Journal articles: 'Speciation at equilibrium'

1

Chen, Min, and R. Stephen Reid. "Solution speciation in the aqueous Na(I)–EDTA and K(I)–EDTA systems." Canadian Journal of Chemistry 71, no. 5 (May 1, 1993): 763–68. http://dx.doi.org/10.1139/v93-100.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Speciation in the aqueous sodium(I) – ethylenediaminetetraacetic acid and potassium(I) – ethylenediaminetetraacetic acid equilibrium systems was investigated by automated gravimetric potentiometric titration. It was found that in both cases, particularly below neutral pH values, speciation includes a previously uncharacterized diprotonated complex. All formation and acid dissociation constants were measured for the full systems. The validity of previous literature equilibrium constants, which are based on incomplete equilibrium models, is discussed.

2

Filella, Montserrat, and Peter M. May. "The aqueous chemistry of tellurium: critically-selected equilibrium constants for the low-molecular-weight inorganic species." Environmental Chemistry 16, no. 4 (2019): 289. http://dx.doi.org/10.1071/en19017.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Environmental contextEquilibrium constants are required in many scientific disciplines such as biology, medicine, engineering, and in particular chemistry. Lack of reliable equilibrium constants for tellurium has restricted our understanding of its speciation and behaviour in the environment. This study presents a reliable set of equilibrium constants for tellurium, thereby providing a more coherent basis for future experimental investigations of the geochemistry, biochemistry and toxicology of this element. AbstractRelatively little information is available in the literature regarding the speciation and solubility of tellurium in aqueous solutions. The available thermodynamic data have been critically evaluated and entered into a thermodynamic database. The Joint Expert Speciation System suite of computer programs has been used to achieve thermodynamic consistency and provide a critically-selected set of equilibrium constants that can later be used for modelling purposes.

3

Arp, Paul A., and Rock Ouimet. "Aluminum speciation in soil solutions: Equilibrium calculations." Water, Air, & Soil Pollution 31, no. 1-2 (1986): 359–66. http://dx.doi.org/10.1007/bf00630852.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Harris, W. R. "Equilibrium Model for Speciation of Aluminum in Serum." Clinical Chemistry 38, no. 9 (September 1, 1992): 1809–18. http://dx.doi.org/10.1093/clinchem/38.9.1809.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Abstract An equilibrium model for the speciation of Al3+ in normal serum has been developed in which 81% of the aluminum is bound to transferrin. The remaining 19% exists primarily as Al(PO4)(OH)-, with minor amounts of citrate and hydroxide species. The model meets several key criteria. The concentration of free aluminum is below the upper limit set by the solubility product of aluminum phosphate. The fraction of low-molecular-mass aluminum species agrees with experimental studies on the fraction of ultrafiltrable aluminum in both normal and uremic serum. Lastly, the model accounts for the relative effectiveness of EDTA, citrate, and desferrioxamine B for binding aluminum in serum by including competition from zinc, magnesium, and calcium for these ligands. Uncertainties in the available thermodynamic database are discussed.

5

Marang, Laura, Pascal Reiller, Monique Pepe, and Marc F. Benedetti. "Donnan Membrane Approach: From Equilibrium to Dynamic Speciation." Environmental Science & Technology 40, no. 17 (September 2006): 5496–501. http://dx.doi.org/10.1021/es060608t.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Wang, Peiming, Jerzy J. Kosinski, Malgorzata M. Lencka, Andrzej Anderko, and Ronald D. Springer. "Thermodynamic modeling of boric acid and selected metal borate systems." Pure and Applied Chemistry 85, no. 11 (November 1, 2013): 2117–44. http://dx.doi.org/10.1351/pac-con-12-07-09.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

A comprehensive thermodynamic model, referred to as the mixed-solvent electrolyte (MSE) model, has been applied to calculate phase equilibria, speciation, and other thermodynamic properties of selected systems that are of interest for understanding the chemistry of salt lakes and natural waters. In particular, solubilities and chemical speciation have been analyzed for various boron-containing systems, which represent an important subset of solution chemistry for such applications. The model has been shown to reproduce the speciation, solubility, and vapor–liquid equilibrium (VLE) data in the boric acid + water system over wide ranges of temperature and concentration. Specifically, solubilities have been accurately represented in the full concentration range of the B2O3 + H2O system (xB2O3 = 0~1), which includes H3BO3. The accuracy of the model has also been demonstrated by calculating solubilities in various aqueous borate systems, i.e., MnO + B2O3 + H2O (where M = Li, Na, Ca, Mg), and their mixtures with a chloride salt or an acid (i.e., LiCl, NaCl, HCl). The model predicts the effects of chemical speciation, temperature, and concentrations of various acid, base, and salt components on the formation of competing solid phases.

7

Halstensen, Maths, Henrik Jilvero, Wathsala N. Jinadasa, and Klaus-J. Jens. "Equilibrium Measurements of the NH3-CO2-H2O System: Speciation Based on Raman Spectroscopy and Multivariate Modeling." Journal of Chemistry 2017 (2017): 1–13. http://dx.doi.org/10.1155/2017/7590506.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Liquid speciation is important for reliable process design and optimization of gas-liquid absorption process. Liquid-phase speciation methods are currently available, although they involve tedious and time-consuming laboratory work. Raman spectroscopy is well suited for in situ monitoring of aqueous chemical reactions. Here, we report on the development of a method for speciation of the CO2-NH3-H2O equilibrium using Raman spectroscopy and PLS-R modeling. The quantification methodology presented here offers a novel approach to provide rapid and reliable predictions of the carbon distribution of the CO2-NH3-H2O system, which may be used for process control and optimization. Validation of the reported speciation method which is based on independent, known, NH3-CO2-H2O solutions shows estimated prediction uncertainties for carbonate, bicarbonate, and carbamate of 6.45 mmol/kg H2O, 34.39 mmol/kg H2O, and 100.9 mmol/kg H2O, respectively.

