Special Issue "Leaching Kinetics of Valuable Metals"

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

Deadline for manuscript submissions: 30 September 2019

Special Issue Editor

Guest Editor
Dr. Stefano Ubaldini

Consiglio Nazionale delle Ricerche (CNR)—Istituto di Geologia Ambientale e Geoingegneria (IGAG), Area della Ricerca di Roma RM 1, Montelibretti, Via Salaria Km 29,300—C.P. 10, 00015 Monterotondo Stazione, Roma, Italy
Website | E-Mail
Interests: primary and secondary raw materials; low-grade georesources; metals recovery; precious metals; heavy metals; leaching; hydrometallurgy; bio-hydrometallurgy; bioprecipitation; electrowinning; remediation processes; environmental innovative technologies; industrial wastes; exhausted batteries; WEEE; minerals; wastewater; acid mine drainage

Special Issue Information

Dear Colleagues,

Leaching is a primary extractive operation in hydrometallurgical processing, by which a metal of interest is transferred from naturally-occurring minerals into an aqueous solution. In essence, it involves the selective dissolution of valuable minerals, where the ore, concentrate, or matte is brought into contact with an active chemical solution known as a leach solution.

Currently, the hydrometallurgical processes have a great application, not only in the mining sector—in particular, for the recovery of precious metals, such as gold and silver—but also in the environmental sector, for the recovery of toxic metals (such as copper, nickel, zinc, manganese, arsenic, cadmium, chromium, lead) from wastes of various types, and their reuse as valuable metals, after purification.

Therefore, there is an increasing need to develop novel solutions, to implement environmentally sustainable practices in the recovery of these valuable and precious metals, with particular reference to the critical metals, that are those included in materials that are indispensable to modern life and for which an exponential increase in consumption is already a reality or will be in a short-term perspective (antimony, indium, vanadium, rare hearts, etc.).

Consequently, the economics of the processes, which is closely linked to the kinetics of leaching, is of great importance.

For publication in this Special Issue, will be considered those articles that will contribute to the optimization of the kinetic conditions of innovative hydrometallurgical processes—economic and of low environmental impact—applied for the recovery of valuable and critical metals.

I hope you accept this invitation, and help us to make a high-impact and high-quality Special Issue on "Leaching Kinetics of Valuable Metals".

Dr. Stefano Ubaldini
Guest Editor

Manuscript Submission Information

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Keywords

  • Primary and secondary raw materials
  • Low-grade georesources
  • Valuable metals
  • Precious metals
  • Heavy metals
  • Leaching
  • Hydrometallurgy
  • Environmental innovative technologies
  • Industrial wastes
  • WEEE

Published Papers (9 papers)

