Special Issue "High-Tech Metals Distribution in Bauxites: From the Ore Genesis to the Bayer Process Residue"

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Deposits".

Deadline for manuscript submissions: 31 May 2019

Special Issue Editor

Guest Editor
Prof. Dr. Giovanni Mongelli

Department of Sciences, University of Basilicata, Viale dell'Ateneo Lucano, 10 - 85100 Potenza, Italy
Website | E-Mail
Interests: ore geochemistry; sedimentary geochemistry; environmental geochemistry; water-rock interaction; applied mineralogy

Special Issue Information

Dear Colleagues,

Bauxite is a residual rock, consisting mainly of a mixture of aluminum hydroxides, of which industrial significance is primarily due to its profitably exploitable alumina contents. In the last few decades, bauxite ores have also been considered as a possible resource for a great number of economically-interesting elements, including some High-Tech Metals (HTM) such as REEs+Y+Sc, V, Co, Ni, Ga, Ge, and In. HTM, which are generally “co-elements”, mainly recovered as byproducts of other metallic ores, are important in a wide range of modern technologies, and their availability is generally poor relative to the current demand. Assuring supplies of HTM, largely used in modern engineered materials but subject to supply risks or concerns about availability, is a compelling challenge. This Special Issue aims to publish papers dealing with HTM behavior in bauxites and in the residue of the Bayer process developed on bauxite ores (Red Muds). Papers providing the assessment of HTM content in bauxite ores and their residue and the evaluation of the structural bonding of HTM into the supergene ore minerals, in the perspective of the determination of the best treatment for making HTM amenable to low-cost recovery are also welcome.

Dr. Giovanni Mongelli
Guest Editor

Manuscript Submission Information

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Keywords

  • Bauxite ores
  • Red muds
  • High tech metals distribution and recovery
  • Mineralogical control

Published Papers (3 papers)

