Electroextraction of lead from a lead trilonate solution

Abstract

The method of extracting lead into a solution from lead cakes of zinc production and the removal of metal impurities from the thus prepared solution were sug gested in [1,2]. We used a complex former, namely, dis odium salt of ethylenediamine acid known as Trilon B, as the leaching reagent. The processing technology of the lead cake is described in [3]. The finishing opera tion is the electroextraction of lead from the purified solution by leaching.The electroreduction of various metals from com plex electrolytes is described in many publications. However, the data presented in them have either aca demic or strictly specialized characters. In connection with this, we investigated the regularities of the elec troreduction of lead from trilonate electrolytes under various conditions. We varied the potential scan rate, the concentration of the lead cation, the pH of the electrolyte, and the process temperature.The cathode reduction of lead from the trilonate solution was studied by recording the polarization curves using an IPC Pro M potentiostat connected to a personal computer. The tests were performed in a standard thermostated electrochemical cell. Mixing of the working solution in the cell with a constant rate for all the experiments was performed using a magnetic stirrer established under the cell. We used a silverchlorine half cell as the reference electrode. The working electrode with an area of 0.5024 cm 2 , which was fabricated from stainless steel and pressed into a vinyl plastic holder, was separated from the reference electrode using an electrolytic key. The platinum electrode was an auxiliary electrode. To hold the temperature of the working solution, water from a thermostat was passed through the jacket of the elec trochemical cell.A working solution in an amount of 100 cm 3 was poured into the electrochemical cell, electrodes and cables were connected, and stirring was switched on. The necessary parameters of the potential scan rate and the ranges of potentials and currents were speci fied; the current-voltage dependence was fixed. The data were processed in Microsoft Excel recalculating cathode currents into the current density.The potentiodynamic discharge curves of metal cations were recorded for a solution with the averaged composition (pH = 7, Pb 2+ of 20 g/dm 3 ) at various potential scan rates (V p = 5, 10, 20, and 50 mV/s) in the E range from -500 to -2500 mV by fixing the cathode currents with recalculation into the current density with the help of special software using a per sonal computer. Before each experiment, the working electrode was carefully cleaned and polished. To ensure the reproducibility of results, each experiment was repeated sixfold averaging the results. Further, averaged curves were combined into a common plot (Fig. 1).The increase in i c at E = -1500 mV is smoothed in the curves at V p = 20 and 50 mV/s (Fig. 1, curves 3 and 4); diffusion limiting is not distinguishable. An increase in the current density and a variation in the slope angle of the curve are also noted for...