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On the Use of Pseudo-Protic Ionic Liquids to Extract Gold(III) from HCl Solutions

Francisco Jose Alguacil
* and
Jose Ignacio Robla
Centro Nacional de Investigaciones Metalurgicas (CSIC), Avda. Gregorio del Amo 8, 28040 Madrid, Spain
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2023, 24(7), 6305;
Submission received: 16 February 2023 / Revised: 13 March 2023 / Accepted: 21 March 2023 / Published: 27 March 2023
(This article belongs to the Special Issue Advances in Ionic Liquids and Their Various Applications)


Solvent extraction of gold(III) from HCl media using pseudo-protic ionic liquids (PPILs) dissolved in toluene as the extractant phase is investigated. Three PPILs are generated from the reaction of commercially available amines and 1 M HCl solution and named as pri-NH2H+Cl (derived from the primary amine Primene 81R), sec-NHH+Cl (derived from the secondary amine Amberlite LA2) and ter-NH+Cl (derived from the tertiary amine Hostarex A327). In the above structures, -NH2H+Cl, -NHH+Cl and -NH+Cl represented the active groups (anion exchangers) of the respective PPIL. In the case of gold(III) extraction, the experimental variables investigated included the equilibration time (2.5–30 min), temperature (20–60 °C), HCl concentrations (1–10 M) in the aqueous phase, gold(III) concentration (0.005–0.05 g/L) in this same phase, and PPILs concentrations in the organic phase. From the experimental data, and using the Specific Interaction Theory, the interaction coefficients (ε) for the pair AuCl4, H+ are estimated for the systems involving the three PPILs. Gold(III) is recovered from the metal-loaded organic phases using sodium thiocyanate solutions, and from these, gold is finally recovered by the precipitation of zero-valent gold (ZVG) nanoparticles.

1. Introduction

In these first years of the third decade of 21st century, and similarly to past centuries, gold is one of the metals, if not the metal, that attracted a major interest from humans. This is due to its inherent attractiveness and rarity, but also to the multiple applications in which this precious metal takes part, which makes its price always high (about USD 1900 per ounce at the time of writing this article (mid-February 2023)).
Gold is recovered from its raw materials by bioleaching or cyanidation, followed by other operations, i.e., adsorption on the activated carbon [1,2,3], zinc precipitation [3,4] and ion exchange [2,5]. However, in recent years, and due to environmental and economic issues, the recovery of this metal (and others) from the wastes generated by humans is of increasing interest, and this is how the concepts of the circular economy and urban mining come in modern life.
Into the concept of urban mining, gold appeared in a series of solid wastes, such as electronic devices and scraps, printed circuit boards, jewelry scraps, etc., and generally after the separation of undesirable components, gold is first dissolved from the solid waste via acidic leaching in aqua regia medium, though the use of ionic liquids as the leaching medium is also considered [6]. From this highly acidic medium, gold is separated from other less valuable metals by different separation technologies prior to its final recovery step.
Considering these various separation technologies, recent published applications of these on gold(III) processing included solvent extraction [7,8,9,10,11], precipitation [12,13], ion exchange [14,15,16], adsorption [17,18,19,20,21] and even polymer inclusion membranes [22].
In recent years, and especially in the case of solvent extraction operations, a group of chemicals under the label of green solvents, such as ionic liquids, is receiving interest for being used as potential extractants for many metals. This importance is due to some of their properties, such as low vapor pressure, low volatility, low flammability, thermal stability, etc. [23], though their friendly environmental status is under debate [24,25]. Ionic liquids can also be divided into some subfamilies [26]: (i) aprotic ionic liquids and task-specific ionic liquids, both types considered as fully ionic; (ii) protic ionic liquids, generated by the reaction of an acid and a base; and (iii) pseudo-protic ionic liquids (PPILs), which are generated by the reaction of an acid and a base, but sometimes considered not fully ionic. A special case of these (iii) compounds is the PPILs formed from tertiary amines [27,28], and also the PPILs derived from primary and secondary amines.
The present work investigates the use of the solvent extraction operation for the recovery of gold(III) from HCl solutions; as extractants for the precious metal, three PPILs dissolved in toluene, generated from the reaction of a primary, secondary and tertiary amine with HCl, are considered. The use of a diluent in the organic phases, such as toluene, which fulfills the security regulations, is considered a necessity because it (i) decreased the high viscosity of the PPILs, favoring phase separation and organic phase flow in the case of scaling up the operation to a continuous mode, and (ii) allowed an adequate range of extractant concentrations for each particular use, avoiding maintaining unused extractant (probably the most expensive item of the inventory) in the solvent extraction circuit. Gold(III) extraction is investigated under various experimental variables, and the experimental data are used to estimate the values of the AuCl4,H+ pair interaction coefficient for each of the three extraction systems. After stripping, gold is precipitated from the stripped solution as zero-valent gold (ZVG) nanoparticles by the use of sodium borohydride.

