Sustainable Mining and Metallurgy

The main process of recovering indium by wet zinc smelting hematite method is to use sulfur dioxide to reduce and leach indium from low acid leaching residue. The acidity of the solution after reduction leaching is about 30g/L, which needs to be neutralized in advance to reduce the acidity to 10g/L, and then calcium carbonate is added to neutralize the precipitation of indium and enrich indium. The precipitation of indium residue is recovered by leaching, purification and extraction. The gypsum slag produced in the pre-neutralization process will entrain part of indium, resulting in the loss of indium. In this paper, the effects of Fe³⁺ concentration, end-point acidity and reaction time on the indium content, settlement and filtration performance of gypsum slag were studied by single factor test. The results show that, due to the similar properties of In³⁺ and Fe³⁺, In³⁺ can partially replace Fe³⁺ to form intergranular compounds and stably enter the slag during the formation of sodium jarosite. Therefore, the higher the content of Fe³⁺, the higher the indium content of pre-neutralized gypsum slag. When the end-point acidity is less than 10g/L, Al and Si in the solution are easy to form gel, which react with Ca to form gehlenite precipitation, affecting the sedimentation performance and filtration performance of the slurry. The lower the end-point acidity is, the higher the indium content of gypsum slag is, and the worse the filtration performance is. With the extension of reaction time, the more Fe²⁺ is oxidized to Fe³⁺ in the solution, the more indium is contained in the gypsum slag.