Bentonite modification and adsorption capacity for Cr(VI) in water

Objective  To improve the adsorption capacity of bentonite for Cr (VI) in water.

Method  NaOH and chitosan were used for modifying bentonite. Alkali modified bentonite (B-NaOH), chitosan modified bentonite (B-CS) and chitosan-alkali modified bentonite (B-NaOH-CS) were obtained. Using sodium bentonite (B) as the control, we characterized physicochemical properties of three kinds of modified bentonite through infrared spectrometer, scanning electron microscope and specific surface area analyzer, and analyzed their adsorption capacities for Cr (VI).

Result  A strong N—H absorption peak and an enhanced C—H symmetric bending peak appeared in B-NaOH-CS. The surface sheet structure of B-NaOH-CS was curly dispersed, the interlayer pores increased, and the specific surface area was 1.2 times more than other bentonite. When the concentration of Cr (VI) was 50 mg·L⁻¹, the equilibrium adsorption capacity of B-NaOH-CS for Cr (VI) was 1.03 mg·g⁻¹, which was 1.84 and 1.26 times of B-NaOH and B-CS respectively. The quasi-second-order kinetic equation and Langmuir equation could more accurately describe adsorption process of bentonite for Cr (VI). Thermodynamic parameters of △H>0, △G<0 and △S>0 indicated the adsorption process of bentonite for Cr (VI) was endothermic, spontaneous and disordered. B-NaOH had the maximum adsorption capacity for Cr (VI) at pH = 7.0, while B-CS and B-NaOH-CS at pH = 3.0.

Conclusion  B-NaOH-CS has the best adsorption effect on Cr (VI). Modified bentonite plays an important role in Cr (VI) pollution remove.