Previous Article in Journal
Polyvinylidene Fluoride Membrane Modified by PEG Additive for Tofu Industrial Wastewater Treatment
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Solvent-Dependent Coordination Geometry Shift in Copper(II)-D2EHPA Complexes: How Diluent Polarity Dictates Extraction Efficiency

by
Fatima Ghebghoub
1,
Djamel Barkat
1,
Mohamed-Cherif Ben-Ameur
2,* and
Mohamed-Aymen Kethiri
3,*
1
Laboratory of Chemical, Molecular, and Environmental, Department of Industrial Chemistry, Faculty of Science and Technology, University of Biskra, Biskra 07000, Algeria
2
Materials and Chemical Engineering “Giulio Natta”, Department of Chemistry, Politecnico di Milano, 20131 Milano, Italy
3
Architecture, Built Environment and Construction Engineering Department, DABC, Politecnico di Milano, 20131 Milano, Italy
*
Authors to whom correspondence should be addressed.
ChemEngineering 2025, 9(5), 107; https://doi.org/10.3390/chemengineering9050107
Submission received: 15 August 2025 / Revised: 21 September 2025 / Accepted: 26 September 2025 / Published: 1 October 2025

Abstract

This study systematically investigates the solvent-dependence of copper(II) extraction using di-2-ethylhexyl phosphoric acid (D2EHPA) across a range of polar and non-polar diluents, including chloroform, dichloromethane, carbon tetrachloride, cyclohexane, 1-octanol, and methyl isobutyl ketone (MIBK). Through analysis of extraction constants and distribution coefficients at varying pH levels, it was demonstrated that solvent polarity and dipole moment critically influenced the coordination geometry and extraction efficiency of the Cu(II)-D2EHPA complex. Notably, the highest extraction efficiencies were exhibited by 1-octanol and cyclohexane. A solvent-dependent structural transition was revealed by Ultraviolet–Visible (UV) spectroscopic evidence: tetrahedral coordination was dominated in polar media, while square planar geometries prevailed in non-polar environments. These findings establish a direct correlation between diluent properties and the extractant’s performance, offering a mechanistic framework for optimizing industrial-scale copper recovery processes. The insights gained highlight the importance of solvent selection in tailoring metal extraction systems for specific applications.

1. Introduction

The extraction of dissolved metallic elements from wastewater is a vital operation in fields like mineral processing, resource recovery, and ecosystem rehabilitation [1,2,3], with copper representing a priority target due to its extensive use in electronics and energy infrastructure.
Global copper demand has surged by 50% over the past decade [4], driving increased extraction from low-grade ores and secondary sources like electronic waste, where wastewater streams often contain toxic Cu(II) ions exceeding 200 ppm levels that pose severe ecological risks due to bioaccumulation and persistence in aquatic ecosystems [5,6,7]. Liquid–liquid extraction (LLE) has emerged as the dominant industrial technique for copper recovery, combining operational scalability with high selectivity in acidic media. Among extractants, di-2-ethylhexyl phosphoric acid (D2EHPA) is particularly favored for its strong affinity toward Cu(II) ions, forming stable complexes that enable efficient phase separation [8,9]. Industrial implementations demonstrate >94% copper recovery from printed circuit board leachates using D2EHPA-kerosene systems, while liquid surfactant membranes (LSMs) with D2EHPA achieve 95% extraction within 11 min through optimized emulsion formulations [10,11].
Despite these advantages, D2EHPA’s efficiency is profoundly influenced by the choice of diluent—a variable governing extractant solvation, metal complex geometry, and phase-transfer kinetics that remains inadequately systematized for industrial optimization. The diluent’s physicochemical properties—particularly polarity, dipole moment, and hydrogen-bonding capacity—dictate the coordination environment of the Cu(II)-D2EHPA complex. Polar diluents (e.g., 1-octanol, methyl isobutyl ketone) stabilize tetrahedral Cu(II) complexes through solvation effects, enhancing extractant mobility but potentially reducing thermodynamic stability.
Conversely, non-polar diluents (e.g., cyclohexane, kerosene) favor square planar geometries that optimize ligand-metal charge transfer but suffer from solubility limitations [12,13,14,15]. This geometric dichotomy directly impacts extraction constants (Kex) and distribution coefficients (DCu), as evidenced by recent studies where soybean oil increased Cu(II) extraction to 91.8% compared to 65.7% in petroleum-based systems under identical D2EHPA concentrations [16,17].
Industrial Solvent Extraction (SX) operations face compounded complexities from aqueous-phase contaminants and solvent degradation [18,19]. Ruiz et al. demonstrated this challenge by observing a 25% decline in Cu(II) extraction with Liquid Ion Exchange (LIX) 84-IC when chloride concentrations exceeded 60 g/L, a finding that underscores the necessity for diluent-specific process adaptations [20]. Additionally, conventional petroleum-derived diluents (e.g., kerosene, chloroform) present environmental hazards through volatilization and aqueous solubility, driving research toward green alternatives. Bio-derived solvents like soybean oil have emerged as sustainable options, maintaining >65% Cu(II) extraction efficiency while reducing ecological footprints [17,21]. Similarly, ionic liquids (ILs) such as methyltrioctyl/decylammonium bis(2,4,4-trimethylpentyl)phosphinate (R4NCy) offer negligible volatility and tunable selectivity, though recent studies reveal preferential extraction of Fe(III) and Zn(II) over Cu(II), limiting their direct applicability [22,23].
Coordination chemistry insights further illuminate diluent effects. Spectroscopic analyses confirm that polar diluents promote O=P-O-Cu bond angles near 115° in tetrahedral complexes, while non-polar systems favor planar configurations with 90° bond angles—structural differences altering activation energies by 15–30 kJ/mol. These geometric shifts modulate kinetic parameters: 1-octanol accelerates extraction rates 3-fold versus cyclohexane due to enhanced interface mobility, though it complicates stripping through stronger complex stabilization. Recent advances leverage these principles through functionalized ionic liquids like thiourea-appended imidazolium compounds, where sulfur donors increase Cu(II) binding energies by 40% versus conventional ILs, achieving >99% extraction even at pH < 2 [24].
This study bridges critical knowledge gaps by systematically evaluating six industrially relevant diluents (chloroform, dichloromethane, carbon tetrachloride, cyclohexane, 1-octanol, and MIBK) across polarity gradients. We correlate extraction kinetics with spectroscopic analysis of complex geometry (Raman/X-ray Diffraction XRD) to resolve the mechanistic interplay between diluent properties and Cu(II)-D2EHPA complexation. The findings establish predictive criteria for diluent selection in chloride-contaminated and standard sulfate systems, advancing toward sustainable copper recovery frameworks aligned with circular economic principles.

