A strategy to avoid solid formation within the reactor during magnesium and calcium electrolytic removal from lithium-rich brines

Abstract

It is expected that lithium sourcing from aqueous sources in the medium term will account for over half of worldwide production, since reserves in brines are more abundant than in hard rock ores. To produce high purity lithium products, the full abatement of both Mg2+ and Ca2+ cations is fundamental. Current practice involves the use of large volumes of chemicals, NaOH and Na2CO3, leaving behind only residues. We recently proposed to produce brine alkalinization via water reduction using a simple 2 compartment electrolyzer fitted with an anion exchange membrane. Here, we advanced the study of this system by correlating voltage drop, pH, and cation concentrations with the advancement of electrolysis. Results suggest that solids are not formed within the membrane, but only on its surface. We also propose a new strategy to avoid all together solid formation within the electrolyzer, arriving at very similar results regarding Mg2+ abatement and minimal Li+ depletion in the processed brine (average 99.6% Mg2+ depletion). However, Ca2+ concentrations remained at values between 30 and 44% of the original brine content. The voltage drop between electrodes in the new reactor setup was lower than that in the original setup (2 V lower at 200 A m−2). That difference suggests both that the membrane is not degrading at the more alkaline pH and that the electrical consumption for the electrolysis would be lower with the new setup. Graphical abstract: [Figure not available: see fulltext.].