INFLUENCE OF CARBONATION ON LEACHING OF CEMENTITIOUS WASTEFORMS

The presented work represents a combined experimental and modeling app roach to evaluate the role of carbon dioxide in the long-term performa nce of cementitious wasteforms. Small wasteforms were cast with Portla nd cement and synthetic wastewater containing known amounts of dissolv ed 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 equati on. Comparison of results for carbonated and noncarbonated samples ind icated that both physical and chemical properties controlling release were altered by carbonation. Carbonation slowed the diffusional releas e of strontium and increased the release of nitrate, calcium, cadmium, lead, and cobalt. Comparison of the leaching rate of each metal relat ive to calcium was used to indicate solid solution in calcium hydroxid e (cadmium) and calcium carbonate (cadmium and strontium). Leaching of cadmium and strontium appears to be heavily influenced by solid solut ion in calcium bearing phases.