Adsorptive elimination of Cr(VI) from wastewater using benzalkonium chloride modified Egyptian bentonite

Abstract

Abstract In this study, Egyptian sodium bentonite (NaB) was modified with the cationic surfactant benzalkonium chloride (BAC) to prepare organo-modified bentonite (OMB), which altered the surface chemistry and introduced positively charged adsorption sites, thereby enhancing the adsorption performance. NaB and OMB were characterized by (FTIR), (XRD), (BET), and zero charge point ( pH pzc ) measurements. After the modification, the OMB was used to remove highly toxic Cr(VI), commonly found in industrial effluents, from aqueous solutions via batch adsorption. The impacts of BAC loading, pH, exposure time, clay dose, initial Cr(VI) concentration, temperature, and shaking speed were systematically investigated in relation to the sorption process. The optimal conditions for removal were found to be 150% BAC loading (w/w relative to NaB), pH = 2, clay dose = 4 g L − 1 , 60 min contact time for NaB and 70 min for OMB, 10 mg L − 1 initial concentration of Cr (VI) ions, and shaking speed of 200 rpm. Under these conditions, OMB achieved 99.6 ± 0.4% removal ( $$\:{Q}_{\text{e}}$$ ≈ 2.27 ± 0.05 mg g − 1 ), whereas NaB removed only 6.6 ± 0.06% of Cr(VI) ions. Adsorption kinetics followed the pseudo-second-order model, while equilibrium data followed the Langmuir isotherm, indicating surface interactions on the clay surface. Thermodynamic parameters indicated that Cr(VI) adsorption on NaB was endothermic and nonspontaneous, whereas adsorption on OMB was spontaneous and exothermic. These results demonstrate that BAC-modified bentonite is an efficient and low-cost adsorbent for Cr(VI) removal from heavy metal-contaminated water.