Solubilities and ion exchange properties of solid solutions between the hydroxyl, chlorine and carbon trioxide end members of the monocalcium aluminate hydrates.

摘要

Friedel's salt (3CaO·Al2O3·CaCl 2·10H2O) is the chloride phase most often identified in hydrated cement pastes and concrete, and is likely the dominant mineralogical control on chloride concentrations in these materials. When exposed to radiation from nuclear reactors (e.g. reactor shielding walls), stable chlorine isotopes present in concrete structures can become activated to radioactive chlorine-36. Chlorine-36 is considered a critical nuclide in radioactive waste disposal, because it has a moderately long half-life (3.01 +/- 0.04 x 10 5 years), and is highly mobile in terrestrial environments. Although detailed studies have been conducted on the crystal structure of Friedel's salt, and on solid solutions formed between the OH and Cl, Cl and CO 3, and OH and CO3 end members, the solubility data published in the literature are limited primarily to the end members. The objectives of this thesis were: (1) to measure the solubility of the solid solutions in these three series at thermodynamic equilibrium, (2) to confirm the miscibility gaps and regions of solid solution as determined by previous researchers, (3) to develop a description of the partitioning of chloride between the solid solution and the aqueous solution phases at thermodynamic equilibrium using solid-solution aqueous-solution (SSAS) theory, and (4) to investigate the rate and extent of exchange of anions from the interlayer of these phases.;The stability of solid phases between the Cl-OH, Cl-CO3 and CO3-OH end members was examined using solubility experiments conducted from both super- and undersaturated conditions. The solid and solution phases were examined for compositional variations, and the positions of miscibility gaps were determined based on the observed mineral phase assemblages and calculated mineral saturation indices in aqueous solution. The results of the solubility studies support the conclusion of previous researchers that the miscibility gap in the OH-Cl series begins at a Cl/(Cl+OH) ratio very close to 0.33, and confirms that the lower limit of the miscibility gap lies between ratios of 0.0 and 0.1. In agreement with previous research, a partial solid solution was observed in solids with carbonate ratios of up to 0.75 between the Cl and CO3 end members. The upper limit of the miscibility gap is extended to a ratio of at least 0.91. From supersaturation, two miscibility gaps were observed in the OH-CO3 series; one between the OH end member and hemicarboaluminate from carbonate ratios of 0.1 to 0.5, and a second between hemicarboaluminate and the CO3 end member at carbonate ratios of 0.6 to 0.8. (Abstract shortened by UMI.)