2. Results and Discussion

2.1. Generation of the PPILs

It is known that amines are bases, thus they react with mineral acids to form the correspondent salt accordingly with the general reaction:
R 3 N org + H aq + + X aq R 3 N H + X org
In the above equation, the subscripts org and aq refer to the organic and aqueous phases, respectively, and the equilibrium is shifted to the right depending on the amine basicity. The species formed in the organic phase is a quaternary ammonium salt, which in other terms is a pseudo-protic ionic liquid. The same type of equilibria result from the reaction of the primary and secondary amines with mineral acids.
In the present work, the PPILs used in the investigation are generated from the reaction of the primary amine Primene 81R, the secondary amine Amberlite LA2 or the tertiary amine Hostarex A327, dissolved in a toluene medium with 1 M HCl solution. The experiments are carried out using equal volumes of both phases, equilibrated during 5 min at 20 °C. The results from these experiments are summarized in Table 1. In all the cases, the rate of conversion from the amine to the PPIL exceeds 98%.
The experimental results are numerically treated by a tailored computer program that minimizes the U function, defined as:
U = Σ log D exp log D cal 2
where Dexp and Dcal are the experimental and calculated-by-the-program distribution coefficients (DHCl), respectively. The values of the respective log Kext, for the reactions as in Equation (1), are also given in Table 1.

2.2. Gold(III) Extraction by the PPILs

2.2.1. Influence of the Equilibration Time on Gold Extraction

The influence of this variable on gold(III) extraction was investigated using aqueous solutions containing 0.01 g/L Au(III) in 2 M HCl medium and the organic phases of the corresponding PPIL (2.1 × 10−2 M in toluene). The experiments were carried out at 20 °C, using a Vorg/Vaq relationship of 1 and equilibration times from 2.5 to 60 min.
The results showed that in all three cases, equilibrium was reached within 5 min of the contact time between both phases, and with extraction rates of 82% in the case of priNH2H+Cl and in excess of 99% for secNHH+Cl and terNH+Cl, which demonstrated that gold(III) extraction seemed to be more favorable in the case of these two PPILs than in the case of the reagent derived from the primary amine.

2.2.2. Influence of the Temperature of Gold Extraction

The variation of gold extraction at various temperatures (20–60 °C) using the PPILs was also investigated using the same aqueous solution from above and organic phases of the corresponding PPIL in toluene (Table 2).
The results derived from these set of experiments are shown in Table 1. It can be seen that in the 3 cases, gold extraction decreased with the increase of the temperature from 20 °C to 60 °C; thus, the gold distribution coefficient values (DAu) decreased with the increase of the variable. At a first approximation:
log D Au = Δ S 0 2.3 R Δ H 0 2.3 R 1 T
and a plot of log DAu versus 1000/T allowed estimating both ΔS° and ΔH° for the three extraction systems. These values are shown in Table 2, indicating the exothermic nature of the gold extraction process and a decrease in randomness with the loading of the precious metal in the respective organic phase.
Δ G 0 = Δ H 0 T Δ S 0
the values of ΔG° for each of the extraction systems are given also in Table 2. All the systems were spontaneous.

