Properties and reactivity of two oxidized and unoxidized South African Highveld fine coal rejects and their density-separated fractions

Mphahlele, Katlego; Matjie, R.H.; Bunt, John R.; Uwaoma, R.C.

doi:10.1080/19392699.2023.2221634

Cited by 2 publications

(1 citation statement)

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“…The ashes of these samples comprised mainly SiO 2 , Al 2 O 3 , CaO, SO 3 , Fe 2 O 3 , and MgO with minor percentages of TiO 2 , K 2 O, Na 2 O, and P 2 O 5 which are consistent with the ash composition of SA feed-coals to commercial gasifiers. 26 , 27 Mphahlele et al 28 found that higher concentrations of trace elements (Co, Zn, As, Rb, Sr, Zr, Ag, Cd, Ba, In, and Sn) and rare earth element (Y) are concentrated in the density-separated fractions of the FCR samples compared to the typical concentrations for SA Highveld ROM coals, as reported by Wagner and Hlatshwayo. 29 This could be associated with health and environmental issues during the storage of FCR samples in stockpiles and slime dams.…”

Section: Resultsmentioning

confidence: 71%

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: Resultsmentioning

confidence: 71%