Application of ionic liquids for metal dissolution and extraction

Application of ionic liquids for metal dissolution and extraction

Journal of Industrial and Engineering Chemistry 61 (2018) 388–397 Contents lists available at ScienceDirect Journal of Industrial and Engineering Ch...

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Journal of Industrial and Engineering Chemistry 61 (2018) 388–397

Contents lists available at ScienceDirect

Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec

Application of ionic liquids for metal dissolution and extraction Byung-Kwon Kima,* , Eui Joo Leea , Yeji Kanga , Jae-Joon Leeb,* a

Sookmyung Women’s University, Department of Chemistry, Seoul 04310, Republic of Korea Dongguk University, Department of Energy & Materials Engineering, Research Center for Photoenergy Harvesting and Conversion Technology, Seoul 04620, Republic of Korea b

A R T I C L E I N F O

Article history: Received 25 July 2017 Received in revised form 16 October 2017 Accepted 19 December 2017 Available online 28 December 2017 Keywords: Ionic liquid Dissolution Extraction Pickling Efficiency

A B S T R A C T

This review summarizes the results of studies on the selective dissolution and extraction of Fe, Cr, Cu, and Zn by ionic liquids, as an alternative to the use of conventional molten salts or pickling agents, for various types of steel. Ionic liquids are classified according to the metals, metal ions, and metal oxides by which they can be extracted or dissolved. The results of the metal extraction efficiency per unit time presented in the literature are summarized in a simple unified graphic format. This provides a comparative understanding of the most efficient ionic liquid for the extraction of specific metals. © 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Introduction The steel manufacturing process is subjected to various heat treatments, which essentially produce scales (mostly oxides) on a metal surface [1]. Such oxides need to be removed before and/or during the following manufacturing industrial operations. The various methods of descaling can be broadly classified into physical methods and chemical methods [2,3]. Typical physical methods include mechanical cleaning, such as scraping, abrasive blasting, and waterjet spraying [4]. Two major chemical methods include aqueous alkaline cleaning (with some mild alkaline solutions, such as sodium hydroxide, sodium phosphate, and sodium carbonates) and acid cleaning, known as pickling (with various strong acids and/or solutions of acid mixture), which are often environmentally hazardous [5–9]. In many cases, for most metal-rich scale removal methods, a very aggressive action needs to be used, with a very strong acid mixture, which is often preceded by pretreatment such as an alkaline salt bath or shot blasting process [4,10]. The choice of acid solution for the pickling process depends on the type of steel and product style. For general carbon steel, hydrochloric acid is mainly used. Also, for a thick stainless steel plate (hot rolled steel sheet, 3–8 mm), sulfuric acid and a mixed acid (nitric acid + hydrofluoric acid) solution are used. In general,

* Corresponding authors. E-mail addresses: [email protected] (B.-K. Kim), [email protected] (J.-J. Lee).

for a thin steel plate (cold rolled steel plate, 0.3–3 mm), molten salt (NaOH + NaNO3), sulfuric acid, and mixed acid are sequentially applied [11,12]. For processes with nitric acid, a DeNOx system needs to be used to remove NOx, while the removal of nitrogen from the waste acid is critical to avoid possible environmental problems [2]. Recently, technologies have been developed in which nitric acid is replaced with sulfuric acid, and have been commercialized as an environmentally friendly pickling process [2,13–16]. Non-nitric acid pickling solutions are often composed of sulfuric acid, hydrofluoric acid, and hydrogen peroxide. While hydrogen peroxide, as a substitute for nitric acid, plays a role similar to nitric acid in the pickling process, it is expensive, and easily decomposes into water and oxygen at the surface of metal at temperatures higher than 45  C [14]. Molten salts are very strong basic compounds, and generally require a high operating temperature of 350–550  C, which makes the process very effective for pickling or oxide removal, particularly for stainless steel [17]. When Fe or Cr metal reacts with NO3 at high temperature, it produces a bulky material, which generates fine cracks between the oxide and the reactant upon immediate water-cooling, due to thermal shock [18]. The permeation of the mixed acid (nitric acid + hydrofluoric acid) into these cracks facilitates the removal of the oxide layer, by dissolving the boundary between the oxide and the base metal. While many environmentally harmful substances are being replaced with other materials, no alternatives have yet been found that outperform the oxide removal ability of toxic molten salts, particularly in a moderate temperature range.

