Special Issue "Hydrometallurgy"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 July 2015)

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Guest Editor
Prof. Suresh Bhargava

Director - Centre of Advanced Materials & Industrial Chemistry, School of Applied Sciences, RMIT University, GPO BOX 2476, Melbourne 3000, Australia
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Interests: nanobiotechnology, resource utilization, applied electrochemistry, organometallic and supramolecular, catalysis and biocatalysis, sensors
Guest Editor
Dr. Mark Pownceby

CSIRO Mineral Resources, Private Bag 10, Clayton South 3169, Victoria, Australia
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Interests: Geology, Uranium Geometallurgy and Mineral Science Related to Hydrometallurgy of Minerals
Editorial Assistant
Dr. Rahul Ram

Post Doctoral Fellow at RMIT University
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Interests: hydrometallurgy; minerals science; chemical engineering

Special Issue Information

Dear Colleagues,

Hydrometallurgy, which involves the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual material, plays an integral role in the multi-billion dollar minerals processing industry. There are numerous hydrometallurgical process technologies used for recovering metals, such as: agglomeration; leaching; solvent extraction/ion exchange; metal recovery; and remediation of tailings/waste.

Modern hydrometallurgical routes to extract metals from their ores are faced with a number of issues related to both the chemistry and engineering aspects of the processes involved. These issues include declining ore grade, variations in mineralogy across the deposits and geo-metallurgical locations of the ore site; which would influence the hydrometallurgical route chosen. The development of technologies to improve energy efficiency, water/resources consumption and waste remediation across the circuit is also an important factor to be considered. Therefore, there is an increasing need to develop novel solutions to these existing problems, to implement environmentally sustainable practices in the recovery of these valuable metals.

Papers on recent advances, and review articles, particularly in regard to fundamental chemistry and the development of novel techniques and technologies in commercial processing of mineral commodities from their ores, are invited for inclusion in this Special Issue on "Hydrometallurgy".

Professor Suresh Bhargava
Dr. Mark Pownceby
Guest Editors

Manuscript Submission Information

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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 1000 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

  • base metals
  • uranium
  • thorium
  • gold
  • silver
  • mineral sands
  • complex sulphides
  • atmospheric leaching
  • pressure leaching
  • bio leaching
  • heap leaching
  • in-situ leaching
  • solvent extraction
  • electrowinning process
  • bio-remediation
  • waste removal
  • hydrometallurgy

Published Papers (23 papers)

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Editorial

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Open AccessEditorial Hydrometallurgy
Metals 2016, 6(5), 122; doi:10.3390/met6050122
Received: 18 May 2016 / Accepted: 18 May 2016 / Published: 23 May 2016
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Abstract
Hydrometallurgy, which involves the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual material, plays an integral role in the multi-billion dollar minerals processing industry.[...] Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available

