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Results of Deposition Scoping Tests

Description: The processes of crystallization and solid deposit formation that led to the shutdown of the 2H evaporator operation at the Savannah River Site (SRS) and that could possibly cause similar problems in the future or in other evaporators need to be better understood. Through experimentation, thermodynamic modeling, and correlation of scaling to historical tank farm operations, progress has been made in developing guidelines as to the concentrations of silicon and aluminum that can be processed by evaporators while avoiding unacceptable levels of scale formation. However, because of limitations of the thermodynamic model and an insufficient amount of operational data at slightly supersaturated concentration levels, uncertainty still exists regarding acceptable feed concentrations. The objective of this effort is to provide information that can be used in defining acceptable levels of silicon and aluminum in evaporator feed solutions. Data collected previously showed that particle formation reactions can be rapid at evaporator temperatures for elevated silicon and aluminum concentrations. However, insufficient data exists to estimate the silicon and aluminum concentrations above which solids will form in the time frame of evaporator processing. The work described in this report was designed to determine the induction period for solutions of decreasing aluminum and silicon concentration such that the supersaturation level corresponding to a 4-h induction time for particle nucleation/growth in bulk solution can be estimated. In addition, experiments were conducted to explore the supersaturation levels that can result in deposition of solids on metal surfaces at varying aluminum-to-silicon concentration ratios. Laboratory studies of particle growth in solution were conducted at relatively low supersaturation levels. Dynamic-light-scattering (DLS) studies and deposition tests, similar to those performed in FY 2001, were conducted with solutions at relatively low supersaturation levels and at elevated temperatures to explore the formation of solids under conditions similar to those encountered in evaporator processing. ...
Date: March 4, 2003
Creator: Hu, M.Z.
Partner: UNT Libraries Government Documents Department

Design and Synthesis of Oriented Guest-Host Nanostructures for Enhanced Membrane Performances

Description: This project has demonstrated a novel nanomaterial design concept and a synthesis method for ''guesthost'' type superionic-conducting nanocomposite membranes. This concept consists of nanophases of oxide electrolyte nanograins (guest) encapsulated inside the nanopore channels of an oxide layer matrix (host), with channels oriented perpendicular to the layer surface. Using ionic conducting YSZ (yttrium stabilized zirconia) as a special case, we have shown that the host-guest design allows orientation of a large number channels, allowing a high density of nanograin boundaries/interfaces to be built into the film to enhance cross-membrane conductivity. This structure allowed conductivity measurements with impedance spectroscopy to be performed for the first time at room temperature. Cross-membrane conductivity values at low temperature ranges of interest are the higher than any reported values. The conductivity-enhancing mechanisms could be attributed to (1) controlled orientation and increased number density of YSZ nanograin-host interfaces and (2) creation and stabilization of YSZ nanocrystalline phases inside nanopore channels (<10 nm dia.). This successful initial demonstration of host-guest nanostructures is expected to have direct impact on fuel cell technologies, and may also have beneficial use in a broad range of applications such as in solar cells, sensors, chemical/gas separations, catalysis, and magnetic memory devices. This work may also lead to a new way to develop membrane technologies that offer orders-of-magnitude higher permeability and selectivity, as well as improved thermal stability of the desirable nanocrystalline phases.
Date: November 15, 2005
Creator: Hu, M.Z.
Partner: UNT Libraries Government Documents Department

Uranium and Aluminosilicate Surface Precipitation Tests

Description: The 2H evaporator at the Savannah River Site has been used to treat an aluminum-rich waste stream from canyon operations and a silicon-rich waste stream from the Defense Waste Processing Facility. The formation of aluminosilicate scale in the evaporator has caused significant operational problems. Because uranium has been found to accumulate in the aluminosilicate solids, the scale deposition has introduced criticality concerns as well. The objective of the tests described in this report is to determine possible causes of the uranium incorporation in the evaporator scale materials. The scope of this task is to perform laboratory experiments with simulant solutions to determine if (1) uranium can be deposited on the surfaces of various sodium aluminosilicate (NAS) forms and (2) aluminosilicates can form on the surfaces of uranium-containing solids. Batch experiments with simulant solutions of three types were conducted: (1) contact of uranium solutions/sols with NAS coatings on stainless steel surfaces, (2) contact of uranium solutions with NAS particles, and (3) contact of precipitated uranium-containing particles with solutions containing aluminum and silicon. The results show that uranium can be incorporated in NAS solids through encapsulation in bulk agglomerated NAS particles of different phases (amorphous, zeolite A, sodalite, and cancrinite) as well as through heterogeneous deposition on the surfaces of NAS coatings (amorphous and cancrinite) grown on stainless steel. The results also indicate that NAS particles can grow on the surfaces of precipitated uranium solids. Particularly notable for evaporator operations is the finding that uranium solids can form on existing NAS scale, including cancrinite solids. If NAS scale is present, and uranium is in sufficient concentration in solution to precipitate, a portion of the uranium can be expected to become associated with the scale. The data obtained to date on uranium-NAS affinity are qualitative. A necessary next step is to quantitatively determine ...
Date: November 27, 2002
Creator: Hu, M.Z.
Partner: UNT Libraries Government Documents Department

