Composites hybridized with Ca(OH)2 and LaMnO3 synergistically improve phosphate adsorption properties

Abstract

Phosphate loading is an important factor in the deterioration of freshwater ecosystems. La-based perovskites, a new type of adsorbent material, suffer from low phosphate adsorption performance and are highly affected by pH. Hence, the construction of materials with high phosphate adsorption performance over a wide pH range for phosphate removal is a challenge. In this study, Ca(OH)₂-hybridized LaMnO₃ perovskite composites (Ca_x–LMO, x = 0, 0.2, 0.4, 0,7) were prepared by impregnating different ratios of CaO on LaMnO₃. Isothermal, kinetic, and influential factor tests showed that the maximum phosphate adsorption capacity of Ca_0.4–LMO for phosphate reached 101.1 mg P g⁻¹, which was 1.14 times higher than that of the original Ca₀–LMO. The phosphate adsorption capacity of Ca_0.4–LMO was minimally affected by pH and only decreased by 17.8% with increasing pH. Therefore, the synergistic effect of Ca(OH)₂ and LaMnO₃ improved the performance of the material for phosphate adsorption over a wide pH range. In the experiments using three types of real wastewater, the removal rate of Ca_0.4–LMO reached 99.6% for high-concentration cattle farm wastewater. Quantitative removal was realized for low-concentration pond wastewater and the effluent of sanitary wastewater, revealing high efficiency in removing phosphate from real water bodies. After eight adsorption–desorption cycles, the phosphate removal rate of Ca_0.4–LMO remained up to 96%, proving its reusability. Characterization results showed that the phosphate adsorption process was mainly chemisorption, and the adsorption mechanisms were ligand exchange, inner-layer complexation, and electrostatic attraction. This study provides a new approach for improving the phosphate adsorption performance of La-based perovskites for phosphate removal over a wide pH range.