Dechlorination of carbon tetrachloride by ferrous ion associated with iron oxide nano particles

Abstract

Dechlorination o f carbon tetrachloride (CT) by Fe(II) ion in suspensions o f crystalline iron oxide minerals including goethite (a-FeOOH), hematite (a-Fe2 0 j), magnetite (Fe^O4), and amorphous ferrihydrite (Fe(OH)s) in Fe(II) ion solution was investigated. Experiments were performed in sealed vials using 10 mM iron oxides and 3 mM Fe(II) to form surface-bound Fe(ll)- iron mineral complexes in the suspension at pH 7.2 under anoxic condition. To understand the effect o f Cu(II) for the dechlorination by Fe(II) associated with iron minerals, 0.5 mM Cu(II) was added to certain batches o f mixtures. Dechlorination followed pseudo first-order kinetics. The rate constants (k0bs) were 0.380 h' 1 and 0.836 h' 1 in goethite and hematite suspensions, respectively. Whereas the k0t>s was 0.061 h' 1 for magnetite and 0.014 h' 1 for ferrihydrite, which were lower than those in the highly crystalline Fe (III) oxide suspensions. The major product o f CT dechlorination was chloroform (CF,) and the ratio o f CT conversion to CF was within the range o f 14 - 57 % during 2.8 h o f incubation, depending on the type o f iron oxides. The rate and efficiency o f dechlorination also depend on the concentration o f Fe(II) and a linear relationship between surface concentration and k0t,s was established. The pH o f the surface-bound Fe (II) system strongly influenced the rate and efficiency o f dechlorination and both k0t,s and sorbed Fe(II) concentrations exponentially increased with the increase in pH within the range o f 4 - 8.5 showing that the increase in k0bs with the increase in pH is mainly attributed to the increase in the surface-bound Fe(II) concentration. Dechlorination o f CT was significantly enhanced by the addition o f 0.5 mM Cu(II) into the suspension o f iron oxide mineral mixed with Fe(II). The k0bs values for CT dechlorination were 119, 100, 30 and 3 times greater than those in the absence o f Cu(II) in the magnetite, goethite, hematite and ferrihydrite suspensions, respectively. Previously we have reported that CF also could be dechlorinated in the Cu(II)-amended iron, which was not observed without Cu(II) addition, indicating that the addition o f Cu(II) into Fe(II)/Fe(III) systems enhances the dechlorination efficiency o f highly chlorinated compounds (Maithreepala and Doong 2004). This method can be used to make environmentally benign compounds from highly chlorinated organic compounds.