Nickel Retention on Callovo-Oxfordian Clay: Applicability of Existing Adsorption Models for Dilute Systems to Real Compact Rock

Abstract

In a waste management context, predicting the mobility of contaminants is essential. A key issue entails assessing the applicability of current knowledge on adsorption processes to natural systems. Such is the focus herein for nickel in interaction with Callovo-Oxfordian (COx) clay rock, a formation selected in France for possible radioactive waste disposal. The challenge is to link predictive modeling results with the experimental data characterizing the behavior of the labile and naturally occurring Ni fraction by implementing a new simple method. Retention studies on compact systems serve to complete this work. Combined electron microprobe and laser ablation high-resolution inductively coupled plasma mass spectrometry data show that natural Ni (∼39 mg kg–1) is homogeneously distributed within the clay matrix, which corresponds to the main reservoir (∼70%). Data interpretation of desorption tests yields an in situ K d value of ∼80 L kg–1 and a labile Ni amount of ∼5 mg kg–1, that is, ∼13% of the Ni inventory. Predictive modeling explains the sorption data in considering that only weak clay fraction sites take part in the adsorption. The role of the clay matrix in Ni retention is confirmed by analyzing the Ni-spiked compact COx samples, whereby an increase of the Ni content in the clay fraction is observed following the retention experiment.

Remarkable damage in talc caused by electron beam irradiation with a dose of up to 1000 kGy: lattice shrinkage in the Z- and Y-axis and corresponding intrinsic microstructural transformation process speculation

“…This notion has been veried adequately, as exfoliation, intercalation and ion-exchange mainly occurring in this direction. [13][14][15][16][17][18][19][20][21][22][23][24][25][26] These descriptions probably explain the observed discrepancy. Normally, discrepancy can be amplied by factor elevation; thus, the ratio seems to increase greatly.…”

Investigation of europium retention on Callovo-Oxfordian clay rock (France) by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and percolation experiments in microcells

“…If we come back to our percolation experiences, a non-transient state can be obtained for Cs/COx (Chen et al, 2014b) or Ni/COx (Montavon et al, 2020) systems. For the case of Eu, which is a strongly retained element, this condition is more complicated to achieve.…”

“…Naturally highly compact samples were used (bulk density of ~2.3 g cm -3 ). The sample preparation methodology was adapted from Montavon et al (2020Montavon et al ( , 2014. First, a 1-cm diameter piece (several centimeters long) was manufactured through core drilling; next, a lathe (Caseneuve HB55) was used to obtain a diameter of 4.99 ± 0.02 mm.…”

“…This approach appears to be feasible for highly compact states with poorly or moderately retained radionuclides. A few number of studies can be found in the literature for: I - (Montavon et al, 2014), Cs + (André et al, 2009;Chen et al, 2014b;Oscarson, 1994;Van Loon et al, 2009), Ni 2+ (Montavon et al, 2020), and Sr 2+ (Van Loon et al, 2005).…”

“…The objective of this work is to propose a non-transient method adapted to the retention study of strongly sorbed elements on compact clay rock samples. It combines the use of pressurized PEEK (Polyetheretherketone) micro cells, thereby limiting adsorption phenomena (Aertsens et al, 2003) and accommodating submillimeter-thick samples, with a percolation mode to accelerate transport so as to overcome the disadvantages of a long experimental duration by using diffusion cells (Montavon et al, 2020 ;Chen et al, 2014b). After the experiment, the strongly sorbed element is analyzed quantitatively on the (inlet) surface and in depth of the compact sample by means of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS).…”