8

Heck, R. J., and A. R. Mermut. "The chemistry of saturation extracts of Solonetzic and associated soils." Canadian Journal of Soil Science 72, no. 1 (February 1, 1992): 43–56. http://dx.doi.org/10.4141/cjss92-005.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Cation speciation in soil extracts from a catenary sequence of salt-affected soils was studied to understand the chemical evolution of Solonetzic soils in a closed basin. Major changes in cation speciation were found to occur at each phase of soil development. The proportion of thermodynamically active cations was greater in the extracts from the more leached profiles. Saturation indices suggested that the extracts achieved equilibrium with calcite and gypsum, when present in the soil, within 24 h. Accumulations and/or losses of gypsum and calcite from saline layers indicate that there are ongoing changes in their stability. The ratio of Ca2+/Mg2+ suggested a possible equilibrium with Mg-bearing calcites; conditions existed in certain horizons for the formation of this group of minerals. Correlations between exchangeable sodium ratios and sodium adsorption ratios calculated using cation concentration and activity were similar; however, using activities to determine the exchange constants resulted in significant differences.Key words: Cation speciation, saturation indices, cation adsorption, exchange selectivity constants, Solonetzic soils

9

Fitzgerald, John, Colton Bentley, and Bas Vriens. "Geochemical Equilibrium Modelling of the Aqueous Speciation of Select Trace Elements in the Great Lakes." Water 15, no. 8 (April 11, 2023): 1483. http://dx.doi.org/10.3390/w15081483.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

The behaviour and fate of trace elements in surface waters are greatly affected by their chemical form in solution, but the aqueous speciation of dissolved trace elements in the North American Great Lakes has received relatively little attention. Here, we present results from geochemical equilibrium modelling with 2021 surface water quality data to examine the spatiotemporal dynamics of trace element speciation in the Great Lakes. The relative abundance of aqueous trace element species appeared consistent with variability in solution chemistry and followed basin-wide trends in pH, alkalinity, salinity, and nutrient levels. The speciation of alkali metals was dominated by free monovalent cations, and that of oxyanion-forming elements by oxoacids, whereas significant fractions (>1%) of other aqueous complexes were also evident for rare earth elements (e.g., Ce and Gd as carbonates), alkaline earth metals (e.g., Sr as sulfates), or transition metals (e.g., Zn as phosphates). Spatially, differences in the relative abundance of aqueous trace element species were <2 orders of magnitude, with the highest variation (~50-fold) occurring for select chloride-complexes, resulting from upstream-to-downstream salinity increases in the basin. Finally, simulations of various future water quality scenarios (e.g., decreasing P levels, increasing temperature and salinity) suggest that the speciation of most trace elements is robust temporally as well. This study demonstrates how considering aqueous speciation may help improve the understanding of trace element dynamics and support water quality management in the Great Lakes.

10

Smith, Bradley J., and Vincent A. Patrick. "Quantitative Determination of Aqueous Dodecatungstophosphoric Acid Speciation by NMR Spectroscopy." Australian Journal of Chemistry 57, no. 3 (2004): 261. http://dx.doi.org/10.1071/ch02037.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

The speciation and equilibria during base decomposition of α-[PW12O40]3– have been determined using 31P and 183W NMR spectroscopy over the pH range 0.7–13.5. NMR spectroscopy was used to directly observe the polytungstate species in aqueous solution at high concentration (0.25 mol L–1) and follows the progressive decomposition of [PW12O40]3– to WO42– and PO43–. It was found unexpectedly in the pH range 1.2–2.3 that [PW12O40]3– did not decompose directly to [PW11O39]7– but first formed an equilibrium with [P2W18O62]6–, [P2W21O71]6–, and some new, stable, intermediate species before converting into α-[PW11O39]7–.

11

O'Meara, Brian C., Stacey D. Smith, W. Scott Armbruster, Lawrence D. Harder, Christopher R. Hardy, Lena C. Hileman, Larry Hufford, et al. "Non-equilibrium dynamics and floral trait interactions shape extant angiosperm diversity." Proceedings of the Royal Society B: Biological Sciences 283, no. 1830 (May 11, 2016): 20152304. http://dx.doi.org/10.1098/rspb.2015.2304.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Why are some traits and trait combinations exceptionally common across the tree of life, whereas others are vanishingly rare? The distribution of trait diversity across a clade at any time depends on the ancestral state of the clade, the rate at which new phenotypes evolve, the differences in speciation and extinction rates across lineages, and whether an equilibrium has been reached. Here we examine the role of transition rates, differential diversification (speciation minus extinction) and non-equilibrium dynamics on the evolutionary history of angiosperms, a clade well known for the abundance of some trait combinations and the rarity of others. Our analysis reveals that three character states (corolla present, bilateral symmetry, reduced stamen number) act synergistically as a key innovation, doubling diversification rates for lineages in which this combination occurs. However, this combination is currently less common than predicted at equilibrium because the individual characters evolve infrequently. Simulations suggest that angiosperms will remain far from the equilibrium frequencies of character states well into the future. Such non-equilibrium dynamics may be common when major innovations evolve rarely, allowing lineages with ancestral forms to persist, and even outnumber those with diversification-enhancing states, for tens of millions of years.

12

Missa, Olivier, Calvin Dytham, and Hélène Morlon. "Understanding how biodiversity unfolds through time under neutral theory." Philosophical Transactions of the Royal Society B: Biological Sciences 371, no. 1691 (April 5, 2016): 20150226. http://dx.doi.org/10.1098/rstb.2015.0226.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Theoretical predictions for biodiversity patterns are typically derived under the assumption that ecological systems have reached a dynamic equilibrium. Yet, there is increasing evidence that various aspects of ecological systems, including (but not limited to) species richness, are not at equilibrium. Here, we use simulations to analyse how biodiversity patterns unfold through time. In particular, we focus on the relative time required for various biodiversity patterns (macroecological or phylogenetic) to reach equilibrium. We simulate spatially explicit metacommunities according to the Neutral Theory of Biodiversity (NTB) under three modes of speciation, which differ in how evenly a parent species is split between its two daughter species. We find that species richness stabilizes first, followed by species area relationships (SAR) and finally species abundance distributions (SAD). The difference in timing of equilibrium between these different macroecological patterns is the largest when the split of individuals between sibling species at speciation is the most uneven. Phylogenetic patterns of biodiversity take even longer to stabilize (tens to hundreds of times longer than species richness) so that equilibrium predictions from neutral theory for these patterns are unlikely to be relevant. Our results suggest that it may be unwise to assume that biodiversity patterns are at equilibrium and provide a first step in studying how these patterns unfold through time.

