Chromium (VI) adsorption characteristics of bentonite under different modification patterns

Abstract

We investigated the Cr(VI) adsorption characteristics of bentonite under different modification patterns by using a mixture of BS-12 (dodecyl dimethyl betaine) and DTAB (dodecyl trimethyl ammonium bromide). DTAB was used to compositely modify 25%, 50%, and 100% BS-12-modified bentonite (three modified modes of bentonite with BS-12). In addition to these modification modes, variations as functions of pH value, temperature, and ionic strength were compared. Results showed: 1. Cr(VI) adsorption capacity of bentonite compositely modified with BS (short for BS-12) + DT (short for DTAB) rapidly increased compared with that of BS-modified bentonite, and the adsorption capacity of 100%BS+100%DT-modified bentonite was the highest among the samples surveyed and 23-fold higher than that of CK (raw bentonite). 2. Cr(VI) adsorption on bentonite exhibited saturated adsorption in ion exchange (IE) mode, distributive adsorption in ion exchange and hydrophobic bond coexisting (IE+HB) pattern, and synergistic adsorption in the hydrophobic bond (HB) pattern. 3. Effects of rising temperature on Cr(VI) adsorption appeared in the IE mode, while negative temperature effect was observed in the HB mode. Higher pH value and ionic strength were unfavorable for Cr(VI) adsorption. 100%BS+100%DT compositely modified bentonite exhibited the optimal adsorption of Cr(VI) at 10°C, pH = 4, and ionic strength of 0.01 mol L-1.