Utilization of a Selective Adsorbent for Phosphorus Removal from Wastewaters

In this study, a synthetic layered double hydroxide modified with chloride ions (LDH-Cl) was employed for the removal of phosphorus from wastewaters. A series of phosphate adsorption experiments demonstrated that the adsorption capacity of LDH-Cl was described well by the three-parameter isotherm model (Langmuir-Freundlich combination model). LDH-Cl was found to have similar to 50 mg P/g of ion exchange capacity for phosphate, which was sufficient for phosphate recovery from wastewaters. Phosphate adsorption by LDH-Cl also followed pseudo-second-order reaction kinetics. Effective replacement of Cl- with PO43- during sorption was confirmed by X-ray diffraction and Fourier transform infrared analyses. Adsorption capacity varied with pH and reached a maximum value at pH 3. Anions commonly present in most wastewaters, such as nitrate, sulfate, and chloride, had a minimal effect on phosphate adsorption by LDH-Cl. On the contrary, the amount of phosphate ions removed by LDH-Cl decreased with increasing bicarbonate ion concentration. LDH-Cl also exhibited a sufficient chemical stability against adsorption/desorption repetitions and similar to 80% of desorption rate was achieved at 5 M NaCl concentration. LDH-Cl exhibited a high phosphate removal capacity and a low sensitivity to the environmental conditions of wastewaters, supporting use as an effective means for the removal of phosphate.