Stabilization of Heavy Metals in Contaminated River Sediment by Nanozero-Valent Iron/Activated Carbon Composite

Abstract

Nanozero-valent iron/activated carbon (nZVI/AC) composite is investigated as a possible stabilization agent for heavy metals in river sediment. Effects of stabilization were tested by leaching tests such as synthetic precipitation leaching procedure (SPLP), atoxicity characteristic leaching procedure (TCLP), and a horizontal method that simulates various environmental conditions. In addition, changes in heavy metal forms before and after the addition of nZVI/AC were studied via sequential extraction method. Heavy metals such as Cu, Cd, and Pb were effectively stabilized by nZVI/AC. The stabilization could be attributed to the changes in bonding of heavy metal with sediment. The nZVI/AC in sediment increased the fraction of strongly bound heavy metals. Investigations on the impacts of nZVI/AC dosage, particle size, and time on stabilization and metal speciation showed that they all had significant effects. Generally, leaching dropped as dosage increased and a high dosage led to more metals in strong bindings with sediment. Particles of size 0.075–0.12 mm manifested the highest stabilization. Tests on the long-term stabilization effect revealed that nZVI/AC stabilization was stable over long period of time and no increase in leaching was observed for up to 150 days.