2.2.3. Influence of the PPIL Concentration in the Organic Phase on Gold Extraction

To investigate the influence of this variable on gold extraction, aqueous phases containing 0.01 g/L Au(III) in different HCl medium (1–10 M) were put into contact with organic solutions containing different PPILs concentrations in toluene. The results from these set of experiments are shown in Figure 1 for the PPILs priNH2H+Cl, secNHH+Cl and terNH+Cl.
Comparison of the three figures showed that a general pattern occurred in the three systems: (i) there was a logical increase of the percentage of gold extraction with the increase of the extractant concentration in the organic phase, (ii) there was a maximum of gold extraction for HCl concentrations in the 2–5 M concentration range, and (iii) a slight decrease in the extraction occurred with the 6 M HCl concentration, though this decrease was only observed with the lower extractant concentrations 2.1 × 10−4 M for priNH2H+Cl, 1.2–2.4 × 10−4 M for secNHH+Cl and 2.1–5.2 × 10−5 M for terNH+Cl. This decrease can be attributed to the formation of non-extractable HAuCl4 species in the aqueous phase as the HCl concentration in the solution increased [29].
In any case, and if the range of extractant concentrations used was compared, it can be clearly seen that there was an apparent gold(III) extractability order in the form: terNH+Cl > secNHH+Cl > priNH2H+Cl, this order being based in the fact that with very diluted terNH+Cl concentrations, i.e., 2.1 × 10−4 M, gold(III) was extracted almost quantitatively from the aqueous solution, whereas in the case of priNH2H+Cl, this extraction rate was achieved using a 0.2 M PPIL concentration that was a threefold concentration relationship, and the performance of secNHH+Cl was situated between both.
Experimental data were also numerically treated, and the results of these calculations are shown in Table 3.
It can be seen that the values of the extraction constants (Kext) increased with the increase of the HCl concentration in the aqueous phase and, thus, with the increase of the corresponding aqueous ionic strength (IM). It can also be noted that in the case of terNH+Cl PPIL, the values of Kext were about two orders of magnitude greater than that corresponding to the other two PPILs, indicating the greater affinity of terNH+Cl to exchange its chloride anion with the AuCl4 anion from the aqueous phase.

2.2.4. Influence of the Initial Gold(III) Concentration in the Aqueous Phase on the Metal Extraction

The evaluation of this variable in the extraction of the precious metal was also under consideration, and organic phases containing different concentrations of the PPILs in toluene were mixed with aqueous solutions of gold (III) (0.005–0.05 g/L) in various HCl media. The results from these experiments are shown in Figure 2 for the three PPILs. Here, a general pattern can also be seen, since with the HCl concentration, a maximum of gold extraction was always reached in all the cases, though this maximum was wider as the initial gold concentration in the aqueous solution decreased. Further, the percentage of gold extraction at the various initial metal concentrations became more similar depending on the PPIL used to extract the gold.
Based on the values found in this and the previous subsection, one can ascertain that the extraction of gold(III) from HCl solutions by these PPILs responded to an anion exchange equilibrium:
terN H + C l org + AuC l 4 aq terN H + AuC l 4 org + C l aq
The above is representative of terNH+Cl PPIL. In the other two cases, the equilibrium led to the formation of priNH2H+AuCl4 or secNHH+AuCl4 in the organic phase after the extraction process.

2.2.5. Estimation of the (AuCl4,H+) Interaction Coefficients

The different Kext values with the ionic strength can be correlated by the Specific Interaction Theory [30], which can be used to estimate the interaction coefficient (ε) values of AuCl4,H+ species in the aqueous solution.
Writing Equation (5) in a general form for the three PPILs, the extraction constant (K0) for the equilibrium was correlated with the ionic strength via the next expression:
K 0 = K ext , m γ PPIL H + AuC l 4 org γ C l aq γ PPIL H + C l org γ AuC l 4 aq
In this expression, Kext,m is the extraction constant in the molality scale, and γ is the activity coefficient of each species. If it was assumed that the organic phase had ideal behavior and input logarithms, the next equation resulted:
log K 0 = log K ext , m log γ AuC l 4 aq + log γ C l aq
The activity coefficient of an ion of charge zi in a solution of a given ionic strength was defined as:
log γ i = Z i 2 D I m + Σ ε i , c I m
where Im represents the aqueous ionic strength in the molality scale; DIm is the Debye-Hückel coefficient, also in the molality scale; and ε is the interaction coefficient between the pairs of charged species (AuCl4 and Cl as anions and H+ as the cation) presented in this system.
Considering the above charged species and the ε term, the substitution in Equation (7) led to the expression:
log K ext , m = log K 0 + ε AuC l 4 , H + ε C l , H + I m
Thus, plotting log Kext,m versus Im as a straight line of slope (ε(AuCl4,H+)–ε(Cl,H+) and intercept log K0 might be obtained. The results from the various plots for the three PPILs used in this work are given in Table 4. The values of the interaction coefficients were calculated from the corresponding slope and considering that ε(Cl,H+) had a value of 0.12 [31,32].

