Adsorption equilibria of di(2-ethylhexyl)phosphoric acid at the water-dodecane-interface. Importance of zinc extraction

Inhaltsverzeichnis (Table of Contents)

• Introduction
• Experimental
• Modelling

Zielsetzung und Themenschwerpunkte (Objectives and Key Themes)

This study investigates the interfacial activity of a cation exchanger complex fully loaded with zinc at the water-dodecane interface. The main objective is to explain the impact of extraction equilibria on the equilibrium interfacial tension. This is achieved by varying electrolyte concentrations and the concentrations of the cation exchanger, di(2-ethylhexyl)phosphoric acid (D2EHPA).

• Interfacial activity of zinc-loaded cation exchanger complex
• Influence of extraction equilibria on interfacial tension
• Modelling of adsorption equilibria in the presence of zinc extraction
• Significance of zinc complex aggregation and its influence on interfacial tension
• Application of Langmuir and Stern isotherms to describe adsorption behavior

Zusammenfassung der Kapitel (Chapter Summaries)

• Introduction: This chapter introduces the concept of interfacial activity and its importance in liquid-liquid extraction, particularly in relation to surfactants and their impact on interfacial tension. It highlights the significance of modelling adsorption equilibria in the context of non-equilibrium processes and discusses the different mechanisms of adsorption: immediate adsorption and kinetically inhibited transfer. The chapter concludes by outlining the focus of this study: extending the previously developed model for D2EHPA adsorption to include zinc extraction.
• Experimental: This chapter details the experimental setup and procedures employed in the study. It describes the preparation of the two-phase system, the extraction process using zinc sulfate solutions, and the variation of electrolyte concentrations. The chapter also outlines the measurement of interfacial tension using the pendant drop method and provides information on the chemicals used and their purity.
• Modelling: This chapter presents the mathematical model developed to describe the adsorption equilibria in the presence of zinc extraction. The Gibbs adsorption equation is extended to include the adsorption of the zinc complex without ligands and the consequential counterion adsorption. The chapter then introduces the Langmuir isotherms to describe the multicomponent adsorption of the monomer, the cation exchanger anion, and the zinc complex, and the Stern isotherms to describe the counterion adsorption. The chapter concludes by deriving the equation for the equilibrium interfacial tension, considering the aggregation of the zinc complex and neglecting the reactive coupling between the monomer and the zinc complex.

Schlüsselwörter (Keywords)

This study focuses on the interfacial activity of a cation exchanger complex fully loaded with zinc at the water-dodecane interface. Key topics include the influence of extraction equilibria on interfacial tension, the adsorption of zinc complexes, the application of Langmuir and Stern isotherms to model adsorption behavior, and the aggregation of the zinc complex.