Preliminary Results of Testing of Flow Effects on Evaporator Scaling

Description: This investigation has focused on the effects of fluid flow on solids deposition from solutions that simulate the feed to the 2H evaporator at the Savannah River Site. Literature studies indicate that the fluid flow (or shear) affects particle-particle and particle-surface interactions and thus the phenomena of particle aggregation in solution and particle deposition (i.e., scale formation) onto solid surfaces. Experimental tests were conducted with two configurations: (1) using a rheometer to provide controlled shear conditions and (2) using controlled flow of reactive solution through samples of stainless steel tubing. All tests were conducted at 80 C and at high silicon and aluminum concentrations, 0.133 M each, in solutions containing 4 M sodium hydroxide and 1 A4 each of sodium nitrate and sodium nitrite. Two findings from these experiments are important for consideration in developing approaches for reducing or eliminating evaporator scaling problems: (1) The rheometer tests suggested that for the conditions studied, maximum solids deposition occurs at a moderate shear rate, approximately 12 s{sup -1}. That value is expected to be on the order of shear rates that will occur in various parts of the evaporator system; for instance, a 6 gal/min single-phase liquid flow through the 2-in. lift or gravity drain lines would result in a shear rate of approximately 16 s{sup -1}. These results imply that engineering approaches aimed at reducing deposits through increased mixing would need to generate shear near all surfaces significantly greater than 12 s{sup -1}. However, further testing is needed to set a target value for shear that is applicable to evaporator operation. This is because the measured trend is not statistically significant at the 95% confidence interval due to variability in the results. In addition, testing at higher temperatures and lower concentrations of aluminum and silicon would more accurately represent conditions in ...
Date: February 15, 2002
Creator: Hu, M.Z.
Partner: UNT Libraries Government Documents Department

Dynamic Particle Growth Testing - Phase I Studies

Description: There is clearly a great need to understand the processes of crystallization and solid scale formation that led to the shutdown of 2H evaporator operation at the Savannah River Site (SRS) and could possibly cause similar problems in the future in other evaporators. Waste streams from SRS operations that enter the evaporators generally contain alkaline, sodium nitrate/nitrite-based solutions with various changing concentrations of silicates and aluminates. It has been determined. that the silicates and aluminates served as precursor reactants for forming unwanted minerals during solution evaporation, upon transport, or upon storage. Mineral forms of the Zeolite Linde A group--sodalites and cancrinite--along with gibbsite, have often been identified as contributing to deposit (scale) formation on surfaces of the 2H evaporator as well as to the formation of solid plugs in the gravity drain line and lift line. Meanwhile, solids (amorphous or crystalline minerals) are believed, without direct evidence, to form in the bulk solutions in the evaporator. In addition, the position of deposits in the 2H evaporator suggests that scale formation depends on the interplay of heat and mass transfer, hydrodynamics, and reaction mechanisms and kinetics. The origin of solid scale formation on walls could be due to heterogeneous nucleation and/or to homogeneous nucleation followed by cluster/particle deposition. Preliminary laboratory tests at the Savannah River Technology Center (SRTC) with standing metal coupons seem to support the latter mechanism for initial deposition; that is, the solid particles form in the bulk solution first and then deposit on the metal surfaces. Further buildup of deposits may involve both mechanisms: deposition and crystal growth. Therefore, there may be a direct linkage between the solid particle growth in bulk solution and the scale buildup on the wall surfaces. On the other hand, even if scale formation is due solely to a heterogeneous mechanism, particle growth ...
Date: May 17, 2001
Creator: Hu, M.Z-C.
Partner: UNT Libraries Government Documents Department

