Behaviors and Mechanism of Iron Extraction from Chloride Solutions

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Industrial & Engineering Chemistry Research

The Behaviors and Mechanism of Iron Extraction from Chloride Solutions Using Undiluted Cyphos IL 101 Li Cui†, ‡, Fangqin Cheng†,∗, and Jingfang Zhou‡,∗ †

Institute of Resources and Environment Engineering, State Environmental Protection Key Laboratory of Efficient Utilization Technology of Coal Waste Resources, Shanxi University, Taiyuan 030006, China ‡

Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095, Australia

Abstract In this study, iron(III) extraction from acidic chloride solutions using undiluted trihexyltetradecylphosphonium chloride (Cyphos IL 101) was carried out in a liquid-liquid extraction process. The extraction behaviors under various HCl, chloride and iron(III) concentrations, selectivity and extraction isotherm of iron(III) were investigated. It was found that iron(III) was extracted fast and efficiently in a wide chloride concentration range. The highly selective separation of iron(III) from aluminum(III), calcium(II), magnesium(II) and potassium(I) in acidic chloride solutions was achieved with a separation factor of Fe(III) over Al(III) at 11,000 from a 3 M HCl solution. The maximum loading capacity of iron(III) reached at 83.2 g·L-1 with a molar ratio of 0.91 for Fe(III)/Cyphos IL 101. Effective stripping of the loaded iron(III) was achieved with a 0.5 M H2SO4 solution. The iron-chloro complexes in both aqueous phase and Cyphos IL 101 phase were characterized using spectroscopic techniques. UV-Visible and Raman spectra confirmed that iron(III) formed a series of iron-chloro complexes in acidic chloride solutions, while present solely in the form of tetrachloroferrate complex ([FeCl4]-) in the Cyphos IL 101 phase. The extraction mechanism was proposed that both FeCl3 ion association and [FeCl4]- anion exchange with the chloride anion of Cyphos IL 101 play the key role during iron(III) extraction. Keywords: Solvent extraction; Cyphos IL 101; Ion association; Anion exchange; Iron removal ∗

Corresponding Authors. Tel.: + 86 351 7018813. E-mail address: [email protected]; Tel: + 61 8 8302 6867. E-mail

address: [email protected]

1

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1. Introduction Hydrometallurgical processes usually consist of three main steps including leaching, leachate purification and metal recovery. During the leaching process, especially acid leaching, iron, which is commonly found in many different ores, is usually present in the leaching solutions as an impurity along with other metals. For example, in the process to recover aluminum from coal gangue via acid leaching, there is about 5-10% (w/w) of iron present in the leach solution, which contaminates the resultant aluminum products by coloring them to yellow. Therefore, the removal of iron from leach liquors is very important in hydrometallurgical processes. At present, iron is usually removed from leach solutions by precipitation.1,2 However, this method has some drawbacks, such as low selectivity due to co-precipitation and generation of fine precipitates which are difficult to remove from the leachate.3 Furthermore, the precipitates, commonly containing heavy metal ions,4,5 are of environmental concern. In addition, their disposal in controlled ponds is becoming more and more expensive due to strict environmental regulations. Solvent extraction can separate, purify and concentrate metal ions, leading to subsequent production of pure products. It has thus been extensively explored as an alternative for the removal of iron from different leach liquors, spent acids and metallurgical wastes.6-8 A variety of different extractants have been investigated to extract iron including di(2-ethylhexyl) phosphoric acid (D2EHPA), tri-n-butyl phosphate (TBP), methyl isobutyl ketone (MIBK), phosphine oxides such as Cyanex 921 and Cyanex 9239-11 and N,N-diethyldodecanamide (DEDA).12 They are effective with high selectivity and efficiency. However, conventional solvent extraction uses both organic extractants and diluents. Organic solvents are commonly flammable and poisonous, causing safety and environmental issues. It is thus of great importance to explore new liquid-liquid systems for the recovery of metals without the use of organic solvents. Room Temperature Ionic Liquids (RTILs) are well known as green and designable solvents. They have many advantageous features including low vapor pressure, thermal stability, low flammability and negligible volatility, which overcome the drawbacks of organic solvents.13 In recent years, hydrophobic RTILs as the extractant have been studied for recovering alkali 2


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metals, alkali earth metals, precious metals and heavy metals.14-18 Among those, Cyphos IL 101 trihexyl(tetradecyl) phosphonium chloride or [P14,6,6,6][Cl] is extensively studied to extract metal ions such as uranium(VI), zinc(II) and palladium(II) from their chloride solutions due to its economical advantage.19-23 However, organic solvents such as toluene, chloroform or xylene are commonly used to dilute Cyphos IL 101 in order to reduce its viscosity. In these cases, Cyphos IL 101 is used solely as the extractant and the advantages of employing RTILs are therefore lost. It has been reported that the viscosity of pure Cyphos IL 101 is 24.69 Pa·S at 20 °C, and it drops to 11.10 Pa·S by mixing with 1% water.24 Therefore, the viscosity of Cyphos IL 101 can be significantly reduced when it contacts with water during the extraction process. The undiluted RTILs as both extractants and diluents to selectively extract precious and base metals without adding any organic extractant and solvent have been carried out in our previous study17. Most recently, a number of researchers used undiluted RTILs to extract various metals including rare earths in batch scales.25-27 They further verified the feasibility of employing undiluted RTILs operated in a continuous process, leading to the practical applications of undiluted RTILs in liquid-liquid extraction. Recently, special attention has been paid to hydrochloric acid leaching due to its mild leaching conditions, fast leaching rate, high metal solubility and ready HCl recycling. Cyphos IL 101 diluted with chloroform to separate iron(III) and nickel(II) from hydrochloride solutions has been reported by Daniel et al.20 It was found that the iron extraction was fast, highly selective and efficient. However, the extraction of iron from hydrochloride solutions using undiluted Cyphos IL 101 has not been found in the literature. In addition, it was generally believed that iron was transferred into the RTIL phase in the form of [FeCl4]- via an anion exchange mechanism. No reports have been found on the detailed mechanism of iron transfer from hydrochloride solutions. In this paper, the behaviors of iron extraction from acidic chloride solutions using undiluted Cyphos IL 101 were investigated. Spectroscopy analysis was applied to establish the extraction mechanism. The feasibility of removal of iron using this technology from coal gangue leachate was verified. 2. Experimental 2.1 Aqueous solutions and ionic liquid phase 3



