Abstract
The validity of the specific reaction rate constants ( k SA) in modelling contaminant removal in Fe 0/H 2O systems is questioned. It is shown that the current k SA-model does not consider the large reactive surface area provided by the in-situ formed oxide film, and thus the adsorptive interactions between contaminants and film materials. Furthermore, neither the dynamic nature of film formation nor the fact that the Fe 0 surface is shielded by the film is considered. Suggestions are made how the k SA-model could be further developed to meet its original goal.
Highlights
Johnson et al [1] performed an analysis of factors effecting the degradation rates of halogenated hydrocarbons by elemental iron with the aim to enable direct comparisons between data from independent sources
Normalization of kobs to iron surface area concentration yields a specific rate constant that varies by only one order of magnitude for individual contaminants
Adsorption was enumerated among the reasons of failure of the kSA model, little was done to correlate the relative affinities of individual contaminants to the iron corrosion products
Summary
Johnson et al [1] performed an analysis of factors effecting the degradation rates of halogenated hydrocarbons by elemental iron (e.g. in Fe0/H2O systems) with the aim to enable direct comparisons between data from independent sources. Their results showed that firstorder rate constants (kobs) from both batch and column studies vary widely and without meaningful correlation. Because the rate of contaminant reduction by Fe 0 appeared to be first order with respect to the available reaction sites on Fe0 (available surface area), Johnson et al [1] introduced kSA as a more general descriptor of Fe0 reactivity. Linear relationships of this sort have not been observed as a rule [1, 2, 5, 8], suggesting that the validity of the model should be closely discussed
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