Smectite Dissolution Kinetics in High-Alkaline Conditions

2003 ◽  
Vol 807 ◽  
Author(s):  
Hiroshi Ohmoto ◽  
Kathryn R. Spangler ◽  
Yumiko Watanabe ◽  
Gento Kamei
Keyword(s):  
Dissolution Kinetics ◽  
Silica Content ◽  
Alkaline Solutions ◽  
Initial Silica ◽  
Alkaline Conditions ◽  
Short And Long Term ◽  
Stock Solutions ◽  
Aqueous Complexes ◽  
Kinetics Of

ABSTRACTTo determine the initial rates and effects of silica in solution on the dissolution kinetics of smectite, short- and long-term batch experiments (0.5 hour to 30 days) were completed at three temperatures (T = 25, 50, and 75°C) using stock solutions pH adjusted by NaOH (pH = 12, 13, and 13.5) with varying initial silica concentrations (0, 30, 60, and 100 ppm). The following important characteristics were observed at pH = 12: (1) The concentrations of Al, Si, Mg, Fe, and Ti in solutions increase rapidly during the first ∼2 hours and reach steady state (equilibrium) within ∼5 days. (2) The concentration ratios of Al, Si, Fe, Mg, and Ti in solutions during the early (<2 hours) reaction phase differ significantly from those of smectite, indicating initial dissolution proceeds non-stoichiometrically; Al dissolves much faster than Si, Mg, Fe, and Ti. (3) Further dissolution of smectite proceeds nearly stoichiometrically, including Fe and Ti. (4) The high solubility of Ti in highly alkaline solutions may be due to the formation of aqueous complexes, such as TiO(OH)3− and TiO2(OH)22−, similar to aqueous silica species. (5) The initial rate of smectite dissolution increases with increasing pH, T, and initial silica content of solution. (6) The silica in solution acts as a promoter and a catalyst, rather than an inhibitor, of smectite dissolution in high-alkaline solutions. This role is easily recognizable when the solubility of smectite and amorphous silica are very high, i.e., at pH >∼9.

Dissolution kinetics of meta-torbernite under circum-neutral to alkaline conditions

2009 ◽  
Vol 6 (6) ◽  
pp. 551 ◽  
Author(s):  
Dawn M. Wellman ◽  
Bruce K. McNamara ◽  
Diana H. Bacon ◽  
Elsa A. Cordova ◽  
Ruby M. Ermi ◽  
...  
Keyword(s):  
Dissolution Kinetics ◽  
Coupled Processes ◽  
Effect Of Temperature ◽  
Subsurface Environments ◽  
Alkaline Conditions ◽  
Flow Through ◽  
Uranium Phosphate ◽  
The Stability ◽  
Kinetics Of

Environmental context. Uranium-phosphate minerals have been identified as a long-term controlling phase that limit the mobility of uranium to groundwater in many contaminated subsurface environments. Complex, coupled processes confound the ability to isolate the rates attributed to individual processes. Results of this investigation provide the necessary information to refine current prediction on the release and long-term fate of uranium in subsurface environments. Abstract. The purpose of this investigation was to conduct a series of single-pass flow-through (SPFT) tests to (1) quantify the effect of temperature (23–90°C) and pH (6–10) on meta-torbernite dissolution; (2) compare the dissolution of meta-torbernite to other autunite-group minerals; and (3) evaluate the effect of aqueous phosphate on the dissolution kinetics of meta-torbernite. Results presented here illustrate meta-torbernite dissolution rates increase by ~100× over the pH interval of 6 to 10, irrespective of temperature. The power law coefficient for meta-torbernite, η = 0.59 ± 0.07, is greater than that quantified for Ca-meta-autunite, η = 0.42 ± 0.12. This suggests the stability of meta-torbernite is greater than that of meta-autunite, which is reflected in the predicted stability constants. The rate equation for the dissolution of meta-torbernite as a function of aqueous phosphate concentration is log rdissol (mol m–2 s–1) = –4.7 × 10–13 + 4.1 × 10–10[PO43–].

