Quantification of kinetic rate law parameters of uranium release from sodium autunite as a function of aqueous bicarbonate concentrations

2013 ◽  
Vol 10 (6) ◽  
pp. 475 ◽  
Author(s):  
Ravi Gudavalli ◽  
Yelena Katsenovich ◽  
Dawn Wellman ◽  
Leonel Lagos ◽  
Berrin Tansel
Keyword(s):  
Dissolution Kinetics ◽  
Fold Increase ◽  
Activation Energies ◽  
Complexing Agent ◽  
Dissolution Mechanism ◽  
Rate Law ◽  
Ph Conditions ◽  
Bicarbonate Solutions ◽  
Ph Range ◽  
Relationship Of

Environmental context Uranium is a key contaminant of concern because of its high persistence in the environment and toxicity to organisms. The bicarbonate ion is an important complexing agent for uranyl ions and one of the main variables affecting its dissolution. Results from this investigation provide rate law parameters for the dissolution kinetics of synthetic sodium autunite that can influence uranium mobility in the subsurface. Abstract Hydrogen carbonate (also known as bicarbonate) is one of the most significant components within the uranium geochemical cycle. In aqueous solutions, bicarbonate forms strong complexes with uranium. As such, aqueous bicarbonate may significantly increase the rate of uranium release from uranium minerals. Quantifying the relationship of aqueous bicarbonate solutions to the rate of uranium release during dissolution is critical to understanding the long-term fate of uranium within the environment. Single-pass flow-through experiments were conducted to estimate the rate of uranium release from Na meta-autunite as a function of bicarbonate solutions (0.0005–0.003M) over the pH range of 6–11 and temperatures of 5–60°C. Consistent with the results of previous investigations, the rate of uranium release from sodium autunite exhibited minimal dependency on temperature, but was strongly dependent on pH and increasing concentrations of bicarbonate solutions. Most notably at pH 7, the rate of uranium release exhibited a 370-fold increase relative to the rate of uranium release in the absence of bicarbonate. However, the effect of increasing concentrations of bicarbonate solutions on the release of uranium was significantly less under higher pH conditions. It is postulated that at high pH values, surface sites are saturated with carbonate, thus the addition of more bicarbonate would have less effect on uranium release. Results indicate that the activation energies were unaffected by temperature and bicarbonate concentration variations, but were strongly dependent on pH conditions. As the pH increased from 6 to 11, the activation energy values were observed to decrease from 29.94 to 13.07kJmol–1. The calculated activation energies suggest a surface controlled dissolution mechanism.

Dissolution of organic solvents from painted surfaces into water

2000 ◽  
Vol 78 (4) ◽  
pp. 464-473 ◽  
Author(s):  
J C Wren ◽  
D J Jobe ◽  
G G Sanipelli ◽  
J M Ball
Keyword(s):  
Organic Compounds ◽  
Organic Solvents ◽  
Nuclear Reactor ◽  
Dissolution Kinetics ◽  
Activation Energies ◽  
Dissolution Mechanism ◽  
Rate Determining Step ◽  
Organic Impurities ◽  
Accident Conditions ◽  
Reactor Accidents

The presence of volatile iodine in containment buildings is one of the major safety concerns in the potential event of nuclear reactor accidents. Organic impurities in containment water, originating from various painted structural surfaces and organic materials, could have a significant impact on iodine volatility following an accident. To determine the source and magnitude of organic impurities and their effects on time-dependent iodine volatility, the dissolution for organic constituents from paints used in reactor buildings has been studied under postulated accident conditions. The studies of the organic dissolution from carbon steel coupons coated with zinc-primed vinyl, epoxy-primed polyurethane or epoxy paints over the temperature range 25-90°C are reported. Relatively large activation energies were measured for the release of the principal organic compounds from painted surfaces, suggesting it is the release of the solvents from the paint matrix rather than their diffusion through the solution that is the rate determining step for the dissolution mechanism. The similarities in the values of activation energies for the dissolution of different organic compounds from the paints suggest the release rate is independent of the nature of the painted surface or the type of organic being released from the surface. These two observations indicate that it may be possible to write a generalized rate expression for the release of organic compounds from painted surfaces in containment following an accident. The possible implications of these results for predicting iodine volatility in containment are also discussed.Key words: dissolution kinetics, organic solvents, painted surfaces, reactor accidents.

