| To simplify current process of indium extraction from jarosite residue, raise direct yield of indium and eliminate the polution of low concentration SO2, a new process of "NaOH decomposition-dilute hydrochloric acid leaching-reduction-TBP extraction" was proposed in this disseration. Jarosite residue was firstly decomposed in NaOH medium to produce Na2SO4 solution and iron residue bearing indium. Na2SO4 solution was concentrated and then refrigerated crystallization to recover mirabilite after arsenic removal, mother liquid was recycled to alkaline decomposition operation. After selective leaching of In and Zn with dilute hydrochloric acid, the magnetic separation of leached residue was carried out to produce iron concentrates that used as raw material in iron smelting. Indium and zinc in pregnant solution were simultaneously solvent extracted by TBP.The results of NaOH decomposition show that he decomposition ratio of ammonium jarosite can reach 98.03% under the following optimum conditions:WNaOH/WJarosite=0.3814:1,60℃, L/S ratio 2:1,2h. Impurity elements like Zn, In, Cu, Cd, Pb, Sb, Sn and Ag, are left in residue, while 83.36% of As is leached into pregnant solution in presence of AsO43-. DSC-TGA thermal analysis and XRD characterization results demonstrate that Fe is precipitated in form of Fe3O4 during alkaline decomposition. The content of Fe, In and Zn in decomposition residue is 38.81%,0.23% and 12.89%, respectively. After selective leaching with dilute HC1, the leaching ratio of In, Zn, Cu, Cd, As, Sn, Sb, Pb and Ag is 98.26%,99.35%,98.79%,98.93%,76.27%,68.50%,80.12%,64.82% and 60.80%, respectively, under the following optimum conditions:40℃, L/S ratio 7:1,2h, MHC1/MTheory=1.8.89.25% of Fe is left in leached residue with grade of 52.48%. After magnetic separation and impurities removal, iron concentrate obtained can be used as raw material for iron smelting.Impurity ions such as As3+, Sb2+ and Bi2+ in pregnant solution were removed by iron scrap, and their removing rate is 63.95%,100%, and 97.65%, respectively, at 50℃for 25min with iron scrap addition of 1.5 times of theoretical consumption. The reduction ratio of Fe3+ is closer to 100%, and the loss ratio of indium is lower than 1% during iron replacement process. Zn2+ and In3+ in purified solution were solvent extracted with 70%TBP+30% sulfated kerosene at room temperature for 10min with phase ratio of 1.5:1. After three-stage of countercurrent solvent extraction, the extraction ratio of Zn and In is 98.13% and 99.05%, respectively, while that of Fe2+ is lower than 1%. Zn2+ and In3+ in loaded organic phase was stripped by distilled water at ambient temperature for 5min with phase ratio of O/A=3:1. After three-stage of countercurrent stripping, the stripping rate of In and Zn is 99.10% and 93.62%, respectively. From purified solution to stripping solution, the total recovery ratio of Zn and In is 92.73% and 97.24%. Zinc plate was added into stripping solution to replacement sponge indium and purified ZnCl2 solution. The replacement rate of In3+ is higher than 99%.In the present process of "NaOH decomposition-dilute hydrochloric acid leaching-reduction-TBP extraction", iron residue and SO2 off-gas are not produced and the direct yield of In and Zn are higher. Iron content in the leached residue is 52.48%, which can be concentrated by magnetic separation as ironmaking raw materials. Consequently, iron resource in zinc concentrates can be utilizated and the environmental pollution due to iron residue emission are also eliminated... |
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