Roles of alkaline-earth cation species in the swelling pressure of smectites – A computational study

Abstract

Interlayer swelling pressure of smectite minerals was investigated at atomic level using molecular dynamics simulation method. Four different alkaline-earth cations were used as interlayer cations for simulated montmorillonite and beidellite minerals. The swelling pressures of the smectite minerals were obtained as function of interlayer cation, layer charge, charge location, dry density and d-spacing. The swelling pressure of the homoionic smectites follows the trend Mg2+ > Ca2+ > Sr2+ > Ba2+. Layer charge and charge location have also a notable effect on swelling pressure. Octahedrally substituted smectites show higher swelling pressure than tetrahedrally substituted, while lower layer charge lead to higher pressure than higher layer charge. The results have practical implications in the selection and predicted behaviour of backfilling clay materials for geodisposal of high-level radioactive waste.