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Stancheva R.,Geo Eco Consulting 2010 | Ivanov P.,Sofia University
Nova Hedwigia | Year: 2011

Cymbella orientalis var. delicatula var. nov., collected from the epilithon of the Vesselina stream in Bulgaria is described. Comparison of C. orientalis var. delicatula and the nominate variety shows differences in frustule outline, the shape of the apices, and the number of the areolae in the striae. A considerable geographical distance separates the Far East populations of C. orientalis and the European population of the newly described variety. Valve morphology of C. orientalis var. delicatula is compared to closely related species from Asia. Both distribution and ecology of C. orientalis var. delicatula are discussed considering its rare occurrence and application in regional stream biomonitoring studies. © 2011 J. Cramer in Gebr. Source


The bromide minerals solubility in the mixed system (m 1NaBr + m 2MgBr 2)(aq) have been investigated at T = 323.15 K by the physico-chemical analysis method. The equilibrium crystallization of NaBr·2H 2O(cr), NaBr(cr), and MgBr 2·6H 2O(cr) has been established. The solubility-measurements results obtained have been combined with all other experimental equilibrium solubility data available in literature at T = (273.15 and 298.15) K to construct a chemical model that calculates (solid + liquid) equilibria in the mixed system (m 1NaBr + m 2MgBr 2)(aq). The solubility modeling approach based on fundamental Pitzer specific interaction equations is employed. The model gives a very good agreement with bromide salts equilibrium solubility data. Temperature extrapolation of the mixed system model provides reasonable mineral solubility at high temperature (up to 100 °C). This model expands the previously published temperature variable sodium-potassium-bromide and potassium-magnesium-bromide models by evaluating sodium-magnesium mixing parameters. The resulting model for quaternary system (Na + K + Mg + Br + H 2O) is validated by comparing solubility predictions with those given in literature, and not used in the parameterization process. Limitations of the mixed solution models due to data insufficiencies at high temperature are discussed. © 2011 Elsevier Ltd. All rights reserved. Source


Christov C.,Geo Eco Consulting 2010
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2012

The experimental solubility data of bromide and sulfate minerals available in the literature are used to construct a chemical model that calculates solidliquid equilibria in mixed systems NaBrNa 2SO 4H 2O, KBrK 2SO 4H 2O, and CaBr 2CaSO 4H 2O from low to high solution concentration within the T=(0100) °C temperature range. The solubility modeling approach based on fundamental Pitzer specific interaction equations is employed. The resulting model for mixed systems gives a very good agreement with bromide and sulfate salts equilibrium solubility data available in the literature. Temperature extrapolation of the mixed system models provides reasonable mineral solubilities at low (0 °C) and high temperature (up to 100 °C). Limitations of the mixed solutions models due to data insufficiencies at high temperature are discussed. The model for mixed system CaBr 2CaSO 4H 2O at T=(050) °C was developed using pure electrolyte parameters of CaSO 4 interactions and without including into a model aqueous species CaSO 4 °(aq). It was showed that solution parameters fully account possible association reactions in low calcium sulfate molality regions of binary CaSO 4H 2O and mixed solutions. The model presented here expands the previously published temperature dependent sodiumpotassiumcalciumsulfate model by evaluating bromidesulfate mixing solution parameters and inclusion of 5 bromide minerals precipitating within NaKCaBrSO 4H 2O system. The model predictions on the effect of bromidesulfate mixing on the equilibrium deliquescence relative humidity (DRH) in NaBrNa 2SO 4H 2O and KBrK 2SO 4H 2O solutions are also given. © 2011 Elsevier Ltd. All rights reserved. Source

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