MINERAL TRAPPING OF CO₂VIA OIL SHALE ASH AQUEOUS CARBONATION: CONTROLLING MECHANISM OF PROCESS RATE AND DEVELOPMENT OF CONTINUOUS-FLOW REACTOR SYSTEM

Abstract

Ash containing considerable amounts of free lime as the most active component requires stabilization to assure safe landfilling. Using CO 2 from flue gases as a neutralizing agent, also the emission of CO 2 is diminished. The most extensive effect could be achieved by treating ash-water suspensions with CO 2 -containing gas. As even minute amounts of extraneous substances present in water influence the extent and rate of lime solubility in water, the behavior of lime as the key component of ash in various conditionswas studied and the mechanism of process deceleration was proposed. As the next step, a laboratory-scale continuous-flow reactor system for aqueous carbonation of oil shale ash and main considerations for industrial pilotscale plant design were developed. IntroductionEmission of greenhouse gases and safe deposition/utilization of solid wastes are among the most serious problems caused by extensive usage of lowgrade solid fuels in the world heat and power production. CO 2 emissions could be decreased by reducing the usage of fossil energy sources, improving energy efficiency and/or by more intensive implementation of carbon capture and storage (CCS) technologies. CO 2 sequestration by mineral carbonation, considering both natural minerals [1,2] and alkali wastes [3][4][5] as CO 2 sorbents, is a prospective option.Carbonation of minerals is similar to natural rock weathering and involves permanent storage of CO 2 under the thermodynamically stable form of calcium and magnesium carbonates [6]. Mg-and Ca-rich silicates such as olivine, serpentine, talc and wollastonite are available worldwide and have * Corresponding author: e-mail maiuibu@staff.ttu.ee Mineral Trapping of CO2 via Oil Shale Ash Aqueous Carbonation 41the potential of sequestrating the total amount of CO 2 emitted from the combustion of all the available fossil fuel reservoirs [7]. Unfortunately, because of very slow reaction rates the carbonation of natural minerals requires chemical additives and/or elevated pressures and temperatures [8].One way of bypassing some draw-backs of accelerated carbonation of primary alkaline earth minerals is using alkaline waste residues from thermal processes or from construction and demolition activities as a feedstock. As these materials are often associated with CO 2 point source emissions and tend to be chemically more unstable than geologically derived minerals [9], they require a lower degree of pre-treatment and less energy-intensive operating conditions to enhance carbonation yields [9,10]. Furthermore, after stabilization by accelerated carbonation, the leaching behavior of alkaline waste materials such as municipal solid waste incinerator (MSWI) bottom ash [11,12], steel slag [4,9,13,14], air pollution control (APC) residues [15,16] and ashes from coal and oil shale power plants [17][18][19] is improved. This allows the usage of stabilized waste materials in civil engineering applications or for safer final disposal to landfill.The energy sector of the Republic of Estonia is predominantly (up to 67...

CO2 Capture by Accelerated Carbonation of Alkaline Wastes: A Review on Its Principles and Applications

“…5 illustrates the proposed mechanism of accelerated carbonation, which indicates that the carbonation reaction occurred in four routes. Similar results were also found in Huntzinger et al (2009b) and Uibu and Kuusik (2009a), suggesting some mechanisms that can affect the rate and extent of carbonation: (a) transportation-controlled mechanisms such as CO 2 and Ca 2+ -ions diffusion to/from reaction sites; (b) boundary layer effects (diffusion across precipitate coatings on particles); (c) dissolution of Ca(OH) 2 at the particle surface; (d) pore blockage; and (e) precipitate coating. Furthermore, their effects can change with time.…”

“…One way to avoid some of these drawbacks is to utilize alkaline waste residues. Table 2 summarizes the example of industrial alkaline solid wastes, e.g., coal-and oil shale-fired power plants (Uibu et al, 2009b;Uibu and Kuusik, 2009a;Uibu et al, 2011), steelmaking slag (Huijgen et al, 2005c;Bonenfant et al, 2008; Huijgen et al, 2005c;Bonenfant et al, 2008;Eloneva et al, 2008b;Kodama et al, 2008;Baciocchi et al, 2009b;Doucet, 2010;Chang et al, 2011a, b Air pollution control (APC) residue Khaitan et al, 2009;Yadav et al, 2010 Sludge (incinerator) ash Sewage sludge incinerator ash (SSA) Steel wastewater sludge (SWS) Paper sludge incinerator ash (PSIA) Gunning et al, 2010 Paper pulping and mill waste…”

The utilisation of fly ash in CO2 mineral carbonation

“…Sulphate ions, alongside carbonate ions (created in the reaction of H 2 O with CO 2 ) will produce insoluble layers of CaSO 4 and CaCO 3 , which will probably coat the surface of ash particles, thus preventing further dissolution of calcium oxide, as observed in the experiments reported elsewhere (Huijgen et al, 2005;Uibu and Kuusik, 2009). Therefore, the content of SO 4 -2 and CO 3 2 ions in the liquid phase has to be closely monitored, as they lead to the formation of insoluble layers on the surface of particles and thereby strongly inhibit dissolution.…”

“…On the other hand, the storage capacity of industrial waste is limited and dependent on developments of technology. The process of neutralising CO 2 with industrial waste has been presented in literature (Back et al, 2008;Bauer et al, 2011;Mun and Cho, 2013;Sanna et al, 2014;Stolaroff et al, 2005;Uibu and Kuusik, 2009). Possibilities of using domestic fly ashes were also examined (Jaschik et al, 2013;Uliasz-Bochenczyk, 2011;Uliasz-Bocheńczyk et al, 2012).…”

An Innovative Approach to Integrated Carbon Mineralization and Waste Utilization: A Review

“…In addition, wastewater or brine, which is a saline-based waste solution (total dissolved solid is generally more than 10,000 mg/L) produced from some industrial procedures such as oil and natural gas extraction (known as oil-field brines), could be used as the liquid agents in the carbonation reaction (Druckenmiller and Maroto-Valer, 2005;Uibu and Kuusik, 2009;Mercedes Maroto-Valer, 2011, 2012). Most wastewater treatments use chemicals as a neutralizing agent to adjust pH and enhance metal precipitation.…”