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Molecules
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Applications of Solvent Extraction and Absorption for Metal Recovery
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Applications of Solvent Extraction and Absorption for Metal Recovery

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Green Chemistry".

Deadline for manuscript submissions: 30 June 2024 | Viewed by 4175

Special Issue Editors

Dr. Qingjun Guan

E-Mail Website
Guest Editor
School of Resource Environment and Safety Engineering, Hunan University of Science and Technology, Xiangtan, China
Interests: solid waste recycling; crystal control; rare earth extraction; solvent extraction; flotation
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Zhenyue Zhang

E-Mail Website
Guest Editor
School of Resource & Safety Engineering, Wuhan Institute of Technology, Wuhan 430073, China
Interests: rare earth extraction; solid waste resource disposal and utilization; rare earth geochemistry; mine environment protection

Special Issue Information

Dear Colleagues,

Metals are essential and valuable resources in modern life. The recovery of metals from minerals, end-of-life products, industrial wastes, etc., is significant for sustainable development and recycling economics. The recycling process mainly involves pyro- and hydrometallurgical approaches. Within a hydrometallurgical route, solvent extraction (SX) is a mature and popular unit operation applied to separate, purify and concentrate metals from leaching solutions due to its strong extraction and absorption ability.

This Special Issue focuses on the latest research devoted to all aspects of innovative SX technology and new extractants. It is also a collection of original research that explores the potentialities of commercial or experimentally synthesized extractants in the design of SX processes to efficiently and selectively recover metals from the complex leaching media. Advances in alternative separation techniques whose functioning relies on SX principles are also welcome. Research articles focusing on the innovative application of SX in other fields and the development of integrated environmentally friendly and cost-effective hydrometallurgical processes to recover metals are encouraged as well.

We look forward to receiving your contributions.

Dr. Qingjun Guan
Prof. Dr. Zhenyue Zhang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • solvent extractant
  • leaching
  • eco-friendly processes
  • strategic and critical metals
  • adsorption
  • separation
  • wastewater treatment

Published Papers (4 papers)

