The processes during the reactive metal salt extraction are significantly influenced by interfacial processes. The interfacial tension in such systems results from the mass transfer operations at the interface. In this work it is shown how the equilibrium interfacial tension can be described a thermodynamic model in the case of zinc extraction with di(2-ethylhexyl)phosphoric acid.
Table of Contents
1 Introduction
2 Experimental
3 Modelling
4 Results
5 Summary
Research Objectives and Themes
This work aims to model the equilibrium interfacial tension during zinc extraction using the cation exchanger D2EHPA. By extending a previously validated model to include zinc complex adsorption and electrolyte influences, the study seeks to quantify interfacial activity and understand the aggregation behavior of zinc complexes at the water-dodecane interface.
- Modelling of equilibrium interfacial tension in liquid-liquid extraction.
- Integration of zinc complex adsorption into the Gibbs-Duhem equation.
- Analysis of counterion adsorption using Stern isotherms.
- Evaluation of the aggregation tendency of D2EHPA-zinc complexes.
- Validation of the model against experimental measurements under varying electrolyte concentrations.
Excerpt from the Book
1 Introduction
In liquid-liquid extraction the concentration profiles of the two different liquids merge continuously into each other the interface. The interface is not a two-dimensional field but a volume with a small thickness. If a local concentration maximum of a substance exists across the interface thickness, the substance is called a surfactant. Because of the resulting concentration elevation in the interface in comparison to the two liquids these substances determine the properties of the interface. The interfacial concentration describes the accumulation of a substance in the interface and it represents an averaging of the concentration profile across the interfacial thickness. At equilibrium the interfacial concentration is correlated with the activities of the surfactants in the two liquids by an adsorption isotherm. Since the adsorbed substances change the interfacial tension between the liquids, this material parameter is used to describe the material accumulation in the interface. The interfacial tension is an essential material parameter, which determines the drop behaviour in disperse systems and influences the design and the equipment of technical extractors [1,2].
Summary of Chapters
1 Introduction: This chapter provides the theoretical foundation for interfacial phenomena in liquid-liquid extraction and defines the role of interfacial tension in technical extraction processes.
2 Experimental: This section details the experimental procedures, including phase mixing, tensiometric measurements of pendant drops, and the analytical methods used to determine zinc concentrations.
3 Modelling: The core chapter derives the mathematical framework, extending the Gibbs-Duhem equation with Langmuir and Stern isotherms to account for zinc extraction and complex aggregation.
4 Results: This chapter presents the simulation results, comparing calculated interfacial tension profiles with experimental data and discussing the impact of aggregation constants.
5 Summary: The final chapter provides a concise review of the developed modelling strategy, acknowledging both its successful reproduction of experimental data and the limitations caused by simplified aggregation assumptions.
Keywords
Zinc extraction, cation exchanger, interfacial activity, adsorption equilibrium, pseudo-nonionic modelling, interfacial tension, D2EHPA, Gibbs-Duhem equation, Langmuir isotherm, Stern isotherm, mass action law, liquid-liquid extraction, surfactant, aggregation, Wilson model.
Frequently Asked Questions
What is the core focus of this research paper?
The paper focuses on modelling the equilibrium interfacial tension in liquid-liquid extraction systems where zinc is extracted using the cation exchanger D2EHPA.
What are the primary thematic fields addressed?
The work covers interfacial science, chemical thermodynamics of extraction equilibria, surfactant adsorption, and mathematical modelling of liquid-liquid systems.
What is the main research objective?
The objective is to refine a pseudo-nonionic modelling strategy to accurately describe and predict interfacial tension when zinc extraction occurs, accounting for multiple components and counterion effects.
Which scientific methodology is employed?
The methodology combines experimental tensiometric measurements using pendant drops with a theoretical framework based on the Gibbs-Duhem equation, Langmuir isotherms, and Stern isotherms.
What is covered in the main body of the work?
The main body covers the experimental setup for zinc extraction, the derivation of a comprehensive adsorption model, the calculation of interaction parameters, and a comparison between theoretical predictions and experimental observations.
Which keywords characterize this study?
Key terms include zinc extraction, D2EHPA, interfacial tension, cation exchange, adsorption isotherm, and pseudo-nonionic modelling.
How does the model handle the aggregation of zinc complexes?
The model treats zinc complexes as polynary aggregates, using a simplified approach analogous to micelle formation to account for their aggregation tendency in the organic phase.
Why are Stern isotherms used in this model?
Stern isotherms are utilized to formulate the adsorption of counterions, which occurs as a consequence of the adsorption of the D2EHPA anion at the interface.
What is the significance of the zinc complex without ligands?
The study concludes that the non-solvated zinc complex exhibits significant interfacial activity, whereas solvated complexes do not, making it a critical component for modelling interfacial tension.
Are there limitations to the proposed model?
Yes, the model exhibits deviations at high zinc sulphate concentrations, which the authors attribute to the simplicity of the current aggregation model and potential inaccuracies in calculating counterion adsorption.
- Quote paper
- Dr.-Ing. Peter Klapper (Author), 2014, Adsorption equilibria of di(2-ethylhexyl)phosphoric acid at the water-dodecane-interface. Importance of zinc extraction, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/281462
