Zinc cathodes produced with highly-variable DC current simulated from solar irradiance data

Abstract

This work is the first of series of two papers with focus on the applicability of highly-variable direct (DC) current for producing high-quality cathodes by electrowinning. Different profiles of electrical current were simulated from solar irradiance data and weather parameters and then applied to the electrowinning cell using a precision, programmable power supply. This approach was motivated considering the use of photovoltaic power plant to directly supply DC current to industrial tankhouses, especially in scenarios of blackout of electric grid, power outages and most expensive electricity hours. The simulated DC current was applied to zinc electrowinning, which was selected as case study due to its intensive energy consumption. The electrowinning tests were carried out under operating conditions similar to those practiced in industry. The zinc cathodes were characterized by morphology, microstructure, crystal structure and mechanical resistance (i.e., bending behavior). Average current densities in the range 261–809 A m−2 were applied to the electrowinning cell, which reflect the different current profiles simulated for each type of solar irradiance variability. Even under wide range of current densities and high amplitude variations (peak values as high as 1816 A m−2 were momently applied to the cell), the current efficiencies and specific energy consumptions were considered satisfactory (>90% and < 3000 kWh t−1, respectively). Analysis by scanning electron microscopy showed that the zinc deposits produced with highly-variable DC current are noticeably rougher than those produced at typical constant currents. The microstructure analysis confirmed that high current densities promote grain refinement. Bending measurements of different materials revealed increasing resistances by increasing the average current density, which, however, did not lead to their fracture or breakage during the stripping.