Comprehensive review and future research directions on using various lanthanum-based adsorbents for selective phosphate removal

Due to the specific affinity of lanthanum (La) toward phosphate over a wide pH range, La compounds such as lanthanum oxide (LO), lanthanum hydroxide (LH), and lanthanum carbonate (LC) have been integrated into various La-based adsorbents in recent years. In order to evaluate the differences among LO, LH, and LC in terms of phosphate removal performance (adsorption capacity, pH-dependent behavior, and selectivity), stability (La leaching), and reusability, data from the literature are consolidated. Furthermore, key properties of the respective compounds such as solubility and speciation are examined to identify possible underlying reasons. LC exhibits superior adsorption capacity and a wider optimum pH range for phosphate binding and lower La leaching, but reusability data of the various compounds remain inconclusive. Based on their superior performance and stability in laboratory studies, LC may have greater lifespan and can serve as a viable alternative to LO and LH for future studies on phosphate removal in order to maximize phosphate removal efficiency while simultaneously reducing secondary pollution. To further develop La-based adsorbents for phosphate removal and recovery, direct comparisons are needed among La compounds using more complex matrices such as wastewater and river water. Furthermore, the role of crystal structure in the phosphate removal performance of different compounds must be carefully assessed. Finally, to evaluate the feasibility of practical application and understand the effects of continuous flow operation on phosphate removal and recovery efficiency, more pilot-scale studies involving La-based adsorbents should be conducted. Graphical Abstract: Performance, stability, and reusability of different La compounds are crucial to the practicability of La-based adsorbents for phosphate removal along with addressing key challenges associated with real-world usage. The simultaneous incorporation of other metals presents a possible way to improve on the inherent properties of La-based adsorbents to enable them to better address these challenges.[Figure not available: see fulltext.].