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All chemical reagents including FeCl3·6H2O (98%), AlCl3·6H2O (98%), HCl (37%), HNO3 (70%), NaCl (99%), LiCl (99%) and C2H5OH (100%) were purchased from Sigma-Aldrich, while Trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101, 95%) was purchased from Io-Ii-Tec, Germany. All chemicals are AR grade and were used without further purification. The aqueous stock solutions were prepared by dissolving the required amounts of FeCl3·6H2O and AlCl3·6H2O in deionized water. The acid concentrations of the solutions were adjusted by adding required volumes of concentrated HCl solution, while the chloride concentrations in acid solutions were controlled by adding required amounts of NaCl or LiCl. The effect of iron(III) concentration on extraction efficiency was investigated in the range between 4.5 and 72 g·L-1 in 3 M HCl solutions. The separation efficiency of Fe(III) over Al(III) was studied under various concentration ratios of Al(III) to Fe(III) in 3 M HCl solutions. 1 mL of undiluted Cyphos IL 101 was used as the extraction phase and was measured by the equivalent mass on a balance. 2.2 Instruments and measurements The metal ion concentrations in the aqueous phase were determined using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-AES, Perkin Elemer-Optima 5300 DV). Each ICP data point was reported based on at least two measurements with a data error within 3% of each other. The average value of the total measurements was then reported. Infrared spectra were recorded on a Thermo Nocolet FT-IR Nexus 470 in an Attenuated Total Reflection (ATR) mode with a 2 cm-1 of resolution. Before IR measurements, the samples were washed three times with deionized water to remove extracted acid in the ionic liquid phase and then evaporated under vacuum to remove water remaining in the ionic liquid. Raman spectra were performed on Alpha300R microscopy /spectroscopy (Witec, Germany) with a spectral resolution down to 1 cm-1. After phase separation, the Fe(III)-loaded Cyphos IL 101 was collected and measured without any further treatment. The forms of iron species present in the aqueous and RTIL phases were qualitatively measured using UV-Visible spectrophotometer (SHIMADZU UV-2600) with a 1 nm of resolution. The Fe(III) concentration in each sample solution was kept at around 0.4 mM to avoid a saturated absorption, while LiCl was selected as a chloride source. Ionic liquid samples containing 4


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extracted iron(III) were diluted using ethanol before measurement. For each sample, Fe-free blank solution was used as the background. 2.3 Extraction Procedure The iron(III) extraction was carried out under room temperature (25±2℃) at a Cyphos IL 101/water volume ratio of 1: 2. Specifically, 1 mL of undiluted Cyphos IL 101 and 2 mL of aqueous phase containing metal ions were brought into contact and mixed vigorously for 30 min using a magnetic stirring apparatus (RT 10, IKA). Phase separation was achieved by centrifugation at 4000 rpm for 5 min (2-16p, Sigma). The effect of contact time on extraction efficiency was studied by varying the mixing time while the remaining experimental conditions were kept constant. The saturation experiments of undiluted Cyphos IL 101 with water at each extraction solution pH were carried out under the same experimental conditions used in the extraction. The volume changes of the aqueous phase and ionic liquid phase after saturation were measured and used in the following calculations. For each influencing factor on iron(III) extraction such as HCl, chloride and iron(III) concentration, at least six variables were chosen in order to observe a reasonable trend for the data points. Each data point represents a single measurement. However the data points appearing at a turning point on a graph or at a distance from a trend line were measured at least three times. The data adopted on the graph was the average of the total measurements. For the ions in a single condition (as shown in Table 2), the experiments were repeated three times in order to minimize data error and the data shown represent the average of these measurements. The concentrations of the metal ions in the aqueous phase were determined via ICP. The extraction efficiency, distribution coefficient and separation factor of metal ions were calculated using the following equations. The extraction percentage (E) of a metal is defined as

% EM =

V0 × [ M ]0 − Vaq × [ M ]aq V0 × [ M ]0

× 100

The distribution ratio (D) of a metal was calculated using the following equation:

5



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D=

[ M ] IL V0 × [ M ]0 − Vaq × [ M ]aq = [ M ]aq VIL × [ M ]aq

where V0 and Vaq denote the volumes of the aqueous phase before and after extraction (mL), [M ]0 and [ M ]aq denote the metal concentrations in the aqueous phase before and after extraction (g·L-1), [ M ]IL denotes the metal concentration in the ionic liquid phase after extraction (g·L-1), VIL is the volume of the ionic liquid (mL). The separation factor (α) expresses the efficiency of a separation between two metals and is defined as

αM

1 ,M 2

=

DM 1 DM 2

where DM 1 and DM 2 are the distribution ratios of metal M1 and M2, respectively. 2.4 Stripping tests The various solutions including water, 0.5 M HCl, 1 M HCl, 0.1 M H2SO4, 0.5 M H2SO4 and 1 M H2SO4 were selected as stripping solutions. The volume ratio of the stripping solution to Fe(Ⅲ)-loaded ionic liquid phase was kept at 4:1. Fe(III)-loaded ionic liquid phase containing approximately 50 g·L-1 Fe (Ⅲ) was contacted with stripping solutions and stirred vigorously at 1000 rpm for 30 min at 25±2°C. The subsequent phase separation was achieved by centrifugation at 4000 rpm for 5 min. The Fe(Ⅲ) concentration in the stripping solutions was measured by ICP. Stripping was repeated four times consecutively using a fresh stripping solution. The stripping percentage (S) of Fe(Ⅲ) is defined as

%S =

Vs × [ Fe]s × 100 Vo × [ Fe]o

VS and VO denote the volumes of the stripping solution and Fe(Ⅲ)-loaded organic phase

(mL). [ Fe]o denotes Fe(Ⅲ) concentration in the organic phase before stripping (g·L-1). [ Fe]s denotes the Fe(Ⅲ) concentration in the aqueous phase after stripping (g·L-1).

