Immobilization of Pb in vitrified and devitrified industrial wastes: Evaluation of structural stability using XAFS spectroscopies

Abstract X-ray Absorption Fine Structure (XAFS) spectroscopies are implemented in a series of thermally treated vitrified industrial wastes in an effort to explain the structural role of Pb in the formation of stable, solidified products. In the vitrified wastes, Pb forms trigonal and tetragonal pyramids and acts as a network modifier. Consequently, Pb is successfully immobilized into a vitreous matrix. Devitrification promotes the formation of magnetoplumbite microcrystallites; nevertheless, the majority of Pb continues to modify the glassy network. The chemical stability of the vitroceramics correlates to the type of microcrystallites formed. Lead is safely trapped in both the crystalline and vitreous regions when microcrystalline growth proceeds via the depletion of both Pb and Fe from the silica matrix. However, if the formation of FexOy microcrystallites prevails, structural integrity is lost due to Fe removal, leading to a weak glassy network that can potentially permit the escape of Pb.