The role of boron in controlling the pH of lithium brines
2025-05-23
The global clean energy transition requires the development of alternative energy technologies that rely on critical raw materials including lithium. Closed-basin brines, which generate ~40% of global lithium production, often have a circumneutral pH; however, during the evaporative concentration required for lithium production, the evaporated brines become acidic. Using primary geochemical and boron isotope data from the Salar de Uyuni (SDU), Bolivia combined with a modeling approach, we show that boron enrichment, which commonly co-occurs with lithium in closed-basin brines, is the primary factor in controlling the pH of brines from the SDU. We demonstrate that boron in global lithium- and boron-rich brines from closed basins exerts a similar influence on brine pH. The unique boron enrichments and its speciation can explain large proportions of alkalinity in these brines (~98% at the SDU), where evaporation alters the dissociation of boric acid, which triggers the formation of acidic evaporated brines.