Highly efficient removal of phosphate by mesoporous Zr-modified calcium silicate hydrate from fly ash

Phosphorus is essential for crop growth and energy transfer in plants. However, its excessive use leads to water pollution, making the effective removal and recovery of phosphate critically important. To optimize phosphate adsorption efficiency and enable resource utilization, this study synthesized a zirconium (Zr)-modified calcium silicate hydrate (CSH) adsorbent using fly ash as the raw material through a hydrothermal method. The interlayer-rich hydrated Ca 2+ in CSH facilitates rapid adsorption via ion exchange, while Zr doping enhances the selectivity and reusability of phosphate adsorption. The maximum adsorption capacity reached 49.83 mg P/g under optimal adsorption conditions at a Zr:Ca molar ratio of 1.25, with an adsorption rate exceeding 99%. Furthermore, the adsorption mechanism was elucidated through kinetic, isotherm, and thermodynamic analyses, mainly containing ligand exchange between layers and electrostatic interactions. This study not only advances green chemistry in pollution control and resource conservation but also provides innovative insights for the development of environmental industries within the context of carbon neutrality. It offers a novel approach for designing phosphate adsorbents and promotes sustainable practices in environmental management. • A novel Zr-modified calcium silicate hydrate (Zr-CSH-x) adsorbent was successfully prepared from industrial waste fly ash. • Zr doping significantly enhances the selectivity and reusability of the adsorbent for phosphate. • Zr-CSH-1.25 exhibits a maximum phosphate adsorption capacity of 49.83 mg P/g, with an adsorption rate exceeding 99%. • The primary adsorption mechanisms are revealed to be ligand exchange between layers and electrostatic interactions.