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高放废物深地质处置库近场环境中,高压实膨润土将长期遭受含盐地下水的循环化学作用,导致其膨胀性能不断衰变。针对干密度为1.7 g/cm3的高压实高庙子(GMZ)膨润土,分别开展了0.5 mol/L和1.0 mol/L两种盐梯度、Na Cl-水-KCl和Na Cl-水不同循环路径下的恒体积膨胀力试验,探讨盐梯度循环化学作用下其膨胀力的衰变特性。结果表明:盐梯度循环作用下,膨润土膨胀力的发展与离子种类、浓度和循环次数等因素有关。盐化阶段膨胀力不断降低,淡化阶段膨胀力有所提高;低盐度梯度循环下各阶段的稳定膨胀力均高于高盐度梯度循环时的膨胀力。随着循环次数的增加,稳定膨胀力逐渐下降,入渗溶液浓度越高,降幅越大,且衰减幅度随着循环次数的增加而减小。KCl溶液的入渗会引起膨润土发生矿物相变,膨胀力显著降低;当KCl溶液浓度达到一定值时,蒙脱石的充分溶解导致膨润土丧失膨胀能力。
In the near-field environment of high-level radioactive waste deep geological repository, high-pressure solid bentonite will suffer long-term chemical reaction of salty groundwater, leading to its decaying performance. Two kinds of salt gradients of 0.5 mol / L and 1.0 mol / L were carried out respectively for high-pressure GMZ bentonite with a dry density of 1.7 g / cm3. NaCl-water-KCl and NaCl- Path of constant volume expansion force test to explore the salt gradient cyclic chemical decay characteristics of its expansion force. The results show that the development of swelling capacity of bentonite under the salt gradient cycling is related to the species, concentration and number of cycles. In the salinization stage, the expansive force decreased while the expansive force in the desalination stage increased. The steady expansive force in all stages under the low salinity gradient cycle was higher than that in the high salinity gradient cycle. With the increase of the number of cycles, the steady expansive force gradually decreases. The higher the concentration of infiltration solution, the larger the decline, and the decreasing amplitude decreases with the increase of cycle number. KCl solution infiltration can cause bentonite mineral phase transition, swelling force decreased significantly; when the concentration of KCl solution reaches a certain value, the dissolution of montmorillonite led to the loss of swelling ability of bentonite.