Oxana Spinu

Moldova State University · Institute of Chemistry

The chapter presents a thermodynamic approach for the complex chemical and redox equilibria investigation of mono- and two-phase systems containing metal ions of slightly soluble solid phases in different oxidation states. For heterogeneous systems, this approach utilizes thermodynamic relationships combined with original mass balance constraints....

The monograph “Practical applications to reactions in homogeneous and heterogeneous aqueous systems (complex chemical equilibria)”, prepared by Igor Povar, Oxana Spinu and Boris Pintilie, presents a model for disseminating the results obtained under the State Program 2020-2023, addressing a wide circle of specialists in different fields. The monogr...

In this chapter, original methods for determining thermodynamic properties such as the equilibrium activity product or solubility product of sparingly soluble compounds and the stability constants of complexes are described. Methods for determining concentration product and solubility are based solely on pH measurements of the saturated aqueous sol...

A thermodynamic approach was developed to predict the precipitation conditions of surfactants using the solubility product relationship between surfactant monomer concentrations, in order to calculate the monomer-precipitate equilibrium. This approach provides an explicit equation which predicts the amount of solid phase which forms in any surfacta...

The paper presents the results of a series of investigations on the indirect chronovoltametric dosing of alkaline earth metals, carried out in the Laboratory of the Analytical Chemistry at the Institute of Chemistry, currently called the Laboratory of Physicochemical Methods of Research and Analysis, conducted in 1971–1993 by the doctor of chemical...

Introducere Sistemele de surfactanți micști prezintă interes științific, precum și o valoare în tehnologia chimică. Agenții tensioactivi utilizați în aplicații practice sunt formați în esență dintr-un amestec de compuși activi de suprafață. Agenții tensioactivi sunt utilizați în numeroase aplicații, inclusiv în calitate de detergenți, în: flotare,...

Long-term prediction of the complex chemical processes and their practical consequences is only feasible by using simulation models. The chapter presents a thermodynamic approach to the study of complex chemical equilibria in natural aqueous multicomponent systems. Its quintessence consists in the thermodynamic analysis of the conditions of various...

A thermodynamic model has been developed and used to predict the precipitation conditions using the solubility product relationship between surfactant monomer concentrations, in order to calculate the monomer-precipitate equilibrium, in the mixtures of anionic and cationic surfactants for a wide range of pH variation and various initial chemical co...

Surfactants have a wide range of applications: in addition to their industrial use as detergents, being at the same time a serious source of drinking water and waste pollution, they play an important role in analytical and preparatory chemistry and biology as a means to reduce surface tension. An example of the precipitation phenomenon is laundry d...

Sodium dodecyl sulfate (SDS) is an anionic surfactant that has found application in personal care products, detergents, in cosmetics and cleaning products. An obvious disadvantage of using anionic surfactants as detergents is the formation of the precipitate with calcium (Ca2+) and magnesium (Mg2+) ions contained in hard water. Below the CMC level,...

The developed method of determining KS from pH metric data has a number of advantages compared to those used traditionally. First, in place of the residual concentrations of the salt components, only the pH value of the saturated solution is used in the derived expressions. Thus, the number of independent variables, which need to be measured experi...

In this paper, original methods for determining such thermodynamic characteristics as solubility K S0 product (KS) or the activity product ( )of slightly soluble hydroxides and acids are communicated. Developed methods for determining KS and solubility S are based only on the pH values of the saturated aqueous solution for a known initial compositi...

The application of a new hydrometallurgical process for gold extraction by thiosulphate leaching from Romanian mining wastes, coming from Balan and Deva deposits, was studied. There was obtained 85% of Au extraction after leaching; moreover, an integrated flow-sheet, including recycling of process solution and carbon, was outlined, based on results...

Aqueous polynuclear systems have been analyzed, for which the family of formation curves intersects at a common point. The analyzed graphical and computational method for determining the stability constants can be used as initial values within the iterative calculation process. In some cases, the stability constants are calculated using only the co...

