Removal of phosphate from activated biochar prepared from bentonite biochar composite: Kinetic, equilibrium, thermodynamic adsorption

Abstract

Excess phosphorus threatens both aquatic ecosystems and human health. This study investigated the kinetic, equilibrium, and thermodynamic behavior of phosphate (PO43–) adsorption using a low-cost composite adsorbent synthesized from bentonite and rice-husk–derived activated carbon. Batch experiments examined the influence of initial PO43– concentration, temperatures, contact time, pH, and co-existing anions. The findings revealed that the PO43– adsorption onto synthesized material was best represented by Langmuir isotherm theory. Kinetic analyses showed that PO43– adsorption follows both pseudo-first and pseudo-second-order models, exhibiting strong correlation coefficients (R² = 0.99). The optimal pH for adsorption was identified as 7. The presence of co-existing anions such as CO32–, SO42–, and Cl⁻ notably decreased the efficiency of PO43– removal. The synthesis of material based on bentonite and biochar from rice husk demonstrates strong potential for PO43– removal and recovery from water.