Research

Jump to: Editorial, Review

Open AccessFeature PaperArticle The Eh-pH Diagram and Its Advances
Metals 2016, 6(1), 23; doi:10.3390/met6010023
Received: 29 July 2015 / Revised: 22 December 2015 / Accepted: 28 December 2015 / Published: 14 January 2016
Cited by 5 | PDF Full-text (12853 KB) | HTML Full-text | XML Full-text
Abstract
Since Pourbaix presented Eh versus pH diagrams in his “Atlas of Electrochemical Equilibria in Aqueous Solution”, diagrams have become extremely popular and are now used in almost every scientific area related to aqueous chemistry. Due to advances in personal computers, such diagrams can
[...] Read more.
Since Pourbaix presented Eh versus pH diagrams in his “Atlas of Electrochemical Equilibria in Aqueous Solution”, diagrams have become extremely popular and are now used in almost every scientific area related to aqueous chemistry. Due to advances in personal computers, such diagrams can now show effects not only of Eh and pH, but also of variables, including ligand(s), temperature and pressure. Examples from various fields are illustrated in this paper. Examples include geochemical formation, corrosion and passivation, precipitation and adsorption for water treatment and leaching and metal recovery for hydrometallurgy. Two basic methods were developed to construct an Eh-pH diagram concerning the ligand component(s). The first method calculates and draws a line between two adjacent species based on their given activities. The second method performs equilibrium calculations over an array of points (500 × 800 or higher are preferred), each representing one Eh and one pH value for the whole system, then combines areas of each dominant species for the diagram. These two methods may produce different diagrams. The fundamental theories, illustrated results, comparison and required conditions behind these two methods are presented and discussed in this paper. The Gibbs phase rule equation for an Eh-pH diagram was derived and verified from actual plots. Besides indicating the stability area of water, an Eh-pH diagram normally shows only half of an overall reaction. However, merging two or more related diagrams together reveals more clearly the possibility of the reactions involved. For instance, leaching of Au with cyanide followed by cementing Au with Zn (Merrill-Crowe process) can be illustrated by combining Au-CN and Zn-CN diagrams together. A second example of the galvanic conversion of chalcopyrite can be explained by merging S, Fe–S and Cu–Fe–S diagrams. The calculation of an Eh-pH diagram can be extended easily into another dimension, such as the concentration of a given ligand, temperature or showing the solubility of stable solids. A personal computer is capable of drawing the diagram by utilizing a 3D program, such as ParaView, or VisIt, or MATLAB. Two 3D wireframe volume plots of a Uranium-carbonate system from Garrels and Christ were used to verify the Eh-pH calculation and the presentation from ParaView. Although a two-dimensional drawing is still much clearer to read, a 3D graph can allow one to visualize an entire system by executing rotation, clipping, slicing and making a movie. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
Open AccessArticle Direct Aqueous Mineral Carbonation of Waste Slate Using Ammonium Salt Solutions
Metals 2015, 5(4), 2413-2427; doi:10.3390/met5042413
Received: 18 October 2015 / Revised: 9 December 2015 / Accepted: 15 December 2015 / Published: 18 December 2015
Cited by 2 | PDF Full-text (1156 KB) | HTML Full-text | XML Full-text
Abstract
The carbonation of asbestos-containing waste slate using a direct aqueous mineral carbonation method was evaluated. Leaching and carbonation tests were conducted on asbestos-containing waste slate using ammonium salt (CH3COONH4, NH4NO3, and NH4HSO4) solutions at various concentrations. The CH3COONH4 solution had the highest Ca-leaching
[...] Read more.
The carbonation of asbestos-containing waste slate using a direct aqueous mineral carbonation method was evaluated. Leaching and carbonation tests were conducted on asbestos-containing waste slate using ammonium salt (CH3COONH4, NH4NO3, and NH4HSO4) solutions at various concentrations. The CH3COONH4 solution had the highest Ca-leaching efficiency (17%–35%) and the NH4HSO4 solution had the highest Mg-leaching efficiency (7%–24%) at various solid dosages and solvent concentrations. The CaCO3 content of the reacted materials based on thermogravimetric analysis (TGA) was approximately 10%–17% higher than that of the as-received material for the 1 M CH3COONH4 and the 1 M NH4HSO4 solutions. The carbonates were precipitated on the surface of chrysotile, which was contained in the waste slate reacted with CO2. These results imply that CO2 can be sequestered by a direct aqueous mineral carbonation using waste slate. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Palladium(II) Recovery from Hydrochloric Acid Solutions by N,N′-Dimethyl-N,N′-Dibutylthiodiglycolamide
Metals 2015, 5(4), 2303-2315; doi:10.3390/met5042303
Received: 27 October 2015 / Revised: 24 November 2015 / Accepted: 30 November 2015 / Published: 8 December 2015
Cited by 4 | PDF Full-text (370 KB) | HTML Full-text | XML Full-text
Abstract
N,N′-dimethyl-N,N′-dibutylthiodiglycolamide (DMDBTDGA) has been synthesized, characterized, and is investigated in this work as a potential liquid-liquid extractant for palladium(II), platinum(IV), and rhodium(III) from hydrochloric acid solutions. Pd(II) is the only ion which is efficiently removed by
[...] Read more.
N,N′-dimethyl-N,N′-dibutylthiodiglycolamide (DMDBTDGA) has been synthesized, characterized, and is investigated in this work as a potential liquid-liquid extractant for palladium(II), platinum(IV), and rhodium(III) from hydrochloric acid solutions. Pd(II) is the only ion which is efficiently removed by DMDBTDGA in toluene from 1.5 M to 4.5 M HCl, but it is not extracted from 7.5 M HCl. Pd(II) stripping is quantitatively achieved by an acidic thiourea solution. Pd(II) extraction kinetics are highly favored (2–5 min). Distribution data points to a DMDBTDGA:Pd(II) species with a 1:1 molar ratio. Pd(II) can selectively be recovered by DMDBTDGA from 4.0 M HCl complex mixtures containing equivalent concentrations of Pt(IV) and Rh(III). When five-fold Fe(III) and Al(III) concentrations are present, only Pt(IV) in the presence of Fe(III), and Fe(III) itself, are extensively co-extracted together with Pd(II). However, Fe(III) can easily be eliminated through an intermediate scrubbing step with water. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Copper and Cyanide Extraction with Emulsion Liquid Membrane with LIX 7950 as the Mobile Carrier: Part 1, Emulsion Stability
