DEMONSTRATION OF A STABILIZATION PROCESS FOR THE TREATMENT OFRADIOACTIVELY CONTAMINATED WASTES CONTAINING MERCURY ATCONCENTRATIONS GREATER THAN 260 PPM

摘要

In an earlier demonstration of an innovative mercury stabilization technology for the Department ofrnEnergy, ATG's full-scale process stabilized mercury in wastes that initially contained less than 260 ppm Hgrn(DOE, 1999b). The treated waste satisfied the applicable leaching standards for mercury and qualified forrnland disposal. This paper describes the extension of that work to demonstrate a full-scale process for thernstabilization of a mixed waste that contained more than 260 ppm of Hg. Mixed waste contains bothrnradioactive and chemically hazardous constituents.rnThe full-scale demonstrations described here produced a stabilized waste that satisfied the leachingrnstandards applicable to wastes containing less than 260 ppm of mercury. This demonstration providesrnstrong support for the designation of stabilization as a BDAT (Best Demonstrated and AvailablernTechnology) for wastes containing more than 260 ppm mercury. Such a designation would allow thesernwastes to be stabilized and disposed of in a permitted land disposal unit.rnFull-scale demonstrations with two different formulations reduced the mercury concentrations in soilrnextracts below the relevant leaching standard, a Universal Treatment Standard (UTS) limit of 0.025 mgrnmercury per liter of leachate generated by the Toxicity Characteristic Leaching Procedure (TCLP).rnThese formulations were based on dithiocarbamate (DTC) and liquid sulfide reagents. The full-scale DTCrnformulation reduced the concentration to about one-half the UTS limit, or 0.013 mg/l, and the full-scalernliquid sulfide formulation to less than one-tenth of the limit, or 0.0025 mg/l. The volume increase resultingrnfrom the stabilization treatment was small, less than 20%. The DTC formulation immobilized the mercuryrnwithin one hour. The liquid sulfide formulation required several hours and more tightly immobilized thernmercury. The sulfide mercury stabilization was more sensitive to the degree of aeration and mixing thanrnthe DTC stabilization. The demonstration showed that aeration and mixing of the sulfide reagent can bernmodeled on the full-scale with lab-scale treatability studies.