Study of the accelerated carbonation of coal fly ash for carbon dioxide sequestration and soil amendment

Elevated levels of carbon dioxide in the atmosphere have created numerous environmental and socio-economic problems, including climate change. The scientific community is experimenting with various emission reduction and carbon capture and storage strategies. Mineral sequestration of carbon with alkaline industrial residues is one such emerging emission reduction technology which is being researched for its ability to be integrated into industrial plants, where both carbon dioxide (CO₂)and alkaline solid residues are generated on site. This concept can be applied to the coal-fired power generation industry, which produces enormous quantities of coal fly ash as a solid by-product along with massive emissions of gaseous CO₂ with the flue gas stream. Therefore, the mineral trapping of CO₂ with coal fly ash can help to sustain coal-based power generation, while bringing added advantages to fly ash disposal due to the favourable chemical changes which occur in fly ash during the above carbonation process. However, mineral carbonation to date remains an immature technology due to its main drawbacks related to kinetics and extensive research is necessary to find acceleration to accelerate mineral sequestration. The main aim of the present thesis is to investigate the effect of operational parameters on the accelerated carbonation of coal combustion fly ash and to study the effect of carbonation on the final disposal of fly ash, especially in relation to agricultural soil amendment. The research work is based on experimental studies conducted in the laboratory and in a greenhouse facility. The accelerated carbonation tests for fly ash were conducted in a newly-developed reactor facility in the Deep Earth Energy Research Laboratory in the Civil Engineering Department at the Clayton campus of Monash University. The main component of this facility is a continuously stirred cylindrical tank equipped with adjustable temperature and pressure mechanisms and monitoring and data acquisition systems. The fly ash materials were collected from the collection ponds of three major power plants located in the Latrobe Valley in Victoria, Australia. The carbonation reactions were designed to test the effect of reaction temperature (in the range of 20 ⁰C to 80 ⁰C), initial CO₂ pressure inside the reactor (in the range of 1MPa to 10 MPa), water-to-solid ratio or solid dosage (in the range of 0.1 to 1) and the super-critical phase of CO₂. In addition, the effect of fly ash particle size was tested with five different particle size categories varying from