2.2.6. Gold Stripping from Metal-Loaded Organic Phases

The affinity of the gold(III) to be complexed by thiocyanate ions and to form the Au(SCN)4 species (log β4 = 43.66) [33] in an aqueous medium was known. Thus, the stripping of gold from the various metal-loaded organic phases was investigated by the use of this complexing agent.
The results derived from the experiments carried out with PPIL organic phases loaded with 0.01 g/L Au(III) indicated that by using 0.75 M sodium thiocyanate solutions, the rate of gold recovered in the strip solution was 82%, 75% and 79% when using the organic phases of priNH2H+Cl, secNHH+Cl or terNH+Cl, respectively, after 15 min of contact between both phases at a temperature of 20 °C and using a Vaq/Vorg ratio of 1. A second equilibration of the gold’s partially depleted organic phase with fresh thiocyanate solution, under the same experimental conditions as above, allowed an overall gold strip rate of 99%.

2.2.7. Precipitation of Zero-Valent Gold from Stripping Solutions

Due to the uses of gold nanoparticles in multiple fields, i.e., biological, chemical, medical, agricultural, etc. [34,35,36,37,38], it was of interest to consider gold recovery as a type of nanomaterial [39]; several methods were proposed [34,36,37], and one was the use of a reducing agent, such as sodium borohydride [40]. In the present work, under very gentle (50 min−1) stirring, 0.1 g of sodium borohydride was added to a thyocianate strip solution containing 5.1 × 10−4 M gold.
The reaction responsible for gold precipitation can be written as [29]:
Au SC N 4 + 1 2 B H 4 + 2 H 2 O A u 0 + 3 HSCN + 1 2 B OH 4 + SC N + 1 2 H 2
From the first addition of the reducing agent, a dark precipitate appeared, and at the end of the addition process, the precipitate was filtered and washed with distilled water. The as-obtained dry solid resulted in zero-valent gold nanoparticles (Figure 3) with some degree of agglomeration (Figure 4).

3. Materials and Methods

The amines Primene 81R (Rohm and Haas), Amberlite LA2 (Fluka) and Hostarex A327 (Sanofi) were used without further purification. All other chemicals were of AR grade.
The extraction and stripping experiments were done in thermostatted separatory funnels that provided mechanical shaking via four glass blade impellers.
In the case of the generation of the PPILs, equilibrated organic and aqueous phases were analyzed by titration with standard NaOH solutions and using blue bromothymol as the indicator. The results (Table 1) were given as the HCl distribution coefficient (DHCl), defined as:
D HCl = HCl org HCl aq
Gold in the aqueous phases was analyzed by AAS (Perkin Elmer 110B spectrophotometer), and the corresponding concentration in the organic phase ([Au]0) was calculated by the mass balance, and the percentage of gold extracted in the organic phase was calculated as:
% gold = Au a q , 0 Au org Au a q , 0 × 100
where [Au]aq,0 is the initial gold concentration in the aqueous phase. The percentage of gold stripped, [Au]st, was calculated as:
% gold = Au st Au org , 0 × 100
where [Au]org,0 is the gold concentration in the metal-loaded organic phase.
The TEM image was obtained at 120 KV using JEOL JEM 1400 equipment.

4. Conclusions

The results derived from this investigation indicated the usefulness of quaternary ammonium chloride PPILs to extract gold(III) from HCl media, though the performance demonstrated by the PPIL derived from a tertiary amine was much better than the ones by PPILs derived from secondary and primary amines.
In all the cases, equilibrium was reached at a short time, and the three systems showed the same behavior with respect to temperature: exothermic and spontaneous extraction processes, with a decrease in randomness as a consequence of gold uploading in the respective organic phase.
Further, in all three extraction systems, the extraction constant depended on the aqueous ionic strength, and on this basis, the interaction coefficients of the AuCl4,H+ pair were estimated.
The sodium thiocyanate medium appeared to respond well as a gold stripper from the metal-loaded organic phases, and from these stripped phases, gold could be conveniently precipitated as zero-valent gold nanoparticles (partially aggregated).

Author Contributions

Conceptualization, F.J.A.; Methodology, F.J.A. and J.I.R.; Investigation, F.J.A. and J.I.R.; Writing—Original Draft Preparation, F.J.A.; Writing—Review and Editing, F.J.A. and J.I.R.; Funding, J.I.R.; Supervision, F.J.A. All authors have read and agreed to the published version of the manuscript.


