Influence of Variable Membrane Behavior of Clay on Solute Transport

Abstract

It is well established that clays can exhibit semipermeable membrane behavior and osmotic efficiency is used to describe the membrane behavior of clays. Several experimental results have already verified that osmotic efficiency is not constant when pore-fluid chemistry changes. In this article, based on the mechanical balance, generalized Darcy's law and the principle of mass conservation, an improved fully coupled hydro-chemo-mechanical model is proposed for saturated clayey materials, in which osmotic efficiency is treated as a variable that depends on the solute concentration, grain density, porosity of soil, and cation exchange capacity. Numerical simulations are conducted to investigate the influence of variable osmotic efficiency on solute transport. The results show that solute transport is very sensitive to osmotic efficiency and when the transport time is 10 years, the difference in influence depth reaches about 13.6 cm with constant (0.069) and variable (initially 0.069) osmotic efficiencies, this indicates that semipermeable membrane behavior of clays with variable osmotic efficiency restricts the solute transport effectively and slows down the solute movement strongly. The difference in breakthrough time reaches 15.8 years with osmotic efficiency (0.069). The proposed coupled model can be used to guide the design of clay liners and evaluate their service performance.