https://doi.org/10.1016/j.jiec.2017.12.038 1226-086X/© 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

B.-K. Kim et al. / Journal of Industrial and Engineering Chemistry 61 (2018) 388–397

We considered the use of an ionic liquid as a substitute for molten salts, as well as some acidic pickling solutions. Ionic liquids are of interest, since they can dissolve some metal oxide even in ambient condition. We therefore investigated the possibility of using some ionic liquids and their mixtures to replace the molten salt system for pickling a number of metal oxides. Selective extraction and dissolution of many metals from ores and various oxidized forms by ionic liquids have attracted significant attention in the steel industry over the last decade [15,16,19–21], and a variety of ionic liquids have been synthesized for this purpose. Further, the use of ionic liquids is more practical and environmentally friendly than molten salt, because of the negligible vapor pressure and recyclability. The main aim of this study was to review the possibilities of (1) a method of dissolving the metal oxide directly in the ionic liquid, (2) a method in which the oxide does not need to be directly dissolved in the ionic liquid, while other acids can transform the oxide layer into a special form that is easily removable, and (3) an efficient method of dissolving metal oxides by an additional secondary process, such as electrochemical anodization. The first point is the main theme of this review, while the second and third points are of continuous ongoing interest as additional strategies with some efficient ionic liquids for pickling. As a first stage, we focused on collecting ionic liquids with dissolution and extraction capabilities for Fe and Cr, which are two major components in stainless steels, as well as Cu and Zn, which are major components in brass.

Ionic liquids for the extraction and dissolution of metal and metal oxides Ionic liquids are substances that exist in a liquid state, where cations and anions are not in a crystalline state at temperatures below 100  C [22,23]. Many ionic liquids are present in a liquid state even at room temperature (25  C); these ionic liquids have the significant advantage of being able to be used in a relatively freely synthesized structure of cations and anions according to the purpose. Table 1 summarizes the structures of several cations and anions commonly used in ionic liquids. It is known that the combinations of cations and anions of these ionic liquids can theoretically synthesize approximately 1018 new ionic liquids. Ionic liquids are used as solvents, refrigerants, absorbents, electrochemical electrolytes, and lubricants because of their low volatility, high thermal stability, and good conductivity. The first ionic liquid synthesized was ethanolammonium nitrate, reported by Gabriel and Weiner in 1888 [24]. Studies on the extraction and separation of metals and metal oxides using ionic liquids started in earnest in the 1980s [25]. In early 1980, Seddon and Hussey reported on the dissolution of transition metal compounds using the ionic liquid chloroaluminate as a non-aqueous polar solution [26]. In the 1990s, several ionic liquids were reported to have been used as solvents for transition metal catalysts [27]. Up to the present day, various ionic liquids containing various cations and anions have been synthesized, and studies on the extraction efficiency of metal and metal oxides using the synthesized ionic

Table 1 General cation and anion structures of ionic liquids that are widely used for the extraction and dissolution of metals and metal oxides. Cation

389

Anion

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Table 2 Structures and names of ionic liquids used for the selective extraction and dissolution of Fe, Cr, Cu, and Zn. IL structure

IL name (abbreviation)

Metals

References

Methyltrioctylammonium chloride ([MTOA+][Cl])

Fe(III), Cu(II), Zn(II)

[41,46]

Trihexyl(tetradecyl)phosphonium chloride ([P66614][Cl])

Fe(III), Fe2O3, CuO, ZnO

[2,20,43,44]

Tricaprylmethyl-ammonium thiosalicylate ([A336][TS])

Cu

[7]

Trihexyl(tetradecyl)phosphonium salicylate ([P66614][SaI])

Cu, Cr

[7]

Trihexyl(tetradecyl)phosphonium thiosalicylate ([P66614][TS])

Cu, Zn

[7]

Trihexyl(tetradecyl)phosphonium 2-(methylthio) benzoate ([P66614][MTBA])

Cu

[7]

Tricapryl methylammonium thiocyanate ([A336][SCN])

Cu, Zn, Cr

[7]

Tricapryl-methylammonium 2-(methylthio) benzoate ([A336][MTBA])

Cu, Zn, Cr

[7]

