Modeling in situ iron removal from ground water

In situ iron removal is conducted routinely in a number of European countries. A volume of oxygenated water is injected, and subsequently a larger volume of ground water can be pumped with a lower iron concentration than is found in native ground water, The underlying reaction mechanism has not been well described so far, and the process has not been modeled quantitatively, The essential problem is how the electron transfer takes place between the dissolved oxygen in injection water and the dissolved iron in ground water, An intermediate reaction step, involving cation exchange of ferrous iron and subsequent oxidation by oxygen of injection water, explains the efficiency increase during the initial cycles and the absence of clogging by precipitated iron-oxyhydroxide, A hydrogeochemical transport model has been used to model column experiments with good results. The quantification of the reaction mechanism allows the assessment of operational conditions. For example, it can be shown that increasing the oxidant concentration in the injected water has an insignificant effect when exchangeable ferrous iron is low.