Reactive soil barriers for removal of chromium(VI) from contaminated soil

The aim of this project was to find effective reactive materials as use in soil-bed barriers, for remediation of soil contaminated with chromium at Stallbacka industrial area in Sweden. Materials with different reduction/ adsorption capacities of Cr(VI)/Cr(III) were tested in laboratory and in a field pilot-scale experiment. Concentrations of total Cr and Cr(VI) in the soil, highly contaminated with ferrochrome slag, were exceeding the guideline values for contaminated sites in Sweden.

Zero-valent iron (Fe⁰) filling, FeSO₄ o7H₂O, Na₂SO₃, field pine bark, modified pine bark, pine sawdust, and sphagnum peat were tested in batch or columns in mixture with the contaminated soil. All the materials, except peat, showed a good ability to reduce Cr(VI) in the batch experiments, and were chosen for further dynamic studies in columns. Iron sulphate and sodium sulphite were both shown to have a good ability to quickly reduce Cr(VI) in the columns, but the use might result in leaching of Fe and SO^2- ₄ to surface and groundwater. For field bark it took a longer time to reduce/ adsorb the same amounts of chromium, but it was functional for a longer time.

Reactive soil-bed barriers were constructed in field: soil with embedded layers of FeSO₄, pine bark underlying the soil, and soil without any reactive material layer. The iron sulphate was determined not to be suitable for the soil treatment, due to the high percentage of coarse materials in the soil texture, and thereby a quick washout of FeSO₄ during the water infiltration. The field reactive soil barrier with pine bark was proven to be effective in reducing Cr(VI), and also had the capacity to adsorb both total and dissolved chromium leaching from the contaminated soil.