Natural Colloids in Groundwater from a Bentonite Mine- Correlation between Colloid Generation and Groundwater Chemistry -

Abstract

ABSTRACTColloids, mainly montmorillonite, generated by erosion of compacted bentonite by groundwater flow might enhance the transport of radionuclides from a radioactive waste repository. The influence of aqueous chemistry (i.e. pH, cation concentration and valence) on the dispersion of montmorillonite colloid was studied. Colloids were flocculated under higher cation concentrations ([Na+] > 10−2 M, [Ca2+] > 10−3 M) and/or under acidic condition (pH = 4) by means of batch-type experiments. Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was applied to estimate the stability of colloidal dispersion and then the limitation of theoretical calculations was pointed out. Groundwater samples were collected from two galleries at different depths of the Tsukinuno bentonite mine (northern Honshu, Japan) and investigated for the populations of colloids. The groundwater flows vertically through Tertiary sedimentary argillaceous rocks and fine tuff beds which are mined for bentonite. Low colloid concentrations were measured in these groundwater samples. This result suggests that the colloids cannot significantly disperse in the groundwaters under higher cation concentration ([Na+] > 10−2 M) or under acidic conditions. This result is consistent with those of the batch-type experiments.