Metals 2015, 5(4), 2034-2047; doi:10.3390/met5042034
Received: 19 August 2015 / Accepted: 14 October 2015 / Published: 4 November 2015
Cited by 3 | PDF Full-text (474 KB) | HTML Full-text | XML Full-text
Abstract
The potential use of emulsion liquid membranes (ELMs) with LIX 7950 as the mobile carrier to remove heavy metals from waste cyanide solutions has been proposed. Relatively stable ELMs with reasonable leakage and swelling can be formed under suitable mixing time and speed
[...] Read more.
The potential use of emulsion liquid membranes (ELMs) with LIX 7950 as the mobile carrier to remove heavy metals from waste cyanide solutions has been proposed. Relatively stable ELMs with reasonable leakage and swelling can be formed under suitable mixing time and speed during emulsification. The concentration of LIX 7950 and Span 80 in the membrane phase, KOH in the internal phase and the volume ratio of membrane to internal phases are also critical to ELM formation. The efficiency of copper and cyanide removal from dilute cyanide solution by ELMs is related to ELM stability to some extent. More than 90% copper and cyanide can be removed from dilute cyanide solutions by ELMs formed under suitable experimental conditions. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle CFD Modelling of Flow and Solids Distribution in Carbon-in-Leach Tanks
Metals 2015, 5(4), 1997-2020; doi:10.3390/met5041997
Received: 29 July 2015 / Revised: 14 October 2015 / Accepted: 23 October 2015 / Published: 28 October 2015
Cited by 1 | PDF Full-text (1009 KB) | HTML Full-text | XML Full-text
Abstract
The Carbon-in-Leach (CIL) circuit plays an important role in the economics of a gold refinery. The circuit uses multiphase stirred tanks in series, in which problems such as dead zones, short-circuiting, and presence of unsuspended solids are detrimental to its efficiency. Therefore, the
[...] Read more.
The Carbon-in-Leach (CIL) circuit plays an important role in the economics of a gold refinery. The circuit uses multiphase stirred tanks in series, in which problems such as dead zones, short-circuiting, and presence of unsuspended solids are detrimental to its efficiency. Therefore, the hydrodynamics of such a system is critical for improving the performance. The hydrodynamics of stirred tanks can be resolved using computational fluid dynamics (CFD). While the flow generated by the impellers in the CIL tanks is complex and modelling it in the presence of high solid concentration is challenging, advances in CFD models, such as turbulence and particle-fluid interactions, have made modelling of such flows feasible. In the present study, the hydrodynamics of CIL tanks was investigated by modelling it using CFD. The models used in the simulations were validated using experimental data at high solid loading of 40 wt. % in a lab scale tank. The models were further used for examining the flow generated by pitched blade turbine and HA-715 Mixtec impellers in lab scale CIL tanks with 50 wt. % solids. The effect of design and operating parameters such as off-bottom clearance, impeller separation, impeller speed, scale-up, and multiple-impeller configuration on flow field and solid concentrations profiles was examined. For a given impeller speed, better solids suspension is observed with dual impeller and triple impeller configurations. The results presented in the paper are useful for understanding the hydrodynamics and influence of design and operating parameters on industrial CIL tanks. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Effect of Polymer Addition on the Structure and Hydrogen Evolution Reaction Property of Nanoflower-Like Molybdenum Disulfide
Metals 2015, 5(4), 1829-1844; doi:10.3390/met5041829
Received: 8 September 2015 / Revised: 24 September 2015 / Accepted: 25 September 2015 / Published: 9 October 2015
Cited by 3 | PDF Full-text (1527 KB) | HTML Full-text | XML Full-text
Abstract
Nano-structured molybdenum disulfide (MoS2) catalysts have been extensively developed for the hydrogen evolution reaction (HER). Herein, a novel hydrothermal intercalation approach is employed to fabricate nanoflower-like 2H–MoS2 with the incorporation of three polymers, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and polyethylenimine
[...] Read more.
Nano-structured molybdenum disulfide (MoS2) catalysts have been extensively developed for the hydrogen evolution reaction (HER). Herein, a novel hydrothermal intercalation approach is employed to fabricate nanoflower-like 2H–MoS2 with the incorporation of three polymers, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and polyethylenimine (PEI). The as-prepared MoS2 specimens were characterized by techniques of scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), together with Raman and Fourier transform infrared spectroscopy (FTIR). The HER properties of these lamellar nanoflower-like composites were evaluated using electrochemical tests of linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The existent polymer enlarges the interlayer spacing of the lamellar MoS2, and reduces its stacked thickness. The lamellar MoS2 samples exhibit a promoting activity in HER at low additions of these three polymers (0.04 g/g MoS2 for PVA and PEI, and 0.08 g/g MoS2 for PVP). This can be attributed to the fact that the expanded interlayer of MoS2 can offer abundant exposed active sites for HER. Conversely, high additions of the polymers exert an obvious interference in the HER activity of the lamellar MoS2. Compared with the samples of MoS2/PVP–0.08 and MoS2/PEI–0.04, the MoS2/PVA–0.04 composite exhibits excellent activity in HER, in terms of higher current density and lower onset potential. Full article
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Open AccessArticle Removal of Zn from Contaminated Sediment by FeCl3 in HCl Solution
Metals 2015, 5(4), 1812-1820; doi:10.3390/met5041812
Received: 28 July 2015 / Revised: 25 September 2015 / Accepted: 5 October 2015 / Published: 8 October 2015
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Abstract
