12 Chlorophenols Dechlorination Water Treatment Using …
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The degradation of CPs using ZVI, other metals or bimetals and a comparison
between CP degradation efficiencies have been studied by previous researchers (Choi
et al. 2008; Kim and Carraway 2000; Ko et al. 2007; Liu et al. 2001; Xu et al. 2012).
Previous studies have concentrated on comparing the reactivity of different metals
or bimetals (with Pd, Ni as the catalyst) for CP degradation. Although these studies
had reported that the ZVI materials used were obtained from different suppliers,
comprehensive studies have not been carried out to identify the potential role of ZVI
surface characteristics (e.g. oxide phases) on the reactivity for CP dechlorination.
Further, PCP sorption using one type of ZVI has been quantified (Kim and Carraway 2000) as well as sorption with bimetals (Ni/Fe, Pd/Fe, Pt/Fe, Cu/Fe, Mg/Ag,
Pd/Mg) (Kim and Carraway 2000; Patel and Suresh 2006; 2007). Nonetheless, there
are no comprehensive studies reported in the literature which uses ZVI-based bimetals to investigate incorporation levels of different CPs with different degree of chlorination. The sorption onto iron oxides could be influenced by the physical–chemical
properties of CPs, which could lead to concerns with CPs dechlorination efficiency
by ZVI and bimetals. Previous research also provides evidence that ligands with a
greater pKa value resulted in increased sorption onto iron oxides such as ferrihydrite (Song et al. 2008). Based on this concept, it may be expected that the tendency
for incorporation will increase as the degree of chlorination decreases, given that
the pKa of 2,4-DCP, 2,4,6-TCP, 2,3,4,6 TeCP and PCP are 7.68, 5.97–7.42, 5.22–
5.62, 4.60–5.25, respectively. Consequently, the possible relationship between iron
oxide formation, CP dechlorination and/or incorporation as well as the effect of
degree of chlorination on CPs incorporation/dechlorination processes when using
bimetals remains uncertain and requires proper studies to understand the underlying
mechanisms.
Therefore, in view of the gaps in the literature, this study aimed at investigating
the effectiveness and efficiency of bimetallic particles for CP dechlorination and
the effect of degree of chlorination and iron oxide phases on CPs incorporation
and dechlorination when using Ni/Fe bimetallic system. Four model contaminants
(PCP, 2,3,4,6-TeCP, 2,4,6-TCP, 2,4-DCP) were chosen for the study. These CPs were
selected as they are common degradation products of PCP dechlorination and due
to the toxic concerns of these CPs in the environment (ATSDR 1999; Tanjore and
Viraraghavan 1994). Both dechlorination and incorporation processes of selected CPs
were examined using Ni/Fe bimetal. The present study also focused on the distinct
role CP removal mechanisms (dechlorination and incorporation) in removing CPs
from the aqueous phase as a function of the different variables considered during the
present study.
275
The degradation of CPs using ZVI, other metals or bimetals and a comparison
between CP degradation efficiencies have been studied by previous researchers (Choi
et al. 2008; Kim and Carraway 2000; Ko et al. 2007; Liu et al. 2001; Xu et al. 2012).
Previous studies have concentrated on comparing the reactivity of different metals
or bimetals (with Pd, Ni as the catalyst) for CP degradation. Although these studies
had reported that the ZVI materials used were obtained from different suppliers,
comprehensive studies have not been carried out to identify the potential role of ZVI
surface characteristics (e.g. oxide phases) on the reactivity for CP dechlorination.
Further, PCP sorption using one type of ZVI has been quantified (Kim and Carraway 2000) as well as sorption with bimetals (Ni/Fe, Pd/Fe, Pt/Fe, Cu/Fe, Mg/Ag,
Pd/Mg) (Kim and Carraway 2000; Patel and Suresh 2006; 2007). Nonetheless, there
are no comprehensive studies reported in the literature which uses ZVI-based bimetals to investigate incorporation levels of different CPs with different degree of chlorination. The sorption onto iron oxides could be influenced by the physical–chemical
properties of CPs, which could lead to concerns with CPs dechlorination efficiency
by ZVI and bimetals. Previous research also provides evidence that ligands with a
greater pKa value resulted in increased sorption onto iron oxides such as ferrihydrite (Song et al. 2008). Based on this concept, it may be expected that the tendency
for incorporation will increase as the degree of chlorination decreases, given that
the pKa of 2,4-DCP, 2,4,6-TCP, 2,3,4,6 TeCP and PCP are 7.68, 5.97–7.42, 5.22–
5.62, 4.60–5.25, respectively. Consequently, the possible relationship between iron
oxide formation, CP dechlorination and/or incorporation as well as the effect of
degree of chlorination on CPs incorporation/dechlorination processes when using
bimetals remains uncertain and requires proper studies to understand the underlying
mechanisms.
Therefore, in view of the gaps in the literature, this study aimed at investigating
the effectiveness and efficiency of bimetallic particles for CP dechlorination and
the effect of degree of chlorination and iron oxide phases on CPs incorporation
and dechlorination when using Ni/Fe bimetallic system. Four model contaminants
(PCP, 2,3,4,6-TeCP, 2,4,6-TCP, 2,4-DCP) were chosen for the study. These CPs were
selected as they are common degradation products of PCP dechlorination and due
to the toxic concerns of these CPs in the environment (ATSDR 1999; Tanjore and
Viraraghavan 1994). Both dechlorination and incorporation processes of selected CPs
were examined using Ni/Fe bimetal. The present study also focused on the distinct
role CP removal mechanisms (dechlorination and incorporation) in removing CPs
from the aqueous phase as a function of the different variables considered during the
present study.