Slag-Based Materials for Toxic Metal and Radioactive Waste Stabilization

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Title: Slag-Based Materials for Toxic Metal and Radioactive Waste Stabilization

Author(s): C. A. Langton

Publication: Special Publication

Volume: 114

Issue:

Appears on pages(s): 1697-1706

Keywords: blast furnace slag; leaching; lysimeters; radioactive wastes; stabilization; waste treatment; Materials Research

Date: 5/1/1989

Abstract:
Approximately 400 x 106 of low-level radioactive alkaline salt solution will be treated at the Savannah River Plant (SRP) Defense Waste Processing Facility (DWPF) prior to disposal in concrete vaults at SRP. Treatment involves the removal of Ca+ and Sr+2 followed by solidification and stabilization of potential contaminants in saltstone--a hydrated ceramic wasteform. The release of chromium, technetium, and nitrate from saltstone can be reduced significantly by substituting hydraulic blast furnace slag for portland cement in the formulation designs. Slag-based mixes are also compatible with Class F fly ash used in saltstone as a functional extender to control heat of hydration and reduce permeability. A monolithic wasteform is produced by hydration of the slag and fly ash. Soluble ion release (NO-3) is controlled by the saltstone microstructure. Chromium and technetium are less leachable from slab mixes than cement-based wasteforms because these species are chemically reduced to a lower faience state by ferrous iron or other ions such as Mn in the slag and are precipitated as relatively insoluble phases, such as Cr(OH)3 and TcO2.