Effect of Ionic Strength, pH and Humic Acid on Sorption of Ni(Ⅱ) on Bentonite

The sorption of Ni(Ⅱ) on bentonite was studied by using batch technique. The effects of contact time, pH, ionic strength, bentonite content and humic acid on the sorption of Ni(Ⅱ) on bentonite were investigated. The results suggest that the sorption of Ni(Ⅱ) on bentonite is strongly dependent on ionic strength at low pH, and independent on it at high pH. The sorption of Ni(Ⅱ) at low pH is mainly dominated by ion exchange and/or outer-sphere surface complexation, whereas the sorption of Ni(Ⅱ) at high pH is mainly dominated by inner-sphere surface complexation. The presence of humic acid in the system enhances Ni(Ⅱ) sorption to HA-bentonite hybrids at low pH, but reduces sorption of Ni(Ⅱ) on HA-bentonite hybrids at high pH.