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The pathways and kinetics of trichloroethylene (TCE) degradation in aerobic pyrite suspension were investigated. The detection of hydroxyl radical in aqueous pyrite suspension suggested that TCE was degraded by this strong oxidant The reaction pathways of TCE degradation were proposed in which the degradation of TCE to formic acid and finally to CO2 was the main route. Degradation of TCE to oxalic acid and to dichloroacetic acid were found as minor pathways. Degradation rates of TCE to formic acid, glyoxylic acid, and dichloroacetic acid were obtained using kinetic model at 1.2 x 10(-2), 9.8 x 10(-4) and 4.6 x 10(-4) h(-1), respectively.

The transformation of trichloroethylene (TCE) in natural mineral iron disulfide (pyrite) aqueous suspension under different oxygen conditions was investigated in laboratory batch experiments. TCE transformation was pursued by monitoring its disappearance and products released with time. The effect of oxygen was studied by varying the initial dissolved oxygen concentration (DO(i)) inside each reactor. Transformation rates depended strongly on DO(i) in the system. In anaerobic pyrite suspension, TCE did not transform as it did under aerobic conditions. The transformation rate increased with an increase in DO(i). The TCE transformation kinetics was fitted to a pseudo-first-order reaction with a rate constant k (h(-1)) varying from 0.004 to 0.013 for closed systems with DO(i) varying from 0.017 to 0.268 mmol/L under the experimental conditions. In the aerobic systems, TCE transformed to several organic acids including dichloroacetic acid, glyoxylic acid, oxalic acid, formic acid, and finally to CO2 and chloride ion. Dichloroacetic acid was the only chlorinated intermediate found. Both TCE and the pyrite surface were oxidized in the presence of O2. Oxygen consumption profiles showed O2 was the common oxidant in both TCE and pyrite oxidation reactions. Ferric ion cannot be used as an alternative oxidant to oxygen for TCE transformation.

An acidophilic heterotrophic bacterium, designated as HIB4, having the ability to oxidize ferrous ion was newly isolated from a sample of an enrichment culture for iron-oxidizing bacteria, using the modified washed agarose/yeast extract (WAYE) medium with ferrous sulphate. The isolate HIB4 was an acidophilic, heterotrophic, mesophilic and gram-positive bacterium. Phylogenetically, it was classified under the genus Alicyclobacillus and was the closest to Alicyclobacillus disulfidooxidans SD-11 with 99.7% 16S rDNA homology. It grew and oxidized ferrous ion in the medium containing 0.02% (w/v) yeast extract. Yeast extract was an essential substrate for this bacterium because it could not grow or oxidize ferrous ion without yeast extract. However, a higher concentration of yeast extract inhibited the growth of HIB4, so that the optimum concentration of yeast extract for this bacterium to grow was 0.02% (w/v) at 0.08 mol/l of ferrous ion. On the other hand, ferrous ion oxidation occurred almost at the end of the bacterium's logarithmic growth phase and the isolate was able to grow without ferrous ion. These results denote that HIB4 did not obtain any energy from the ferrous ion oxidation and that HIB4 is an obligate heterotrophic and aerobic bacterium even though it oxidized ferrous ion. Also, HIB4 could not utilize any organic compounds, among the several organic chemicals used in this study, as a carbon source except yeast extract. These characteristics were completely different from these of A. disulfidooxidans SD-11 so that HIB4 might be a different species.

The dechlorination of trichloroethene (TCE) with metallic iron is an advantageous method for the remediation of contaminated groundwater and soil. The toxic reaction intermediates such as dichloroethenes (DCEs) and vinyl chloride (VC), however, occasionally accumulate in the pathway of the reaction. We have been trying to suppress these intermediates by using metallic iron powder containing impurities. In order to investigate the reaction pathways, we measured the production rates of the intermediates and the final products of the dechlorination of TCE such as DCEs, VC, ethyne or ethene. Ethyne, ethene, ethane and cis-DCE were observed as the major products, and trans-DCE, 1,1-DCE, VC, C3-hydrocarbons (such as propane, propylene), C4-hydrocarbons (such as n-butane) and methane were observed as the minors. Also the rate constants of TCE to ethyne and ethyne to ethene were larger than any other constants. These fact show the production of ethene/ethane via ethyne is the main pathway of the dechlorination of TCE using the metallic iron powder.

Abstract: The copper extraction yield from thermophilic bioleaching of chalcopyrite depends on temperature, pH, and the oxidation-reduction potential (ORP), as well as on the activity of the thermophile used. The copper extraction yields obtained with three thermophiles under various pH and temperature conditions and with different initial amounts of Fe3+ were studied. The results indicated that because of the low ability of Acidianus brierleyi to leach iron as Fe3+, high biomass concentrations were reflected by ORP close to a critical value (450 mV, Ag0/AgCl reference), at which copper extractions were highest. By contrast, because of the higher ability of Sulfolobus metallicus and Metallosphaera sedula to leach iron as Fe3+, high biomass concentrations were reflected by high ORP which in combination with the precipitation of Fe3+ as jarosite attenuated the leaching rates. Therefore, optimum temperatures for the growth of thermophiles did not always mean high copper extraction yields. Generally, highest copper extractions were obtained at initial pH 1.5. However, higher copper extractions were observed at initial pH 2.5 than at pH 2.0, suggesting that at high pH the bioleaching of chalcopyrite is controlled by the ORP rather than by the pH or temperature. The bioleaching capacity of A. brierleyi was reduced or suppressed when insufficient initial Fe3+ was provided to trigger the leaching reaction, whereas S. metallicus and M. sedula were less sensitive to the initial availability of Fe3+. This result confirmed that a direct enzymatic attack on the mineral surface could initiate the leaching reaction, but later ORP governed the leaching rate of chalcopyrite. [Copyright &y& Elsevier]