Chelyabinsk State University, Chelyabinsk, Russia:

A. V. Kolesnikov, head of the department of analytical and physical chemistry, e-mail: avkzinc@csu.ru

Technical University of UMMC, Verkhnyaya Pyshma, Russia:
P. A. Kozlov, Deputy Director on Science, e-mail: p.kozlov@tu-ugmk.com

The purpose of this work was to study the electroreduction of zinc in sulfate solutions on a solid electrode with the acquisition of new experimental data, allowing deeper understanding of the processes taking place in industrial electrolysis. Electrochemical studies were carried out on a sulfate electrolyte containing 0.005, 0.0125 and 0.025 mol/l ZnSO₄ in a background 0.5 mol/l solution of Na2SO₄. Some studies were performed using electrolytes of composition: 0.25 mol/l ZnSO₄; 0.25 and 0.75 mol/l ZnSO₄ + 18 and 54 g/l H₂SO₄. The exchange current was calculated from galvanostatic measurements, building the Tafel semi logarithmic dependences of the polarization change on the logarithm of the current density at the initial instant of time. In the region of low deviations in the potential from the equilibrium calculation of the exchange currents, it was estimated from micro-polarization measurements in the overvoltage region of less than 515 mV. The total polarization capacitance was calculated by the equation, assigning a linearly varying voltage to the electrode at a sweep rate of 100 mV/s and recording the dependence of the current on the electrode potential in the initial fractions of the seconds of the process. As a result of the work performed, it was shown that additives of flocculants reduce the total polarization capacity in the entire range of zinc content in the background electrolyte of sodium sulfate, in contrast to the additions of lignosulfonate, what is associated with a higher molecular weight of flocculants. At the same time, molecules of organic substances are relatively large in size, and their adsorption leads to an increase in the distance between the capacitor plates in the double layer and thereby increases the polarization capacity. It is noted that the exchange current and the total polarization capacitance are increases substantially under conditions of intense mixing. Using the example of electrolysis of zinc sulfate solutions with lignosulfonate additives, it was shown that the exchange current decreases with increasing surfactant of addition, and with increasing concentration of zinc, the exchange current and total polarization capacity are increases. The performed investigations was made it possible to obtain new data of the exchange currents and the polarization capacity of zinc electrolysis on a solid electrode in the presence of various surfactants.

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