Kinetics of oxidation of thiocyanate by aqueous iodine

1973 ◽  
Vol 26 (9) ◽  
pp. 1863 ◽  
Author(s):  
GT Briot ◽  
RH Smith
Keyword(s):  
Rate Constants ◽  
Activation Energies ◽  
Stopped Flow ◽  
Kinetics Of Oxidation ◽  
Rate Law ◽  
General Base ◽  
Present Rate ◽  
Rapid Equilibrium ◽  
Ph Range ◽  
Kinetics Of

The kinetics of oxidation of thiocyanate to sulphate by aqueous iodine in the pH range 9.2-12.5 have been studied using a spectrophotometric stopped flow technique. The reaction is general base-catalysed, having the rate law ��������������������� -d[I2]a/dt = ([SCN-][I3-]/[I-]2)Σ kB[B] where [I2]a is the total analytical concentration of iodine, [B] is the concentration of base, and where the summation is taken over all bases present. Rate constants, kB, and activation energies have been measured for the bases, OH-, PO43- and CO32-. ��� A mechanism involving the initial steps ����������������� I2+SCN- ↔ ISCN+I- �����������������(rapid equilibrium) ������������� ISCN+H2O+B → HOSCN+I- + HB+ �����������(rate determining) followed by rapid reactions of HOSCN with itself or with iodine is proposed.

The dissolution of calcite at pH > 7: kinetics and mechanism

1990 ◽  
Vol 330 (1609) ◽  
pp. 47-70 ◽  
Keyword(s):  
Calcium Carbonate ◽  
Solubility Product ◽  
Dissolution Kinetics ◽  
Theoretical Modelling ◽  
Normal Rate ◽  
Bulk Solution ◽  
Rate Law ◽  
Rate Laws ◽  
Ph Conditions ◽  
Kinetics Of

A technique is described that allows an assessment of the various candidate rate laws that have been proposed to predict the dissolution kinetics of calcite under high pH conditions. A combination of theoretical modelling and experimentation allows us to choose the following rate law as that which best fits the observed data: rate ( mol c m − 2 s − 1 ) = k − k ′ [ C a 2 + ] s [ CO 3 2 − ] s ′ , where k ′ = k / K sp and K sp is the solubility product of calcium carbonate. The modelling developed differs from previous studies in that it deals in terms of surface concentrations of reactants, [ Ca 2 + ] s and [ CO 3 2 − ] , as opposed to those present in bulk solution.

scholarly journals Biochar Volatile Matter and Feedstock Effects on Soil Nitrogen Mineralization and Soil Fungal Colonization

2021 ◽  
Vol 13 (4) ◽  
pp. 2018
Author(s):  
Tai McClellan Maaz ◽  
William C. Hockaday ◽  
Jonathan L. Deenik
Keyword(s):  
Hydrolytic Enzyme ◽  
Fold Increase ◽  
Volatile Matter ◽  
Fungal Colonization ◽  
Nitrogen Transformations ◽  
Production Methods ◽  
Carbon And Nitrogen ◽  
13C Nuclear Magnetic Resonance ◽  
Carbon And Nitrogen Dynamics ◽  
Relationship Of