The paper presents a new thermodynamic approach to studying mixed ligand complex formation reactions in the multi-component two-phase system “cuprous oxide-ammoniacal copper (I) thiosulfate aqueous solution” under real conditions. The quintessence of the developed approach consists in the thermodynamic analysis of concurrent reactions in the hetero...

p> The forms of occurrence of vanadium metal are determined by the major chemical reactions in the aquatic environment such as hydrolysis, oxidation, reduction, and precipitation. Depending on pH, potential and total concentration of inorganic ions and organic ligands, vanadium compounds may undergo various transformations to produce a whole range...

A thermodynamic method of the global Gibbs energy variation calculation for describing heterogeneous equilibria of transformations of calcium, strontium, and barium polyvanadates, that occur in systems MeO-V 2 O 5 -H 2 O, where Me is the alkaline earth element, has been developed and used. Its quintessence consists in the thermodynamic analysis of...

The paper presents a new thermodynamic approach to studying polynuclear complex formation reactions in multicomponent two-phase systems, solid phase plus saturated aqueous solution, under real conditions. The quintessence of this developed approach consists in the thermodynamic analysis of concurrent reactions on the basis of the introduced notion...

The influence of the interaction of calcium carbonate (CaCO3) and surface-active substances (SAS; surfactants) with different chain lengths and cationic and anionic hydrophilic centers has been analyzed. Laboratory simulations indicate reduced negative influences on cationic SAS nitrification/self-purification processes in the presence of anionic s...

On the basis of selected thermodynamic data, the standard electrode potentials of pos­sible half reactions in the Ru-H2O and Ru-Cl--H2O systems have been calculated. Using the thermodynamic approach developed by the authors, the potential - pH and potential - pCl diagrams for the considered system have been built.

On the basis of the selected thermodynamic data for Ru(III) and Ru(IV) compounds in addition to original thermodynamic and graphical approach used in this paper, the thermodynamic stability areas of sparingly soluble hydroxides as well as the repartition of their soluble and insoluble chemical species towards the solution pH and initial concentrati...

The key property of Frost diagram has been confirmed using thermodynamic and linear algebra methods. On the basis of the thermodynamic data, the areas of thermodynamic stability of ruthenium chemical species in different valence states as a function of pH for each degree of oxidation have been determined. Subsequently, based on the diagrams, calcul...

A novel type of diagrams based on graphical and numerical methods, which quantitatively describe the distribution of soluble and insoluble, inorganic and organic, monomeric and polymeric aluminium species in heterogeneous multicomponent systems "basaluminite - soil solution" has been used. This approach utilizes the thermodynamic relationships toge...

The main focus in this review is showing how to use the developed buffer theory for assessing and predicting the long-term phenomena of attenuation and natural remediation of ionic pollutants in contaminated aquatic ecosystems, as well as for analyzing the way by which metals move and transform within the environment, the distribution of metals in...

The correlation between global thermodynamic functions and such experimental data, which quantitatively characterize the precipitation – dissolution processes of sparingly soluble compounds, as the degree of precipitation and residual concentrations of the solid phase components in saturated solutions under real conditions, taking into account the...

The quantitative basis of the theory of buffer properties for two-phase acid-base buffer systems was derived. The analytical equations for buffer action with respect to all components βi of acid-base pairs for diverse multicomponent systems were deduced. A remarkable relation of proportionality was found between quantities . In heterogeneous system...

A 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 influe...

A thermodynamic approach for calculating heterogeneous equilibria in natural waters has been developed. The overall heterogeneous processes in the “solid phase – aqueous solution” system have been described by the generalized equation of reactions, where the soluble species are thought to be formed in quantities proportional to their molar fraction...

An approach has been developed to determine the equilibrium model in heterogeneous aqueous systems containing a mixture of solid phases from the initial composition of the heterogeneous mixture and the equilibrium values of the pH. This approach allows to significantly reduce the quantity of measured data, properly for solubility measurements. By u...