Efficient separation of rhenium and molybdenum in phosphoric – sulfuric mixed-acid media via tertiary amine extraction

Abstract

The selective recovery of rhenium (Re) from molybdenum-rich (Mo) hydrometallurgical solutions is a persistent challenge, hindered by the chemical similarity of the two elements and the poor performance of conventional extraction systems. This study elucidates a highly efficient separation strategy using the tertiary amine extractant N235, uniquely enabled by a synergistic phosphoric–sulfuric mixed-acid medium. We reveal a novel dual-pathway separation mechanism termed “acidity regulation and ion competition.” Specifically, sulfuric acid modulates the solution acidity to promote the dissociation of extractable molybdate anions (PMo₁₂O₄₀³⁻) into non-extractable MoO₂²⁺. Concurrently, phosphoric acid introduces a high concentration of competitive phosphate anions that saturate the extractant’s active sites, effectively suppressing the co-extraction of any residual anionic Mo species. This synergistic effect, corroborated by FTIR and DFT calculations, leads to exceptional selectivity. Under optimized conditions, a single-stage Re extraction of 98.6% was achieved with only 1.4% Mo co-extraction, yielding an outstanding separation factor (β_Re/Mo) of 4183. Furthermore, the loaded Re was efficiently stripped (>98.2%) using 1 mol/L aqueous ammonia, and the organic system demonstrated excellent stability, maintaining over 96.3% extraction efficiency after six cycles. This work presents not only a robust and industrially viable process but also a new mechanistic paradigm for separating chemically analogous metals by synergistically manipulating solution speciation and competitive equilibria.

Keywords

rhenium / molybdenum / separation / solvent extraction / tertiary amine / mixed-acid media

References

[1] Hong T, Liu M-b, Ma Jet al. . Selective recovery of Rhenium from industrial leach solutions by synergistic solvent extraction [J]. Separation and Purification Technology. 2020, 236: 116281.

[2] Lunk H J, Drobot D V, Hartl H. Discovery, properties and applications of rhenium and its compounds [J]. ChemTexts. 2021, 7(1): 6.

[3] Ren Z, Leng C-b, Yang Y-pet al. . Microstructure and trace element occurrence in molybdenite (MoS₂) from the Dexing ore field: Implications for the differential enrichment of rhenium [J]. Ore Geology Reviews. 2025, 177106473.

[4] Aghajani H, Soflaei F G. Introduction and calculation of interaction coefficients in solvent extraction of rhenium from molybdenite [J]. Minerals Engineering. 2022, 190107869.

[5] Qi W, He J-h, Li M-jet al. . Efficient extraction of rhenium through demulsification of imidazolium ionic liquid-based microemulsions from aqueous solution [J]. Separation and Purification Technology. 2022, 297121574.

[6] Wang Y, Wang C-Y. Recent advances of rhenium separation and enrichment in China: Industrial processes and laboratory trials [J]. Chinese Chemical Letters. 2018, 293345-352.

[7] Salehi H, Tavakoli H, Aboutalebi M Ret al. . Recovery of molybdenum and rhenium in scrub liquors of fumes and dusts from roasting molybdenite concentrates [J]. Hydrometallurgy. 2019, 185: 142-148.

[8] Hou Y-r, Fu Z-q, Luo Jet al. . Selective separation of rhenium from oxygen-pressure leach solution of molybdenite concentrate using modified D201 resin: Experiments and theoretical calculations [J]. Journal of Molecular Liquids. 2024, 408: 125371.

[9] Shen L-t, Tesfaye F, Li X-bet al. . Review of rhenium extraction and recycling technologies from primary and secondary resources [J]. Minerals Engineering. 2021, 161106719.

[10] Li W-j, Dong X-l, Zhu L-het al. . Highly selective separation of Re(VII) from Mo(VI) by using biomaterial-based ionic gel adsorbents: Extractive adsorption enrichment of Re and surface blocking of Mo [J]. Chemical Engineering Journal. 2020, 387124078.

[11] Srivastava R R, Lee J C, Kim M S. Complexation chemistry in liquid–liquid extraction of rhenium [J]. Journal of Chemical Technology & Biotechnology. 2015, 90101752-1764.

[12] Zhang B, Liu H-z, Wang Wet al. . Recovery of rhenium from copper leach solutions using ion exchange with weak base resins [J]. Hydrometallurgy. 2017, 173: 50-56.

[13] Feng J-h, Yu H-q, Wang Y-cet al. . Sorption of rhenium on synthetic cyclohexylamine anion exchange resin LSC-436 [J]. Journal of Applied Polymer Science. 2022, 1392352315.