3. Results and discussion 6


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3.1 Extraction behaviors 3.1.1. Effect of HCl concentration The extraction of 13.5 g·L-1 Fe(III) in the feed solutions using undiluted Cyphos IL 101 was carried out by varying HCl concentrations ranging from 0 to 10 M. The results are given in Figure 1. Without the addition of HCl in the feed solution, 88.3% of Fe(III) was extracted by Cyphos IL 101. With the increase of HCl concentration, the extraction percentage of Fe(Ⅲ) increased and reached a plateau at HCl concentrations above 3 M, where more than 99.7% of Fe(III) was extracted. A turning point where the Fe(III) extraction percentage decreased with the increase of HCl concentration was observed by Vander Hoogerstraete et al. at a HCl concentration of about 10 M, which was the highest HCl concentration used in our study, implying the same trend was observed in our experiments.28. As the Cyphos IL 101 was not pre-saturated with water at the extraction pH, the HCl was also extracted into Cyphos IL 101 phase together with Fe(III), leading to the acidity decrease of the aqueous phase. After extraction, the acidity of the aqueous solution was measured using pH paper and found more acidic than pH 2.8 under all extraction conditions. As the hydrolysis and precipitation of FeCl3 occur in aqueous solution at pH 2.8, precipitates were not observed in the aqueous phase after extraction. The effect of contact time on the extraction of Fe(Ⅲ) was further studied. It was found that the maximum extraction percentage was achieved within 5 min, indicating Fe(III) extraction using Cyphos IL 101 was fast. In addition, phase separation after mixing was very fast and the formation of emulsions or the third phase was not observed during extraction. On the contrary, the formation of a third phase was generally encountered especially in HCl media during conventional solvent extraction where organic extractants and dilutes were applied.29 3.1.2. Effect of Cl- concentration When varying HCl concentrations, both solution acidity and chloride concentration are changing. In order to study the effect of Cl- concentration on iron(III) extraction, the Clconcentrations were adjusted by adding required amounts of NaCl in the feed solutions, while the HCl concentration was fixed at 1 M. The extraction of 13.5 g·L-1 Fe(III) in the feed solutions was then studied by varying Cl- concentrations in the range of 1.72 to 5.72 M. The 7



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results were plotted and shown in Figure 2. With the increase of chloride concentrations, the extraction percentage of Fe(III) increased from 98.3 to 99.7%. The influence of NaCl concentrations on Fe(III) extraction had the same trend as that of HCl, indicating NaCl can be used as a chloride source to enhance Fe(III) extraction. This implies that highly efficient extraction of Fe(III) using Cyphos IL 101 can be achieved at lower acid concentration media, while high concentration of HCl is needed when organic phosphine such as TBP, Cyanex 921 and Cyanex 923 are used to extract Fe(III) from acid chloride solutions.9 It was proposed that chloride ion concentrations in the feed solutions play the key role in iron(III) extraction, while the hydrolysis of Fe(Ⅲ) is depressed by the acidity of the solutions. 3.1.3. Isotherm of iron extraction The isotherm of iron(III) extraction was conducted to understand the extraction mechanism of Fe(III) using Cyphos IL 101. 1 mL of Cyphos IL 101 was used, while the Fe(III) concentrations in 2 mL of 3 M HCl aqueous solution were varied from 4.5 to 72 g·L-1. The concentrations of Fe(Ⅲ) in Cyphos IL 101 phase against the corresponding ones in the aqueous phase were plotted and shown in Figure 3. It can be seen that the loading of Fe(Ⅲ) in Cyphos IL 101 was increased with the increase of Fe(Ⅲ) concentrations and then reached a maximum. The maximum loading of Fe(Ⅲ) in Cyphos IL 101 was calculated at about 83.2 g·L-1, which is equivalent to 1.49×10-3 mole of Fe(Ⅲ). As 1 mL of Cyphos IL 101 is equal to 1.64×10-3 mole of Cyphos IL 101, the molar ratio of Fe(Ⅲ) to Cyphos IL 101 is about 0.91. It has been reported that the HCl can be extracted in the Cyphos IL 101 phase and present in the form of [HCl2]-.26 Water can interact with Cyphos IL 101 via the formation of a weak hydrogen bond between the Cl- anion of Cyphos IL 101 and water molecules. The excess of the Cyphos IL 101 is thus assumed to be occupied by HCl and water due to their co-extraction with Fe(III). The maximum loading of Fe(III) can be affected by the co-extraction of acid. 3.1.4 Selective extraction of Fe (Ⅲ) against other metal ions Acid leaching is a common method used in the treatment of coal gangue. The major metal ions present in HCl leach solution from coal gangue include Al(III), Mg(II), Ca(II) and K(I), apart from Fe(III). The presence of Fe(III) in the leach solution affects the extraction and 8


