Reaction of CO, with Clean Coal Technology Ash to Reduce Trace Element Mobility

The combustion of coal in power plants generates solids (e-g., fly ash, bottom ash) and flue gas (e.g., SOX, C02). New Clean Air Act mandated reduction of SOX emissions from coal burning power plants. As a result, a variety of Clean Coal Technologies (CCT) are implemented to comply with these amendments. However, most of the CCT processes transfer environmentally sensitive elements (e.g., As, Cd, Pb, Se) from flue gas to CCT ash. The objective of this study was to determine the effect of a pressurized CO;! treatment on the chemistry of CCT ash. Three CCT ash samples, produced from lime injection, atmospheric fluidized bed combustion, and sodium carbonate injection processes were reacted under different C02 pressure treatment conditions. Treated and untreated samples were subjected to various experiments including, X-ray diffraction (XRD) analysis, calcium carbonate solubility studies, and trace element extraction studies. Factors influencing the efficiency of a C02 treatment for CCT ash samples include combustion process, moisture, C02 concentration, and pressure. The CO;! pressure treatment resulted in the precipitation of calcite in CCT ash samples, and thus lowered the pH and the concentration of extractable trace elements (e.g., Cd, Pb, Cr, As, Se). Furthermore, we found that CO;! pressure treatment was more effective for lime injection and atmospheric fluidized bed combustion processed samples than for sodium carbonate injection processed samples.