Development of a hydrometallurgical route for the production of high-purity indium

Indium is essential for many electronic applications, e.g. photovoltaics and laptops. Due to the increasing demand for indium in high-tech applications and China’s dominance in the indium production, this metal is labelled as a critical raw material by the European Commission. To keep pace with the increasing demand, efficient industrial processes for the recovery of indium from ore-processing by-products and end-of-life consumer goods must be developed. The Umicore Precious Metals Refining business unit at Hoboken (Belgium) produced 4N5 indium metal. This recycling process was quite energy- and time-consuming, had a low efficiency and yielded indium metal with fluctuating purity levels. Therefore, the production process is stopped halfway between the raw materials and pure indium metal, manufacturing an intermediate crude indium(III) hydroxide (In(OH)3, containing 80–90% indium). Given Umicore’s drive towards sustainable development, the aim of this PhD thesis is to design an alternative sustainable indium refinery process for the production of high-purity indium (5N) starting from crude In(OH)3. This will be done by developing several new hydrometallurgical unit processes and combining them into a new process flowsheet. With the aim of developing a sustainable refining process, ionic liquids are taken into account. This PhD thesis shows how ionic liquids can be used as green alternative solvents to replace the conventional aqueous or organic solvents in the leaching, solvent extraction and electrowinning stages. In a first approach, the extraction of indium from chloride media by the commercially available ionic liquids Cyphos IL 101 and Aliquat 336 is presented. High percentages extraction, high loadings and fast kinetics make these solvent extraction systems very suitable for extraction of indium. Indium was recovered as In(OH)3 by precipitation stripping with NaOH, regenerating the ionic liquid at the same time. Moreover, the extraction process was selective for In(III), over many other metal ions (As(III), Mn(II), Ni(II), Cu(II)) that are commonly found as impurities in process solutions of indium refineries. Cd(II), Fe(III), Pb(II), Sn(IV) and Zn(II) were co-extracted to the ionic liquid phase. Speciation of indium complexes in the aqueous and ionic liquid phase can provide more insight in the extraction mechanism and allows proper tuning of conditions and selection of extractants. In an aqueous HCl solution (0–12 M), indium(III) exists as mixed octahedral complexes, [In(H2O)6–nCln]3–n (0 ≤ n ≤ 6), while in the ionic liquid phase indium(III) is present as the tetrahedral [InCl4]– unaffected by the HCl concentration in the aqueous phase. An extraction mechanism was proposed based on the speciation studies in which indium(III) can be extracted as a neutral complex, In(H2O)3Cl3. In a second approach, a combined leaching/extraction system was proposed for the selective recovery of indium from crude In(OH)3 based on the thermomorphic and acidic properties of the ionic liquid [Hbet][Tf2N]. Efficient indium leaching was obtained by a 1:1 wt/wt [Hbet][Tf2N]–H2O mixture. The formation of a biphasic system induced metal separation where In(III) is extracted to the ionic liquid phase, whereas Al(III), Ca(II), Cd(II), Ni(II) and Zn(II) remain in the aqueous phase. Fe(III), As(V) and Pb(II) are co-extracted to the ionic liquid phase. Iron remained in the aqueous phase by addition of ascorbic acid to the aqueous phase, thereby reducing Fe(III) to Fe(II). A HCl solution was used to strip indium(III) to the aqueous phase, regenerating at the same time the ionic liquid. By combining a prehydrolysis and hydrolysis step on the aqueous phase obtained after stripping, the purity of the crude In(OH)3 was improved. In a final approach, Cyphos IL 101 was used as an electrolyte for the recovery of indium by electrodeposition at elevated temperatures. Indium is electrochemically reduced from In(III) to In(I) and subsequently from In(I) to In(0). Droplet-like deposits were observed between 100 and 180 °C, but their origin is not clear yet: melting-point depression of very small primary indium particles in combination with undercooling or