High-efficiency phosphorus removal from real wastewater using ZnAl-layered double hydroxides: Performance and limitations.

In this study, the phosphate uptake performance of ZnAl-Layered Double Hydroxides (LDHs) with different interlayer anions (nitrate and chloride) was investigated. Zn(2)Al-NO3 and Zn(2)Al-Cl were synthesised via the coprecipitation method and characterised regarding mineral composition, particle size distribution, specific surface area, and density. Batch sorption experiments were conducted to evaluate the phosphate removal efficiency, and the experimental data were fitted using the Langmuir and Freundlich isotherm models. The kinetics data for phosphate uptake were best described by the Elovich model for Zn(2)Al-NO3 and the pseudo-second-order model for Zn(2)Al-Cl. The phosphate loading capacities were 72.41 mg P g-1 for Zn(2)Al-NO3 3 and 72.05 mg P g-1 for Zn(2)Al-Cl, using an initial P concentration of 100 mg L-1 and a sorbent dosage between 0.1 and 2 g L-1. The influence of key operational parameters, such as sorbent dosage, initial phosphate concentration, initial pH, and the presence of competing anions, was also investigated. Phosphate removal efficiency decreased as the initial pH increased from 6 to 8, while carbonate anions significantly interfered with phosphate uptake. While NaOH desorption resulted in zinc phosphate precipitation and hindered LDH regeneration, the resulting phosphate-loaded material remains suitable for application in fertiliser formulations. ZnAl-LDH demonstrated excellent performance in treating real wastewater, achieving phosphorus removal efficiencies exceeding 90% for both materials. Overall, the results highlight Zn(2)Al-Cl as a promising sorbent for phosphate removal from aqueous solutions, particularly in real wastewater treatment, as the release of chloride into the treated effluent is generally less problematic than the release of nitrate (the other interlayer anion investigated).