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Minerals and Elements from Fly Ash and Bottom Ash as a Source of Secondary Raw Materials

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

Deadline for manuscript submissions: closed (10 October 2020) | Viewed by 21705

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Special Issue Editors

Dr. Alexandra Guedes

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Departamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto and Instituto de Ciências da Terra, 4169-007 Porto, Portugal
Interests: mineral analytical techniques; mineralogy of fly ash and bottom ash; ore deposits
Special Issues, Collections and Topics in MDPI journals

Dr. Bruno Valentim

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Departamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto and Instituto de Ciências da Terra, 4169-007 Porto, Portugal
Interests: organic petrology; ashes; spent LIB; circularity
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Large volumes of coal, biomass, and municipal solid waste ashes are generated globally every year. Therefore, the knowledge of the mineralogy and geochemistry of these materials is essential to their valorization and to contributing towards a Circular Economy. This Special Issue represents a cross-disciplinary appeal covering all aspects of fly ash and bottom ash, from their formation to their utilization as a source of secondary raw materials.

We invite researchers to contribute to the Special Issue: “Minerals and Elements from Fly Ash and Bottom Ash as a Source of Secondary Raw Materials”.

Prof. Alexandra Guedes
Dr. Bruno Valentim
Guest Editors

Manuscript Submission Information

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

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals 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 2400 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

fly ash
bottom ash
coal
biomass
municipal solid waste
minerals
mineral matter
toxic elements
radioactive elements
trace elements
critical elements
circular economy

Published Papers (6 papers)

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Editorial

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2 pages, 176 KiB

Open AccessEditorial

Editorial for Special Issue “Minerals and Elements from Fly Ash and Bottom Ash as a Source of Secondary Raw Materials”

by Alexandra Guedes and Bruno Valentim

Minerals 2021, 11(5), 438; https://doi.org/10.3390/min11050438 - 21 Apr 2021

Cited by 1 | Viewed by 1252

Abstract

The sustainability of primary resources depends on recycling, resource efficiency and the search for alternative materials [...] Full article

(This article belongs to the Special Issue Minerals and Elements from Fly Ash and Bottom Ash as a Source of Secondary Raw Materials)

Research

Jump to: Editorial

27 pages, 20126 KiB

Open AccessArticle

Assessment of Graphitized Coal Ash Char Concentrates as a Potential Synthetic Graphite Source

by Charlotte Badenhorst, Cláudia Santos, Juan Lázaro-Martínez, Barbara Białecka, Mihai Cruceru, Alexandra Guedes, Renato Guimarães, Karen Moreira, Georgeta Predeanu, Isabel Suárez-Ruíz, Ignacio Cameán, Bruno Valentim and Nicola Wagner

Minerals 2020, 10(11), 986; https://doi.org/10.3390/min10110986 - 06 Nov 2020

Cited by 18 | Viewed by 4003

Abstract

Coal ash char concentrates from four countries (Portugal, Poland, Romania, and South Africa) were prepared, characterised, and graphitized under the scope of the Charphite project (Third ERA-MIN Joint Call (2015) on the Sustainable Supply of Raw Materials in Europe). Coal ash chars may be a secondary raw material to produce synthetic graphite and could be an alternative to natural graphite, which is a commodity with a high supply risk. The char concentrates and the graphitized material derived from the char concentrates were characterised using proximate analysis, X-ray fluorescence, X-ray diffraction (structural), Raman microspectroscopy, solid-state nuclear magnetic resonance, scanning electron microscopy, and petrographic analyses to determine if the graphitization of the char was successful, and which char properties enhanced or hindered graphitization. Char concentrates with a lower proportion of anisotropic particles and a higher proportion of mixed porous particles showed greater degrees of graphitization. It is curious to see that embedded Al₂O₃ minerals, such as glass and clay, influenced graphitization, as they most likely acted as catalysts for crystal growth in the basal direction. However, the graphitized samples, as a whole, do not compare well against a reference natural graphite sample despite some particles in select char concentrates appearing to be graphitized following graphitization. Full article

(This article belongs to the Special Issue Minerals and Elements from Fly Ash and Bottom Ash as a Source of Secondary Raw Materials)

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15 pages, 1187 KiB

Open AccessArticle

Assessment of the Mode of Occurrence and Radiological Impact of Radionuclides in Nigerian Coal and Resultant Post-Combustion Coal Ash Using Scanning Electron Microscopy and Gamma-Ray Spectroscopy

by Ilemona C. Okeme, Thomas B. Scott, Peter G. Martin, Yukihiko Satou, Theophilus I. Ojonimi and Moromoke O. Olaluwoye

Minerals 2020, 10(3), 241; https://doi.org/10.3390/min10030241 - 07 Mar 2020

Cited by 7 | Viewed by 3076

Abstract

Natural radionuclide concentrations in coal and coal ash can occur at levels sufficient to raise potential health and environmental concerns when (re)suspended or disposed into the environment. To evaluate such concerns, this study characterized coal and simulant coal ash samples obtained from two Nigerian coal mines (Okaba and Omelewu) using high resolution gamma spectroscopy combined with scanning electron microscopy and energy dispersive spectroscopy. Discrete uraninite particles were observed dispersed within the coal ash samples, alongside U and Th containing mineral grains (monazite and zircon) with monazite the most abundant radioactive mineral particles. The pitted and cracked surface morphologies of these radioactive particles (with sizes between 10 μm and 80 μm) indicate their susceptibility for disintegration into more harmful and readily inhalable PM2.5 aerosol particles, with the potential to deliver a localized dose and cause chronic respiratory diseases. The results of activity concentrations and radiological hazard indices for the coal ash samples from both mines were between three and five times higher than world average in soil, which imply that these coal ash materials should be suitably contained in slurry ponds to prevent hazards due to increased risk of prolonged indoor exposure to gamma radiation, radon gas, and inhalation of liberated radioactive particles. Full article

