Ruthenium redox equilibria 1. Thermodynamic stability of Ru(III) and Ru(IV) hydroxides

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 concentrations of ruthenium in heterogeneous mixture solid phase–saturated solution have been investigated. By means of the ΔG–pH diagrams, the areas of thermodynamic stability of Ru(III) and Ru(IV) hydroxides have been established for a number of analytical concentrations in heterogeneous mixtures. The diagrams of heterogeneous and homogeneous chemical equilibria have been used for graphical representation of complex equilibria in aqueous solutions containing Ru(III) and Ru(IV). The obtained results, based on the thermodynamic analysis and graphic design of the calculated data in the form of the diagrams of heterogeneous chemical equilibria, are in good agre-ement with the available experimental data

Ruthenium redox equilibria 3. Pourbaix diagrams for the systems Ru-H2O and Ru-Cl--H2O

On the basis of selected thermodynamic data, the standard electrode potentials of pos-sible 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

Ruthenium redox equilibria 2. Thermodynamic analysis of disproportionation and comproportionation conditions

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 species of different valence states as a function of pH for each degree of oxidation have been determined. Subsequently, based on the diagrams calculated for several values of pH, a narrow ΔpH value is determined, in which the dismutation of appropriate form takes place. Based on thermodynamic analysis, the exact value of the beginning of disproportionation (or comproportionation) is found. Finally, the developed revised Frost diagrams of ruthenium heterogeneous chemical and redox equilibria, as a function of pH and the total concentration of metal ion in solution, have been built

DISTRIBUTION OF SOLUBLE AND INSOLUBLE CHEMICAL SPECIES OF CHROMIUM (III) AND (VI) IN AQUEOUS SOLUTIONS

Abstract. On the basis of currently revised thermodynamic data for Cr(III) and Cr(VI) hydrolysis and photolytic equilibria in addition to original thermodynamic and graphical approach, used in this paper, the repartition of their soluble and insoluble chemical species has been investigated. By means of the diagrams "ΔG -pH", the areas of thermodynamic stability of chromium(III) hydroxide have been established for a number of the analytical concentration of Cr(III) in heterogeneous mixtures. The degree of polynuclearity for Cr (III) and Cr(VI) has been calculated for different initial composition of aqueous solutions. The diagrams of heterogeneous and homogeneous chemical equilibria have been used for graphical representation of complex equilibria in aqueous solutions containing Cr(III) and Cr(VI). The obtained calculated results correlate well with existing experimental data. Keywords: chemical equilibrium, chromium complexes, distribution diagram, Gibbs energy. Introduction The increased knowledge regarding the behavior of chromium in natural waters and soils is essential for the complete and accurate determination of its possible toxicity to the particular ecosystem, as well as for the development of methods which minimize the risk of pollution areas. Due to the complex, heterogeneous nature of the soil and surface waters, the determination of the chromium behavior may be a very diffi cult task. Only by understanding the specifi c mechanism of the reactions, in which chrome may participate, one can expect a truthful forecast of its behavior. Chromium Chromium is rarely found in nature as a free metal. Chromium can exist in all degrees of oxidation from 0 to VI. The most typical chromium degrees of oxidation are +2, +3 and +6, but +3 and +6 are most stable ones, while the oxidation states +1, +4 and +5 are rare found in nature. Cr(III) is much less toxic than Cr(VI) According to the World Health Organization (WHO) and the International Agency for Research on Cancer Cr(VI) is a carcinogen form. The inhalation of Cr(VI) can cause irritation of the nose and nosebleeds. After the contact of Cr(VI) with the human body, skin rashes, indigestion and ulcers, respiratory diseases, weakness of immune system, kidney and liver damage, alteration of genetic material, lung cancer and death may appear or be caused The concentration of chromium in contaminated area may be much higher. The local increase in the concentration of chromium in waters (mainly in rivers) is due to wastewater discharges from the metallurgy, electroplating, chemical and leather industries, as well as the health leach dumps etc. The concentration and type of substances present in the effl uent depend on the nature of industrial processes using chromium In natural waters, chromium exists in only two stable states, Cr(III) and Cr(VI). The presence and the ratio between these two forms dependent on the various processes that include chemical, photochemical, and redox processes, reactions of precipitation/dissolution and adsorption/desorption. The high concentrations of chromium in the nature cause mutagenic, teratogenic or carcinogenic effects. The highest concentration of chromium in the Chisinau city was found in samples of snails collected in the industrial zone, indicating a strong pollution of nearby territory by this metal (snails were collected in the vicinity of the factory of leather processing "Piele SA") and near the gas statio

pH-metric method determining the solubility and solubility products of slightly soluble salts of arbitrary composition

