2013 Volume 54 Issue 8 Pages 1510-1516
The accelerated carbonation process with CO2 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 CO2 chamber. Only the temperature of the chamber at atmospheric pressure was varied and the CO2 concentration was kept constant at 30% while the water-to-solid ratio was held at 0.3 dm3/kg. The result of an XRD analysis indicated that CO2 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 CO2 was sequestrated in MSWI bottom ash with a particle size of less than 0.15 mm after a carbonation time of 120 min.