Evaluation of mineral matter transformations in low-temperature ashes of South African coal feedstock samples and their density separated cuts using high-temperature X-ray diffraction

Rautenbach, Rudelle; Matjie, R.H.; Strydom, Christien A.; Bunt, John R.; Ward, Colin R.

doi:10.1080/19392699.2019.1677629

Cited by 5 publications

(10 citation statements)

References 25 publications

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“…Also, the XRD detected traces of anatase (TiO 2 ), apatite [Ca 5 (PO 4 ) 3+ (F,Cl, or OH)], goyazite [SrAl 3 (PO 4 )(PO 3 OH)(OH) 6 ], microcline (KAlSi 3 O 8 ), rutile (TiO 2 ), and muscovite (KF) 2 (Al 2 O 3 ) 3 (SiO 2 ) 6 (H 2 O) in the case of FCR CF. These results are consistent with those of SA feed-coals and their density-separated fractions reported by Rautenbach et al Raman studies performed on FCR in the previous study by Mphahlele et al confirmed the presence of minerals detected by XRD in lower proportions.…”

Section: Resultssupporting

confidence: 92%

“…17 XRD results indicate that the FCR, Fl 1.5, Fl 1.9, Sl 1.9, FCR CF, and FCR D contain 39.3, 13.4, 28.9, 59.7, 38.7, and 1.8% MM contents, respectively (Table 3). Also, the XRD 12 Raman studies performed on FCR in the previous study by Mphahlele et al 24 confirmed the presence of minerals detected by XRD in lower proportions. Higher proportions of MM contents in Sl 1.9 and FCR are associated with higher total proportions of fluxing cleat minerals (calcite, dolomite, and pyrite) (>7%) compared to those of other beneficiated FCR samples.…”

Section: Coal and Char Compositionssupporting

confidence: 61%

“…17 Calcite, dolomite, and pyrite in the FCR sample are linked to the cleats and could release Ca, Mg, and Fe to catalyze the pyrolysis reactions and achieve higher pyrolytic product efficiencies. According to Rautenbach et al 12 the >1.9 g/cm 3 sink samples are characterized by the highest proportions of calcite, dolomite, siderite, and pyrite cleats and zero % or lowest proportion of inherent minerals compared to feed-coal and its density separated fractions. This could imply that Sl 1.9 evaluated in this study may achieve the highest carbon conversion value during pyrolysis.…”

Section: Coal and Char Compositionsmentioning

confidence: 99%

“…However, like feed-coal, FCR which is generated during the preparation of Highveld feed-coals comprises various types of MM such as extraneous minerals (EM) (i.e., discrete mineral particles) and inherent MM (i.e., submicron mineral cleats and nonmineral inorganics), and macerals of vitrinite, inertinite and liptinite groups, all of which undergo a chemical transformation during thermochemical treatment of coal. ,, For instance, either extraneous fluxing minerals (i.e., dolomite, calcite, and pyrite) or inherent fluxing minerals which are associated with either extraneous or inherent kaolinite in the coals react to each other at elevated temperatures (>900 °C) to form the molten solution. , The heated rock fragments (mudstone, sandstone, and siltstone) present in the coals are attached to the molten solution to form lump heterogeneous clinkers in the commercial gasifiers or commercial boilers. The slow cooling of the molten material at lower temperatures (<340 °C) in the commercial gasifier-bed, mullite (Al 6 Si 2 O 13 ), and anorthite (CaAl 2 Si 2 O 8 ) crystals and Ca/Fe/Mg-bearing aluminosilicate glasses are formed.…”

Section: Introductionmentioning

confidence: 99%

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Catalytic Effect of Reactive Extraneous Mineral Composites on Char and Tar Distribution during Pyrolysis of Highveld Partially Oxidized Fine-Coal Reject and Its Beneficiated Residues

Mphahlele,

Matjie,

Bunt

2023

ACS Omega

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In this study, the South African partially oxidized fine-coal reject (FCR), which is associated with human health and environmental problems and sustains high disposal expenses, was subjected to density-separation, chemical fractionation, and demineralization experiments to isolate and evaluate the mode of occurrence of mineral-matter (MM) effects on the FCR pyrolysis. A unique composite of two reactive oxides (i.e., MgO and Fe2O3) and a hydrated oxide [i.e., Ca(OH)2] representing major extraneous coal–minerals were blended with either FCR, demineralized FCR, and its beneficiated samples to evaluate the yields of pyrolytic products and activation energy following a novel procedure. The properties of FCR samples and their pyrolytic products were determined by different analyses. Results indicate that the reactive oxides and a hydrated oxide composite addition increased the average activation energy (332.0–476.5 kJ/mol) for FCR due to the initial Ca(OH)2 decomposition and Fe2O3 reduction that took place under pyrolysis conditions. The FCR mineral-rich sink fractions achieved the highest carbon conversion (char yield = 78.8% and tar yield = 5.1%) compared to those of other samples (e.g., <1.9 g/cm3 float char yield = 87.3% and tar yield = 2.3%) evaluated due to higher proportions of calcite/dolomite/pyrite cleats and nonmineral inorganics (Ca, Mg, Na, and Fe) which catalyzed the pyrolysis reactions. On the other hand, CaCO3, CaMg(CO3)2, and metakaolinite formations in the char derived from a blend of reactive oxides and a hydrated oxide composite and FCR interfere with the pyrolysis reactions. Also, deoxygenation reactions were impeded by oxygen present in the reactive oxides and a hydrated oxide composite. The potent catalytic effects of cleat minerals and the extraneous minerals associated with cracking of heavy tars to lighter fractions open opportunities to further understand the mode of occurrence of MM present in FCR during utilization in global pyrolysis. This may reduce waste disposal costs, health-hazards, air-pollution, and FCR volumes and augments feed-coals.

