Studies on the Adsorption of p-Aminoazobenzene onto Kaolinite

As one of the most important soil components, kaolinite plays an important role in transport and fixation of organic pollutants in soils. P-Aminoazobenzene (PAAB) is a sort of the carcinogenic aromatic amine which is commonly used as the intermediates of azo dyes. It can cause mutations and cancer of aquatic biota as well as humans. In this study, adsorption of PAAB on kaolinite in aqueous solution under different pHs, temperature and ionic strength was examined. Adsorption kinetic experiments indicated that the adsorption of PAAB on kaolinite at pH 1.4 and 4.0 followed the Elovich kinetics. The adsorption isotherm of PAAB onto kaolinite was well described by the Langmuir model, with an adsorption capacity of 2.2 mg/g at pH 1.4 and 1.43mg/g at pH 4.0. Adsorption of PAAB increased with decreasing solution pH and ionic strength. The negative free energy change ( G) after adsorption indicated that the adsorption process is a spontaneous process. The enthalpy change ( H) at pH 1.4 and 4.0 was -6.93 and -4.72 kJ/mol, respectively, suggesting that PAAB adsorption was an exothermal process and the physical adsorption predominated in the adsorption of PAAB on kaolinite. The adsorption affinity of PAAB for kaolinite surface was attributed to the electrostatic attractive and van der