Sorption of antibiotics onto montmorillonite and kaolinite: competition modelling

ABSTRACTAntibiotic contaminants, which are generally present in bi-solute systems, can be competitively adsorbed onto clays. Single- and bi-solute sorptions of sulfadiazine (SDZ) and ciprofloxacin (CIP) onto montmorillonite and kaolinite were investigated at pH values of 5 and 8. Freundlich and Langmuir models were used and fit the experimental data well for single-solute sorption. The sorption isotherms were nonlinear (NF = 0.265–0.730), and the maximum sorption capacities (qmL) of the SDZ and CIP onto montmorillonite were higher than those onto kaolinite. The octanol–water distribution ratio (Dow), cation exchange capacity (CEC), Brunauer–Emmett–Teller (BET) surface area (ABET), pore size, point of zero charge (pHPZC), and basal spacing predominantly affected the Freundlich constant (KF) and qmL of SDZ0 and CIP+ at pH 5 more than SDZ− and CIP± at pH 8. For bi-solute sorption, the presence of CIP inhibited the SDZ sorption onto montmorillonite and kaolinite. Competitive sorption models such as Sheindorf–...