Trichloroethylene Transformation by Natural Mineral Pyrite: The Deciding Role of Oxygen

Abstract

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.

Role of hydrogen peroxide and hydroxyl radical in pyrite oxidation by molecular oxygen

“…This is consistent with the lack of adenine decomposition (Fig. 5d) and TCE decomposition (Pham et al, 2008) in pyrite slurries with ferric iron as the sole oxidant.…”

“…In addition, the adenine experiments indicate that ROS are not formed if ferric iron is the sole electron acceptor. This notion is corroborated by a study of the oxidative decomposition of TCE in the presence of pyrite (Pham et al, 2008). This reaction only goes forward if molecular oxygen is the oxidant.…”

Degradation of trichloroethylene by Fenton reaction in pyrite suspension

“…Estimated kinetic rate constant for the degradation of TCE in the pyrite Fenton system was 0.0417 ± 0.0028 min −1 . Surface area normalized rate constant calculated by dividing the estimated kinetic rate constant by measured surface area of pyrite (1.2 m 2 /g) was 0.0162 ± 0.0011 L m −2 min −1 , which was 1500 times greater than that for the degradation of TCE in aerobic pyrite suspension without H 2 O 2 [21]. The recoveries of TCE in all control samples were more than 97% at 300 min, which indicates that TCE losses by volatilization in a batch reactor, sorption on the surfaces of pyrite and reactor wall, and oxidation with hydrogen peroxide were not significant during the oxidative degradation of TCE.…”

“…The degradation kinetics of 2,4,6-TNT in the Fenton reaction with pyrite was faster than that with other iron-bearing soil minerals (ferrihydrite, hematite, goethite, lepidocrocite, and magnetite), which is due to the oxidation state of iron on the pyrite surface and its dissolution rate of Fe(II) [19]. Recently, moderate oxidative degradation of TCE in aerobic pyrite suspension has been reported and its reaction kinetics and mechanism with O 2 has been identified [21]. Pyrite has been known to be a potential and promising heterogeneous iron source for the modified Fenton reaction to treat a variety of environmental contaminants in wastewater and groundwater systems.…”

Impact of iron sulfide transformation on trichloroethylene degradation

“…Due in part to the limitations of biotic processes, abiotic reductive dechlorination has attracted considerable attention in recent years (e.g., Sivavec and Horney, 1997;Butler and Hayes, 1999;Lee and Batchelor, 2002;Elsner et al, 2004a,b;. Abiotic transformation of carbon tetrachloride (CT), trichloroethane (TCA), trichloroethylene (TCE), and tetrachloroethylene (PCE) by iron sulfides has been investigated using pyrite, troilite, and mackinawite Hayes, 1999, 2001;Lee and Batchelor, 2002;Gander et al, 2002;Hansson et al, 2008;Pham et al, 2008;Choi et al, 2009). There are also a few field related studies providing evidence that iron sulfides and abiotic degradation have important contributions to the degradation of chlorinated solvents in natural and engineered systems (Devlin and Mü ller, 1999;Davis et al, 2003;Kenneke and Weber, 2003;Lookman et al, 2005;Kennedy et al, 2006a,b;Shen and Wilson, 2007;Darlington et al, 2008).…”