1-Butyl-3-methylimidazolium hexafluorophosphate ([BMIM+][PF6])

Fe(III), Cu(II), Zn(II), Cr(III), Cr (IV)

[46,41,63]

1-Butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide ([BMIM+][NTf2]) Fe(III), Cu(II), Zn(II)

[46,41]

1-Octyl-3-methylimidazolium hexafluorophosphate ([OMIM+][PF6])

Cu(II), Zn(II), Cr(III), Cr(IV)

[41,46,63]

1-Octyl-3-methylimidazolium tetrafluoroborate ([OMIM+][BF4])

Fe(III), Zn(II)

[41,46]

1-Octyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide ([OMIM+] [NTf2])

Fe(III), Cu(II)

[41,46]

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391

Table 2 (Continued) IL structure

IL name (abbreviation)

Metals

References

Trihexyl(tetradecyl)phosphonium bis 2,4,4-trimethylpentylphosphinate (CYPHOS IL Fe(III), Zn(II) 104)

[48]

1-Butyl-3-methylimidazolium chloride ([BMIM+][Cl])

Fe, Cu, Zn

[6]

1-Butyl-3-methylimidazolium hydrogen sulfate ([BMIM+][HSO4])

Fe, Cu, Zn

[6]

2-Hydroxyethyltri-methylammonium chloride (choline chloride[ChCl])

FeO, Fe3O4, Fe2O3, Cu2O, ZnO

[42]

Betaine bis{(trifluoromethyl)sulfonyl}imide ([Hbet][Tf2N])

CuO

[9]

1-Hexylpyridinium hexafluorophosphate ([HPy][PF6])

Zn(II)

[91]

1-Hexyl-3-methylimidazolium hexafluorophosphate ([HMIM+][PF6])

Cr(III), Cr(IV)

[63]

1-Octyl-3-methylimidazolium salicylate ([OMIM+][salicylate])

Cr(III), Cr(IV)

[62]

1-Butyl-3-methylimidazolium salicylate ([BMIM+][salicylate])

Cr(III), Cr(IV)

[62]

1-Butyl-3-methylimidazolium thiosalicylate ([BMIM+][thiosalicylate])

Cr(III), Cr(IV)

[62]

1-Hexyl-3-methylimidazolium thiosalicylate ([HMIM+][thiosalicylate])

Cr(III), Cr(IV)

[62]

1-Hexyl-3-methylimidazolium salicylate ([HMIM+][salicylate])

Cr(III), Cr(IV)

[62]

1-Octyl-3-methylimidazolium thiosalicylate ([OMIM+][thiosalicylate])

Cr(III), Cr(IV)

[62]

392

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liquids have been published. Table S1 (in Supporting information) summarizes in alphabetical order the various types of metals that can be extracted and dissolved by ionic liquids. These results show that most of the metals, metal ions, and metal oxides can be dissolved and extracted in a single ionic liquid, or an appropriate combination of ionic liquids [28–91]. Dissolution and extraction of Fe and FexOx using ionic liquids Fe is the most common metal in the natural environment, is rich in reserves, and has high hardness. It is mainly extracted from iron ore, and after smelting and steelmaking, is used to make various types of steel products. According to the World Steel Association, the annual global steel production in 2015 was 1621 million tons, and a considerably large number of iron products were produced and used [92]. To produce steel with various characteristics, heat treatment at approximately 1300  C is performed, which results in the formation of iron oxide scales on the steel surface [93]. These iron oxide scales reduce the strength of the product and deteriorate its workability, and are therefore removed through a pickling process [14], in which nitric acid, sulfuric acid, hydrofluoric acid, and various combinations of these acids are used depending on the type of steel. As mentioned in the introduction, ionic liquids can be used to replace the pickling process and effectively remove the iron oxide scales due to their chemical and physical properties (e.g. metal extractability, low volatility, high stability, and possibility of recovery after use) [2,94]. Thus, such a process using ionic liquids is expected to enable an environmentally and technologically improved process. Table 2 summarizes the names and structures of ionic liquids used to dissolve and extract Fe and FexOx. In addition, Fig. 1 summarizes the extraction efficiencies of Fe and FexOx using ionic liquids. The figure shows that several ionic liquids can extract Fe3+ with good efficiency in a short period of time. De los Riós et al. reported the use of methyltrioctylammonium chloride ([MTOA+][Cl]) with 1 M hydrochloric acid and the use of 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM+] [PF6]) with 5 M hydrochloric acid [41,46]. In both cases, the extraction efficiency was almost 100% within 5 min. 1 M hydrochloric acid with other ionic liquids, such as 1-butyl-3-