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Research

Open AccessArticle
Optimizing Conditions for Scandium Extraction from Bauxite Residue Using Taguchi Methodology
Minerals 2019, 9(4), 236; https://doi.org/10.3390/min9040236
Received: 14 March 2019 / Revised: 10 April 2019 / Accepted: 15 April 2019 / Published: 17 April 2019
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Abstract
Bauxite residue is the voluminous by-product of alumina production after Bayer process. Its high alkalinity causes disposal problems and harmful environmental impacts. However, the residue contains significant amounts of valuable elements, such as rare earth elements, including scandium. Greek bauxite residue contains a [...] Read more.
Bauxite residue is the voluminous by-product of alumina production after Bayer process. Its high alkalinity causes disposal problems and harmful environmental impacts. However, the residue contains significant amounts of valuable elements, such as rare earth elements, including scandium. Greek bauxite residue contains a high amount of scandium close to its main resources. Taking into account scandium’s limited availability coupled with its high demand in modern technology, bauxite residue could be considered as a potential resource for scandium recovery. In this study, the optimization of scandium extraction from bauxite residue with sulfuric acid is investigated using Taguchi methodology. Based on previous studies, acid molarity, leaching time, solid/liquid ratio, and reaction temperature were selected as control parameters for the selective Sc recovery. Method optimization targeted the highest concentration of scandium combined with the lowest concentration of iron without taking into account application constraints. Maximization of scandium concentration can be achieved only by reduced selectivity. The predicted values resulted from the Taguchi methodology were affirmed by a confirmation experiment conducted at optimal conditions. Regression analysis provided the respective equations to be applied on several conditions, depending on different applications. Full article
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Open AccessArticle
Semi-Smelting Reduction and Magnetic Separation for the Recovery of Iron and Alumina Slag from Iron Rich Bauxite
Minerals 2019, 9(4), 223; https://doi.org/10.3390/min9040223
Received: 7 March 2019 / Revised: 30 March 2019 / Accepted: 4 April 2019 / Published: 9 April 2019
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Abstract
This work presents a semi-smelting reduction and magnetic separation process for the recovery of iron and alumina slag from iron rich bauxite ore. The effect of the process parameters on the recovery rate of iron, maximum particle size of the iron nugget, and [...] Read more.
This work presents a semi-smelting reduction and magnetic separation process for the recovery of iron and alumina slag from iron rich bauxite ore. The effect of the process parameters on the recovery rate of iron, maximum particle size of the iron nugget, and the Al2O3 content of the alumina slag was investigated and optimized. The results show that the iron nuggets and alumina slag can be obtained in a short time through a semi-smelting reduction and magnetic separation process. The maximum particle size of iron nugget is about 15 mm, and the recovery rate of the iron and Al2O3 grade of the alumina slag are 96.84 wt % and 43.98 wt %, respectively. The alumina slag consisted mainly of alumina (α-Al2O3), calcium hexaluminate (CaAl12O19), gehlenite (Ca2Al2SiO7), and small amounts of hercynite (FeAl4O7), and metallic iron (M.Fe). Full article
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Open AccessArticle
Increased As Adsorption on Maghemite-Containing Red Mud Prepared by the Alkali Fusion-Leaching Method
Minerals 2019, 9(1), 60; https://doi.org/10.3390/min9010060
Received: 20 December 2018 / Revised: 16 January 2019 / Accepted: 17 January 2019 / Published: 20 January 2019
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Abstract
This study investigates the use of red muds as adsorbents for As (V) removal. Red mud is a waste that contains a large amount of iron oxides and hydroxides, which are excellent adsorbents of arsenic, especially those possessing magnetic properties and a large [...] Read more.
This study investigates the use of red muds as adsorbents for As (V) removal. Red mud is a waste that contains a large amount of iron oxides and hydroxides, which are excellent adsorbents of arsenic, especially those possessing magnetic properties and a large specific surface area. The purpose of the experiments was to study the possibility of obtaining an effective adsorbent by the direct extraction of alumina from bauxite using the caustic alkali fusion method and to compare the arsenic removal effectiveness and other properties of these red muds with industrial samples. Red muds were described using methods such as X-ray diffraction spectrometry (XRD), X-ray fluorescence spectrometry (XRF), SEM, vibrating sample magnetometry (VSM), and the Brunauer–Emmett–Teller (BET) method. The main iron-containing phase of the red muds obtained by fusing bauxite with caustic alkali is maghemite, which has a large specific surface area. The specific surface area of the obtained samples varied in the range of 6.1–54.9 m2/g. Arsenic adsorption experiments were carried out using five different types of red muds: industrial Bayer, industrial sintering, and red mud obtained through bauxite alkali fusion at 300, 500, and 700 °C. The red muds obtained by fusing bauxite with caustic alkali at 300 and 500 °C had the highest effectiveness removing arsenic; their As(V) uptake capacity was over 30 mg/g. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Overview of Known Alkaliphilic Bacteria from Red Mud
Author: Gunther Brucha
Abstract: Alkaliphilic bacteria typically grow well at pH 9, with the most extremophilic strains growing up to pH values as high as pH 12–13. This group of bacteria have the ability to metabolically reduce alkalinity and have tolerance of high concentrations of ions and metals. Interest in extreme alkaliphiles arises because they are sources of useful, stable enzymes, and the cells themselves can be used for biotechnological and other applications at high pH. Many industrial processes produce highly alkaline wastes that are contaminated with toxic trace metals/metalloid. In this way, the use of alkaliphilic microorganisms is considered an attractive alternative method for treatment of industrial alkaline residues. Bauxite refining is one of activities that most produce highly alkaline wastes. Alumina extraction from bauxite using concentrated sodium hydroxide in the Bayer process generates a slurry and an extremely alkaline (pH of 9 to 13) byproduct known as bauxite residue or red mud. For each ton of alumina extracted from bauxite, approximately 1.5-2.0 tons of bauxite residue is generated. Disposal of such a byproduct is a serious problem at alumina plants because of environmental risks and financial costs. In this way, it is very important to know bacteria that can survive in such an extreme environmental since these bacteria could be used as a method for treatment of alkaline residues. Firmicutes has been described as one of the most representative bacterial phyla in bauxite residue, and the Bacillus genus as one of the most frequent. Different species of Bacillus were already isolated from red muds and showed a great potential for bioremediation process. For this reason, the aim of this article is to do a review about the study of alkaliphilic bacteria isolated from red mud.

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