Investigation of Novel Electrode Materials for Electrochemically-Based Remediation of High- and Low-Level Mixed Wastes in the DOE Complex - Final Report

Abstract

Executive Summary:One of the key issues that must be solved to achieve a successful remediation of the high level liquid wastes at the Hanford and at Savannah River sites is the removal of the significant quantities of nitrate and nitrite in the existing liquid waste streams that are presently on these sites in the DOE complex. One method of waste stream remediation is electrochemical oxidation, which is an in-situ method that has been well-documented to have significant advantages in many areas with respect to pump-and-treat approaches to waste remediation. There are, however, significant aspects of the electrochemical oxidation process that need to be addressed from a basic research viewpoint. The research be performed under this proposal has investigated new materials, based on degenerately-doped titanias, for use in the electrochemical degradation of organics and nitrogen-containing compounds in sites of concern to the DOE remediation effort. 5 Research Objectives:To achieve a successful remediation of the high level liquid wastes (HLW) at the Hanford and at Savannah River sites, the significant quantities of nitrate and nitrite must be removed from the existing liquid waste streams that are presently on these sites in the DOE complex. In addition, either prior to or after separation of the high level waste components (for eventual vitrification of the high level components), the Hanford waste stream has a substantial concentration of organics that must be processed in such a fashion that the organics are either removed entirely or are degraded into CO 2 or other benign carboncontaining materials. These process steps are needed so that the low level waste stream obtained after separation of the high level waste components (Cs and Sr, primarily) is suitable for conversion into grout (or possibly vitrified), which is now not feasible due to the high concentration of organic materials currently present in the existing liquid wastes.One very promising method of waste stream remediation, which is the focus of this proposal, is electrochemical oxidation. Electrochemical oxidation is well-documented to have some significant advantages relative to high and low temperature steam oxidation processes, including the fact that electrochemical treatment is an in-situ remediation process whereas the water oxidation processes and most other proposed methods are pump-andtreat technologies. In fact, electrochemical degradation of nitrate, nitrite, and organic components in the DOE HLW streams or simulants thereof graded out very highly in a recent DOE assessment of potential remediation methods, with its main drawback relative to high temperature water oxidation processes merely being a lack of prior experience with the operation of electrochemical processes on the scale of, and under the harsh conditions anticipated to be present in, the radioactive waste environment of the DOE sites.There are, however, significant aspects of the electrochemical oxidation process that need to be addressed from a basic research viewpoint, esp...