DEMONSTRATION OF PACKAGING OF FERNALD SILO I WASTE IN CHEMICALLY BONDED PHOSPHATE CERAMIC

摘要

This paper summarizes our experience in bench-scale packaging of Fernald Silo I waste inchemically bonded phosphate ceramics. The waste was received from the FernaldEnvironmental Management Project (FEMP), and its treatability was studied in our laboratory.This waste contained As5+, Ba, Cr6+, Ni, Pb, Se4+, and Zn as the hazardous contaminants. Inaddition, the total specific activity of all the radioactive isotopes in the waste was 3.85 μCi/g, ofwhich that of radium alone was 0.477 μCi/g. This indicated that radon (a daughter product of theradium) in the waste could present a serious handling problem during this study. For this reason,the waste was handled and stored in a flowing-air glovebox. We made waste form samples withan actual waste loading of 66.05 wt.% and subjected them to the Environmental ProtectionAgency (EPA) Toxicity Characteristic Leaching Procedure (TCLP). The results showedexcellent stabilization of all contaminants. Actual levels detected in the leachate were wellbelow the EPA's most stringent Universal Treatment Standards and in almost all cases were oneorder of magnitude below this limit. Radioactivity in the leachate was also very low. Alphaactivity was 25 ± 2.5 pCi/mL, while beta activity was 9.81 ± 0.98 pCi/mL. This very low activitywas attributed to the efficient stabilization of radium as insoluble radium phosphate in the wasteform, thus prohibiting its leaching. This study indicates that the chemically bonded phosphateceramic process may be a very suitable way to package Silo I waste for transportation and storageor disposal.