Ferrous iron removal by limestone and crushed concrete in dynamic flow columns

In-situ passive reactive barriers containing carbonate minerals show potential for dissolved iron removal from groundwater at landfill sites. The removal of Fe(II) from synthetic groundwater using limestone and crushed concrete (7-10 mm) was evaluated using dynamic flow columns. Solutions of 50 mg/L Fe(II) were passed through duplicate columns of limestone and concrete until breakthrough (250-300 days); water quality was evaluated at distinct column depths throughout the study. Each material was successful in reducing the concentration of Fe(II), with both achieving an average of greater than 99.4% iron removal (<0.3 mg/L effluent concentration) over 288 and 216 pore volumes, resulting in effective removal capacities of 4.06 and 3.80 g Fe/kg reactive material for limestone and crushed concrete, respectively. These values are less than removal capacities achieved from a sequencing batch test (32.9 and 27.9 g Fe/kg limestone and crushed concrete, respectively), a possible result of preferential flow pathways, shorter equilibration time, and formation of surface films on the reactive materials in the columns.