13

Basafa, Mahsan, and Kelly Hawboldt. "Sulfur speciation in soured reservoirs: chemical equilibrium and kinetics." Journal of Petroleum Exploration and Production Technology 10, no. 4 (January 2, 2020): 1603–12. http://dx.doi.org/10.1007/s13202-019-00824-0.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

AbstractReservoir souring is a widespread phenomenon in reservoirs undergoing seawater injection. Sulfate in the injected seawater promotes the growth of sulfate-reducing bacteria (SRB) and archaea-generating hydrogen sulfide. However, as the reservoir fluid flows from injection well to topside facilities, reactions involving formation of different sulfur species with intermediate valence states such as elemental sulfur, sulfite, polysulfide ions, and polythionates can occur. A predictive reactive model was developed in this study to investigate the chemical reactivity of sulfur species and their partitioning behavior as a function of temperature, pressure, and pH in a seawater-flooded reservoir. The presence of sulfur species with different oxidation states impacts the amount and partitioning behavior of H2S and, therefore, the extent of reservoir souring. The injected sulfate is reduced to H2S microbially close to the injection well. The generated H2S partitions between phases depending on temperature, pressure, and pH. Without considering chemical reactivity and sulfur speciation, the gas phase under test separator conditions on the surface contains 1080 ppm H2S which is in equilibrium with the oil phase containing 295.7 ppm H2S and water phase with H2S content of 8.8 ppm. These values are higher than those obtained based on reactivity analysis, where sulfur speciation and chemical reactions are included. Under these conditions, the H2S content of the gas, oil, and aqueous phases are 487 ppm, 134 ppm, and 4 ppm, respectively.

14

Wieser, Penny, Maurizio Petrelli, Jordan Lubbers, Eric Wieser, Sinan Ozaydin, Adam Kent, and Christy Till. "Thermobar: An open-source Python3 tool for thermobarometry and hygrometry." Volcanica 5, no. 2 (November 9, 2022): 349–84. http://dx.doi.org/10.30909/vol.05.02.349384.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

We present Thermobar, a new open-source Python3 package for calculating pressures, temperatures, and melt compositions from mineral and mineral-melt equilibrium. Thermobar allows users to perform calculations with >100 popular parametrizations involving liquid, olivine-liquid, olivine-spinel, pyroxene only, pyroxene-liquid, two pyroxene, feldspar-liquid, two feldspar, amphibole only, amphibole-liquid, and garnet equilibria. Thermobar is the first open-source tool which can match up all possible pairs of phases from a given region, and apply various equilibrium tests to identify pairs from which to calculate pressures and temperatures (e.g. pyroxene-liquid, two pyroxene, feldspar-liquid, two feldspar, amphibole-liquid). Thermobar also contains functions allowing users to propagate analytical errors using Monte-Carlo methods, convert pressures to depths using different crustal density profiles, plot mineral classification and mineral-melt equilibrium diagrams, calculate liquid viscosities, and convert between oxygen fugacity values, buffer positions and Fe speciation in a silicate melt. Thermobar can be downloaded using pip and extensive documentation is available at https://thermobar.readthedocs.io/.

15

Mattigod, S. V., P. F. Pratt, and E. B. Schalscha. "Trace Metal Speciation in a Soil Profile Irrigated with Waste Waters." Water Science and Technology 17, no. 9 (September 1, 1985): 133–42. http://dx.doi.org/10.2166/wst.1985.0087.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

A chemical equilibrium computer model: GEOCHEM, was used to predict the trace metal behavior in a soil profile if subjected to a long-term irrigation with waste waters. Various categories of interactions such as acid-base equilibria, soluble complex formation of metals with organic and inorganic ligands, dissolution-precipitation reactions and ion-exchange reactions were included in simulation. The metal-soluble organic interactions were accounted for by a mixture model. The computations included a 10 metal - 15 ligand system with 262 soluble complex species and 21 possible solid phases. The results predicted that a major fraction of alkali elements in solution tend to be in free ionic forms, whereas, major fractions of the alkaline earths were predicted to be present in adsorbed and/or precipitated forms. In marked contrast, significant soluble fractions of transition series metals were predicted to be in adsorbed and/or complexed forms. The degree of attenuation of these transition series elements moving through the soil profile seems to be governed mainly by the degree of adsorption on soil surfaces and the tendency of these elements to form soluble organic complexes. The predicted mobilities of these elements in this soil profile was Cu > Ni > Zn > Cd. Application of this equilibrium model appears to provide a first approximation approach to simulate the trace element behavior in soil profiles.

16

Smith, Bradley J., and Vincent A. Patrick. "Quantitative Determination of Sodium Metatungstate Speciation by 183W N.M.R. Spectroscopy." Australian Journal of Chemistry 53, no. 12 (2000): 965. http://dx.doi.org/10.1071/ch00140.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

The speciation and equilibria of sodium metatungstate, Na6[H2W12O40], has been determined by a combination of 183W n.m.r. spectroscopy and gravimetry over the p[H] range 4.5–10.0. The use of n.m.r. spectroscopy allowed the direct observation of polytungstate anions in aqueous solution and high concentration (0.25 mol l–1). Sodium metatungstate, with the progressive addition of base, was found to decompose to paratungstate A, [W7O24]6–. Paratungstate A then slowly converted to paratungstate B, [H2W12O42]10–. The kinetics of equilibrium was found to be slow, requiring up to 8 months to stabilize. With the addition of further base paratungstate B decomposed to orthotungstate, WO42–. Logarithmic constants (logK) for these transformations were determined as 195, 20 and 118, respectively. The solubility product for sodium paratungstate B was determined to be 6.89 ( 0.80) 10–6.

