Study on the improvement of the zinc pressure leaching process

Abstract

The first two-stage zinc pressure leaching plant with 100 kt-Zn/a capacity in China was put into production in 2009, to recover zinc, rare metals, germanium and gallium. However, the total extraction of zinc is limited to just 93% in initial production. To improve the co-recovery of metals, pressure leaching tests were carried out on the first-stage leach residue from the initial flowsheet. The effects of Fe(III) concentration, oxygen partial pressure, reaction time, sulfuric acid dosage, and particle size of the residues were investigated. The results showed that particle size and acid dosage greatly affected the zinc, iron, gallium, and germanium extraction. The particles of size above 74 μm are the main obstacles to improve extraction. Grinding can effectively improve the recovery of the main metals. The zinc extraction can reach 96.7% after grinding the coarse particles (> 74 μm) prior to leaching. The extraction of other metals are 84.7%, 81.7% and 81.4% for iron, gallium, and germanium, respectively. The total recovery of the two-stage leaching is 98.2%, 90.0%, 86.3% and 87.8% for zinc, iron, gallium, and germanium, respectively.