Mechanisms of chromate adsorption by surfactant-modified zeolite
阳离子表面活性剂改性沸石对铬酸根的吸附机制

The adsorption of chromate on zeolite modified by cation surfactant CTAB and its mechanism were investigated. The results showed that the modified zeolite had a greater adsorption capacity for chromate as compared with non-modified zeolite. The amount of chromate absorbed by the modified zeolite decreased with the increase in ionic strength, which suggested that the electrostatic interaction between the modified zeolite and chromate was the major mechanism. The Zeta potential of zeolite changed from negative value to positive value after modified by cation surfactant, and this indicated that the adsorption of cation surfactant on zeolite induced a change in its surface charge properties. The increase in positive value of surface potential was the main reason for electrostatic adsorption of chromate on the modified zeolite. Both adsorption of chromate by the modified zeolite and desorption of pre-adsorbed chromate increased with the increase in pH, and reached a maximum value at pH 5.0 and 6.0, respectively, and then decreased. While after that, the difference between adsorption and desorption of chromate decreased with the increase of pH, suggesting that the adsorption through none electrostatic mechanisms increased at low pH value.