Effect of the structural change of an iron–iron oxide mixture on the decomposition of trichloroethylene

Abstract

The effect of the structure of a mixture of industrially produced iron and iron oxide on the decomposition of trichloroethylene (TCE) was investigated by gas chromatography, scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, X-ray diffractometry, and 57Fe-Mossbauer spectroscopy. The concentration of 10 mg L−1 TCE aqueous solution decreased to 0.41, 0.52, 0.26, and 0.09 mg L−1 when stirred for 7 days with iron–iron oxide mixtures having mass ratios of 2:8, 3:7, 4:6, and 5:5, respectively. The Mossbauer spectra of the mixtures after leaching were composed of two sextets with respective isomer shifts (δ) and internal magnetic fields (H) of 0.29±0.01 mm s−1 and 48.8±0.1 T, and 0.64±0.01 mm s−1 and 45.5±0.1 T, attributed to the Fe3+ species in tetrahedral (Td) and the Fe2+ and Fe3+ mixed species (Fe2.5+) in octahedral (Oh) sites, respectively. Mossbauer spectra of a 3:7 mass ratio iron–iron oxide mixture showed a gradual decrease in the absorption area (A) of zero valent iron (Fe0) from 40.6. to 12.6, 13.2, 3.8 2.8, and 1.0±0.5 % and an increase in A of Fe3O4 from 31.8 to 59.4, 71.4, 93.2, 95.6, and 98.0±0.5 % after leaching with 10 mg L−1 TCE aqueous solution for 1, 2, 3, 7, and 10 days, respectively. Consistent values of the first-order rate constant were calculated as 0.32 day−1 for Fe0 oxidation, 0.34 day−1 for Fe3O4 production, and 0.30 day−1 for TCE decomposition, which indicates that the oxidation of Fe0 was the rate-controlling factor for Fe3O4 production and TCE decomposition. It is concluded from the experimental results that an iron–iron oxide mixture is very effective for the decomposition of TCE.