Sustainable Low-Temperature Metakaolin-Based Reactive Materials for Phosphate Removal from Agricultural Drainage Water

Phosphate concentrations in agricultural drainage water frequently exceed those observed in municipal wastewater and, when discharged directly into river systems, pose a significant risk to their ecological status and potential. Developing cost-effective and scalable solutions for phosphate interception at the source is therefore essential for achieving the water quality goals outlined in environmental sustainability frameworks. This study evaluated the phosphate removal capacity of calcium hydroxide-modified metakaolin-based reactive materials as a sustainable approach to limiting agricultural nutrient loads entering river ecosystems. Two synthesis methods were compared: a fusion method and a low-temperature method. The resulting materials—metakaolin (M), low-temperature synthesized metakaolin (MLT), and Ca(OH)2-modified low-temperature metakaolin (CaMLT)—were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), textural property analysis, and scanning electron microscopy (SEM). Phosphate removal performance was evaluated in batch experiments under varying reactive material dosages (2.5–10.0 g·L−1), initial phosphate concentrations (1.0–7.0 mg·L−1), and contact times (1–144 h). The CaMLT material achieved the highest phosphate removal efficiency of 56% at a phosphate concentration of 1.0 mg·L−1, a dose of 10.0 g·L−1, and a contact time of 144 h. At higher phosphate concentrations (3.0 and 7.0 mg·L−1), removal efficiencies decreased to 23% and 21%, respectively, under the same experimental conditions. The results were benchmarked against data reported in the literature. The findings indicate that low-temperature synthesized metakaolin modified with calcium hydroxide demonstrates potential as a reactive material for phosphate capture in agricultural drainage systems, offering a promising pathway toward more sustainable water resource management and freshwater ecosystem protection.