Effect of heavy metals on dechlorination of carbon tetrachloride by iron nanoparticles

Effects of heavy metals on the dechlorination of carbon tetrachloride by iron nanoparticles were investigated in terms of reaction kinetics and product distribution using batch systems. Removal of heavy metals and the interaction between heavy metals and iron nanoparticles at the iron surface were also examined. It was found that Cu(II) enhanced the carbon tetrachloride dechlorination by iron nanoparticles and led to produce more benign products (i.e., CH4). Pb(II) may increase reduction rate slightly but also increase the production of more toxic intermediates such as dichloromethane. In comparison to the iron reduction system without heavy metals, effects of As(V) were negligible while Cr(VI) decreased the dechlorination rate by a factor of 2. Removal of As(V) by iron nanoparticles behaved pseudo-first-order reaction kinetics but a fast initial removal followed by a slow subsequent process was found in the cases of Cu(II) and Pb(II). Scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis indicated the deposition of heavy metals onto the iron surface. X-ray diffraction (XRD) analysis showed Cu(II) was reduced to metallic copper and cuprite (Cu2O) at the iron surface while no reduced lead species was observed from the Pb(II)-treated iron nanoparticles. Limited data suggested an oxidized lead species formed. The enhanced dechlorination by Cu(II) can be attributed to the deposition of metallic copper and cuprite at the iron surface. This study suggests that implementation of iron nanoparticles rather than engineered bimetallic iron nanoparticles for remediation of mixed contamination with both chlorinated organics and heavy metals is sufficient.