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Municipal solid waste is being produced in large quantities, in keeping with a dramatic population increase and the growth of industrialization. Most of this waste is sent to landfills in South Korea. However, current treatment methods including incineration and recycling is limited owing to insufficient landfill space and the generation of leachates and soil contamination. Generally, 250-300 kg of bottom ash and 30 -50 kg of fly ash are generated from one ton of incinerated municipal solid waste. This study seeks to determine the degree of influence of several main factors, such as the optimum temperature, solid-to-water ratio and CO 2 concentration, on the process of accelerated carbonation of the bottom ash. The results show that the carbonation rate was at its highest at a temperature of 208C, a solid-to-liquid ratio of 0.2 and with 20% CO 2 . This implies that the CO 2 gas emitted from incinerators can be used directly as part of an accelerated carbonation process of bottom ash, as the water content of raw bottom ash is 15 , 25% and the CO 2 concentration emitted from incinerators is 5 , 20%. However, the temperature should remain at less than 208C for more effective carbonation.

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The accelerated carbonation process with CO 2 absorption to confirm the leaching behavior of Cr in municipal-solid-waste incinerator (MSWI) bottom ash was investigated. This investigation was performed by placing samples in a CO 2 chamber. Only the temperature of the chamber at atmospheric pressure was varied and the CO 2 concentration was kept constant at 30% while the water-to-solid ratio was held at 0.3 dm 3 /kg. The result of an XRD analysis indicated that CO 2 could combine with portlandite, ettringite and hydrocalumite to form mainly an amorphous Al-rich material and calcite. Comprehension of the Cr leaching behavior during the carbonation reaction was gained by understanding the results obtained in this study. The carbonation kinetics includes a two-step process with a phase-boundary chemical reaction and diffusion through the product layer. As the carbonation process proceeds, the rate-controlling step was switched from a chemical reaction to diffusion by means of product layer control. The experimental data showed that the increase in the reaction temperature increased the carbonation rate. The carbonation kinetics of two types of mechanisms for varying temperatures was analyzed and an equation fitted to the experimental data was formulated. The variations of the rate constant with the temperature obeyed the Arrhenius equation with activation energies of 13.82 and 21.98 kJ/mol. Approximately 34 g/kg CO 2 was sequestrated in MSWI bottom ash with a particle size of less than 0.15 mm after a carbonation time of 120 min.

To effectively pre-treat the alkaline inorganic waste by carbonation reaction with CO 2 , it is necessary to understand a mineralogical change. This is because mineralogical changes serve as an important key to leaching behavior or stabilization of heavy metals, such as Pb, Cu, Cr, and Ni, contained in the inorganic waste, at the point of environmental influence. Therefore, in this study we investigated the chemical composition and mineralogical characteristics of municipal solid waste incineration bottom ash, which is a type of alkaline inorganic waste, and the material changed by the carbonation reaction in bottom ash. In addition, minerals affected by carbonation reactions were identified based on the ternary diagram of Ca-Al-Si in bottom ash. The relationship between mineralogical changes caused by carbonation reactions and stabilization of heavy metals was also examined.