Harbor sediments contaminated with ZnS concentrate were treated by ferric chloride in HCl solution to remove Zn. The sediments were evaluated using Tessier’s sequential extraction method to determine the different metal phase associations of Zn. Leaching tests were performed to investigate the effects
[...] Read more.
Harbor sediments contaminated with ZnS concentrate were treated by ferric chloride in HCl solution to remove Zn. The sediments were evaluated using Tessier’s sequential extraction method to determine the different metal phase associations of Zn. Leaching tests were performed to investigate the effects of experimental factors, such as agitation speed, ferric ion concentration, temperature, and pulp density, on the removal of Zn. The sequential extraction procedure revealed that about 17.7% of Zn in the sediment was associated with soluble carbonate and oxide phases. The results of the leaching tests indicated that higher ferric concentration and temperature increased the leaching efficiencies significantly, while the agitation speed has a negligible effect on the removal of Zn. The removal ratio increased to more than 99% within 120 min of treatment at 1 kmol·m−3 HCl solution with 1 kmol·m−3 Fe3+, 10% pulp density, and 400 rpm at 90 °C. The dissolution kinetics of Zn were discussed by comparing the two shrinking core models. It was determined that the kinetic data followed the diffusion controlled model well compared to the surface chemical reaction model. The activation energies were calculated to be 76.9 kJ/mol, 69.6 kJ/mol, and 58.5 kJ/mol for 0.25 kmol·m−3, 0.5 kmol·m−3, and 1 kmol·m−3 Fe3+, respectively. Full article
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Open AccessArticle Decontamination of Uranium-Contaminated Soil Sand Using Supercritical CO2 with a TBP–HNO3 Complex
Metals 2015, 5(4), 1788-1798; doi:10.3390/met5041788
Received: 31 July 2015 / Revised: 18 September 2015 / Accepted: 18 September 2015 / Published: 25 September 2015
Cited by 4 | PDF Full-text (750 KB) | HTML Full-text | XML Full-text
Abstract
An environmentally friendly decontamination process for uranium-contaminated soil sand is proposed. The process uses supercritical CO2 as the cleaning solvent and a TBP–HNO3 complex as the reagent. Four types of samples (sea sand and coarse, medium, and fine soil sand) were
[...] Read more.
An environmentally friendly decontamination process for uranium-contaminated soil sand is proposed. The process uses supercritical CO2 as the cleaning solvent and a TBP–HNO3 complex as the reagent. Four types of samples (sea sand and coarse, medium, and fine soil sand) were artificially contaminated with uranium. The effects of the amount of the reagent, sand type, and elapsed time after the preparation of the samples on decontamination were examined. The extraction ratios of uranium in all of the four types of sand samples were very high when the time that elapsed after preparation was less than a few days. The extraction ratio of uranium decreased in the soil sand with a higher surface area as the elapsed time increased, indicating the possible formation of chemisorbed uranium on the surface of the samples. The solvent of supercritical CO2 seemed to be very effective in the decontamination of soil sand. However, the extraction of chemisorbed uranium in soil sand may need additional processes, such as the application of mechanical vibration and the addition of bond-breaking reagents. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Preparation of Potassium Ferrate from Spent Steel Pickling Liquid
Metals 2015, 5(4), 1770-1787; doi:10.3390/met5041770
Received: 31 July 2015 / Revised: 7 September 2015 / Accepted: 18 September 2015 / Published: 24 September 2015
Cited by 1 | PDF Full-text (678 KB) | HTML Full-text | XML Full-text
Abstract
Potassium ferrate (K2FeO4) is a multi-functional green reagent for water treatment with considerable combined effectiveness in oxidization, disinfection, coagulation, sterilization, adsorption, and deodorization, producing environment friendly Fe(III) end-products during the reactions. This study uses a simple method to lower
[...] Read more.
Potassium ferrate (K2FeO4) is a multi-functional green reagent for water treatment with considerable combined effectiveness in oxidization, disinfection, coagulation, sterilization, adsorption, and deodorization, producing environment friendly Fe(III) end-products during the reactions. This study uses a simple method to lower Fe(VI) preparation cost by recycling iron from a spent steel pickling liquid as an iron source for preparing potassium ferrate with a wet oxidation method. The recycled iron is in powder form of ferrous (93%) and ferric chlorides (7%), as determined by X-ray Absorption Near Edge Spectrum (XANES) simulation. The synthesis method involves three steps, namely, oxidation of ferrous/ferric ions to form ferrate with NaOCl under alkaline conditions, substitution of sodium with potassium to form potassium ferrate, and continuously washing impurities with various organic solvents off the in-house ferrate. Characterization of the in-house product with various instruments, such as scanning electron microscopy (SEM), ultraviolet-visible (UV-Vis), X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS), proves that product quality and purity are comparative to a commercialized one. Methylene blue (MB) de-colorization tests with in-house potassium ferrate shows that, within 30 min, almost all MB molecules are de-colorized at a Fe/carbon mole ratio of 2/1. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Exploring the Possibilities of Biological Fabrication of Gold Nanostructures Using Orange Peel Extract
Metals 2015, 5(3), 1609-1619; doi:10.3390/met5031609
Received: 22 July 2015 / Revised: 3 September 2015 / Accepted: 6 September 2015 / Published: 11 September 2015
Cited by 2 | PDF Full-text (908 KB) | HTML Full-text | XML Full-text
Abstract
Development of nanotechnology requires a constant innovation and improvement in many materials. The exploration of natural resources is a promising eco-friendly alternative for physical and chemical methods. In the present work, colloidal gold nanostructures were prepared using orange peel extract as a stabilizing
[...] Read more.
