Removal of chromate in a permeable reactive barrier using zero-valent iron

Chromate is a commonly found groundwater contaminant. Permeable reactive barriers containing zero-valent iron as iron filings are able to remove the chromate by a combined reduction/precipitation reaction. However, due to the passivation of the reduction capability of the iron surfaces by the precipitation of chromate and other groundwater constituents, the barrier may have a limited capacity for chromate removal. By performing a column experiment with iron filings it was shown that the capacity was slightly lower at high chromate concentration (500 ppm) in comparison to low concentration (20 ppm). Mixing in sand had no significant enhancing effect on the removal capacity, in contrast to a pH adjustment of the groundwater to pH 4, which significantly increased the removal capacity.