Solvent extraction of metals: Role of ionic liquids and microfluidics

https://doi.org/10.1016/j.seppur.2020.118289Get rights and content

Highlights

  • Up-to-date progress of the metal extraction process.

  • Solvents and technologies were used in conventional and current extraction methods.

  • Important parameters in the process and how effective each method is.

  • The advantages of new emerging reactors over the conventional ones.

Abstract

Microfluidic technology has attracted great interest across industry and academia. Its engineering characteristics, through miniaturization, can enhance mass- and heat transfer rates together with allowing operation at high concentrations. Combining this technology with a green designer solvent is one of the most recent advances in separation processes. Ionic liquids have negligible volatility and flammability and have an exceptionally large chemical diversity space, which these days can be better utilised through solvent modelling. Ionic liquids have been demonstrated to increase the efficiency and selectivity of extraction by orders of magnitude.

Different types of microfluidic devices have been designed until now, and among those, the segmented flow with alternate regular slugs is the most prominent. Helical coiling can further intensify the internal recirculation by convection, which is the motor of the advanced mass transfer. This is done by liberating Dean forces. A device that leverages such mass transfer intensification in the best possible way is the Coiled flow inverter (CFI) (Saxena Nigam, 1984) [1]. The coil periodicity is just 4 turnings, and then the winding direction is inversed, e.g. changed from clockwise to counter-clockwise, and this is repeated multiple times. The CFI extraction performance is typically much better than for a straight and a non-inverted helical capillary.

Separation of metals using liquid–liquid extraction methodology is an important research subject of large economical relevance. The common types of equipment in metal extraction have some disadvantages such as long mixing time and huge plant footprint for the coalescence of the multi-phase, which might take very long due to emulsion formation. In this regard, microfluidic devices and ionic liquids provide an alternative as more compact, more efficient, and faster technology. This review shall help researchers to understand the recent improvement in metal extraction processes, and what the addition of disruptive technology can add to an industrial transformation.

Introduction

Metal ion extraction has always drawn extensive attention from researchers due to a wide range of applications in the industry including metallurgy, electronics, pigments and ceramics, catalysis and medical treatment, nuclear technologies, synthetic chemicals, transport, and communication sectors [2], [3], [4]. It has stimulated rapid growth of industries, and delivered a large economical profit, yet also raised environmental problems. Metal extraction is applied for three main business cases: a) extraction of metal ions from natural resources, b) recycling the materials from secondary resources, and c) treatment of wastewater [5], [6], [7], [8], [9].

Presently, one of the major industrial-scale techniques for the separation and recovery of metals is Solvent Extraction (SX), which is part of hydrometallurgical processing. The principle of the SX technique is based on the preferential distribution of the dissolved target substance between two immiscible phases. Generally, aqueous and organic phases are used for this purpose [10]. The transport of dissolved substances in the aqueous phase from the aqueous phase to the organic phase is provided by using an extracting agent called extractant [11]. This method has become popular because of its several advantages including high selectivity, simple operation, high metal purity, and low power consumption, and has been increasingly applied in the separation of metal ion process [12]. There are many different kinds of extractant employed in separation processes that were continuously improved during the decades and have been utilised for extractors as diverse as batch units, counter-current stages, and microfluidic devices [13], [14].

Many reviews have been presented on the constitutional technologies of this review, which are metal extraction, ionic liquids, and microfluidic devices [10], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]. Most of them constrict, however, to the extraction process for special groups of metals or solvents. To the best of our knowledge, no manuscript compiles recent improvements in metal extraction technology, advanced microfluidic device design, and the optimised ionic liquid selection and how this affects the separation performance. To fill such a knowledge gap, we hereby present a review providing oversight about the improvement in metal extraction from the past until the present, with particular focus on both utilising microscale technology and ionic liquids to increase the efficiency of metal extraction. The purpose of this review study is to answer the following questions:

  • What has been the progress of the metal extraction process so far?

  • Which solvents and technologies were used in the past and now?

  • What are the effective parameters in the process and how effective is each method?

  • What advantage may new emerging reactors provide over old ones?

Section snippets

Extraction of metal ions in the past

The extraction of metal ions using the solvent extraction method has been started in the 1950s with the extraction of uranium from its ores and later for tantalum and niobium [25], [26].

