China Nonferrous Metallurgy

Some zinc leaching residues used for silver flotation concentrates have high zinc content (Zn 18%-20%), which is not conducive to subsequent silver extraction. To solve this problem, this study first used a carbon-added microwave roasting process to pretreat the residues, aiming to increase zinc ferrite decomposition. Then, it used selective leaching under low-acid conditions, as oxidized zinc dissolves more easily than oxidized iron. This aimed to maximize zinc leaching and minimize iron leaching. Under the optimal carbon-added microwave roasting conditions of 1.2kW microwave power, 8% carbon addition, 700℃ roasting temperature, -150 mesh ore particle size, and 60-minute roasting time, the soluble zinc rate in the product reached 88.72%. Under the optimal selective leaching conditions pH 2 for the leaching solution, 5∶1 liquid-to-solid ratio, 70℃ temperature, and 90 minutes leaching time, zinc and iron leaching rates reached 88.53% and 41.68%, respectively. After microwave reduction roasting and low-acid leaching, about 93.5% silver in the raw material was enriched in the leaching residue, increasing its grade by approximately 2.3 times. The insoluble zinc in the material is mainly the undecomposed zinc ferrite, which is wrapped in the larger lead sulfate and calcium sulfate particles during the microwave roasting process and is difficult to leach.