Scarpitta S C, Harley N H
U.S. Department of Energy, Environmental Measurements Laboratory, New York, NY 10014.
Health Phys. 1990 Oct;59(4):393-404. doi: 10.1097/00004032-199010000-00002.
The adsorptive and desorptive characteristics of canisters containing a petroleum-based charcoal were investigated under controlled conditions of temperature, relative humidity, and Rn concentration. Charcoals exposed in a monolayer and packed bed during exposure intervals of 1-7 d demonstrate that Rn adsorption and desorption are dependent on bed depth and the amount of water adsorbed. Changes in the adsorptive and desorptive properties of the charcoal occurred near the break-point where the pores became occluded by water vapor that condenses in the entrance capillaries. Radon-222 adsorption is decreased by an order of magnitude as the amount of adsorbed water exceeds the break-point of the charcoal. The reduction in pore surface due to adsorbed water results in a marked increase in the rate of Rn loss from exposed canisters, accounting for reduced adsorption. The apparent desorption time-constant for a 2-cm bed of loose Witco 6 x 10 mesh charcoal containing 0.220-0.365 kg H2O kg-1 is typically between 2-8 h. The apparent desorption time-constant for an equivalent packed bed containing a water vapor content of 0.026-0.060 kg H2O kg-1, which is below the break-point of the charcoal, is about 15-30 h. Conventional charcoal canisters, if exposed in the fully-opened configuration, can achieve the break-point in less than 4 d at 70% humidity. The use of a diffusion barrier would allow for longer exposure times until the break-point of the charcoal is achieved.
在温度、相对湿度和氡浓度的受控条件下，研究了装有石油基活性炭的滤罐的吸附和解吸特性。在1 - 7天的暴露间隔期间，单层暴露和填充床中的活性炭表明，氡的吸附和解吸取决于床层深度和吸附的水量。活性炭的吸附和解吸特性在断点附近发生变化，此时孔隙被入口毛细管中凝结的水蒸气堵塞。当吸附的水量超过活性炭的断点时，氡-222的吸附量降低一个数量级。由于吸附水导致孔隙表面积减小，使得暴露滤罐中氡的损失速率显著增加，这解释了吸附量的减少。对于含有0.220 - 0.365 kg H₂O kg⁻¹的2厘米厚松散的威特科6×10目活性炭床层，表观解吸时间常数通常在2 - 8小时之间。对于等效填充床，其水蒸气含量为0.026 - 0.060 kg H₂O kg⁻¹（低于活性炭的断点），表观解吸时间常数约为15 - 30小时。如果传统活性炭滤罐以完全打开的配置暴露，在70%湿度下不到4天就能达到断点。使用扩散屏障可以延长暴露时间，直到达到活性炭的断点。
