Effects of Nanoporous Montmorillonite Types on the Separation Process of Chromium(III)

Abstract

Bentonites contain a large amount of nanoporous and nanostructured montmorillonite, which is the dominant mineral determining the adsorptive properties of bentonites. In this study, the analyses of the characterization of bentonites for adsorption application include cation exchange capacity (CEC) measurements, swell index, dry screen (granulometric) analysis, x-ray diffraction (XRD), BET-BJH surface area and pore size distribution measurements, and scanning electron microscopy (SEM). The adsorption of chromium(III) from a 0.01 N Cr(III) solution using bentonites has been studied. The results showed that BNT3 and BNT2 have high CEC values of 100 and 95 mEq/100 g and swell index values of 30 and 24 mm, respectively. The high amounts of CEC and the swell index with high amount of granulometric (particles finer than 36 µm) values indicate that the amount of clay minerals (motmorillonite) is very high. Successful chromium removal efficiencies changed from 94.5% for BNT4 to 99.4% for BNT3. The maximum Cr(III) removal of adsorbents decreased in the following order: BNT3 > BNT2 > BNT5 > BNT1 > BNT4. The removal of chromium was correlated with the variation of bentonite types. This study aims at investigating the effects of different bentonite types on the removal of Cr(III) from synthetic wastewater using low-cost bentonites.