Comparison of hematite/Fe(II) systems with cement/Fe(II) systems in reductively dechlorinating trichloroethylene.
Reactive reductants of cement/Fe(II) systems in dechlorinating chlorinated hydrocarbons are unknown. This study initially evaluated reactivities of potential reactive agents of cement/Fe(II) systems such as hematite (alpha-Fe(2)O(3)), goethite (alpha-FeOOH), lepidocrocite (gamma-FeOOH), akaganeite (beta-FeOOH), ettringite (Ca(6)Al(2)(SO(4))(3)(OH)(12)), Friedel's salt (Ca(4)Al(2)Cl(2)(OH)(12)), and hydrocalumite (Ca(2)Al(OH)(6)(OH).3H(2)O) in reductively dechlorinating trichloroethylene (TCE) in the presence of Fe(II). It was found that a hematite/Fe(II) system shows TCE degradation characteristics similar to those of cement/Fe(II) systems in terms of degradation kinetics, Fe(II) dose dependence, and final products distribution. It was therefore suspected that Fe(III)-containing phases of cement hydrates in cement/Fe(II) systems behaved similarly to the hematite. CaO, which was initially introduced as a pH buffer, was observed to participate in or catalyze the formation of reactive reductants in the hematite/Fe(II) system, because its addition enhanced the reactivities of hematite/Fe(II) systems. From the SEM (scanning electron microscope) and XRD (X-ray diffraction) analyses that were carried out on the solids from hematite/Fe(II) suspensions, it was discovered that a sulfate green rust with a hexagonal-plate structure was probably a reactive reductant for TCE. However, SEM analyses conducted on a cement/Fe(II) system showed that hexagonal-plate crystals, which were presumed to be sulfate green rusts, were much less abundant in the cement/Fe(II) than in the hematite/Fe(II) systems. It was not possible to identify any crystalline minerals in the cement/Fe(II) system by using XRD analysis, probably because of the complexity of the cement hydrates. These observations suggest that major reactive reductants of cement/Fe(II) systems may differ from those of hematite/Fe(II) systems.
Kim
Hong-Seok
HS
School of Civil and Environmental Engineering, Pusan National University, 30 Jangjeon-Dong, Geumjeong-Gu, Busan 609-735, Republic of Korea.
Kang
Wan-Hyup
WH
Kim
Meejeong
M
Park
Joo-Yang
JY
Hwang
Inseong
I
D003252:Construction Materials; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry; D058085:Iron Compounds / Q000737:chemistry; D007700:Kinetics; D008855:Microscopy, Electron, Scanning; D008903:Minerals; D010084:Oxidation-Reduction; D014241:Trichloroethylene / Q000737:chemistry*; D014961:X-Ray Diffraction
D005290:Ferric Compounds; D005296:Ferrous Compounds; D058085:Iron Compounds; D008903:Minerals; C094886:goethite; C000499:ferric oxide; D014241:Trichloroethylene