Using Recycled Concrete as an Adsorbent to Remove Phosphate from Polluted Water

Phosphate pollution remains a significant hazard to terrestrial and aquatic ecosystems. We developed an economical and efficient method for phosphate adsorption on waste construction concrete modified with seawater. Compared with raw concrete materials, the phosphate adsorption capacity of seawater-modified waste concrete was highly efficient, especially at low phosphate concentrations. The inflection point for seawater-modified concrete was 0.66 and 1.22 mg L for the raw material. The relative phosphate adsorption was 4.64 and 2.39 mg g, respectively. Phosphate removal was >90% over a pH range of 3 to 11 for the raw and modified materials. Chemical and physical analysis of the modified concrete indicated that Ca and Mg particles were uniformly sequestrated on the surface, and Ca was the determinant controlling phosphate uptake. Phosphate adsorption isotherms fit well using the Freundlich, Temkin, Elovich, Fowler-Guggenheim, and Hill-de Boer models and indicated that intermolecular forces in the concrete particles were enhanced by calcium oxides from seawater. This method can efficiently remove phosphate from polluted water and repurposes waste construction concrete.