methylimidazolium hexafluorophosphate ([BMIM+][PF6]), 1-butyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl}imide ([BMIM+][NTf2]), and 1-octyl-3-methylimidazolium bis{(trifluoromethyl) sulfonyl}imide ([OMIM+][NTf2]), showed approximately 20% extraction efficiency. In the case of 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIM+][BF4]), the extraction efficiency was less than 10%. Iron oxides such as FeO, Fe2O3, and Fe3O4 have been reported to require longer extraction times than Fe ion [41,46]. According to the results reported by Wellens et al., when Fe2O3 was extracted with trihexyl(tetradecyl)phosphonium chloride ([P66614][Cl]) + 12 M hydrochloric acid, it was extracted with approximately 65% efficiency in a relatively short period of time of 2 h [20]. The results of the extraction of FeO, Fe2O3, and Fe3O4 using choline chloride ([ChCl]) + 3.14 M hydrochloric acid, one of the most commonly used ionic liquids, were reported by Abbott et al. [42]. The extraction efficiency in this case was relatively low, at approximately 5%, even though it was treated for 48 h. Other interesting results in the direct extraction of Fe from ore have been reported using ionic liquids such as 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM+][HSO4]) [6]. It has also been reported that by using these ionic liquids, Fe can be extracted at an efficiency of approximately 35% in 48 h [6]. These results indicate that the Fe3+ ions dissolved in an aqueous solution can be extracted with relatively good efficiency over a short period of time using a relatively wide variety of ionic liquids. However, iron oxide samples require longer extraction time, and the extraction efficiency is poor. The synthesis of ionic liquids with good extraction efficiency for the extraction of iron oxide should therefore be further studied. Dissolution and extraction of Cr using ionic liquids The abundance of Cr is approximately 0.010% in the Earth’s crust, and Cr is the 21st most abundant element in the order of elemental reserves. Cr is a silver-colored transition metal that is easily broken, but not discolored. Alloys containing Cr are hard with excellent corrosion resistance, giving it a wide application range. Cr is mostly obtained from chromite (FeCr2O4) [95,96]. Cr reacts with oxygen in the air to form a thin, very dense chromium

Fig. 1. Comparison of the extraction and dissolution efficiencies of Fe and FexOx according to ionic liquids.

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oxide (Cr2O3) film that blocks further penetration of oxygen. Because of these characteristics, Cr is present in the air without rusting, and thus it is widely used for the electroplating of metal. In addition, when Cr is added in stainless steel at a ratio of 10%–20%, the strength of the stainless steel is increased, and the corrosion resistance is improved. Among stainless steels, the most commonly used steels are austenitic (or 300 series) stainless steels [97]. In particular, austenitic steels containing 18% Cr and 10% Ni are called 18/10 stainless steel, which is commonly used to manufacture tableware. Cr is also widely used in pigments, oxidants, glass cleaners, etchants, wood preservative, magnetic tapes, and leather mordants. However, the Cr often used in pigments is a Cr6+ compound, which is a highly toxic carcinogen, and should be avoided whenever possible. In rare cases, environmental problems arise when paint manufacturers release heavy metal contaminants, including Cr6+, into rivers or lakes. Therefore, it is important to develop a technique for selectively extracting Cr from various materials. Several studies have reported extracting Cr using ionic liquids (Fig. 2). In 2016, Sadeghi and Moghaddam reported the selective extraction of Cr using the imidazolium series of ionic liquids [62]. According to the report, [HMIM+][thiosalicylate] showed the best efficiency of 80.3% for the extraction of Cr6+, and [OMIM+][salicylate] showed the best efficiency of 92.5% for the extraction of Cr3+ during an 8.5 min extraction time. In a previous study, Sadeghi and Moghaddam extracted Cr3+ and Cr6+ by substituting three imidazolium cations with the [PF6] anion [63]. According to their paper, the extraction efficiency of the three ionic liquids was 80%–90% for a treatment time of 25 min for the Cr6+, and 61%–87% for a treatment time of 5 min for the Cr3+. The ionic liquid with the highest efficiency was [HMIM+][PF6]. If [HMIM+][PF6] is used, hexavalent and trivalent Cr can be extracted with an efficiency of approximately 90%. Other results for the extraction of Cr that include ionic liquids such as [A336] [SCN], [A336][MTBA], and [P66614][salicylate] have been reported [7]. In all three cases, approximately 10%–16% of Cr was extracted within 120 min. In another paper, it was reported that ca. 99% of Cr was extracted using trioctylammoniumpropanesulfonic acid bis (trifluoromethylsulfonyl)imide ([N888C3SO3H] [Tf2N]) [61]. However, because the extraction time of Cr was not given, it was not possible to compare the extraction efficiency with other results.