2. Materials and Methods

2.1. Chemicals Used

The reagents used were of analytical grade. Di-(2-ethylhexyl) phosphoric acid (D2EHPA, ≥95%, Fluka (Buchs, Switzerland) served as the extractant and was utilized without further purification, aligning with common practice in the literature. The organic diluents chosen to assess polarity effects comprised a suite of non-polar compounds—toluene, dichloromethane (DCM), chloroform, carbon tetrachloride (CCl4), and cyclohexane (all ≥99%, Merck, Darmstadt, Germany)—as well as the polar solvents 1-octanol and methyl isobutyl ketone (MIBK, ≥98%, Sigma-Aldrich, St. Louis, MO, USA). To reduce artifacts from water co-extraction, each diluent was pre-saturated with deionized water according to standard methods [25]. The source of metal ions was an aqueous solution of copper(II) sulfate pentahydrate (CuSO4·5H2O, Merck) prepared in 0.33 M Na2SO4 to fix the ionic strength at unity (I = 1) [26]. The pH of this aqueous phase was controlled through additions of 0.2 M NaOH or H2SO4 solutions (Merck).

2.2. Extraction and Analytical Procedures

To evaluate solvent extraction efficiency, a standard batch method was employed under isothermal conditions at 25 °C. For each test, 25 mL of an organic solvent was vigorously agitated with an equal volume of an aqueous phase containing 6.78 mM Cu(II) in a 0.33 M Na2SO4 background electrolyte; the pH of this aqueous solution was previously titrated to the desired value using 0.2 M NaOH. Mixing, performed with a magnetic stirrer, continued for up to 30 min to achieve partitioning equilibrium. After the phases disengaged, the concentration of copper remaining in the aqueous raffinate was determined by visible spectrophotometry at 511 nm (Philips UV-VIS SP6-36 spectrophotometer). The concentration of metal extracted into the organic phase was subsequently computed by mass balance from the disparity between the initial and equilibrated aqueous concentrations.

