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.

This paper examines the main results of an accelerated carbonation treatment applied to different types and size fractions of stainless steel slag. The objectives of this work were essentially to assess the CO 2 uptake achievable by each type of slag under mild operating conditions and to investigate the effects of carbonation on the mineralogy and leaching behaviour of the residues. The following types of materials were tested: different size fractions of commingled slag, milled electric arc furnace (EAF) slag and argon oxygen decarburization (AOD) slag. Each material was thoroughly characterized in terms of elemental composition, mineralogy and leaching behaviour. Accelerated carbonation batch experiments were performed exposing humidified (with liquid to solid ratios \0.6 l/kg) slag to 100% CO 2 for operating times between 0.5 and 24 h, at controlled temperature and pressure. Maximum CO 2 uptakes of 130, 180 and 300 g CO 2 /kg slag were achieved (at 50°C and 3 bar) for the finest fraction of the mixture, the milled EAF slag and the AOD slag, respectively. The mineralogy of each type of residue showed to be affected by the treatment, exhibiting an increase in calcite concentration and a decrease in the content of specific silicate and oxide phases. The leaching behaviour of all types of carbonated slag was also modified, exhibiting a reduction by 1-2 units of the natural pH of the materials, accompanied by a decrease of Ca release and an increase of Si leaching, as a result of modified leaching-controlling phases. In conclusion, at the tested operating conditions, AOD slag was the most reactive material with CO 2 . Milling, however, proved effective in increasing the carbonation yield of the EAF slag compared to that measured for the different size fractions of the commingled slag mixture.

The main aims of this work were to assess the CO2storage capacity of different particlesize fractions of stainlesssteelslag subjected to accelerated carbonation under mild operating conditions, to study the influence on reaction kinetics of some of the main operating parameters (temperature, pressure and liquid to solid ratio) and to determine the effects of the process on slag mineralogy and leaching behavior. Maximum CO2 uptakes of 130 g CO2/kg residues were measured for the finest grain size and decreased with particlesize owing to differences in reacting species availability and specific surface. Process kinetics proved relatively fast, achieving completion in around 2 hours with a CO2 pressure of 3 bar and an optimal liquid to solid ratio of 0.4; temperature was the parameter that most influenced CO2 uptake, due to its enhancement effect on silicates dissolution

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