Mudstones as Landfill Liner Material for Heavy Metal Removal: Equilibrium and Dynamic Sorption Study

Abstract

Clay materials used as low-permeability barriers at landfill sites can also chemically attenuate inorganic contaminants (heavy metals) in leachate. In this study, Cu(II) removal capacity from aqueous media of a raw calcareous mudstone, used as a liner material, was evaluated through both batch and column tests. Batch experiments were conducted varying contact time, pH, and Cu(II) concentration. In order to simulate waste leachates composition, the effect of the presence of some organic compounds on Cu(II) uptake was also evaluated. Column tests of compacted calcareous mudstone-sand mixtures were performed to evaluate sorption in dynamic systems. The studied calcareous mudstone exhibited higher removal capacity in a wider pH range than a commercial Na-bentonite, which is a widely used heavy metal sorbent and clay liner. It was evidenced that calcite, an important component of the calcareous mudstone and found as very small and highly porous calcareous nannofossils, contributed to its sorption properties playing a significant role in the Cu(II) removal. The presence of an anionic surfactant or phenol slightly affected the removal of Cu(II). In the clay fraction (< 2 µm), Cu(II) sorption was favored by the presence of humic acids, which add new adsorption sites for this metal. The extremely high retardation factor obtained for the raw calcareous mudstone is in good agreement with the high adsorption capacity experimentally proved in batch tests and demonstrated a great ability of this material to retain heavy metal mass during the transport in solution within porous media.