Study on the high-efficiency adsorption mechanism and performance of cetyltrimethylammonium bromide and hydroxy-iron pillared modified montmorillonite granules for Cr(VI) in water

Water pollution control is critical, with hexavalent chromium (Cr(VI)) posing severe threats. Adsorption technology is widely adopted for its operational simplicity. This study developed a high-efficiency adsorbent by modifying montmorillonite (MMT) with cetyltrimethylammonium bromide (CTAB) and hydroxyl-iron (OH/Fe) pillaring, and the resulting CTAB-OH/Fe-MMT powder was then engineered into robust granules(SA-CTAB-OH/Fe-MMT) by mixing with a sodium alginate(SA) solution and solidifying with calcium chloride. Materials were characterized using SEM, BET, XRD, and FT-IR. Effects of adsorbent dosage, pH, time, and initial Cr(VI) concentration were investigated. Dynamic adsorption evaluated flow rate, bed height, and initial Cr(VI) concentration on SA-CTAB-OH/Fe-MMT granules, fitted with Thomas and Yoon-Nelson models. Results demonstrate optimal preparation: mass ratio 0.5:1 for CTAB:OH/Fe-MMT and 1 %(w/v) sodium alginate. Granules exhibited smooth surfaces and expanded interlayer spacing. Under optimized conditions (pH=4, dosage=6 g/L, T = 120 min, initial Cr(VI)= 10 mg/L), Cr(VI) removal reached 91.5 %. Breakthrough time decreased with increasing flow rate/initial concentration but extended with bed height. Adsorption followed pseudo-second-order kinetics and Langmuir isotherm (max capacity=11.629 mg/g), confirming an endothermic process. Both models effectively described adsorption. This provides a novel material for efficient Cr(VI) removal, offering insights for functionalizing layered minerals.