Comparison of Competitive and Synergistic Adsorption of Tetrabromobisphenol-A and Its Metabolites on Two Different Organic-Modified Clays

Experimental data of the adsorption of tetrabromobisphenol-A (TBBPA) and its metabolites [bisphenol-A (BPA) and 2,6-dibromophenols (2,6-DBP)] on two different organic-modified clays were determined in single, binary, and ternary solute systems. In a single solute system, both the adsorbents showed high adsorption selectivity for TBBPA; the logarithms of adsorption coefficients (K(d)s) for three organics are nonlinearly related to the logarithm of their octanol-water partition coefficients (K(ow)s). In the binary solute system, the uptake of TBBPA was reduced by the presence of BPA and the reduction depended on the initial concentration of BPA. Meanwhile, the uptake of TBBPA was enhanced by the presence of 2,6-DBP at high initial concentrations because of synergetic adsorption. The Freundlich model and the Sheindorf-Rebuhn-Sheintuch model provided the best fit for the adsorption of TBBPA and its metabolites in the binary solute system. On the basis of the comparison between the single and multiple solute systems, the K-F value of TBBPA decreased in the order: K-F of TBBPA (6.0 mu mol/L-2,6-DBP) > K-F of TBBPA > K-F of TBBPA (6.0 mu mol/l-BPA); the K-F value of BPA and 2,6-DBP decreased in the order: K-F of a single solute system > K-F of a binary solute system > K-F of a ternary solute system; and no enhancement for BPA and 2,6-DBP adsorption was observed. The adsorption kinetic of TBBPA and its metabolites followed the pseudo second-order equation in single and binary solute systems. The adsorption capacity of TBBPA and its metabolites was reduced compared with that in the single system. However, the total adsorption capacity in the binary system was increased.