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 (PO₄^3–) adsorption using a low-cost composite adsorbent synthesized from bentonite and rice-husk–derived activated carbon. Batch experiments examined the influence of initial PO₄^3– concentration, temperatures, contact time, pH, and co-existing anions. The findings revealed that the PO₄^3– adsorption onto synthesized material was best represented by Langmuir isotherm theory. Kinetic analyses showed that PO₄^3– 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 CO₃^2–, SO₄^2–, and Cl⁻ notably decreased the efficiency of PO₄^3– removal. The synthesis of material based on bentonite and biochar from rice husk demonstrates strong potential for PO₄^3– removal and recovery from water.