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Research

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13 pages, 7070 KiB  
Article
Activation Mechanism of Fe2+ in Pyrrhotite Flotation: Microflotation and DFT Calculations
by Qiang Song, Xiong Tong, Pulin Dai, Xian Xie, Ruiqi Xie, Peiqiang Fan, Yuanlin Ma and Hang Chen
Molecules 2024, 29(7), 1490; https://doi.org/10.3390/molecules29071490 - 27 Mar 2024
Viewed by 423
Abstract
In industrial manufacturing, pyrrhotite(Fe1−xS), once depressed, is commonly activated for flotation. However, the replacement of CuSO4 is necessary due to the need for exact control over the dosage during the activation of pyrrhotite, which can pose challenges in industrial settings. [...] Read more.
In industrial manufacturing, pyrrhotite(Fe1−xS), once depressed, is commonly activated for flotation. However, the replacement of CuSO4 is necessary due to the need for exact control over the dosage during the activation of pyrrhotite, which can pose challenges in industrial settings. This research introduces the use of FeSO4 for the first time to efficiently activate pyrrhotite. The impact of two different activators on pyrrhotite was examined through microflotation experiments and density functional theory (DFT) calculations. Microflotation experiments confirmed that as the CuSO4 dosage increased from 0 to 8 × 10−4 mol/L, the recovery of pyrrhotite initially increased slightly from 71.27% to 87.65% but then sharply decreased to 16.47%. Conversely, when the FeSO4 dosage was increased from 0 to 8 × 10−4 mol/L, pyrrhotite’s recovery rose from 71.27% to 82.37%. These results indicate a higher sensitivity of CuSO4 to dosage variations, suggesting that minor alterations in dosage can significantly impact its efficacy under certain experimental conditions. In contrast, FeSO4 might demonstrate reduced sensitivity to changes in dosage, leading to more consistent performance. Fe ions can chemically adsorb onto the surface of pyrrhotite (001), creating a stable chemical bond, thereby markedly activating pyrrhotite. The addition of butyl xanthate (BX), coupled with the action of Fe2+ on activated pyrrhotite, results in the formation of four Fe-S bonds on Fe2+. The proximity of their atomic distances contributes to the development of a stable double-chelate structure. The S 3p orbital on BX hybridizes with the Fe 3d orbital on pyrrhotite, but the hybrid effect of Fe2+ activation is stronger than that of nonactivation. In addition, the Fe-S bond formed by the addition of activated Fe2+ has a higher Mulliken population, more charge overlap, and stronger covalent bonds. Therefore, Fe2+ is an excellent, efficient, and stable pyrrhotite activator. Full article
(This article belongs to the Special Issue Applications of Solvent Extraction and Absorption for Metal Recovery)
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15 pages, 2500 KiB  
Article
Solvent Extraction with Cyanex 923 to Remove Arsenic(V) from Solutions
by Francisco Jose Alguacil, Esther Escudero and Jose Ignacio Robla
Molecules 2024, 29(2), 470; https://doi.org/10.3390/molecules29020470 - 17 Jan 2024
Viewed by 770
Abstract
The removal of harmful arsenic(V) from aqueous solutions using Cyanex 923 (solvation extractant) was investigated using various experimental variables: equilibration time, the acidity of the aqueous phase, temperature, extractant and arsenic concentrations, and O/A ratio. Cyanex 923 extracted As(V) (and sulfuric acid) from [...] Read more.
The removal of harmful arsenic(V) from aqueous solutions using Cyanex 923 (solvation extractant) was investigated using various experimental variables: equilibration time, the acidity of the aqueous phase, temperature, extractant and arsenic concentrations, and O/A ratio. Cyanex 923 extracted As(V) (and sulfuric acid) from acidic solutions; however, it could not be used to remove the metal from slightly acid or neutral solutions. The extraction of arsenic is exothermic and responded to the formation of H3AsO4·nL species in the organic phase (L represents the extractant, and the stoichiometric factor, n = 1 or 2, depends on the acidity of the aqueous phase). Extraction isotherms are derived from the experimental results. Both arsenic and sulfuric acid loaded onto the organic phase can be stripped with water, and stripping isotherms are also derived from the experimental results. The selectivity of the system against the presence of other metals (Cu(II), Ni(II), Bi(III), and Sb(III)) is investigated, and the ability of Cyanex 923 to extract As(V) and sulfuric acid compared to the use of other P=O-based solvation reagents, such dibutyl butylphosphonate (DBBP) and tri-butyl phosphate (TBP), is also investigated. Full article
(This article belongs to the Special Issue Applications of Solvent Extraction and Absorption for Metal Recovery)
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12 pages, 4840 KiB  
Article
Selective Adsorption of Gadolinium by Nitrogen-Doped Carboxymethylated Cellulose Nanocrystalline Carbon Aerogels Functionalized in the Ammonia–Urea System
by Tongtong Xu, Xudong Zheng, Ang Li and Biao Ji
Molecules 2023, 28(24), 7965; https://doi.org/10.3390/molecules28247965 - 06 Dec 2023
Viewed by 736
Abstract
In this paper, an ammonia–urea system was developed to induce the shedding of carboxymethylcellulose carbon aerogels to form defects, and the specific surface area of the aerogels was significantly increased after carbonization, and the three-dimensional disordered pore structure of cellulose was preserved. The [...] Read more.
In this paper, an ammonia–urea system was developed to induce the shedding of carboxymethylcellulose carbon aerogels to form defects, and the specific surface area of the aerogels was significantly increased after carbonization, and the three-dimensional disordered pore structure of cellulose was preserved. The material showed the selective adsorption of gadolinium ions using the carboxylate active sites provided by carboxymethylation and the microporous or mesoporous structures formed after carbon burning. The successful synthesis of the material was demonstrated by relevant characterization, and the results of static adsorption experiments showed that the material was more consistent with the quasi second-order kinetic model at pH = 5.0. The maximum adsorption capacity was 99.65 mg g−1. The material showed a high adsorption capacity for gadolinium ions in the presence of competing ions and maintained 84.07% of the adsorption performance after five adsorption cycles. The simple use of urea ensured that the cellulose maintained its pore structure, and the specific surface area was greatly increased after carbonization, which provided a feasible direction for the industrial adsorption and recycling of rare-earth elements for reuse. Full article
(This article belongs to the Special Issue Applications of Solvent Extraction and Absorption for Metal Recovery)
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Review

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20 pages, 5241 KiB  
Review
A Critical Review of the Enhanced Recovery of Rare Earth Elements from Phosphogypsum
by Gang Xie, Qingjun Guan, Fujia Zhou, Weijian Yu, Zhigang Yin, Honghu Tang, Zhenyue Zhang and Ru’an Chi
Molecules 2023, 28(17), 6284; https://doi.org/10.3390/molecules28176284 - 28 Aug 2023
Cited by 5 | Viewed by 1668
Abstract
The increasing demand for rare earth elements (REEs), especially from new and innovative technology, has strained their supply, which makes the exploration of new REE sources necessary, for example, the recovery of REEs from phsophogypsum (PG). PG is a byproduct during the wet [...] Read more.
The increasing demand for rare earth elements (REEs), especially from new and innovative technology, has strained their supply, which makes the exploration of new REE sources necessary, for example, the recovery of REEs from phsophogypsum (PG). PG is a byproduct during the wet production of phosphoric acid, which is an attractive secondary resource for REEs due to a large amount of REEs locked in them. In most cases, REEs contained in PG are mainly encapsulated in the gypsum crystal, leading to a low leaching efficiency. Therefore, it is particularly important to use various methods to enhance the leaching of REEs from PG. In this review, we summarized and classified various enhanced leaching methods for the recovery of REEs from PG, and the advantages and disadvantages of different methods were compared. A joint method of recrystallization and RIL may be a promising enhanced leaching approach for the recovery of REEs from PG. Recrystallization could achieve both the complete REE release and simultaneous preparation of industrial materials with high value added, such as high-strength α-hemihydrate gypsum by phase transformation of PG, and the RIL technology could adsorb the releasing REEs and realize their efficient extraction. Such a combination appears to show significant advantages because of high REE recovery, as well as high value-added product preparation at low cost. Full article
(This article belongs to the Special Issue Applications of Solvent Extraction and Absorption for Metal Recovery)
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