Study On The Enrichment Of Indium In High - Iron Zinc Sulfate Solution

The high-iron sphalerite storage in Yunnan belongs to the high-added values and refractory zinc mineral resources. A process for enrichment of indium from zinc sulfate solution, which contains high concentration of Fe and In was investigated in this dissertation. This dissertation studies the process of iron powder reduction-displacement, pre-neutralization by zinc calcine with high iron, indium precipitation by zinc power, indium leaching from indium-enriched cementation by sulfuric acid and extraction of indium from leaching solution. At the same time, this dissertation investigated the enrichment and separation result of indium, copper and iron. The main research results are as follows:(1) The effect of iron powder reduction Fe3+ and displacement Cu2+ was investigated for the zinc sulfate solution, which contains a high concentration of iron and indium. According to the thermodynamic analysis, the sequence of iron powder reduction-replacement can be established in the theory:Fe3+> Cu2+> Sn2+> In3+. At the iron powder reduction-displacement process, the reaction temperature at 80 ℃, the amount of iron powder adding amount was 1.1 times about the amount of theory, iron powder granularity of -150 mesh, stirring speed 400 r/min and the reaction time for 20 min. Almost all of the Fe3+ was reduced of Fe2+ in the solution, and more than 99% copper in the solution by replacement to enriched in the reduced cementation. At the same time, the loss rate of indium is very small, most of the tin and part of arsenic would reduce in the solution, and it will reduce the risk of AsH3 in the subsequent operation.(2) The effect of pre-neutralization by zinc calcine with high iron was investigated for the solution, which came from the process of reduction-displacement. The optimum experiment conditions as follows:reaction temperature at 80 ℃, reaction time 30 min and stirring speed 400 r/min, zinc calcine with high iron amount was 55 g/L, pH at the end of this reaction was about 1.7, the loss rate of indium in this process was less than 1%.(3) The effect of indium precipitation by zinc power was investigated for the solution, which came from the process of pre-neutralization. According to the thermodynamic analysis, the sequence of zinc powder replacement can be established in the theory:Cu2+> Fe3+> In3+> Fe2+, and the sequence of precipitation by hydrolyzed can be established in the theory:Fe3+> In3+> Cu2+> Zn2+> Fe2+. Through the condition experiments, the optimum experiment conditions as follows: the reaction temperature control at 80～85 ℃, the reaction time of 40～60 min, zinc powder adding amount was 7 g/L, the end point pH of this reaction was controlled between 4.0～4.2.Under this condition, indium precipitation rate can reach about 97%, and indium cementation grade can reach 2.3%, enrichment effect is fine.(4) The effect of indium leaching from indium-enriched cementation by sulfuric acid was investigated. The optimum experiment conditions as follows:the reaction temperature was 80 ℃, reaction time 6h, liquid-solid ratio of 10 ml/g, stirring speed of 500 r/min, H2O2 content of 2 ml/g, initial concentration of sulfuric acid was 0.26 mol/L, the end point pH of this reaction was controlled about 1.4, total acid was 0.75 mol/L. Under those conditions, almost all of the zinc and copper were completely leaching and enrichment in the leaching solution, the indium leaching rate can reached more than 92%, the precipitation rate of iron and arsenic was 53% and 62%. Realized the indium leached with high rate, at the same time, separation arsenic and iron in the form of precipitation. The leaching solution was extracted through three adverse current steps with 30% P204, extraction rate of indium could reach 99%, and back extraction with 4mol/L hydrochloric acid. The stripping solution containing indium was 31.5g/L, realized a better separation and enrichment of indium.Compared with the traditional process, the copper and indium can be effective recovery from high-iron zinc sulfate solution with high enrichment, indium cementation grade can reached 2.3%, and the direct recovery of indium is about 88%. Without the process of volatilization by rotary kiln or iron precipitation by iron vitriol, avoid the loss of indium in the residue. This process had the characteristic of high indium recovery rate, low energy consumption and environment friendly.