This investigation was performed under CSIC-Project 202250E019.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.


We thank the CSIC (Spain) for support. We acknowledge the support of the publication fee from the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). In addition, we give our gratitude to Centro Nacional de Microscopia Electronica (F. CC. Quimicas), UCM (Spain), for obtaining the TEM image.

Conflicts of Interest

The authors declare no conflict of interest.


  1. Nie, Y.; Chen, J.; Wang, Q.; Shi, C.; Xing, B.; Jiang, Y.; Wang, S. Calcined high-sulfur coal for highly efficient adsorption of Au(S2O3)23− from a gold thiosulfate leaching solution using an external reduction potential. ACS Sustain. Chem. Eng. 2022, 10, 11782–11790. [Google Scholar] [CrossRef]
  2. Msumange, D.A.; Yazici, E.Y.; Celep, O.; Deveci, H. A comparison of ion-exchange resins and activated carbon in recovering gold from cyanide leach solutions with low levels of copper. Bull. Miner. Res. Explor. 2022, 168, 35–41. [Google Scholar] [CrossRef]
  3. Jeon, S.; Bright, S.; Park, I.; Tabelin, C.B.; Ito, M.; Hiroyoshi, N. A simple and efficient recovery technique for gold ions from ammonium thiosulfate medium by galvanic interactions of zero-valent aluminum and activated carbon: A parametric and mechanistic study of cementation. Hydrometallurgy 2022, 208, 105815. [Google Scholar] [CrossRef]
  4. Nie, Y.; Wang, S.; Wang, Q.; Chen, J.; Jiang, Y. Applying an external reduction potential to reduce the consumption of zinc powder during gold cementation. Miner. Eng. 2023, 191, 107981. [Google Scholar] [CrossRef]
  5. Msumange, D.A.; Yazici, E.Y.; Celep, O.; Deveci, H.; Kritskii, A.; Karimov, K. Recovery of Au and Ag from the roasted calcine of a copper-rich pyritic refractory gold ore using ion exchange resins. Miner. Eng. 2023, 195, 108017. [Google Scholar] [CrossRef]
  6. Vallejos-Michea, C.; Barrueto, Y.; Jimenez, Y.P. Life cycle analysis of the ionic liquid leaching process of valuable metals from electronic wastes. J. Clean. Prod. 2022, 348, 131357. [Google Scholar] [CrossRef]
  7. Zupanc, A.; Install, J.; Jereb, M.; Repo, T. Sustainable and selective modern methods of noble metal recycling. Angew. Chem.-Int. Ed. 2023, 62, e202214453. [Google Scholar] [CrossRef]
  8. Liu, X.; Wang, Y.; Liu, R.; Lv, P.; Xue, W.; Guo, J.; Wei, H.; Wei, H.; Yang, Y. Selective and efficient gold extraction from e-waste by pyrrolidinium-based ionic liquids with various N-ubstituents. ACS Sustain. Chem. Eng. 2023, 11, 638–648. [Google Scholar] [CrossRef]
  9. Liu, R.; Hao, J.; Wang, Y.; Meng, Y.; Yang, Y. A separation strategy of Au(III), Pd(II) and Pt(IV) based on hydrophobic deep eutectic solvent from hydrochloric acid media. J. Mol. Liq. 2022, 365, 120200. [Google Scholar] [CrossRef]
  10. Wang, Y.; Chen, S.; Liu, R.; Zhang, L.; Xue, W.; Yang, Y. Toward green and efficient recycling of Au(III), Pd(II) and Pt(IV) from acidic medium using UCST-type ionic liquid. Sep. Purif. Technol. 2022, 298, 121620. [Google Scholar] [CrossRef]
  11. Matsumiya, M.; Kinoshita, R.; Sasaki, Y. Recovery of gold by solvent extraction and direct electrodeposition using phosphonium-based ionic liquids. J. Electrochem. Soc. 2022, 169, 082513. [Google Scholar] [CrossRef]
  12. Huang, Y.-F.; Chou, S.-L.; Lo, S.-L. Gold recovery from waste printed circuit boards of mobile phones by using microwave pyrolysis and hydrometallurgical methods. Sustain. Environ. Res. 2022, 32, 6. [Google Scholar] [CrossRef]