393

Dissolution and extraction of Cu and CuxOx using ionic liquids Cu is one of the most commonly used metals in the steel manufacturing industry, along with Fe. Cu is relatively soft compared to Fe, and has good machinability because of its fine malleability and ductility. In addition, because it has good thermal and electrical conductivity, Cu is widely used in electric wires and Cu tubes to facilitate heat transfer. Cu is used with zinc as the main material of brass [98]. Brass (generally made of 60%–70% Cu and 30–40% Zn) is widely used for ornaments, musical instruments, and parts of machines, because of its attractive color, high hardness, and strength [99,100]. Cu is mainly collected from minerals such as chalcopyrite (CuFeS2) through smelting [101]. The manufacturing process of Cu is similar to that of Fe, whereby it is placed into a furnace and melted. However, the sulfur contained in the chalcopyrite generates SO2, which is toxic [102]. This SO2 is used in the sulfuric acid production process, depending on the concentration, or is blown out into the atmosphere [32,102]. To obtain high-purity Cu, Cu needs to be further separated from metals such as Zn, Fe, and Ni using electrolysis. It has been reported that Cu can also be selectively purified and dissolved through ionic liquids. Table 2 shows the names and structures of ionic liquids used in the extraction and purification of Cu and CuxOx. Fig. 3 also shows the efficiency of Cu extraction using ionic liquids. Among the studies on the extraction of Cu, the selective extraction of Cu using ionic liquids from industrial wastewater was conducted in 2011 by Fischer et al. [7]. According to this report, treatment with tricaprylmethylammonium thiosalicylate ([A336][TS]) for 2 h can be used to collect Cu from industrial wastewater with 95% efficiency. Results were also reported for trihexyl(tetradecyl) phosphonium thiosalicylate ([P66614][TS]), where Cu was extracted at an efficiency of 81% [7]. The extraction of Cu from minerals using ionic liquids has also been reported. According to the reports, when [BMIM+][HSO4] + NaCl was used to treat Cu at 50  C for 48 h, Cu was extracted with an efficiency of approximately 22%, and the extraction efficiency of [BMIM+][Cl] + NaI at 50  C was approximately 13% [6]. [MTOA+][Cl] used for the extraction of Fe ions was also effective for the extraction of Cu ions [41,46]. According to a 2012 article by de los Riós, [MTOA+][Cl] + hydrochloric acid solution was used to extract ca. 80% of Cu ions [41]. The same

Fig. 2. Comparison of the extraction and dissolution efficiencies of Cr according to ionic liquids.

394

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Fig. 3. Comparison of the extraction and dissolution efficiencies of Cu and CuxOx according to ionic liquids.

