288
B. Gunawardana et al.
phases and (2) greater desorption and extraction efficiency of such lower degree CP
degradation products (2,4,6-TCP and 2,4-DCP) and higher mass balance.
Nonetheless, the exact reasons for the variations observed in the formation/accumulation of different oxide phases during the reaction of Ni/Fe with various
CPs of different degree of chlorination (i.e. PCP, 2,3,4,6-TeCP, 2,4,6-TCP, and 2,4DCP) could not be explained by the findings of the present study. Therefore, specific
studies need to be conducted to understand the behaviour and surface chemistry of
ZVI and Ni/Fe bimetallic reactions when reacting with the CPs with different degree
of chlorination.
12.3.3 Accumulation of Hydrogen Gas in Batch Reactors
Hydrogen gas accumulated in batch reactors was measured at each sampling time.
The data of hydrogen gas formed during the reaction of the four CPs (PCP, 2,3,4,6TeCP, 2,4,6-TCP, and 2,4-DCP) with Ni/Fe bimetal is presented in Fig. 12.6a. The
hydrogen gas formation was observed with all the treatments, although the total
hydrogen pressure remained <0.5 atm even after 25 days of reaction.
In a Ni/Fe bimetal system, Ni can perform as a catalyst to enhance the formation
of atomic hydrogen or a metal hydride phase on the iron surface. Hence, Ni can
potentially enhance the CP degradation via hydrodechlorination (Ko et al. 2007;
Tian et al. 2009). Also, the catalytic activity of Ni is known to enhance the H 2
gas production as a result of enhanced ZVI corrosion and encourage H 2 to react as
a reductant (Feng and Lim 2005; Matheson and Tratnyek 1994). However, in this
study, low hydrogen gas accumulation (Fig. 12.6a) and partial CP dechlorination were
observed (Fig. 12.1). The lower hydrogen gas formation with Ni/Fe is indicative
of (1) lower reactivity of Ni/Fe, (2) inhibition of production of H 2 gas due to the
deposition of Ni possibly as a thin layer concealing the reactive sites on the ZVI
Fig. 12.6 a Hydrogen gas accumulated in the batch reactors b variation in solution pH for 25 days
reaction of CPs with Ni/Fe. Error bars represent ± one standard deviation
B. Gunawardana et al.
phases and (2) greater desorption and extraction efficiency of such lower degree CP
degradation products (2,4,6-TCP and 2,4-DCP) and higher mass balance.
Nonetheless, the exact reasons for the variations observed in the formation/accumulation of different oxide phases during the reaction of Ni/Fe with various
CPs of different degree of chlorination (i.e. PCP, 2,3,4,6-TeCP, 2,4,6-TCP, and 2,4DCP) could not be explained by the findings of the present study. Therefore, specific
studies need to be conducted to understand the behaviour and surface chemistry of
ZVI and Ni/Fe bimetallic reactions when reacting with the CPs with different degree
of chlorination.
12.3.3 Accumulation of Hydrogen Gas in Batch Reactors
Hydrogen gas accumulated in batch reactors was measured at each sampling time.
The data of hydrogen gas formed during the reaction of the four CPs (PCP, 2,3,4,6TeCP, 2,4,6-TCP, and 2,4-DCP) with Ni/Fe bimetal is presented in Fig. 12.6a. The
hydrogen gas formation was observed with all the treatments, although the total
hydrogen pressure remained <0.5 atm even after 25 days of reaction.
In a Ni/Fe bimetal system, Ni can perform as a catalyst to enhance the formation
of atomic hydrogen or a metal hydride phase on the iron surface. Hence, Ni can
potentially enhance the CP degradation via hydrodechlorination (Ko et al. 2007;
Tian et al. 2009). Also, the catalytic activity of Ni is known to enhance the H 2
gas production as a result of enhanced ZVI corrosion and encourage H 2 to react as
a reductant (Feng and Lim 2005; Matheson and Tratnyek 1994). However, in this
study, low hydrogen gas accumulation (Fig. 12.6a) and partial CP dechlorination were
observed (Fig. 12.1). The lower hydrogen gas formation with Ni/Fe is indicative
of (1) lower reactivity of Ni/Fe, (2) inhibition of production of H 2 gas due to the
deposition of Ni possibly as a thin layer concealing the reactive sites on the ZVI
Fig. 12.6 a Hydrogen gas accumulated in the batch reactors b variation in solution pH for 25 days
reaction of CPs with Ni/Fe. Error bars represent ± one standard deviation