Dynamic sorptive behavior of tributyltin on quartz sand at low concentration levels: Effect of pH, flow rate, and monovalent cations
Résumé
The highly toxic organotin compounds which have been used as biocides in ship antifouling paints have been introduced into aquatic ecosystems. Among them, tributyltin (TBT) is the most important organotin compound which has been produced on the largest scale. Understanding its fate in the environment is therefore of primary importance to prevent its migration. TBT sorption from aqueous solutions was studied at much lower concentrations (10 nM to 2 μM) than those used in previous studies. Experiments were performed using column reactors filled with a quartz sand. The influence of physicochemical parameters on TBT partitioning, i.e. ionic strength, pH; and nature of electrolyte cation was investigated. Equilibrium times were short as TBT retention appeared to be independent of the mean pore velocity. TBT sorption was affected strongly by the pH and slightly by the ionic strength of the solution. Competitions with monovalent alkaline cations showed a small influence of Li+, Na+, K+, Rb+, with respect to Cs+ on TBT retardation. Moreover, the injection of two different TBT concentrations accounted for the nonlinearity of TBT sorption. The theory of nonlinear chromatography was used for the calculation of convex adsorption isotherms. Retardation factors and distribution coefficients were estimated. The highly toxic organotin compounds which have been used as biocides in ship antifouling paints have been introduced into aquatic ecosystems. Among them, tributyltin (TBT) is the most important organotin compound which has been produced on the largest scale. Understanding its fate in the environment is therefore of primary importance to prevent its migration. TBT sorption from aqueous solutions was studied at much lower concentrations (10 nM to 2 μM) than those used in previous studies. Experiments were performed using column reactors filled with a quartz sand. The influence of physicochemical parameters on TBT partitioning, i.e. ionic strength, pH, and nature of electrolyte cation was investigated. Equilibrium times were short as TBT retention appeared to be independent of the mean pore velocity. TBT sorption was affected strongly by the pH and slightly by the ionic strength of the solution. Competitions with monovalent alkaline cations showed a small influence of Li+, Na+, K+, Rb+, with respect to Cs+ on TBT retardation. Moreover, the injection of two different TBT concentrations accounted for the nonlinearity of TBT sorption. The theory of nonlinear chromatography was used for the calculation of convex adsorption isotherms. Retardation factors and distribution coefficients were estimated.