Complexation of sulfamethazine with Cd(II) and Pb(II): implication for co-adsorption of SMT and Cd(II) on goethite.

This study quantified the complex stability constants of sulfamethazine (SMT) with cadmium (Cd2+) and lead (Pb2+) under different pH conditions. The UV-Vis spectrophotometer was used for acquiring the complexation data. Results showed that the complex stability constants of SMT with cadmium (Cd2+) and lead (Pb2+) increased as a function of the solution pH. In the investigated pH range, Cd2+ showed stronger complex affinity with SMT than Pb2+. It appeared that cation-π interactions might dominate the complex between SMT with Pb2+ and Cd2+ at acid environment, and the covalent bonding might play a major role at neutral environment. Batch adsorption equilibrium experiment showed that the sorption capacity of Cd2+ on goethite increased from 3.83 to 7.64 mg/g along with the addition of 1 mg/L SMT, indicating SMT can impede the transportation of Cd. In general, this study worked out the complexation constants and clarified the complexation mechanism between SMT with lead and cadmium, while sorption experiment indicated that sorption of Cd onto goethite was enhanced with SMT.