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purity of the target Al products. The selective removal of Fe(III) against these metal ions especially Al(III) is thus of very importance. The feasibility of the current technique was then testified in a synthetic solution to mimic the industrial HCl leach solutions from coal gangue. The chemical composition and concentration of the metal ions in the coal gangue leach solutions vary significantly. Generally, there are 6-18.5 g·L-1 Fe(III), 1-7.5 g·L-1 Mg(II), 1.5-9.3 g·L-1 Ca(II), and 1.3 -7.7 g·L-1 K(I) in the leach solutions. The Fe(III) concentration was then chosen at 13.5 g·L-1 and each of other metal ions such as Mg(II), Ca(II) and K(I) was kept at 5 g·L-1 in the synthetic solution. Initially, the selective extraction of Fe(III) over Al(III) was carried out at different Al(III) / Fe(III) concentration ratios in 3 M HCl solutions. The Fe(III) and Al(III) concentrations remaining in the feed solutions after extraction, the distribution coefficient, and separation factor of Al(III) over Fe(III) are listed in Table 1. The distribution coefficient of Fe(Ⅲ) is big, indicating Fe(III) was largely extracted into Cyphos IL 101, while Al(III) has a very small distribution coefficient, implying that most of the Al(III) was remained in the aqueous phase. Cyphos IL 101 is thus a highly selective extractant to separate Fe(III) from Al(III). Furthermore, the distribution coefficient and separation factor of Fe(III) increased significantly with the concentration increase of Al(III), which can be attributed to the salting-out effect during liquid-liquid extraction. It has been reported that Al(Ⅲ) can have a strong salting-out effect due to its smaller ion radii and higher charge. Furthermore, the presence of Al(III) in the aqueous phase can decrease the dielectric constant of the aqueous phase and thus depress Fe(Ⅲ) hydration, which can further enhance Fe(Ⅲ) extraction.30 The extraction of Fe(III) from mixed solutions containing Mg(II), Ca(II) and K(I) was further carried out in 3 M HCl solutions. The results shown in Table 2 indicate that Mg(II), Ca(II) and K(I) are hardly extracted by Cyphos IL 101. The presence of these metal ions in the solution did not interfere with the extraction of Fe(Ⅲ), on the contrary, they enhanced the extraction of Fe(III) due to salting out effect. 3.1.5. Stripping The back extraction of Fe(III) from Cyphos IL 101 using selected stripping solutions was carried out. The stripping percentage of Fe(Ⅲ) for each back extraction stage is given in 9



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Table 3. Fe(III) was back extracted with 0.5 and 1 M HCl, respectively. Less than 10% of total Fe(III) was stripped after three stages of stripping, indicating that HCl is not effective to strip Fe(III) from Cyphos IL 101. Water can back extract about 50.8% of Fe(Ⅲ) after four stages of stripping. However, sulfuric acid was found to be the most effective stripping solution. The stripping percentage of Fe(III) increased with the increase of H2SO4 concentration in the stripping solution. Fe(Ⅲ) was fully back extracted with 1 M H2SO4 after four stages of stripping. The Cyphos IL 101 after stripping was washed with 3 M HCl to scrub off residual metal ions and regenerate Cyphos IL 101. The recycled Cyphos IL 101 was reused to extract Fe(Ⅲ) from freshly prepared solutions. The extraction percentage of Fe(Ⅲ) can reach 99%, which is as high as that achieved using fresh Cyphos IL 101. The regeneration of Cyphos IL 101 after extraction and stripping stages is of great significance in the practical applications of Cyphos IL 101 in metal extraction. The detailed experiments on Fe(III) stripping from Cyphos IL 101 and its recycling have been completed and the results will be announced soon.

3.2 Spectroscopic characterizations of Iron-chloro species 3.2.1 Characterizations of Iron-chloro species in aqueous solutions Iron-chloro complexes in aqueous solutions have been studied by many researchers using UV-Visible spectroscopic analysis.31-34 In the aqueous solutions, iron has the tendency to form a series of iron chloride complexes in acid chloride media with a distinct distribution of the species Fe3+, [FeCl]2+, [FeCl2]+, FeCl3 and [FeCl4]-, depending on chloride concentrations and solution conditions.35 In this study, the formation of Fe(Ⅲ) species both in 1 M HCl solutions in the Cl- concentration range from 1 to 13 M and in concentrated HCl solutions was investigated, respectively. The detailed compositions in each sample solution can be found in the supporting information. The UV-Visible spectra of the samples were collected at 25℃ and shown in Figures 4 and 5. When the Cl- concentration is lower than 3 M, two major bands appears at 222 and 336 nm due to the formation of [FeCl]2+ complex. A new broad band appears at 344 nm when the chloride concentration was increased above 5 M, which is attributed to the formation of [FeCl2]+. When the chloride concentration was increased above 7 M, a new peak at 360 nm 10


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and a shoulder at 314 nm appear due to the absorption of FeCl3(aq). When the chloride concentration exceeded 9 M, a new peak at 258 nm appears, meanwhile, the absorption maximum at 360 nm is shifted 4 nm to a longer wavelength and becomes more intensive, indicating [FeCl4]- is the dominate species in the solution. These results and the calculated molar absorptivity (ε) of each species are in accordance with those reported in previous studies .33,35 However, the UV-Visible absorption spectra of iron(Ⅲ)-chloro complexes in concentrated HCl solutions have not been reported so far to the best of our knowledge. Figure 5 shows the UV-Visible spectra of iron(Ⅲ)-chloro complexes in a series of HCl concentrations ranging from 6 to 12 M. Three distinct absorption bands appearing at 242, 314 and 362 nm were observed, which are different from those shown in Figure 4 under the same chloride concentrations. These three bands have been reported when the spectrum of [FeCl4]- was recorded in organic phase.25,

35

The shift of the characteristic bands of [FeCl4]- in

concentrated LiCl and HCl solutions can be explained by solvent effects on UV-Visible spectra, which are affected by solvent polarity and acid concentration. As H+ ion is more hydrophobic than Li+ ion, concentrated HCl solutions show less polarity or become more hydrophobic than concentrated LiCl solutions. On the other hand, H+ ions have stronger tendency than Li+ ions to replace the water molecules associated with iron-chloro complexes. This might explain why the UV-Visible absorption bands originated from concentrated HCl solutions appeared at the same wavelengths as those from hydrophobic organic media. 3.2.2. Characterizations of Fe(Ⅲ) species loaded in Cyphos IL 101 In order to understand the Fe(III) species present in Cyphos IL 101 phase, the UV-Visible spectra of Fe(Ⅲ)-loaded Cyphos IL 101 were recorded and shown in Figure 6 (in ultraviolet range) and Figure 7 (in visible range). Three bands appear at 242, 315 and 362 nm in UV region and another three major bands are found at 530, 620 and 685 nm in visible region, which can be assigned to the characteristic absorption bands of [FeCl4]- according to the results shown in Figure 5, as well as previous reports.25,