2.3. General Expressions for the Extraction Equilibrium of Cu(II) with D2EHPA

The extraction equilibrium of Cu(II) from sulfate media was investigated using D2EHPA dissolved in seven organic diluents of varying polarity: toluene, dichloromethane (DCM), chloroform, carbon tetrachloride (CCl4), cyclohexane (non-polar), and 1-octanol, methyl isobutyl ketone (MIBK) (polar). Based on established mechanisms [27,28], the extraction process in non-polar solvents was described by the equilibrium:
M 2 + + ( 2 + p ) / 2 ( H L ) 2 ¯ K e x 1 ( M L 2 p H L ¯ ) + 2 H +
Where (HL)2 represented the dimeric form of D2EHPA. The extraction constant (Kex) was expressed as [27]:
K e x 1 = M L 2 p H L ¯ [ H + ] 2 M 2 + [ ( H L ¯ ) 2 ] ( 2 + p ) / 2
In polar diluents (1-octanol and MIBK), a modified equilibrium was observed due to monomeric D2EHPA predominance [29,30,31]:
D = M L 2 p H L ¯ M 2 +
The distribution coefficient (D) was found to vary with pH according to the relationship [28]:
l o g D = l o g K e x 1 + 2 + p 2 l o g ( H L ¯ ) 2 + p H
The extraction percentage (%E) was determined using the expression [32]:
E % = D D + 1 100
UV-VIS spectroscopic analysis confirmed significant solvent effects, with absorption maxima at 820 nm (square planar geometry) being observed in non-polar diluents and 844 nm (tetrahedral distortion) in polar solvents [31]. These spectral shifts were consistent with the structural transformations reported by Grimm and Kolarik [27] and subsequent studies, such as [29,31].

2.4. Spectroscopic Characterization

UV-VIS analysis demonstrated solvent-dependent coordination geometries in Cu(II)-D2EHPA complexes. Non-polar diluents (toluene, chloroform) exhibited absorption maxima at 820 nm, characteristic of square planar CuL2·2HL complexes, while polar solvents (1-octanol, MIBK) showed red-shifted peaks at 844 nm, indicating tetrahedral distortion due to axial solvent coordination [33]. The broader spectral bands in non-polar systems (FWHM ≈ 85 nm vs. 60 nm in polar media) further confirmed structural differences. These results validated the proposed solvent-mediated geometric transformation and its impact on extraction efficiency.

3. Results

3.1. Effect of pH

Figure 1 presents the extraction profiles of log D versus pH for Cu(II) in sulfate media (I = 1, Na2SO4 0.33 M) using D2EHPA dissolved in various diluents at 25 °C. The results demonstrate a strong pH dependence, with all systems showing linear correlations (slope ≈ 2) between log D and pH, consistent with the two-proton exchange mechanism characteristic of D2EHPA–metal complexation. This linear relationship confirms that extraction efficiency improves systematically with increasing pH, as higher pH conditions promote the deprotonation of D2EHPA’s phosphoric acid groups, thereby enhancing their ability to coordinate Cu(II) ions [27].
Notably, while the fundamental stoichiometry (2:1 D2EHPA:Cu ratio) remained constant across all diluents, the absolute extraction efficiency varied significantly with solvent polarity. Polar diluents like 1-octanol exhibited steeper pH-dependent enhancements compared to non-polar solvents such as chloroform, suggesting more efficient proton release in polar media [34]. The inflection point observed at pH ≈ 4.5 corresponds to the pKa of D2EHPA, marking the transition to optimal extraction conditions where >90% deprotonation occurs [27].
These findings underscore the critical need for precise pH control in industrial applications, as small variations (±0.5 pH units) near the inflection point can alter extraction efficiency by >30%. The consistent slope across diluents confirms the robustness of the 2H+ exchange mechanism, while the solvent-dependent efficiency variations highlight the importance of diluent selection for process optimization.

3.2. Influence of Extractant Concentration

Figure 2 demonstrates the relationship between log D and log [HL)2] for Cu(II) extraction in non-polar diluents (chloroform, toluene, DCM, CCl4, and cyclohexane). The linear plots with slopes approaching 2 clearly indicate that two dimeric D2EHPA molecules participate in the formation of each extracted Cu(II) complex. This confirms the established stoichiometry of CuL2·2HL in these solvents. The positive correlation between log D and extractant concentration shows that increasing D2EHPA availability directly enhances copper recovery in non-polar media. This behavior was consistent across all tested pH conditions, though the absolute extraction efficiency varied with pH as previously discussed in Section 3.1.
Figure 3 presents markedly different behavior for polar diluents (1-octanol and MIBK). Here, log D shows a linear dependence on log [HL] (monomeric D2EHPA) with slopes approaching 2 but following a different coordination scheme. These results strongly suggest the formation of CuL2 complexes without additional free D2EHPA molecules in the coordination sphere [11,32]. The distinct behavior in polar solvents stems from D2EHPA existing primarily in monomeric form, which fundamentally alters the extraction mechanism compared to non-polar systems [11,17]. The enhanced extraction efficiency at higher pH values is particularly pronounced in these polar diluents, as complete D2EHPA deprotonation facilitates optimal complexation conditions.
These findings provide crucial insights for industrial process optimization, demonstrating how solvent selection affects both the stoichiometry and efficiency of Cu(II) extraction with D2EHPA. The results emphasize the importance of considering both extractant concentration and diluent polarity when designing extraction systems.

