Effects of transition metal and sulfide on the reductive dechlorination of carbon tetrachloride and 1,1,1-trichloroethane by FeS

Reductive dechlorination of carbon tetrachloride (CT) and 1,1,1-trichloroethane (1,1,1-TCA) by FeS with transition metals (Cu(II), Co(II), and Ni(II)) and hydrosulfide was characterized in this study. The batch kinetic experiments were conducted by spiking each stock solution of CT and 1,1,1-TCA into 33 g/L of FeS suspensions with and without transition metals at pH 7.5. No significant enhancement was observed in the reductive dechlorination of target compounds by FeS with 1 mM transition metals. However, except the addition of Cu(II), the reduction rate of 1,1,1-TCA increased with increasing the concentration of transition metals. The rate constants with 10 mM Co(II) and Ni(II) were 0.06 and 0.11 h−1, approximately 1.3 and 3.0 times greater than those by FeS alone. The addition of 20 mM HS− also increased the rate constants of 1,1,1-TCA by FeS by one order of magnitude. SEM analysis showed that the addition of transition metal (Ni(II)) and HS− caused a noticeable morphologic change of FeS surface. The transition metal added was substituted by the structural iron resulting in the decrease of iron content of FeS (52.6-46.9%). One third of the transition metal in FeS suspension existed as zero-valent form playing a catalyst role to accelerate the reaction kinetics.