Biochar has important biogeochemical functions in soil—first as a means to sequester carbon, and second as a soil conditioner to potentially enhance soil quality and fertility. Volatile matter (VM) content is a property of biochar that describes its degree of thermal alteration, which can have a direct influence on carbon and nitrogen dynamics in soil. In this study, we characterized the VM in biochars derived from two locally sourced feedstocks (corncob and kiawe wood) and evaluated the relationship of VM content to nitrogen transformations and culturable fungal biomass. Using 13C nuclear magnetic resonance (NMR) spectroscopy, we found that the VM content of biochar primarily consisted of alkyl (5.1–10.1%), oxygen-substituted alkyl (2.2–6.7%), and phenolic carbon (9.4–11.6%). In a series of laboratory incubations, we demonstrated that corncob biochars with high VM (23%) content provide a source of bioavailable carbon that appeared to support enhanced viable, culturable fungi (up to 8 fold increase) and cause nitrogen immobilization in the short-term. Corncob biochar with bioavailable VM was nitrogen-limited, and the addition of nitrogen fertilizer resulted in a four-fold increase in total hydrolytic enzyme activity and the abundance of culturable fungal colonies. In contrast, kiawe biochar with an equivalent VM content differed substantially in its composition and effect on these same biological parameters. Therefore, the rapid measurement of VM content is too coarse to differentiate chemical composition and to predict the behavior of biochars across feedstocks and production methods.

Analysis of Whey Proteins Solubility at High Temperatures

2012 ◽  
Vol 8 (3) ◽  
Author(s):  
Daniela Helena Guimarães Pelegrine ◽  
Maria Thereza Moraes Santos Gomes
Keyword(s):  
Heat Exchangers ◽  
Protein Unfolding ◽  
Protein Solubility ◽  
Whey Proteins ◽  
Protein Isolate ◽  
Cow Milk ◽  
Ph Conditions ◽  
Effects Of Temperature ◽  
Ph Range ◽  
Integrated Study

Abstract This work showed the whey proteins solubility curves, according with temperature and pH conditions. The product constituted of a whey protein isolate obtained from cow milk (ALACENTM 895), acquired by New Zeland Milk Products Ltd. There is a straight analogy between fouling and protein unfolding when milk derived fluids are processed in equipments of heat exchangers, where whey proteins are unfolded in an irreversible way, exposing hidrophobic groups, and they become insoluble and form aggregates. An integrated study was conducted on the effects of temperature and pH on the solubility of whey proteins. The solubility was determined experimentally in the temperature range of 40-90 °C, and pH range of 5.0 - 6.8. The results showed that, both the temperature and pH influenced in the protein solubility; besides, the solubility values were minimum at the pH 4.0 for all temperature values. It was also observed that solubility decreased with temperature increased.

Isolated flagellar apparatus of Chlamydomonas: characterization of forward swimming and alteration of waveform and reversal of motion by calcium ions in vitro

1978 ◽  
Vol 33 (1) ◽  
pp. 235-253 ◽  
Author(s):  
J.S. Hyams ◽  
G.G. Borisy
Keyword(s):  
Calcium Ions ◽  
Beat Frequency ◽  
Flagellar Apparatus ◽  
Adenosine Monophosphate ◽  
Adenosine Diphosphate ◽  
Living Cells ◽  
Exogenous Calcium ◽  
Ph Range ◽  
Relationship Of

The control of flagellar activity in the biflagellate green alga, Chlamydomonas reinhardtii was investigated by the in vitro reactivation of the isolated flagellar apparatus (the 2 flagella attached to their respective basal bodies plus accessory structures). The waveform and beat frequency of the isolated apparatus in the presence of 1 mM adenosine triphophate (ATP) were comparable to those recorded for living cells. Equimolar concentrations of adenosine diphosphate (ADP) could be substituted for ATP with little change in beat frequency and no apparent change in waveform, suggesting that the latter is converted to ATP by axonemal adenylate kinase. No reactivation occurred in adenosine monophosphate (AMP). But frequencies in cytidine, guanosine and uridine triphosphates (CTP, GTP and UTP) were approximately 10% that obtained in ATP. Reactivation was optimal over a broad pH range between pH 6.4 and pH 8.9 in both APT and ADP. Isolated flagellar apparatus could be induced to change from forward to reverse motion in vitro by manipulation of exogenous calcium ions. The 2 types of motion were directly comparable to recorded responses of living cells. Forward swimming occurred at levels of calcium below 10(−6)M, the isolated apparatus changing to backward motion above this level. Motility was inhibited at concentrations above 10(−3)M. The threshold for reversal of motion by calcium was lowered to 10(−7)M when the flagellar membranes were solubilized with detergent, indicating that the flagellar membranes are involved in the regulaion of the level of calcium within the axoneme. The reversal of motion by calcium was itself freely reversible. The relationship of these observations to the known tactic responses of Chlamydomonas is discussed.

