Diffusive transport of selenium oxyanions in compacted natural clays: role of selenium speciation and clay geochemistry

Predictive subsurface transport of selenium oxyanions is important for the assessment of long-term nuclear waste repository performance, as well as monitoring compliance of selenium presence in groundwater once discharged from industry, agriculture or natural seleniferous minerals. The aim of the present study is to quantify the diffusion of selenite and selenate through water-saturated compacted clays of smectite and illite rich geochemistry. Diffusion coefficient (D_e) values for selenium oxyanions in argillaceous clay are ̴ 10^–12 m²s⁻¹ and are nearly an order of magnitude higher in the bentonite clay. Results indicate the role of clay geochemistry in controlling migration of selenium oxyanions through natural clay.