Preparation of a granular montmorillonite and fly ash composite adsorbent and application for Pb2+ and butyl xanthate adsorption

This study systematically investigated the adsorption performance of montmorillonite-fly ash composite particles (Mt-FA) and modified Mt-FA (OTAC/Mt-FA) with octadecyltrimethylammonium chloride for Pb²⁺ and butyl xanthate (BX) removal, focusing on critical experimental conditions: initial solution pH, adsorbent dosage, and contact time. The results demonstrated that at pH 5 with a dosage of 4 g/L for both Mt-FA and OTAC/Mt-FA, the equilibrium removal efficiencies of Pb²⁺ were approximately 100 % (adsorption capacity: 49.9 mg/g) and 79.8 % (39.9 mg/g), respectively. Under the conditions of dosage 10 g/L and pH 7, the equilibrium removal of BX by OTAC/Mt-FA was approximately 100 % (10.0 mg/g), while Mt-FA exhibited negligible adsorption of BX. This discrepancy is attributed to the introduction of OTAC, which not only provides hydrophobic interactions but also additional electrostatic interaction sites, enabling more efficient adsorption of BX. Characterization analysis combined with kinetic results confirmed the successful intercalation of OTAC into montmorillonite interlayers and elucidated the adsorption mechanisms: 1) for Pb²⁺, involving electrostatic attraction, chemical precipitation, and ion exchange; 2) for butyl xanthate (BX), involving electrostatic and hydrophobic interactions. These results highlight that montmorillonite-fly ash functionalized composite particles exhibit significant application potential in the efficient adsorption of heavy metals or organic contaminants, while providing notable advantages in the solid–liquid separation of the adsorbent after adsorption.