Development of nanotechnology requires a constant innovation and improvement in many materials. The exploration of natural resources is a promising eco-friendly alternative for physical and chemical methods. In the present work, colloidal gold nanostructures were prepared using orange peel extract as a stabilizing and reducing agent. The initial pH value of the solution and the concentration of the gold precursor had an effect on the formation and morphology of nanoparticles. The method developed is environmentally friendly and allows control of nanoparticles. By controlling the pH and, especially, the gold concentration, we are able to synthesize crystalline gold nanowires using orange peel extract in the absence of a surfactant or polymer to direct nanoparticle growth, and without external seeding. UV-VIS spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to characterize the nanoparticles obtained by biosynthesis. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Nickel Extraction from Olivine: Effect of Carbonation Pre-Treatment
Metals 2015, 5(3), 1620-1644; doi:10.3390/met5031620
Received: 19 August 2015 / Revised: 2 September 2015 / Accepted: 6 September 2015 / Published: 11 September 2015
Cited by 6 | PDF Full-text (1483 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this work, we explore a novel mineral processing approach using carbon dioxide to promote mineral alterations that lead to improved extractability of nickel from olivine ((Mg,Fe)2SiO4). The precept is that by altering the morphology and the mineralogy of
[...] Read more.
In this work, we explore a novel mineral processing approach using carbon dioxide to promote mineral alterations that lead to improved extractability of nickel from olivine ((Mg,Fe)2SiO4). The precept is that by altering the morphology and the mineralogy of the ore via mineral carbonation, the comminution requirements and the acid consumption during hydrometallurgical processing can be reduced. Furthermore, carbonation pre-treatment can lead to mineral liberation and concentration of metals in physically separable phases. In a first processing step, olivine is fully carbonated at high CO2 partial pressures (35 bar) and optimal temperature (200 °C) with the addition of pH buffering agents. This leads to a powdery product containing high carbonate content. The main products of the carbonation reaction include quasi-amorphous colloidal silica, chromium-rich metallic particles, and ferro-magnesite ((Mg1−x,Fex)CO3). Carbonated olivine was subsequently leached using an array of inorganic and organic acids to test their leaching efficiency. Compared to leaching from untreated olivine, the percentage of nickel extracted from carbonated olivine by acid leaching was significantly increased. It is anticipated that the mineral carbonation pre-treatment approach may also be applicable to other ultrabasic and lateritic ores. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Heavy Metal Behavior in Lichen-Mine Waste Interactions at an Abandoned Mine Site in Southwest Japan
Metals 2015, 5(3), 1591-1608; doi:10.3390/met5031591
Received: 13 July 2015 / Revised: 26 August 2015 / Accepted: 28 August 2015 / Published: 2 September 2015
Cited by 3 | PDF Full-text (1324 KB) | HTML Full-text | XML Full-text
Abstract
The lichen, Stereocaulon exutum Nylander, occurring in a contaminated abandoned mine site was investigated to clarify (1) the behavior of heavy metals and As during the slag weathering processes mediated by the lichen; and (2) the distribution of these elements in the lichen
[...] Read more.
The lichen, Stereocaulon exutum Nylander, occurring in a contaminated abandoned mine site was investigated to clarify (1) the behavior of heavy metals and As during the slag weathering processes mediated by the lichen; and (2) the distribution of these elements in the lichen thallus on slag. The heavy metals and As in the slag are dissolved from their original phases during the weathering process by lichen substances (organic acids) and hypha penetration, in addition to non-biological weathering. The dissolved elements are absorbed into the lichen thallus. Some of these dissolved elements are distributed in the cells of the hyphae. The others are distributed on the surface of the hyphae as formless particles and show lateral distribution inside the cortex of the thallus. The Cu and Zn concentrations in the thalli are positively correlated with the concentrations in the corresponding substrata and a positive intercept in the regression curve obtained using a linear function. These chemical characteristics make this lichen a good biomarker for Cu and Zn contamination of the substrata of the lichen. Therefore, the present study supposes that Stereocaulon exutum has a possible practical application in biomonitoring or risk assessment of heavy metal pollution at abandoned mine sites. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Chalcopyrite Dissolution at 650 mV and 750 mV in the Presence of Pyrite
Metals 2015, 5(3), 1566-1579; doi:10.3390/met5031566
Received: 6 August 2015 / Revised: 21 August 2015 / Accepted: 25 August 2015 / Published: 28 August 2015
Cited by 1 | PDF Full-text (721 KB) | HTML Full-text | XML Full-text
Abstract
The dissolution of chalcopyrite in association with pyrite in mine waste results in the severe environmental issue of acid and metalliferous drainage (AMD). To better understand chalcopyrite dissolution, and the impact of chalcopyrite’s galvanic interaction with pyrite, chalcopyrite dissolution has been examined at
[...] Read more.
The dissolution of chalcopyrite in association with pyrite in mine waste results in the severe environmental issue of acid and metalliferous drainage (AMD). To better understand chalcopyrite dissolution, and the impact of chalcopyrite’s galvanic interaction with pyrite, chalcopyrite dissolution has been examined at 75 °C, pH 1.0, in the presence of quartz (as an inert mineral) and pyrite. The presence of pyrite increased the chalcopyrite dissolution rate by more than five times at Eh of 650 mV (SHE) (Cu recovery 2.5 cf. 12% over 132 days) due to galvanic interaction between chalcopyrite and pyrite. Dissolution of Cu and Fe was stoichiometric and no pyrite dissolved. Although the chalcopyrite dissolution rate at 750 mV (SHE) was approximately four-fold greater (Cu recovery of 45% within 132 days) as compared to at 650 mV in the presence of pyrite, the galvanic interaction between chalcopyrite and pyrite was negligible. Approximately all of the sulfur from the leached chalcopyrite was converted to S0 at 750 mV, regardless of the presence of pyrite. At this Eh approximately 60% of the sulfur associated with pyrite dissolution was oxidised to S0 and the remaining 40% was released in soluble forms, e.g., SO42. Full article
