Thermodynamic Modeling of Sr/TRU Removal

Felmy, AR

Pacific Northwest National Laboratory (U.S.)

关键词: Removal;    Alpha-Bearing Wastes;    Europium;    Chelating Agents;    Radioactive Waste Processing;   

DOI  :  10.2172/760089
RP-ID  :  PNWD-3044
RP-ID  :  AC06-76RL01830
RP-ID  :  760089

美国|英语

来源: UNT Digital Library

【 摘 要 】

This report summarizes the development and application of a thermodynamic modeling capability designed to treat the Envelope C wastes containing organic complexants. A complete description of the model development is presented. In addition, the model was utilized to help gain insight into the chemical processes responsible for the observed levels of Sr, TRU, Fe, and Cr removal from the diluted feed from tank 241-AN-107 which had been treated with Sr and permanganate. Modeling results are presented for Sr, Nd(III)/Eu(III), Fe, Cr, Mn, and the major electrolyte components of the waste (i.e. NO{sub 3}, NO{sub 2}, F,...). On an overall basis the added Sr is predicted to precipitate as SrCO{sub 3}(c) and the MnO{sub 4}{sup {minus}} reduced by the NO{sub 2}{sup {minus}} and precipitated as a Mn oxide. These effects result in only minor changes to the bulk electrolyte chemistry, specifically, decreases in NO{sub 2}{sup {minus}} and CO{sub 3}{sup 2{minus}}, and increases in NO{sub 3}{sup {minus}} and OH{sup {minus}}. All of these predictions are in agreement with the experimental observations. The modeling also indicates that the majority of the Sr, TRU's (or Nd(III)/Eu(III)) analogs, and Fe are tied up with the organic complexants. The Sr and permanganate additions are not predicted to effect these chelate complexes significantly owing to the precipitation of insoluble Mn oxides or SrCO{sub 3}. These insoluble phases maintain low dissolved concentrations of Mn and Sr which do not affect any of the other components tied up with the complexants. It appears that the removal of the Fe and TRU'S during the treatment process is most likely as a result of adsorption or occlusion on/into the Mn oxides or SrCO{sub 3}, not as direct displacement from the complexants into precipitates. Recommendations are made for further studies that are needed to help resolve these issues.