Organo-Illite as a Low Permeability Sorbent to Retard Migration of Anionic Contaminants

Landfill leachate, often having high concentrations of metal cations, anions, and organic compounds, presents a great threat to nearby groundwater. Due to negative charges on soil particles, regular clay liners cannot effectively retard the movement of anionic contaminants such as chromate. In this paper, a natural illite was modified by cationic surfactants with different chain lengths and tested for its chromate removal efficiency. When the surfactant tail group is relatively short and the solution critical micelle concentration is high, the sorbed surfactant molecules form a monolayer on illite, resulting no chromate sorption by the organo-illite. As the chain length of surfactant tail group increases, the critical micelle concentration reduces and the surfactant molecules sorb as admicelles on illite with the surfactant sorption exceeding the illite’s cation-exchange capacity. Such admicelle modification makes the organoclay capable of retaining chromate instantaneously and retarding the movement of chromate by 1–2 orders of magnitude. The illite’s hydraulic conductivity showed a slight increase after surfactant modification, from $1\times {10}^{-7}$ to $8\times {10}^{-7} \mathrm{cm}/s\text{,}$ probably due to reduced packing density after modification. Chromate breakthrough data from column transport experiments were well described by a one-dimensional advection-dispersion model that incorporated Langmuir sorption.