Study of ⁸⁵ Sr transport through a column filled with crushed granite in the presence of bentonite colloids

Abstract

The present work is focused on the study of strontium transport through crushed granite in the presence of bentonite colloids under dynamic arrangement. The aim of the experiments was to investigate the effect of bentonite colloids on strontium migration in crushed granite. The tracer behaviour was studied in a column set-up under aerobic conditions with a continuous inlet of the liquid phase of a constant tracer concentration (activity) and flow rate. Defined volumes of liquid phase were sampled at periodic time intervals at the column outlet for the measurements of tracer concentrations (activity). The transport was described by breakthrough curves. The stepwise approach included these steps: (1) an evaluation of the hydrodynamic column properties by the non-sorbing tracer 3 H; (2) a column experiment with bentonite colloids in deionized water was performed; (3) migration of 85 Sr solution in two liquid phases (deionized and synthetic granitic water); and (4) the transport of a radiocolloid suspension in deionized water was studied. Results showed different behaviour of bentonite colloids and strontium in the column. Bentonite colloids behaved as a non-sorbing tracer: conversely, strontium showed strong sorption on granitic material. The strontium transport in the presence of bentonite colloids differed from strontium transport itself. The strontium transport in the presence of colloids was faster than transport without the bentonite colloids. The observed retention of strontium on granite suggests a higher affinity of strontium towards granitic rock than towards bentonite colloids, and showed the reversibility of the sorption of strontium on bentonite colloids.

How the Solid/Liquid Ratio Affects the Cation Exchange Process and Porosity in the Case of Dioctahedral Smectite: Structural Analysis?

“…Clays are considered among the best candidates as a depolluting agent, specifically montmorillonite (2 : 1 phyllosilicate groups), which belongs to the smectite family [1][2][3][4]. In addition to their great use in the pharmaceutical and cosmetic fields, smectite is used in the concept of the natural geological barrier for industrial and radioactive waste confinement [5][6][7][8][9][10]. The phyllosilicate structure specificity (layered structure, cation exchange capacity (CEC), permeability, hydration characteristics, specific surface area (SSA), porosity, mechanical resistance, great availability in nature, low-cost materials…) makes it possible to achieve these objectives [11][12][13].…”

Mobility of Radionuclides in Fractured Carbonate Rocks: Lessons from a Field-Scale Transport Experiment

“…Like Ce, geochemical analysis conducted with Visual Minteq suggests that Sr may also precipitate (strontianite; SrCO 3 ) under the conditions of the injection borehole (Figure S2). Strontium is also known to sorb to bentonite, and thus the observed partitioning of Sr may be attributed to a combination of Sr precipitation and Sr association with bentonite. Cesium is not known to form stable complexes with other ligands in solution or to precipitate, and thus the small fraction of Cs measured in the particulate fraction (6%) in the injection borehole can be attributed to sorption to bentonite particles …”

“…Thus, from a purely hydrological standpoint, there is potential for radionuclides to migrate unrestricted through fractured carbonate rock formations. Transport of radionuclides through single fractures has previously been investigated on a laboratory benchtop scale. ,− However, it is difficult to use these studies to predict field-scale processes, as they do not take into account the geochemical, physical, and hydrological heterogeneities of field-scale transport processes that are likely to impact radionuclide transport behavior . The present study investigates the potential mobility of the radionuclide analogs (RAs) Ce, Re, Sr, and Cs through a chalk rock fracture network by use of a forced-gradient field-scale tracer experiment.…”