Enhanced phosphate adsorption in low-concentration solutions using La/Zr hydroxide-modified diatomite: mechanisms and efficiency

Rare-earth element-based materials have attracted extensive interest due to their effectiveness in phosphate removal. However, there are ongoing challenges related to enhancing the phosphate adsorption capacity and regenerating the lanthanum-based adsorbents. This study focused on the preparation of La-Zr bimetallic modified diatomite composites with different molar ratios using a simple coprecipitation method. These composites were employed as efficient adsorbents for the removal of low-concentration phosphate. After conducting a preliminary assessment of the phosphate adsorption capacities of the synthesized La-Zr bimetallic modified diatomite composites, the composite with the La/Zr molar ratio of 1:1 (designated as La₁Zr₁-DE) was selected for further characterization and evaluation. The maximum phosphate adsorption capacity of La₁Zr₁-DE, determined using the Langmuir isotherm model, was found to be 116.2 mg P/g. The adsorption process of phosphate by La₁Zr₁-DE can be primarily attributed to mechanisms such as ligand exchange, inner-sphere complexation, and surface precipitation. Furthermore, La₁Zr₁-DE exhibited excellent selectivity for phosphate and demonstrated good regeneration capabilities. This study offers a comprehensive exploration of the adsorption mechanisms, providing a theoretical basis for the development of more effective and sustainable phosphate adsorbents.