Tank Waste Treatment Science Task quarterly report for October--December 1994

Abstract

SummaryThis report describes the work performed by Pacific Northwest Laboratory (PNL) during the first quarter of FY 1995 (October -December 1994) under the Tank Waste Treatment Science Task of the Tank Waste Remediation System (TWRS) Pretreatment Technology Development Project. Work was performed in the following areas: 1) analytical methods development, 2) sludge dissolution modeling, 3) sludge characterization studies, 4) sludge component speciation, 5) pretreatment chemistry evaluation, and 6 ) colloidal studies for solid-liquid separations. Significant accomplishnients are highlighted below:Installation and testing of a particle size analysis system and a capillary'ion analyzer.Testing the existing thermodynamic model for the major electrolyte components of tank wastes by comparing predicted solubilities of NaNO, and NaNO, in simulated waste with direct exper-.imental observations. Submission of three papers for publication in the ACS Symposium Series on Scientific IssuesRelated to Safety and Treatment of Hanford Wastes. Presentation of a seminar entitled "Speciation of Sr and Ni in Tanks C-112 and C-109Sludges. " Fabrication (Los Alamos National Laboratory) of eight sample holders and two sample assemblies from a corrosion-resistant alloy for x-ray absorption spectroscopy experiments performed in March 1995 at the Stanford Synchrotron Radiation Laboratory.Development of the data structure for the statistical analysis of physical and rheological tank waste properties using the Sort on Radioactive Waste Type (SORWT) methodology.Obtaining and structuring the "Braun database" that contains records of historical analytical data for evaluation with the SORWT model to provide a tank-by-tank estimate of analyte concentrations.Preparation and characterization of colloidal suspensions of boehmite (AlOOH) and gibbsite [AI(OH),], in terms of primary particle size and shape, surface charge, and degree of agglomeration. While it is too early to draw definitive conclusions, the work performed to date suggests the following information about current guidelines.1. It appears that many of the current guidelines used in evaluating the baseline processes for solid-liquid separations are valid if the primary particles in sludge are larger than 10 pm in size. With large particles it is possible to achieve low slurry viscosities (< 60 cp) at high solids loadings (> 10 ~0 1 % ) for retrieval and transport, to have reasonable initial sedimentation velocities ( > 3 c d h r ) for settle-decant operations, and to achieve rapid filtration rates (> 1 cm/hr).iii 2 . The current processing guidelines do not appear to be valid if the bulk of the material to be processed consists of submicron particles. Fine colloidal particles can form highly viscous (> 25,000 cp) shear-thinning liquids at solids loadings as low as 3 vol%, can form suspensions that exhibit negligible sedimentation velocities (either in the form of highly dispersed suspensions or as highly agglomerated gels), and can form impermeable filter cakes that will clog most filtra...

Potential for criticality in Hanford tanks resulting from retrieval of tank waste

“…First, studies of plutonium solids by Grebenshchikova and Davydov (1965) show that plutonium (IV) hydroxide particles undergo a change from positive to negative surface charge at about pH = 8.5. This change is similar to the behavior observed for the metal oxide and hydroxide solids in the Hanford tank waste (Virden et al 1994b). …”

Washing and caustic leaching of Hanford tank sludge: Results of FY 1997 studies

“…This report This report This report This report LaFemina 1995Lumetta, Wagner, Hoopes, Steele 1996LaFemina 1995LaFemina 1995 LaFemina 1995 (a) (a) LaFemina 1995 This report This report LaFemina 1995 LaFemina 1995LaFemina 1995 This report LaFemina 1995Lumetta, Wagner, Hoopes, Steele 1996This report Lunietta et al 1996LaFemina 1995 Table 8.3 summarizes the amounts of Cr removed by dilute hydroxide washing and by caustic leaching. Here the trends are much less clear than with AI.…”

“…-Microscopic examination of the C-112 sludge revealed a uranium-rich phosphate phase with diameters on the order of several !lm. Caustic leaching caused these particles to break up into nm-sized particles, and the P was removed (LaFemina 1995). This suggests that the uranium phosphate was converted to uranium hydroxide, and the P was removed as Na3P04; Sodium phosphate is easily removed by dilute hydroxide washing, provided adequate wash solution is used to sufficiently lower theNa activity .…”

Status Report on Phase Identification in Hanford Tank Sludges

“…In this report, we summarize the results obtained through FY 1999. Aspects of this summary already have been reported (Lafemina 1995;Lumetta et al 1998;Rapko et al 1996).…”