Study On The Electrochemical Behavior Of Copper, Nickel And Iron Recovered By Direct Electrolytic Graded Electrowinning Method Of Copper-nickel Alloy Waste

Copper-nickel based alloys are widely used because of its'good conductivity,high strength and corrosion resistance.However,with the increase of service time and mechanical wear,the properties of the alloy decrease and eliminate year by year,resulting in a large number of copper-nickel based alloy waste.Under the background of relative shortage of copper and nickel resources in China,the recycling of copper-nickel based alloy waste has become an important way to supplement the gap of copper and nickel resources in China.At present,most enterprises use pyrometallurgy method to treat copper-nickel based alloy waste,but this method requires high copper grade(more than90%).On the premise of technical exploration and reducing carbon emission,our research group puts forward a new idea of hydrometallurgy recovery of copper and nickel by direct electrolytic graded electrodeposition of copper-nickel based alloy waste,which reduces the carbon emission by about 50%compared with the pyrometallurgy recovery process,and reduces the copper grade requirements for the treatment of copper-nickel based alloy waste.In the previous research,the process parameters of copper and nickel recovery were determined,the selective recovery of copper and nickel was realized,and the anodic dissolution mechanism of copper-nickel based alloy waste was studied.This paper uses electrochemical means to explore the effects of alloy components such as Sn,Ni and Fe on the cathodic electrodeposition process of direct electrolytic graded electrodeposition process.The method of recovering ferronickel alloy by direct electrodeposition(Fe²⁺about 0.5 g/L)is proposed.On the premise of obtaining high-quality ferronickel alloy(nickel more than 95%),the process parameters are optimized.The achievements are as follows:(1)It is found that Sn²⁺ion has a great influence on the cathode copper deposits'morphology.The influence of Ni²⁺ion on Cu²⁺ion is mainly in the ion diffusion stage,while Fe²⁺ion has little effect on the deposition of Cu²⁺ion.At the same time,it is found that the content of tin ion in the solution should not exceed 5 g/L.The diffusion coefficient of Cu²⁺decreases when the concentration of Ni²⁺increases.The existence of Ni²⁺in the solution hindered the diffusion of Cu²⁺to a certain extent.When the solution contains Ni²⁺ions,it is clear that the stirring can promote the diffusion of Cu²⁺ions,the nucleation point of cathode copper increases,and the cathode copper product is smaller and relatively uniform.(2)The effect of Ni²⁺ion on the nucleation model of copper cathodic electrodeposition was investigated.It was found that Ni²⁺ions inhibited the diffusion and mass transfer of Cu²⁺ions in the solution and the cathodic electroreduction.Ni²⁺ions will enter the the cathode electric double layer together with Cu²⁺ions,so the number of Cu²⁺ions in the cathode electric double layer is relatively reduced,thus inhibiting the cathodic electrodeposition of Cu²⁺ions.It was also found that the nucleation model of copper cathodic electrodeposition was changed by changing the solution temperature and sulfuric acid concentration.Thiourea could hydrolyze into S^2-ion and react with Cu²⁺and Ni²⁺ions to formed copper sulfide(Cu S)and nickel sulfide(Ni S),and make the cathode copper deposition products more uniform and refine.It is found that the thiourea can effectively reduce the influence of Ni²⁺ion on cathodic copper electrodeposition,and the quality of cathodic copper is better when Ni²⁺ion and thiourea exist in the solution at the same time.(3)The Sn²⁺in the solution can inhibit the cathodic reduction of Cu²⁺.When the concentration of Sn²⁺ion in the solution reached to 5 g/L,Sn²⁺ions are easily oxidized to Sn⁴⁺by reaction with dissolved oxygen in acidic solution and formed Sn O₂ carries a positive charge and is directly attached to the cathode surface,cause the Sn content in the cathode copper product increases sharply.When the concentration of Sn²⁺ion in the solution is 2 g/L,the co-deposition of Cu and Sn in the cathode will lead to the decrease of cathode quality.The addition of thiourea,thiourea complexes(Cu[CS(NH₂)₂]²⁺and Sn[CS(NH₂)₂]²⁺)will be formed,resulting in cathodic depolarization,and the nucleation mode of cathodic electrodeposition will gradually change to progressive nucleation.This results in the decrease of tin content in the product and the refinement of the product surface particle size.The tin content in cathodic electrodeposition product reaches a relatively small amount(about 0.05%(wt%).(4)The internal stress of electrodeposited Ni-Fe alloy was investigated.The results are as follows:when the concentration of saccharin sodium in solution is 14 g/L,the grain size of Ni-Fe alloy is obviously refined.Due to the adsorption of thiourea and its complexation with Ni²⁺and/or Fe²⁺,the cathodic electrodeposition potential shifts to the positive direction in the solution presence of thiourea.It shows that thiourea promotes the grain growth of Ni-Fe alloy.The Ni-Fe deposition potential shifted positively in the presence of thiourea,and it should not be added together with saccharin Na during the nucleation stage for the grain refinement of the deposits.It is found that the optimum conditions for recovery of Ni-Fe alloy were as follows:first,electrodeposition was carried out in the sulfate solution containing 60 g/L Ni²⁺,0.5 g/L Fe²⁺,8 g/L H₃BO₃,60 g/L sodium sulfate 14 g/L saccharin sodium at 60°C,and then quickly move to the solution containing 4 mg/L thiourea for further electrodeposition,Ni-Fe alloy was effectively recovered and the internal stress was eliminated.