Precipitation of Aluminum Containing Species in Tank Wastes

Mattigod, Shas V. ; Hobbs, David ; Parker, Kent E. ; McCready, David E.

Pacific Northwest National Laboratory (U.S.)

关键词: Evaporators;    Aluminium Silicates;    Zeolite;    Testing;    Silicate;   

DOI  :  10.2172/15001320
RP-ID  :  PNNL-13881
RP-ID  :  AC05-76RL01830
RP-ID  :  15001320

美国|英语

来源: UNT Digital Library

【 摘 要 】

Aluminisilicate deposit buildup experienced during the tank waste volume-reduction process at the Savannah River Site (SRS) required an evaporator to be shut down in October 1999. The Waste Processing Technology Section (WPTS) of Westinghouse Savannah River Company at SRS is now collaborating with team members from Pacific Northwest National Laboratory (PNNL) to verify the steady-state thermodynamic stability of aluminosilicate compounds under waste tank conditions in an attempt to eliminate the deposition and clogging problems. The data obtained at 40 ?C showed that formation and persistence of crystalline phases was dependent on the initial hydroxide concentrations. The formation and persistence of zeolite A occurred only at lower hydroxide concentrations, whereas increasing hydroxide concentrations appeared to promote the formation of sodalite and cancrinite. The data also showed that although zeolite A forms initially, it is a metastable phase that converts to more stable crystalline materials such as sodalite and cancrinite. Additionally, the rate of transformation of zeolite A appeared to increase with increasing hydroxide concentration. The data from tests conducted at 80 ?C revealed relatively rapid formation of sodalite and cancrinite. Although minor amounts of zeolite A were initially detected in some cases, the higher reaction temperatures seemed to promote very rapid transformation of this phase into more stable phases. Also, the higher temperature and hydroxide concentrations appeared to initiate kinetically fast crystallization of sodalite and cancrinite. More recent testing at SRS in support of the HLW evaporator plugging issue has shown similar trends in the formation of aluminosilicate phases. These tests were carried out under conditions more similar to those that occur in HLW tanks and evaporators. Comparison of our results with those reported above show very similar trends.