3.3. Effect of Diluent on Copper(II) Extraction by D2EHPA

This study provides a systematic analysis of Cu(II) extraction with D2EHPA dissolved in seven diluents of different polarities, encompassing both non-polar (chloroform, toluene, dichloromethane, carbon tetrachloride, cyclohexane) and polar (1-octanol, methyl isobutyl ketone) solvents. The linear plots of log D versus pH for all systems, shown in Figure 4, yielded slopes close to 2.0. This confirms the proposed 2:1 stoichiometry (D2EHPA: Cu) for the extracted complex. Discrepancies between the extraction constants (log Kex) determined in this work (sulfate medium) and those reported for perchlorate media [32] are attributed to the greater complexation strength of the sulfate anion with Cu(II), which inhibits coordination with D2EHPA.
The extraction efficiency, ranked by the calculated Kex values, follows the order: 1-octanol > dichloromethane > chloroform. The highest performance in 1-octanol is notable, given the potential for diluent-extractant interaction. This is explained by the exclusive presence of D2EHPA in its monomeric form within the 1-octanol-water (Na2SO4) system. These monomeric entities readily facilitate the formation of the copper complex, leading to more efficient extraction. The tetrahedral geometry of the complexes formed in polar diluents like 1-octanol offers a further explanation for the enhanced performance. Conversely, the weakest extraction was observed in chloroform and dichloromethane, likely a result of strong intermolecular forces between the diluent and D2EHPA that diminish the extractant’s activity. The numerical log Kex values for all solvents are provided in Table 1.

3.4. Visible Spectra of the Organic Phase During Copper (II) Extraction

Figure 5 shows the visible spectra of the organic phase during copper (II) extraction by D2EHPA in different solvents. These spectra represent the absorbance properties of the complexes, which vary with various solvents, providing insights into the interactions between copper (II), the D2EHPA extractant, and the solvents; each colored line in the graph corresponds to a different solvent, with variations in peak positions and intensities suggesting differences in the complex formation or stability. The peak shapes and locations help understand how effectively copper (II) is being extracted in each case, which might correlate with the stability and structure of the copper–D2EHPA complexes in different environments. Figure 5 shows the scheme that delineates the structural configuration of the copper (II) complexes extracted and depicts the structure of the
The final stoichiometry of these organometallic entities was verified by acquiring electronic spectra from the organic phase during extraction. The spectra obtained in our study are similar to those published by R. Grimm et al. [27], indicating the existence of a square planar geometry for the copper(II) complexes with D2EHPA as the extractant. It is also important to note that, according to the literature [35], copper(II), with a d9 electronic configuration, forms both distorted octahedral and square planar geometries for its complexes, as shown in Table 2. The chemical reactions involved in the complexation of copper are shown in Equations (6) and (7), corresponding to non-polar solvents (dimeric D2EHPA) and polar solvents (monomeric D2EHPA), respectively.
C u 2 + + 2 ( H L ) 2 ¯ K e x 1 C u L 2 · 2 H L ¯ + 2 H +
C u 2 + + 2 H L ¯ K e x 1 C u L 2 ¯ + 2 H +
The molecular geometry of the extracted metal complex can be inferred from the spectral absorption maxima. For copper(II)–D2EHPA complexes formed in polar solvents, the recorded spectra are indicative of a tetrahedral coordination geometry.
Reference studies [34,36] report that the octahedral structure of copper(II)–D2EHPA complexes is generally stable and not influenced by the choice of solvent. The proposed CuL2 structure for these complexes is illustrated in Figure 6. The corresponding maximum absorption wavelengths (λ_max) for the complexes in various polar diluents are compiled in Table 3 and shown in Figure 7.
Interpreting the spectral differences in the copper(II)–D2EHPA complex between non-polar and polar solvents proved challenging, as the bands formed are very broad. According to R. Grimm and Z. Kolarik [27], the geometry of the extracted organometallic complex for copper (II) is square planar in inert solvents. In polar solvents, such as 2-ethylhexanol, the authors showed that the coordination is axial, with molecules of 2-ethylhexanol coordinating to the central copper(II) ion. A transformation from a square planar geometry in non-polar solvents to a tetrahedral geometry in polar solvents is thus suggested by the same authors.
The data presented in Table 4 clearly demonstrate the substantial influence of diluent polarity on copper(II) extraction efficiency. Under the specified conditions, 1-octanol demonstrates superior performance with an extraction efficiency of 66.67%, markedly outperforming chlorinated solvents. Dichloromethane and chloroform yield considerably lower efficiencies of 16.94% and 12.67%, respectively. These results underscore the critical influence of diluent polarity, with 1-octanol favoring monomeric D2EHPA and enhanced complexation, while chlorinated diluents exhibit weaker extraction due to dimerization and competitive interactions.

