Effect of temperature, current density and mass transport during the electrolytic removal of magnesium ions from lithium rich brines

Abstract

Full depletion of magnesium cations from lithium rich brines is vital for the successful crystallization of battery grade lithium salts in subsequent production steps. In a three compartment water electrolyser, we demonstrate the full abatement of Mg2+, with concomitant recovery of magnesium hydroxide. We have studied the influence of three operational variables, current density, temperature and forced mass transport in the coulombic efficiency, cell voltage between the electrodes, solid purity and lithium ions loss. Response surface methodology was used to model the system. Our results show that both in terms of energy efficiency, product purity and minimal Li+ loss it is best to work at very low current density, high flow rate, and high temperature (32 A m−2, 60 °C, and 18 L h−1). Working at higher current density, low temperature, and high flow rate (100 A m−2, 26.5 °C, and 18 L h−1) still guarantees a product of acceptable quality while keeping a moderate electrical consumption. The current density is the factor that affects results the most. High current densities are correlated with a faster nucleation, and smaller particle size, resulting in higher adsorption from other ions and co-precipitation of Ca[sbnd]B by-products.