Efeito da densidade de corrente, simulada a partir da variabilidade da irradiância solar, sobre a eficiência da eletrorrecuperação de zinco e qualidade do produto

Abstract

The present work evaluates the effects of current density at fixed or highly-variable intensities on the energy efficiency of the zinc electrowinning process and quality of the final product. Considering the uncertainties regarding the availability and future price of electricity, it is demanding to evaluate the use of renewable sources, such as solar energy, in metallurgical processes. Different current profiles were simulated from the variability of solar irradiance, which depends on the Earth's revolution and rotation and movement of different types of clouds in the atmosphere. The approach followed in this work consisted in the use of multiparameter procedure for classifying days according to the variability of solar irradiance and use of classical algorithm to simulate the performance of photovoltaic systems. The simulated direct current (DC), generated from numerical simulations, was then applied to the zinc electrodeposition process, which was selected as a case study mainly due to its intensive energy consumption. The simulations resulted in average current densities in the range 261-809Am-2. The current efficiencies and specific energy consumptions calculated for the process were considered satisfactory (>90% and <3000kWht-1). The characterization of zinc deposits, which are porous due to typical secondary cathodic reaction (i.e., hydrogen evolution), revealed that the products obtained with highly-variable current density are rougher than those produced with constant current density. Bending measurements of different samples revealed increasing resistances by increasing the average current density, which, however, did not lead to their fracture or breakage during the stripping. Zinc electrowinning tests from electrolytes containing magnesium ions (Mg2+), an impurity commonly present in the industrial solution, indicated a small and gradual decrease of current efficiency and increase of energy consumption by increasing the impurity concentration in the solution. Regarding the main features of zinc deposits obtained from electrolytes containing Mg2+ ions, increases in the amount of pores and nodules were observed, which, however, did not affect their behavior during the bending tests. Hence, the results obtained in this work suggest the applicability of highly-variable current density, obtained from PV systems, for producing zinc with efficiency and quality suitable for industrial production.