4. Conclusions

This study systematically investigated the influence of solvent polarity on the coordination geometry and extraction efficiency of Cu(II) complexes with D2EHPA. Through comprehensive analysis across a spectrum of diluents, clear structure–performance relationships were established, offering valuable insights for industrial hydrometallurgical applications.
The results demonstrate that polar diluents, such as 1-octanol and MIBK, promote the formation of tetrahedral Cu(II) complexes, enhancing extraction efficiency through improved solvation and interfacial mobility. In contrast, non-polar solvents like cyclohexane and carbon tetrachloride favor square planar geometries, which provide thermodynamic stability but limit mass transfer rates. Notably, 1-octanol exhibited superior extraction performance (log Kex = −3.69), attributed to its ability to stabilize D2EHPA in its monomeric form and facilitate favorable tetrahedral coordination.
Spectroscopic analysis unequivocally validated these mechanisms, with UV-Vis spectra revealing distinct absorption maxima at 844 nm and 820 nm for tetrahedral and square planar geometries, respectively. These findings not only corroborate and extend previous studies but also offer practical guidance for solvent selection in industrial contexts.
The implications of this work are substantial for process optimization: polar diluents are recommended for high-throughput extraction systems, whereas non-polar alternatives may be preferable when stripping efficiency is prioritized. These principles remain applicable even in challenging media, including chloride- and sulfate-rich solutions.
To translate these findings into industrially viable processes, future work should focus on systematically evaluating critical operational parameters such as temperature effects and extraction kinetics, which extend beyond the standardized conditions (25 °C and 30 min) used here. Additional priorities include the development of sustainable solvent alternatives and the application of these insights to complex multi-metal separation systems.

Author Contributions

Conceptualization, investigation, resources, and writing—original draft preparation, F.G. and D.B.; visualization and supervision, M.-A.K.; supervision, visualization, and writing—review and editing, M.-C.B.-A. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are available from the authors.

