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Transfer of co2 to groundwaters through the capillary fringe in porous medium : i. laboratory study

出版	AECL Research., 1993
URL	http://books.google.com.hk/books?id=8wpm0AEACAAJ&hl=&source=gbs_api

註釋Significant quantities of 14-c are present in low- and intermediate-level wastes. many waste forms containing 14-c have the potential to release this radioisotope as carbon dioxide, which is then transported to the bioshpere either by gas-phase diffusion in soils, or by dissolution and transport by groundwater. the major mode of release of 14-c is not known, but it is suspected that the capillary fringe of the water table provides a barrier to groundwater transport. experimental parameters are required to model the 14-co2 diffusion through the capillary fringe, so the mass transfer to groundwaters can be modelled and the major release mode can be determined. the scope of this experimental program is to obtain the main parameters required to model the co2 diffusion from the gaseous phase to the liquid phase. in this laboratory-scale experiment, a gas mixture continuously supplied into a wet sand column is allowed to equilibrate with porewaters. the dissolved inorganic carbon (dic, or dissolved co2) of the porewaters is measured using probes placed along the column at various times, so several transient profiles are obtained. each dic profile is fitted to a diffusion equation to obtain the diffusion coefficient (d). the equation also provides the location of the diffusion interface between the gaseous and liquid phases in the porous medium. results show that the vertical profile of dic can be adequately fitted with a diffusion equation. the value of d is close to the theoretical value of dissolved co2 in pure water in a porous medium. the diffusion equation also suggests that the top of the capillary fringe is the boundary of the diffusion into a semi-infinite medium. our experiments suggest that the ph of water (6-7) does not have an influence on the diffusion (dispersion) coefficient of dissolved co2.