17

Gopalapillai, Yamini, Chuni L. Chakrabarti, and David R. S. Lean. "Assessing toxicity of mining effluents: equilibrium- and kinetics-based metal speciation and algal bioassay." Environmental Chemistry 5, no. 4 (2008): 307. http://dx.doi.org/10.1071/en08027.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Environmental context. The release of mining effluents exposes natural waters to excess metals and thereby threatens both human and environmental health. The present study explores the toxicity of aqueous mining effluents collected from a mining area in Sudbury (Ontario, Canada), using two different methods for determination of metal speciation, and an algal toxicity study. The results show reasonable correlation between metal speciation and the observed toxicity and suggest the importance of taking into account other factors related to water quality criteria such as nutrient concentrations, diluent water and presence of other toxic metals that can greatly influence the toxicological result. Abstract. The present study explores the toxicity of aqueous mining and municipal effluents from the Sudbury area (Canada) using equilibrium- and kinetics-based estimates of metal speciation and chronic toxicity studies using algae (Pseudokirchneriella subcapitata). Free metal ion concentration was determined by the Ion Exchange Technique (IET) and a computer speciation code, Windermere Humic Aqueous Model (WHAM) VI. Labile metal concentration was determined using the Competing Ligand Exchange Method. In general, no correlation was found between the observed IC25 (concentration of test substance that inhibits growth of organism by 25%) and the [Ni]labile, [Ni2+]IET or [Ni2+]WHAM, probably because of contributions by other metals such as Cu and Zn being also significant. Reasonable correlation (r2 = 0.7575) was found when the observed toxicity was compared with the sum of free metal ions of Cu, Ni, and Zn predicted by WHAM. The results of the present study reveal the importance of taking into account other factors related to water quality criteria such as nutrient concentrations, diluent water, and the presence of other toxic metals, which greatly influence the toxicological result in complex, multi-metal contaminated waters.

18

Wolfram, Olaf, and Ralf E. Krupp. "Hydrothermal solubility of rhodochrosite, Mn (II) speciation, and equilibrium constants." Geochimica et Cosmochimica Acta 60, no. 21 (November 1996): 3983–94. http://dx.doi.org/10.1016/s0016-7037(96)00224-4.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Valkai, László, Gábor Peintler, and Attila K. Horváth. "Clarifying the Equilibrium Speciation of Periodate Ions in Aqueous Medium." Inorganic Chemistry 56, no. 18 (August 31, 2017): 11417–25. http://dx.doi.org/10.1021/acs.inorgchem.7b01911.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Ge, Ying, Sébastien Sauvé, and William H. Hendershot. "Equilibrium Speciation of Cadmium, Copper, and Lead in Soil Solutions." Communications in Soil Science and Plant Analysis 36, no. 11-12 (June 2005): 1537–56. http://dx.doi.org/10.1081/css-200059044.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Idris, Zulkifli, Klaus J. Jens, and Dag A. Eimer. "Speciation of MEA-CO2 Adducts at Equilibrium Using Raman Spectroscopy." Energy Procedia 63 (2014): 1424–31. http://dx.doi.org/10.1016/j.egypro.2014.11.152.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Povar, Igor, and Oxana Spinu. "The role of hydroxy aluminium sulfate minerals in controlling Al3+ concentration and speciation in acidic soils." Open Chemistry 12, no. 8 (August 1, 2014): 877–85. http://dx.doi.org/10.2478/s11532-014-0540-4.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

AbstractA thermodynamic approach for the complex chemical equilibria investigation of two-phase systems containing hydroxy aluminium sulfate (HAS) minerals in soils has been developed. This approach utilizes thermodynamic relationships combined with original mass balance constraints, where the HAS mineral phases are explicitly expressed. The factors influencing the distribution and concentrations of various soluble aluminium species have been taken into account. The new type of diagrams, based on thermodynamic, graphical and computerized methods, which quantitatively describe the distribution of soluble and insoluble inorganic, and organic, monomeric and polymeric aluminium species in acidic soil solutions in a large range of pH values has been used. The thermodynamics of equilibria of different natural HAS in soils, the conditions under which solids involving common ions can coexist at equilibrium, the acid-base and mineral equilibria and complex formation have been examined. It has been proved that the presence of sulfate ion dramatically alters the HAS mineral solubility under acidic conditions. The obtained data regarding the factors influencing Al speciation, based on the constructed diagrams of heterogeneous chemical equilibria, are in good agreement with the current experimental and theoretical evidence. The proposed approach is intended to determine the dominant processes that are responsible for the Al3+ concentration levels and its speciation in acidic soils.

23

Medvedev, Alexander G., Oleg Yu Savelyev, Dmitry P. Krut’ko, Alexey A. Mikhaylov, Ovadia Lev, and Petr V. Prikhodchenko. "Speciation of Tellurium(VI) in Aqueous Solutions: Identification of Trinuclear Tellurates by 17O, 123Te, and 125Te NMR Spectroscopy." Molecules 27, no. 24 (December 7, 2022): 8654. http://dx.doi.org/10.3390/molecules27248654.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Tellurates have attracted the attention of researchers over the past decade due to their properties and as less toxic forms of tellurium derivatives. However, the speciation of Te(VI) in aqueous solutions has not been comprehensively studied. We present a study of the equilibrium speciation of tellurates in aqueous solutions at a wide pH range, 2.5–15 by 17O, 123Te, and 125Te NMR spectroscopy. The coexistence of monomeric, dimeric, and trimeric oxidotellurate species in chemical equilibrium at a wide pH range has been shown. NMR spectroscopy, DFT computations, and single-crystal X-ray diffraction studies confirmed the formation and coexistence of trimeric tellurate anions with linear and triangular structures. Two cesium tellurates, Cs2[Te4O8(OH)10] and Cs2[Te2O4(OH)6], were isolated from the solution at pH 5.5 and 9.2, respectively, and studied by single-crystal X-ray diffractometry, revealing dimeric and tetrameric tellurate anions in corresponding crystal structures.

24

Dahl, Amy L., John Sanseverino, and Jean-François Gaillard. "Bacterial bioreporter detects mercury in the presence of excess EDTA." Environmental Chemistry 8, no. 6 (2011): 552. http://dx.doi.org/10.1071/en11043.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Environmental contextUnderstanding the uptake of mercury by bacteria is essential for predicting the amount of toxic methyl mercury formed in the environment. This study shows that the uptake of mercury by a whole-cell bacterial biosensor as a function of a strong ligand was greater than predicted by chemical speciation measurements or equilibrium calculations. These results call into question the use of chemical measurements and equilibrium modelling for predicting the toxicity of metals to living organisms in the environment and suggest that direct biological methods yield more accurate results. AbstractA whole-cell bacterial reporter was used to probe the bioavailability of mercury in the presence of a strong metal chelator, ethylenediaminetetraacetic acid (EDTA). Strain ARL1 was constructed by inserting a merR::luxCDABE fusion into the chromosome of Escherichia coli. The response of the bioreporter to HgII was monitored as a function of added EDTA. In parallel, square-wave voltammetry (SWV) measurements and thermodynamic calculations using MINEQL were performed to study the chemical speciation of mercury. The amount of electro-labile HgII measured by SWV was similar to the amount of non-complexed HgII predicted from equilibrium calculations. In contrast, the bioavailable fraction measured by the bioreporter was greater than the fraction predicted by either equilibrium calculation or electrochemical analysis. These results suggest that conventional chemical measurements and equilibrium calculations are not necessarily good proxies for predicting the bioavailable metal fraction. Additional factors such as kinetic effects or biological ligand competition must be considered.