Continuous, Rapid Production of Uniform Microparticles by Electrodispersion

Description: Ultrafine particles constitute the key building blocks for diverse advanced structural and functional materials, such as high-performance ceramics and alloys. These advanced materials have tremendous impact in many areas, including catalysis, separations, electronics, energy production processes, and environmental applications. Of particular importance, nanophase ceramic or metallic materials that contain nanosized (<100 nm) particles/grains show dramatically improved performance (mechanical, electrical, optical, magnetic, and/or catalytic). The characteristics of ultrafine particles (i.e. size, morphology, monodispersity, purity, and homogeneity of composition) directly determine the properties of the materials that are made from them. Thus, the future application of advanced materials depends strongly on the capability to produce particles with outstanding characteristics.
Date: November 15, 1998
Creator: DePaoli, D.W. & Hu, M.Z.-C.
Partner: UNT Libraries Government Documents Department

Design and testing of a continuous metal biosorption system. Final report, March 10, 1994--June 9, 1995

Description: The research pursued in this project consisted of two portions that were conducted with constant coordination to allow the ultimate merger of research results. ORNL was assigned the task of developing the biomass portion of the bioreactor, while SCSC was responsible for the mechanical portions of the bioreactor. This report describes the technical aspects of a novel biological sorbent, consisting of microbial biomass immobilized within a polyurethane gel matrix, that was developed and characterized (on a bench scale, within batch and flow-through systems) for use in a novel, continuous-flow bioreactor system. The report also addresses an initial effort to develop a delivery technology that takes advantage of the specific characteristics of the biosorbent material to permits its deployment against contamination problems. The report concludes with recommendations for future work that would allow the designated wastes to be treated on a large scale.
Date: December 31, 1995
Creator: Faison, B.D.; Hu, M.Z.C.; Reeves, M.E.; McGraw, T.F.; Gupte, U. & Haris, W.G.
Partner: UNT Libraries Government Documents Department

Development and demonstration of biosorbents for clean-up of uranium in water. CRADA final report

Description: Pseudomonas aeruginosa strain CSU, a nongenetically engineered bacterial strain known to bind dissolved hexavalent uranium, shows particular promise as the basis of an immobilized-cell process for removal of dissolved uranium from contaminated wastewaters. It was characterized with respect to its sorptive active. Living, heat-killed, permeabilized, and unreconstituted lyophilized cells were all capable of binding uranium. The uranium biosorption equilibrium could be described by the Langmuir isotherm. The rate of uranium adsorption increased following permeabilization of the outer and/or cytoplasmic membrane by organic solvents such as acetone. P. aeruginosa CSU biomass was significantly more sorptive toward uranium than certain novel, patented biosorbents derived from algal or fungal biomass sources. P. aeruginosa CSU biomass was also competitive with commercial cation-exchange resins, particularly in the presence of dissolved transition metals. Uranium binding by P. aeruginosa was clearly pH dependent. Uranium loading capacity increased with increasing pH under acidic conditions, presumably as a function of uranium speciation and due to the H{sup +} competition at some binding sites. Nevertheless, preliminary evidence suggests that this microorganism is also capable of binding anionic hexavalent uranium complexes. Ferric iron was a strong inhibitor of uranium binding to P. aeruginosa CSU biomass, and the presence of uranium also decreased the Fe{sup 3+} loading when the biomass was not saturated with Fe{sup 3+}, suggesting that Fe{sup 3+} and uranium may share the same binding sites on biomass.
Date: August 1997
Creator: Faison, B.D.; Hu, M.Z.C.; Norman, J.M.; Reeves, M.E.; Williams, L.; Schmidt-Kuster, W. et al.
Partner: UNT Libraries Government Documents Department

Nanoscale Science, Engineering and Technology Research Directions

Description: This report describes important future research directions in nanoscale science, engineering and technology. It was prepared in connection with an anticipated national research initiative on nanotechnology for the twenty-first century. The research directions described are not expected to be inclusive but illustrate the wide range of research opportunities and challenges that could be undertaken through the national laboratories and their major national scientific user facilities with the support of universities and industry.
Date: January 1, 1999
Creator: Lowndes, D. H.; Alivisatos, A. P.; Alper, M.; Averback, R. S.; Jacob Barhen, J.; Eastman, J. A. et al.
Partner: UNT Libraries Government Documents Department