Extraction of Ga and Ge from zinc refinery residues in H2C2O4 solutions containing H2O2

A new oxalic acid (H₂C₂O₄) and hydrogen peroxide (H₂O₂) based extraction process was developed to recover valuable metals - in particular Ga and Ge - from the zinc refinery residues. H₂C₂O₄ and H₂O₂ leaching studies indicated that the selective leaching of metals in the residues, that primarily contain Zn, Cu, Fe, SiO₂, Ga and Ge, can be achieved. Under the optimal leaching conditions ([H₂C₂O₄] = 110 g/L, [H₂O₂] = 0.12 mol/L, L/S ratio = 8, T = 40 °C and t = 30 min), 99.32% of the Ga, 98.86% of the Ge and 30.25% of the Fe were leached out, whereas the leaching of Zn, Cu and Si only reached 0.30%, 0.82% and 0.43%, respectively. Concerning leachate purification, 98.31% of the iron could be removed in the form of FeC₂O₄·2H₂O with minor losses of Ga and Ge (1.08% and 0.68%) using an ultrasound-assisted iron powder replacement method under optimal conditions. The Ga (99.36%) and Ge (99.89%) were subsequently extracted by tri(octyl-decyl)amine (N235). After extraction, the loaded organic phase was stripped of Ga (98.91%) and Ge (99.21%) into separate solutions using sequential treatments of 2 mol/L H₂SO₄ and 4 mol/L NaOH respectively. Based on these results, a process flow sheet of efficient separation and recovery of Ga and Ge is presented.