Organic solvents such as xylene [27], kerosene [28], n-heptane [29], methyl-isobutyl ketone (MIBK) [30] and chloroform [31] are commonly used for the extraction process. From the 1980s onwards, the development of powerful extracting agents added much value to increase the performance of the extraction process

Ionic liquid in the metal extraction process

From an environmental point of view, the finding of green solvents, e.g. with lower toxicity and vapor pressure than conventional solvents, has attracted much interest [21]. Ionic liquids (ILs) could establish a prime role to be considered as future solvent or extractant in the metal extraction process. Ionic liquids consist of organic cations in combination with various inorganic anions. Depending on the cationic or anionic structure of ILs, they can be miscible with water and/or nonpolar

Ionic liquids as a solvent for extraction of metal ions in microfluidic system

The limitations of using ILs for extractions have already been pointed out as high production cost and high viscosity. The first issue might also pose an environmental problem due to the need for a larger solvent amount and the corresponding accruing waste. The latter might be known to cause lower mass transfer efficiency in conventional extractors [141]. To overcome these obstacles, a novel technology with high performance and a low solvent holdup is needed. Microflow technology with its

Process intensification of microfluidic - ionic liquids extraction

Reducing plant size while keeping or increasing its production efficiency was the original aim of process intensification and indeed the microfluidic chemical plants commonly have smaller footprints [144]. The motivation of microfluidics for metal extraction is to improve the mass transfer between the two immiscible liquid phases. Because of their large specific surface to volume ratio, interfacial mass transfer is largely facilitated [144]. Microfluidics benefits from unique, highly regular

Conclusions

Nowadays, the resourcing and recovery of metals are big challenges for manifold major global industries, both economically and environmentally, facing an increasing demand for declining resources (element criticality). This work investigated different methods and technologies used to extract metal ions from the aqueous solution from the past until now, in the context of minerals processing for mining;

The following conclusions can be drawn:

  • Past – successful implementation: Metal extraction

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

Volker Hessel acknowledges the support of the start-up grant provided by The University of Adelaide, Australia.

References (147)

  • G. Chauhan et al.

    Novel technologies and conventional processes for recovery of metals from waste electrical and electronic equipment: challenges & opportunities–a review

    J. Environ. Chem. Eng.

    (2018)
  • C.A.D. Morais et al.

    Process development for the recovery of high-grade lanthanum by solvent extraction

    Hydrometallurgy

    (2004)
  • Y. Zhao et al.

    Solid phase extraction of uranium (VI) onto benzoylthiourea-anchored activated carbon

    J. Hazard. Mater.

    (2010)
  • J. Preston

    Solvent extraction of metals by carboxylic acids

    Hydrometallurgy

    (1985)
  • M. Lee et al.

    Solvent extraction separation of indium and gallium from sulphate solutions using D2EHPA

    Hydrometallurgy

    (2002)
  • K.C. Sole et al.

    Solvent extraction characteristics of thiosubstituted organophosphinic acid extractants

    Hydrometallurgy

    (1992)
  • R. Banda et al.

    Solvent extraction separation of Pr and Nd from chloride solution containing La using Cyanex 272 and its mixture with other extractants

    Sep. Purif. Technol.

    (2012)
  • Z. Li et al.

    Separation of transition metals from rare earths by non-aqueous solvent extraction from ethylene glycol solutions using Aliquat 336

    Sep. Purif. Technol.

    (2018)
  • J. Brits et al.

    Palladium stripping rates in PGM refining

    Hydrometallurgy

    (2007)
  • G.A. Pinto et al.

    Design optimisation study of solvent extraction: chemical reaction, mass transfer and mixer–settler hydrodynamics

    Hydrometallurgy

    (2004)
  • R.-S. Juang et al.

    Extraction separation of Co (II)/Ni (II) from concentrated HCl solutions in rotating disc and hollow-fiber membrane contactors

    Sep. Purif. Technol.

    (2005)
  • A. Bhowal et al.

    Continuous removal of hexavalent chromium by emulsion liquid membrane in a modified spray column

    Sep. Purif. Technol.

    (2012)
  • N. Kabay et al.

    Packed column study of the sorption of hexavalent chromium by novel solvent impregnated resins containing aliquat 336: Effect of chloride and sulfate ions

    React. Funct. Polym.

    (2005)
  • L. Zhang et al.

    Co and Ni extraction and separation in segmented micro-flow using a coiled flow inverter

    Chem. Eng. J.

    (2017)
  • B. Reddy et al.

    Extraction of iron (III) at macro-level concentrations using TBP, MIBK and their mixtures

    Hydrometallurgy

    (1996)
  • J. Saji et al.

    Liquid–liquid extraction separation of iron (III) from titania wastes using TBP–MIBK mixed solvent system

    Hydrometallurgy

    (2001)
  • A.A. Leopold et al.

