Simultaneous adsorption of malachite green and hydrophobic organic compounds onto bentonite

This work aims to remove both Malachite Green (MG) and hydrophobic organic compounds (HOCs) from water using bentonite. The adsorption capacity of MG on bentonite was first examined. Then the adsorption of HOCs (2-naphthol and naphthalene) on bentonite, simultaneously with the adsorption of MG or successively after the adsorption of MG, was further investigated. The experimental results showed that MG could be efficiently adsorbed by bentonite, and the maximum adsorption amounts reached 430 mg/g, which was comparable to that on activated carbon. With the adsorption of MG, the interlayer spaces of bentonite changed from hydrophilic to hydrophobic. Thereby, 2-naphthol and naphthalene could also be adsorbed on bentonite, and the adsorption efficiency was shown to strongly depend on the adsorption process. That was, the simultaneous adsorption process was more efficient in the removal of HOCs than the successive adsorption process, and the removal efficiencies reached 94% for 2-naphthol and 95% for naphthalene respectively for the simultaneous adsorption process. Results of this work showed that the low cost bentonite could be used as efficient adsorbent for the removal of both cationic dyes and HOCs from wastewater.