35-38

The molar absorptivity of

[FeCl4]- is strong in the 200 - 500 nm wavelength region, indicating that these bands originate from ligand to metal (L→Fe(III)) charge transfer transitions. In the 500 - 900 nm wavelength 11



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region, its molar absorptivity is much weaker (≤ 1.5 L·cm-1·mol-1), which is caused by d-d transitions.39,40 The above results indicate that [FeCl4]- is the only complex formed in Cyphos IL 101 phase. Fe(III)-loaded Cyphos IL 101 was further characterized by Raman and FT-IR spectroscopy. A sharp peak appears at 333.75 cm-1 in Raman spectrum (in Figure 8), which is assigned to the stretching vibrations of the symmetric Fe–Cl bond present in [FeCl4]-.41,42 Raman analysis further proves the existence of [FeCl4]- anion in Cyphos IL 101. IR spectra of undiluted Cyphos IL 101 and purified Fe(III)-loaded Cyphos IL 101 were recorded and shown in Figure 9. Both samples have absorption bands appearing at 2928, 2855 and 1457 cm-1, which are assigned to the aliphatic C-H vibrations from [P14,6,6,6]+ cation. However, undiluted Cyphos IL 101 presents three extra absorption bands at 3370, 3380 and 1626 cm-1. These bands are caused by the absorption of free water in Cyphos IL 101, which wasn’t purified to remove water before measurement. These bands disappeared for purified Fe(III)-loaded Cyphos IL 101 sample due to the removal of water from Cyphos IL 101 phase. Apart from water absorption bands, the FTIR spectra of both samples are identical, indicating that [P14,6,6,6]+ cation was not altered during extraction process.

3.3 Discussion It has been well known that metal ions tend to stay in aqueous phase due to their hydrated nature. Replacing water molecules associated with metal ions with ligands to form metal complexes can change the hydration environment of the metal ions, therefore enhancing their affinity to hydrophobic phase. In acidic chloride solutions, chloride ions act as ligands. When they replace the water molecules associated with metal ions to form chloride complexes in the aqueous solutions, metal chloro complex becomes more hydrophobic and extractable to the oil phase. However, different metal ions have different affinity to water molecules and chloride ions, which can be explained by the Hard Soft Acid Base (HSAB) principle. According to this principle, both water molecule and chloride ion are hard bases, but the former is harder than the latter. On the other hand, Group IA and IIA metals belong to hard acids. When the order of group A metals moves from IA to VA, the hardness decreases and the softness increases. The well-accepted empirical rule is that ‘hard likes hard and soft likes 12


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soft’, indicating group I and II A metals have higher affinity to water molecules, so they are highly hydrated and tend to stay in water.17 This explains why metal ions including Na+, K+, Ca2+ and Mg2+ cannot be extracted into Cyphos IL 101 from acidic chloride solutions. Aluminum ion, Al3+, in Group IIIA, has inert electronic structure and is weakly polarizable. It thus belongs to hard acid due to its high charge and small ion radii. Therefore, it shows the same trend as Ca2+, Mg2+ and K+, which prefers to stay in the aqueous phase. Fe3+, in Group VIII, belongs to a hard acid, however, compared to Al3+, alkaline and alkaline earth metal ions, Fe3+ has unoccupied d orbitals and free d electrons, which can easily accept the electron pair of ligands to form a stronger bond with them. It thus has the tendency to form softer and more extractable chloride complexes in acidic chloride solution. However, iron-chloro species can form different types of complexes depending on the iron and chloride concentrations and solution pH. Which type of iron-chloro complex is extracted into oil phase and its mechanism depend on the solution conditions. In most studies, the mechanism of metal ion extraction from acid chloride solutions using Cyphos IL 101 was generally believed via an anion exchange process.19-22 During the process, metal complex anions move from aqueous phase to organic phase, while anions in the organic phase transfer from organic phase into aqueous phase. Specifically, [FeCl4]- complex moves into Cyphos IL 101 phase, while Cl- transfers into aqueous phase to achieve charge balance in each phase. In order to understand the underlying mechanism of Fe(III) extraction using Cyphos IL 101 from acidic chloride solutions, the iron(III) extraction was carried out by varying Clconcentrations in the range of 1 - 13 M in both 0.3 and 1 M HCl solutions, respectively. The results are shown in Table 4. It can be seen that Fe(III) can be highly extracted into Cyphos IL 101 from all solution conditions except for the one containing 1 M Cl- and 0.3 M HCl solution. It has been confirmed by UV-Visible spectra that [FeCl]2+ is the main species in the [Cl-] range from 1 to 3 M, while [FeCl2]+ at 3 to 5 M of [Cl-], FeCl3 at 7 to 9 M of [Cl-], and [FeCl4]- at above 11 M of [Cl-], respectively. The anionic complex [FeCl4]- dominates in high concentration chloride solutions and its concentration decreases with the decrease of chloride concentration in the aqueous solution. A very low concentration of [FeCl4]- exists at a low chloride concentration shown in ours and previous spectroscopic studies.31,35 Under this condition, [FeCl4]- may be extracted into Cyphos IL 101, but reach a distribution equilibrium 13



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between the two phases, leading to a low extraction percentage of Fe(III) at low chloride concentrations. However, Fe(III)-chloro complexes can transfer into Cyphos IL 101 efficiently from the solutions containing low chloride concentrations, implying not only [FeCl4]- but also other types of iron-chloro complexes can be extracted. As [FeCl]2+ and [FeCl2]+ cations are more hydrophilic than the organic cation of Cyphos IL 101, iron(III) extraction via an cation exchange is not favorable. However, FeCl3 neutral molecules present in the chloride solutions and have higher concentrations than [FeCl4]- at chloride concentrations below 11 M. The maximum chloride concentration used in our experiments on the Fe(III) extraction was 10 M, indicating Fe(III) extraction was conducted in our experiments under the conditions where the neutral FeCl3 was dominate instead of [FeCl4]-. Previous report has confirmed that the extraction of Fe(III) from hydrochloric acid solutions can proceed via FeCl3 ion association with the chloride anion of Hyamine 1622, a long chain quaternary ammonium chloride.28 We proposed that a same extraction process exist for the extraction of Fe(III) using Cyphos IL 101. From the above experimental results and analysis, the following extraction reactions are proposed and expressed in the Equations from (1) to (6): Complexation reactions in the aqueous solution numbered from (1) to (4):