  13. Wang, R.; Zhang, L.; Zhang, C.; Wang, J.; Guan, J.; Jian, Z.; Bu, Y. Selective extraction of precious metals in the polar aprotic solvent system: Experiment and simulation. Waste Manag. 2022, 153, 1–12. [Google Scholar] [CrossRef]
  14. Xu, Q.; Du, X.-H.; Luo, D.; Strømme, M.; Zhang, Q.-F.; Xu, C. Gold recovery from E-waste using freestanding nanopapers of cellulose and ionic covalent organic frameworks. Chem. Eng. J. 2023, 458, 141498. [Google Scholar] [CrossRef]
  15. Zhang, B.; Wang, Y.; Lin, G.; Zhang, H. Extraction of gold from the leachate of copper anode slime by quaternary ammonium rice husk lignin. Solvent Extr. Ion Exch. 2023, 41, 1–19. [Google Scholar] [CrossRef]
  16. Hao, F.; Du, J.; Peng, L.; Zhang, M.; Dong, Z.; Shen, Y.; Zhao, L. Selective and effective gold recovery from printed circuit boards and gold slag using amino-acid-functionalized cellulose microspheres. Polymers 2023, 15, 321. [Google Scholar] [CrossRef]
  17. Lin, X.; Song, M.-H.; Tran, D.T.; Lee, Y.-S.; Yun, Y.-S. Development of polyethylenimine-functionalized cellulose fibers for recovery of Au(0) from Au(III)-containing acidic solutions through an adsorption–reduction–detachment–aggregation mechanism. J. Clean. Prod. 2023, 389, 136019. [Google Scholar] [CrossRef]
  18. Zhang, L.; Fan, J.-Q.; Zheng, Q.-Q.; Xiao, S.-J.; Zhang, C.-R.; Yi, S.-M.; Liu, X.; Jiang, W.; Tan, Q.-G.; Liang, R.-P.; et al. A 2D mesoporous hydrazone covalent organic framework for selective detection and ultrafast recovery of Au(III) from electronic waste. Chem. Eng. J. 2023, 454, 140212. [Google Scholar] [CrossRef]
  19. Niu, H.; Yang, H.; Tong, L.; Kamali, A.R. The adsorption characteristics and performance of gold onto elemental carbon extracted from refractory carbonaceous gold concentrate. Colloids Surf. A Physicochem. Eng. Asp. 2023, 658, 130635. [Google Scholar] [CrossRef]
  20. Xia, J.; Twinney, J.; Marthi, R.; Ghahreman, A. Ultra-efficient and selective recovery of Au(III) using magnetic Fe3S4/Fe7S8. Sep. Purif. Technol. 2023, 306, 122611. [Google Scholar] [CrossRef]
  21. Melnyk, I.V.; Vaclavikova, M.; Ivanicova, L.; Kanuchova, M.; Seisenbaeva, G.A.; Kessler, V.G. Features of the surface layer structure of the magnetosensitive materials functionalized by silica with thiourea groups and their applying for selective Cu(II) and Au(III) ions removal. Appl. Surf. Sci. 2023, 609, 155253. [Google Scholar] [CrossRef]
  22. Bożejewicz, D.; Kaczorowska, M.A.; Witt, K. Recent advances in the recovery of precious metals (Au, Ag, Pd) from acidic and WEEE solutions by solvent extraction and polymer inclusion membrane processes–a mini-review. Desalination Water Treat. 2022, 246, 12–24. [Google Scholar] [CrossRef]
  23. Meseret, M.; Liu, J.-F.; Pang, L. Environmental application, fate, effects, and concerns of ionic liquids: A review. Environ. Sci. Technol. 2015, 49, 12611–12627. [Google Scholar]
  24. Bystrzanowska, M.; Pena-Pereira, F.; Marcinkowski, L.; Tobiszewski, L. How green are ionic liquids?—A multicriteria decision analysis approach. Ecotoxicol. Environ. Saf. 2019, 174, 455–458. [Google Scholar] [CrossRef] [PubMed]
  25. Marcionilio, S.M.L.O.; Araújo, D.M.; Nascimento, T.V.; Martínez-Huitle, C.A.; Linares, J.J. Evaluation of the toxicity reduction of an ionic liquid solution electrochemically treated using BDD films with different sp3/sp2 ratios. Electrochem. Commun. 2020, 118, 106792. [Google Scholar] [CrossRef]