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Research

Open AccessArticle Leaching Kinetics of Sulfides from Refractory Gold Concentrates by Nitric Acid
Metals 2019, 9(4), 465; https://doi.org/10.3390/met9040465
Received: 5 April 2019 / Revised: 19 April 2019 / Accepted: 19 April 2019 / Published: 22 April 2019
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Abstract
The processing of refractory gold-containing concentrates by hydrometallurgical methods is becoming increasingly important due to the depletion of rich and easily extracted mineral resources, as well as due to the need to reduce harmful emissions from metallurgy, especially given the high content of [...] Read more.
The processing of refractory gold-containing concentrates by hydrometallurgical methods is becoming increasingly important due to the depletion of rich and easily extracted mineral resources, as well as due to the need to reduce harmful emissions from metallurgy, especially given the high content of arsenic in the ores. This paper describes the investigation of the kinetics of HNO3 leaching of sulfide gold-containing concentrates of the Yenisei ridge (Yakutia, Russia). The effect of temperature (70–85 °C), the initial concentration of HNO3 (10–40%) and the content of sulfur in the concentrate (8.22–22.44%) on the iron recovery into the solution was studied. It has been shown that increasing the content of S in the concentrate from 8.22 to 22.44% leads to an average of 45% increase in the iron recovery across the entire range temperatures and concentrations of HNO3 per one hour of leaching. The leaching kinetics of the studied types of concentrates correlates well with the new shrinking core model, which indicates that the reaction is regulated by interfacial diffusion and diffusion through the product layer. Elemental S is found on the surface of the solid leach residue, as confirmed by XRD and SEM/EDS analysis. The apparent activation energy is 60.276 kJ/mol. The semi-empirical expression describing the reaction rate under the studied conditions can be written as follows: 1/3ln(1 − X) + [(1 − X)−1/3 − 1] = 87.811(HNO3)0.837(S)2.948e−60276/RT·t. Full article
(This article belongs to the Special Issue Leaching Kinetics of Valuable Metals)
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Open AccessArticle Enhanced Desilication of High Alumina Fly Ash by Combining Physical and Chemical Activation
Metals 2019, 9(4), 411; https://doi.org/10.3390/met9040411
Received: 14 March 2019 / Revised: 31 March 2019 / Accepted: 2 April 2019 / Published: 4 April 2019
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Abstract
In this work, a physical–chemical activation desilication process was proposed to extract silica from high alumina fly ash (HAFA). The effects of fly ash size, hydrochloric acid concentration, acid activation time, and reaction temperature on the desilication efficiency were investigated comprehensively. The phase [...] Read more.
In this work, a physical–chemical activation desilication process was proposed to extract silica from high alumina fly ash (HAFA). The effects of fly ash size, hydrochloric acid concentration, acid activation time, and reaction temperature on the desilication efficiency were investigated comprehensively. The phase and morphology of the original fly ash and desilicated fly ash were analyzed by X-ray diffraction (XRD) and scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS). Compared with the traditional desilication process, the physical–chemical activation desilication efficiency is further increased from 38.4% to 53.2% under the optimal conditions. Additionally, the kinetic rules and equations were confirmed by the experimental data fitting with shrinking core model of liquid–solid multiphase reaction. Kinetic studies show that the enhanced desilication process is divided into two processes, and both steps of the two-step reaction is controlled by chemical reaction, and the earlier stage activation energy is 52.05 kJ/mol and the later stage activation energy is 58.45 kJ/mol. The results of mechanism analysis show that physical activation breaks the link between the crystalline phase and the amorphous phase, and then a small amount of alkali-soluble alumina in the amorphous phase is removed by acid activation, thereby suppressing the generation of side reactions of the zeolite phase. Full article
(This article belongs to the Special Issue Leaching Kinetics of Valuable Metals)
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Open AccessArticle Oxidation of Thiosulfate with Oxygen Using Copper (II) as a Catalyst
Metals 2019, 9(4), 387; https://doi.org/10.3390/met9040387
Received: 2 March 2019 / Revised: 19 March 2019 / Accepted: 25 March 2019 / Published: 28 March 2019
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Abstract
Thiosulfate effluents are generated in the photography and radiography industrial sectors, and in a plant in which thiosulfates are used to recover the gold and silver contained in ores. Similar effluents also containing thiosulfate are those generated from the petrochemical, pharmaceutical and pigment [...] Read more.
Thiosulfate effluents are generated in the photography and radiography industrial sectors, and in a plant in which thiosulfates are used to recover the gold and silver contained in ores. Similar effluents also containing thiosulfate are those generated from the petrochemical, pharmaceutical and pigment sectors. In the future, the amounts of these effluents may increase, particularly if the cyanides used in the extraction of gold and silver from ores are substituted by thiosulfates, or if the same happens to electronic scrap or in metallic coating processes. This paper reports a study of the oxidation of thiosulfate, with oxygen using copper (II) as a catalyst, at a pH between 4 and 5. The basic idea is to avoid the formation of tetrathionate and polythionate, transforming the thiosulfate into sulfate. The nature of the reaction and a kinetic study of thiosulfate transformation, by reaction with oxygen and Cu2+ at a ppm level, are determined and reported. The best conditions were obtained at 60 °C, pH 5, with an initial concentration of copper of 53 ppm and an oxygen pressure of 1 atm. Under these conditions, the thiosulfate concentration was reduced from 1 g·L−1 to less than 20 ppm in less than three hours. Full article
