Low-Temperature Thermal Treatment and Boron Speciation Analysis from Coals

Jonah Gamutan (), Shunsuke Kashiwakura, Richard Alorro and Tetsuya Nagasaka
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Jonah Gamutan: Western Australia School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, 117 Egan Street, Kalgoorlie, WA 6430, Australia
Shunsuke Kashiwakura: Research Organization of Science and Technology, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu City 525-8577, Japan
Richard Alorro: Western Australia School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, 208 Kent Street, Bentley, WA 6102, Australia
Tetsuya Nagasaka: New Industry Creation Hatchery Center, Tohoku University, 6-6-10 Aoba Aramaki Aza-Aoba, Aoba-ku, Sendai 980-8579, Japan

Sustainability, 2024, vol. 16, issue 13, 1-13

Abstract: Despite urgent calls for decarbonization, the continued increasing demand for electricity, primarily from coals, has presented challenges in managing coal-derived wastes such as coal fly ash (CFA), which are enriched with environmentally hazardous substances like boron. This study explores a low-temperature heating process to remove boron from coal, aimed at preventing its condensation and enrichment into CFA during combustion. Initial boron concentrations in coals varied widely from 50 to 500 ppm by weight and were found to correlate with fixed carbon content (FC) through the following polynomial equation: [B] o = 0.0929(FC) 2 − 14.388(FC) + 601.85; R 2 = 0.9173. This relationship suggests that as coal undergoes coalification, boron-containing compounds are decomposed and released, resulting in a decline in boron levels as the coal matures. Boron-removal efficiency was investigated by drying coal samples at 110 °C, 160 °C, and 210 °C under natural air convection, and nuclear magnetic resonance (NMR) spectroscopy was used to assess changes in boron speciation during heating. Our results demonstrate that boron removal ranged from 5% to 82%, with minimal improvements observed beyond 110 °C. In addition, the 11 B MAS-NMR spectra of the coal samples showed four peaks at isotropic chemical shift values of −1.0, 2.0, 8.0, and 14.0 ppm and suggested that the species of boron volatilized at low temperatures is the inorganic BO 4 assigned to peak no. 0 at −1.0 ppm. The association of boron with inorganic components in coal suggests potential for efficient removal, particularly in coals with higher fixed carbon content. These findings highlight the viability of low-temperature thermal treatment as a cost-effective method for boron removal, which is crucial in mitigating the risks associated with coal combustion by-products.

Keywords: boron removal; coal; MAS-NMR; low-temperature heating (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2024
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