Cosolvent Effects on Dechlorination of Soil-Sorbed Polychlorinated Biphenyls Using Bentonite Clay-Templated Nanoscale Zero Valent Iron.

Zero-valent iron synthesized using bentonite clay as a template (CZVI) was tested for its reactivity toward polychlorinated biphenyl (PCB) dechlorination in soil slurries. Aqueous-phase decachlorobiphenyl (PCB209) was rapidly dechlorinated by CZVI with a reaction rate 10 times greater than that by conventional nanoscale zerovalent iron. This superior reactivity was due largely to the nanoscale size (∼0.5 nm) of the ZVI particles located in the clay galleries. In soil slurries where PCB209 was strongly soil-bound, adding ethanol as an organic cosolvent led to increased PCB209 desorption into the liquid phase, thereby enhancing the PCB209 dechlorination with CZVI. The more effective PCB209 dechlorination in such a cosolvent system also promoted the subsequent stepwise dechlorinative process, leading to a relatively more removal of chlorine in the product mixture. The dechlorination became more rapid as the ethanol fraction increased from 10% to 50%, due apparently to the increasingly greater PCB209 desorption and thus facilitated contact with CZVI. Further increase in ethanol fraction above 50% led to an insignificant enhancement in degradation rate, due partially to attenuated contact of PCB209 with CZVI and reduced proton source from limited water content in the liquid. It is suggested that addition of organic cosolvents may make CZVI potentially useful for remediation of soils containing halogenated organic contaminants.