Abstract

Calcium silicate hydrate is a favorite candidate used for phosphate adsorption due to its cost-effective and ubiquitous in nature. Herein, the amorphous silica nanotube derived from acid etching halloysite clay was employed as the silicon resource to synthesize the magnetic calcium silicate hydrate. The optimized magnetic calcium silicate hydrate sample demonstrated adsorption process closely fitted pseudo-second-order model. Both chemical and physical adsorption took place on the heterogeneous adsorption surfaces, as suggested by the Redlich-Peterson isotherm model. According to the Langmuir model, the maximal equilibrium adsorption capacity is about 136.7 mg/g. Additionally, the optimized sample showed selectivity across a broad pH range and under coexistence of different anions and humic acid. The thermodynamics evaluation demonstrated that the adsorption of phosphate onto the optimized sample is endothermic, spontaneous, and disordered. Finally, research results revealed that the electrostatic interaction, ligand exchange and the precipitation reaction might all play a role in the phosphate adsorption process.

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