Large amounts of 137Cs have been accidentally released to the subsurface from the Hanford nuclear site in the state of Washington, USA. The cesium-containing liquids varied in ionic strengths, and often had high electrolyte contents, mainly in the form of NaNO3 and NaOH, reaching concentrations up to several moles per liter. In this study, we investigated the effect of ionic strengths on Cs migration through two types of porous media: silica sand and Hanford sediments. Cesium sorption and transport was studied in 1, 10, 100, and 1000 mM NaCl electrolyte solutions at pH 10. Sorption isotherms were constructed from batch equilibrium experiments and the batch-derived sorption parameters were compared with column breakthrough curves. Column transport experiments were analyzed with a two-site equilibrium-nonequilibrium model. Cesium sorption to the silica sand in batch experiments showed a linear sorption isotherm for all ionic strengths, which matched well with the results from the column experiments at 100 and 1000 mM ionic strength; however, the column experiments at 1 and 10 mM ionic strength indicated a nonlinear sorption behavior of Cs to the silica sand. Transport through silica sand occurred under one-site sorption and equilibrium conditions. Cesium sorption to Hanford sediments in both batch and column experiments was best described with a nonlinear Freundlich isotherm. The column experiments indicated that Cs transport in Hanford sediments occurred under two-site equilibrium and nonequilibrium sorption. The effect of ionic strength on Cs transport was much more pronounced in Hanford sediments than in silica sands. Effective retardation factors of Cs during transport through Hanford sediments were reduced by a factor of 10 when the ionic strength increased from 100 to 1000 mM; for silica sand, the effective retardation was reduced by a factor of 10 when ionic strength increased from 1 to 1000 mM. A two order of magnitude change in ionic strength was needed in the silica sand to observe the same change in Cs retardation as in Hanford sediments. 相似文献
An activated carbon bed adsorption process is influenced by the adsorbents' characteristics, volatile organic compound (VOC) characteristics, and process conditions. In the literatures, the adsorption processes of the adsorbents and VOCs were usually considered to be in equilibrium. In this study, the VOC adsorption processes by activated carbon were considered to be a kinetic process, i.e. they are not in equilibrium. Then, isothermal adsorption curves and a small column experiment were simulated. 相似文献
The desorption kinetics of in situ chlorobenzenes (dichlorobenzenes, pentachlorobenzene and hexachlorobenzene) and 2,4,4′-trichlorobiphenyl (PCB-28) were measured with a gas-purge technique for river Rhine suspended matter sampled in Lobith, The Netherlands. This suspended matter is the main source of sediment accumulation in lake Ketelmeer. In lake Ketelmeer sediment earlier observations showed that slow and very slow fractions dominate the desorption profile.
For the river Rhine suspended matter, only for PCB-28 a fast desorbing fraction of around 1.6% could be detected. The observed rate constants were on the average 0.2 h−1 for fast desorption, 0.004 h−1 for slow desorption, and 0.00022 h−1 for very slow desorption. These values are in agreement with previous findings for the sediment from lake Ketelmeer and with available literature data on fast, slow, and very slow desorption kinetics.
The results from this study show the similarity of desorption profiles between river Rhine suspended matter, and the top layer sediment from lake Ketelmeer. This indicates that slow and very slow fractions are already present in material forming the top layer of lake Ketelmeer, and were not formed after deposition of this material in the lake. The absence of detectable fast fractions for most compounds could be caused by the absence of recent pollution of the suspended matter. But, the observations may also be explained by a rapid disappearance of compounds from the fast fraction due to a combination of a high affinity of very slow sites for these compounds, and their relatively high volatility. 相似文献