Waste titanate

Hazardous waste sites, aetive Probably fewer titan 100 eaneers amiuiilly estimates sensitive to assumptions regarding proximity of future wells to waste sites. 

The Authors would like to thank the NSERC Polytechnique-UQAT Chair in environment and mine wastes management for financial support, and are grateful to QIT-Fer et Titane Inc. for making this research possible and the URSTM personnel for their technical support. The Authors are also grateful to the NSERC Collaborative Research and Development (CRD) Grants. 

Yudintsev, S. V., Stefanovsky, S. V. Ewing, R. C. 1999. Structural and compositional relationships in titanate-composed ceramics for actinide-bearing waste immobilization. In Proceedings of the 7th International Conference on Radioactive Waste Management and Environmental Remediation ICEM 99. Nagoya, Japan, CD-ROM. 

Hart, K. P., Zhang, Y. et al. 2000. Aqueous durability of titanate ceramics designed to immobilise excess Pu. In Smith, R. W. Shoesmith, D. W. (eds) Scientific Basis for Nuclear Waste Management XXIII. Materials Research Society Symposium Proceedings, 608, 353-358. 

ICENHOWER, J. P., STRACHAN, D. M., LlNDBERG, M. M., Rodriquez, E. A. Steele, J. L. 2003. Dissolution Kinetics of Titanate-Based Ceramic Waste Forms Results from Single-Pass Flow Tests on Radiation Damaged Specimens. Pacific Northwest National Laboratory, Report No. PNNL-14252. 

Mitamura, H., Matsumoto, S. et al. 1992. Aging effects on curium-doped titanate ceramic containing sodium-bearing high-level nuclear waste. Journal of the American Ceramic Society, 75, 392-400. 

Stewart, M. W. A., Begg, B. D. et al. 2003. Ion irradiation damage in zirconate and titanate ceramics for plutonium disposition. Proceedings of ICEM 03 The 9th International Conference on Radioactive Waste Management and Environmental Remediation, in press. 

Avner Offer, The British Empire, 1870-1914 a waste of money . Economic History Review, 46 (1993), 215-38, at 224-5 John M. Hobson, The military-extraction gap and the wary titan the fiscal-sociology of British defence policy 1870-1913 , Journal of European Economic History, 22 (1993), 461-506, at 479 John M. Hobson, The Wealth of States A Comparative Sociology of International Economic and Political Change (Cambridge University Press, 1997), pp. 67-8, 171, 202. 

Another reaction of the titanate which has an important effect in waste solidification is the reaction with hydrogen ion, as in the hydrolysis reaction shown in Eq. 3 ... 

This reaction is significant for sodium titanate (Keq — 10 moles /l ) and sodium zirconate, but is negligible for sodium niobate and some other "titanates" such as Mg(Ti205H)2. Gelatinous hydroxide precipitates which would appear likely based on Eq. 3 were not observed in the reaction of sodium titanate with aqueous waste, and stoichiometric loading was achieved with polyvalent cations which form insoluble hydroxides as well as for those forming soluble hydroxides. 

The fixed bed ion exchange column provided a much higher level of decontamination and since the goal was to produce an effluent with mini mi im contamination, it was eventually considered to be the baseline process. In this approach, the waste solution which were approximately IM in HNOo, were adjusted to a pH of 0.5-1 by addition of sodium hydroxide and flowed through a titanate bed at one column volume per hour. The columns were subsequently washed with water to remove excess sodium. 

Figure 1. Elemental distribution of fission waste nuclides on a sodium titanate column. The distribution shown on the left was determined from qualitative analyses of the numbered column segments. The Cs and Na distributions on the right were obtained by quantitative analyses of each numbered segment. (O), Cs ( ), Na.

The waste nuclides were fractionated on the column into several hands as shown in Fig. 1 for a sodium titanate column. 