（1）

Fe 3+ + Cl − ⇔ [ FeCl ]2+ 2+

-

[ FeCl ] + Cl ⇔ [ FeCl2 ]

+

[ FeCl2 ]+ + Cl - ⇔ FeCl3 -

-

FeCl3 + Cl ⇔ [ FeCl4 ] Ion association extraction: Anion exchange extraction:

（2）（3）（4）

[ FeCl3 ]aq + P14,6,6,6 • Cl → P14，6，6，6 • FeCl4 [ FeCl 4 ]- aq + P14,6,6,6 • Cl → P14，6，6，6 • FeCl 4 + Cl − aq

（5）（6）

Both inorganic chloride salts and hydrochloric acid can provide chloride source, while Clanions from Cyphos IL 101 might transfer into aqueous phase as another chloride source. In the aqueous solution, chloride ions replace the water molecules associated with Fe(III) to form Fe(III)-chloro complexes (Equations 1 - 4). It is proposed that anion exchange (Equation 6) is not the only mechanism in the extraction of Fe(III) using Cyphos IL 101. 14


Page 15 of 28

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FeCl3 ion association (Equation 5) also plays an important role during iron(III) extraction. Both of the mechanisms contribute to the iron(III) extraction, however, which mechanism is dominant depends on the solution conditions, such as chloride concentrations. When the chloride concentration in the aqueous solution is high, anion exchange process is potentially dominant. On the contrary, FeCl3 ion association is the main extraction process.

4. Conclusions Undiluted phosphonium ionic liquid Cyphos IL 101 can extract Fe(III) effectively from acid chloride solutions without the need of dilution and an additional extractant. The Fe(III) extraction was fast and highly efficient with a high loading capacity. Because chloride salts like LiCl can be used as the chloride ion source, the iron(III) extraction can be carried out effectively at mild conditions. The stripping of Fe(III) from Cyphos IL 101 was feasible, indicating Cyphos IL 101 can be recovered and reused. Cyphos IL 101 is relatively cheap, therefore, the extraction process can be cost effective. In addition, Cyphos IL 101/aqueous system can provide a “greener” and safer extraction process as none of the organic solvent and extractant does not need to be introduced. Another advantage is that iron-chloro complexes were extracted into Cyphos IL 101 to form an ion pair [P14,6,6,6][ FeCl4-], which is a new type of magnetic ionic liquid.36 This technique can be applied effectively in the removal of Fe(III) from HCl leach solutions of coal gangue, which is essential to obtain high quality Al(III) chloride product from coal gangue. Furthermore, the chloride anion of Cyphos IL 101 was transferred into the aqueous phase during iron(III) extraction, which provided another chloride source, facilitating the production of Al(III) chloride products at high yield. This work has been carried out in our lab and the manuscript will be submitted shortly. We believe that this process can be applied in the treatment and recycling of not only coal gangue, but also aluminum-silicate ores. As undiluted Cyphos IL 101 can be operated by a continuous liquid-liquid extraction mode, the practical applications of this system in industry might be feasible.

Acknowledgements 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Financial support from the following funding bodies including National High Technology Research Development Program of China (863 Program, No. 2011AA06A103), Key Technology Project of Shanxi Province (No. 20131101027), National Nature Science Foundation of China (No. 21306109) and Australian Research Council (ARC) DECRA project (DE120101788) has been greatly acknowledged.

Supporting Information The results on the compositions of the solutions used for UV-Visible measurement and extraction efficiency of iron(III) as a function of iron(III) concentration can be found in Supporting Information, which is available free of charge via the Internet at http://pubs.acs.org/.

References (1) Chang, Y.; Zhai, X.; Li, B.; Fu, Y. Removal of iron from acidic leach liquor of lateritic nickel ore by goethite precipitate. Hydrometallurgy, 2010, 101, 84-87. (2) Swarnkar, S. R.; Gupta, B. L.; Sekharan, R. D. Iron control in zinc plant residue leach solution. Hydrometallurgy, 1996, 42, 21-26. (3) Cohen, B.; Shipley, D. S.; Tong, A. R.; Casaroli, S. J. G.; Petrie, J. G. Precipitation of iron from concentrated chloride solutions: Literature observations, challenges and preliminary experimental results, Miner. Eng., 2005, 18, 1344-1347. (4) Michelis, I. D.; Ferella, F.; Beolchini, F.; Vegliò, F. Reducing acid leaching of manganiferous ore: Effect of the iron removal operation on solid waste disposal. Waste Manage., 2009. 29, 128-135. (5) Oncel, M. S;, Muhcu, A.; Demirbas, E.; Kobya, M. A comparative study of chemical precipitation and electrocoagulation for treatment of coal acid drainage wastewater. J. Env. Chem. Eng., 2013, 1, 989-995. (6) Agrawal, A.; Sahu, K. K. Treatment of Chloride Waste Pickle Liquor by Solvent Extraction for the Recovery of Iron. Extr. Metall. Rev., 2010, 31, 121-134. (7) Agrawal, A.; Kumari, S.; Sahu, K. K. Iron and Copper Recovery/Removal from 16