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 experimentally, is reduced. Furthermore, the potentiometric method, used to determine the pH, is sufficiently accurate, simple, and universal and does not necessitate the use of ion-selective electrodes. At the same time, the residual concentrations are usually measured by chemical methods, which are inferior in most cases, for several reasons, compared to the potentiometric method. Second, the KS value calculated by the developed method has a thermodynamic character. The organization of the experiment must be appropriate to the applied equations. Therefore, it is necessary to draw attention to the need for high accuracy in the process of preparing the initial solutions, because the initial concentrations of the precipitate components are included in the calculation formulas. The developed method for determining Ks can be applied for systems of any degree of complexity, which contain additional complexing agents

PH-metric method for determining the solubility and solubility products of slightly soluble hydroxides and acids

In this paper, original methods for determining such thermodynamic characteristics as solubility 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 composition of the heterogeneous mixture and the equilibrium constants of an arbitrary set of possible side reactions in the aqueous natural systems. The determination of solubility S and solubility product KS is also possible in the presence of other hydroxides or acids of known concentrations. Deduced equations allow the calculation of such characteristics, as the equilibrium concentrations of the components of slightly soluble compounds in aqueous phase and the degree of precipitation γ of the solid phase for different initial concentrations of the components of the heterogeneous mixture which are known in the process of preparing the mixture, requiring only experimental pH values of a saturated solution. From the known experimental pH data, S and KS were calculated for a series of hydroxides and acids of arbitrary composition. The obtained results correlated well with the known tabular values. Analysis of a number of real systems illustrated the deduced expressions, including calculations and theoretical explanations

Revised Pourbaix diagrams for the vanadium – water system

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 of chemical forms in aqueous systems. In this paper, a novel approach has been applied for calculating potential-pH (Pourbaix) diagrams, based on the developed thermodynamic analysis of chemical equilibria in the V–H2O system. On the basis of currently revised thermodynamic data for V(III), V(IV) and V(V) hydrolysis and original thermodynamic and graphical approach used, the repartition of their soluble and insoluble chemical species has been investigated. By means of ΔG–pH diagrams, the areas of thermodynamic stability of V(IV) and V(V) hydroxides have been established for a number of analytical concentrations of vanadium in heterogeneous mixtures. The obtained results, based on the thermodynamic analysis and graphic design of calculated data, are in good agreement with available experimental data

Influence of the interaction of calcium carbonate particles with surfactants on the degree of water pollution in small rivers

Introduction: 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. Results: Laboratory simulations indicate reduced negative influences on cationic SAS nitrification/self-purification processes in the presence of anionic species. This suggests the role of complex ionic formation [anionic SAS * cationic SAS] as a cause of this effect. UV-Vis spectra of lauryl sulfate (LS) and of cetyltrimethylammonium (CTMA), as well as of their mixtures in ratios of 2:1 and 1:1, treated by fine particles of CaCO3, display decreased amounts of SAS in analyzed solutions and their presence on the surface of CaCO3 nanoparticles. UV-Vis spectra reveal the decomposition of the complex [anionic SAS (SAS-An) * cationic SAS (SAS-Ct)] in solutions when CaCO3 is added. CTMA can be bonded by LS through hydrophobic chains, on the surface of CaCO3 particles. Therefore, CaCO3 modifies the nature of LS and CTMA interactions. This leads to an increased degree of toxicity of cationic SAS in aquatic environment. The amounts of CTMA in aqueous solutions are diminished in the presence of ammonium ion NH4 + (2 mg/L). In the presence of two orders higher concentration of ammonium ion, this effect strongly increases, making the association obvious. The structure of cationic SAS does not influence this effect. The obtained results have been confirmed both by timed natural aquatic sample analysis and laboratory simulations using water from Moldovan small rivers (Isnovat, Raut, and Bic). Conclusions: UV-Vis spectra and laboratory simulations demonstrate the change due to the addition of calcium carbonate. Simulations and laboratory tests of water samples from Isnovat, Bic, and Raut Rivers, establish the cationic SAS negative influence on treatment and self-purification processes

Application of Innovative Processes for Gold Recovery from Romanian Mining Wastes

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 obtained at a laboratory scale, using a schematic chemical circuit of treatment. Global recovery of the process (leaching-adsorption-desorption-electrodeposition) of about 75-80% of Au was achieved. The developed integrated flow-sheet, allows to recycle the reagents during the process, with a loss of only 5-10%, in particular thiosulphate and alcohol, for each complete circuit of treatment