Electrochemical Anodic Dissolution Behavior Of Copper-zinc-nickel Alloy Scrap In Copper Sulfate Electrolyte

Copper and its alloys have wide industrial applications due to their high technological value,including in marine environments,building materials,electric materials,and the mechanical industry.Correspondingly,due the end of the service life of these copper-based alloys,there will be large amounts of copper-based alloy scraps that are produced.As a result of the depletion of natural copper resources,the recovery of copper from these copper-based scraps has been studied in recent years.At present,there are many ways to deal with this kind of alloy waste,but each has many defects.It is noteworthy that,a direct electrolysis process has also been developed in which the copper-based alloy scraps are used as anode and the copper is selectively deposited at the cathode due to the potential difference between copper and other associated metals including Ni,Zn,Al,etc.In Chile,the process of recovering copper from copper scraps with the copper scraps used as anode has been applied in industry.Meanwhile,the copper qualitatively free from impurities could also be obtained from printed circuit board wastes through the similar process.Also through a direct electrolysis process,a copper with purity of99.98 wt%was produced from the anodes of Cu-based alloy scraps.Firstly,the anodic dissolution properties of Cu-Zn-Ni alloy scraps in 45 g/L^-1Cu SO₄solutions have been analyzed.We have shown from the electrochemical measurements and electron probe microscopic analysis how the sulfuric acid concentration,potential scan rate,temperature and heat treatment affect the anodic dissolution behavior of the Cu-Zn-Ni alloy scraps.The results show that with the H₂SO₄ concentration increasing from 0 to 160 g/L and the temperature increasing from 25 to 60°C,the dissolution rate of the Cu-Zn-Ni alloy scraps increases.The anode peak current density that was derived from the cyclic polarization curves and the square root of the scan rate have a good linear correlation,and the activation energy of the anodic dissolution process is 14.6 k J/mol,both of which indicate that the anodic dissolution process is under the control of diffusion.With the Cu-Zn-Ni alloy scraps that were first heat treated in proper conditions,the size of grains increases,and the particle size uniformity decreases,which results in the resistances of the surface layer and the charge transfer process decreasing and alloy scraps being more soluble.Secondly,the effect of different chloride ions on the electrochemical dissolution of Cu-Zn-Ni alloy was studied.In order to obtain the effect of chloride ions on the electrochemical dissolution of Cu-Zn-Ni alloy.We set up three groups of experiments:the first group,pure copper and Cu-Zn-Ni alloy were compared in 45g/L^-1 Cu SO₄electrolyte containing 80g/L H₂SO₄,mainly studying the effect of Cu-Zn-Ni alloy.In the first group,different concentrations of chloride ions（0,0.01,0.02,0.03,0.05mol/L Cl^-）were added to Cu-Zn-Ni alloy to study the pitting effect of chloride ions on the electrochemical dissolution of the alloy and the effect on the combination of passivation film.The results show that the appropriate addition of chloride ion is beneficial to accelerate the dissolution of the alloy.When the amount of chloride ion is more than0.02 mol/L,the copper chloride with excessive insolubility and poor conductivity is attached to the contact surface of the alloy and the electrolyte,which hinders the continuous dissolution of the alloy.In the third group,sulfuric acid（80,140,160,200g/L H₂SO₄）was added into 45g/L Cu SO₄ solution with 0.02 mol/L Cl^-to study the effect of sulfuric acid concentration on passivation film.The results show that the electrochemical dissolution rate of Cu-Zn-Ni alloy is the highest in the electrolyte containing 160g/L sulfuric acid.Further increasing the concentration of sulfuric acid will increase the viscosity and density of the solution,instead of using the dissolution of Cu-Zn-Ni alloy.