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(19) Cieszynska, A.;Wisniewski, M. Extraction of palladium(II) from chloride solutions with Cyphos®IL 101/toluene mixtures as novel extractant. Sep. Purif. Technol., 2010. 73, 202-207. (20) Kogelnig, D.; Stojanovic, A.; Kammer, F. V. D.; Terzieff, P.; Galanski, M.; Jirsa, F.; Krachler, R.; Hofmann, T.; Keppler, B. K. Tetrachloroferrate containing ionic liquids: Magnetic- and aggregation behavior. Inorg. Chem. Commun., 2010, 13, 1485-1488. (21) Magdalena, R. R. Extractive removal of zinc(II) from chloride liquors with phosphonium ionic liquids/toluene mixtures as novel extractant. Sep. Purif. Technol., 2009, 66, 19-24. (22) Quinn, J. E.; Ogden, M. D.; Soldenhoff, K. Solvent Extraction of Uranium (VI) from Chloride Solutions using Cyphos IL-101. Solvent Extr. Ion Exch., 2013. 31, 538-549. (23) Stojanovic, A.; Morgenbesser, C.; Kogelnig, D.; Krachler, R.; Keppler, B. K. Quaternary Ammonium and Phosphonium Ionic Liquids in Chemical and Environmental Engineering, in: Kokorin A., Ionic Liquids: Theory, Properties, New Approaches, InTech, Croatia, 2011, pp. 657-680. (24) Bradaric, C. J.; Downard, A.; Kennedy, C.; Robertson, A. J.; Zhou, Y. Industrial preparation of phosphonium ionic liquids. Green Chem., 2003, 5, 143-152. (25) Vander Hoogerstraete, T; Wellens, S.; Verachtert, K.; Binnemans, K. Removal of transition metals from rare earths by solvent extraction with an undiluted phosphonium ionic liquid: Separations relevant to rare-earth magnet recycling. Green Chem., 2013, 15, 919 927. (26) Wellens, S.; Thijs, B.; Binnemans, K. An environmentally friendlier approach to hydrometallurgy: highly selective separation of cobalt from nickel by solvent extraction with undiluted phosphonium ionic liquids. Green Chem., 2012, 14, 1657-1665. (27) Wellens, S.; Goovaerts, R.; Möller, C.; Luyten, J.; Thijs, B.; Binnemans, K. A continuous ionic liquid extraction process for the separation of cobalt from nickel. Green Chem., 2013, 15, 3160-3164. (28) El-Yamani, I. S.；Shabana, E. I. Studies on extraction of iron(III) and cobalt(II) chlorides by quaternary ammonium halides. Trans. Metal Chem., 1984, 5, 199-202. (29) Zhu, T. Solvent extraction and ion exchange, first ed., metallurgical industry press, 18


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Beijing, 2005. (30) Yu, S.Q.; Wu, Z. C. Application of the principle of hard and soft acids and bases to salting-out effect in solvent extraction. Journal of Nuclear and Radiochemistry, 1986, 3, 181-184. (31) Rabinowitch, E.; Stockmayer, W. H. Association of ferric ions and chloride, bromide and hydroxyl ions(A spectroscopic study). J. Am. Chem. Soc.1942, 64, 335-347. (32) Stefansson, A. Iron(III) Hydrolysis and Solubility at 25 °C. Environ. Sci. Technol., 2007, 41, 6117-6123. (33) Stefánsson, A.; Seward, T. M. A spectrophotometric study of iron(III) hydrolysis in aqueous solutions to 200 °C. Chem. Geol., 2008, 249, 227-235. (34) Zhao, R. H.; Pan, P. J. A spectrophotometric study of Fe(II)-chloride complexes in aqueous solutions from 10 to 100°C. Can. J. Chem., 2001.79, 131-144. (35) Liu, W. H.; Etschmann, B.; Brugger,J.; Spiccia,L.; Foran,G.; Mcinncs,B. UV–Vis spectrophotometric and XAFS studies of ferric chloride complexes in hyper-saline LiCl solutions at 25–90 °C. Chem. Geol., 2006, 231, 326-349. (36) Deng, N.; Li, M.; Lu, C.; Rooy, S.;L. De; Warner, I. M. Highly efficient extraction of phenolic compounds by use of magnetic room temperature ionic liquids for environmental remediation. J. Hazard. Mater., 2011,192, 1350-1357. (37) Kogelnig, D.; Stojanovic, A.; Jirsa, F.; Korner, W.; Krachler, R.; Keppler, B. K. Transport

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from

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the

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trihexyl(tetradecyl)phosphonium chloride. Sep. Purif. Technol., 2010, 72, 56-60. (38) Wang, J. L.; Yao, H. W.; Nie, Y.; Zhang, X. P.; Li, J. W. Synthesis and characterization of the iron-containing magnetic ionic liquids. J. Mol. Liq. , 2012, 169, 152-155. (39) Chang, J. H.; Dong, Q. G. Spectrum Analysis , 2nd ed., Science Press, Beijing, 2006. (40)

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Complexes

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(42) Krieger, B. M.; Lee, H. Y.; Emge, T. J.; Wishart, J. F.; Castner, E. W. Jr. Ionic liquids and solids with paramagnetic anions. Phys. Chem. Chem. Phys., 2010, 12, 8919-8925.

20


Page 20 of 28

Page 21 of 28

Figures:

100

EFe, %

95

90

85 0

2

4

6

8

[HCl], mol· L

10

-1

Fig. 1 The extraction percentage of Fe(III) as a function of HCl concentration using Cyphos IL 101. (13.5 g·L-1 of [Fe(III)]0, 0 - 10 M of HCl)

100.0

99.5

EFe, %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


99.0

98.5

98.0 1.6

2.4

3.2

4.0

4.8

[Cl - ], mol· L

5.6

6.4

-1

Fig. 2 Effect of Cl- concentration on the extraction of Fe(III) from chloride media using Cyphos IL 101. (13.5 g·L-1 of [Fe(III)]0, 1 M HCl, 1.72 to 5.72 M of [NaCl], NaCl as chloride source, [Cl-] is the sum of the Cl- in the aqueous solution from NaCl, HCl and FeCl3)

21



100 80

[Fe]IL, g·L

-1

60 40 20 0 0

10

20

30

40

[Fe]0, g·L

50

60

70

-1

Fig. 3 Extraction isotherm of Fe(III) using Cyphos IL 101. (4.5 - 72 g·L−1 of [Fe(III)] 0, 3 M

-1

HCl).

