Study On The Clean Recovery Of Copper Metal From Waste Printed Circuit Boards Based On The Variable-valence Characteristic Of Cerium

Waste printed circuit boards（WPCBs）are important copper resources with a high value of recovery and utilization,which is an important supplement to copper resources in China.Improper disposal of WPCBs may cause serious environmental problems,resulting that heavy metal elements such as lead,cadmium,and chromium enter groundwater and soil,seriously endangering the ecological environment and human health.Therefore,developing a new process for clean and efficient recovery of copper metal from WPCBs is of great significance in guaranteeing the safety of copper resources in China and protecting the ecological environment.Based on the strong oxidation of Ce⁴⁺ions in ceric ammonium nitrate（CAN）solution and the characteristics of Ce⁴⁺ions regeneration by electrolysis,a new cleaning process was proposed to recycle copper from WPCBs via the variable-valence characteristic of cerium,which includes leaching,purification,and electrolysis processes.The leaching process of WPCBs,purification process of leaching solution,electrodeposition process of copper metal,and electrolytic regeneration process of Ce⁴⁺were systematically studied.The effects of different factors on the leaching process,purification process,and electrolysis process were investigated.Thermodynamic analysis showed that copper metal can be thermally leached by Ce⁴⁺ions.The effects of temperature,CAN concentration,stirring speed,and particle size on copper leaching rate were investigated.The results showed that increasing temperature,CAN concentration,stirring speed,and reducing particle size could improve copper leaching rate.The optimal leaching conditions for WPCBs were75°C,CAN solution of 1.5 mol/L,stirring speed of 400 r/min,and particle size of0.038-0.075 mm.Under these conditions,the copper leaching rate could reach99.9%.In CAN solution,the leaching processes of copper powder and WPCBs were controlled by the mixing kinetics model,whose reaction activation energies were34.00 k J/mol and 47.56 k J/mol,respectively.The combined process of oxidation,precipitation,and adsorption was used to investigate the effects of dosage of hydrogen peroxide,oxidation time,dosage of activated carbon,adsorption time,and p H value on Ag and Sn removal rates.The mechanism of the purification process was explored.The results showed that the optimal conditions for purification of the leaching solution were as follows:The dosage of hydrogen peroxide was V hydrogen peroxide/V leaching solution=1/250;the oxidation time was 30 min;dosage of activated carbon was m activated carbon/V leaching solution=1/250（g/m L）;the adsorption time was 60 min;and the p H value was 2.0.Under these conditions,the removal rates of Ag and Sn were 97.41%and 93.74%,respectively.The purification mechanism indicated that the adsorption process of activated carbon for Ag,Sn,Ce,and Cu could be described by the pseudo-second-order model.By using simulated purified liquid as the electrolyte,the effects of electrolysis time,current density,and p H value of the electrolyte on cerium oxidation rate,copper reduction rate,current efficiency,morphology,and purity of cathode copper were investigated.Under the optimal electrolysis conditions for simulated purified liquid,the electrolysis process of actual purified liquid was studied.The cathode copper had a flat surface,and the purity of cathode copper was up to 99.998%.The current efficiency of Ce⁴⁺regeneration at the anode was 90.9%,and the current efficiency of copper electrodeposition at the cathode was 99.5%.