Zinc Leaching Residue Reduces The Separation And Recovery Of Copper And Indium In The Leaching Solution

In China’s hydrometallurgical zinc enterprises,the annual output of zinc leaching residue is huge,reaching millions of tons per year.There are a lot of valuable metals such as zinc,copper and indium in zinc leaching residue.It is necessary to recycle zinc leaching residue efficiently.However,zinc,copper and indium in the residue mainly exist in the form of insoluble phase.In the early stage of this research group,zinc leaching residue was reduced by SO₂ to achieve efficient leaching of valuable metals zinc,copper and indium in the residue.At the same time,Fe（III）was reduced to Fe（II）,which created favorable conditions for subsequent separation of zinc,copper and indium from iron.In order to separate valuable metals such as zinc,copper and indium efficiently,the experiments of iron powder reduction precipitation of copper,liquid pre-neutralization after copper precipitation and limestone neutralization precipitation of indium were carried out in this paper.The main research work and results are as follows:1)The reaction behavior of iron powder with copper（II）and As（III）in the reductive leaching solution of zinc leaching residue was studied.The effects of reaction time,reaction temperature and iron powder addition coefficient on the reaction behavior were investigated.The experimental results showed that increasing iron powder addition coefficient,increasing reaction temperature and prolonging reaction time could effectively promote the formation of Cu₂O and Cu₃As.The precipitation rate of copper and arsenic can reach more than 99%under the experimental conditions of iron powder addition coefficient 1.2,reaction time 25 min and reaction temperature 70℃.The main phases in copper residue are Cu₂O and Cu₃As.Cu₂O and Cu₃As are scattered and dotted on the surface of iron powder,and no compact wrapping is formed on the surface of iron powder,which makes the reaction fully carried out.2)In order to solve the problem of excessive acidity of liquid after copper precipitation,limestone was used as neutralizer and pretreated by pre-neutralization process.The expected goal of producing gypsum residue and reducing acidity was achieved.In the pre-neutralization experiment,the relationship between CaCO₃content and pH,the effect of solution end-point pH on residue content,and the effect of solution end-point pH on zinc and in content in residue were investigated under the basic conditions of reaction temperature 70℃,reaction time 30 min and stirring speed400 r/min.When the pH is adjusted to 2,the loss rate of valuable metals is low,and the contents of Zn and In in the residue are 0.028%and 0.00202%respectively,which is conducive to the comprehensive recovery of Zn and In.Limestone is used as neutralizer to pre-neutralize the liquid after copper precipitation,while neutralizing and consuming sulphuric acid in the solution,the loss of Zn and In is minimized and the expected goal is achieved.Limestone is used as preneutralizer with low production cost and gypsum residue can also be recycled as building materials.3)Limestone is used to neutralize the free sulfuric acid in the reductive leaching solution and adjust the pH of the reductive leaching solution to hydrolyze and precipitate indium.The effects of neutralization end point pH,reaction time and reaction temperature on the precipitation behavior of indium were investigated.The results showed that under the optimum reaction conditions,the precipitation rate of indium reached 98%and the loss rate of zinc was 2.9%at the end point of solution pH=4.5,reaction time 120min,reaction temperature 85℃,seed 5g/L and stirring speed 400r/min.Indium is fully enriched in the residue,and the content of indium in the sediment reaches 3600g/t.The main phases of indium sediment are CaSO₄·2H₂O and In（OH）₃,and In（OH）₃ is scattered on the surface of CaSO₄·2H₂O.In view of the separation and recovery of copper and indium from zinc leaching residue reductive leaching solution,copper is enriched in copper sediment,indium is hydrolyzed and enriched in gypsum residue,which creates favorable conditions for the separation and recovery of copper and indium in the whole zinc hydrometallurgy process.