scholarly journals GLYPHOSATE AND TURBIDITY REMOVAL IN WATER CONDITIONS BY CLARIFICATION WITH TANFLOC

2018 ◽  
Vol 15 (30) ◽  
pp. 489-497
Author(s):  
J. T. B. SILVA ◽  
K. C. ROCHA ◽  
R. M. F. CUBA
Keyword(s):  
Turbidity Removal ◽  
Natural Coagulant ◽  
Agriculture Sector ◽  
Jar Test ◽  
Low Concentrations ◽  
Water Conditions ◽  
Ph Conditions ◽  
Percentage Removal ◽  
Ph Range ◽  
Herbicide Glyphosate

With the progress in the agriculture sector, improper domains of pesticides, herbicides, and insecticides have grown, which have been negatively affected the environment until the present day. Therefore, the present work has as objective to evaluate the efficiency of the natural coagulant Tanfloc in the clarification stage with respect the herbicide glyphosate removal and the turbidity parameter by using jar test with different pH conditions and coagulant concentration. As a result, was obtained that for the pH range of 5-5.5 the natural coagulant has shown more efficient, with a glyphosate percentage removal of approximately 98.0% using low concentrations and turbidity removal of 21.69%. On the other hand, for the pH range of 6.8 to 7.3, the coagulant has not shown profitable results, considering that, for some concentrations, it was not possible to detect the herbicide removal. In the concentrations that were detected removal, the average glyphosate percentage removal was approximately 89% and an average of 20.24% of turbidity removal. In summary, although the natural coagulant has not shown remarkably efficient in the neutral pH range, the product may be considered an alternative device in water treatment with the respect of the use of metallic coagulants, which produce sludge with chemistry characteristics that may negatively affect the environment.

scholarly journals Introducing a Thermo-Alkali-Stable, Metallic Ion-Tolerant Laccase Purified From White Rot Fungus Trametes hirsuta

2021 ◽  
Vol 12 ◽  
Author(s):  
Jing Si ◽  
Hongfei Ma ◽  
Yongjia Cao ◽  
Baokai Cui ◽  
Yucheng Dai
Keyword(s):  
Specific Activity ◽  
Endocrine Disrupting Chemicals ◽  
Environmental Pollutants ◽  
Fold Increase ◽  
Industrial Applications ◽  
White Rot ◽  
White Rot Fungus ◽  
Metallic Ions ◽  
Trametes Hirsuta ◽  
Ph Range

This study introduces a valuable laccase, designated ThLacc-S, purified from white rot fungus Trametes hirsuta. ThLacc-S is a monomeric protein in nature with a molecular weight of 57.0 kDa and can efficiently metabolize endocrine disrupting chemicals. The enzyme was successfully purified to homogeneity via three consecutive steps consisting of salt precipitation and column chromatography, resulting in a 20.76-fold increase in purity and 46.79% yield, with specific activity of 22.111 U/mg protein. ThLacc-S was deciphered as a novel member of the laccase family and is a rare metalloenzyme that contains cysteine, serine, histidine, and tyrosine residues in its catalytic site, and follows Michaelis-Menten kinetic behavior with a Km and a kcat/Km of 87.466 μM and 1.479 s–1μM–1, respectively. ThLacc-S exerted excellent thermo-alkali stability, since it was markedly active after a 2-h incubation at temperatures ranging from 20 to 70°C and retained more than 50% of its activity after incubation for 72 h in a broad pH range of 5.0–10.0. Enzymatic activities of ThLacc-S were enhanced and preserved when exposed to metallic ions, surfactants, and organic solvents, rendering this novel enzyme of interest as a green catalyst for versatile biotechnological and industrial applications that require these singularities of laccases, particularly biodegradation and bioremediation of environmental pollutants.

