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A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Extractive Metallurgy".

Deadline for manuscript submissions: 30 June 2024 | Viewed by 20043

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Prof. Dr. Antonije Onjia

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Faculty of Technology and Metallurgy, University of Belgrade, Belgrade, Serbia
Interests: environmental chemistry; analytical chemistry; chemometrics; environmental radioactivity; chromatographic techniques; environmental pollution; physical chemistry
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Special Issue Information

Dear Colleagues,

The rapid technological development that we have witnessed in recent years has caused an increase in demand for metals. An essential step in the production of metals is their separation from aqueous solutions obtained from leaching ore or recycling waste. Adsorption is considered an effective technique for the recovery or removal of metals from aqueous media. It offers excellent workability in process operation and design, and sorbent can be reused after proper regeneration. Many traditional sorbents, including inorganic clays/zeolites, activated carbon, and polymeric resins, have been used for metal ion separation. Recently, advanced sorbents, such as modified natural inorganic/organic materials, modified carbons/biochar, agricultural waste (biosorbent), metal–organic frameworks, synthesized polymers, magnetic sorbents, hydrogels, and nanosorbents, were successfully applied in the separation of metals.

In this Special Issue in Metals, we welcome reviews and articles in the areas of separation of metal ions, including new and modified sorbent preparation, characterization and applications, mechanism elucidation, and theoretical calculation.

This issue will be focused but not limited to advances in:

Synthesis and characterization of advanced sorbent materials;
Physical and chemical modifications and functionalization of sorbents;
Theoretical considerations of interactions between dissolved metals and solid surfaces;
Adsorption mechanism of metal cations, metal oxyanions, and metal complexes;
Process design in static and flow systems;
Automatization of the adsorption processes;
Miniaturization of adsorption and solid-phase extraction of metals;
Novel applications of sorbents for metal ion separation.

This open access issue aims to outline the current state of the art in the area of separation of metals by modern sorbents.

Prof. Dr. Antonije Onjia
Guest Editor

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. Metals is an international peer-reviewed open access monthly 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 2600 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

Adsorption
Cations
Oxyanions
Removal
Leaching
Hydrometallurgy

Published Papers (10 papers)

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Research

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22 pages, 5046 KiB

Open AccessArticle

Performance Assessment of Wood Ash and Bone Char for Manganese Treatment in Acid Mine Drainage

by Ivana Smičiklas, Bojan Janković, Mihajlo Jović, Jelena Maletaškić, Nebojša Manić and Snežana Dragović

Metals 2023, 13(10), 1665; https://0-doi-org.brum.beds.ac.uk/10.3390/met13101665 - 28 Sep 2023

Cited by 1 | Viewed by 807

Abstract

Developing efficient methods for Mn separation is the most challenging in exploring innovative and sustainable acid mine drainage (AMD) treatments. The availability and capacity of certain waste materials for Mn removal warrant further exploration of their performance regarding the effect of process factors. This study addressed the influence of AMD chemistry (initial pH and concentrations of Mn, sulfate, and Fe), the solid/solution ratio, and the contact time on Mn separation by wood ash (WA) and bone char (BC). At an equivalent dose, WA displayed higher neutralization and Mn removal capacity over the initial pH range of 2.5–6.0 due to lime, dicalcium silicate, and fairchildite dissolution. On the other hand, at optimal doses, Mn separation by BC was faster, it was less affected by coexisting sulfate and Fe(II) species, and the carbonated hydroxyapatite structure of BC remained preserved. Efficient removal of Mn was feasible only at final pH values ≥ 9.0 in all systems with WA and at pH 6.0–6.4 using BC. These conclusions were confirmed by treating actual AMD with variable doses of both materials. The water-leaching potential of toxic elements from the AMD/BC treatment residue complied with the limits for inert waste. In contrast, the residue of AMD/WA treatment leached non-toxic quantities of Cr and substantial amounts of Al due to high residual alkalinity. To minimize the amount of secondary waste generated by BC application, its use emerges particularly beneficial after AMD neutralization in the finishing step intended for Mn removal. Full article

