Separation of lithium from magnesium in salt lake brine via ammonium carbonate precipitation

To address the persistent challenge of severe magnesium interference in lithium extraction from high Mg/Li ratio salt-lake brines, this study proposes an innovative two-stage process: magnesium mineralization followed by lithium extraction, enabling efficient separation and utilization of lithium and magnesium resources. Leveraging a homogeneous (NH 4 ) 2 CO 3 -Mg 2+ mineralization system, we elucidate the three-stage kinetic mechanism of mineralization and the crystallographic regulation of magnesium carbonate. At low temperatures (40 °C), rod-shaped MgCO 3 ·3H 2 O crystals are formed, achieving 88 % Mg 2+ mineralization efficiency with 5 % Li + loss. Elevated temperatures (>50 °C) trigger anisotropic crystal growth, transforming the product into porous spherical 4MgCO 3 ·Mg(OH) 2 ·4H 2 O, increasing Li + loss to 15 %. Higher CO 3 2− concentrations shorten nucleation induction periods but promote surface-attached flaky structures. Optimized drying temperatures suppress dehydration-induced phase transitions, yielding high-purity products. In the subsequent lithium extraction stage, a Tributyl phosphate(TBP)-FeCl 3 -kerosene system demonstrates enhanced efficiency via Al 3+ -induced salting-out effects. With 70 % TBP −30 % kerosene and 1.2 mol/L AlCl 3 , single-stage Li + extraction efficiency reaches 67 %, while Al 3+ co-extraction remains below 4 %. FTIR analysis confirms that Al 3+ optimizes TBP coordination by releasing free Cl − , effectively mitigating Mg 2+ competition. This work provides a novel approach for synergistic CO 2 utilization and lithium-magnesium resource recovery from salt lakes, enhancing the sustainable utilization of critical minerals.