Coupled Transformation of Carbon Tetrachloride and Copper Ion by Nanocrystalline Ferric Oxides and Ferrous Ions

Abstract

The transformation of carbon tetrachloride (CT) and copper ions by Fe(II) ions associated with nanocrystalline iron oxides minerals including hematite (α-Fe2O3) and ferrihydrite (Fe(OH)3) was investigated. Experiments were performed using 10 mM iron oxides and 3 mM Fe(II) to form surface-bound iron suspensions at pH 7.2 under anoxic condition. X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) showed that the particle sizes of synthesized iron oxides were in the range of 30 - 100 nm. In addition, the specific surface areas of nanocrystalline hematite and ferrihydrite were 39.4 and 222 m^2/g, respectively. The sorption of Fe(II) ions onto hematite followed Langmuir sorption equation, while sorption of Fe(II) ions onto ferrihydrite obeyed Freundlich isotherm kinetics, presumably due to the high specific surface area of ferrihydrite. In addition, the sorption of Cu(II) ion onto iron oxides also followed Langmuir isotherm. The dechlorination of CT by surface-bound iron species followed pseudo first-order kinetics. The rate constants (kobs) for CT dechlorination were 0.0836 and 0.0609 h^(-1) in hematite and ferrihydrite suspensions, respectively. The produced chloroform ranged 7.3-13 μM, depicting that reductive dechlorination is the major pathway for CT dechlorination in surface-bound iron system. Addition of 0.5 mM Cu(II) greatly enhance the dechlorination efficiency and rate of CT. The kobs for CT dechlorination were 3 and 30 times greater than those in the absence of Cu(II) in the ferrihydrite and hematite systems, respectively. These results show that the Cu(II) plays a positive role in enhancing the dechlorination efficiency and rate of CT by Fe(II) associated with nanocrystalline iron oxides.