Mineral Reactions, Passivation and Degradation Rates

Passivation of iron granulates in permeable barriers used for in situ groundwater remediation may result in a shorter life time and in contaminant breakthrough earlier than expected. Therefore, mineral reactions or generally the effect of other groundwater constituents on the long term reactivity of iron is of major interest for the application of this technology in environmental clean up. For interpretation of column experiments it is also important to estimate the effect of flow velocity on the extent of passivation due to mineral reactions. 

In simplified iron reactor systems in the laboratory, e.g. deion. water and moderate TCE concentration ( 20 mg/L), the degradation behaviour stays constant over longer time periods ( 1 year). The concentration profiles in column experiments then show nearly steady state conditions. The addition of other common ground water constituents to the influent solution may result in lower degradation rates or in higher turnover rates, respectively (Dahmke et al., 2000 Gavaskar et al., 1997). 

The concentration profiles often indicate a slower degradation at the beginning and a forced decrease of contaminant concentration at the end, which might be a result of a superposition of sorption at non reactive sites and degradation. The different degradation rates along the flow path may result in concentration profiles divided into two parts as 

Strong inhibition of cis-l,2-Dichloroethene (ci5-l,2-DCE) degradation was observed over short times (Fig. 13.5a). The same was observed for PCE degradation (Fig. 13.5b). 

Input solution -c(PCE) = 0.15mmol/L - NaCl = 1 mmol/L - Calcite saturation at p(C02) = 10 atm 

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