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Open AccessArticle Separation and Recycling for Rare Earth Elements by Homogeneous Liquid-Liquid Extraction (HoLLE) Using a pH-Responsive Fluorine-Based Surfactant
Metals 2015, 5(3), 1543-1552; doi:10.3390/met5031543
Received: 27 July 2015 / Accepted: 25 August 2015 / Published: 27 August 2015
Cited by 3 | PDF Full-text (422 KB) | HTML Full-text | XML Full-text
Abstract
A selective separation and recycling system for metal ions was developed by homogeneous liquid-liquid extraction (HoLLE) using a fluorosurfactant. Sixty-two different elemental ions (e.g., Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga,
[...] Read more.
A selective separation and recycling system for metal ions was developed by homogeneous liquid-liquid extraction (HoLLE) using a fluorosurfactant. Sixty-two different elemental ions (e.g., Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, In, Ir, La, Lu, Mg, Mn, Mo, Nb, Nd, Ni, Os, P, Pb, Pd, Pr, Pt, Re, Rh, Ru, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Tb, Te, Ti, Tl, Tm, V, W, Y, Yb, Zn, and Zr) were examined. By changing pH from a neutral or alkaline solution (pH ≥ 6.5) to that of an acidic solution (pH < 4.0), gallium, zirconium, palladium, silver, platinum, and rare earth elements were extracted at >90% efficiency into a sedimented Zonyl FSA® (CF3(CF2)n(CH2)2S(CH2)2COOH, n = 6–8) liquid phase. Moreover, all rare earth elements were obtained with superior extraction and stripping percentages. In the recycling of rare earth elements, the sedimented phase was maintained using a filter along with a mixed solution of THF and 1 M sodium hydroxide aqueous solution. The Zonyl FSA® was filtrated and the rare earth elements were recovered on the filter as a hydroxide. Furthermore, the filtrated Zonyl FSA was reusable by conditioning the subject pH. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Use of Nanoscale Zero-Valent Iron (NZVI) Particles for Chemical Denitrification under Different Operating Conditions
Metals 2015, 5(3), 1507-1519; doi:10.3390/met5031507
Received: 9 July 2015 / Revised: 7 August 2015 / Accepted: 18 August 2015 / Published: 21 August 2015
Cited by 8 | PDF Full-text (658 KB) | HTML Full-text | XML Full-text
Abstract
The nitrate pollution of waters and groundwaters is an important environmental and health concern. An interesting method to remove the oxidized forms of nitrogen from waters and wastewaters is chemical denitrification by means of metallic iron (Fe0). Particularly advantageous is the
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The nitrate pollution of waters and groundwaters is an important environmental and health concern. An interesting method to remove the oxidized forms of nitrogen from waters and wastewaters is chemical denitrification by means of metallic iron (Fe0). Particularly advantageous is the use of nanoscopic zero-valent iron particles due to the elevated surface area, which allows reaching extremely high reaction rates. In the present paper, the efficiency of nitrate reduction by means of nanoscopic Fe0 has been investigated under several operating conditions. The iron nanoparticles were synthesized by the chemical reduction of ferric ions with sodium borohydride. The effects of Fe0 dosage, initial N–NO3 concentration and pH on chemical denitrification were identified. In particular, the results of the tests carried out showed that it is possible to reach an almost complete nitrate reduction in treating solutions with a nitrate nitrogen concentration higher than 50 mg/L. Moreover, the process performance was satisfactory also under uncontrolled pH. By means of the trends detected during the experiments, the kinetic-type reaction was identified. Furthermore, a relation between the kinetic constant and the process parameters was defined. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle A Straightforward Route to Tetrachloroauric Acid from Gold Metal and Molecular Chlorine for Nanoparticle Synthesis
Metals 2015, 5(3), 1454-1461; doi:10.3390/met5031454
Received: 5 June 2015 / Revised: 12 August 2015 / Accepted: 12 August 2015 / Published: 18 August 2015
Cited by 4 | PDF Full-text (539 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Aqueous solutions of tetrachloroauric acid of high purity and stability were synthesised using the known reaction of gold metal with chlorine gas. The straightforward procedure developed here allows the resulting solution to be used directly for gold nanoparticle synthesis. The procedure involves bubbling
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Aqueous solutions of tetrachloroauric acid of high purity and stability were synthesised using the known reaction of gold metal with chlorine gas. The straightforward procedure developed here allows the resulting solution to be used directly for gold nanoparticle synthesis. The procedure involves bubbling chlorine gas through pure water containing a pellet of gold. The reaction is quantitative and progressed at a satisfactory rate at 50 °C. The gold(III) chloride solutions produced by this method show no evidence of returning to metallic gold over at least twelve months. This procedure also provides a straightforward method to determine the concentration of the resulting solution using the initial mass of gold and volume of water. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Copper Recovery from Polluted Soils Using Acidic Washing and Bioelectrochemical Systems
Metals 2015, 5(3), 1328-1348; doi:10.3390/met5031328
Received: 1 July 2015 / Revised: 10 July 2015 / Accepted: 14 July 2015 / Published: 23 July 2015
Cited by 6 | PDF Full-text (666 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Excavation followed by landfilling is the most common method for treating soils contaminated by metals. However, as this solution is not sustainable, alternative techniques are required. Chemical soil washing is one such alternative. The aim of this experimental lab-scale study is to develop
