Electrochemical studies of ionic liquid additives during the zinc electrowinning process

Abstract

1-Ethyl-3-methylimidazolium methanesulfonate ([EMIM]MSO3) and 1-butyl-3 methylimidazolium bromide ([BMIM]Br) were evaluated individually as additives compared to gelatin and a previously studied additive ([BMIM]Cl) in zinc electrowinning from a synthetic acidic sulfate electrolyte containing 8gdm−3 of Mn2+ ions. A metallic impurity of 0.0055mgdm−3 of Sb3+ ions was examined in combination with 1 and 3mg of each additive. Galvanostatic measurements have been employed to investigate the cathodic and anodic potentials individually and also the current efficiency of the deposited zinc metal in the acidic sulfate electrolyte for 2h at 50mAcm−2 and 38°C. The effect of each additive on surface morphology and crystallographic orientation was studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Lead impurities in the deposit have been measured by using an inductively coupled plasma (ICP). Among five different additive concentrations (1, 3, 5, 10 and 40mgdm−3) tested, results revealed that the addition of 1 and 3mgdm−3 of [EMIM]MSO3 reduced the cell voltage by ≈15 and 10mV, respectively, while [BMIM]Br at 1 and 3mgdm−3 reduced the cell voltage by ≈10 and 5mV, respectively. Current efficiencies of 93.6%–94.4% have been obtained by adding 1–3mgdm−3 of [EMIM]MSO3 or 1–3mgdm−3 of [BMIM]Br as compared to 92.8% obtained from the standard electrolyte. Maximum reduction of power consumption of ≈165kWhton−1 was obtained from adding 3mgdm−3 of [EMIM]MSO3 in the presence of Sb3+ ions followed by a reduction of ≈154kWhton−1 by adding 3mgdm−3 of [BMIM]Br. Potentiodynamic polarization and voltammetric studies indicate that polarization for zinc electrodeposition decreased in the presence of antimony. Apparently, the two additives have approximately similar polarization behaviors on the aluminum electrode in the acidic sulfate electrolyte.