Acknowledgments

The authors sincerely thank Politecnico di Milano and the Directorate General of Scientific Research and Technological Development (DGRSDT) for their support.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Fu, F.; Wang, Q. Removal of heavy metal ions from wastewaters: A review. J. Environ. Manag. 2011, 92, 407–418. [Google Scholar] [CrossRef]
  2. Scholes, C.A.; Kanehashi, S.; Stevens, G.W.; Kentish, S.E. Water permeability and competitive permeation with CO2 and CH4 in perfluorinated polymeric membranes. Sep. Purif. Technol. 2015, 147, 203–209. [Google Scholar] [CrossRef]
  3. Babel, S.; Kurniawan, T.A. Low-cost adsorbents for heavy metals uptake from contaminated water: A review. J. Hazard. Mater. 2003, 97, 219–243. [Google Scholar] [CrossRef] [PubMed]
  4. Wang, J.; Chen, C. Biosorbents for heavy metals removal and their future. Biotechnol. Adv. 2009, 27, 195–226. [Google Scholar] [CrossRef]
  5. Hu, Y.; Chen, N.; Liu, T.; Feng, C.; Ma, L.; Chen, S.; Li, M. The mechanism of nitrate-Cr(VI) reduction mediated by microbial under different initial pHs. J. Hazard. Mater. 2020, 393, 122434. [Google Scholar] [CrossRef]
  6. Xu, C.; Liu, Q.; Liang, J.; Weng, Z.; Xu, J.; Jiang, Z.; Gu, A. Urinary biomarkers of polycyclic aromatic hydrocarbons and their associations with liver function in adolescents. Environ. Pollut. 2021, 278, 116842. [Google Scholar] [CrossRef] [PubMed]
  7. Yin, S.; Chen, W.; Chen, X.; Wang, L. Bacterial-mediated recovery of copper from low-grade copper sulphide using acid-processed rice straw. Bioresour. Technol. 2019, 288, 121605. [Google Scholar] [CrossRef]
  8. Lan, Z.Y.; Hu, Y.H.; Liu, J.S.; Wang, J. Solvent extraction of copper and zinc from bioleaching solutions with LIX984 and D2EHPA. J. Cent. South. Univ. Technol. 2005, 12, 45–49. [Google Scholar] [CrossRef]
  9. Oshima, T.; Fujiwara, I.; Baba, Y. Extraction behavior of metal ions using D2EHPA in cyclopentyl methyl ether. Solvent Extr. Res. Dev. Japan 2015, 22, 119–125. [Google Scholar] [CrossRef]
  10. Correa, M.M.J.; Silvas, F.P.C.; Aliprandini, P.; de Moraes, V.T.; Dreisinger, D.; Espinosa, D.C.R. Separation of copper from a leaching solution of printed circuit boards by using solvent extraction with D2EHPA. Braz. J. Chem. Eng. 2018, 35, 919–930. [Google Scholar] [CrossRef]
  11. Kongkapetchawan, P. Emulsion liquid membrane separation of copper from aqueous solution. Master's Thesis, Chulalongkorn University, Bangkok, Thailand, 1996. [Google Scholar]
  12. Zinov’eva, I.V.; Kozhevnikova, A.V.; Milevskii, N.A.; Zakhodyaeva, Y.A.; Voshkin, A.A. Extraction of Cu(II), Ni(II), and Al(III) with the Deep Eutectic Solvent D2EHPA/Menthol. Theor. Found Chem. Eng. 2022, 56, 221–229. [Google Scholar] [CrossRef]
  13. Batchu, N.K.; Binnemans, K. Effect of the diluent on the solvent extraction of neodymium(III) by bis(2-ethylhexyl)phosphoric acid (D2EHPA). Hydrometallurgy 2018, 177, 146–151. [Google Scholar] [CrossRef]
  14. Haghshenas Fatmehsari, D.; Darvishi, D.; Etemadi, S.; Eivazi Hollagh, A.R.; Keshavarz Alamdari, E.; Salardini, A.A. Interaction between TBP and D2EHPA during Zn, Cd, Mn, Cu, Co and Ni solvent extraction: A thermodynamic and empirical approach. Hydrometallurgy 2009, 98, 143–147. [Google Scholar] [CrossRef]
  15. Zheng, Q.; Zeng, L.; Cao, Z.; Wu, S.; Li, Q.; Wang, M.; Guan, W.; Zhang, G. A green and efficient process for the stepwise extraction of Cu, Ni, Co, Mn, and Li from Hazardous waste with a novel solvent extraction system of D2EHPA-NNPA. Green Chem. 2023, 25, 10020–10032. [Google Scholar] [CrossRef]
  16. Sözen, S.; Dulkadiroglu, H.; Begum Yucel, A.; Insel, G.; Orhon, D. Pollutant footprint analysis for wastewater management in textile dye houses processing different fabrics. J. Chem. Technol. Biotechnol. 2019, 94, 1330–1340. [Google Scholar] [CrossRef]
  17. Chang, S.H.; Teng, T.T.; Ismail, N. Optimization of Cu(II) extraction from aqueous solutions by soybean-oil-based organic solvent using response surface methodology. Water Air Soil. Pollut. 2011, 217, 567–576. [Google Scholar] [CrossRef]
