Role of Carbonation in Transient Leaching of Cementitious Wasteforms

A combined experimental and modeling program approach was applied to evaluate the role of the carbon dioxide reactive component of soil gas on the long-term performance of cementitious wasteforms. Small wasteforms were cast with Portland cement and synthetic wastewater containing metals and nitrate as a tracer. A series of wasteforms was exposed to an accelerated environment for carbonation and then subjected to transient leaching tests in deionized water. A second set of control wasteforms was not carbonated but was otherwise treated identically. Results are analyzed by comparison of experimental data with theoretical models of the leaching process. The results indicate that carbonation increases the apparent diffusion coefficient for unreactive species while resulting in chemical binding of metals through solid solution in calcite. For strontium, carbonation resulted in lower net leaching while leaching of calcium and nitrate was increased by carbonation.