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Excavation followed by landfilling is the most common method for treating soils contaminated by metals. However, as this solution is not sustainable, alternative techniques are required. Chemical soil washing is one such alternative. The aim of this experimental lab-scale study is to develop a remediation and metal recovery method for Cu contaminated sites. The method is based on the washing of soil or ash (combusted soil/bark) with acidic waste liquids followed by electrolytic Cu recovery by means of bioelectrochemical systems (BES). The results demonstrate that a one- or two-step acidic leaching process followed by water washing removes >80 wt. % of the Cu. Copper with 99.7–99.9 wt. % purity was recovered from the acidic leachates using BES. In all experiments, electrical power was generated during the reduction of Cu. This clearly indicates that Cu can also be recovered from dilute solutions. Additionally, the method has the potential to wash co-pollutants such as polycyclic aromatic hydrocarbons (PAHs) and oxy-PAHs. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
Open AccessArticle The Effect of Grinding and Roasting Conditions on the Selective Leaching of Nd and Dy from NdFeB Magnet Scraps
Metals 2015, 5(3), 1306-1314; doi:10.3390/met5031306
Received: 7 June 2015 / Revised: 10 July 2015 / Accepted: 14 July 2015 / Published: 17 July 2015
Cited by 2 | PDF Full-text (570 KB) | HTML Full-text | XML Full-text
Abstract
The pretreatment processes consisting of grinding followed by roasting were investigated to improve the selective leaching of Nd and Dy from neodymium-iron-boron (NdFeB) magnet scraps. The peaks of Nd(OH)3 and Fe were observed in XRD results after grinding with NaOH as the
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The pretreatment processes consisting of grinding followed by roasting were investigated to improve the selective leaching of Nd and Dy from neodymium-iron-boron (NdFeB) magnet scraps. The peaks of Nd(OH)3 and Fe were observed in XRD results after grinding with NaOH as the amount of water addition increased to 5 cm3. These results indicate that the components of Nd and Fe in NdFeB magnet could be changed successfully into Nd(OH)3 and Fe, respectively. In the roasting tests using the ground product, with increasing roasting temperature to 500 °C, the peaks of Nd(OH)3 and Fe disappeared while those of Nd2O3 and Fe2O3 were shown. The peaks of NdFeO3 in the sample roasted at 600 °C were observed in the XRD pattern. Consequently, 94.2%, 93.1%, 1.0% of Nd, Dy, Fe were leached at 400 rpm and 90 °C in 1 kmol·m−3 acetic acid solution with 1% pulp density using a sample prepared under the following conditions: 15 in stoichiometric molar ratio of NaOH:Nd, 550 rpm in rotational grinding speed, 5 cm3 in water addition, 30 min in grinding time, 400 °C and 2 h in roasting temperature and time. The results indicate that the selective leaching of Nd and Dy from NdFeB magnet could be achieved successfully by grinding and then roasting treatments. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessArticle Experimental Simulation of Long Term Weathering in Alkaline Bauxite Residue Tailings
Metals 2015, 5(3), 1241-1261; doi:10.3390/met5031241
Received: 18 June 2015 / Revised: 6 July 2015 / Accepted: 7 July 2015 / Published: 14 July 2015
Cited by 3 | PDF Full-text (1254 KB) | HTML Full-text | XML Full-text
Abstract
Bauxite residue is an alkaline, saline tailings material generated as a byproduct of the Bayer process used for alumina refining. Developing effective plans for the long term management of potential environmental impacts associated with storage of these tailings is dependent on understanding how
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Bauxite residue is an alkaline, saline tailings material generated as a byproduct of the Bayer process used for alumina refining. Developing effective plans for the long term management of potential environmental impacts associated with storage of these tailings is dependent on understanding how the chemical and mineralogical properties of the tailings will change during weathering and transformation into a soil-like material. Hydrothermal treatment of bauxite residue was used to compress geological weathering timescales and examine potential mineral transformations during weathering. Gibbsite was rapidly converted to boehmite; this transformation was examined with in situ synchrotron XRD. Goethite, hematite, and calcite all precipitated over longer weathering timeframes, while tricalcium aluminate dissolved. pH, total alkalinity, and salinity (electrical conductivity) all decreased during weathering despite these experiments being performed under “closed” conditions (i.e., no leaching). This indicates the potential for auto-attenuation of the high alkalinity and salinity that presents challenges for long term environmental management, and suggests that management requirements will decrease during weathering as a result of these mineral transformations. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
Open AccessArticle “High-Throughput” Evaluation of Polymer-Supported Triazolic Appendages for Metallic Cations Extraction
Metals 2015, 5(1), 418-427; doi:10.3390/met5010418
Received: 25 February 2015 / Revised: 5 March 2015 / Accepted: 7 March 2015 / Published: 12 March 2015
Cited by 2 | PDF Full-text (836 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this work was to find and use a low-cost high-throughput method for a quick primary evaluation of several metal extraction by substituted piperazines appendages as chelatants grafted onto Merrifield polymer using click-chemistry by the copper (I)-catalyzed Huisgen’s reaction (CuAAC) The
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The aim of this work was to find and use a low-cost high-throughput method for a quick primary evaluation of several metal extraction by substituted piperazines appendages as chelatants grafted onto Merrifield polymer using click-chemistry by the copper (I)-catalyzed Huisgen’s reaction (CuAAC) The polymers were tested for their efficiency to remove various metal ions from neutral aqueous solutions (13 cations studied: Li+, Na+, K+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Cd2+, Ba2+, Ce3+, Hg+ and Pb2+) using the simple conductimetric measurement method. The polymers were found to extract all metals with low efficiencies ≤40%), except for Fe3+ and Hg+, and sometimes Pb2+. Some polymers exhibited a selectively for K+, Cd2+ and Ba2+, with good efficiencies. The values obtained here using less polymer, and a faster method, are in fair correspondence (average difference ±16%) with another published evaluation by atomic absorption spectroscopy (AAS). Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available