The use of ion exchange resins and natural or synthetic inorganic exchange materials in the nuclear industry is well documented ( ). In the waste solidification application, the titanates or niobates offer no unique sorption properties. They do, however, provide a relatively high overall sorption capacity for a variety of nuclides in materials which can be converted into a stable ceramic host for the sorbed ions. After the sorption process, the column bed must be consolidated to reduce surface area. The project emphasis was directed toward a stable waste form and a considerable effort was devoted to producing and characterizing a highly dense form with favorable physical, chemical and thermal properties (l ). 

At temperatures of 6OO°-65O°C, the waste form dehydrates and crystallizes to form a mixture of titanates (niobates, zirconates) and titania (niobia, zirconia) as illustrated for the case of U. 

During development, evaluation of the consolidated materials was based primarily on two criteria, leachability and the concentration factor, i.e., the concentration of waste oxides on a volume basis. The concentration factor is directly affected by the residual porosity in a consolidated waste as well as by the dilution caused by the addition of consolidation aids. This factor can be as high as 1.2 g/cm3 for a fully dense ( 5 g/cm ) titanate waste prepared from the projected Barnwell plant solution composition. The factor is slightly lower for a titanate waste containing silicon and zeolite additions, which has a typical density of U.2 g/cm3. The leachability was determined by an "instantaneous leach test developed for fast, comparative evaluations of materials, the details of which are described elsewhere (l6). 

The consolidated titanate waste pellets are similar in appearance to their glass counterparts, i.e., both are dense, black and apparently homogeneous. Microscopic analyses, however, reveal important differences between these two waste forms. While little definitive work has been done with glassy waste forms, it is apparent that several readily soluble oxide particulates of various nuclides are simply encapsulated in the glass matrix. The titanate waste form has undergone extensive analyses which includes optical microscopy, x-ray, scanning electron microscopy, microprobe, and transmission electron microscopy (l ) The samples of titanate examined were prepared by pressure sintering and consisted of material from a fully loaded titanate column. Zeolite and silicon additions were also present in the samples. 

The second most abundant crystalline compound (estimated volume fraction 0.1) was gadolinium titanate, Gd2Ti20y. There is evidence that U, Zr, Y, and possibly Sm and Eu are in solid solution with this gadolinium phase. Elemental silicon crystals remaining in the waste were found to be surrounded by Si02. 

Figure 2. Transmission electron photomicrograph of a ceramic titanate waste form. The sample was prepared by pressure sintering a titanate fully loaded with fission waste oxides and includes zeolite and silicon additions.

Comparison of the Radionuclide Activity-in Effluent from Titanate Solidification Process with the Activity in the High Level Waste Feed Solution... 

Phases Identified in Ceramic Titanate Waste Energy Dispersive Analysis Ti... 

The characterization work has shown that, although the titanate ceramic appears to be homogeneous on a macro scale, it is actually quite heterogeneous on an atomic scale and contains at least l4 different phases and possibly more. Since interactions of the waste form with any environment surrounding it will also occur on an atomic scale, it is important that this type of information be available when speculating on the long term stability of any waste form. 

A long term leaching study to compare the behavior of a titanate waste with glassy waste forms and to attempt to elucidate a leaching mechanism has been in progress for l6 months (15) ... 

Based on dissolved ions only, the titanate waste showed an overall leach rate of x 10 5 g/cm day and a rate of 5 3 x 10 7 g/cm day for the fission waste oxides only. The results indicate that the leaching which is occurring is associated with the silicate phases in the ceramic, i.e., the Si02 formed from the silicon and the zeolite. The glass samples showed overall leach rates of 6-15 x 10 5 g/cm day and fission waste oxide leach rates of 1.8-2.7 x 10 g/cm day, where the higher rates in both cases were observed in the phosphate-containing glass. 

The waste forms were a fully loaded, pressure sintered titanate waste containing zeolite and silicon additions, a copper boro-silicate glass prepared from Frit 199 supplied by Battelle Northwest Laboratories, and a copper borosUicate glass prepared from the same frit and containing 30% by weight of waste oxides. 

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