Increasing groundwater
temperatures caused by global warming, subsurface
infrastructure, or heat storage projects may interfere with groundwater
remediation techniques using zero-valent iron (ZVI) technology by
accelerating anaerobic corrosion. The corrosion behavior of three
ZVIs widely used in permeable reactive barriers (PRBs), Peerless cast
iron (PL), Gotthart-Maier cast
iron (GM), and an ISPAT iron sponge (IS), was investigated at temperatures
between 25 and 70 °C in half-open batch reactors by measuring
the volume of hydrogen gas generated. Initially, the corrosion rates
of all tested ZVIs increased with temperature; at temperatures ≤40
°C, a material-specific steady state is reached, and at temperatures
>40 °C, passivation causes a decrease in long-term corrosion
rates. The observed corrosion behavior was therefore assumed to be
superimposed by accelerating and inhibiting effects, caused by surface
precipitates where the fitting of measured corrosion rates by a modeling
approach, using the corroded amount of Fe0 to account for
passivating minerals, yields intrinsic activation energies (E
a, ZVI) of 81, 90, and 107 kJ mol–1 for IS, GM, and PL, respectively. An increase in
H2 production might not be directly transferable to an
increase in general ZVI reactivity; however, the results suggest that
an increase in chlorinated hydrocarbon degradation rates can be expected
for ZVI-PRBs in the immediate vicinity of low-temperature underground
thermal energy storages (UTESs) or in the impact areas of high-temperature
UTES with temperatures of ≤40 °C.