The goethite residue generated from zinc hydrometallurgy is classified as hazardous solid waste, produced in large quantities, and results in significant zinc loss. The study was conducted on removing iron from FeSO 4 -ZnSO 4 solution, employing seed-induced nucleation methods. Analysis of the iron removal rate, residue structure, morphology, and elemental composition involved ICP, XRD, FT-IR, and SEM. The existing state of zinc was investigated by combining step-by-step dissolution using hydrochloric acid. Concurrently, iron removal tests were extended to industrial solutions to assess the influence of seeds and solution pH on zinc loss and residue yield. The results revealed that seed addition increased the iron removal rate by 3%, elevated the residual iron content by 6.39%, and mitigated zinc loss by 29.55% in the simulated solution. Seed-induced nucleation prevented excessive nuclei formation, fostering crystal stable growth and high crystallinity. In addition, the zinc content of surface adsorption and crystal internal embedding in the residue was determined, and the zinc distribution on the surface was dense. In contrast, the total amount of zinc within the crystal was higher. The test results in the industrial solution demonstrated that the introduction of seeds expanded the pH range for goethite formation and growth, and the zinc loss per ton of iron removed was reduced by 50.91 kg (34.12%) and the iron residue reduced by 0.17 t (8.72%).
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.
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