Jarosite residues recycling by slurry electrolysis: Iron recovery and detoxification in one step

Jarosite residues, rich in iron and zinc as well as heavy metals such as As, Cd, Cu, Mn, Pb, is a typical hazardous waste, resourceful but hazardous. Here, a novel and short process for directly recovering iron from jarosite residues by slurry electrolysis is put forward. The results show that metallic iron could be recovered in the cathode with a recovery efficiency of 69.95 % under the conditions of pulp density of 70 g/L, pH value of 2.0, 1 mol/L Fe 2 + , 30 mA/cm 2 and 8 h. Meanwhile, the recovery rates of Zn, As, Cd, Cu, Mn and Pb are respectively 27.49 %, 20.99 %, 52.20 %, 41.18 %, 36.18 % and 22.95 %. After slurry electrolysis, its heavy metal leaching toxicity are lower than the limits specified in GB5085.3 and TCLP. Heavy metals in the anode residues after slurry electrolysis are mainly in the residual state, higher than 90 %, and its bioavailability is greatly improved. During the slurry electrolysis, Fe-(OH)-O bond of the [(OH,Fe 3+ )(SO 4 ) 2 ] octahedral in the crystal structure of NH 4 Fe 3 (SO 4 ) 2 (OH) 6 octahedral are partly destroyed, and Fe 3+ is released from the crystal lattice, migrated to the cathode and reduced to metallic iron. While ZnFe 2 O 4 hardly dissolves due to its stable spinel structure, resulting a lower iron recovery rate.