dewetting. Also, droplet-on-droplet deposition took place indicating that there is a surface indium oxide layer present preventing the droplets to coalesce. Moreover, the electrowinning process was selective for In(III) over Zn(II). High-temperature electrowinning requires thermally stable electrolytes. The thermal stability of Cyphos IL 101 was investigated, both by dynamic and static TGA. Dynamic TGA overestimated the real thermal stability, while addition of metal chlorides to the ionic liquid increased the thermal stability. It was shown that Cyphos IL 101 had a long-term thermal stability at 180 °C in an inert atmosphere.ACKNOWLEDGEMENT ABSTRACT SAMENVATTING ABBREVIATIONS AND SYMBOLS TABLE OF CONTENT THESIS OUTLINE CHAPTER 1: INTRODUCTION 1.1 Indium 1.2 Hydrometallurgy as a tool for metal recovery 1.2.1 Leaching 1.2.2 Precipitation and cementation 1.2.3 Solvent extraction 1.2.4 Electrochemistry 1.3 Ionic liquids in hydrometallurgy 1.3.1 Processing of minerals and metal oxides 1.3.2 Separation of metals using solvent extraction 1.3.3 Electrodeposition of metals in ionic liquids 1.4 Indium recovery 1.4.1 Indium recovery from primary and secondary sources 1.4.2 Ionic liquid technology for indium recovery 1.4.3 Indium recovery at Umicore 1.5 References CHAPTER 2: OBJECTIVES CHAPTER 3: PURIFICATION OF INDIUM BY SOLVENT EXTRACTION WITH UNDILUTED IONIC LIQUIDS 3.1 Introduction 3.2 Experimental 3.2.1 Chemicals 3.2.2 Instrumentation and analysis methods 3.2.3 Extraction experiments 3.2.4 Mono-element system 3.2.5 Multi-element system 3.3 Results and discussion 3.3.1 Mono-element system 3.3.2 Multi-element system 3.4 Conclusions 3.5 References 3.6 Supplementary information CHAPTER 4: SPECIATION OF INDIUM(III) CHLORO COMPLEXES IN THE SOLVENT EXTRACTION PROCESS FROM CHLORIDE AQUEOUS SOLUTIONS TO IONIC LIQUIDS 4.1 Introduction 4.2 Experimental 4.2.1 Chemicals 4.2.2 Instrumentation and analysis methods 4.2.3 Solvent extraction 4.2.4 Distribution ratio 4.3 Results and discussion 4.3.1 Indium(III) speciation in the aqueous phase 4.3.2 Solvent extraction of indium(III) 4.3.3 Indium(III) speciation in the ionic liquid phase 4.3.4 Solvent extraction mechanism 4.4 Conclusions 4.5 References 4.6 Supplementary information CHAPTER 5: PURIFICATION OF CRUDE IN(OH)3 USING THE FUNCTIONALIZED IONIC LIQUID BETAINIUM BIS(TRIFLUOROMETHYLSULFONYL)IMIDE 5.1 Introduction 5.2 Experimental 5.2.1 Chemicals 5.2.2 Instrumentation and analysis methods 5.2.3 Synthesis of [Hbet][Tf2N] 5.2.4 Leaching 5.2.5 Quantitative 1H NMR 5.2.6 Scrubbing 5.2.7 Stripping 5.3 Results and discussion 5.3.1 Leaching of crude In(OH)3 in [Hbet][Tf2N] 5.3.2 Thermomorphic leaching/extraction in a [Hbet][Tf2N]–H2O system 5.3.3 Metal scrubbing/stripping and recovery of ionic liquid 5.4 Conclusions 5.5 References 5.6 Supplementary information CHAPTER 6: THERMAL STABILITY OF TRIHEXYL(TETRADECYL)PHOSPHONIUM CHLORIDE 6.1 Introduction 6.2 Experimental 6.2.1 Chemicals 6.2.2 Instrumentation and analysis methods 6.2.3 Cyphos IL 101 Purification 6.3 Results and discussion 6.3.1 Short-term stability 6.3.2 Long-term stability 6.3.3 Decomposition products 6.4 Conclusions 6.5 References 6.6 Supplementary information CHAPTER 7: ELECTRODEPOSITION OF INDIUM FROM THE IONIC LIQUID TRIHEXYL(TETRADECYL)PHOSPHONIUM CHLORIDE 7.1 Introduction 7.2 Experimental 7.2.1 Chemicals 7.2.2 Instrumentation and analysis methods 7.2.3 Cyphos IL 101 Purification 7.3 Results and discussion 7.3.1 Electrochemical study in commercial Cyphos IL 101 7.3.2 Electrochemical stability of purified Cyphos IL 101 7.3.3 Electrochemical study of indium on Mo and Pt in purified Cyphos IL 101 7.3.4 Electrochemical study of zinc and iron on Mo in purified Cyphos IL 101 7.3.5 Diffusion coefficient of indium in purified Cyphos IL 101 7.4 Conclusions 7.5 References 7.6 Supplementary information CHAPTER 8: FLOWSHEET DESIGN 8.1 Introduction 8.2 Experimental 8.2.1 Chemicals 8.2.2 Instrumentation and analysis methods 8.2.3 Leaching 8.2.4 Solvent extraction 8.3 Results and discussion 8.3.1 Leaching 8.3.2 Solvent extraction 8.3.3 Electrowinning 8.3.4 Flowsheet design 8.4 Conclusions 8.5 References CHAPTER 9: CONCLUSIONS AND OUTLOOK HEALTH, SAFETY & ENVIRONMENT LIST OF PUBLICATIONS LIST OF CONFERENCESnrpages: 284status: publishe

