Simultaneous Electrowinning Of Lead And Manganese Dioxide In Chloride Medium

Electrowinning of lead from aqueous solution of PbCl2 and electrowinning of manganese dioxide from aqueous solution of MnCl2 are two research focuses in hydrometallurgy. To realize the electrowinning of lead without liberation of chlorine at anodes in cell, simultaneous electrowinning of lead and manganese dioxide from a mixture solution of PbCl2 and MnCl2 was investigated for the first time. This simultaneous electrowinning of lead and manganese dioxide not only can prevent chlorine from liberating at anodes but also obtain two electrolysis products simultaneously, which result in decrease of electric energy consumption for the electrowinning process.Firstly two separate electrowinning tests, electrowinning of lead from PbCl2 solution and electrowinning of manganese dioxide from MnCl2 solution, were carried out. And then, tests for simultaneous electrowinning of lead and manganese dioxide in chloride medium were conducted. The simultaneous electrowinning of lead and manganese dioxide includes two methods:electrowinning processes without and with diaphragm between anode and cathode in cell. Experimental results indicated that simultaneous electrowinning process, especially the simultaneous electrowinning process with diaphragm is feasible.The optimum process conditions of simultaneous electrowinning without diaphragm are summarized as follows:concentration of Pb2+and Mn2+in electrolyte is 15 g/L and 50g/L respectively, concentration of HCl and NaCl in electrolyte is 4g/L and 2mol/L respectively, temperature of electrolyte is 90℃, and current density is 80A/m2. By electrowinning for 2 hours under the optimum process conditions, current efficiency of cathode and anode is 98% and 92% respectively, weight ratio of lead and manganese dioxide produced at electrodes is 2.61:1, average cell voltage is 1.667V, direct current consumption to produce 2.61 kg of lead and lkg of manganese dioxide is 1.131kWh, the save of electric energy reaches 55.47% by comparison with the separate electrowinning of lead and manganese dioxide. Anode products are y-MnO2, content of MnO2 in the products is more than 91%. The optimum process conditions of simultaneous electrowinning with diaphragm are determined as:material of diaphragm is polyster cotton, height difference between surface of anolyte and surface of catholyte is 20mm, concentration of Pb2+ and NaCl in the catholyte is 25g/L and 4.5mol/L respectively, concentration of Mn2+and HCl in the anolyte is 50g/L and 8g/L respectively, temperature of electrolyte is 80℃, current density is 80A/m2. By electrowinning for 2 hours under the optimum process conditions, current efficiency of cathode and anode is both more than 99%, current efficiency of cathode and anode for 5 hours is 96% and 99% respectively, the average cell voltage is 1.701V, the weight ratio of lead and manganese dioxide produced in electrodes is 2.39:1, direct current consumption to produce 2.39 kg of lead and lkg of manganese dioxide is 1.056kWh, the save of electric energy reaches 56.58% by comparison with the separate electrowinning of lead and manganese dioxide, anode products are y-MnO2, content of which is more than 92%.Although two electrowinning process without and with diaphragm are both feasible on the basis of the experimental results, current efficiency of anode for electrowinning process without diaphragm is only 92%, which show that there must be some chlorine liberating from anodes. Therefore, electrowinning process with diaphragm is the optimum technology for extraction of lead and manganese dioxide in chloride medium. The results of expanding test are basically the same with that of laboratory experiment. According to results of present work, a suggested principle flow sheet for the extraction of lead and manganese dioxide from lead concentrate and manganese carbonate ore is given in the fifth chapter of this paper.