Spontaneous separation of Pb from PbSO4-coprecipitated jarosite using freeze-thaw cycling with thiourea

To separate Pb from PbSO4-coprecipitated jarosite, a novel thiourea-induced freeze-thaw cycling (T-FTC) process was investigated. Results show that distributed PbSO4 particles are pressed and aggregated around the jarosite particles by T-FTC. Under the freezing-concentration effect of T-FTC, the reaction between PbSO4 and thiourea is also promoted, forming lead thiourea sulfate (Pb-tu). As the cycles of T-FTC increase, PbSO4 around jarosite disappears for the reaction of forming Pb-tu. After 12 cycles of T-FTC, a spontaneous separation is observed between Pb-tu and jarosite, i.e., Pb-tu is separated into the upper layer while jarosite-rich phases remain in the lower layer. Due to this spontaneous separation, leaching toxicity of the jarosite coprecipitates is reduced by 73.7%. These results suggest that T-FTC process can achieve the separation of Pb from PbSO4-coprecipitated jarosite and is a promising approach for removing and recovering metals from iron-rich jarosite residues.