article compared several imidazolium- and ammonium-based ionic liquids. [MTOA+][Cl] was only effective in the extraction of Cu ions (but not other imidazolium- and ammonium-based ionic liquids). The results of the high-efficiency extraction of CuO using ionic liquids were reported by Wellens et al. in 2014 [20]. According to their report, [P66614][Cl] + 9 M hydrochloric acid was used to extract CuO at almost 99% efficiency in 2 h. In addition, [P66614][Cl] showed excellent efficiency in the extraction of divalent cationic metal oxides, such as NiO, CaO, CoO, MnO, and ZnO. For these reasons, the authors assumed that a tetrachlorometallate(II) complex had been generated [20]. 2[P66614][Cl] + MO + 2HCl ! [P66614]2[MCl4] + H2O (M = Cu(II), Co (II), Zn(II), Ni(II), Mn(II)) (1) Another study that extracted CuO was reported by Nockemann et al. [9]. In this study, betaine bis{(trifluoromethyl)sulfonyl}imide ([Hbet][Tf2N]) was used, and the extraction efficiency was ca. 99% after 12 h [9]. Table S1 (in Supporting information) lists the names and structures of various ionic liquids that have been used for the extraction of Cu. Some of the ionic liquids used to extract Cu have been used as examples. Cu is an industrially important metal, along with Fe, and an extremely large amount is produced and used annually. If an ionic liquid could be used for the extraction and purification of Cu, it would offer considerable environmental and economic advantage. Dissolution and extraction of Zn and ZnO using ionic liquids Zn (together with Al and Cu) is one of the most commonly produced and consumed nonferrous metals. According to the International Lead and Zinc Study Group (ILZSG), approximately 13 million tons of Zn had been produced and consumed annually worldwide by 2014 [103]. Although Zn production is not comparable to that of Fe, it is clear that Zn is also an industrially important metal. When Zn is heated to 100–115  C, its ductility and malleability increase, which is advantageous for making thin films. Zn also has a zinc hydroxide carbonate ([ZnCO3]2[Zn(OH)2]3) coating on the surface in air to prevent internal corrosion; it is thus plated on the surfaces of other metals and used for corrosion prevention. It is also widely used as an electrode plate, a paint

pigment, and an alloy material with other metals. Zn is usually produced from zinc ore, and the most commonly used zinc ore is sphalerite (ZnS) [104]. The Zn smelting process is divided into wet and dry processes, although most Zn is now made by the wet process. In the wet process, a variety of zinc/iron oxides such as zinc ferrite (ZnOFe2O3) are formed, and a strong acid dissolution process using sulfuric acid is used to further extract Zn from the zinc/iron oxide. Large amounts of heavy metals and sulfide waste are generated during this process. Usually, because of the high disposal costs, these wastes are permanently stored. Therefore, it is necessary to develop a low-cost, high-efficiency, environmentally friendly process that does not use a strong acid in Zn smelting. Various ionic liquids capable of selectively dissolving and extracting Zn have been reported. Table 2 summarizes the names and structures of ionic liquids reported to be able to selectively extract Zn, while Fig. 4 summarizes the efficiency of the selective extraction of Zn. The figure shows that [MTOA+][Cl], [P66614][Cl], and [OMIM+][BF4] have been found to extract Zn at an efficiency of ca. 90% or more within a relatively short period of time of 2 h [20,46]. [MTOA+][Cl] and [P66614][Cl] also extract Fe and Cu with good efficiency (more than 60%). However, [OMIM+][BF4] is rarely used to extract Fe and Cu; only Zn is selectively extracted at an efficiency close to 95%. This selective metal extraction capability of the ionic liquid can increase its utilization. If several metals need to be extracted from samples simultaneously with Fe, Cu, and Zn, an ionic liquid such as [MTOA+][Cl] or [P66614][Cl] can be used. However, if only specific metal ions need to be selectively extracted, an ionic liquid such as [OMIM+][BF4] can be used. Then, only a specific metal (e.g. Zn) would be extracted with good efficiency according to the purpose. Although a variety of ionic liquids have already been reported, ionic liquids with better efficiencies through the combination of cations and anions are likely to be synthesized in the future. One study reported the selective extraction of Zn using 1-hexylpyridinium hexafluorophosphate ([HPy+][PF6]) in water and milk samples [91]. According to the report, when a [HPy+][PF6] + 55 mM oxine solution was treated in a pH 9.5 borate buffer solution for 5 min, almost 99% of the Zn in the water and milk was selectively extracted. It was also reported that when trihexyl(tetradecyl) phosphonium bis 2,4,4-trimethylpentylphosphinate ([CYPHOS IL

B.-K. Kim et al. / Journal of Industrial and Engineering Chemistry 61 (2018) 388–397

395

Fig. 4. Comparison of the extraction and dissolution efficiencies of Zn and ZnO according to the ionic liquids.

104]) + 0.5 M HCl was used, approximately 83% of the Zn was extracted in 6 min [48].

electrochemical potential control, and application of ultrasonic waves, as well as various simultaneous optical treatments with UV or IR wavelength range.