(This article belongs to the Special Issue Minerals and Elements from Fly Ash and Bottom Ash as a Source of Secondary Raw Materials)

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15 pages, 3280 KiB

Open AccessArticle

Distribution of Lanthanides, Yttrium, and Scandium in the Pilot-Scale Beneficiation of Fly Ashes Derived from Eastern Kentucky Coals

by James C. Hower, John G. Groppo, Prakash Joshi, Dorin V. Preda, David P. Gamliel, Daniel T. Mohler, John D. Wiseman, Shelley D. Hopps, Tonya D. Morgan, Todd Beers and Michael Schrock

Minerals 2020, 10(2), 105; https://doi.org/10.3390/min10020105 - 26 Jan 2020

Cited by 34 | Viewed by 3835

Abstract

In this study, Central Appalachian coal-derived fly ashes from two power plants were beneficiated in a pilot-scale facility in order to produce a product with a relatively consistent concentration of rare earth elements (REE). The <200-mesh final fly ash product was produced by removing the carbon- and Fe-rich particles prior to screening at 200 mesh (75 µm). The Plant D fly ash had high concentrations of CaO and SO₃, which were diminished through the two months when the ash was being beneficiated, representing a consequence of the heat, humidity, and excessive rainfall in the Kentucky summer. The high CaO and SO₃ concentrations through the early runs likely contributed to the lower REE in the <200-mesh products of those runs. Of the non-REE minor elements, Ba, V, Mn, Zn, and As showed the greatest between-run variations within the runs for each plant. The overall REE concentrations proved to be similar, both on a between-run basis for the individual fly ash sources and on a between-plant basis. Variations in fly ash quality will occur in larger-scale operations, so on-going attention to the fly ash quality and the response of the fly ash to beneficiation is necessary. Changes in the Plant D fly ash with time imply that both the freshness of the original ash and the length and conditions of its storage at the site of beneficiation could be factors in the quality and consistency of the processed fly ash. Full article

(This article belongs to the Special Issue Minerals and Elements from Fly Ash and Bottom Ash as a Source of Secondary Raw Materials)

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12 pages, 5646 KiB

Open AccessArticle

The Effect of Fly Ash Microspheres on the Pore Structure of Concrete

by Elzbieta Haustein and Aleksandra Kuryłowicz-Cudowska

Minerals 2020, 10(1), 58; https://doi.org/10.3390/min10010058 - 09 Jan 2020

Cited by 31 | Viewed by 5020

Abstract

The fly ash microspheres (FAMs) formed during the mineral transformation stage in coal combustion are hollow spherical particles with a density less than water. This paper presents the results of X-ray micro-computed tomography and an automatic image analysis system of the porosity in the structure of hardened concrete with microspheres. Concrete mixtures with ordinary Portland cement and two substitution rates of cement by microspheres—5% and 10%—are investigated. For all considered mixes, a constant water/binder ratio (w/b) equal to 0.50 was used. The distribution of the air voids and the compressive strength of the concrete were tested after 28 days. With the increasing mass of cement replacement by FAMs, the compressive strength decreases after 28 days. The total volume of the air voids in hardened concrete with fly ash microspheres tested by X-ray varies from 5.1% to 7.4%. The closed pores constitute more than 80% of the total content of air pores. The study proves that the use of microspheres grains with specific dimensions has a significant impact on concrete porosity. Their application in concrete technology can be an alternative aeration solution for fresh concrete mixes and an effective method for utilization. Full article

(This article belongs to the Special Issue Minerals and Elements from Fly Ash and Bottom Ash as a Source of Secondary Raw Materials)

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14 pages, 4877 KiB

Open AccessArticle

Alumina Extraction from Coal Fly Ash via Low-Temperature Potassium Bisulfate Calcination

by Chunbin Guo, Jingjing Zou, Shuhua Ma, Jianlin Yang and Kehan Wang

Minerals 2019, 9(10), 585; https://doi.org/10.3390/min9100585 - 27 Sep 2019

Cited by 31 | Viewed by 3771

Abstract

Owing to the depletion of bauxite and increasing demand for alumina, calcination methods for extracting alumina from coal fly ash (CFA) were developed. However, these methods have disadvantages such as the need for high temperatures and the emission of toxic gases. Hence, in this study, Al₂O₃ was extracted from CFA via low-temperature potassium bisulfate calcination technology. Effects of the potassium bisulfate amount, calcination temperature, and calcination time on the alumina extraction efficiency were investigated using X-ray diffraction, thermal gravimetry, scanning electron microscopy, differential scanning calorimetry, and energy-dispersive spectroscopy. It was found that this technique could recover alumina efficiently, and potassium bisulfate significantly contributed to the degradation of mullite and corundum phases. Al₂O₃ in CFA was converted into soluble K₃Al(SO₄)₃. With a KHSO₄/Al₂O₃ molar ratio of 7:1, calcining temperature of 230 °C, and calcining time of 3 h, the alumina extraction efficiency reached a maximum of 92.8%. The Avrami–Erofeev equation showed the best fit with the kinetic data for the low-temperature calcination of CFA with KHSO₄. The activation energy was 28.36 kJ/mol. Full article

(This article belongs to the Special Issue Minerals and Elements from Fly Ash and Bottom Ash as a Source of Secondary Raw Materials)

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