25

McInnes, Lynsey, C. David L. Orme, and A. Purvis. "Detecting shifts in diversity limits from molecular phylogenies: what can we know?" Proceedings of the Royal Society B: Biological Sciences 278, no. 1722 (March 23, 2011): 3294–302. http://dx.doi.org/10.1098/rspb.2011.0241.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Large complete species-level molecular phylogenies can provide the most direct information about the macroevolutionary history of clades having poor fossil records. However, extinction will ultimately erode evidence of pulses of rapid speciation in the deep past. Assessment of how well, and for how long, phylogenies retain the signature of such pulses has hitherto been based on a—probably untenable—model of ongoing diversity-independent diversification. Here, we develop two new tests for changes in diversification ‘rules’ and evaluate their power to detect sudden increases in equilibrium diversity in clades simulated with diversity-dependent speciation and extinction rates. Pulses of diversification are only detected easily if they occurred recently and if the rate of species turnover at equilibrium is low; rates reported for fossil mammals suggest that the power to detect a doubling of species diversity falls to 50 per cent after less than 50 Myr even with a perfect phylogeny of extant species. Extinction does eventually draw a veil over past dynamics, suggesting that some questions are beyond the limits of inference, but sudden clade-wide pulses of speciation can be detected after many millions of years, even when overall diversity is constrained. Applying our methods to existing phylogenies of mammals and angiosperms identifies intervals of elevated diversification in each.

26

Shoukry, Mohamed M., and Samir M. El-Medani. "Equilibrium Studies of Alkyltin(IV) Complexes with D-Glucosamine." Collection of Czechoslovak Chemical Communications 62, no. 7 (1997): 1023–28. http://dx.doi.org/10.1135/cccc19971023.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

The acid-base and complex-formation equilibria involving glucosamine and its complexes with alkyltin(IV) chlorides have been studied by potentiometric technique. The results prove to a formation of 1 : 1 complex with trialkyltin(IV) and both 1 : 1 and 1 : 2 complexes with dialkyltin(IV) species. The stability constants in water were determined, the effects of temperature (from 15 to 35 °C) and ethanol (up to 88 vol.%) was studied and the speciation of the complexes was resolved.

27

Barton, N. H. "What role does natural selection play in speciation?" Philosophical Transactions of the Royal Society B: Biological Sciences 365, no. 1547 (June 12, 2010): 1825–40. http://dx.doi.org/10.1098/rstb.2010.0001.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

If distinct biological species are to coexist in sympatry, they must be reproductively isolated and must exploit different limiting resources. A two-niche Levene model is analysed, in which habitat preference and survival depend on underlying additive traits. The population genetics of preference and viability are equivalent. However, there is a linear trade-off between the chances of settling in either niche, whereas viabilities may be constrained arbitrarily. With a convex trade-off, a sexual population evolves a single generalist genotype, whereas with a concave trade-off, disruptive selection favours maximal variance. A pure habitat preference evolves to global linkage equilibrium if mating occurs in a single pool, but remarkably, evolves to pairwise linkage equilibrium within niches if mating is within those niches—independent of the genetics. With a concave trade-off, the population shifts sharply between a unimodal distribution with high gene flow and a bimodal distribution with strong isolation, as the underlying genetic variance increases. However, these alternative states are only simultaneously stable for a narrow parameter range. A sharp threshold is only seen if survival in the ‘wrong’ niche is low; otherwise, strong isolation is impossible. Gene flow from divergent demes makes speciation much easier in parapatry than in sympatry.

28

Liow, Lee Hsiang, and John A. Finarelli. "A dynamic global equilibrium in carnivoran diversification over 20 million years." Proceedings of the Royal Society B: Biological Sciences 281, no. 1778 (March 7, 2014): 20132312. http://dx.doi.org/10.1098/rspb.2013.2312.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

The ecological and evolutionary processes leading to present-day biological diversity can be inferred by reconstructing the phylogeny of living organisms, and then modelling potential processes that could have produced this genealogy. A more direct approach is to estimate past processes from the fossil record. The Carnivora (Mammalia) has both substantial extant species richness and a rich fossil record. We compiled species-level data for over 10 000 fossil occurrences of nearly 1400 carnivoran species. Using this compilation, we estimated extinction, speciation and net diversification for carnivorans through the Neogene (22–2 Ma), while simultaneously modelling sampling probability. Our analyses show that caniforms (dogs, bears and relatives) have higher speciation and extinction rates than feliforms (cats, hyenas and relatives), but lower rates of net diversification. We also find that despite continual species turnover, net carnivoran diversification through the Neogene is surprisingly stable, suggesting a saturated adaptive zone, despite restructuring of the physical environment. This result is strikingly different from analyses of carnivoran diversification estimated from extant species alone. Two intervals show elevated diversification rates (13–12 Ma and 4–3 Ma), although the precise causal factors behind the two peaks in carnivoran diversification remain open questions.

29

Rabosky, D. L., and R. E. Glor. "Equilibrium speciation dynamics in a model adaptive radiation of island lizards." Proceedings of the National Academy of Sciences 107, no. 51 (December 6, 2010): 22178–83. http://dx.doi.org/10.1073/pnas.1007606107.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Leal, Allan M. M., Martin J. Blunt, and Tara C. LaForce. "Efficient chemical equilibrium calculations for geochemical speciation and reactive transport modelling." Geochimica et Cosmochimica Acta 131 (April 2014): 301–22. http://dx.doi.org/10.1016/j.gca.2014.01.038.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Gerber, W. J., P. H. van Wyk, D. M. E. van Niekerk, and K. R. Koch. "The fundamental flaw of the HSAB principle is revealed by a complete speciation analysis of the [PtCl6−nBrn]2−(n = 0–6) system." Physical Chemistry Chemical Physics 17, no. 8 (2015): 5712–24. http://dx.doi.org/10.1039/c4cp05294c.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Bjerrum's model of step-wise ligand exchange is extended to compute a complete speciation diagram for the [PtCl_6−nBr_n]²⁻(n= 0–6) system including all 17 equilibrium constants concerning the Pt^IVchlorido–bromido exchange reaction network (HERN).