[14] Cheema H A, Ilyas S, Masud Set al. . Selective recovery of rhenium from molybdenite flue-dust leach liquor using solvent extraction with TBP [J]. Separation and Purification Technology. 2018, 191: 116-121.

[15] Petrova A M, Kasikov A G. Rhenium(VII) solvent extraction with mixtures of tertiary amine and oxygen-containing extractants from sulphate media [J]. Hydrometallurgy. 2016, 165: 270-274.

[16] Fang D-w, Shan W-j, Yan Qet al. . Extraction of rhenium from sulphuric acid solution with used amine N235 [J]. Fluid Phase Equilibria. 2014, 383: 1-4.

[17] Kang J-g, Kim Y U, Joo S Het al. . Behavior of extraction, stripping, and separation possibilities of rhenium and molybdenum from molybdenite roasting dust leaching solution using amine based extractant tri-otyl-amine (TOA) [J]. Materials Transactions. 2013, 5471209-1212.

[18] Wang H-d, Wang S-r, Gan Met al. . Selective extraction Re by N₂₃₅ in eluent of flue gas [J]. The Chinese Journal of Nonferrous Metals. 2017, 27(6): 1302-1309(in Chinese)

[19] Fan R-b, Liu R-z, Zhao Z-wet al. . Hydrometallurgical separation of Mo and Re from Rhenium-Containing molybdenum calcine for efficient rhenium recovery [J]. Separation and Purification Technology. 2025, 363: 132135.

[20] Wang Y-m, He Y, Yin S-het al. . Research on extraction of zinc from spent pickling solution using Aliquat 336 [J]. Hydrometallurgy. 2020, 193105322.

[21] He J, Cao S-q, Chen Y-met al. . Selective and efficient extraction of Cu(II) from a complex sulfate solution containing Co(II), Fe(II), Cu(II), and Zn(II) using DZ988N [J]. Journal of Central South University. 2023, 30(2): 454-464. in Chinese)

[22] Zhong X, Du J-w, Qing J-let al. . Deep removal of minor silicon in the crude nickel sulfate solution by solvent extraction of Si-Mo heteropoly acid [J]. Journal of Environmental Chemical Engineering. 2025, 131115021.

[23] Liu K, Cheng Y-f, Wu Yet al. . Efficient extraction of aluminum from leaching solutions of waste alnico alloys by CA12-N235 system [J]. Separation and Purification Technology. 2022, 281: 119938.

[24] Nabardi S, Aghazadeh V, Esrafili M Det al. . Separation of rhenium and molybdenum from autoclave acid-leach liquor of molybdenite concentrate using bifunctional ionic liquid [A336] [Cy272] in xylene [J]. Hydrometallurgy. 2025, 235106472.

[25] Liu R-z, Zhao Z-w, Li Y-li. Acid leaching–extraction–circulation process based on Mo(VI) coordination with H₃PO₄ to efficiently extract molybdenum from different components of molybdenum calcine [J]. Separation and Purification Technology. 2023, 322124269.

[26] Chen W-j, Zhai H-j, Huang Xet al. . On the electronic structure of mono-rhenium oxide clusters: ReOn- and ReO (n= 3, 4) [J]. Chemical Physics Letters. 2011, 5121–349-53.

[27] Dong L-m, Jiao F, Liu Wet al. . Optimization of AlN hydrolysis in aluminum dross based on response surface methodology and reaction kinetics [J]. Journal of Central South University. 2023, 3092993-3005.

[28] Cao X-y, Liu C-y, Huang X-pet al. . Uncovering the flotation performance and adsorption mechanism of a multifunctional thiocarbamate collector on malachite [J]. Powder Technology. 2022, 407: 117676.

[29] Jauhar R M, Era P, Viswanathan Vet al. . Crystal structure, molecular packing, FMO, NBO, nonlinear optical and optical limiting properties of an organic imidazolium diphenylacetate diphenylacetic acid single crystal [J]. New Journal of Chemistry. 2018, 4242439-2449.

[30] Shao Z-w, Jiang W-c, Zeng J-bet al. . pH-dependent degradation mechanisms of tetracyclines by non-radical 1O₂: A theoretical perspective based on DFT [J]. Separation and Purification Technology. 2025, 375133790.

[31] He H-x, Yang X-t, Li S-fet al. . Quaternary amine-functionalized electrospun nanofibers for selective gold capture: Experimental and DFT calculation study [J]. Separation and Purification Technology. 2025, 376133945.

[32] Zheng X-h, Zhang J-p, Shen J-det al. . Synergistic extraction of zinc from spent acid using P507-P204: A novel approach for efficient separation [J]. Journal of Environmental Chemical Engineering. 2024, 126114515.

RIGHTS & PERMISSIONS

Central South University