(This article belongs to the Special Issue Advanced Sorbents for Separation of Metal Ions)

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15 pages, 2399 KiB

Open AccessArticle

Selection of Operation Conditions for a Batch Brown Seaweed Biosorption System for Removal of Copper from Aqueous Solutions

by Henrik K. Hansen, Claudia Gutiérrez, Natalia Valencia, Claudia Gotschlich, Andrea Lazo, Pamela Lazo and Rodrigo Ortiz-Soto

Metals 2023, 13(6), 1008; https://0-doi-org.brum.beds.ac.uk/10.3390/met13061008 - 23 May 2023

Cited by 1 | Viewed by 1006

Abstract

Heavy metal exposure from wastewater is an important environmental issue worldwide. In the search for more efficient treatment technologies, biosorption has been presented as an alternative for contaminant removal from wastewaters. The aim of this work is to determine the operation parameters of copper adsorption followed by biosorbent regeneration. The algae Durvillaea antarctica and Lessonia trabeculata were used as biosorbents in batch experiments. These biosorbents were exposed to different conditions, such as pH, copper concentration, exposure time, mass-to-volume ratios and regeneration reagents. Batch sorption tests revealed an adequate pH of 4.5–5.0. The selected biosorbent was D. antarctica due to a considerably higher copper retention capacity. As a regenerating reagent, sulfuric acid was more efficient. For diluted copper solutions (10 to 100 mg L⁻¹), a biosorbent particle size of between 1.70 and 3.36 mm showed better retention capacity than larger particles and a biosorbent mass-to-volume ratio of 10 g L⁻¹ was desirable for these metal concentrations. Full article

(This article belongs to the Special Issue Advanced Sorbents for Separation of Metal Ions)

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18 pages, 6871 KiB

Open AccessArticle

Raw Eggshell as an Adsorbent for Copper Ions Biosorption—Equilibrium, Kinetic, Thermodynamic and Process Optimization Studies

by Miljan Marković, Milan Gorgievski, Nada Štrbac, Vesna Grekulović, Kristina Božinović, Milica Zdravković and Milovan Vuković

Metals 2023, 13(2), 206; https://0-doi-org.brum.beds.ac.uk/10.3390/met13020206 - 20 Jan 2023

Cited by 3 | Viewed by 2209

Abstract

The study on the biosorption of copper ions using raw eggshells as an adsorbent is presented in this paper. The influence of different process parameters, such as: initial pH value of the solution, initial Cu²⁺ ions concentration, initial mass of the adsorbent, and stirring rate, on the biosorption capacity was evaluated. The SEM-EDS analysis was performed before and after the biosorption process. SEM micrographs indicate a change in the morphology of the sample after the biosorption process. The obtained EDS spectra indicated that K, Ca, and Mg were possibly exchanged with Cu²⁺ ions during the biosorption process. The equilibrium analysis showed that the Langmuir isotherm model best describes the experimental data. Four kinetic models were used to analyze the experimental data, and the results revealed that the pseudo-first order kinetic model is the best fit for the analyzed data. Calculated thermodynamic data indicated that the biosorption process is spontaneous, and that copper ions are possibly bound to the surface of the eggshells by chemisorption. The biosorption process was optimized using Response Surface Methodology (RSM) based on the Box-Behnken Design (BBD), with the selected factors: adsorbent mass, initial metal ion concentration, and contact time. Full article

(This article belongs to the Special Issue Advanced Sorbents for Separation of Metal Ions)

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13 pages, 2941 KiB

Open AccessArticle

Use of Ion-Exchange Resins to Adsorb Scandium from Titanium Industry’s Chloride Acidic Solution at Ambient Temperature

by Eleni Mikeli, Danai Marinos, Aikaterini Toli, Anastasia Pilichou, Efthymios Balomenos and Dimitrios Panias

Metals 2022, 12(5), 864; https://0-doi-org.brum.beds.ac.uk/10.3390/met12050864 - 18 May 2022

