MODELING CHEMICAL AND PHYSICAL PROCESSES IN LEACHING SOLIDIFIED WASTES zq # n ?
Solidification is an important treatment process in hazardous waste management and will continue to be so until waste minimization and waste recycle processes are perfected for all hazardous wastes. It is generally recognized that immobilization of contaminants in solidified wastes occurs through both physical and chemical mechanisms. Standard techniques for analyzing contaminant leaching measure only an observed diffusivity that does not separate chemical and physical factors. The suitability of the standard data analysis procedure is reviewed and alternative models developed that describe the separate effects of chemical and physical processes. These models describe physical transport through a solidified waste matrix according to Fick's law. Chemical reactions of sorption/desorption and precipitation/ dissolution are described. The observed diffusivity that would be calculated by ignoring chemical processes is shown to depend on the true effective diffusivity and coefficients that describe the chemical phenomena.
Assessment of the loss of radioactive isotopes from waste solids to the environment. Part I. Background and theory
A report is given of several theoretical expressions based on mass transport phenomena that relate the radioactivity escaping from such solids to diffusion, dissolution processes, surface conditions, and radioactive decay. Representative available data for radioactive waste solids incorporated in cement, asphalt, ceramic, and glass media are analyzed using the theoretical expressions presented. These analyses show that an expression taking into account diffusion and concentration-dependent dissolution gives good agreement with the data for most of the products considered. In the main, these products can be categorized as waste solids of low solubility incorporated in inert matrices. The effective diffusivities obtained are in the range of mid 10$sup - 17$ to mid 10$sup -12$ cm$sup 2$/sec, the dissolution rate constants are in the range of high 10$sup -9$ to low 10$sup -7$ sec$sup -1$, and the surface transfer constants are in the range of low 10$sup -4$ to low 10$sup -3$ sec$sup -1$ for the products analyzed. Once determined, such parameters can be used to compare various waste products and to estimate releases from these products, in particular, long-term releases. (auth)
Review of leaching test methods and the leachability of various solid media containing radioactive wastes
A review o f experimental techniques which have been employed t o measure Factors y are described. The need two (1 ) a r a p i d co~nparison t e s t , and (2) a more comprehensive performance t e s , wherein t h e actual exposure environment i s simulated.