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Open AccessReview Hydrometallurgical Recovery of Precious Metals and Removal of Hazardous Metals Using Persimmon Tannin and Persimmon Wastes
Metals 2015, 5(4), 1921-1956; doi:10.3390/met5041921
Received: 3 June 2015 / Revised: 24 September 2015 / Accepted: 29 September 2015 / Published: 23 October 2015
Cited by 3 | PDF Full-text (1157 KB) | HTML Full-text | XML Full-text
Abstract
Novel and environmentally benign adsorbents were prepared via a simple sulfuric acid treatment process using the wastes of astringent persimmon, a type of biomass waste, along with persimmon tannin extract which is currently employed for the tanning of leather and as natural dyes
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Novel and environmentally benign adsorbents were prepared via a simple sulfuric acid treatment process using the wastes of astringent persimmon, a type of biomass waste, along with persimmon tannin extract which is currently employed for the tanning of leather and as natural dyes and paints. The effectiveness of these new biosorbents was exemplified with regards to hydrometallurgical and environmental engineering applications for the adsorptive removal of uranium and thorium from rare earths, cesium from other alkaline metals such as sodium, hexa-valent chromium from zinc as well as adsorptive recovery of gold from chloride media. Furthermore, reductive coagulation of gold from chloride media for the direct recovery of metallic gold and adsorptive recovery of palladium and platinum using chemically modified persimmon tannin extract were studied. OPEN Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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Open AccessReview Tannins in Mineral Processing and Extractive Metallurgy
Metals 2015, 5(3), 1520-1542; doi:10.3390/met5031520
Received: 28 July 2015 / Revised: 18 August 2015 / Accepted: 21 August 2015 / Published: 27 August 2015
Cited by 3 | PDF Full-text (811 KB) | HTML Full-text | XML Full-text
Abstract
This study provides an up to date review of tannins, specifically quebracho, in mineral processing and metallurgical processes. Quebracho is a highly useful reagent in many flotation applications, acting as both a depressant and a dispersant. Three different types of quebracho are mentioned
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This study provides an up to date review of tannins, specifically quebracho, in mineral processing and metallurgical processes. Quebracho is a highly useful reagent in many flotation applications, acting as both a depressant and a dispersant. Three different types of quebracho are mentioned in this study; quebracho “S” or Tupasol ATO, quebracho “O” or Tupafin ATO, and quebracho “A” or Silvafloc. It should be noted that literature often refers simply to “quebracho” without distinguishing a specific type. Quebracho is most commonly used in industry as a method to separate fluorite from calcite, which is traditionally quite challenging as both minerals share a common ion—calcium. Other applications for quebracho in flotation with calcite minerals as the main gangue source include barite and scheelite. In sulfide systems, quebracho is a key reagent in differential flotation of copper, lead, zinc circuits. The use of quebracho in the precipitation of germanium from zinc ores and for the recovery of ultrafine gold is also detailed in this work. This analysis explores the wide range of uses and methodology of quebracho in the extractive metallurgy field and expands on previous research by Iskra and Kitchener at Imperial College entitled, “Quebracho in Mineral Processing”. Full article
(This article belongs to the Special Issue Hydrometallurgy) Printed Edition available
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