| With the development of science and technology,the iteration speed of Mobile Phones is accelerated,which leads to the huge generation of waste mobile phones.Therefore,the number of Waste Printed Circuit Boards of Mobile Phones（WPCB-MPs）is also increasing.WPCB-MPs is rich in metals,i.e.,Cu content is about 34%,much higher than that of its primary ore.Thus,WPCB-MPs has great economic value.Alkaline slurry electrolysis has been proven to be an effective method for metal recovery from WPCB-MPs.However,the electrolyte after slurry electrolysis contains high concentrations of metals,which will cause pollution if not properly treated,and most importantly it is also a waste of resources.In view of this,based on the thermodynamic and electrochemical analysis,this paper disccusses the recovery mechanism of copper from WPCB-MPs by ammonia-ammonium chloride alkaline slurry electrolysis;carried out electrolyte circulation experiment to explore the influence of its circulation runs on Cu recovery,purity and current efficiency,as well as the migration and transformation of Cu and other metals;conducted laboratory amplification experiment to explore the optimal reaction conditions,and also its electrolyte circulation to verify its feasibility.The research results could provide theoretical and technical support for the industrialization of copper recovery from WPCBs by alkaline slurry electrolysis.The main conclusions are as follows:（1）The potential-p H diagram of Cu-NH3-H2O system shows that the oxidation potential of Cu decreases with the increase of p H value.In the process of alkaline ammonia leaching,it is necessary to control p H of the electrolyte in the range of 9-10,which is conducive to the generation of[Cu（NH3）4]2+and[Cu（NH3）2]+,while the impurity ions form insoluble substances.If p H is lower or higher than this range,insoluble Cu O or Cu2O may be generated.Linear sweep voltammetry（LSV）results show that there are two reduction peaks and two oxidation peaks in the NH3·H2O-NH4Cl-Cu SO4-Na Cl alkaline slurry electrolysis system.After the addition of WPCB-MPs,the copper element in the WPCB-MPS helped the electrode reaction to reduce the potential,and the peak position shifted to the right.The reduction process is controlled by electrochemistry,that is,substances in the solution are adsorbed to the electrode surface to participate in the reaction of gaining and losing electrons,which could help improve the current efficiency.（2）Electrolyte can be successfully reused for the alkline slurry electrolysis.The electrolyte circulation cycles have a significant effect on the metal distribution and current efficiency.Copper is mainly distributed in the cathode product,and other metals are mainly distributed in the electrolyte and anode residues.With the increase of the number of cycles,the total metal concentration in the electrolyte gradually increases,showing an enrichment phenomenon.The current efficiency fluctuates but is basically higher than 90%.In addition,the recovery rate and purity of copper are basically unaffected,higher than 99%and 99.9%for all the 20 runs.And all the cathode copper foils are easily to be peeled.（3）The optimal conditions for the 5 L electrolyte amplification experiment are:4 mol/L NH3·H2O,25 g/L Cu2+（Cu SO4·5H2O）,0.5 mol/L Na Cl,0.5 mol/L NH4Cl,20 m A/cm2,solid-liquid ratio of 30 g/L,8 h.Under these conditions,the current efficiency is 90.47%,the copper recovery rate is 92.04%,and the purity of the obtained cathode copper is 99.78%.Under these conditions,five electrolyte reuse experiments were carried out,and it is found that the number of electrolyte circulation cycles have no effect on the purity of cathode copper in the amplification experiment,and the purity of cathode products of the five runs are all above99%.Due to the uneven mixing,copper recovery rate is basically 90%-92%,which is lower than that of the small experiment.The current efficiency is more stable than the small test,higher than 90%.In addition,as in the small-scale experiment,the total metal in the electrolyte is accumulated. |
