Modified geosynthetic clay liners bentonite for barriers of Cr (VI) in contaminated soil

Hydroxy-Fe-Al and cetyltrimethylammonium bromide (CTMAB) were chosen to modified Na-bentonite (Na-bent). The characteristics of Na-bent and modified bentonites were determined with scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR) and zeta potential. It was found that CTMAB mainly entered the interlayer and hydroxy-Fe-Al groups were mostly loaded on the external surface of the Na-bent, respectively. The efficiency to remove Cr (VI) of Na-bent, organic modified bentonite (O-bent), inorganic modified bentonite (I-bent) and composite modified bentonite (Co-bent) followed the order: Co-bent > I-bent > O-bent > Na-bent. Adsorption experiments were carried out by the batch contact method. The highest removal rate of Cr (VI) by Co-bent was found to be 96.2% at optimal pH = 4. The Cr (VI) uptake on Co-bent from 50 mg/L solution rapidly attained equilibrium within 10 min, and the pesudo-second-order kinetic model could provide satisfactory fitting of the kinetic data (R² = 0.999) compared to the intraparticle diffusion model (R² = 0.585). The adsorption data were applied to the Langmuir, Freundlich, Temkin isotherm model. The Langmuir was found to be the most suitable equation to fit the experimental data (R² = 0.956) with a high Cr (VI) adsorption capacity of 27.472 mg/g, and R_L values (0.012-0.035) also indicated the adsorption could be accepted. The present study confirmed that Co-bent would be one of candidates for Cr (VI) adsorbent.