  26. Castillo-Ramírez, C.; Janssen, C.H.C. Pseudo-protic ionic liquids for the extraction of metals relevant for urban mining. Ind. Eng. Chem. Res. 2023, 62, 627–636. [Google Scholar] [CrossRef]
  27. Kobrak, M.N.; Yager, K.G. X-Ray scattering and physicochemical studies of trialkylamine/carboxylic acid mixtures: Nanoscale structure in pseudoprotic ionic liquids and related solutions. Phys. Chem. Chem. Phys. 2018, 20, 18639–18646. [Google Scholar] [CrossRef]
  28. Patsos, N.; Lewis, K.; Picchioni, F.; Kobrak, M.N. Extraction of acids and bases from aqueous phase to a pseudoprotic ionic liquid. Molecules. 2019, 24, 894. [Google Scholar] [CrossRef] [Green Version]
  29. Alguacil, F.J. Mechanistic investigation of facilitated transport of gold(III) from HCl media using ionic liquid Cyphos IL102 as carrier across a supported liquid membrane. Gold Bull. 2019, 52, 145–151. [Google Scholar] [CrossRef]
  30. Ciavatta, L. The specific interaction theory in evaluating ionic equilibria. ChemSusChem 1980, 70, 551–567. [Google Scholar]
  31. Ciavatta, L. The specific interaction theory in equilibrium analysis. Some empirical rules for estimation interaction coefficients of metal-ion complexes. Ann. Di Chim. 1990, 80, 255–263. [Google Scholar]
  32. Bretti, C.; Foti, C.; Sammartano, S. A new approach in the use of SIT in determining the dependence on ionic strength of activity coefficients. Application to some chloride salt of interest in the speciation of natural fluids. Chem. Speciat. Bioavailab. 2004, 16, 105–110. [Google Scholar] [CrossRef] [Green Version]
  33. Barbosa-Filho, O.; Monhemius, A.J. Leaching of gold in thiocyanate solutions. Part 1: Chemistry and thermodynamics. Trans. IMM 1994, 103, C105–C110. [Google Scholar]
  34. Balaji, R.; Ilangeswaran, D. Choline chloride–Urea deep eutectic solvent an efficient media for the preparation of metal nanoparticles. J. Indian Chem. Soc. 2022, 99, 100446. [Google Scholar] [CrossRef]
  35. Proniewicz, E. Metallic nanoparticles as effective sensors of bio-molecules. Spectrochim. Acta-Part A Mol. Biomol. Spectrosc. 2023, 288, 122207. [Google Scholar] [CrossRef] [PubMed]
  36. Zhou, Y.; Zou, Y.; Jiang, J. Synthesis of chorogi-like Au nanoparticles with chiral plasmonic response and enantioselective electrocatalytic activity. Mater. Lett. 2023, 331, 133432. [Google Scholar] [CrossRef]
  37. Ding, Y.; Huang, P.-J.J.; Zandieh, M.; Wang, J.; Liu, J. Gold nanoparticles synthesized using various reducing agents and the effect of aging for DNA sensing. Langmuir 2023, 39, 256–264. [Google Scholar] [CrossRef]
  38. Wei, D.; Li, M.; Wang, Y.; Zhu, N.; Hu, X.; Zhao, B.; Zhang, Z.; Yin, D. Encapsulating gold nanoclusters into metal–organic frameworks to boost luminescence for sensitive detection of copper ions and organophosphorus pesticides. J. Hazard. Mater. 2023, 441, 129890. [Google Scholar] [CrossRef]
  39. Oestreicher, V.; García, C.S.; Soler-Illia, G.J.A.A.; Angelomé, P.C. Gold recycling at laboratory scale: From nanowaste to nanospheres. ChemSusChem 2019, 12, 4882–4888. [Google Scholar] [CrossRef]
  40. Alguacil, F.J.; Adeva, P.; Alonso, M. Processing of residual gold (III) solutions via ion exchange. Gold Bull. 2005, 38, 9–13. [Google Scholar] [CrossRef] [Green Version]
Figure 1. Variation of the percentage of gold(III) versus the HCl concentration in the aqueous phase at various PPILs concentrations in toluene. (a): priNH2H+Cl. (b): secNHH+Cl. (c): terNH+Cl. Equilibration time: 5 min. Temperature: 20 °C.
