CHEMICAL SPECIATION OF SELENIUM IN FLY ASH (TRACE ELEMENTS, STABILITY CONSTANTS)

Coal combustion is responsible for the mobilization of large quantities of a wide variety of elements. Some of these elements have been found to have the potential for adverse and beneficial effects on the environment. These beneficial and adverse effects may be better understood with knowledge of the concentration and stability of the Se species present in coal ash residues. The objectives of this dissertation were: (1) to characterize the content and oxidation states of Se present in fly ash from western U.S. coals; (2) to determine the distribution of elements in density and particle size fractions of fly ash; and (3) to determine stability constants for CaSeO(,4), CaSeO(,3), MgSeO(,4), and MgSeO(,3). These constants will permit estimation of the solution species of Se through the use of computer programs such as GEOCHEM. This knowledge could allow better understanding of the behavior of Se in fly ash amended soils.; A method for the determination of Se oxidation states present in coal fly ash was developed. Subsequent analysis of fly ash samples from different sources indicated the presence of significant quantities of Se(iv) species. This presence of such Se(iv) species had not been previously reported. Other elemental concentrations analyzed by means of instrumental neutron activation analysis (INAA). The concentration of other elements present in the fly ash samples was determined by means of instrumental neutron activation analysis. Elemental concentrations were found to be within ranges reported for fly ash with the exception of Tb which exceeded previously reported values. Potentiometric titrations yielded values for the conditional stability constants of MgSeO(,3), MgSeO(,4), CaSeO(,3), and CaSeO(,4). Titrations were conducted at ionic strengths of 0.01, 0.05, and 0.10 mol/liter.