Cited by 5 | Viewed by 2295

Abstract

Scandium metal has generated a lot of interest during the past years. This is due to the various crucial applications it has found ground in and the lack of production in countries outside China and Russia. Apart from rare earth ores, scandium is present in a variety of wastes and by-products originating from metallurgical processes and is not currently being sufficiently valorised. One of these processes is the production of titanium dioxide, which leaves an acidic iron chloride solution with a considerably high concentration of scandium (10–140 ppm) and is currently sold as a by-product. This research aims to recover scandium without affecting the solution greatly so that it can still be resold as a by-product after the treatment. To achieve this, two commercial ion-exchange resins, VP OC 1026 and TP 260, are used in the column setup. Their breakthrough curves are plotted with mathematical modelling and compared. Results indicate that VP OC 1026 resin is the most promising for Sc extraction with a column capacity of 1.46 mg/mL, but Zr, Ti, and V coextract have high capacities, while Fe does not interfere with the adsorption. Full article

(This article belongs to the Special Issue Advanced Sorbents for Separation of Metal Ions)

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11 pages, 1076 KiB

Open AccessArticle

Dispersive Solid–Liquid Microextraction Based on the Poly(HDDA)/Graphene Sorbent Followed by ICP-MS for the Determination of Rare Earth Elements in Coal Fly Ash Leachate

by Latinka Slavković-Beškoski, Ljubiša Ignjatović, Guido Bolognesi, Danijela Maksin, Aleksandra Savić, Goran Vladisavljević and Antonije Onjia

Metals 2022, 12(5), 791; https://0-doi-org.brum.beds.ac.uk/10.3390/met12050791 - 04 May 2022

Cited by 11 | Viewed by 1721

Abstract

A dispersive solid-phase microextraction (DSPME) sorbent consisting of poly(1,6-hexanediol diacrylate)-based polymer microspheres, with embedded graphene microparticles (poly(HDDA)/graphene), was synthesized by microfluidic emulsification/photopolymerization and characterized by optical microscopy and X-ray fluorescence spectrometry. This sorbent was applied for simple, fast, and sensitive vortex-assisted DSPME of rare earth elements (RREs) in coal fly ash (CFA) leachate, prior to their quantification by inductively coupled plasma mass spectrometry (ICP-MS). Among nine DSPME variables, the Plackett–Burman screening design (PBD), followed by the central composite optimization design (CCD) using the Derringer desirability function (D), identified the eluent type as the most influencing DSPME variable. The optimum conditions with maximum D (0.65) for the chelating agent di-(2-ethylhexyl) phosphoric acid (D2EHPA) amount, the sorbent amount, the eluting solvent, the extraction temperature, the centrifuge speed, the vortexing time, the elution time, the centrifugation time, and pH, were set to 60 μL, 30 mg, 2 M HNO₃, 25 °C, 6000 rpm, 1 min, 1 min, 5 min, and 4.2, respectively. Analytical validation of the DSPME method for 16 REEs (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in CFA leachate samples estimated the detection limits at the low ppt level, the recovery range 43–112%, and relative standard deviation within ± 22%. This method was applied to a water extraction procedure (EP) and acetic acid toxicity characteristic leaching procedure (TCLP) for leachate of CFA, from five different coal-fired thermoelectric power plants. The most abundant REEs in leachate (20 ÷ 1 solid-to-liquid ratio) are Ce, Y, and La, which were found in the range of 22–194 ng/L, 35–105 ng/L, 48–95 ng/L, and 9.6–51 μg/L, 7.3–22 μg/L, 2.4–17 μg/L, for EP and TCLP leachate, respectively. The least present REE in TCLP leachate was Lu (42–125 ng/L), which was not detected in EP leachate. Full article

(This article belongs to the Special Issue Advanced Sorbents for Separation of Metal Ions)

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13 pages, 23016 KiB

Open AccessArticle

Recovery of Vanadium (V) Oxyanions by a Magnetic Macroporous Copolymer Nanocomposite Sorbent

by Ljiljana Suručić, Tamara Tadić, Goran Janjić, Bojana Marković, Aleksandra Nastasović and Antonije Onjia

Metals 2021, 11(11), 1777; https://0-doi-org.brum.beds.ac.uk/10.3390/met11111777 - 04 Nov 2021

