Thermodynamic and kinetic coupling modeling for thallium(I) sorption at a heterogeneous titanium dioxide interface

Area of Science:

• Environmental Chemistry
• Geochemistry
• Surface Chemistry

Background:

• Monovalent thallium (Tl) transformations in water are significantly impacted by its partitioning at the solid-water interface during sorption.
• Accurate prediction of thallium's environmental fate requires models that quantify Tl(I) adsorption kinetics on heterogeneous adsorbents and complex formation under diverse water chemistry conditions.

Purpose of the Study:

• To investigate Tl(I) sorption on titanium dioxide across various pH levels and loading concentrations.
• To develop and apply unified adsorption models (diffuse layer and kinetics) for predicting Tl(I) binding behavior.
• To identify and characterize key Tl(I) surface complexes and their contribution to adsorption.

Main Methods:

• Utilized diffuse layer modeling and kinetics modeling to study Tl(I) sorption on titanium dioxide.
• Investigated the influence of solution pH and loading concentrations on adsorption.
• Employed spectroscopic analyses to validate surface complexation models.
• Coupled thermodynamics and kinetics modeling to derive adsorption and desorption rate coefficients.

Main Results:

• Three Tl(I) surface complexes (TiOTl, TiOHTl+, TiOTlOH-) were identified and successfully described batch adsorption data.
• The TiOHTl+ complex dominated adsorption under neutral to weakly alkaline conditions.
• The TiOTlOH- complex was predominant in strongly alkaline environments.
• Adsorption and desorption rates were influenced by the characteristics of different Tl(I) complexes.

Conclusions:

• A comprehensive model was developed to predict the dynamic binding behavior of Tl(I) at heterogeneous solid-water interfaces.
• The study provides insights into the pH-dependent speciation and sorption mechanisms of thallium.
• Understanding these interactions is crucial for assessing the environmental risks and fate of thallium.