Characterization and adsorption performance of surfactant-modified zeolite for chromium(VI) removal from aqueous solutions

This study examined the surface modification of natural zeolite sourced from Pangasinan, Philippines to assess its potential as an adsorbent for Cr(VI) removal.The natural zeolite (NZ) and surfactant-modified zeolite (SMZ) were characterized to evaluate their composition and alterations in surface properties.Characterization revealed a reduction in specific surface area (SSA) from 165.84 m g -1 to 37.68 m g -1 and a reversal in zeta potential from -16.9 mV to +46.73 mV, enabling Cr(VI) adsorption.Adsorption performance was investigated under varying conditions, including adsorbent dosage, contact time, solution pH, ionic strength, competing ions, and dissolved organic matter (DOM).Optimal Cr(VI) adsorption occurred at pH 3, with equilibrium reached rapidly, favoring the univalent HCrO species over the divalent CrO species prevalent at higher pH levels.Increased ionic strength and competing ions reduced Cr(VI) adsorption, while the presence of DOM had no significant effect.SMZ exhibited a maximum adsorption capacity of 13.603 mg g -1 , as described by the Langmuir isotherm model (R = 0.970), indicating a uniform monolayer adsorption mechanism.Comparative performance tests demonstrated Cr(VI) removal efficiencies of 61.52% for SMZ, 73.82% for powdered activated carbon (PAC), and 1.03% for NZ.Although the removal efficiency of SMZ is lower than PAC, it offers a cost-effective, resource-efficient alternative with potential scalability.The study has shown its applicability in wastewater treatment, particularly under acidic conditions, with proper management of ionic strength and competing ions.Future research should investigate regeneration capabilities and evaluate the SMZ performance in real-world conditions.