The layered chalcogenide KMS-1 was modified by La/Ca/Mg via a simple ion exchange process for the removal of phosphate from water. La-modified KMS-1 (KLa), Ca-modified KMS-1 (KCa) and Mg-modified KMS-1 (KMg) were comparatively characterized using X-ray diffraction, BET surface area, zeta potential and scanning electron microscopy, respectively. It was found that the adsorption capacity of KLa was higher than that of KCa and KMg. Kinetic data were fitted well to a pseudo-second-order kinetic model. Solution pH slightly affected the removal of phosphate by KLa in the range of 3–9. Compared to KCa and KMg, KLa exhibited a high selectivity to phosphate in the presence of coexisting anion such as SO₄^2-, CO₃^2-, F^-, Cl^- or NO^3- with same molar concentration. Importantly, KLa had the capacity to remove phosphate effectively from real sewage. Moreover, the used KLa could be successfully regenerated by KOH and HCl solution. Zeta potential, scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis indicated that the precipitation, surface deposition and complexation were responsible for the mechanism of the phosphate removal by KLa.

Schematic illustration of KLa preparation and adsorption mechanism of KLa