Perturbation induced by EDTA on HDO, Br- and EuIII diffusion in a large-scale clay rock sample

• A large-scale clay rock sample was perturbed by a 10 mM EDTA plume for 450 days.
• Dissolution of carbonates (fast) and iron-rich phases (slow) was monitored.
• Perturbation modified speciation equilibrium but had a limited effect on transport.
• Transport parameters of HDO, Br, EDTA, Eu, including anisotropy were quantified.
• EDTA and Eu-EDTA complexes displayed a strong desorption hysteresis.

Clay rocks are widely studied in the context of waste landfill leachates or as geological barriers for nuclear waste management. The release of organic co-contaminants by wastes may alter clay rocks, depending on the ratio between the volume of wastes and the mass of rock. In this work, a 10 mM EDTA plume was injected in a large-scale clay rock sample with a low V/m ratio (<< 1.0 L kg- 1) close to environmental conditions. The chemical perturbation was monitored for 450 days, as well as its effect on HDO, Br-, and EuIII diffusion. Alteration of carbonates and iron-rich phases was evidenced in addition to the decrease of tracer concentration. Negatively charged complexes of EDTA and Eu are slightly adsorbed on minerals surface and display a desorption hysteresis. Transport parameters including diffusion anisotropy of HDO, Br, and EDTA complexes are estimated. Results are discussed with emphasis on determination of the mechanisms governing such a perturbation and the corresponding transitory state.

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