AN548 – Carbonation of bottom ash-zh

REFERENCE

Carbon dioxide sequestration in municipal solid waste incinerator (MSWI) bottom ash, E. Rendek, G. Ducom, P. Germain, Journal of Hazardous Materials B128 (2006) 73–79

INTRODUCTION

The incineration of municipal solid waste generates solid residues, bottom ash and fly ash, as well as atmospheric emissions containing about 12% of CO2, this last being completely released with the atmosphere. In France, for 64% of MSWI bottom ash, a period of weathering, several months, is required before reuse as, for example, a secondary building material or in road sub-bases. However, it has been proved that the natural carbonation process can be accelerated, using different sources of CO2 as atmospheric CO2. This process could both help reducing the greenhouse effect and reducing bottom ash storage duration by accelerating weathering reactions.

AN-548EXPERIMENTAL

Simultaneous TG/DSC was used before and after a complete carbonation to investigate calcite formation resulting from accelerated carbonation. Experiments were carried out in a Labsys TG-DSC at a heating of 10K/min to 1000°C under an inert atmosphere of argon. For these analyses, a mass of about 20 mg of the uncarbonated or carbonated bottom ash was placed inside an alumina crucible. The temperature of the sample and reference were recorded by a platinum/rhodium thermocouple (type S), and a high-precision balance registered the potential weight loss due to evaporation/decomposition of the sample.

RESULTS

TG/DSC curves of uncarbonated and carbonated bottom ash are represented in the figure. The first endothermic effect at 90°C accompanied by a mass loss of about 20% corresponds to the sample dehydration. Between 200°C and 600°C TG/DSC curves show a slight decrease and an exothermic phenomenon, which is attributed to the pyrolysis of the 1.5% of organic matter.
Then, DSC curves present a small endothermic peak from 600°C to 750°C due to the dissociation of carbonates according to the following dissociation equation:

CaCO3 (s) → CaO (s) +CO2 (g)

It is accompanied by a mass loss of 3.3% and 6.2% for respectively fresh and carbonated bottom. The mass difference is about 2.9%. This value is in agreement with the one obtained on the accelerated ageing set up, where the gain of mass was about 3.2%. It confirms that the gain of weight of samples was really due to a chemical carbonation and not to physical adsorption of CO2.