Environmental evaluation and nano-mineralogical study of fresh and unsaturated weathered coal fly ashes

Segun A Akinyemi; Wilson M Gitari; Leslie F Petrik; Bemgba B Nyakuma; James C Hower; Colin R Ward; Marcos L S Oliveira; Luis F O Silva

doi:10.1016/j.scitotenv.2019.01.308

Environmental evaluation and nano-mineralogical study of fresh and unsaturated weathered coal fly ashes

Sci Total Environ. 2019 May 1:663:177-188. doi: 10.1016/j.scitotenv.2019.01.308. Epub 2019 Jan 25.

Authors

Segun A Akinyemi¹, Wilson M Gitari², Leslie F Petrik³, Bemgba B Nyakuma⁴, James C Hower⁵, Colin R Ward⁶, Marcos L S Oliveira⁷, Luis F O Silva⁸

Affiliations

¹ Environmental Remediation and Geopollution Group, Department of Geology, Faculty of Science, Ekiti State University, Ado Ekiti, P.M.B. 5363, Ado Ekiti, Nigeria; Environmental Remediation and Water Pollution Chemistry Group, Department of Ecology and Resources Management, School of Environmental Studies, University of Venda, Private Bag, X5050, Thohoyandou, 0950, South Africa. Electronic address: segun.akinyemi@eksu.edu.ng.
² Environmental Remediation and Water Pollution Chemistry Group, Department of Ecology and Resources Management, School of Environmental Studies, University of Venda, Private Bag, X5050, Thohoyandou, 0950, South Africa.
³ Environmental and Nano Sciences Group, Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa.
⁴ School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru, Malaysia.
⁵ University of Kentucky Centre for Applied Energy Research, 2540 Research Park Drive, Lexington, KY 40511, United States of America.
⁶ School of Biological, Earth, and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
⁷ Department of Civil and Environmental, Universidad de la Costa, CUC, Calle 58 # 55-66, Barranquilla, Atlantico, Colombia; Universidade do Vale do Rio do Sinos, Av. Unisinos, 950-Cristo Rei, RS 93022-000, Brazil; Faculdade Meridional IMED, 304-Passo Fundo, RS, 99070-220, Brazil.
⁸ Department of Civil and Environmental, Universidad de la Costa, CUC, Calle 58 # 55-66, Barranquilla, Atlantico, Colombia. Electronic address: felipeqma@hotmail.com.

PMID: 30711584
DOI: 10.1016/j.scitotenv.2019.01.308

Abstract

Coal combustion and the disposal of combustion wastes emit enormous quantities of nano-sized particles that pose significant health concerns on exposure, particularly in unindustrialized countries. Samples of fresh and weathered class F fly ash were analysed through various techniques including X-ray fluorescence (XRF), X-ray diffraction (XRD), focused ion beam scanning electron microscopy (FIB-SEM), field-emission gun scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM) coupled with energy dispersive x-ray spectroscopy (EDS), and Raman Spectroscopy. The imaging techniques showed that the fresh and weathered coal fly ash nanoparticles (CFA-NPs) are mostly spherical shaped. The crystalline phases detected were quartz, mullite, ettringite, calcite, maghemite, hematite, gypsum, magnetite, clay residues, and sulphides. The most abundant crystalline phases were quartz mixed with Al-Fe-Si-K-Ti-O-amorphous phases whereas mullite was detected in several amorphous phases of Al, Fe, Ca, Si, O, K, Mg, Mn, and P. The analyses revealed that CFA-NPs are 5-500 nm in diameter and encapsulate several potentially hazardous elements (PHEs). The carbon species were detected as 5-50 nm carbon nanoballs of graphitic layers and massive fullerenes. Lastly, the aspects of health risks related to exposure to some detected ambient nanoparticles are also discussed.

Keywords: Coal fly ash; Human health; Nanomineralogy; Nanoparticles; Potential hazardous elements.