Experimental study on chemico-osmotic membrane behaviors of reactive MgO-activated slag-bentonite backfill in vertical cutoff walls exposed to Pb-laden groundwater

The reactive magnesia (MgO) is used as an alkali activator to activate granulated blast furnace slag (GGBS) to prepare alkali activated slag-bentonite-soil vertical barrier (MSBS) material. The chemico-osmotic memberane behavior test using lead nitrate Pb(NO₃)₂ solutions with different concentrations as testing liquids is conducted on the MSBS specimen, and the effects of Pb(NO₃)₂ concentration on the Pb²⁺ containment performance including chemico-osmotic efficiency coefficient, effective diffusion coefficient and retardation factor are evaluated. Comparative assessment of performance is made between the MSBS material in this study and other engineered barrier materials including soil-bentonite (SB) vertical cutoff wall backfill and geosynthetic clay liner (GCL) reported in previously published studies. The results show that the MSBS backfill has noticeable chemical-osmotic membrane behavior, and the chemico-osmotic efficiency coefficient decreases rapidly with the increasing Pb²⁺ concentration. The effective diffusion coefficient of Pb²⁺in the MSBS increases slightly with the increasing Pb²⁺concentration, and its change magnitude is significantly lower than that for the SB backfill materials. The retardation factor for Pb²⁺ in the MSBS backfill remains practically constant with the increasing Pb²⁺concentration, whereas it decreases significantly with the increasing Pb²⁺ concentration for the SB backfill materials.