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 m2/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.