32

Clifford, Sarah E., Geoffrey A. Lawrance, Yorck-Michael Neuhold, and Marcel Maeder. "Conjoint Analysis of Kinetic and Equilibrium Data for Mechanistic Elucidation in Polynuclear Complexation Reactions, Exemplified by Metal(II) Helicate Complex Formation." Australian Journal of Chemistry 63, no. 1 (2010): 141. http://dx.doi.org/10.1071/ch09316.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Combined kinetic and equilibrium studies of the complexation of the ligand N,N′-bis[2-(2-pyridyl)methyl]pyridine-2,6-dicarboxamide with copper(ii) and nickel(ii), examined conjointly employing advanced chemometric methods, provides elucidation of speciation and formation pathways in solution for complexes such as M2L2 and M2L3 helicates, respectively.

33

Kumar, Ajay, R. M. Tripathi, Sabyasachi Rout, Manish K. Mishra, P. M. Ravi, and A. K. Ghosh. "Characterization of groundwater composition in Punjab state with special emphasis on uranium content, speciation and mobility." Radiochimica Acta 102, no. 3 (February 10, 2014): 239–54. http://dx.doi.org/10.1515/ract-2014-2109.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Abstract Groundwaters (borewell and handpump) were sampled from two districts (Bathinda and Mansa) of Punjab state and analyzed for their major ionic concentrations and uranium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The major ionic concentrations of waters were plotted on a Piper diagram and grouped into four dominant hydrochemical facies as (Na+K)-SO4+Cl type (69% – 73%), (Ca+Mg)-SO4+Cl type (6% – 21%), (Ca+Mg)–HCO3 type (4% – 6%) and (Na+K)-HCO3 type (2% – 19%). It was observed that mobility of uranium in groundwater was very much influenced by TDS (total dissolved solids). To investigate the various mechanisms for deriving the elevated uranium concentrations in groundwater, 234U/238U activity ratios (ARs) were calculated using the determined activity levels of 234U and 238U. The mean ARs was found to be near unity (i.e. secular equilibrium) in the study regions confirmed that uranium in groundwaters was mainly resulted from its host/parent rocks through weathering processes. The concentration of HCO3 − in ground water showed one order of magnitude higher than the total dissolved SiO2 indicates that carbonate weathering was the dominant process due to major water–rock interaction. The uranium speciation in groundwaters was investigated by an equilibrium model calculation using MEDUSA (make equilibrium diagrams using sophisticated algorithms) under the influence of redox conditions and complexant concentration. At the observed range of pH values, the predominant redox speciation of uranium was observed as hydroxo-carbonato complexes of (UO2)2(CO3)(OH)3 − and hydroxyl complexes of UO2(OH)3 − which might be caused for increasing the solubility of uranium. Due to very low concentration of phosphate in groundwater, its effects on U(VI)-aqueous speciation was negligible.

34

Rachou, Julien, and Sébastien Sauvé. "Evaluation of affinity constants of Cu, Cd, Ca and H for active soil surfaces for a solid phase-controlled soil ligand model." Environmental Chemistry 5, no. 2 (2008): 150. http://dx.doi.org/10.1071/en07093.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Environmental context. The speciation of metals in soils is controlled by the equilibrium between the solid and aqueous phases and by several parameters such as pH and total metal concentrations. The integration of affinity constants between several cations and active soil surfaces of different soils in the chemical equilibrium modelling software MINEQL+ allows a good evaluation of the chemical speciation of the metals. Abstract. A new approach, derived from the concept of the biotic ligand model, was used for the determination of the affinity constants of Ca, Cu, Cd and H to the active surfaces of different kinds of soils. This approach allowed us to obtain consistent data and to integrate these values in the chemical equilibrium modelling software MINEQL+ and eventually into a solid phase-controlled soil ligand model. This could then very easily be transformed into a terrestrial biotic ligand model by adding constants for biological components. We obtained the chemical speciation of the metals of interest by integrating the initial characteristics of the soil (pH; cation exchange capacity, CEC; total metal concentrations in soil extracts; ionic strength; and CO2 pressure). Comparison of the predicted and measured values of free Cu2+ is excellent using soil-specific affinity constants as well as average values. The average affinity constants between the active soil surfaces (S) and the target cations are log KCa–S = –0.84 (±0.01), log KCu–S = 5.3 (±0.1), log KCd–S = 4.4 (±0.2) and log KH–S = 4.1 (±0.2). External soils have been used to validate the conceptual model and the results show a very good correlation between the predicted and the measured free Cu (pCu) except for an acidic soil (pH < 5.2), highlighting the importance of integrating Al into the model.

35

Barton, Richard H., and Charmian J. O'Connor. "Uncatalysed Intramolecular Acyl Transfer in a Lipid Hydrolysis Product Mixture." Australian Journal of Chemistry 50, no. 4 (1997): 355. http://dx.doi.org/10.1071/c96112.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

The speciation of short-chain mixed acylglycerols in the product mix from enzymatic hydrolysis has been examined by 13C n.m.r. spectroscopy. Under conditions similar to those of the enzymatic reaction, but in the absence of any enzyme, sample mixtures were allowed to stand in buffered emulsions of known pH and temperature. There is clear evidence of uncatalysed conversion of rac-1,2-diacylglycerol into the 1,3-isomer to form an equilibrium mixture. Conversion kinetics to reach equilibrium are first order and do not depend on the state of the emulsion.

36

Fu, X., L. Cueto-Felgueroso, D. Bolster, and R. Juanes. "Rock dissolution patterns and geochemical shutdown of –brine–carbonate reactions during convective mixing in porous media." Journal of Fluid Mechanics 764 (January 5, 2015): 296–315. http://dx.doi.org/10.1017/jfm.2014.647.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

AbstractMotivated by the process of $\text{CO}_{2}$ convective mixing in porous media, here we study the formation of rock-dissolution patterns that arise from geochemical reactions during Rayleigh–Bénard–Darcy convection. Under the assumption of instantaneous chemical equilibrium, we adopt a formulation of the local reaction rate as a function of scalar dissipation rate, a measure that depends solely on flow and transport, and chemical speciation, which is a measure that depends only on the equilibrium thermodynamics of the chemical system. We use high-resolution simulations to examine the interplay between the density-driven hydrodynamic instability and the rock dissolution reactions, and analyse the impact of geochemical reactions on the macroscopic mass exchange rate. We find that dissolution of carbonate rock initiates in regions of locally high mixing, but that the geochemical reaction shuts down significantly earlier than shutdown of convective mixing. This early shutdown feature reflects the important role that chemical speciation plays in this hydrodynamics–reaction coupled process. Finally, we extend our analysis to three dimensions and explore the morphology of dissolution patterns in three dimensions.

