A Microkinetic Model of Calcite Step Growth Andersson, M. P.; Dobberschütz, S.; Sand, K. K. ...
Angewandte Chemie (International ed.),
September 5, 2016, Letnik:
55, Številka:
37
Journal Article
Recenzirano
In spite of decades of research, mineral growth models based on ion attachment and detachment rates fail to predict behavior beyond a narrow range of conditions. Here we present a microkinetic model ...that accurately reproduces calcite growth over a very wide range of published experimental data for solution composition, saturation index, pH and impurities. We demonstrate that polynuclear complexes play a central role in mineral growth at high supersaturation and that a classical complexation model is sufficient to reproduce measured rates. Dehydration of the attaching species, not the mineral surface, is rate limiting. Density functional theory supports our conclusions. The model provides new insights into the molecular mechanisms of mineral growth that control biomineralization, mineral scaling and industrial material synthesis.
A robust model: A microkinetic model is presented that accurately reproduces calcite growth over a wide range of experimental parameters for solution composition, saturation index, pH and impurities. Polynuclear complexes play a central role at high supersaturation and a classical complexation model is sufficient to reproduce measured rates.
Citrate has been shown to inhibit CaCO3 growth and it is also found in biogenic calcite, but full understanding about how citrate controls CaCO3 formation, and hence CaCO3 polymorph stability and ...crystal morphology, is still lacking. We investigated the effect of citrate (CIT) on CaCO3 crystallization by monitoring crystallization rates and crystal polymorph, size, and morphology as a function of increasing mol % CIT/Ca (Ca2+ = CO3 2– = 4 mM). At CIT/Ca ≤ 50%, both vaterite and calcite formed, but nucleation and growth were retarded as CIT/Ca was increased, demonstrated by the increase in induction time and decrease in the reaction rate constant, fitted using the Johnson-Mehl-Avrami-Kolmogorov model. This is partly explained by increased CIT-Ca complexation with higher CIT, thus reducing saturation state with respect to vaterite and calcite. Simultaneously, CIT sorption inhibited crystal growth, demonstrated by smaller vaterite spheres and more elongated calcite crystals as CIT/Ca increased. At CIT/Ca ≥ 75%, vaterite formation was completely inhibited, with only elongated calcite forming and growth rate decreased further as CIT/Ca was increased. Overall, citrate inhibited growth rates most at CIT/Ca ≤ 50%, while nucleation was less affected. In contrast, at CIT/Ca > 50%, citrate strongly inhibited nucleation but had less effect on the growth rate. The results illustrate the spectrum of impacts that complexing compounds can have on CaCO3 crystallization, by forming complexes in solution, affecting CaCO3 saturation state, and also by interacting with the crystal surfaces, thereby controlling nucleation and growth. The extent and the type of effect depend on concentration regimes.
A range of nuclear magnetic resonance (NMR) techniques are employed to provide novel, non-invasive measurements of both the structure and transport properties of porous media following a biologically ...mediated calcite precipitation reaction. Both a model glass bead pack and a sandstone rock core were considered. Structure was probed using magnetic resonance imaging (MRI) via a combination of quantitative one-dimensional profiles and three-dimensional images, applied before and after the formation of calcite in order to characterise the spatial distribution of the precipitate. It was shown through modification and variations of the calcite precipitation treatment that differences in the calcite fill would occur but all methods were successful in partially blocking the different porous media. Precipitation was seen to occur predominantly at the inlet of the bead pack, whereas precipitation occurred almost uniformly along the sandstone core. Transport properties are quantified using pulse field gradient (PFG) NMR measurements which provide probability distributions of molecular displacement over a set observation time (propagators), supplementing conventional permeability measurements. Propagators quantify the local effect of calcite formation on system hydrodynamics and the extent of stagnant region formation. Collectively, the combination of NMR measurements utilised here provides a toolkit for determining the efficacy of a biological–precipitation reaction for partially blocking porous materials.
•Microbially-induced calcite precipitation is an effective permeability reducer.•NMR toolkit was able to probe structural and hydrodynamic changes following plugging.•Shown the potential of blocking fractured systems with calcite precipitate•NMR velocimetry was able to probe calcite fracture plugging.
The pathways of CaCO3 crystallization are manifold, often involving one or several metastable amorphous or nanocrystalline intermediate phases. The presence of such intermediates is often overlooked, ...because they are short-lived and/or occur at small molar fractions. However, their occurrence does not just impact the mechanisms and pathways of formation of the final stable CaCO3 phase, but also affects their crystal size, shape, and structure. Here we document the presence of a short-lived intermediate through in situ and time-resolved small and wide-angle X-ray scattering combined with high resolution electron microscope observations. When ikaite forms concomitant with the dissolution of amorphous calcium carbonate (ACC) but prior to calcite formation, fairly large glendonite-type calcite crystals grow despite the presence of citrate ligands that usually reduce crystal size. These were ideal seeding crystals for further crystallization from supersaturated ions in solution. In contrast, in the absence of ikaite the crystallization of calcite proceeds through transformation from ACC, resulting in fine-grained spherulitic calcite with sizes ∼8 times smaller than when ikaite was present. Noteworthy is that the formation of the intermediate ikaite, although it consumes less than 3 mol % of the total precipitated CaCO3, still clearly affected the calcite formation mechanism.
