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.

Surface and bulk characterization of an ultrafine South African coal fly ash with reference to polymer applications

“…The beneficiation of South African FA after it has been put through a process of air classification, electrostatic recovery and/or density separation has been described before [1], and specific size fractions of FA, with specific physical and chemical properties, may be used in suitable applications. The country's research and development involving FA includes its application in building and construction as cement extender and into lightweight aggregates [4], environmental rehabilitation in the form of counteracting acid mine drainage, wastewater treatment, and toxic element immobilization by zeolites [5][6][7], mine backfilling, the recovery of alumina [8,9], production of geopolymers [10,11] and hydrotalcites [12], soil amelioration [13], refractories and bricks, road stabilization, CO 2 capture [14], and as a processing aid and functional filler in polymers [15].…”

Mineralization of Carbon Dioxide: A Literature Review

“…Muriithi et al [133] compared the carbonation processes of fresh fly ash and of weathered fly ash. Fresh fly ash can capture up to 6.5 wt % CO 2 with a 60 % conversion from calcium to CaCO 3 via accelerated carbonation within 2 h under 90°C and 4 MPa conditions; while, for comparison, 6.8 wt % CO 2 was found to have been captured by natural carbonation of wet disposed fly ash in situ over a period of 20 years.…”

Challenges and Perspectives on Carbon Fixation and Utilization Technologies: An Overview

“…Several studies have been carried out to evaluate the effect of carbonation curing on the properties of blended cement and/or (Teir et al, 2007;Reddy et al, 2010;Sanna et al, 2012;Abo-El-Enein et al, 2013;Dri et al, 2013;Hekal et al, 2013;Muriithi et al, 2013;Santos et al, 2013a;Dri et al, 2014;Jo et al, 2014;Reynolds et al, 2014;Salman et al, 2014;Santos et al, 2014;Fujii et al, 2015;Ukwattage et al, 2015). concrete masonry (El-Hassan and Shao, 2015).…”