-1

Molar Absorptivity, L·cm ·mol

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 28

258

10000

-1

-1

8000 364 6000 2 22

4000

364 360

314

-

1 m ol· L Cl -1 3 m ol· L Cl -1 5 m ol· L Cl -1 7 m ol· L Cl -1 9 m ol· L Cl -1 11 m ol· L Cl -1 13 m ol· L Cl

1mol· L H Cl

344 2000 0 200

336

300

400

500

W avelength, nm

Fig. 4 UV-Visible spectra of iron(III) - chloro complexes in a series of chloride concentration solutions. (1 M HCl, 1-13 M of [Cl-], LiCl as chloride source)

22


Page 23 of 28

10000 -1

8000

6 mol·L HCl -1 8 mol·L HCl 1 10 mol·L HCl -1 12 mol·L HCl

242

-1


-1

225

6000

362

314

4000 2000 0 200

346

250

300

350

400

450

500

Wavelength, nm

Fig. 5 UV-Visible spectra of iron(Ⅲ)-chloro complexes in a series of HCl concentration

054tn h eg(l)m 3

0.51

318

M 3rlB C 6% ()

2. 0

av0e253 W

3504elgtn (h m )

8000 -1

2M 64.35 91 0

0352evW a

-1

613

.02


.015

A sb

solutions. (6 -12 M of [HCl]) A sb

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


242 6000 362 315

4000

2000

0 200

250

300

350

400

450

500

Wavelength, nm

Fig. 6 UV-Visible absorption spectrum of Fe(III)-loaded Cyphos IL 101 in the wavelength range of 200 – 500 nm.

23



530

-1


-1

1.5

1.0

0.5

685 620

0.0 500

600

700

800

900

Wavelength, nm

Fig. 7 UV-Visible absorption spectrum of Fe(III)-loaded Cyphos IL 101 in the wavelength range of 500 – 900 nm.

333.75

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 28

100

200

300

400

500

600

-1

Wavenumber, cm

Fig. 8 Raman spectrum of Fe(III)-loaded Cyphos IL 101. (50 g·L-1 of [Fe(III)]IL)

24


Page 25 of 28

3684 1626

Transmittance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3385 718

1457

2855

2928

4000

3500

3000

2500

F e(III)-C yp h o s IL 1 0 1 C yp h o s IL 1 0 1

2000

W a v e n u m b e r, c m

1500

1000

-1

Fig. 9 FTIR spectra of undiluted Cyphos IL 101 (before extraction) and Fe(III)-loaded Cyphos IL 101 (after extraction).

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 28

Tables:

Table 1 The remaining concentration of Fe(III) and Al(III) in the aqueous solution, the distribution coefficient, and separation factor at different [Al(III)] / [Fe(III)] concentration ratios. (13.5 g·L-1 of [Fe(III)]0, 0 - 40.5 g·L-1 of [Al(III)]0 , 3 M HCl)

[Al(Ⅲ)]/[ Fe(Ⅲ)]

0

0.2

0.5

1

3

[Fe(III)]aq (mg· L-1)

28.4

28.5

16.9

12.0

6.5

[Al(III)]aq (mg· L-1)

0

2280

5510

11020

34390

DFe(III)

898

900

1517

2141

3975

DAl(III)

-

0.35

0.43

0.43

0.34

α

-

2578

3541

5048

11760

F e ,A l

Table 2 Distribution ratio of Fe(III), Mg(II), Ca(II) and K(I) (3 M HCl, 13.5 g·L-1 of [Fe(III)]0, 5 g·L-1 of [Mg(II)]0, [Ca(II)]0 and [K(I)]0, respectively)

Metal Ions

DM

Fe(III)

2653

Ca(II)

0.51

Mg(II)

0.01

K(I)

0.29

Fe(III) †

898

Fe(III) † denotes Fe(III) in FeCl3 solution, Fe(III) denotes Fe(III) in FeCl3 solution in the presence of Ca(II), Mg(II) and K(I).

26


Page 27 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 3 Stripping efficiency of Fe (Ⅲ) using various stripping solutions (50 g·L-1 of [Fe(III)] in Cyphos IL 101)

Stripping solutions

S1

S1+2

S1+2+3

S1+2+3+4

E(%)2

H2O

16.3

29.2

40.1

50.8

83.70

0.5 M HCl

2.8

5.9

8.7

-

60

1 M HCl

1.2

2.4

3.5

-

52.59

0.1 M H2SO4

22.8

48.9

70.1

91.4

99.71

0.5 M H2SO4

26.29

55.86

78.86

99.6

99.55

1 M H2SO4

26.08

57.05

79.88

100

99.82

Footnotes: S1+2 represents the sum of the iron(III) stripping efficiency from the first stage (S1) and the second stage (S2). S1+2+3 and S1+2+3+4 represent the sum of the iron stripping efficiency from the consecutive three and four stages, respectively. E(%)2 stands for the extraction percentage of iron(III) with the recycled Cyphos IL 101.

Table 4 Fe(III) concentration in the aqueous solutions before ([Fe(III)]0) and after ([Fe(III)]aq) extraction

[HCl] (M)

0.3

[Fe(III)] (mg·L-1)

[Cl-] (M)

1

[Fe(III)]0

[Fe(III)]aq

[Fe(III)]0

[Fe(III)]aq

1

23.0

7.3

23.0

＜1.0

3

21.8

＜1.0

24.6

＜1.0

5

24.1

＜1.0

24.1

＜1.0

7

24.6

＜1.0

22.2

＜1.0

9

23.0

＜1.0

24.6

＜1.0

11

21.2

＜1.0

24.6

＜1.0

13

22.2

＜1.0

21.5

＜1.0

27



Graphical Abstract 8000

10000 8000

-

[FeCl4] FeCl3

6000

Molar Absorptivity, L·cm-1·mol-1

6 M HCl 8 M HCl 10 M HCl 12 M HCl

-1 -1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 28

+

[FeCl2]

4000 2000 0 200

250

300

350

400

450

500

242 6000

-

[FeCl4]

362 315

4000

2000

0 200

250

Wavelength, nm

300

350

400

450

500

Wavelength, nm

Fe(III) species in concentrated HCl solutions

Fe(III)-loaded in Cyphos IL 101

28


Behaviors and Mechanism of Iron Extraction from Chloride Solutions

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