Undifferentiated Inorganics in Coal Fly Ash and Bottom Ash: Calcispheres, Magnesiacalcispheres, and Magnesiaspheres

Valentim, Bruno; Białecka, Barbara; Gonçalves, Paula Alexandra; Guedes, Alexandra; Guimarães, Renato; Cruceru, Mihai; Moszko, Joanna Całus; Popescu, Luminiţa; Predeanu, Georgeta; Santos, Ana Cláudia

doi:10.3390/min8040140

Cited by 24 publications

(23 citation statements)

References 41 publications

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“…The CaO generally reacts with SO x in the boiler atmosphere, resulting in the formation of sulfate minerals in the FA and BA (Huffman et al, 1990;Moreno et al, 2005;Kostova et al, 2016). This reaction could explain the abundance of Ca-sulfate minerals (anhydrite and ettringite) in the studied FA and BA samples; however, slightly high Ca concentrations of FC samples could allow the reaction between CaO and aluminosilicate glass and Fe-oxides during combustion (Sokol et al, 2002;Vassilev et al, 2005b;Dai et al, 2014;Valentim et al, 2018). Thus, FeCa-rich glass and Ca-silicate minerals (e.g., gehlenite) in the crystalline phases were identified in the studied combustion residues (Figures 5a, 5b, 6a, 6b).…”

Section: Mineralogical Compositionmentioning

confidence: 97%

Mineralogy and geochemistry of feed coals and combustion residues of the Kangal power plant (Sivas, Turkey)

Karayi̇ǧi̇t¹,

Oskay²,

Gayer³

2019

Turkish J Earth Sci

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This study focuses on mineralogical and geochemical compositions of feed coal (FC) and combustion residues, namely fly ash (FA) and bottom ash (BA) samples, obtained from the Kangal coal-fired power plant in central Turkey. The X-ray powder diffraction data indicate that carbonate and clay minerals are dominant phases in the FC samples. In the FA samples, quartz, hematite, anhydrite, lime, and feldspar are generally dominant and abundant phases, whereas calcite, ettringite, and portlandite are generally more abundant in the BA samples. The elements Mo, Cs, and U are significantly enriched in the studied FC, FA, and BA samples. The statistical analysis and SEM-EDX data show that Ca, Ti, and the vast majority of trace elements are inorganically affiliated, and only Tl and U have probable organic affinity in the FC. In addition, the redox conditions in the paleomires presumably resulting in Mo and U enrichment in FC, whereas their enrichment in FA and BA is most likely related to retention by CaO and Ca-sulfate. The Cs enrichment in FA is due to retention by glass. The elements in the FA and BA are distinguished into four groups according to their volatility during combustion. The elements As, Mo, Cd, Tl, and U (Group I) are the most volatile elements during combustion and condensation in the FA. The elements Li, Zn, Ga, Rb, Nb, Cs, Ba, La, and Pb (Group IV) did not become more volatile or less volatile during combustion and are located in BA. Nevertheless, Zn and Pb in the BA seem to be related to the presence of unaffected pyrite and sphalerite, and are due to low combustion efficiency of the boiler during the sampling period. Overall, enriched elements and minerals in FA and BA suggest that their disposal should be undertaken with caution.

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Section: Mineralogical Compositionmentioning

confidence: 97%

Mineralogy and geochemistry of feed coals and combustion residues of the Kangal power plant (Sivas, Turkey)

Karayi̇ǧi̇t¹,

Oskay²,

Gayer³

2019

Turkish J Earth Sci

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“…The most common method widely used to assess the diffusion coefficient of chloride in cement-based materials is the measuring of the chloride profile after a time and fitting it in Fick’s second law of diffusion [14,28]. Such a coefficient could either overestimate or underestimate the time to initiation of corrosion due to the great influence of the surface chloride concentration on the result, which changes with time leading to errors in the prediction of the diffusion coefficient of chloride based on Fick’s second law.…”

Section: Resultsmentioning

confidence: 99%

“…Given that, manufactured CBA sand with different sizes may be produced in a crushing plant. It is well known that size and particle size distribution will influence the material characteristics [12,13,14]. Other types of bottom ashes, from a municipal solid waste incinerator [15] or circulating fluidized bed combustion (CFBC) [16], are also reported in the literature.…”

Section: Introductionmentioning

confidence: 99%

Chloride Induced Reinforcement Corrosion in Mortars Containing Coal Bottom Ash and Coal Fly Ash

Menéndez

Argiz

Sanjuán³

2019

Materials

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Coal bottom ash is normally used as aggregate in mortars and concretes. When it is ground, its characteristics are modified. Therefore, the assessment of its long-term durability must be realized in depth. In this sense, an accelerated chloride ingress test has been performed on reinforced mortars made of Portland cement with different amounts of coal bottom ash (CBA) and/or coal fly ash (CFA). Corrosion potential and corrosion rate were continuously monitored. Cement replacement with bottom and fly ash had beneficial long-term effects regarding chloride penetration resistance. Concerning corrosion performance, by far the most dominant influencing parameter was the ash content. Chloride diffusion coefficient in natural test conditions decreased from 23 × 10−12 m2/s in cements without coal ashes to 4.5 × 10−12 m2/s in cements with 35% by weight of coal ashes. Moreover, the time to steel corrosion initiation went from 102 h to about 500 h, respectively. Therefore, this work presents experimental evidence that confirms the positive effect of both types of coal ashes (CBA and CFA) with regard to the concrete steel corrosion.

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“…There were three types of particles: spheres, agglomerates of irregular shape, and porous structures. In previous research, it was shown that spheres consists of alumosilicates and magnetite crystals are located on its surface [26,27]. Agglomerates of irregular shape consist only of alumosilicates.…”

Section: Dry Magnetic Separationmentioning

confidence: 98%

Magnetite and Carbon Extraction from Coal Fly Ash Using Magnetic Separation and Flotation Methods

et al. 2019

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In this study, enrichment methods for coal fly ash (CFA) from Omsk thermal power station No. 4 (TPS-4) were investigated. The magnetite and unburned carbon concentrates were obtained by magnetic separation and flotation methods. The wet magnetic separation used in the study increased the magnetite content in the magnetic fraction from 10.48 to 12.72 wt % compared to dry magnetic separation. The XRD analysis showed that the magnetic fraction primarily consists of magnetite, mullite, and quartz. The SEM analysis demonstrated that magnetite is located primarily on the surface of alumosilicate spheres and has three types of shape: dendritic structures, hexagonal bulk agglomerates, and star-like structures. For the flotation tests, a low-price diesel was used as the collector. It was found that, if CFA particles of 40–71 µm are used, ~99% of unburned carbon can be recovered. It was also found by SEM that, if CFA particles of 71–100 µm are used, alumosilicates on a carbon surface prevent complete interaction of diesel with carbon particles and decrease thereby carbon recovery to 83%.

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Undifferentiated Inorganics in Coal Fly Ash and Bottom Ash: Calcispheres, Magnesiacalcispheres, and Magnesiaspheres

Cited by 24 publications

References 41 publications

Mineralogy and geochemistry of feed coals and combustion residues of the Kangal power plant (Sivas, Turkey)

Mineralogy and geochemistry of feed coals and combustion residues of the Kangal power plant (Sivas, Turkey)

Chloride Induced Reinforcement Corrosion in Mortars Containing Coal Bottom Ash and Coal Fly Ash

Magnetite and Carbon Extraction from Coal Fly Ash Using Magnetic Separation and Flotation Methods

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