Current status and perspectives of accelerated carbonation processes on municipal waste combustion residues

Abstract

The increasing volumes of municipal solid waste produced worldwide are encouraging the development of processes to reduce the environmental impact of this waste stream. Combustion technology can facilitate volume reduction of up to 90%, with the inorganic contaminants being captured in furnace bottom ash, and fly ash/APC residues. The disposal or reuse of these residues is however governed by the potential release of constituent contaminants into the environment. Accelerated carbonation has been shown to have a potential for improving the chemical stability and leaching behaviour of both bottom ash and fly ash/APC residues. However, the efficacy of carbonation depends on whether the method of gas application is direct or indirect. Also important are the mineralogy, chemistry and physical properties of the fresh ash, the carbonation reaction conditions such as temperature, contact time, CO(2) partial pressure and relative humidity. This paper reviews the main issues pertaining to the application of accelerated carbonation to municipal waste combustion residues to elucidate the potential benefits on the stabilization of such residues and for reducing CO(2) emissions. In particular, the modification of ash properties that occur upon carbonation and the CO(2) sequestration potential possible under different conditions are discussed. Although accelerated carbonation is a developing technology, it could be introduced in new incinerator facilities as a "finishing step" for both ash treatment and reduction of CO(2) emissions.

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

“…Nature's carbon cycle sequesters CO 2 as mineral carbonates by precipitation from the ocean in a geological timescale (Gerdemann et al, 2007). However, the kinetics of natural carbonation is extremely slow due to the relatively low CO 2 concentration, about 0.03-0.06% (Lackner, 2002;Costa et al, 2007). According to an investigation by Haug et al (2010), the weathering rate of olivine is estimated to be 10 −8.5 mol/(m 2 s) using the average ground temperature in Norway of 6°C and a pH of 5.6, which corresponds to the acidity of rainwater.…”

“…Currently, accelerated carbonation has been primarily investigated through the direct aqueous route (Huijgen and Comans, 2006a;Costa, 2009;Uibu et al, 2009;Chang et al, 2011a). Carbonation can result in lowering of pH, affecting the solubility, and leaching of metals which are mobilized at high pH and fixed at low pH (Costa et al, 2007).…”

“…Besides that, carbonation is an exothermal reaction, so energy consumption and costs may be reduced by its inherent properties (Lackner, 2003;Eloneva et al, 2008a;Baciocchi et al, 2009a). In all cases, carbonation must provide base ions, such as monovalent sodium and potassium, or divalent calcium and magnesium ions to neutralize the carbonic acid (Costa et al, 2007;Gerdemann et al, 2007). Other carbonate-forming elements such as iron carbonates are not practical due to their unique and precious features (Lackner, 2002).…”

“…The potential advantages of accelerated carbonation of applied industrial alkaline solid wastes include: (a) carbonation is an exothermal reaction and hence energy consumption and costs may be reduced by its inherent properties; (b) carbonation products such as calcium or magnesium carbonates are thermodynamically stable under ambient conditions, that is, in the absence of acidification. ; (c) it offers great sequestration capacity due to the high availability of deposits; (d) it does not require transport at sites within steel-works and is therefore cost-effective; (e) products may be beneficially reused in a variety of application, such as construction materials; (f) carbonation eliminates environmental impacts due to decreased leaching of heavy metal trace elements such as Pb, Ni, and Cd from residues and stabilizing of the waste leading to an improvement of environmental quality; and (g) it could neutralise the pH of the solution as carbonate precipitations are formed if alkaline wastewater is used as the liquid agents (Lackner, 2003;Fernandez-Bertos et al, 2004a;Huijgen et al, 2005b, c;Costa et al, 2007;Eloneva et al, 2008a;Bonenfant et al, 2009;Huntzinger et al, 2009a;Gunning et al, 2010;Lim et al, 2010). This paper focuses on accelerated carbonation of industrial alkaline wastes, e.g., steelmaking slags and metalworking wastewater.…”

Mineral CO2 sequestration by environmental biotechnological processes

“…Various sources of alkalinity have been suggested for CO 2 sequestration purposes. For example, alkaline solid residues from different industries such as steel slag (Huijgen & Comans, 2005;Kelly et al, 2011), cement kiln dust (Huntzinger et al, 2009), and fly ashes (Back et al, 2008;Costa et al, 2007), have been identified as alkalinity sources. The quantity and distribution of these alkaline solid wastes is however limited on a global scale (Huijgen & Comans, 2005).…”