Vitrification of Simulated Fernald K-65 Silo Waste at Low Temperature (1998)

Vitrification is the technology that has been chosen to solidify approximately 15,500 tons of geologic mill tailings at the Fernald Environmental Management Project (FEMP) in Fernald, Ohio. The geologic mill tailings are residues from the processing of pitchlende ore during 1949-1958. These waste residues are contained in silos in Operable Unit 4 (OU4) at the FEMP facility. Operable Unit 4 is one of five operable units at the FEMP. Operating Unit 4 consists of four concrete storage silos and their contents. Silos 1 and 2 contain K-65 mill tailing residues and a bentonite cap, Silo 3 contains non-radioactive metal oxides, and Silo 4 is empty. The K-65 residues contain radium, uranium, uranium daughter products, and heavy metals such as lead and barium.The K-65 waste leaches lead at greater than 100 times the allowable Environmental Protection Agency (EPA) Resource, Conservation, and Recovery Act (RCRA) concentration limits when tested by the Toxic Characteristic Leaching Procedure (TCLP). Vitrification was chosen by FEMP as the preferred technology for the Silos 1, 2, 3 wastes because the final waste form met the following criteria: controls radon emanation, eliminates the potential for hazardous or radioactive constituents to migrate to the aquifer below FEMP, controls the spread of radioactive particulates, reduces leachability of metals and radiological constituents, reduces volume of final wasteform for disposal, silo waste composition is favorable to vitrification, will meet current and proposed RCRA TCLP leaching criteria Glasses that melt at 1350 degrees C were developed by Pacific Northwest National Laboratory (PNNL) and glasses that melt between 1150-1350 degrees C were developed by the Vitreous State Laboratory (VSL) for the K-65 silo wastes. Both crucible studies and pilot scale vitrification studies were conducted by PNNL and VSL. Subsequently, a Vitrification Pilot Plant (VPP) was constructed at FEMP capable of operating at temperatures up to 1450 degrees C. The VPP began operation on June 19, 1996. The VPP was used to test surrogate FEMP wastes at melt temperatures between 1130 degrees C and 1350 {degrees}C. The VPP failed on December 26, 1996 while processing surrogate waste. After the failure of the FEMP VPP, vitrification technology and glass chemistry were reevaluated. This report documents the glass formulation development for K-65 waste completed at SRTC in April, 1993 in conjunction with Associated Technical Consultants (ATC) of Toledo, Ohio. The glass developed for the FEMP was formulated in a lithia substituted soda-lime-silica (SLS) glass per the Savannah River Technology Center (SRTC) patented Lithia Additive Melting Process (LAMP)* to avoid problematic phase separation known to occur in the borosilicate glass system (MO-B{sub 2}O{sub 3}- SiO{sub 2}), where (MO = CaO, MgO, BaO, and PbO). Lime, MgO, BaO and PbO are all constituents of the FEMP wastes and thus subject to phase separation when vitrified in borosilicate glass. Phase separation is known to compromise waste glass stability. The SRTC soda-lithia-lime- silica (SLLS) glass melted at 1050 degrees C. Similar SLLS glass formulations have recently been demonstrated at the Oak Ridge Reservation (ORR) in a full scale melter with mixed (radioactive and hazardous) wastes.The low melting temperatures achieved with the SLLS glass minimize volatilization of hazardous species such as arsenic, lead, and selenium during vitrification. An 81 percent K-65 waste loading was demonstrated. The SRTC SLLS glass passed the Environmental Protection Agency (EPA) Toxic Characteristic Leach Procedure (TCLP) for all the hazardous constituents of concern under the current regulations. The SLLS glass is as durable as the high melting PNNL SLS glass and is more durable than the borosilicate glasses previously developed by VSL for the K-65 wastes.