Ion Exchange and Solvent Extraction

Volume 23, Changing the Landscape in Solvent Extraction

Bruce A Moyer

• Publisher: CRC Press
• Year: 2019
• Print ISBN:
  9781032401379
• eBook ISBN:
  9781351627511
• Topic: Physical Sciences
• Subtopic: Analytic Chemistry

This volume will capture transformational changes in both the chemistry and engineering side of solvent extraction, creating new directions and deepening our understanding of the structure and dynamics of liquid-liquid systems from the molecular- to nano- to meso- to bulk-scale. Reviews will cover advances in microfluidics, new tools for understanding the structure and dynamics of the liquid-liquid interface, ionic liquids in liquid-liquid extraction, molecular dynamics to visualize interactions in the solvent phase, liquid-liquid electrochemistry to interrogate the energetics of interfacial transport and complexation, design of new extractants, and the streamlining of process applications.

1	New Insights into the Recovery of Strategic and Critical Metals by Solvent Extraction

The Effects of Chemistry and the Process on Performance

Jason B. Love , Manuel Miguirditchian , and Alexandre Chagnes

CONTENTS

1.1 Introduction

1.2 Extractant Design

1.2.1 The Role of Coordination Chemistry and Supramolecular Chemistry on the Design of New Extractants

1.2.1.1 Complex Formation

1.2.1.2 Ion Pairs and Metalates

1.2.1.3 Reverse Micelles

1.2.1.4 Conclusion

1.2.2 The Role of Physicochemistry for a Rational Design of New Extractants

1.2.3 Case Studies

1.2.3.1 Design of New Extractants for Uranium Recovery from Wet Phosphoric Acid

1.2.3.2 Chemical Design in Gold Recovery by Urban Mining

1.3 Flowsheet Optimization

1.3.1 Effect of Flowrates on Flowsheet Performances

1.3.2 Influence of Degradation on Flowsheet Performance

1.3.3 Combining Chemistry and Engineering for Flowsheet Optimization

1.3.4 Perspective in the Development of Tools for Flowsheet Optimization

1.4 Conclusion

References

1.1 Introduction

The exploitation of nonthermal chemical separation processes, which would lower global energy use, emissions, and pollution, is particularly pertinent to the recovery of metals from their primary ores and secondary resources [1]. In principle, the separation of metals by hydrometallurgical processes such as solvent extraction (SX, Figure 1.1) can achieve these outcomes due to ambient-temperature operation and the maintenance of materials balance through reagent recycling [2]. However, significant challenges remain, not least with attaining high levels of separation between metals, but also with issues such as reagent stability, complexity, cost, safety, and recyclability [3,4].

FIGURE 1.1 Schematic describing the separation of metals using solvent extraction. Circles in the organic phase represent extractant molecules or aggregates.

The optimization of SX processes is one of the challenges for treating new unconventional primary and secondary resources, especially polymetallic and low-grade resources. Although the ease of contacting two liquid phases is one of the key advantages of SX, the physicochemistry involved is very complex due to the existence of associations at molecular and supramolecular levels, nonideality, and the presence of various reactions in the aqueous and organic phases as well as in the liquid–liquid interface, which governs the kinetics of extraction (Figure 1.2) [5].

FIGURE 1.2 Main reactions involved in the liquid–liquid extractions of metals. Here, L is the conjugate anion of an acidic organic extractant, HL, often a chelant; B is a neutral coordinating extractant; X is an anion co-extracted with the metal M from the aqueous phase.

The performance of solvent extraction processes mainly relies on the properties of extractant molecules for the selectivity needed for increasingly challenging problems. Surprisingly, there are relatively few extracting agents available on the market, and these molecules were mostly found more than 15 to 20 years ago in spite of great efforts to develop new ones. Industry representatives repeatedly cite the high costs of chemical development and long times for testing and regulatory approval of new reagents as impediments. Developing faster and better approaches to designing new extractants, therefore, appears of great importance toward building efficient, low-cost, and sustainable processes capable of extracting metals from new complex resources. However, the design of new extracting agents cannot be performed by considering only their chemical structures, because interactions involving extractants strongly influence extractant properties. The molecular environment around the extractant, including diluent, phase modifier, other extractant molecules, etc., must thus be first understood and then taken into account during extraction solvent design. For this goal, modeling tools such as DFT (density functional theory), semi-empirical, and QSPR (quantitative structure–property relationship) calculations are increasingly playing an important role [6–8]. Nevertheless, the degree of reliability of the predictions is still limited, and in the present state of the art, these techniques are likely more useful for optimization within a given family of extractants than to build in silico new reagents. The molecular modeling techniques provide binding energies between target metals and given ligands, as well as optimized chemical structures of the formed complexes. Thus, in principle, the information that can be deduced from the molecular modeling computations is richer than that provided by QSPR methods. Modeling tools are an asset to understand liquid–liquid extraction phenomena. The comprehension of the physicochemistry involved during liquid–liquid extraction is therefore particularly important to optimize solvent extraction processes. It paves the way of the development of simulation process tools which are of great importance for optimizing processes.

Likewise, the optimization of the flowsheets is another way to improve the performances of solvent extraction processes in terms of extraction efficiency and selectivity. The classical McCabe–Thiele approach is usually used to choose the number of contactors to implement in the process. Such an approach is only based on engineering process calculations. Undoubtedly, the development of new approaches combining both the physicochemistry of extraction solvent and the engineering process calculations would help the engineer to optimize its process while using a minimum of expensive experiments.

This chapter gives an overview of the new insights into the recovery of strategic and critical metals by solvent extraction. Particular attention is paid to explaining how it is possible to improve existing processes by playing both on the chemistry and the flowsheet design.

1.2 Extractant Design

1.2.1 The Role of Coordination Chemistry and Supramolecular Chemistry on the Design of New Extractants

The development of new reagents for solvent extraction processes requires an understanding of the fundamental solution chemistry of metals and their compounds in both aqueous and organic phases. Ultimately...

Table of contents

• Cover
• Half-Title
• Series
• Title
• Copyright
• Contents
• Preface
• Acknowledgements
• Editor
• Contributors
• Chapter 1 New Insights into the Recovery of Strategic and Critical Metals by Solvent Extraction
• Chapter 2 Liquid–Liquid Separation by Supramolecular Systems
• Chapter 3 Task-Specific Ionic Liquids for Metal Ion Extraction
• Chapter 4 X-Ray Studies of Liquid Interfaces in Model Solvent Extraction Systems
• Chapter 5 Solvent Extraction through the Lens of Advanced Modeling and Simulation
• Chapter 6 A Review of Mass-Transfer and Reaction-Kinetics Studies in Microfluidic Solvent Extraction Processes
• Chapter 7 Drop-Based Modeling of Extraction Equipment
• Index