37

Dickson, Okechukwu V., Thomas Deleau, Christophe Coquelet, Fabienne Espitalier, Julien Lombart, and Antoine Tardy. "Influence of the model used for the calculation of equilibrium constants at moderate temperature for electrolytes." MATEC Web of Conferences 379 (2023): 01003. http://dx.doi.org/10.1051/matecconf/202337901003.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

The formation of a solid mineral deposit can cause major problems in the conduct of industrial processes such as high pressure acid leaching. Knowledge of the chemical speciation and solubility product of the mineral can help control or inhibit its formation. This speciation is based on knowledge of the thermodynamic equilibrium constants of the dissociation/complexation reactions involved in the system and their temperature dependence. It also depends on the concentration of the different species in the system, the pressure and the activity coefficients of the chemical species present in their molecular or electrolytic form. From these thermodynamic quantities and the state of the system, it is possible to predict the direction of evolution of the reaction, i.e. whether the reactants or the products of the chemical reactions are favoured. This work presents and compares different models for the calculation of activity coefficients for ionic strengths between 0.001 – 6 molal and the calculation of thermodynamic equilibrium constants at temperatures up to 300°C (at zero ionic strength). It confirms the need for reliable thermodynamic data for modeling aqueous systems.

38

Brockman, Richard. "The End of Evolution." Psychodynamic Psychiatry 52, no. 1 (March 2024): 46–67. http://dx.doi.org/10.1521/pdps.2024.52.1.46.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Charles Darwin's theory of evolution was founded on the core belief that natural history is one of slow, incremental change, a concept he called “speciation.” A hundred years later Eldredge and Gould challenged Darwin's theory, arguing that the data of paleontology reveals something quite different: long periods of stasis followed by bursts of change, a concept they called “punctuated equilibria.” This article will follow that progression and then describe the three punctuated equilibria that I believe led to Homo sapiens. I argue that two of the three transitions are revealed in the hard data of the fossil record. The third is in the soft tissue of the brain. This third punctuated equilibrium placed Homo sapiens outside of evolution. Its arrival, 50,000 years ago, marked the beginning of the end of evolution.

39

Monk, Paul M. S., Robert Janes, and Robert D. Partridge. "Speciation modelling of the electroprecipitation of rare-earth cuprate and nickelate materials Speciation of aqueous solutions not at equilibrium." Journal of the Chemical Society, Faraday Transactions 93, no. 22 (1997): 3991–97. http://dx.doi.org/10.1039/a706095e.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Földényi, Rita, and Aurél Marton. "Organisation of the Analytical, Stoichiometric, and Thermodynamic Information for water Chemistry Calculations." Hungarian Journal of Industry and Chemistry 43, no. 1 (June 1, 2015): 33–38. http://dx.doi.org/10.1515/hjic-2015-0006.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Abstract A common feature of the chemical processes of the hydrosphere and water treatment plants is that essentially the same types of chemical equilibrium reactions occur in both fields. These equilibria could be acid/base, complexation, redox, precipitation, and interfacial processes. Since these reactions may also occur in combination, the aqueous environments are unavoidably multispecies systems. Due to multiple equilibria, the state of aggregation, the state of oxidation, as well as the electric charge of the species may change dramatically. Calculation of the equilibrium concentration of the species is facilitated by the availability of analytical, stoichiometric, and thermodynamic information that are consistently organised into an ASTI matrix. The matrix makes it possible to apply a uniform algebraic treatment for all occurring equilibria even, if later on, further reactions have to be included in the chemical model. The use of the ASTI matrix enables us to set up the necessary mass balance equations and equilibrium relationships, which together form a non-linear system of equations (NLSE). The goal of our paper is to show that the use of the ASTI matrix approach in cooperation with the powerful engineering calculation software, MATHCAD14, results in fast and easy handling of the NLSE-s and, consequently, the calculations of speciation in aqueous systems. The paper demonstrates the method of application in three examples: the calculation of the pH dependence of the solubility of calcite in closed and open systems, the calculation of the pH and pε in a system where acid/base reactions, complexation equilibria, and redox equilibria occur, and a study of adsorption of lead ions on aluminium oxide.

41

Al-Ananzeha, Nada M., John A. Bergendahlb, and Robert W. Thompsona. "A Kinetic Model for the Aqueous Degradation of MTBE by Fe0/H2O2." Progress in Reaction Kinetics and Mechanism 32, no. 3 (September 2007): 131–51. http://dx.doi.org/10.3184/146867807x244030.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Methyl tertiary-butyl ether (MTBE) is a possible human carcinogen that has been used as a gasoline oxygenate at concentrations of up to 15% by volume for about 45 years in the US. However, its high water solubility has exacerbated spills at gasoline stations, sometimes resulting in local groundwater MTBE contamination levels of over 100 mg/L. Advanced oxidation using Fe0 and H2O2 is a promising technique for mineralizing organic contaminants, but current understanding of the remediation chemistry needs to be improved to facilitate design of subsurface or engineered systems. A kinetic model for the degradation of MTBE in batch systems applying zero-valent iron (Fe0) andhydrogen peroxide (H2O2) oxidation in aqueous solution was developed. The model includes: H2O2 and water chemistry, iron speciation, and MTBE oxidation reactions. H2O2/water and MTBE degradation equilibrium and reaction rate parameters were taken from the literature. Reaction rate and equilibrium parameters for iron speciation were taken from the literature, or from our prior work. The rate constant for the dissolution of Fe0 was found from this work. The model was compared to experimental data from the literature for MTBE degradation using Fe0/H2O2

42

Li, Jiazhou, Jiantao Zhao, Linxian Zhang, Xin Dai, and Yitian Fang. "Predicting the vanadium speciation during petroleum coke combustion by thermodynamic equilibrium calculation." Journal of Thermal Analysis and Calorimetry 130, no. 3 (July 19, 2017): 2239–47. http://dx.doi.org/10.1007/s10973-017-6571-2.

