Hydrobiotite (HBT) obtained from Sigma-Aldrich was used as the clay substrate after being ground in a milling machine and sieved through a 20 μm mesh. Other clay minerals, including illite (Yong Koong illite Co., Korea), kaolinite (Sigma-Aldrich) and montmorillonite (Clay Minerals Repository, USA), were used for comparison. A soil sample was collected near the site of the Korea Atomic Energy Research Institute (KAERI), Daejeon, Korea, and was used after being sieved to a size of less than 2 mm and then dried at room temperature for one week.
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