(This article belongs to the Special Issue Leaching Kinetics of Valuable Metals)
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Open AccessArticle High-Pressure Oxidative Leaching and Iodide Leaching Followed by Selective Precipitation for Recovery of Base and Precious Metals from Waste Printed Circuit Boards Ash
Metals 2019, 9(3), 363; https://doi.org/10.3390/met9030363
Received: 1 March 2019 / Revised: 16 March 2019 / Accepted: 18 March 2019 / Published: 20 March 2019
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Abstract
This paper deals with the recovery of gold from waste printed circuit boards (WPCBs) ash by high-pressure oxidative leaching (HPOL) pre-treatment and iodide leaching followed by reduction precipitation. Base metals present in WPCB ash were removed via HPOL using a diluted sulfuric acid [...] Read more.
This paper deals with the recovery of gold from waste printed circuit boards (WPCBs) ash by high-pressure oxidative leaching (HPOL) pre-treatment and iodide leaching followed by reduction precipitation. Base metals present in WPCB ash were removed via HPOL using a diluted sulfuric acid solution at elevated temperatures. Effects of potassium iodide concentration, hydrogen peroxide concentration, sulfuric acid concentration, leaching temperature, and leaching time on gold extraction from pure gold chips with KI–H2O2–H2SO4 were investigated. The applicability of the optimized iodide leaching process for the extraction of gold from the leach residue obtained after HPOL were examined at different pulp densities ranging from 50 g/t to 200 g/t. Results show that the removal efficiency was 99% for Cu, 95.7% for Zn, 91% for Ni, 87.3% for Al, 82% for Co, and 70% for Fe under defined conditions. Under the optimal conditions, the percentage of gold extraction from the gold chips and the residue of WPCBs was 99% and 95%, respectively. About 99% of the gold was selectively precipitated from the pregnant leach solution by sequential precipitation with sodium hydroxide and L-ascorbic acid. Finally, more than 93% of gold recovery was achieved from WPCB ash by overall combined processes. Full article
(This article belongs to the Special Issue Leaching Kinetics of Valuable Metals)
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Open AccessArticle Valorization of Mining Waste by Application of Innovative Thiosulphate Leaching for Gold Recovery
Metals 2019, 9(3), 274; https://doi.org/10.3390/met9030274
Received: 18 January 2019 / Revised: 20 February 2019 / Accepted: 23 February 2019 / Published: 28 February 2019
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Abstract
The metals and industrial minerals contained in the tailings of mining and quarrying activities, can degrade natural environments as well as human health. The objective of this experimental work is the application of innovative and sustainable technologies for the treatment and exploitation of [...] Read more.
The metals and industrial minerals contained in the tailings of mining and quarrying activities, can degrade natural environments as well as human health. The objective of this experimental work is the application of innovative and sustainable technologies for the treatment and exploitation of mining tailings from Romania. Within this approach, the recovery of high grade raw materials to be placed on the market is achieved and reduction of these wastes volume are achieved. The current study is focused on hydrometallurgical process for the recovery of gold. The innovative treatment chosen is the thiosulphate process that, compared with the conventional cyanide, has several advantages (e.g., it is more ecologically friendly and is not toxic to humans). The conventional cyanidation process shows operating limits in the case of auriferous refractory minerals, such as Romanian wastes, the object of the study. An important characteristic of thiosulphate leaching process it has the best selectivity towards gold; it does not attack the majority of the gangue mineral constituents. Gold extraction of 75% was obtained under ambient conditions of temperature. Moreover, the overall process achieved about 65–67% Au recovery, this being in line with the conventional cyanidation process. As these results are obtained by application of the thiosulfate process on a low gold content ore, they may be considered encouraging. The optimization of process parameters and operating conditions, should permit the best results in terms of process yields to be achieved. Full article
(This article belongs to the Special Issue Leaching Kinetics of Valuable Metals)
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Open AccessArticle Leaching Chalcopyrite Concentrate with Oxygen and Sulfuric Acid Using a Low-Pressure Reactor
Metals 2019, 9(2), 189; https://doi.org/10.3390/met9020189
Received: 7 January 2019 / Revised: 29 January 2019 / Accepted: 1 February 2019 / Published: 6 February 2019
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Abstract
This article presents a copper leaching process from chalcopyrite concentrates using a low-pressure reactor. The experiments were carried out in a 30 L batch reactor at an oxygen pressure of 1 kg/cm2 and solid concentration of 100 g/L. The temperature, particle size [...] Read more.
This article presents a copper leaching process from chalcopyrite concentrates using a low-pressure reactor. The experiments were carried out in a 30 L batch reactor at an oxygen pressure of 1 kg/cm2 and solid concentration of 100 g/L. The temperature, particle size and initial acid concentration were varied based on a Taguchi L9 experimental design. The initial and final samples of the study were characterized by chemical analysis, X-ray diffraction and particle size distribution. The mass balance showed that 98% of copper was extracted from the chalcopyrite concentrate in 3 h under the following experimental conditions: 130 g/L of initial sulfuric acid concentration, temperature of 100 °C, oxygen pressure of 1 kg/cm2, solid concentration of 100 g/L and particle size of −105 + 75 μm. The ANOVA demonstrated that temperature had the greatest influence on copper extraction. The activation energy was 61.93 kJ/mol. The best fit to a linear correlation was the chemical reaction equation that controls the kinetics for the leaching copper from chalcopyrite. The images obtained by SEM showed evidence of shrinking in the core model with the formation of a porous elemental sulfur product layer. Full article
