Optimized preparation, characterization and the adsorption mechanism of magnesium-modified bentonite-based porous adsorbents: thermodynamic and kinetic analysis

Abstract

Nitrogen and phosphorus are common pollutants that cause eutrophication and environmental degradation in aquatic systems. This study investigates the optimization, characterization, and adsorption properties of Mg-modified bentonite-based porous adsorbents for the simultaneous removal of nitrogen and phosphorus from wastewater using the struvite method. The MgO–SBt material demonstrated strong adsorption capabilities for both nitrogen and phosphorus. However, due to the recovery challenges associated with powder materials, a porous bio-adsorbent was prepared using MgO–SBt, cement, CaO, CaSO₄, aluminum powder, and a foam stabilizer, following the production process of autoclaved aerated concrete. The influence of ratio parameters on the strength and adsorption performance of the porous adsorbents was examined through single-factor experiments. The morphology and structural characteristics of the Mg-modified bentonite-based porous adsorbents were tested using XRD, FT-IR, BET, and SEM characterization methods. Adsorption experiments explored the effects of the porous adsorbents' dosage, initial solution pH, and nitrogen-to-phosphorus ratio on adsorption performance. The adsorption mechanism was analyzed through adsorption isotherms, kinetics, and thermodynamics. The results indicated that the optimal preparation conditions were 20% MgO–SBt, 9% CaO, 2% CaSO₄, and 0.08% aluminum powder. Under these conditions, the porous adsorbents exhibited good strength and adsorption performance, achieving removal ratios of 38.68% for nitrogen and 98.95% for phosphorus. This study provides a novel approach for the economical and efficient treatment of nitrogen and phosphorus in wastewater and offers a theoretical basis for further research on the application of Mg-modified bentonite-based porous adsorbents.