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Section: Resultssupporting

confidence: 92%

Section: Coal and Char Compositionssupporting

confidence: 61%

Section: Coal and Char Compositionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Catalytic Effect of Reactive Extraneous Mineral Composites on Char and Tar Distribution during Pyrolysis of Highveld Partially Oxidized Fine-Coal Reject and Its Beneficiated Residues

Mphahlele,

Matjie,

Bunt

2023

ACS Omega

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“…During coal mining and feed preparation in South Africa, approximately 60 Mt of coal fines (byproduct) are generated and discarded per annum (Reddick, von Blottnitz, and Kothuis, 2007;Bunt et al, 2015). These coal discards have similar chemical and mineralogical properties to South African gasification and combustion ROM feed coals; however, they are characterized by a higher mineral matter (48% versus 29-32%) and highervitrinite (26% versus 24%) content (Matjie et al, 2015;Bunt et al, 2015;Rautenbach et al, 2019;2020). Globally, colliery and thermochemical plant activities generate 30 Gt of coal fine discards annually.…”

Section: Introductionmentioning

confidence: 99%

Production of sodium-based zeolites and a potassium-containing leach liquor by alkaline leaching of South African coal fines ash

Collins

Strydom

Matjie

et al. 2023

J. S. Afr. Inst. Min. Metall.

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South African coal discards derived from feed coal for thermoprocesses pose human health and environmental problems and incur high disposal costs. These issues need to be resolved. Coal fines and a coal fines/ K2CO3 blend were combusted at 700°C in a laboratory rotary kiln to produce ashes containing metakaolinite (Al2O3.2SiO2) and illite/muscovite/orthoclase amorphous materials. The blend ash and coal fines ash, containing 18% K2O and <1% K2O respectively, were leached with water and with 1 M and 8 M NaOH at 80°C for 4 hours using a solid to liquid ratio of 1:5. The 8 M NaOH leach yielded 17% sodalite (Na8Si6Al6O24(OH)2) formation through SiO32-, Al(OH)4_, and Na+ precipitation in the leached ashes. The 1 M NaOH leach yielded no sodalite. X-ray fluorescence analysis of the original ashes and leached ashes showed low Al and Si dissolution efficiencies due to the sodalite formation. Sequential NaOH leaching resulted in the highest potassium dissolution efficiency of 89% for the ashes of fines/K2CO3 blend and 59% for the fines. It may be possible to increase the ash-derived zeolite concentration by using even higher NaOH concentrations (12-20 M NaOH) during leaching. Sodalite derived from coal ash could possibly be utilized for water purification in industrial applications, or as molecule separators. The potassium-containing liquid could be used in fertilizer manufacture.

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Strong, lightweight, thermally stable, and hydrophobic sustainable structural composites produced from coal-based waste and polymer-derived SiOC ceramics

Eterigho-Ikelegbe

Ricohermoso

Harrar

et al. 2023

Clean Techn Environ Policy

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Recycling coal-based waste (CBW) into composites suitable as a building material might be a necessary response to combat its risk to the environment. Therefore, the objective of this study was to investigate the microstructure and performance of coal composites produced from CBW and polysiloxane polymer (SPR-212). Four types of CBW that differ in physicochemical properties were examined. Fourier transform infrared spectroscopy results indicated that the higher the intensity of the C=C bonds in the CBW, the higher the pyrolysis mass loss and shrinkage experienced by the composites during pyrolysis. The continuous operating temperature of the composites is up to 600 °C. However, at temperatures above 600 °C, composites containing carbon content greater than 36% manifested dramatic degradation. Pyrolysis mass loss in the range of 5.28 to 29.62% was obtained for all the composites. The density range of the composites is between 1.5 and 1.9 g per cubic centimetre. The water absorption of all the composites is within the range of 0 to 25% and is comparable to many building materials. Notably, the composites containing total carbon less than 10% registered a water contact angle greater than 90°, indicating the low wettability of their surface. Furthermore, composites that embodied the highest total carbon (63%) displayed the worst structural property. The findings of this study lay the foundation for further development of high-quality structural coal composites from CBW and the SPR-212 preceramic polymer through optimisation of the processing conditions. Graphical abstract

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Evaluation of mineral matter transformations in low-temperature ashes of South African coal feedstock samples and their density separated cuts using high-temperature X-ray diffraction

Cited by 5 publications

References 25 publications

Catalytic Effect of Reactive Extraneous Mineral Composites on Char and Tar Distribution during Pyrolysis of Highveld Partially Oxidized Fine-Coal Reject and Its Beneficiated Residues

Catalytic Effect of Reactive Extraneous Mineral Composites on Char and Tar Distribution during Pyrolysis of Highveld Partially Oxidized Fine-Coal Reject and Its Beneficiated Residues

Production of sodium-based zeolites and a potassium-containing leach liquor by alkaline leaching of South African coal fines ash

Strong, lightweight, thermally stable, and hydrophobic sustainable structural composites produced from coal-based waste and polymer-derived SiOC ceramics

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