La/Fe-Bimetallic-Modified Red Brick Powder for Phosphate Removal from Wastewater: Characterization, Adsorption, and Mechanism

The use of construction waste red brick powder (RBP) to prepare adsorbents for phosphate removal from wastewater represents a promising technology with substantial research potential. This study investigates the preparation of La-based magnetic red brick powder (La-Fe-RBP) via bimetallic modification to enhance its adsorption performance. The key characteristics, adsorption process, adsorption mechanism, and practical applications of the modified adsorbent were analyzed. The obtained results suggested that the underlying adsorption mechanism of La-Fe-RBP was best described by the Langmuir and pseudo-second-order kinetic models, which suggested that the adsorption mechanism was monolayer chemical adsorption. La-Fe-RBP exhibited rapid kinetics, achieving adsorption saturation in just 40 min, significantly faster than RBP (360 min). Additionally, isotherm experiments determined the highest theoretical adsorption capacity as 42.835 mg/g. More importantly, La-Fe-RBP exhibited efficient phosphate adsorption within a pH ranging from 3 to 8. Furthermore, La-Fe-RBP exhibited high selectivity for phosphate ions in the presence of coexisting ions (SO42-, NO3-, Cl^-, HCO3-, Mg²⁺, and Ca²⁺), demonstrating its robustness and effectiveness in complex water conditions. FTIR and XPS analyses demonstrated that ligand exchange and electrostatic attraction were the primary mechanisms underlying phosphate adsorption by La-Fe-RBP. Domestic sewage treated with La-Fe-RBP met the Class IV surface water environmental quality standards in China. The findings of this study prove that the La-Fe-RBP composite material, characterized by high adsorption efficiency and strong selectivity, holds significant potential for removing phosphates from real wastewater.