Cited by 9 | Viewed by 1527

Abstract

An amino-functionalized magnetic macroporous copolymer of glycidyl methacrylate (GM) and ethylene glycol (E) dimethacrylate (m-poly(GME)-deta) was synthesized, fully characterized, and used to investigate the adsorption of vanadium (V) oxyanions from aqueous solutions (Ci = 0.5 mM) in a batch system at room temperature (298 K). Pseudo-first-order (PFO), pseudo-second-order (PSO), Elovich, and intra-particle diffusion (IPD) models were used to analyze the kinetic data. The study showed that sorption is rapid, i.e., the sorption half-time is approximately one minute. Initially, the sorption process primarily involved surface sorbent particles, and it was best described by the PSO model. However, after saturation of the surface active sites is attained, the sorption rate decreases significantly because of limitations of the diffusion rate, which is then primarily controlled by the IPD process. The sorption process is favorable in the pH range of 3–6 due to the strong electrostatic interactions between the absorption centers of copolymer and vanadium (V) oxyanions. In the stated pH range, deta absorption centers with two and three protonated N atoms are in equilibrium as studied by quantum chemical modeling. Among V(V) species present in diluted aqueous media, the adsorption of H₂VO₄⁻ ions dominates. Full article

(This article belongs to the Special Issue Advanced Sorbents for Separation of Metal Ions)

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10 pages, 1178 KiB

Open AccessArticle

Extraction of Cu(II), Fe(III), Zn(II), and Mn(II) from Aqueous Solutions with Ionic Liquid R₄NCy

by Jonathan Castillo, Norman Toro, Pía Hernández, Patricio Navarro, Cristian Vargas, Edelmira Gálvez and Rossana Sepúlveda

Metals 2021, 11(10), 1585; https://0-doi-org.brum.beds.ac.uk/10.3390/met11101585 - 05 Oct 2021

Cited by 5 | Viewed by 2151

Abstract

The leaching of copper ores produces a rich solution with metal interferences. In this context, Fe(III), Zn(II), and Mn(II) are three metals contained in industrial copper-rich solutions in high quantities and eventually can be co-extracted with the copper. The purpose of the current study was to determine the feasibly of solvent extraction with the use of ionic liquid methyltrioctyl/decylammonium bis (2,4,4-trimethylpentyl)phosphinate (R₄NCy) as an extractant of Cu(II) in the presence of Fe(III), Zn(II), and Mn(II). In general terms, the results showed a high single extraction efficiency of all the metals under study. In the case of Fe(III) and Zn(II), the extraction was close to 100%. On the contrary, the stripping efficiency was poor to Fe(III) and discrete to Zn(II), but very high to Cu(II) and Mn(II). Finally, the findings of this study suggest that the ionic liquid R₄NCy is feasible for the pre-treatment of the copper solvent extraction process to remove metal impurities such as Fe(III) and Zn(II). Full article

(This article belongs to the Special Issue Advanced Sorbents for Separation of Metal Ions)

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22 pages, 6243 KiB

Open AccessArticle

Influence of Electrolyte Impurities from E-Waste Electrorefining on Copper Extraction Recovery

by Jovana Djokić, Dragana Radovanović, Zlatko Nikolovski, Zoran Andjić and Željko Kamberović

Metals 2021, 11(9), 1383; https://0-doi-org.brum.beds.ac.uk/10.3390/met11091383 - 31 Aug 2021

Cited by 2 | Viewed by 2455

Abstract

In order to reflect possible issues in future sole e-waste processing, an electrolyte of complex chemical composition reflecting system of sole e-waste processing was obtained by following a specially designed pyro-electrometallurgical method. The obtained non-standard electrolyte was further used for the purpose of comprehensive metal interference evaluation on the copper solvent extraction (SX) process. Optimization of the process included a variation of several process parameters, allowing determination of the effect of the most abundant and potentially the most influential impurities (Ni, Sn, Fe, and Zn) and 14 other trace elements. Moreover, comparing three commercial extractants of different active chelating groups, it was determined that branched aldoxime reagent is favorable for Cu extraction from the chemically complex system, as can be expected in future e-waste recycling. The results of this study showed that, under optimal conditions of 20 vol.% extractant concentration, feed pH 1.5, O/A ratio 3, and 10-min phase contact time, 88.1% of one stage Cu extraction was achieved. Co-extraction of the Fe, Zn, Ni, and Sn was under 8%, while Pb and trace elements were negligible. Optimal conditions (H₂SO₄ 180 g/L, O/A = 2, and contact time 5 min) enabled 95.3% Cu stripping and under 6% of the most influential impurities. In addition, an impurity monitoring and distribution methodology enabled a better understanding and design of the process for the more efficient valorization of metals from e-waste. Full article

