Abstract:
Fe(II) is one of the most abundant reductants available in subsurface condition. Fe(II) ions are able to reduce
priority pollutants if they are associated with iron mineral surfaces or available as structural Fe(II). Reductive
dechlorination of chlorinated hydrocarbons byFe(II) associated with iron minerals has been studied before
several years for possible use of such systems for natural attenuation of ground water in contaminated sites. The
pH of the system, concentration of surface-bound Fe(II) ions and surface area of iron oxide have been identified
as major controlling factors for the dechlorination reaction rates. However, there is no detailed reports documented
the effect of humic substances on the reactivity of Fe(II)-iron mineral systems although they are ubiquitous in
natural environment. Present study was carried out to study the effect of humic acid (HA) on the reactivity of
Fe(II) associated with goethite (-a-FeOOH) system for the dechlorination of CC14. Since quinone compounds
containin functional groups those are supposed to be active in redox reactions, Anthraquinone 2,6-disulphonic
acid (AQDS) (Cl4H(OsS2Na:) and Lawson (2-hydroxy-1,4-naphthoquinone (Cl(lH(0.,) were also used
representing quinone compounds (QC) instead of HA. Reactors used were 50-ml amber bottles sealed with black
viton caps and aluminum crimps. All the preparations were done in an anaerobic glovebox. Parallel replicates of
experiments were carried out using Goethite (a FeOOH) alone, and equilibrated heterogeneous system of goethite
- aqueous Fe(II) in the absence and presence of reduced form of both HA and QC separately for dechlorination
of CCl, (0.65 M) at 7.1 ± 0.1. The major target compound CCl, and its product were identified and quantified by
GC-MS head space method. Results show that HA and QC could degrade CCl, following T' order reaction
kinetics with the observable rate constant (klilj4) of 0.024d', 0.014d ' ,0.028d 1 and 0.029d ' for AQDS, LQ, reduced
HA and native HA amended systems respectively. Under the same conditions but in the presence of Fe(II) (0.1 mM)
the k(,,„ values were 0.035d"', 0.051d’’,041d' and 0.04d' respectively showing that Fe(II) ions can increase the rate
constant by 1.45, 3.64, 2.92 and 1.42 times making the system more reductive. Dissolved Fe(II) alone could not
dechlorinate CC14. Dechlorination of CC14 occurred with ko|„ of 0.087d', 0.3d’1, 0.46d', 0.38d' and 0.37d1 in the
systems of Goethite-Fe(II) alone, and with AQDS, Lawson HA(reduced) and LIA (native) respectively. This study
clearly shows that HA andQC can significantly increase the reactivity if iron mineral—Fe (I I) system for degradation
of CC14.