Erratum to: Electrochemical dissolution of metallic platinum in ionic liquids

The electrochemical dissolution of Pt in several ionic liquids (IL's) was studied. Different IL's were tested assessing their potential to dissolve Pt. Dissolution rate and current efficiency were evaluated. The main focus was on Cl containing IL's: first generation, eutectic based IL's and second generation IL's with discrete anions. Pt dissolution only occurred in type 1 eutectic-based IL's with a max. dissolution rate of 192.2 g m(-2) h(-1) and a max. current efficiency of 99 % for the ZnCl2-1-ethyl-3-methylimidazolium chloride IL, and 9.090 g m(-2) h(-1) and 96 % for the 1:1 ZnCl2-choline chloride ionic liquid. The dissolution occurred via the formation of [PtCl (x) ] (y-) complexes. To form these complexes, addition of a metal chloride was necessary. Furthermore, an IL with an electrochemical window of 1.5 V, preferably 2.0 V is required to achieve Pt dissolution. The added metal salt needed to have a higher decomposition potential than 1.5 V or should be a Pt salt.status: publishe

Electrochemical dissolution of metallic platinum in ionic liquids

The electrochemical dissolution of Pt in several ionic liquids (IL's) was studied. Different IL's were tested assessing their potential to dissolve Pt. Dissolution rate and current efficiency were evaluated. The main focus was on Cl containing IL's: first generation, eutectic based IL's and second generation IL's with discrete anions. Pt dissolution only occurred in type 1 eutectic-based IL's with a max. dissolution rate of 192.2 g m(-2) h(-1) and a max. current efficiency of 99 % for the ZnCl2-1-ethyl-3-methylimidazolium chloride IL, and 9.090 g m(-2) h(-1) and 96 % for the 1:1 ZnCl2-choline chloride ionic liquid. The dissolution occurred via the formation of [PtCl (x) ] (y-) complexes. To form these complexes, addition of a metal chloride was necessary. Furthermore, an IL with an electrochemical window of 1.5 V, preferably 2.0 V is required to achieve Pt dissolution. The added metal salt needed to have a higher decomposition potential than 1.5 V or should be a Pt salt.status: publishe

Indium electrodeposition from indium(iii) methanesulfonate in DMSO

The electrochemical behavior and electrodeposition of indium was investigated at 26 °C and 160 °C from a solution composed of indium(III) methanesulfonate and dimethylsulfoxide (DMSO). Indium(III) methanesulfonate was synthesized from indium(III) oxide and methanesulfonic acid (MSA). Cyclic voltammetry, quartz crystal microbalance measurements and rotating ring disk electrode experiments indicated that reduction of indium(III) to both indium(I) and indium(0) occurs. Yet, reduction to metallic indium was found to be the predominant process. Deposited indium could be stripped to indium(I). This unstable species disproportionated to indium(III) and indium(0), leading to the formation of micron-sized metallic indium particles in the electrolyte. At 26 °C, indium deposited on glassy carbon as smooth, flat films whereas at 160 °C, it deposits as droplets.status: publishe

Electrodeposition of indium from non-aqueous electrolytes

The electrochemical behaviour and deposition of indium in electrolytes composed of 0.4 mol dm-3 In(Tf2N)3 and 0.4 mol dm-3 InCl3 in the solvents 1,2-dimethoxyethane and poly(ethylene glycol) (average molecular mass of 0.400 kg mol-1, PEG400) was investigated. Indium(i) was identified as the intermediate species that disproportionated to indium(iii) and indium(0) nanoparticles. The presence of nanoparticles was verified by TEM analysis. SEM analysis showed that deposits obtained at room temperature from 1,2-dimethoxyethane were rough, while spherical structures were formed in PEG400 at 160 °C.status: publishe

Electrodeposition of Indium from a Phosphonium-Based Ionic Liquid

Oral presentation by Jan Fransaerstatus: publishe

Purification of crude In(OH)3 using the functionalized ionic liquid betainium bis(trifluoromethylsulfonyl)imide