(This article belongs to the Special Issue Advanced Sorbents for Separation of Metal Ions)

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Review

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20 pages, 1808 KiB

Open AccessReview

Metal Recovery from Wastewater Using Electrodialysis Separation

by Maria del Mar Cerrillo-Gonzalez, Maria Villen-Guzman, Jose Miguel Rodriguez-Maroto and Juan Manuel Paz-Garcia

Metals 2024, 14(1), 38; https://0-doi-org.brum.beds.ac.uk/10.3390/met14010038 - 28 Dec 2023

Cited by 1 | Viewed by 1401

Abstract

Electrodialysis is classified as a membrane separation process in which ions are transferred through selective ion-exchange membranes from one solution to another using an electric field as the driving force. Electrodialysis is a mature technology in the field of brackish water desalination, but in recent decades the development of new membranes has made it possible to extend their application in the food, drug, and chemical process industries, including wastewater treatment. This work describes the state of the art in the use of electrodialysis (ED) for metal removal from water and wastewater. The fundamentals of the technique are introduced based on the working principle, operational features, and transport mechanisms of the membranes. An overview of the key factors (i.e., the membrane properties, the cell configuration, and the operational conditions) in the ED performance is presented. This review highlights the importance of studying the inter-relation of parameters affecting the transport mechanism to design and optimize metal recovery through ED. The conventional applications of ED for the desalination of brackish water and demineralization of industrial process water and wastewater are discussed to better understand the key role of this technology in the separation, concentration, and purification of aqueous effluents. The recovery and concentration of metals from industrial effluents are evaluated based on a review of the literature dealing with effluents from different sources. The most relevant results of these experimental studies highlight the key role of ED in the challenge of selective recovery of metals from aqueous effluents. This review addresses the potential application of ED not only for polluted water treatment but also as a promising tool for the recovery of critical metals to avoid natural resource depletion, promoting a circular economy. Full article

(This article belongs to the Special Issue Advanced Sorbents for Separation of Metal Ions)

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30 pages, 4142 KiB

Open AccessReview

Methacrylate-Based Polymeric Sorbents for Recovery of Metals from Aqueous Solutions

by Aleksandra Nastasović, Bojana Marković, Ljiljana Suručić and Antonije Onjia

Metals 2022, 12(5), 814; https://0-doi-org.brum.beds.ac.uk/10.3390/met12050814 - 08 May 2022

Cited by 9 | Viewed by 2973

Abstract

The industrialization and urbanization expansion have increased the demand for precious and rare earth elements (REEs). In addition, environmental concerns regarding the toxic effects of heavy metals on living organisms imposed an urgent need for efficient methods for their removal from wastewaters and aqueous solutions. The most efficient technique for metal ions removal from wastewaters is adsorption due to its reversibility and high efficiency. Numerous adsorbents were mentioned as possible metal ions adsorbents in the literature. Chelating polymer ligands (CPLs) with adaptable surface chemistry, high affinity towards targeted metal ions, high capacity, fast kinetics, chemically stable, and reusable are especially attractive. This review is focused on methacrylate-based magnetic and non-magnetic porous sorbents. Special attention was devoted to amino-modified glycidyl methacrylate (GMA) copolymers. Main adsorption parameters, kinetic models, adsorption isotherms, thermodynamics of the adsorption process, as well as regeneration of the polymeric sorbents were discussed. Full article

(This article belongs to the Special Issue Advanced Sorbents for Separation of Metal Ions)

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