Effects of Environmental Factors on Exercise in Fish

1991 ◽  
Vol 160 (1) ◽  
pp. 113-126 ◽  
Author(s):  
DAVID RANDALL ◽  
COLIN BRAUNER
Keyword(s):  
Swimming Velocity ◽  
Functional Requirements ◽  
Muscle Contractility ◽  
Oxygen Transport Capacity ◽  
Wide Range ◽  
Alkaline Conditions ◽  
External Conditions ◽  
Critical Swimming Velocity ◽  
Short And Long Term

The critical swimming velocity of fish is affected by environmental conditions and the highest swimming speed is obtained only under specific circumstances. The mechanisms causing a reduction in exercise capacity depend on the type of environmental change. Acid waters exert an effect by reducing oxygen transport capacity, whereas reduced temperatures act largely on muscle contractility. Alkaline conditions and salinity change may affect both gas transport and muscle contractility. A fish must operate over a wide range of internal and external conditions and must possess both short- and long-term mechanisms to maintain function under a wide variety of conditions. These mechanisms may be part of the immediate reflex arsenal available to the fish (for example, catecholamine release) or they may be mechanisms induced during acclimation. The nature of the acclimation process is an indication of what may be limiting exercise under a particular set of circumstances. The concept of symmorphosis, especially when applied to ectotherms, needs to be viewed in a broader context. A symmetry of component parts may exist such that structures are designed to satisfy functional requirements for operation over a wide range of conditions, rather than optimally for a given set of conditions. This must involve compromises in design, especially for ectotherms such as fish. Thus, the more variable the conditions under which a system must operate, the less apparent it will be that symmorphosis exists between the component parts.

Dissolution kinetics of synthetic LaPO4-monazite in acidic media

MRS Advances ◽  
2018 ◽  
Vol 3 (21) ◽  
pp. 1133-1137 ◽  
Author(s):  
Yulia Arinicheva ◽  
Stefan Neumeier ◽  
Felix Brandt ◽  
Dirk Bosbach ◽  
Guido Deissmann
Keyword(s):  
Single Phase ◽  
Dissolution Kinetics ◽  
Dissolution Process ◽  
Temperature Range ◽  
Long Term Stability ◽  
Aqueous Environments ◽  
Fundamental Understanding ◽  
Acidic Conditions ◽  
Kinetics Of

Single-phase monazite-type ceramics are discussed as waste forms for the safe disposal of surplus plutonium or separated minor actinides. To derive a fundamental understanding of the long-term stability of these materials under repository relevant conditions, the dissolution kinetics of synthetic lanthanum monazite (LaPO4) were studied in dynamic dissolution experiments in the temperature range from 50 to 90°C under acidic conditions. The surface area normalised dissolution rates increased with temperature from 3.2·10-5 g m-2 d-1 at 50°C to 1.8·10-4 g m-2 d-1 at 90°C. The apparent activation energy Ea of the dissolution process was determined to be about 44 kJ mol-1, indicating a predominantly surface reaction controlled dissolution process in this temperature range. From thermodynamic considerations it can be inferred that the dissolution of the LaPO4 ceramics is governed by the dissolution of a thin layer of La-rhabdophane (LaPO4 · 0.667H2O) forming at the monazite surface in low temperature aqueous environments.

Alterations in the Effects of Warfarin in Dogs by Halofenate

1975 ◽  
Vol 34 (02) ◽  
pp. 445-545 ◽  
Author(s):  
Michael Weintraub ◽  
Paul F Griner
Keyword(s):  
Combined Therapy ◽  
Lipid Lowering ◽  
Concomitant Increase ◽  
Factor Ii ◽  
Long Term Experiments ◽  
Short And Long Term ◽  
The Mean ◽  
Lipid Lowering Agent ◽  
Kinetics Of

SummaryThe interaction between warfarin and the new lipid lowering agent halofenate (MK 185) [2 - acetamidoethyl (p-chlorophenyl) (m-trifluoromethylphenoxy) acetate] was studied in dogs in both short- and long-term experiments. Our data suggest that halofenate potentiates the anticoagulant effect of warfarin by increasing the degradation of prothrombin (factor II) (Kdeg on placebo = 211 ± 32 × 10−4 × Hr−1 mean ± SEM; on halofenate = 268 ± 39 × 10−4 × Hr−1 mean ± SEM; P < 0.01). However, a concomitant increase in factor II synthesis of 34% results in resistance to warfarin’s effect if halofenate is administered prior to warfarin. The mean prothrombin time of 4 dogs on 2 mg of warfarin following halofenate pretreatment for 8 weeks was 74.8% ± 17.3 (SE) of the anticoagulated control dog. On 2 mg of warfarin alone, it was 133.7% ± 42.0 (P < 0.001). Cessation of halofenate from combined therapy results in a delayed augmentation of warfarin effect. These data suggest that the nature of the interaction between warfarin and drugs such as halofenate which alter the kinetics of prothrombin may depend on the sequence of administration.

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