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 A New Rate Law Describing Microbial Respiration

2003 ◽  
Vol 69 (4) ◽  
pp. 2340-2348 ◽  
Author(s):  
Qusheng Jin ◽  
Craig M. Bethke
Keyword(s):  
Respiration Rate ◽  
Microbial Respiration ◽  
Biomass Concentration ◽  
Rate Law ◽  
Monod Equation ◽  
Rate Laws ◽  
General Law ◽  
Threshold Phenomena ◽  
Transport Chain ◽  
Kinetics Of

ABSTRACT The rate of microbial respiration can be described by a rate law that gives the respiration rate as the product of a rate constant, biomass concentration, and three terms: one describing the kinetics of the electron-donating reaction, one for the kinetics of the electron-accepting reaction, and a thermodynamic term accounting for the energy available in the microbe's environment. The rate law, derived on the basis of chemiosmotic theory and nonlinear thermodynamics, is unique in that it accounts for both forward and reverse fluxes through the electron transport chain. Our analysis demonstrates how a microbe's respiration rate depends on the thermodynamic driving force, i.e., the net difference between the energy available from the environment and energy conserved as ATP. The rate laws commonly applied in microbiology, such as the Monod equation, are specific simplifications of the general law presented. The new rate law is significant because it affords the possibility of extrapolating in a rigorous manner from laboratory experiment to a broad range of natural conditions, including microbial growth where only limited energy is available. The rate law also provides a new explanation of threshold phenomena, which may reflect a thermodynamic equilibrium where the energy released by electron transfer balances that conserved by ADP phosphorylation.

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 kinetics of calcium carbonate in equatorial Pacific sediments

1994 ◽  
Vol 8 (2) ◽  
pp. 219-235 ◽  
Author(s):  
William M. Berelson ◽  
Douglas E. Hammond ◽  
James McManus ◽  
Tammy E. Kilgore
Keyword(s):  
Calcium Carbonate ◽  
Dissolution Kinetics ◽  
Equatorial Pacific ◽  
Kinetics Of

Kinetics of oxidation of nitrite by aqueous bromine

1973 ◽  
Vol 26 (9) ◽  
pp. 1847 ◽  
Author(s):  
JN Pendlebury ◽  
RH Smith
Keyword(s):  
Perchloric Acid ◽  
Acetate Buffer ◽  
Stopped Flow ◽  
Kinetics Of Oxidation ◽  
Rate Law ◽  
Rate Laws ◽  
Temperature Dependences ◽  
Ph Range ◽  
Kinetics Of

The kinetics of oxidation of nitrite to nitrate by aqueous bromine have been investigated using a spectrophotometric stopped flow technique. In the pH range 4.2-5.8 (acetate buffer) the rate law is: - d[Br21,/dt = [Br21[N02 -I2 (a + b/[Br-1) (where [Br,], = [Br2]+[Br,-1) with a = (4.61-0-1) x lo4 l2 m01-~ s-l and b = (3.3 1-0.1) x lo4 1. mol-l s-l at 298.2 K and with the temperature dependences, - R d(lna)/d(l/T) = (46k 4) kJ mol-l and - R d(ln b)/d(l/T) = (45 k 2) kJ mol-'. In the pH range 0.8-2.5 (perchloric acid) the rate law is : - d[Br2],/dt = [HN0212[Br21 (w + v/[Br-l)/(l+ z[H+ItBr,l,) with w = (5.9+0.2)x lo4 l2 m01-~ s-l, v = (3.41-0.1)~ lo4 1, mol-l s-I, and z = (1.90i 0.06) x lo7 l2 mol-2 at 298.2 K. In addition: - R d ln(w/z)/d(l/T) = (31 1 4 ) kJ mol-I and - R d ln(v/z)/d(l/T) = (46 f 4) kJ mol-l In the pH range 2.8-3.3 (chloroacetate buffer) a combination of these two rate laws adequately describes the kinetic results. These rate laws have been interpreted in terms of two reversible initial reactions: 6) NO2- +Br2 + N02Br +Br- (followed by attack on N02Br by NO2-) (ii) NO2-+NO2- (or HNOJ + N204'- (or HN204-) (followed by attack by Br2 upon N204'- or HNZO4- or upon N203 formed from HN204-).

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