As, Pb and Cu Stabilization By a Mixture Type of Mg-Fe Layered Double Hydroxide (LDH) with Oyster Shell: Laboratory and Field Evaluations.

Oyster shell has been studied as effective stabilizer for heavy metals that exist as cationic forms in soil-aqueous system, but its stabilization capacity for arsenic was very low because of its anionic existence forms. Layered double hydroxide (LDH) shows excellent oxyanion As fixation capacity in soil because of interlayer anion (or complex) exchange, but has relatively low fixation capabilities for other heavy metals. Because of different main mechanism to fix arsenic in the stabilizer compared to other heavy metals, there are limitations in applying only a single stabilizer to the site contaminated with both the arsenic and other heavy metals. The use of a powdered type stabilizer in the field could also be limited because of the risk of suffering mass loss, fugitive dust generation, and low sustainability of the stabilization effect. To overcome these problems, the granular and the slurry type of Mg-Fe LDH mixed with oyster shell were manufactured as the stabilizer to fix As, Pb, and Cu in the soil at the same time and their stabilization efficiencies were investigated by field scale demonstration tests in this study. Results from experiments confirmed that when a mixed granular type stabilizer was added into the soil, the extraction reducing efficiency for all three, As, Pb and Cu, from soil was more than 75%, which indicated that the mixed stabilizer has great potential to fix all of them in soil at the same time. In field demonstration tests (a total of 3 test beds; each bed: 3 m × 3 m × 2 m), the concentration of As and Pb in groundwater from treated test beds decreased by more than 60%, and their extraction reducing efficiencies were higher than 40%. Both As and Pb fractionation transition to more stable phases in test beds by the mixed stabilizer was clearly observed, supporting the Mg-Fe LDH mixed with oyster shell could be successfully used as a single stabilizer for sites contaminated with both heavy metals and As. [ABSTRACT FROM AUTHOR]