Towards a higher level of circularity in lithium brine mining: CO2 absorption in concentrated brines

Abstract

The transition to sustainable lithium production from brines requires innovations that address chemical consumption, water use, and carbon emissions. This work proposes a novel six-step treatment of real, highly saline lithium-rich brine to simultaneously recover lithium carbonate (Li₂CO₃), co-produce sodium carbonate (Na₂CO₃), and achieve permanent CO₂ storage through mineralization. The strategy integrates five electrochemical steps—employing an anion exchange membrane—with one chemical CO₂ absorption step. Electrolysis initially raises the brine pH to eliminate divalent cations without chemical additives. Subsequent CO₂ sparging in alkaline brines induces Li₂CO₃ and later Na₂CO₃ precipitation. Results demonstrate 78% Li⁺ recovery as impure Li₂CO₃ and 71.8% Na⁺ recovery as Na₂CO₃. Notably, 205.8 g of CO₂ per litre initial brine were absorbed, of which 189.7 g were permanently stored in solid carbonates. The process minimizes chemical input, reduces reliance on remote chemical delivery, and leverages high brine salinity to enhance CO₂ capture kinetics and electrochemical efficiency. Though not optimized for energy consumption, this proof-of-concept study reveals a circular approach to lithium extraction, integrating critical material recovery with climate-relevant carbon capture. Future improvements could enable direct air capture integration and Li₂CO₃ purification. This study introduces an industrially relevant pathway to reduce the environmental impact of lithium brine mining by turning waste brine constituents into valuable, stable products while closing the carbon cycle through mineralization.