Full text

APA, Harvard, Vancouver, ISO, and other styles

43

Facq, Sébastien, Isabelle Daniel, Gilles Montagnac, Hervé Cardon, and Dimitri A. Sverjensky. "Carbon speciation in saline solutions in equilibrium with aragonite at high pressure." Chemical Geology 431 (August 2016): 44–53. http://dx.doi.org/10.1016/j.chemgeo.2016.03.021.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

Serkiz, Steven M., Jerry D. Allison, E. Michael Perdue, Herbert E. Allen, and David S. Brown. "Correcting errors in the thermodynamic database for the equilibrium speciation model MINTEQA2." Water Research 30, no. 8 (August 1996): 1930–33. http://dx.doi.org/10.1016/0043-1354(96)00138-8.

Full text

APA, Harvard, Vancouver, ISO, and other styles

45

Li, Jiazhou, Jiantao Zhao, Shuai Guo, Xing Zhou, Yubo Liu, Jin Bai, and Yitian Fang. "Predicting the vanadium speciation during petroleum coke gasification by thermodynamic equilibrium calculation." Fuel 176 (July 2016): 48–55. http://dx.doi.org/10.1016/j.fuel.2016.02.007.

Full text

APA, Harvard, Vancouver, ISO, and other styles

46

Wu, Chang Y., and Pratim Biswas. "An equilibrium analysis to determine the speciation of metals in an incinerator." Combustion and Flame 93, no. 1-2 (April 1993): 31–40. http://dx.doi.org/10.1016/0010-2180(93)90082-e.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Zhang, Rui, Ruixi Liu, Francesco Barzagli, Meher Geetika Sanku, Chao'en Li, and Min Xiao. "CO2 absorption in blended amine solvent: Speciation, equilibrium solubility and excessive property." Chemical Engineering Journal 466 (June 2023): 143279. http://dx.doi.org/10.1016/j.cej.2023.143279.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Tella, Eleni, Antonios Trimpalis, Athanasios Tsevis, Christos Kordulis, Alexis Lycourghiotis, Soghomon Boghosian, and Kyriakos Bourikas. "Advanced Synthesis and Characterization of Vanadia/Titania Catalysts through a Molecular Approach." Catalysts 11, no. 3 (March 2, 2021): 322. http://dx.doi.org/10.3390/catal11030322.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Vanadia/titania catalysts were synthesized by the equilibrium deposition filtration (EDF) method, which is a synthesis route that follows a molecular-level approach. The type of interfacial deposition as well as the interfacial speciation of the deposited oxo-V(V) species were determined by means of a model that takes into account experimental “proton-ion” curves and “adsorption edges”. It is shown that at pH ≥ 9.5, the deposition proceeds exclusively through the formation of mono-substituted inner sphere monomeric species in an “umbrella”-like Ti–OV(OH)2O configuration, whilst with lowering of the pH, a second species, namely the disubstituted inner sphere quadrameric species in a (Ti-O)2V4O10 configuration possessing two mono-oxo V=O and two di-oxo V(=O)2 terminations gradually prevails, which is in co-existence with the monomeric species. Raman spectroscopy is used for verifying the solution speciation, which is different compared to the interfacial speciation of the deposited oxo-V(V) species. Furthermore, in situ Raman spectroscopy was used to verify the model-predicted interfacial speciation of the deposited oxo-V(V) species and to monitor the temperature-dependent evolution up to 430 °C. Hence, a controlled formation of a specific vanadia species on a titania surface is enabled, which, depending on the synthesis conditions, can result in specific catalyst characteristics and thus possibly different catalytic behavior for a specific reaction.

49

Gunneriusson, Lars, and Staffan Sjöberg. "Equilibrium Speciation Models for Hg, Cd, and Pb in the Gulf of Bothnia and its Catchment Area." Hydrology Research 22, no. 1 (February 1, 1991): 67–80. http://dx.doi.org/10.2166/nh.1991.0005.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Equilibrium speciation models were established for Hg (II), Cd (II) and Pb (II) in bog-, river- and sea water having a composition corresponding to that of the Gulf of Bothnia (6 ‰ salinity). The calculations were performed using the computer program SOLGASWATER. The models were based on available thermodynamic data at 25°C and included the inorganic ligands OH−, Cl−, Br−, HPO42− and CO2 (aq). Furthermore, complex formation with organic substances originating from a bog water was considered, Mg (II) and Ca (II) were also included as competing cations. All water types were assumed to be oxic and in equilibrium with atmospheric carbon dioxide, 10−3.5 atm (32 Pa). The calculations showed that the speciation of Hg (II) and Pb (II) in bog and river waters is dominated by complexation with the organic substance, except for lead (II), where the Pb2+ -ion dominates at pH⩽5. In the Gulf of Bothnia, the chloro complexes HgCl2 and HgCl3− becomes prevailing as the salinity increases. Besides Pb2+, the species PbCl+ and PbCO3 become important upon increasing the salinity and pH. The dominating fraction of Cd (II) is Cd2+ in bog water, in river water and in waters of salinity lower than 4.5 ‰. With increasing salinity CdCl+ and CdCl2predominate.

50

Solis, JS, G. Hefter, and PM May. "Chemical Speciation in the Copper (I)-Ammonia-Chloride System." Australian Journal of Chemistry 48, no. 7 (1995): 1283. http://dx.doi.org/10.1071/ch9951283.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Abstract:

Chemical speciation in the system CuI/NH3/Cl- which may be represented by the general equilibrium pCuI(aq)+qNH3(aq)+rCl-(aq)↔ Cup(NH3)qClr(p-r)+(aq) has been studied by glass electrode potentiometry at 25.0°C and an ionic strength of 1.00 M (NaClO4). A number of binary and ternary complexes were detected with formation constants, βpqr: logβ120 = 11.381�0.077, logβ111 = 8.920�0.045, logβ112 = 8.82�0.18 and logβ121 = 11.33�0.24. The ionization constant of water (pKw) and the protonation constant of ammonia (pKa) obtained by the same procedures were 13.7462�0.0012 and 9.4613�0.0010 at I = 1 (NaClO4), and 13.7165�0.0010 and 9.4521�0.0007 at I = 1 (NaCl) respectively.

Journal articles on the topic 'Speciation at equilibrium'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles