Influence of Carbonation on Leaching of Cementitious Wasteforms

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Abstract
The presented work represents a combined experimental and modeling approach to evaluate the role of carbon dioxide in the long-term performance of cementitious wasteforms. Small wasteforms were cast with Portland cement and synthetic wastewater containing known amounts of dissolved metals and nitrate as a tracer. A series of wasteforms was exposed to a control (CO2-free) and an accelerated environment for carbonation (50% CO2). The samples were subjected to dynamic leaching tests, and the results were fit to the two-dimensional diffusional release equation. Comparison of results for carbonated and noncarbonated samples indicated that both physical and chemical properties controlling release were altered by carbonation. Carbonation slowed the diffusional release of strontium and increased the release of nitrate, calcium, cadmium, lead, and cobalt. Comparison of the leaching rate of each metal relative to calcium was used to indicate solid solution in calcium hydroxide (cadmium) and calcium carbonate (cadmium and strontium). Leaching of cadmium and strontium appears to be heavily influenced by solid solution in calcium bearing phases.