enhanced sodium sulfide process for efficient and rapid As removal. The influence of factors such as S/As molar ratio, pH, temperature, reaction time, and ultrasonic intensity on As removal efficiency was evaluated. Results identified the S/As ratio and pH as the most influential parameters. When the pH of zinc sulfate solution is greater than 1, zinc will enter the residue more with the increase of pH, resulting in increased zinc loss. Under optimized conditions, As removal reached 99.39%. Compared to the lime-ferric salt method, the sulfidation process reduced As-bearing residue by 73.72% and shortened the reaction time by 90%. The enhancement is attributed to ultrasonic cavitation and associated mechanical effects. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and Field-emission scanning electron microscopy (FE-SEM-EDS) analyses confirmed that the ultrasound irradiation improves sodium sulfide's As removal. Kinetic studies show that the process under ultrasonic enhancement follows internal diffusion and chemical reaction mixing control, whereas conventional conditions follow internal diffusion control. Ultrasonic enhancement reduces activation energy from 14.48 to 9.16   kJ/mol, lowering the reaction barrier and improving efficiency. The results demonstrate that ultrasound-assisted sodium sulfide treatment is a highly effective alternative for arsenic removal from ZnSO 4 solutions.