Environmental Engineering Reference
In-Depth Information
In contrast, when plated with certain metals in order to produce highly reac-
tive local elements at the surface, carbonyl ZVI production batches become
highly reactive regarding the degradation of PCE (Figure 5.2).
Checking different technical ZVI brands and production batches used
for applications in PRBs, a wide range of differing trace element contents
is encountered for both the average bulk composition of the particles and
the surface compositions (Figures 5.3 and 5.4). To get an overview of the
true (surface dependent) first-order rate constants for the reaction of PCE
(10 mg/L) in groundwater from the Rheine PRB site, different technical
ZVI brands and production batches as well as artificially produced combi-
nations of pure ZVI with certain elements (produced by ion beam deposi-
tion of the trace element to the surface of a highly pure iron waver) were
investigated in an electrochemical batch cell, equipped with electrodes
comprising a particular metal of concern embedded into an epoxide resin
(Figure 5.5).
From Figure 5.6 it can be seen that peerless iron as well as certain combi-
nations of pure iron doped with trace elements such as sulfur, nickel, and
manganese show the highest rate constants. Hence, it can be demonstrated,
regarding only one groundwater type and contaminant (PCE) at a certain
1.0
I-1
I-2
0.8
II-1
II-2
III-2
IV-1
IV-2
V-1
V-2
VI-1
VI-2
0.6
0.4
0.2
0.0
FIGURE 5.2
Different NZVI types/brands (they can differ in average particle sizes, their coatings with
silicates, etc.) plated with around 0.2% nickel metal show different reactivities toward PCE
in groundwater from the Rheine site (results of double-batch experiments at 10°C). Brand #IV
and #VI show the highest turnovers of PCE within 21 days (type VI being the most effective
one), only type #V showed poor turnover. As delivered/received, for pure carbonyl iron there
is virtually no dehalogenation over 28 days. When plated with nickel, a virtually total degra-
dation of PCE can be observed within 21 days. Note that a recently introduced new carbonyl
micro-ZVI type shows high degradation of PCE within a few hours without any additional
plating.
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