(This article belongs to the Special Issue Leaching Kinetics of Valuable Metals)
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Open AccessArticle A Kinetic Study on the Preparation of AlNi Alloys by Aluminothermic Reduction of NiO Powders
Metals 2018, 8(9), 675; https://doi.org/10.3390/met8090675
Received: 9 July 2018 / Revised: 26 July 2018 / Accepted: 31 July 2018 / Published: 28 August 2018
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Abstract
In this work, the experimental results obtained during the preparation of Al-Ni and Al-Ni-Mg alloys using the aluminothermic reduction of NiO by submerged powder injection, assisted with mechanical agitation are presented and discussed. The analyzed variables were melt temperature, agitation speed, and initial [...] Read more.
In this work, the experimental results obtained during the preparation of Al-Ni and Al-Ni-Mg alloys using the aluminothermic reduction of NiO by submerged powder injection, assisted with mechanical agitation are presented and discussed. The analyzed variables were melt temperature, agitation speed, and initial magnesium concentration in the molten alloy. For some of the experiments performed, it was found that the Ni concentration increased from 0 to about 3 wt-% after 90 min of treatment at constant temperature and constant agitation speed. In order to determine the values of the kinetic parameters of interest, such as the activation energy and the rate constants, the values of the results obtained were fitted to the kinetic formulae available. Moreover, the kinetics of the reaction were found to be governed by the diffusion of Al and Mg to the NiO boundary layer, where MgAl2O4 or Al2O3 were formed as the main reaction products. Finally, from a thermodynamic study of the system, the main reactions that took place are explained. Full article
(This article belongs to the Special Issue Leaching Kinetics of Valuable Metals)
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Open AccessArticle Uranium Removal from Groundwater by Permeable Reactive Barrier with Zero-Valent Iron and Organic Carbon Mixtures: Laboratory and Field Studies
Metals 2018, 8(6), 408; https://doi.org/10.3390/met8060408
Received: 31 March 2018 / Revised: 22 May 2018 / Accepted: 24 May 2018 / Published: 1 June 2018
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Abstract
Zhovty Vody city, located in south-central Ukraine, has long been an important center for the Ukrainian uranium and iron industries. Uranium and iron mining and processing activities during the Cold War resulted in poorly managed sources of radionuclides and heavy metals. Widespread groundwater [...] Read more.
Zhovty Vody city, located in south-central Ukraine, has long been an important center for the Ukrainian uranium and iron industries. Uranium and iron mining and processing activities during the Cold War resulted in poorly managed sources of radionuclides and heavy metals. Widespread groundwater and surface water contamination has occurred, which creates a significant risk to drinking water supplies. Hydrogeologic and geochemical conditions near large uranium mine tailings storage facility (TSF) were characterized to provide data to locate, design and install a permeable reactive barrier (PRB) to treat groundwater contaminated by leachate infiltrating from the TSF. The effectiveness of three different permeable reactive materials was investigated: zero-valent iron (ZVI) for reduction, sorption, and precipitation of redox-sensitive oxyanions; phosphate material to transform dissolved metals to less soluble phases; and organic carbon substrates to promote bioremediation processes. Batch and column experiments with Zhovty Vody site groundwater were conducted to evaluate reactivity of the materials. Reaction rates, residence time and comparison with site-specific clean-up standards were determined. Results of the study demonstrate the effectiveness of the use of the PRB for ground water protection near uranium mine TSF. The greatest decrease was obtained using ZVI-based reactive media and the combined media of ZVI/phosphate/organic carbon combinations. Full article
(This article belongs to the Special Issue Leaching Kinetics of Valuable Metals)
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Open AccessArticle Neural Network Modeling for the Extraction of Rare Earth Elements from Eudialyte Concentrate by Dry Digestion and Leaching
Metals 2018, 8(4), 267; https://doi.org/10.3390/met8040267
Received: 8 March 2018 / Revised: 8 April 2018 / Accepted: 10 April 2018 / Published: 13 April 2018
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Abstract
Eudialyte is a promising mineral for rare earth elements (REE) extraction due to its good solubility in acid, low radioactive, and relatively high content of REE. In this paper, a two stage hydrometallurgical treatment of eudialyte concentrate was studied: dry digestion with hydrochloric [...] Read more.
Eudialyte is a promising mineral for rare earth elements (REE) extraction due to its good solubility in acid, low radioactive, and relatively high content of REE. In this paper, a two stage hydrometallurgical treatment of eudialyte concentrate was studied: dry digestion with hydrochloric acid and leaching with water. The hydrochloric acid for dry digestion to eudialyte concentrate ratio, mass of water for leaching to mass of eudialyte concentrate ratio, leaching temperature and leaching time as the predictor variables, and the total rare earth elements (TREE) extraction efficiency as the response were considered. After experimental work in laboratory conditions, according to design of experiment theory (DoE), the modeling process was performed using Multiple Linear Regression (MLR), Stepwise Regression (SWR), and Artificial Neural Network (ANN). The ANN model of REE extraction was adopted. Additional tests showed that values predicted by the neural network model were in very good agreement with the experimental results. Finally, the experiments were performed on a scaled up system under optimal conditions that were predicted by the adopted ANN model. Results at the scale-up plant confirmed the results that were obtained in the laboratory. Full article
(This article belongs to the Special Issue Leaching Kinetics of Valuable Metals)
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