A stable and selective LaOCl sorbent for advanced phosphorus removal from phosphogypsum leachate: Design, application and mechanism

A porous LaOCl adsorbent was synthesized via 2-methylimidazole regulation. • It achieves an exceptional phosphate adsorption capacity of 138.85 mg P/g. • It demonstrated remarkable adsorption stability under the PG leachate conditions. • A dual ligand-exchange mechanism was identified for selective phosphate adsorption. • LaOCl rapidly lowered the DTP concentration of PG leachate below 0.5 mg P/L. Phosphogypsum (PG) leachate, characterized by high phosphorus concentration and strong acidity, poses significant environmental risks due to its potential to cause eutrophication and soil contamination. In this study, a hierarchically porous LaOCl adsorbent was synthesized via a 2-methylimidazole-regulated precipitation-calcination strategy. By modulating the La/2-methylimidazole ratio, the crystallinity of the precursor and the porosity of the resulting LaOCl were effectively tailored. The optimized material (LaOCl-1) exhibited a high surface area, abundant mesopores, and exposed active sites, which collectively contributed to rapid mass transfer and an exceptional phosphate adsorption capacity of 138.85 mg P/g. The LaOCl adsorbent also demonstrated remarkable adsorption stability under acidic conditions and high selectivity toward phosphate, even in the presence of common interfering ions in PG leachate, such as F⁻. A dual ligand-exchange mechanism—involving both Cl and OH groups as exchangeable sites—was identified as the primary pathway for selective phosphate adsorption. In practical tests using authentic (or pre-treated) PG leachate, LaOCl rapidly lowered the dissolved total phosphorus concentration below 0.5 mg P/L, complying with strict discharge limits, while maintaining consistent performance over extended durations and under varying conditions. This study underscores an effective regulation strategy for constructing advanced LaOCl-based adsorbents aimed at efficient phosphorus removal from PG leachate. Download: Download high-res image (213KB) Download: Download full-size image