In Situ Production of Carbonate Anions from Water Electrolysis and CO₂ Absorption for Li₂CO₃ Crystallization from Preconcentrated Brines

Lithium carbonate (Li2CO3) is normally crystallized from concentrated brines via the addition of sodium carbonate (Na2CO3, soda ash). While this is a methodology largely proved and in implementation in almost all facilities in operation today, it is a chemical intensive procedure. Both the associated costs of sodium carbonate and the logistic issues of bringing large amounts of chemicals to the remote locations where lithium mining from brines takes place should be considered. Here a new prospective technology is proposed for the in situ production of carbonate anions via water reduction and direct CO2 absorption on alkaline media. Experiments were performed on a real concentrated brine sample obtained from an operating facility in the Lithium Triangle. In the first electrolysis, traces of divalent cations were removed with only 1.3% of the total Li+ content in the original brine being trapped in the obtained solid. The second electrolysis produced removal from the brine from 67.2% of the originally contained Li+. Studies were conducted to improve the purification of the solid, since in the highly saline brine (total dissolved solids of 412 g L–1) the as obtained solid was only 70.5% pure. Upon 2 purification steps, a solid 99.1% pure could be obtained. A third electrolysis step could crystallize further 11.8% extra of the original Li+ content, albeit at a much higher energy cost. Upon brine treatment, 88.0 g CO2 per liter of brine fed to the first electrolysis could be absorbed; 63.2 g of which remain in the Li+ depleted brine, and only 24.8 g in the obtained solids.