Experimental Study On Acid Hydrolysis And Enrichment Of Waste Tungsten Residue And Leaching Of Sodium Tungstate By Soda Roasting

Tungsten residue is generally a kind of hazardous waste remained after the alkaline leaching treatment of tungsten concentrate.It contains varieties of harmful elements such as As and part of heavy metals including W,Sn,Fe,Mn,Ta,Nb,SC,which results in a violent leaching toxicity and big environmental damage.At present,the accumulated stock of tungsten residue in China is more than 1 million tons and is still growing at a rate of over 70000 tons per year.This leads to a huge potential threat to the ecological environment and becomes a major environmental issue in the non-ferrous metal industry.Tungsten residue contains approximately 22%Fe,31%Mn,1%-5%WO₃and a small amount of valuable metals such as Ta,Nb and SC,thus is of great value to be recycled.It will be an enormous waste of resources if the Tungsten residue is not rationally utilized.For these reasons,the harmless treatment and comprehensive utilization for Tungsten residue have a dual significance for environmental protection and resources saving.In the present paper,the waste Tungsten residue of a domestic tungsten smelter was used as raw material to study the decomposition of Tungsten residue caused by acid leaching using hydrochloric acid,the soda roasting of acid leaching residue and water leaching of sodium tungstate origins from soda roasting,aimed at exploring an approach for the harmless treatment and recovery of Tungsten residue.The results of XRF analysis show that the Tungsten residue mainly consists of Fe,Mn,Si,Al and Ca and only a tiny amount of W,about 0.66%.The results of XRD analysis show that Fe,Mn,Si and W mainly exist in Tungsten residue in the form of Fe₂O₃,Si O₂,Mn O₂and Fe WO₄.The results of acid leaching experiments show that the optimum conditions for the decomposition of tungsten residue and the enrichment of tungsten are as follows:hydrochloric acid concentration 3mol/L,leaching temperature 70℃,leaching time 80min,ratio of liquid to solid ratio5:1.Under these conditions,the yield of acidolysis product is 48.1%,the content of tungsten increases from 0.66%to 1.33%,the enrichment ratio is 2.02,the recovery of tungsten is 94.59%,90.67%of Ca is removed,and the leaching efficiency of manganese and iron are 51.38%and 67.63%respectively.These experimental results lay a foundation for the subsequent treatment of Tungsten residue.The acid leaching residue mostly consists of Si,Fe,Al and Mn.In the acid leaching residue,Fe mainly exists in the form of Fe₂O₃,Si mainly exists in the form of Si O₂,Al exists in the form of Al₂Si O₄F₂,and W exists in the form of H₂WO₄ and Fe WO₄.The main elements in the acid hydrolysis solution are Mn,Fe and Ca.Mn and Fe in the solution are precipitated by adding Ca（OH）₂to achieve the harmless treatment and recovery iron and manganese.A large amount of Ca element left in the solution is subsequently utilized to produce gypsum whiskers.The results of soda roasting-water leaching experiments for acid leaching residue show that the optimum process conditions are as follows:roasting temperature 800℃,roasting time60min,mass ratio of soda to acid leaching residue 1:1,leaching time 80min,ratio ofliquid to solid for water leaching 7:1.Under these conditions,the leaching efficiency of tungsten reaches a highest value of 94.66%and the total recovery ratio of tungsten is 90.74%,which realizes the effective recovery of tungsten resource.At the same time,the leaching efficiency of Al and Si are less than 5%,and Mn and Fe can’t be extracted by water.The yield of water leaching residue is75.82%,and 36.47%of tungsten residue is left after water leaching.The remained tungsten residue mainly consists of Si,Na,Fe,Al,Mn,and the content of tungsten is reduced to 0.15%.In the remained tungsten residue mainly consisted of sodium salt,Si exists in the form of Na₂Si₂O₅,Fe exists in the form of Na₂Fe O₄ and Al exists in the form of Al₂Si O₅.In conclude,it realizes the reduction and harmlessness of waste tungsten residue through a series of experiments.