    Mathematical modeling of cadmium (II) solvent extraction from neutral and acidic chloride media using Cyanex 923 extractant as a metal carrier

    J. Hazard. Mater.

    (2010)
  • Z. Zhu et al.

    Separation and recovery of copper, nickel, cobalt and zinc in chloride solutions by synergistic solvent extraction

    Hydrometallurgy

    (2012)
  • Q. Ye et al.

    Solvent extraction behavior of metal ions and selective separation Sc3+ in phosphoric acid medium using P204

    Sep. Purif. Technol.

    (2019)
  • J. Preston et al.

    Separation of nickel and calcium by solvent extraction using mixtures of carboxylic acids and alkylpyridines

    Hydrometallurgy

    (2000)
  • J. Preston et al.

    The recovery of rare earth oxides from a phosphoric acid by-product. Part 1: Leaching of rare earth values and recovery of a mixed rare earth oxide by solvent extraction

    Hydrometallurgy

    (1996)
  • Ł. Marcinkowski et al.

    Opportunities and shortcomings of ionic liquids in single-drop microextraction

    TrAC, Trends Anal. Chem.

    (2015)
  • Z. Chen et al.

    Extraction of heavy metal ions using ionic liquids

  • C. Zhang et al.

    Ionic liquid based three-liquid-phase partitioning and one-step separation of Pt (IV), Pd (II) and Rh (III)

    Sep. Purif. Technol.

    (2013)
  • L.Y. Wang et al.

    Recent advances in metal extraction improvement: Mixture systems consisting of ionic liquid and molecular extractant

    J. Sep. Purif. Technol.

    (2019)
  • M. Rzelewska-Piekut et al.

    Separation of Pt (IV), Pd (II), Ru (III) and Rh (III) from model chloride solutions by liquid-liquid extraction with phosphonium ionic liquids

    Sep. Purif. Technol.

    (2019)
  • G. Zante et al.

    Separation of lithium, cobalt and nickel from spent lithium-ion batteries using TBP and imidazolium-based ionic liquids

    J. Ind. Eng. Chem.

    (2020)
  • N. Wang et al.

    Extraction and stripping of platinum (IV) from acidic chloride media using guanidinium ionic liquid

    J. Mol. Liq.

    (2019)
  • F.J. Alguacil et al.

    Solvent extraction of indium (III) from HCl solutions by the ionic liquid (A324H+)(Cl−) dissolved in Solvesso 100

    Hydrometallurgy

    (2019)
  • F. Alguacil et al.

    Extraction of indium(III) from sulphuric acid medium by the ionic liquid (PJMTH+ HSO4−)

    Sep. Purif. Technol.

    (2019)
  • M. Khodakarami et al.

    Separation and recovery of rare earth elements using novel ammonium-based task-specific ionic liquids with bidentate and tridentate O-donor functional groups

    Sep. Purif. Technol.

    (2020)
  • T.T. Tran et al.

    Synthesis of succinimide based ionic liquids and comparison of extraction behavior of Co (II) and Ni (II) with bi-functional ionic liquids synthesized by Aliquat336 and organophosphorus acids

    Sep. Purif. Technol.

    (2020)
  • S. Platzer et al.

    Task-specific thioglycolate ionic liquids for heavy metal extraction: synthesis, extraction efficacies and recycling properties

    J. Hazard. Mater.

    (2017)
  • J. Flieger et al.

    Extraction of cobalt (II) using ionic liquid-based bi-phase and three-phase systems without adding any chelating agents with new recycling procedure

    J. Sep. Purif. Technol.

    (2019)
  • N.L. Mai et al.

    Methods for recovery of ionic liquids—a review

    J. Process Biochem.

    (2014)
  • W. Wei et al.

    Selective recovery of Au (III), Pt (IV), and Pd (II) from aqueous solutions by liquid–liquid extraction using ionic liquid Aliquat-336

    J. Mol. Liq.

    (2016)
  • S. Li et al.

    Recovery of palladium from acidic nitrate media with triazole type extractants in ionic liquid

    Hydrometallurgy

    (2019)
  • A. Cieszynska et al.

    Extractive recovery of palladium (II) from hydrochloric acid solutions with Cyphos® IL 104

    Hydrometallurgy

    (2012)
  • S. Martınez et al.

    Solvent extraction of gold (III) by the chloride salt of the tertiary amine Hostarex A327. Estimation of the interaction coefficient between AuCl4− and H+

    Hydrometallurgy

    (1999)
  • M.L. Good et al.

    Liquid-liquid extraction with long-chain quaternary ammonium halides

    Anal. Chim. Acta

    (1964)
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