Triiodothyronine (T3), inflammation and mortality risk in patients with acute myocardial infarction

2022 ◽  
Author(s):  
Salman Razvi ◽  
Avais Jabbar ◽  
Arjola Bano ◽  
Lorna Ingoe ◽  
Peter Carey ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Acute Myocardial Infarction ◽  
Confidence Interval ◽  
Mortality Risk ◽  
Fold Increase ◽  
Lower Serum ◽  
Reactive Protein ◽  
All Cause Mortality ◽  
Relationship Of ◽  
The Relationship

Objectives: To study the relationship between serum free T3 (FT3), C-reactive protein (CRP), and all-cause mortality in patients with acute myocardial infarction (AMI). Design: Prospective multicentre longitudinal cohort study. Methods: Between December 2014 and December 2016, thyroid function and CRP were analysed in AMI (both ST- and non-ST-elevation) patients from the ThyrAMI-1 study. The relationship of FT3 and CRP at baseline with all-cause mortality up to June 2020 was assessed. Mediation analysis was performed to evaluate if CRP mediated the relationship between FT3 and mortality. Results: In 1919 AMI patients [29.2% women, mean (SD) age 64.2 (12.1) years and 48.7% STEMI] followed over a median (inter-quartile range) period of 51 (46 to 58) months, there were 277 (14.4%) deaths. Overall, lower serum FT3 and higher CRP levels were associated with higher risk of mortality. When divided into tertiles based on levels of FT3 and CRP, the group with the lowest FT3 and highest CRP levels had 2.5-fold increase in mortality risk [adjusted hazard ratio (95% confidence interval) of 2.48 (1.82 to 3.16)] compared to the group with the highest FT3 and lowest CRP values. CRP mediated 9.8% (95% confidence interval 6.1 to 15.0%) of the relationship between FT3 and mortality. Conclusions: In AMI patients, lower serum FT3 levels on admission are associated with a higher mortality risk, which is partly mediated by inflammation. Adequately designed trials to explore potential benefits of T3 in AMI patients are required.

scholarly journals pH and Phosphate Induced Shifts in Carbon Flow and Microbial Community during Thermophilic Anaerobic Digestion

2020 ◽  
Vol 8 (2) ◽  
pp. 286
Author(s):  
Nina Lackner ◽  
Andreas O. Wagner ◽  
Rudolf Markt ◽  
Paul Illmer
Keyword(s):  
Microbial Community ◽  
Microbial Community Composition ◽  
Amplicon Sequencing ◽  
Carbon Flow ◽  
Rrna Gene ◽  
Organic Substrates ◽  
Ch4 Production ◽  
Ph Conditions ◽  
Ph Range ◽  
In The Beginning

pH is a central environmental factor influencing CH4 production from organic substrates, as every member of the complex microbial community has specific pH requirements. Here, we show how varying pH conditions (5.0–8.5, phosphate buffered) and the application of a phosphate buffer per se induce shifts in the microbial community composition and the carbon flow during nine weeks of thermophilic batch digestion. Beside monitoring the methane production as well as volatile fatty acid concentrations, amplicon sequencing of the 16S rRNA gene was conducted. The presence of 100 mM phosphate resulted in reduced CH4 production during the initial phase of the incubation, which was characterized by a shift in the dominant methanogenic genera from a mixed Methanosarcina and Methanoculleus to a pure Methanoculleus system. In buffered samples, acetate strongly accumulated in the beginning of the batch digestion and subsequently served as a substrate for methanogens. Methanogenesis was permanently inhibited at pH values ≤5.5, with the maximum CH4 production occurring at pH 7.5. Adaptations of the microbial community to the pH variations included shifts in the archaeal and bacterial composition, as less competitive organisms with a broad pH range were able to occupy metabolic niches at unfavorable pH conditions.

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