Aqueous Dissolution and Surface Alteration Studies of Nd-bearing Zirconolite in 0.001M Citric Acid at 90°C

2003 ◽  
Vol 807 ◽  
Author(s):  
Peter J. McGlinn ◽  
Terry McLeod ◽  
Gilles Leturcq ◽  
Zaynab Aly ◽  
Mark G. Blackford ◽  
...  
Keyword(s):  
Citric Acid ◽  
Secondary Phase ◽  
Citric Acid Solution ◽  
Release Rates ◽  
Water Release ◽  
Phase Development ◽  
Surface Alteration ◽  
Order Of Magnitude ◽  
Parallel Tests ◽  
Influence Of Ph

ABSTRACTNd-bearing zirconolite was leached at 90°C for 6 months in 0.001M citric acid, and also in deionised water, to determine the effect of organic-bearing solutions on durability. The pH of the citric acid solution was adjusted to 5 using KOH, approximating that of the water in the parallel tests, to avoid the influence of pH on chemical durability of the zirconolite.Releases were incongruent in the tests carried out in water. Release rates of Ti, Zr and Nd were comparatively very low (commonly too low to be measured) over the first 80 days of leaching. Rates for Ca and Al were 2 to 4 orders of magnitude higher than Ti, Zr and Nd over this same period. At about 80 days, there was an anomalous decrease in pH from 6 to 4 which enhanced release rates of Ti and Nd in particular. There was development of titania crystals, and the suggestion of hydrolysed titania, on the surface after 6 months. Thermodynamic equilibrium between the leachates and hydrolysed species on the surface of the zirconolite may be the key to apparent cessation of alteration, at least during thefirst 80 days of leaching.By contrast, zirconolite leached in 0.001M citric acid maintained release rates of Ti, Zr and Nd 2 to 4 orders of magnitude greater than those in water for the first 80 days, values sustained, within an order of magnitude, for the remainder of the leach tests. Releases were congruent. The surface of the zirconolite showed no signs of secondary phase development. This suggests complexation by citrate ions prevented control by hydrolysed species on zirconolite solubility.

Durability of Pu-doped Titanate and Zirconate Ceramics Designed for Pu Immobilisation

2002 ◽  
Vol 713 ◽  
Author(s):  
Y. Zhang ◽  
K.P. Hart ◽  
B.D. Begg ◽  
E.A. Keegan ◽  
A.R. Day ◽  
...  
Keyword(s):  
Secondary Phase ◽  
Processing Temperature ◽  
Processing Conditions ◽  
Release Rates ◽  
Rich Phase ◽  
Glass Forming ◽  
Order Of Magnitude ◽  
Ceramic Sintering ◽  
Impurity Elements ◽  
Titanate Ceramic

ABSTRACTCeramics rich in pyrochlore-structured titanate and fluorite-structured zirconate phases designed for surplus Pu immobilisation, with and without process impurities, have been leach tested at 90°C in deionised water. The zirconates consist mainly of a defect-fluorite with secondary impurity-containing phase-powellite/scheelite (when sintered in Ar but not when sintered in air), a spinel or magnetoplumbite type phase, a glass forming silicate and a secondary U-rich phase (when sintered in air with added impurities). The pyrochlore-rich baseline titanate ceramic consists of pyrochlore, brannerite and Hf-rutile. When impurities are added zirconolite and a silicate glass are also present. The pyrochlore-rich titanate with 5 wt% of impurities sintered at 1300°C is highly durable. A well-densified zirconate version without impurities has comparable elemental releases to those of the titanate ceramic but a zirconate with 5 wt% of impurities sintered at 1400°C in air or Ar shows much higher U and Ca releases than the titanate ceramic. Sintering atmospheres, changing from Ar to air, can influence Pu and U release rates up to an order of magnitude. High Ga releases from zirconates with impurities show that the secondary phase containing Ga is not durable. The higher processing temperature and the apparent inability to incorporate many impurity elements suggest that zirconates are not as flexible as titanates in respect of processing conditions and aqueous durability.

Dissolution of Synthetic Brannerite at 90°C

2000 ◽  
Vol 663 ◽  
Author(s):  
Y. Zhang ◽  
K.P. Hart ◽  
B.S. Thomas ◽  
Z. Aly ◽  
H. Li ◽  
...  
Keyword(s):  
Surface Layer ◽  
Deionized Water ◽  
Minor Phase ◽  
Release Rates ◽  
Static Tests ◽  
Surface Alteration ◽  
Order Of Magnitude ◽  
Synthetic Groundwater ◽  
A Minor ◽  
Titanate Ceramic

ABSTRACTBrannerite, as a minor phase, exists in the pyrochlore-rich titanate ceramic formulations designed for immobilization of surplus weapons Pu. The dissolution of synthetic brannerite was studied at 90°C using static tests in pH 4 solution, deionized water and Finnsjön synthetic groundwater.After 140 days the normalized U release rates into a pH 4 solution and deionized water reach similar values, ~10−2 g m−2 d−1, and are about 2 orders of magnitude higher than those in Finnsjön synthetic groundwater. The normalized Ti release rate into Finnsjön synthetic groundwater is about an order of magnitude higher than those in pH 4 solution and deionized water. The dissolution of brannerite is incongruent in the pH 4 solution and deionized water (preferential release of U over Ti), and nearly congruent in Finnsjön synthetic groundwater. SEM observations of the samples after 140 days in pH 4 solution and deionized water revealed minor surface alteration, in the form of a thin surface layer, probably TiO2, as a result of preferential releases of U in both cases.

Waste Glass Leaching: Chemistry and Kinetics

1986 ◽  
Vol 84 ◽  
Author(s):  
Bruce C. Bunker
Keyword(s):  
Release Kinetics ◽  
Glass Structure ◽  
Waste Glass ◽  
Release Rates ◽  
Glass Dissolution ◽  
Surface Alteration ◽  
Order Of Magnitude ◽  
Level Of Understanding ◽  
Radionuclide Release ◽  
Glass Leaching

AbstractNuclear waste glass leaching has been studied extensively during the past ten years. Although much has been learned concerning the kinetics and mechanisms of glass dissolution, it does not appear that accurate predictions can yet be made concerning the release kinetics for specific elements from a given glass as a function of environmental conditions. In order to reliably predict elemental release rates, one needs to know: 1) how a given element is incorporated into the glass structure, 2) how specific sites in the glass react with water, 3) how the composition and reactivity of the leachate influence glass reactivity, 4) how the structure and reactivity of the glass changes in surface alteration layers, and 5) how glass dissolution modifies the chemistry of the leachate. At our current level of understanding, we are only able to make qualitative predictions concerning each of the above factors which allow us to make “order of magnitude” or “upper limit” predictions for radionuclide release rates.

Leaching Behaviour of Zirconolite in 0.001M Citric Acid at 90°C Under Various Flow Regimes

2006 ◽  
Vol 932 ◽  
Author(s):  
Peter J. McGlinn ◽  
Thierry Advocat ◽  
Gilles Leturcq ◽  
Terry I. McLeod ◽  
Zaynab Aly ◽  
...  
Keyword(s):  
Citric Acid ◽  
Flow Rate ◽  
Solubility Limit ◽  
Complexing Agents ◽  
Significant Finding ◽  
Citric Acid Concentration ◽  
Flow Rates ◽  
Order Of Magnitude ◽  
Leaching Behaviour ◽  
Parallel Tests

ABSTRACTNd-bearing zirconolite was leached at 90°C for 157 days in 0.001M citric acid under single-pass-flow-through conditions (modified MCC-4 protocol). Three different flow rates were used, ranging in an order of magnitude from 10 mL per day to 100 mL per day, to determine the effect of the rate of leachant replenishment on the durability of the zirconolite. Results of previous studies on the role of complexing agents on the leaching behaviour of single-phase zirconolite have been included in the discussion.The pH of the citric acid solution was adjusted to 5 using KOH, mimicking that of the water in the parallel tests, to avoid the influence of pH on chemical durability of the zirconolite.Simulated groundwater containing 0.001M citric acid at 90°C led to congruency in elemental releases and a diminution of release rate with time of about an order of magnitude, reaching virtual constancy after about 50 to 60 days to a level of about 10−5 g m−2 day−1. The most significant finding was that the elemental release rates of Nd, Ti and Zr (and Ca and Al where detected) were similar for all flow rates. Clearly, varying flow rate by up to an order of magnitude had no effect on elemental releases i.e. there is no solubility limit control on releases at 0.001M citric acid concentration.An important finding of previous studies using identical leaching protocols with 0.001M citric acid, and inferred in our latest investigations reported here, was that there is no secondary layer development at the surface of the zirconolite to affect leach rates. In contrast, parallel tests carried out in deionised water instead of citric acid showed that hydroxides form in situ on the zirconolite surface, effectively forming hydrolysed zirconolite. This controls further dissolution of the zirconolite matrix due to the solubility limit being reached with respect to the hydrolysed phases rather than with zirconolite. Complexation by citrate ions prevents such control by hydrolysed species on zirconolite solubility.Even under the more aggressive conditions imposed in these studies (0.001M citric acid), and regardless of flow rate of the leachant, elemental releases from zirconolite are very low for a candidate wasteform and demonstrate its attributes as a ceramic-based wasteform for the containment of actinides.

