Sorption of chlorinated hydrocarbons from synthetic and natural groundwater by organo-hydrotalcites: Towards their applications as remediation nanoparticles

Abstract

Chlorinated hydrocarbons (CHCs) are recalcitrant compounds frequently found as contaminants in groundwater. Hydrotalcites (HT) have emerged as promising sorbents due to their tunable properties and anion exchange capacity. Here, two types of organo-HT were synthesized, via coprecipitation, by intercalation of two different anionic surfactants, sodium dodecyl sulfate and sodium 1-dodecane sulfonate. These compounds were first characterized by a suite of techniques to quantify surfactant intercalation and to evaluate their physico-chemical properties. Next, the sorption affinity of these organo-HT towards a suite of CHCs was tested under various conditions, including interlayer surfactant type, single and multiple CHCs systems, and different water chemistry (pH, ionic composition). Sorption coefficients (K_d) and organic-matter-normalized partition coefficient (K_om) derived from linear sorption isotherms for individual CHC were inversely correlated to their hydrophobicity in the order of: tetrachloroethylene > tetrachloromethane > trichloroethylene> 1,1,2-trichloroethane > trichloromethane. K_om values were further affected by the organo-HT drying process. In contrast, varying water chemistry and pH, and the co-existence of multiple CHCs had little effect on K_om values, indicating that competition between CHCs and ionic strength have a marginal effect on the sorption affinity. The inverse linear relationship between CHC hydrophobicity and K_om is shown to be a suitable tool to predict organo-HT's sorption efficiency in complex CHCs contaminated groundwaters. Overall, organo-HT's might be used as potential sorbents for ex situ treatment of CHCs in groundwater.

Keywords: Contaminated groundwater; Layered double hydroxide; Nanomaterials; Organic pollutants; Solvents; Sorption isotherms.