Conclusion Acknowledgements We reviewed studies of the effective extraction and dissolution of a number of major components in various types of steel and brass, such as Fe, Cr, Cu, and Zn, by ionic liquids. An important aim of this study was to present the general trends and tendencies of applicability of ionic liquids for the removal of various metal oxide scales. In particular, we summarized the extraction efficiencies of various ionic liquids reported in the literature, and arranged them into a unified framework for easy comparison. In general, ionic liquids can be used to extract metals in specific ionic states in an aqueous solution phase with relatively high efficiency in a short period of time. However, it is more difficult to extract or dissolve metals from their solid oxide form, and it is not yet effectively applicable for scale removal processes such as pickling in the steel industry. In addition, the application of ionic liquids in industrial fields has so far been ineffective, due to the lack of economic feasibility, length of synthesis time, and low possibility of mass production [105]. However, some research has recently been carried out on the economic feasibility of ionic liquids [106,107]. Especially, Zhai and Rubin examined the technical application and evaluation for the economic cost of ionic liquid used in power plants [106]. Thus, on the basis of these efforts, it is expected that economic ionic liquids will be developed that are applicable to viable industrial systems for the dissolution and extraction of metals in the near future [108]. According to this review, it is expected that several ionic liquids will be designed for extracting and dissolving some specific metals with high selectivity from scales of various types of novel steels and their sludge. Further experimental works and studies are ongoing to deduce the optimum conditions of metal extraction/dissolution, as well as the compositional design of the ionic liquids solution, which includes additives and co-solvents for effective application as alternatives to various oxide removal processes. Additionally, the applicability and effectiveness can be considerably improved by combination with other experimental techniques, such as

J. Lee was supported by a grant from the Dongguk University Research Fund of 2016, and B. Kim was supported by the Basic Science Research Program through the National Research Foundation (NRF) of Korea, funded by the Ministry of Science, ICT and Future Planning (NRF-2015R1C1A1A01055250). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.jiec.2017.12.038. References [1] A.P. Abbott, G. Capper, D.L. Davies, R.K. Rasheed, P. Shikotra, Inorg. Chem. 44 (2005) 6497, doi:http://dx.doi.org/10.1021/ic0505450. [2] C. Pedrazzini, P. Giordani, Process for stainless steel pickling and passivation without using nitric acid, US 5843240 A, 1998. https://www.google.tl/ patents/US5843240. [3] L.F. Li, P. Caenen, M. Daerden, D. Vaes, G. Meers, C. Dhondt, J.P. Celis, Corros. Sci. 47 (2005) 1307, doi:http://dx.doi.org/10.1016/j.corsci.2004.06.025. [4] American Iron and Steel Institute, Cleaning and Descaling Stainless Steels, American Iron and Steel Institute, Washington, DC, 1982. [5] J.A. Whitehead, J. Zhang, N. Pereira, A. McCluskey, G.A. Lawrance, Hydrometallurgy 88 (2007) 109, doi:http://dx.doi.org/10.1016/j.hydromet.2007.03.009. [6] J.A. Whitehead, J. Zhang, A. McCluskey, G.A. Lawrance, Hydrometallurgy 98 (2009) 276, doi:http://dx.doi.org/10.1016/j.hydromet.2009.05.012. [7] L. Fischer, T. Falta, G. Koellensperger, A. Stojanovic, D. Kogelnig, M. Galanski, R. Krachler, B.K. Keppler, S. Hann, Water Res. 45 (2011) 4601, doi:http://dx.doi. org/10.1016/j.watres.2011.06.011. [8] A.P. Abbott, J.C. Barron, M. Elhadi, G. Frisch, S.J. Gurman, A.R. Hillman, E.L. Smith, M.A. Mohamoud, K.S. Ryder, ECS Trans. 16 (2009) 47, doi:http://dx.doi. org/10.1149/1.3114008. [9] P. Nockemann, B. Thijs, S. Pittois, J. Thoen, C. Glorieux, K. Van Hecke, L. Van Meervelt, B. Kirchner, K. Binnemans, J. Phys. Chem. B 110 (2006) 20978, doi: http://dx.doi.org/10.1021/jp0642995. [10] H.E. Everson, F.P. Ilenda, Alkaline composition, US 2931778 A, 1954. [11] Z. Shanghuai, Pickling treatment technique for stainless steel, CN 105671566 A, 2014.

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