Application of Lanthanum Hydroxide as a Phosphorus-Selective Adsorbent: Fabrication of Bead-type Adsorbent Using Polyacrylonitrile and Its Adsorption Properties

In this study, lanthanum hydroxide (La(OH)₃) was investigated as a selective phosphate adsorbent to reduce eutrophication caused by excessive phosphorus in aquatic ecosystems. A bead-type adsorbent, termed La-PAN bead, was developed by combining lanthanum hydroxide with polyacrylonitrile (PAN). The optimal formulation for synthesizing La-PAN beads was determined to include 0.3 g of PAN, 0.1 g of polyvinyl alcohol, 2 g of lanthanum hydroxide, and 5 mL of dimethyl sulfoxide. This composition produced uniform, spherical beads with sufficient porosity, facilitating effective phosphate adsorption. The adsorption properties of La-PAN beads were systematically evaluated in terms of pH, ionic selectivity, adsorption equilibrium, and kinetics. The results demonstrated that La-PAN beads exhibited high phosphate adsorption capacity and selectivity, achieving optimal performance at pH≤6 and minimal interference from competing anions such as chloride, nitrate and sulfate. The adsorption equilibrium of PO₄-P on La(OH)₃ was well described by the Langmuir isotherm model, with a maximum adsorption capacity of 294.1 mg/g. The adsorption process followed a second-order kinetic model and was governed by both surface and pore diffusion mechanisms. This study highlights the potential of La-PAN beads as an efficient and environmentally friendly phosphate-selective adsorbent in wastewater treatment.