Technical And Theoretical Studies On Indium Extraction And Iron Resource Value-added Utilization From Zinc Hydrometallurgical Residues In HCl Medium

Aimed at value-added utilization of iron resource in sphalerite concentrate and complete elimination of environmental pollution caused by waste ferric residue heaping,a new process for indium extraction and iron resource utilization in HCl medium was proposed in present dissertation. Adopting this process for jarosite residue treatment,the recovery flow sheet of indium and zinc can be simplified obviously,and the extraction ratio of valuable metals is enhanced consequently.Simultaneously,low concentration of SO₂ offgas emission is prohibited.Thermodynamic and kinetic analysis on the In & Zn solvent extraction,ferric yellow preparation and alkaline decomposition of jarosite residue was systematically carried out,respectively. Adopting double equilibrium method,the equilibrium relationship among [Zn]_T,[Fe]_T,[NH₃]_T,[CO₃^2-]_T and pH was also discussed in detail during zinc ferrite precursor preparation in Zn(â…¡)-Fe(â…¢)-NH₃-CO₃^2--Cl^--H₂O system.The optimum pH value for Zn²⁺,Fe³⁺ co-precipitation was determined as 6.3＜pH＜7.3.Using zinc hydrometallurgical residue as raw material,technical studies on HCl hot-acid leaching,pregnant solution reduction and purification,In & Zn solvent extraction with tributyl phosphate(TBP) was carried out, respectively.The experimental results show that the leaching ratio of Zn,Fe and In is higher than 95%under the following conditions:90℃, M_HCl/M_Theory＝1.5～2.5,2h～4h,L/S ratio(3～5):1.Adopting pyrrhotite as reductive reagent,Fe³⁺ ion in hot-acid leaching solution is reduced to Fe²⁺ with reduction ratio of 96.30%under the following conditions: W_pyrrhotite/W_Theory＝1.4,90℃,2h,pyrrhotite particle size 0.088mm～0.106mm. And the removing ratio of As³⁺,Sb³⁺ is 67.70%and 24.77%,respectively. Using sphalerite concentrate as reductive reagent,the optimum conditions was obtained as follow:90℃,2h,ZnS concentrate particle size 45μm, W_ZnS/W_Theory＝1.1.Under above optimum conditions,the leaching ratio of Zn, Fe and In is 93.89%,94.46%and 97.89%,respectively,and the reduction ratio of Fe³⁺ is 96.62%.Iron powder cementation was.conducted at 50℃for 25min. The removing ratio of Cu²⁺,Pb²⁺ and Cd²⁺ is 99.90%,32%,and 17%, respectively,when the addition of iron powder is 1.4 times of theoretical amount.And the loss ratio of indium is lower than 1%.Zn²⁺ and In³⁺ in purificatory solution were simultaneously solvent extracted with 70% TBP+30%sulfated kerosene under the following conditions:room temperature,agitation time 10rain,phase ratio O/A＝1.51,acid concentration of water phase 1.5mol·L^-1.After three-stage of countercurrent solvent extraction,the extraction ratio of Zn,In and Sn is larger than 99%, respectively,and that of Fe²⁺ is lower than 1%.Consequently,iron is completely separated from zinc and indium chloride solution.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 solvent extraction,the stripping ratio of In and Zn is 99%and 60～90%, respectively,and that of Sn is lower than 3%.Zinc plate was added into stripping solution to produce sponge indium and purificatory ZnCl₂ solution. The cementation ratio of In³⁺ is higher than 99%.Purifatory FeCl₂ solution and 2mol·L^-1 NH₄HCO₃ was added drop by drop into reaction vessel to prepare Fe(OH)₂+FeCO₃ suspension,which was subsequently oxidated by air to produce ferric yellow.The oxidation of Fe(OH)₂+FeCO₃ suspension follows"dissolving ionization-oxidative precipitation"mechanism,and whole course can be divided into nucleation period and crystal growth that controlled by oxidative reaction on interface. The activation energy of nucleation and crystal growth is 127.26kJ·mol^-1and 237.86kJ·mo1^-1,respectively.Temperature,air flow and initial pH value has remarkable influences on the oxidation rate of Fe(OH)₂+FeCO₃ suspension. The morphology of ferric yellow obtained is a sphere aggregated by needle or spindleα-FeOOH particles.FeCl₂ raffinate was firstly oxidated by H₂O₂,and one-stage of solvent extraction of obtained FeCl₃ solution was carried out under the following conditions:room temperature,agitation time 5min,organic phase composition 80%TBP+30%sulfated kerosene,phase ration O/A＝3:1,acid concentration of water phase 3.5mol·L^-1.The extraction ratio of Fe³⁺ is 99.69%.Fe³⁺ ion in loaded organic phase was stripped by distilled water at ambient temperature for 3min with phase ratio of O/A＝1.5:1.After three-stage of countercurrent solvent extraction,the stripping ratio of Fe is 97.30%.Using FeCl₃ stripping solution and purificatory ZnCl₂ solution as raw material,zinc ferrite precursor was obtained with co-precipitation method under the following conditions:50℃,60min,n_Zn:n_Fe＝1:2,C₁6H₃3(CH₃)₃NBr as radditive,C_ZnCl2+FeCl3＝0.3mol·L^-1, M₍NH₄CO₃:M_Theory＝1.2:1,C₍NH₄CO₃＝0.5mo·L^-1.The results show that Zn²⁺ and Fe³⁺ are co-precipitated with theoretical ratio,and the precipitation ratio of Zn²⁺,Fe³⁺ is 99.83%and 99.92%,respectively.Zinc ferrite precursor obtained is a single,dispersive sphere with average particle size of 100nm～120nm.The Zn/Fe molar ratio of precursor is 0.999:2.According to DSC-TGA analysis results,the precursor was calcined at 500℃～700℃to obtain well crystallized zinc ferrite powder with narrow particle size distribution.The aggregation of zinc ferrite particle enhances with calcine temperature increasing,and the optimum temperature is determined as 500℃.The average particle size of zinc ferrite sample obtained at 500℃is about 150nm.A new hydrometallurgical process for indium extraction from jarosite residue was also proposed in this dissertation.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 as former mentioned.Technical studies on the alkaline decomposition ofjarosite and HCI leaching of decomposition residue were carried out.Obtained results show that the decomposition ratio of ammonium jarosite can reach 98.03%under the following optimum conditions: W_NaOH/W_Jarosite＝0.3814:1,60℃,liquid-solid 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 AsO₄^3-.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 HCl,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℃,liquid-solid ratio 7:1,2h,M_HCl/M_Theory＝1.8.89.25%of Fe is left in leached residue,and the content of Fe is 52.48%.After magnetic separation and impurities removal,iron concentrate obtained can be used as raw material for iron smelting.In conclusion,the present process proposed for indium extraction and iron resource value-added utilization in HCl medium can achieve zero emission of ferric residue and SO₂ off-gas.The recovery flow sheet of indium and zinc is simple and flexible,and the direct recovery ratio of valuable metal like In,Zn is enhanced dramatically.Iron resource in raw material is value-added utilization in form of zinc ferrite,ferric yellow and iron concentrate.The environmental pollution caused by ferric residues heaping is originally prohibited.The present process has extensive application in the treatment of zinc leached residue and jarosite.Furthermore,tt is significant in the exploitation of sphalerite concentrate bearing high iron and indium.