Effect of Non-aqueous Phase Liquid (NAPL) on Heavy Metal Adsorption by Nanoscale Zero-valent Iron (nZVI)

Soil-water resources co-contaminated with multiple pollutants may undergo various chemical interactions under prevailing conditions. Remediating such systems requires a detailed understanding of the existing pollutants and their complex associations as conventional methods often target a single pollutant type. Nano-zero valent iron (nZVI) particulates effectively remove heavy metals from water through the process of adsorption. However, the efficiency of adsorption may vary under co-contamination by other substances. In this study, the impact of a common non-aqueous phase liquid (toluene) on chromium (VI) adsorption efficiency by nZVI was investigated using a series of microcosm experiments. The results showed a reduction in the adsorption under toluene co-presence by almost 20%. The experiments were further performed to understand the impact of contact time, initial pH, and Cr (VI) concentration on the adsorption efficiency. The results obtained for the Cr (VI) reaction mixtures without toluenes presence show that pH had a significant impact on Cr (VI) adsorption (highest adsorption at pH 3), where the efficiency decreased with increased pH. When toluene was co-present, all pH ranges offered similar trends while the overall adsorption rates were reduced. With an increase in the initial concentration of Cr (VI), adsorption efficiency decreased, while it increased in the presence of toluene. With these results, this study presented interesting findings by understanding the challenges of remediating co-contaminated soil-water resources.