Environmental Remediation of Chlorinated Hydrocarbons Using Biopolymer Stabilized Iron Loaded Halloysite Nanotubes

Dense nonaqueous phase chlorinated compounds such as trichloroethylene (TCE) and tetrachloroethylene (PCE) are widespread groundwater and soil contaminants which cause long-term environmental pollution. Extensive efforts have been carried out to develop materials for in situ remediation particularly using nanoscale zerovalent iron (NZVI) to reduce TCE to relatively innocuous products such as ethane and ethylene. A novel technology is described here that uses earth-abundant natural tubular aluminosilicate clays known as halloysite (HNT) to support NZVI. These systems are efficient at the reductive dechlorination of such chlorinated hydrocarbons indicating a pseudo-first order rate constant of 0.1 L g^–1 h^–1 with NZVI particle size between 5 and 10 nm. The adsorption of the naturally derived polyelectrolytes chitosan and carboxymethyl cellulose on the surface of HNT provides easy dispersibility in aqueous solutions and colloidal stability to the NZVI supported on HNT, with chitosan adsorption leading to stability over a period of 60 h. Observations of transport through packed capillaries using optical microscopy indicate that these biopolymer-stabilized composites transport efficiently through porous media at flow rates representative of groundwater flow. Such efficient transport is attributed to the tubular morphology with the particles aligning along flow streamlines. Calculations of the sticking coefficient indicate values as low as 0.1 indicating low attachment to sediment. Such composite materials using sustainable biopolymers and earth abundant clay minerals have potential in the groundwater remediation of chlorinated ethenes.