Sorption characteristics of nitrosodiphenylamine (NDPhA) and diphenylamine (DPhA) onto organo-bentonite from aqueous solution

• CTMAB-bentonite was used as sorbent to remove NDPhA and DPhA from aqueous solution.
• Pseudo-second-order kinetics model provided the best fit for the sorption process.
• Slips isotherm model best fitted for DPhA sorption, whereas linear model for NDPhA.
• Removal efficiency was evaluated via sorbate initial concentration and sorbent dosage.

The recent emergence of nitrosamine contaminants in aquatic environments has received great attention due to their high carcinogenic potency for humans. In this study, an organo-bentonite modified with cetyltrimethylammonium bromide (CTMAB) was utilized as sorbent for the removal of nitrosodiphenylamine (NDPhA) and its precursor diphenylamine (DPhA) from aqueous solution. The sorption characteristics, including kinetics, isotherm and removal efficiency, were studied by batch experiments. The sorption kinetics of both NDPhA and DPhA were best described by the pseudo-second-order model (R2 > 0.995), and equilibrium was attained within 6 h. The sorption isotherm for NDPhA was nearly linear, indicating that partition process is dominant in the sorption of NDPhA. However, the nonlinear sorption isotherm of DPhA was best represented by the Slips model because both partition and electrostatic interaction were involved in the sorption of DPhA. The removal efficiency for NDPhA just only depended on the dosages of CTMAB-bentonite, with a linear correlation between their reciprocal. However, it was found that additional sorbent should be used in conditions of higher initial DPhA concentration in order to achieve high removal efficiency and the maximum sorption amount of CTMAB-bentonite for DPhA decreased with increasing sorbent dosage.