Immobilization of Cr(VI) in soil through injection of nanoscale Fe^II-Al^III LDH suspension into the soil column

We synthesized nanoscale Fe^II-Al^III layered double hydroxide (LDH) and investigated its efficiency for reductive immobilization of Cr(VI) in a Cr-spiked alkaline loam soil using both batch and column experiments. Results of batch experiments indicated that addition of fresh LDH suspension to the soil at a mole ratio of Cr(VI) to structural Fe^II in LDH [Fe^II_(s)] = 0.2, completely immobilized Cr(VI). Column experiments, using same Cr(VI)/Fe^II_(s) ratio, were conducted under four various modes of LDH suspension application to the soil. Addition of LDH suspension to the saturated and unsaturated packed soil columns at a pressure head of 2 cm was inefficient in reducing Cr(VI) to Cr(III) because of shallow penetration of LDH particles into the soil. Injection of LDH suspension into the soil columns greatly improved penetration of LDH particles into the soil. However, only 18.8% of leachable Cr(VI) was immobilized in the saturated soil column, while the same operation in the unsaturated column experiment increased Cr(VI) immobilization efficiency to 70.0%, a significant improvement in immobilization. In summary, nanoscale Fe^II-Al^III LDH was shown to be a fast and strong reductant, which successfully remediated a Cr(VI)- contaminated alkaline soil.