Organic molecules control calcite growth and crystal morphology, influence biomineralization processes, and offer clues for optimizing antiscalants for industry. Here we quantified the effect of ...amino acid monomers, aspartic acid (Asp1), and glycine (Gly1), and their polymers (Aspn, Asp5, and Gly5), on calcite growth rate, in a constant composition setup. Asp1 and its polymers inhibit growth, with rate decreasing as amino acid chain length increases. For 2 mM Asp1, fractional inhibition (FI, where 1 represents complete inhibition) was 0.54; for 0.0012 mM Aspn, FI = 0.94. Gly1 and Gly5 only marginally affect growth (−0.1 < FI < 0.1); indeed, they slightly promote growth at most tested concentrations. Fitting of adsorption isotherms (Langmuir, Langmuir–Freundlich, Flory–Huggins) confirmed that Asp polymers adsorb strongly, explaining their strong control on calcite growth, but Gly1 and Asp1 adsorb less due to competition with carbonate ions. ΔG ads (Aspn) = −39 kJ/mol; ΔG ads (Asp5) = −50 kJ/mol; ΔG ads (Asp1) = −21 kJ/mol; and ΔG ads (Gly1) = −22 kJ/mol. The morphology was equally affected. Crystal edges became rougher, and corners, more rounded. Overall, the number of carboxyl groups and length of the carbon chain correlated with the lowest growth rate.
National blood donor screening for West Nile virus (WNV) RNA using minipool nucleic acid amplification testing (MP-NAT) was implemented in the United States in July 2003. We compiled national NAT ...yield data and performed WNV immunoglobulin M (IgM) testing in 1 WNV-epidemic region (North Dakota). State-specific MP-NAT yield, antibody seroprevalence, and the average time RNA is detectable by MP-NAT were used to estimate incident infections in 2003. WNV donor screening yielded 944 confirmed viremic donors. MP-NAT yield peaked in August with >0.5% of donations positive for WNV RNA in 4 states. Peak IgM seroprevalence for North Dakota was 5.2% in late September. The average time viremia is detectable by MP-NAT was 6.9 days (95% confidence interval CI 3.0-10.7). An estimated 735,000 (95% CI 322,000-1,147,000) infections occurred in 2003, with 256 (95% CI 112-401) infections per neuroinvasive case. In addition to preventing transfusion-transmitted WNV infection, donor screening can serve as a tool to monitor seasonal incidence in the general population.
Humans cannot live at very high altitude for reasons, which are not completely understood. Since these reasons are not restricted to cardiorespiratory changes alone, changes in the endocrine system ...might also be involved. Therefore, hormonal changes during prolonged hypobaric hypoxia were comprehensively assessed to determine effects of altitude and hypoxia on stress, thyroid and gonadal hypothalamus–pituitary hormone axes. Twenty-one male and 19 female participants were examined repetitively during a high-altitude expedition. Cortisol, prolactin, thyroid-stimulating hormone (TSH), fT4 and fT3 and in males follicle-stimulating hormone (FSH), luteinizing hormone (LH) and total testosterone were analysed as well as parameters of hypoxemia, such as SaO2 and paO2 at 550 m (baseline) (n = 40), during ascent at 4844 m (n = 38), 6022 m (n = 31) and 7050 m (n = 13), at 4844 m (n = 29) after acclimatization and after the expedition (n = 38). Correlation analysis of hormone concentrations with oxygen parameters and with altitude revealed statistical association in most cases only with altitude. Adrenal, thyroid and gonadal axes were affected by increasing altitude. Adrenal axis and prolactin were first supressed at 4844 m and then activated with increasing altitude; thyroid and gonadal axes were directly activated or suppressed respectively with increasing altitude. Acclimatisation at 4844 m led to normalization of adrenal and gonadal but not of thyroid axes. In conclusion, acclimatization partly leads to a normalization of the adrenal, thyroid and gonadal axes at around 5000 m. However, at higher altitude, endocrine dysregulation is pronounced and might contribute to the physical degradation found at high altitude.
We examined effects of state statutory changes in DUI fine or jail penalties for firsttime offenders from 1976 to 2002.
A quasi-experimental time-series design was used (n=324 monthly observations). ...Four outcome measures of drivers involved in alcohol-related fatal crashes are: single-vehicle nighttime, low BAC (0.01-0.07g/dl), medium BAC (0.08-0.14g/dl), high BAC (>/=0.15g/dl). All analyses of BAC outcomes included multiple imputation procedures for cases with missing data. Comparison series of non-alcohol-related crashes were included to efficiently control for effects of other factors. Statistical models include state-specific Box-Jenkins ARIMA models, and pooled general linear mixed models.
Twenty-six states implemented mandatory minimum fine policies and 18 states implemented mandatory minimum jail penalties. Estimated effects varied widely from state to state. Using variance weighted meta-analysis methods to aggregate results across states, mandatory fine policies are associated with an average reduction in fatal crash involvement by drivers with BAC>/=0.08g/dl of 8% (averaging 13 per state per year). Mandatory minimum jail policies are associated with a decline in single-vehicle nighttime fatal crash involvement of 6% (averaging 5 per state per year), and a decline in low-BAC cases of 9% (averaging 3 per state per year). No significant effects were observed for the other outcome measures.
The overall pattern of results suggests a possible effect of mandatory fine policies in some states, but little effect of mandatory jail policies.
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