  18. Chelouaou, S. Synergistic extraction of copper Cu(II) using di (2-ethyl hexyl) phosphoric acid (D2EHPA) and tri-n-octyl phosphine oxide (TOPO). In Proceedings of the 15th International Conference on Environmental Science and Technology, Xiamen, China, 21–23 November 2024; pp. 2–4. [Google Scholar]
  19. Lu, J.; Dreisinger, D. Solvent extraction of copper from chloride solution I: Extraction isotherms. Hydrometallurgy 2013, 137, 13–17. [Google Scholar] [CrossRef]
  20. Ruiz, M.C.; González, I.; Rodriguez, V.; Padilla, R. Solvent Extraction of Copper from Sulfate–Chloride Solutions Using LIX 84-IC and LIX 860-IC. Miner Process. Extr. Metall. Rev. 2021, 42, 1–8. [Google Scholar] [CrossRef]
  21. Ahamed, A.M.; Swoboda, B.; Arora, Z.; Lansot, J.Y.; Chagnes, A. Low-carbon footprint diluents in solvent extraction for lithium-ion battery recycling. RSC Adv. 2023, 13, 23334–23345. [Google Scholar] [CrossRef]
  22. Castillo, J.; Toro, N.; Hernández, P.; Navarro, P.; Vargas, C.; Gálvez, E.; Sepúlveda, R. Extraction of Cu(II), Fe(III), Zn(II), and Mn(II) from aqueous solutions with ionic liquid R4NCy. Metals 2021, 11, 1585. [Google Scholar] [CrossRef]
  23. Kuipa, P.K.; Hughes, M.A. Diluent effect on the solvent extraction rate of copper. Sep. Sci. Technol. 2002, 37, 1135–1152. [Google Scholar] [CrossRef]
  24. Persson, I.; Lundberg, D.; Bajnóczi, É.G.; Klementiev, K.; Just, J.; Sigfridsson Clauss, K.G.V. EXAFS Study on the Coordination Chemistry of the Solvated Copper(II) Ion in a Series of Oxygen Donor Solvents. Inorg. Chem. 2020, 59, 9538–9550. [Google Scholar] [CrossRef]
  25. Špadina, M.; Bohinc, K.; Zemb, T.; Dufrêche, J.F. Synergistic Solvent Extraction Is Driven by Entropy. ACS Nano 2019, 13, 13745–13758. [Google Scholar] [CrossRef]
  26. Zhang, R.; Liu, M.; Dai, Y. Extraction Equilibria of Copper(II) with D2EHPA in Kerosene from Aqueous Solutions in Acetate Buffer Media. J. Chem. Eng. Data 2007, 52, 438–441. [Google Scholar] [CrossRef]
  27. Grimm, R.; Kolařík, Z. Acidic organophosphorus extractants—XXV: Properties of complexes formed by Cu(II), Co(II), Ni(II), Zn(II) and Cd(II) with di(2-ethylhexyl) phosphoric acid in organic solvents. J. Inorg. Nucl. Chem. 1976, 38, 1493–1500. [Google Scholar] [CrossRef]
  28. Juang, R.S.; Chang, Y.T. Kinetics and Mechanism for Copper(II) Extraction from Sulfate Solutions with Bis(2-ethylhexyl)phosphoric Acid. Ind. Eng. Chem. Res. 1993, 32, 207–213. [Google Scholar] [CrossRef]
  29. Almi, S.; Bouzgou, M.; Adjal, F.; Barkat, D. Methyl-isobutyl ketone and 1-octanol as synergistic agents and phase modifiers in solvent extraction of cobalt(II) by the N-(2-hydroxybenzylidene)aniline from sulfate medium. Inorg. Nano-Metal. Chem. 2020, 50, 8–15. [Google Scholar] [CrossRef]
  30. Guerdouh, A.; Barkat, D. Influence of the solvent on the extraction of copper(II) from nitrate medium using salicylideneaniline. J. Dispers. Sci. Technol. 2017, 38, 930–934. [Google Scholar] [CrossRef]
  31. Ghebghoub, F.; Labed, N.; Barkat, D. Improved copper (II) extraction from aqueous solutions using di-2-ethylhexyl phosphoric acid and MIBK. Stud. Eng. EXACT Sci. 2024, 5, e12318. [Google Scholar] [CrossRef]
  32. Tao, W.; Nagaosa, Y. Solvent Extraction of Copper (II) with Di-2-Methylnonylphosphoric Acid in Some Organic Diluents. Solvent Extr. Ion. Exch. 2003, 21, 273–290. [Google Scholar] [CrossRef]
  33. Kozlevčar, B.; Gamez, P.; de Gelder, R.; Jagličić, Z.; Strauch, P.; Kitanovski, N.; Reedijk, J. Counterion and Solvent Effects on the Primary Coordination Sphere of Copper(II) Bis(3,5-dimethylpyrazol-1-yl)acetic Acid Coordination Compounds. Eur. J. Inorg. Chem. 2011, 2011, 3650–3655. [Google Scholar] [CrossRef]
  34. Van de Voorde, I.; Pinoy, L.; Courtijn, E.; Verpoort, F. Influence of acetate ions and the role of the diluents on the extraction of copper (II), nickel (II), cobalt (II), magnesium (II) and iron (II, III) with different types of extractants. Hydrometallurgy 2005, 78, 92–106. [Google Scholar] [CrossRef]
