Chemical stabilization of chromate in blast furnace slag mixed cementitious materials

Abstract

Cement waste form (CWF) technology is among the leading approaches to disposing of metals and liquid low-level nuclear waste in the United States. One such material, saltstone, includes slag, fly ash and Portland cement to enhance the immobilization of contaminants (e.g., Cr, (99)Tc) in alkaline liquid wastes. To evaluate the stability of such redox sensitive contaminants in saltstone, the effects of slag as a source of reductant on Cr immobilization was evaluated in aged (<300 d) saltstone monoliths. Specifically, we investigated the effects of artificial cement pore waters on the Cr release and the spatially resolved Cr chemical state analysis using synchrotron based microfocused X-ray microprobe analysis. The microprobe analysis indicated the heterogeneous distribution of insoluble Cr(III)-species in saltstone. Although at most of 20% Crtotal was leached at the top few (2-3) millimeter depth, the release of Cr(VI) was small (<5%) at 5-30 mm with slight changes, indirectly suggesting that Cr is likely present as insoluble Cr(III) species throughout the depths. The study suggests that this saltstone formulation can effectively retain/immobilize Cr under the oxic field condition after ⩽300 d of aging time.

Sulfur speciation in untreated and alkali treated ground-granulated blast furnace slag

“…X-ray fluorescence (XRF) spectrometry was used for total elemental analysis. The results of elemental analysis are reported in our previous work (Meena et al, 2015). Briefly, the major elements in wt.…”

Development of a Geochemical Speciation Model for Use in Evaluating Leaching from a Cementitious Radioactive Waste Form

“…Cast Stone is a waste form produced from coal fly ash (FA), granular ground blast furnace slag (BFS), and ordinary Portland cement (OPC) that has been proposed to solidify and immobilize a fraction of radioactive waste, such as secondary waste created during the vitrification treatment of low-activity radioactive waste (LAW) at the Department of Energy Hanford Site in Richland, Washington. − During its service life, Cast Stone is likely to come in contact with infiltrating water, and constituents of potential concern (COPCs) could be remobilized. Moreover, Cast Stone is subject to evolving physical and chemical properties because of oxidation and carbonation from oxygen and carbon dioxide in the air or soil gas and dissolved in infiltrating water; , reactions with oxygen and carbon dioxide could impact the retention of COPCs. − Therefore, it is important to improve the understanding of the complex mechanisms that are responsible for the leaching behavior of constituents, where insights can be gained through use of leaching tests coupled with geochemical speciation modeling …”

Cementitious Behavior of Argon Oxygen Decarburization Stainless Steel Slag and Its Stabilization on Chromium

“…The S/S process plays its role by mixing solid waste with cementitious materials to reduce mobility, as well as the toxicity of the contaminants [32,34], and this process usually accompanies encapsulation, absorption, precipitation, and finally detoxification [35,36]. S/S by cementitious materials like cement is in an extensive application for immobilization of chromium [37,38]. Chromium can be efficiently immobilized by the hydration products of the cured cement-based composite cementitious materials [39].…”