黄土中Sr阻滞因子的实验研究

【作者】 陈勇；

【导师】 钱天伟；

【作者基本信息】 太原科技大学 ， 流体力学， 2010， 硕士

【摘要】 核能的利用,一方面给人类社会带来了极大的经济效益,另一方面,核废物若处置不当,将对生态环境造成很严重的污染,威胁到人类的健康。目前,放射性废物的地质处置是国际上唯一接受的、安全的处置方法。一个适宜的核废物处置库库址的选定需要综合各种因素,其中核素迁移是其核心问题之一。本文通过实验考察了Sr在饱和黄土中的迁移行为,为浅地层处置场的适宜性评价提供依据。首先,在25±1℃的条件下,系统的研究了Sr在供试黄土中的吸附行为及其影响因素。动力学吸附结果表明:黄土对Sr的吸附能力极强,几乎瞬间就能达到吸附平衡。采用批量平衡法,在5～100mg/L的浓度范围内,开展了Sr平衡吸附行为的实验研究,以Freundlich方程拟合实验数据,计算出Sr在黄土中的吸附特性参数1/n和Kf,1/n为0.6791,Kf值为117.67。Freundlich方程线性化的拟合效果也比较令人满意,获得了该浓度范围内的分配系数Kd,其值为55.01 mL/g。此外,就温度、土壤粒径、初始液质量浓度、pH值和钙离子强度对Sr吸附的影响开展了实验,结果显示:随着温度的降低、土壤粒径的减小、初始液质量浓度的增大、pH值的升高和钙离子浓度的降低,Sr在黄土中的吸附量都有不同程度的升高。其次,进行了土柱模拟实验。以Br-为示踪溶质,在稳定流条件下,得到了Br-的穿透曲线。用时7个月约210天,进行Sr在饱和黄土中的淋溶动态实验,获得了Sr在土柱中的垂直浓度分布曲线。实验结果显示:Sr在土柱中的浓度峰出现在11.25cm处,动态阻滞因子为283.6。最后,根据易混合置换实验获得的Br-的BTC,应用软件HYDRUS-1D,求解一维溶质运移对流-弥散方程数学模型的反问题,估算出Sr的峰值距离,进行Kd和Rd实验数据的修正。更多还原

【Abstract】 On the one hand, radionuclide is used for industry, which promotes the economic development; on the other hand, radionuclide is harmful to human health and ecological environment if it is not treated properly. Nowadays, the geologic disposal is considered as one of the best methods. And the superficial disposing is widely applied to treat the VLLW. Many factors need to be considered for choosing a suitable site to treat the radionuclide. And the migration of nuclide is one of the most important factors and must be considered.Firstly, we studied the behavior of Sr in contact with test loess through kinetic adsorption and the equilibrium was reached almost instantaneously. Then, adsorption isotherms of Sr on the test loess were studied using laboratory batch system and experimental concentration of Sr is rang from 5mg/l to 100mg/l. The adsorption isotherms of Sr were described by the Freundlich equation. The Kf value and 1/n value are 117.67 and 0.6791 respectively. And the Kd value is 55.01mL/g when the 1/n value is 1. The Kd values are all increased with the decreasing of temperature、the reducing of particle size、the increasing of initial concentration and the increasing of pH and have negative correlation of Ca2+ ion concentration.Secondly, the migration experiment lasted seven months about 215 days. The miscible displacement experiments were carried out on saturated homogeneous loess under steady-state flow at a specific pore water velocity to investigate the movement of Sr using bromide as a tracer. The vertical concentration distribution of Sr in column was obtained, which was used to compute the retardation coefficient. The results from leaching experiment suggested that maximum of concentration is located in 11.25cm. then the retardation coefficient was calculated and its value is 283.6.Finally,the computer code(HYDRUS-1D) was applied to fit the breakthrough curve of bromide. And by solving inverse problem of the convection dispersion equation, the relative parameters were obtained. Then the least-squares optimization approach was used to estimate the position of concentration of Sr in column.更多还原