Novel calcite-enriched material derived from fly ash for efficient and selective phosphate removal from wastewater

Abstract

Efficient and selective advanced phosphorus treatment from wastewater remains a significant challenge. In this study, we developed a novel calcite-enriched material (M-Res) for advanced phosphorus recovery from wastewater. This material was synthesized from high-aluminum fly ash through calcination, Na₂CO₃ leaching, and ball-milling modification. Characterization results indicated that ball-milling introduced lattice defects, creating abundant active calcium sites with a strong affinity for capturing phosphate ions. Batch adsorption experiments demonstrated that M-Res has a high phosphate adsorption capacity of 74.8 mg-P/g and exhibits excellent performance in terms of anti-interference and selective adsorption. When the initial concentration was 10 mg/L, the post-adsorption phosphate concentration met the first-level surface water quality standards (0.02 mg/L, GB 3838-2002). At 50 mg/L, it met the second-level discharge standards for urban sewage treatment plants (3 mg/L, GB 18918-2002). The adsorption mechanism involves the release of Ca²⁺ from calcite, which interacts with phosphate ions through complexation, surface precipitation, and electrostatic attraction. Derived from a by-product of high-aluminum fly ash in aluminum extraction processes, M-Res is economical and simple to produce, making it a promising adsorbent for the advanced treatment of low-concentration phosphate.