Solubility of Phosphorus in Citric Acid Solution as an Index of Biological Availability

1979 ◽  
Vol 16 (5) ◽  
pp. 290-292 ◽  
Author(s):  
Minoru YOSHIDA ◽  
Michiyuki ISHIKAWA ◽  
Hiroki NAKAJIMA ◽  
Saburo HOTTA
Keyword(s):  
Citric Acid ◽  
Acid Solution ◽  
Biological Availability ◽  
Citric Acid Solution

Effect of Processing and Drying on Quality Evaluation of Ready-To-Cook Jackfruit

2021 ◽  
Vol 7 (2) ◽  
pp. 19-29
Author(s):  
Md. Hafizul Haque Khan ◽  
◽  
Mohammad Mainuddin Molla ◽  
Ashfak Ahmed Sabuz ◽  
Md. Golam Ferdous Chowdhury ◽  
...  
Keyword(s):  
Citric Acid ◽  
Nutritional Quality ◽  
Sensory Quality ◽  
Quality Evaluation ◽  
Antioxidant Activities ◽  
Physicochemical Characteristics ◽  
Quality Attributes ◽  
Citric Acid Solution ◽  
Sensory Score ◽  
Low Potassium

The study was conducted with the aim of processing and developing ready to cook jackfruit to evaluate their nutritional and sensory quality attributes. In this study, green tender jack fruits were harvested from 60 to 70 days after synthesis. Then the fruits were washed, peeled and cut into slices. The slices were treated by dipping into different solutions for each treatments viz. control (T1), 0.5% salt solution (T2), 0.2% citric acid solution (T3), 1000 ppm potassium metabisulfite (KMS) (T4), 1000 ppm KMS + 0.5% salt (T5), 1000 ppm KMS + 0.2% citric acid (T6), 0.5% salt + 0.2% citric acid (T7) and 1000 ppm KMS+ 0.2% citric acid+ 0.5% salt (T8). Then the treated sliced was steam blanched at 85°C temperature for 8 min. The roasted beef spices were mixed and then dried at 50°C, 60°C and 70°C temperature owing to preparation of ready to cook. Results revealed that ready to cook dried at 50°C, 60°C and 70°C temperature took 72 hrs, 48 hrs and 36 hrs respectively. Low potassium metabisulfite residue was observed with increasing blanching time and drying temperature. The physicochemical characteristics, phytochemical and antioxidant activities were retained more and the highest sensory score was obtained at 60°C temperature. The marketable life of the RTC jackfruit could be extended to more than 6 months. However, the findings suggest that green tender jackfruit treated with 1000 ppm KMS, blanched for 8 min and dried at 60°C is a quick and healthy option in terms of good marketable life, nutritional and sensory quality attributes. Keywords:Tender jackfruit, ready to cook, nutritional quality, sensory attributes, marketable life

Effect of Cu-Excess on the Microstructure and Microwave Dielectric Properties of CaCu3Ti4O12 Ceramics

2015 ◽  
Vol 1087 ◽  
pp. 50-54 ◽  
Author(s):  
Mohamad Johari Abu ◽  
Julie Juliewatty Mohamed ◽  
Mohd Fadzil Ain ◽  
Zainal Arifin Ahmad
Keyword(s):  
Dielectric Constant ◽  
Microwave Dielectric Properties ◽  
Secondary Phase ◽  
Solid State Reaction Method ◽  
Lattice Parameter ◽  
Tangent Loss ◽  
Conventional Solid State Reaction ◽  
Microwave Dielectric ◽  
Order Of Magnitude ◽  
Grain Growth Behavior

CaCu(3+x)Ti4O12 (CCTO) ceramics with different Cu-excess (x = 0 – 0.6) were prepared by conventional solid-state reaction method. Characterization of the prepared ceramics with XRD and FESEM showed that lattice parameter and grain size are slightly increased, indicating Cu-excess to have the big impact on the both phase structure and microstructure. The XRD profiles indicated that the secondary phase (CuO or Cu2O) existed at edge/corner of CCTO grain, which promoted inhibited grain growth behavior. The CCTO ceramics exhibited two trends of dielectric constant related to frequency, which showed a flatter curve about ~50 in 1 – 25 GHz regions, and it’s dropped rapidly to ~35 in 25 – 50 GHz region. With Cu-excess, the dielectric constant of the ceramics was increased for an average of a quarter-order of magnitude, while the tangent loss also increased up to triple times than x = 0, for the same frequency range. Despite enormous increase of dielectric constant related to varying Cu-excess, the tangent loss also increased.

scholarly journals Сitric acid influence on electroreduction processes in low concentrated Cu(NO3)2 solutions

2017 ◽  
Vol 5 (2) ◽  
pp. 136-143
Author(s):  
Alla Pravda ◽  
Vasil Larin
Keyword(s):  
Citric Acid ◽  
Ph Value ◽  
Reduction Reaction ◽  
Copper Electrodeposition ◽  
Nitrate Ions ◽  
Low Concentrations ◽  
Physico Chemical ◽  
Influence Of Ph ◽  
Kinetics Of ◽  
Cathode Reduction

Physico-chemical regularities citric acid influence on processes of copper and nitrate-ions reduction in low concentrated nitrate solutions were established. An influence of pH value on inhibitor action of low concentrations of the additive according to cathode reduction reaction of nitrate-ions, on kinetics of copper electrodeposition, on structure of the precipitates obtained was shown. Polarization measurements show us changes of copper electrodeposition at introduction of citric acid in Cu(NO3)2 solution. By the methods of traced elements and extraction into aqueous phase the reversible inclusion complexes into electrolytic copper, was established that proves participation of complexes in cathode process.

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