Research On Electroreduction Of CuS,PbS And Sb₂S₃ In Strongly Alkaline Solution

Copper,lead and antimony metals and their alloy materials occupy an important position in the development of the national economy and are widely used in national defense,science and technology,industry and agriculture.Copper,lead and antimony always exist in the form of sulphides in nature,such as chalcopyrite(Cu2S),galena(PbS),boulangerite(Pb5Sb4S11),stibnite(Sb2S3),jamesonite(Pb4FeSb6S14)and so on.The traditional smelting method is mainly based on pyro-metallurgical pathways,means that it will make high energy consumption and cause serious pollution.The electrochemical metallurgy method provids a method of smelting using electrons as a reducing agent.In recent years,the strong alkaline aqueous system electrolyte has achieved the electrolytic reduction of hematite by using the extremely low hydrogen evolution potential under this alkaline condition.In this thesis,50 wt.%NaOH strong alkaline solution was used as electrolyte.Firstly,the thermodynamic data of the possible decomposition reactions of CuS,Cu2S,PbS and Sb2S3 were calculated to illustrate the reactions sequence and prove the feasibility of extracting metals from their sulfides in this alkaline solution,and the hydrogen evolution potential in the system was 1.05V lower than that in neutral aqueous solution.Moreover,a home-made three-electrode system was employed to study the electrochemical reduction behaviors of CuS,Cu2S,PbS and Sb2S3,the CuS reduction process was proved to involve a two-step reaction with Cu2S as the transition,then the electrolytic reductions of PbS and Sb2S3 are one-step reactions,and the peak potentials of the reduction peaks in the cyclic voltammetry test are in agreement with the thermodynamic calculation results.Then,the effects of different electrolysis voltages and different electrolysis times on the product types and product morphology were studied by a two-electrode system.The results show that when the electrolysis time of CuS and PbS was more than 4h,the products dominantly grow in the(111)crystal plane with the electrolysis time increasing,and the morphologies of the products gradually change from the agglomerated tumor-like block to the agglomerated spherical particle.When the electrolysis voltage is increased,the electrolysis reactions can be carried out at a faster rate,and all reduction reactions could be finished at 2.0V after 4h electrolysis.The morphology of the product of Sb2S3 gradually changes to the regular shape of the agglomerated cube under 1.8V and 2.0V.When electrolysis is completed,the current efficiency of all the reactions were calculated to be higher than 90%.These results confirm the feasibility of electrolysis of the sulfides in this system.