title: Comparison of CO2 capture by ex-situ accelerated carbonation and in in-situ naturally weathered coal fly ash.
abstract: Natural weathering at coal power plants ash dams occurs via processes such as carbonation, dissolution, co-precipitation and fluid transport mechanisms which are responsible for the long-term chemical, physical and geochemical changes in the ash. Very little information is available on the natural carbon capture potential of wet or dry ash dams. This study investigated the extent of carbon capture in a wet-dumped ash dam and the mineralogical changes promoting CO2 capture, comparing this natural phenomenon with accelerated ex-situ mineral carbonation of fresh fly ash (FA). Significant levels of trace elements of Sr, Ba and Zr were present in both fresh and weathered ash. However Nb, Y, Sr, Th and Ba were found to be enriched in weathered ash compared to fresh ash. Mineralogically, fresh ash is made up of quartz, mullite, hematite, magnetite and lime while weathered and carbonated ashes contained additional phases such as calcite and aragonite. Up to 6.5 wt % CO2 was captured by the fresh FA with a 60% conversion of calcium to CaCO3 via accelerated carbonation (carried out at 2 h, 4Mpa, 90 °C, bulk ash and a S/L ratio of 1). On the other hand 6.8 wt % CO2 was found to have been captured by natural carbonation over a period of 20 years of wet disposed ash. Thus natural carbonation in the ash dumps is significant and may be effective in capturing CO2.
authors.affiliation: Environmental Nano Sciences Group, Chemistry Department, University of the Western Cape, South Africa. 2593gram@gmail.com
authors.forename: Grace N
authors.initials: GN
authors.lastname: Muriithi
authors.forename: Leslie F
authors.initials: LF
authors.lastname: Petrik
authors.forename: Olanrewaju
authors.initials: O
authors.lastname: Fatoba
authors.forename: Wilson M
authors.initials: WM
authors.lastname: Gitari
authors.forename: Frédéric J
authors.initials: FJ
authors.lastname: Doucet
authors.forename: Jaco
authors.initials: J
authors.lastname: Nel
authors.forename: Sammy M
authors.initials: SM
authors.lastname: Nyale
authors.forename: Paul E
authors.initials: PE
authors.lastname: Chuks
mesh_terms: D002244:Carbon / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry*; D060729:Coal Ash / Q000737:chemistry*; D004787:Environmental Pollution; D011210:Power Plants; D013052:Spectrometry, X-Ray Emission
chemical_list: D060729:Coal Ash; D002245:Carbon Dioxide; D002244:Carbon
keywords: Ash dam; CO(2) capture; Ex-situ mineral carbonation; Fly ash; Weathered ash