Degradation of chlorinated aliphatic compounds by fenton reaction in pyrite suspension system

Abstract

Degradation of trichloroethylene (TCE) and carbon tetrachloride (CT) by Fenton reaction in pyrite suspension was investigated in a closed batch system under various experimental conditions. TCE was oxidatively degraded by OH $\bull$ in the pyrite Fenton system and its degradation kinetics was significantly enhanced by the catalysis of pyrite to form OH $\bull$ by decomposing $H_2O_2$. In contrast to an ordinary classic Fenton reaction showing a second-order kinetics, the oxidative degradation of TCE by the pyrite Fenton reaction was properly fitted by a pseudo-first-order rate law. Degradation kinetics of TCE in the pyrite Fenton reaction was significantly influenced by concentrations of pyrite and $H_2O_2$, and initial suspension pH. Kinetic rate constant of TCE increased proportionally ($0.0030\plusmm0.0001$ to $0.1910\plusmm0.0078min^{-1}$) as the pyrite concentration increased 0.21 to 12.82 g/L. TCE removal was more than 97%, once $H_2O_2$ addition exceeded 125 mM at initial pH 3. The kinetic rate constant also increased (0.0160 $\plusmm$ 0.005 to 0.0516 $\plusmm$ 0.0029 $min^{-1}$) as $H_2O_2$ concentration increased 21 to 251 mM, however its increase showed a saturation pattern. The kinetic rate constant decreased (0.0516 $\plusmm$ 0.0029 to 0.0079 $\plusmm$ 0.0021 $min^{-1}$) as initial suspension pH increased 3 to 11. We did not observe any significant effect of TCE concentration on the degradation kinetics of TCE in the pyrite Fenton reaction as TCE concentration increased. Slight enhancement of CT degradation was observed with 2-propanol (rate constant from 0.0396 $min^{-1}$ to 0.0650 $min^{-1}$, removal efficiency from 85.1% to 90.4%), while the degradation of TCE was significantly inhibited with 2-propanol (rate constant from 0.0495 $min^{-1}$ to 0.0146 $min^{-1}$, removal efficiency from 99.5% to 47.4%).