From lepidolite acid leachate to phosphate adsorbent: selective Al/Fe recovery and conversion to Al-Fe composite hydroxide

Driven by the global energy transition and growing lithium demand, the utilization of low-grade lithium resources such as lepidolite has attracted increasing attention. Effective treatment of lepidolite acid leachate is crucial for mitigating environmental risks and enabling downstream lithium recovery. However, high concentrations of Al 3 + and Fe 3+ in the leachate cause conventional purification methods to suffer from poor selectivity, high lithium loss, and excessive solid-waste generation. Herein, an integrated resource-oriented strategy combining Al pre-removal, selective Al/Fe co-precipitation, precipitant regeneration, and synthesis of an Al-Fe composite hydroxide phosphate adsorbent was developed. Potassium alum crystallization removed 76.01% of Al 3+ , leaving 5.61 g·L −1 Al 3+ and 2.05 g·L −1 Fe 3+ at pH 1.65. Sodium benzoate selectively precipitated the remaining Al 3+ and Fe 3+ with > 99% removal efficiencies and < 3% Li + loss. Density functional theory (DFT) calculations revealed a binding energy order of Al 3+ > Fe 3+ > Li + , explaining the selective precipitation mechanism. After dilute H 2 SO 4 leaching, > 99% benzoic acid was regenerated, and the recovered Al/Fe solution was converted into a composite adsorbent with a maximum phosphate adsorption capacity of 70 mg·g −1 at pH 7 and 298.15 K. This work offers a feasible route for impurity recovery, reagent recycling, and value-added utilization of lithium leachate.