The recovery of indium from a crude indium(III) hydroxide using the ionic liquid betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N], was investigated. Leaching and solvent extraction were combined in one step using the thermomorphic properties of the [Hbet][Tf2N]–H2O system. During leaching (80 °C) a homogeneous phase was formed. Upon lowering the temperature below the lower critical solution temperature (UCST), the dissolved metals distributed themselves between the two phases. The optimal leaching/extraction conditions were determined to be a leaching time of 3 hours at 80 °C in a 1 : 1 wt/wt [Hbet][Tf2N]–H2O mixture. Large separation factors (>100) between In(III) and Al(III), Ca(II), Cd(II), Ni(II) and Zn(II) were obtained implying an easy separation. Fe(III), As(V) and Pb(II) are co-extracted. The separation factor between indium and iron was improved to >1000 by addition of ascorbic acid to reduce Fe(III) to Fe(II). The stripping was done very efficiently by HCl solution. The ionic liquid was regenerated during the stripping step. By combining a prehydrolysis and hydrolysis step, indium(III) hydroxide with a purity >99% was obtained.status: publishe

Purification of indium by solvent extraction with undiluted ionic liquids

A sustainable solvent extraction process for purification of indium has been developed from a chloride aqueous feed solution using the ionic liquids Cyphos® IL 101 and Aliquat® 336. The high affinity of indium(III) for the ionic liquid phase gave extraction percentages above 95% over the HCl concentration range from 0.5 to 12 M. Attention was paid to the loading capacity of the ionic liquid phase and the kinetics of the extraction process. An extraction mechanism was proposed based on the relationship between the viscosity of the ionic liquid phase and the loading with indium(III) ions. Even for loadings as high as 100 g L−1, equilibrium was reached within 10 min. Due to the very high distribution ratio for indium(III), stripping of indium(III) from the ionic liquid phase was very difficult with water or acid solutions. However, indium could conveniently be recovered as In(OH)3 by precipitation stripping with a NaOH solution. Precipitation stripping has the advantage that no ionic liquid components are lost to the aqueous phase and that the ionic liquid is regenerated for direct re-use. The extraction of some metal ions that are commonly found as impurities in industrial indium process solutions, i.e. cadmium(II), copper(II), iron(III), manganese(II), nickel(II), tin(IV) and zinc(II), has been investigated. The distribution ratios for the different metal ions show that indium(III) can be purified efficiently by a combination of extraction, scrubbing and stripping stages. This new ionic liquid process avoids the use of volatile organic solvents.crosscheck: This document is CrossCheck deposited related_data: Supplementary Information copyright_licence: The Royal Society of Chemistry has an exclusive publication licence for this journal copyright_licence: This article is freely available. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (CC BY 3.0) history: Received 29 February 2016; Accepted 9 May 2016; Accepted Manuscript published 9 May 2016; Advance Article published 17 May 2016; Version of Record published 11 July 2016status: publishe

Thermal stability of trihexyl(tetradecyl)phosphonium chloride

Dynamic TGA studies of phosphonium ionic liquids have reported thermal stabilities of 300 °C or higher for these compounds. This is often an overestimation of the real thermal stability. The chosen technique as well as the experimental parameters can influence the thermal stability. In this paper, the thermal stability of commercially available Cyphos IL 101 is studied. The effect of the nature of the atmosphere (air or inert gas), the purity of the sample, the heating rate and presence of a metal on the short-term and long-term stability of commercial Cyphos IL 101 is investigated. The thermal decomposition products are characterized using thermogravimetric analysis coupled to mass spectrometry (TGA-MS). Impurities present and higher heating rates lead to an under- and overestimation of the thermal stability, respectively. The presence of oxygen leads to a lower thermal stability. In contrast, adding metal chlorides to the ionic liquid causes an increase in the thermal stability. The chloride anions are coordinated to the metal ion, so that the Lewis basicity of the anions is reduced. Also this paper gives insights in the behavior of Cyphos IL 101 at high temperatures, which is of relevance for possible application of this ionic liquid in high-temperature industrial processes.status: publishe

Electrodeposition of indium from the ionic liquid trihexyl(tetradecyl)phosphonium chloride

The electrochemical behavior of indium in the ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) was studied. Cyphos IL 101 first had to be purified, as the impurities present in commercial Cyphos IL 101 interfered with the electrochemical measurements. Electrochemical deposition of indium metal from this electrolyte occurs without hydrogen evolution, increasing the cathodic current efficiency compared to deposition from water and avoiding porosity within the deposited metal. Indium(iii) is the most stable oxidation state in the ionic liquid. This ion is reduced in two steps, first from indium(iii) to indium(i) and subsequently to indium(0). The high thermal stability of Cyphos IL 101 allowed the electrodeposition of indium at 120 °C and 180 °C. At 180 °C indium was deposited as liquid indium which allows for the easy separation of the indium and the possibility to design a continuous electrowinning process. On molybdenum, indium deposits as liquid droplets even below the melting point of indium. This was explained by the combination of melting point depression and undercooling. The possibility to separate indium from iron and zinc by electrodeposition was tested. It is possible to separate indium from zinc by electrodeposition, but iron deposits together with indium.status: publishe