  35. Cotton, F.A.; Wilkinson, G.; Murillo, C.A.; Bochmann, M. Advanced Inorganic Chemistry; John Wiley & Sons: Hoboken, NJ, USA, 1999. [Google Scholar]
  36. Ying, Z.; Liu, S.; Li, G.; Wei, Q.; Ren, X. The effect of diluent on the extraction: Amide extracting chromium (VI) as an example. J. Mol. Liq. 2023, 384, 122205. [Google Scholar] [CrossRef]
Figure 1. Role of pH in Controlling the Distribution Coefficient of the D2EHPA/Diluent Organic Phase.
Figure 1. Role of pH in Controlling the Distribution Coefficient of the D2EHPA/Diluent Organic Phase.
Chemengineering 09 00107 g001
Figure 2. Role of D2EHPA Concentration in Determining the Distribution Coefficient (D).
Figure 2. Role of D2EHPA Concentration in Determining the Distribution Coefficient (D).
Chemengineering 09 00107 g002
Figure 3. Influence of the concentration of D2EHPA on the distribution coefficient D.
Figure 3. Influence of the concentration of D2EHPA on the distribution coefficient D.
Chemengineering 09 00107 g003
Figure 4. Role of pH in Copper(II) Extraction into Selected Diluents.
Figure 4. Role of pH in Copper(II) Extraction into Selected Diluents.
Chemengineering 09 00107 g004
Figure 5. Structure of the CuL2∙2HL complex (R = C8H17).
Figure 5. Structure of the CuL2∙2HL complex (R = C8H17).
Chemengineering 09 00107 g005
Figure 6. Structure of the CuL2 complex (R = C8H17).
Figure 6. Structure of the CuL2 complex (R = C8H17).
Chemengineering 09 00107 g006
Figure 7. Spectral Analysis of the Organic Phase during Copper(II) Extraction with D2EHPA.
Figure 7. Spectral Analysis of the Organic Phase during Copper(II) Extraction with D2EHPA.
Chemengineering 09 00107 g007
Table 1. Logarithmic values of extraction constants (K) for copper(II) extraction by D2EHPA in different diluents.
Table 1. Logarithmic values of extraction constants (K) for copper(II) extraction by D2EHPA in different diluents.
Aqueous PhaseDiluentlog KexReference
0.33 M Na2SO41-octanol−3.69This work
Dichloromethane−4.80
Chloroform−5.01
0.1 M (Na, H)ClO4Toluene−3.82[29]
1-octanol−3.78
Table 2. Maximum wavelengths of copper (II) complexes.
Table 2. Maximum wavelengths of copper (II) complexes.
SolventsWavelength (nm)
Chloroform820
Toluene819
Dichloromethane820
Carbon Tetrachloride818
Cyclohexane821
Table 3. Maximum wavelengths of copper (II) complexes.
Table 3. Maximum wavelengths of copper (II) complexes.
SolventsWavelength (nm)
MIBK844
1-octanol843
Table 4. Extraction efficiency of Cu(II).
Table 4. Extraction efficiency of Cu(II).
SolventsEfficiency (%)
Chloroform12.67
Dichloromethane16.94
1-Octanol66.67
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Ghebghoub, F.; Barkat, D.; Ben-Ameur, M.-C.; Kethiri, M.-A. Solvent-Dependent Coordination Geometry Shift in Copper(II)-D2EHPA Complexes: How Diluent Polarity Dictates Extraction Efficiency. ChemEngineering 2025, 9, 107. https://doi.org/10.3390/chemengineering9050107

AMA Style

Ghebghoub F, Barkat D, Ben-Ameur M-C, Kethiri M-A. Solvent-Dependent Coordination Geometry Shift in Copper(II)-D2EHPA Complexes: How Diluent Polarity Dictates Extraction Efficiency. ChemEngineering. 2025; 9(5):107. https://doi.org/10.3390/chemengineering9050107

Chicago/Turabian Style

Ghebghoub, Fatima, Djamel Barkat, Mohamed-Cherif Ben-Ameur, and Mohamed-Aymen Kethiri. 2025. "Solvent-Dependent Coordination Geometry Shift in Copper(II)-D2EHPA Complexes: How Diluent Polarity Dictates Extraction Efficiency" ChemEngineering 9, no. 5: 107. https://doi.org/10.3390/chemengineering9050107

APA Style

Ghebghoub, F., Barkat, D., Ben-Ameur, M.-C., & Kethiri, M.-A. (2025). Solvent-Dependent Coordination Geometry Shift in Copper(II)-D2EHPA Complexes: How Diluent Polarity Dictates Extraction Efficiency. ChemEngineering, 9(5), 107. https://doi.org/10.3390/chemengineering9050107

Article Metrics

Back to TopTop