Magnetic Seed-Assisted Iron Recovery from the Reductive Leaching Solution in Hydrometallurgical Process

The recovery of iron is the key step for zinc recycling by electrolysis in zinc hydrometallurgy industry. Iron exists mainly as ferrites in the zinc neutral leaching residue and is difficult to decompose. In this paper, the reductive leaching process using sulfur dioxide was adopted to replace the traditional hot-acid leaching method, and the magnetic seed-assisted iron precipitation was developed. Under the optimum reductive leaching conditions, the initial concentration of sulfuric acid, the temperature and the partial pressure were determined as: 80 g/L H 2 SO 4 , 90 °C, 200 kPa at the fixed liquid/solid ratio of 10:1 and the stirring speed of 400 rpm. The most suitable iron precipitation reaction conditions were as follows: the pH: 3.0–3.5; the temperature: 95 °C. The recovery of iron mainly depended on the oxydrolysis of the ferrous. The ferrous precipitated as goethite and its crystallinity noticeably decreased with decreasing pH. The addition of the magnetic seeds shortened the reaction time from 4.5 to 3.0 h when the iron precipitation rate reached more than 99%. Simultaneously, the loss rates of zinc and cadmium in the iron process were also reduced from 10.96% and 9.27% to 4.23% and 3.73%, respectively. Besides, the sedimentation and filtration performance were greatly improved after the addition of magnetic seeds. The adsorption and inclusion were the main reasons for better sedimentation and filtration performance and higher metal loss rate.