Figure 1. Variation of the percentage of gold(III) versus the HCl concentration in the aqueous phase at various PPILs concentrations in toluene. (a): priNH2H+Cl. (b): secNHH+Cl. (c): terNH+Cl. Equilibration time: 5 min. Temperature: 20 °C.
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Figure 2. Variation of the percentage of gold(III) extraction versus HCl concentration in the aqueous phase at various initial metal concentrations. (a): 2.1 × 10−2 M priNH2H+Cl. (b): 2.3 × 10−4 M secNHH+Cl. (c): 1.1 × 10−4 M terNH+Cl. Equilibration time: 10 min. Temperature: 20 °C.
Figure 2. Variation of the percentage of gold(III) extraction versus HCl concentration in the aqueous phase at various initial metal concentrations. (a): 2.1 × 10−2 M priNH2H+Cl. (b): 2.3 × 10−4 M secNHH+Cl. (c): 1.1 × 10−4 M terNH+Cl. Equilibration time: 10 min. Temperature: 20 °C.
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Figure 3. Zero-valent gold.
Figure 3. Zero-valent gold.
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Figure 4. TEM image of the precipitated zero-valent gold.
Figure 4. TEM image of the precipitated zero-valent gold.
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Table 1. Generation of the PPILs.
Table 1. Generation of the PPILs.
PrecursorConcentration, MDHClPPIL FormedAcronysmlog Kext
Primene 81R0.110.11RNH2H+ClpriNH2H+Cl2.99 a
Amberlite LA20.060.063R´R´´NHH+ClsecNHH+Cl2.90 b
Hostarex A3270.060.056R3NH+ClterNH+Cl2.65 c
a U = 3.1 × 10−4, b U = 3.0 × 10−4, c U = 2.3 × 10−5.
Table 2. Influence of the temperature on gold extraction.
Table 2. Influence of the temperature on gold extraction.
PPIL, M1000/T, K−1log DAuΔH°, kJ/molΔS°, J/mol KΔG°, kJ/mol
a 2.1 ××10−23.4a 1.6−10−31−1
b 2.3 × 10−43.4b 4.6−21−59−4
c 5.3 × 10−53.4c 0.28−26−82−2
a priNH2H+Cl (r2 = 0.979), b secNHH+Cl (r2 = 0.996), c terNH+Cl (r2 = 0.983). Vorg/Vaq = 1. Equilibration time: 5 min.
Table 3. Values of Kext at various HCl concentrations.
Table 3. Values of Kext at various HCl concentrations.
HCl, MIMpriNH2H+ClsecNHH+ClterNH+Cl
11.024.9 × 1037.1 × 1036.0 × 105
22.028.3 × 1031.4 × 1047.6 × 105
33.191.3 × 1042.2 × 1041.1 × 106
44.361.7 × 1043.0 × 1041.6 × 106
55.572.2 × 1043.9 × 1042.0 × 106
66.852.8 × 1044.9 × 1042.5 × 106
78.193.2 × 1045.6 × 1043.9 × 106
89.613.7 × 1046.6 × 1044.9 × 106
911.114.2 × 1047.6 × 1046.0 × 106
1012.694.7 × 1048.7 × 1047.1 × 106
IM = ionic strength in the molar scale. Kext values rounded to one decimal.
Table 4. Results of plotting of log Kext,m versus Im.
Table 4. Results of plotting of log Kext,m versus Im.
Ima log Kext,mb log Kext,mc log Kext,m
log K03.804.015.74
a Values for priNH2H+Cl. b Values for secNHH+Cl. c Values for terNH+Cl.
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Alguacil, F.J.; Robla, J.I. On the Use of Pseudo-Protic Ionic Liquids to Extract Gold(III) from HCl Solutions. Int. J. Mol. Sci. 2023, 24, 6305.

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Alguacil FJ, Robla JI. On the Use of Pseudo-Protic Ionic Liquids to Extract Gold(III) from HCl Solutions. International Journal of Molecular Sciences. 2023; 24(7):6305.

Chicago/Turabian Style

Alguacil, Francisco Jose, and Jose Ignacio Robla. 2023. "On the Use of Pseudo-Protic Ionic Liquids to Extract Gold(III) from HCl Solutions" International Journal of Molecular Sciences 24, no. 7: 6305.

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