Preparation of lanthanum-modified bentonite and its combination with oxidant and coagulant for phosphorus and algae removal

Currently, the problem of eutrophication is becoming more serious and has caused widespread concern. In this study, we investigated the optimal preparation conditions of bentonite modified with lanthanum to obtain Lanthanum-Modified Bentonite (LMB) with high efficiency for phosphate removal. The experiment combined LMB with oxidant (NaClO) and coagulant (PAC) to study the process of simultaneous phosphorus and algae removal. Characterization analysis confirmed that bentonite successfully adsorbed La, resulting in an increase in the percentage weight of La from 1.65 % to 22.93 %. Electrostatic attraction and ligand exchange were the main phosphorus adsorption mechanisms. LMB efficiently removed phosphorus within a pH range of 2.0-6.0 and exhibited good adsorption capacity even in the presence of anions and dissolved organic matter. The kinetic behavior at various initial concentrations was portrayed by the pseudo-second-order model, revealing chemisorption of phosphate on the surface of LMB. According to the isotherm study, the adsorption behavior of phosphate fitted well with the Sips isotherm equation, indicating both homogeneous monolayer adsorption and heterogeneous multilayer coverage of phosphate on the surface of LMB under the given conditions. The combination of oxidant and coagulant found that the extracellular organic matter of algae could be removed by oxidant, and net trapping and electro-neutralization were the main mechanisms. The process reduced the consumption of coagulant by extracellular substances and improved the efficiency of coagulant in removing algae. Coagulant not only adsorbed and settled algae but also removed organic phosphorus in water, rapidly removing algae and controlling the concentration of total phosphorus. The results demonstrated that the removal of total phosphorus and algae exceed 90 %, indicating a potential means for solving eutrophication.