Dissolved and Colloidal Transport of Cesium in Natural Discrete Fractures

Abstract

Transport of cesium (Cs) was investigated in a saturated natural chalk fracture with an average equivalent hydraulic aperture of 129 microm. The results show that Cs (inflow concentration of 0.22 mmol L(-1)) can be transported in its dissolved form and in association with montmorillonite. Humic acid (HA) did not sorb Cs but enhanced colloid-associated Cs transport by 12.5% in terms of breakthrough curve (BTC) recovery. The BTCs clearly showed desorption of Cs from the fracture walls during the artificial rainwater (ARW)-injection period. Cesium transport associated with montmorillonite colloids was significant, with a maximum colloid-associated Cs C/C(0) (outflow-to-inflow concentration ratio) value of 16.6 +/- 1.1% during the tracer (colloids and LiBr)-injection period. However, the relative contribution of colloid-associated Cs transport to total Cs transport was relatively low, amounting to 10.3 +/- 0.7% and 14.5 +/- 0.7% with montmorillonite (500 mg L(-1)) and the montmorillonite-HA (10 mg L(-1)) mixture, respectively. Readsorption of Cs onto the colloids occurred immediately on switching from the tracer suspension to the background solution of ARW. The significant colloid-associated Cs transport, the stripping effect of Cs from colloids, and the slow desorption of Cs from fracture walls reported in this study have important implications for risk assessments of Cs mobility in fractured carbonatic rocks.

Influence of Intrinsic Colloid Formation on Migration of Cerium through Fractured Carbonate Rock

“…The core was technically prepared for use in previous studies. 7 The mineral composition of the core determined by X-ray diffraction is 80% CaCO 3 , 2% quartz, 10% opal-CT, 5% clinoptlolite, and <5% smectite and palygorskite. 7 The core is 38.5 cm long and has a 21 cm diameter.…”

“…7 The mineral composition of the core determined by X-ray diffraction is 80% CaCO 3 , 2% quartz, 10% opal-CT, 5% clinoptlolite, and <5% smectite and palygorskite. 7 The core is 38.5 cm long and has a 21 cm diameter. Inlet and outlet cells installed on either side of the fracture are ~20 mL in volume in order to prevent clogging.…”

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

“… 15 The lower K d reported for crushed chalk is because of the fact that most surface sites available for exchange are those on calcite, which exhibit low sorption potential for Cs. 45 Natural fractures in the subsurface, meanwhile, are often coated with precipitated minerals (e.g., clays), which have greater sorption capacity, and therefore, are expected to yield a greater K d . 45 , 46 Furthermore, uncertainty in fracture aperture estimation impacts the deduced K d , as described in detail in Supporting Information Section 9.…”

Prediction of vertical soil organic carbon profiles using soil properties and environmental tracer data at an untilled site

“…Tang et al (2002) suggest that a relationship between SOC and 137 Cs may only hold in rich organic soils. Some authors suggest that SOC is likely to be transported down the soil profile using colloidal pathways (see Tang and Weisbrod (2010) for a review of this issue). The lack of any relationship between clay content and SOC or tracer concentrations in this study however suggests that this is not a likely transport process at the Young River site rather that it is the activities (bioturbation) of soil flora and fauna are more likely driving these species down the soil column.…”

“…When 137 Cs and 210 Pb isotopes are deposited on the soil surface they are strongly adsorbed onto the clay fraction of soil (Tang and Weisbrod, 2010). The action of wind, water flow and bioturbation then transports the 137 Cs and 210 Pb ex labelled soil particles both laterally and vertically through the soil landscape (Zapata et al, 2002).…”