Revised Pourbaix diagrams for the vanadium – water system

Igor Povar,Stefano Ubaldini,Boris Pintilie,Inga Zinicovscaia,Oxana Spinu

doi:10.5599/jese.620

Abstract

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.

Highlights

Vanadium oxides (V-O) have been widely studied during the last three decades [1,2,3,4,5,6,7,8,9,10,11,12], mostly due to their broad applications in catalysis and microelectronics
In order to create the complete picture of thermodynamic properties of elemental compounds in different valence states both in aqueous solution and in solid phases, the potential-pH) (or ΔGr (pH) diagrams, so-called Pourbaix diagrams, have to be used
Within the used thermodynamic approach, the solid phase is stable for ΔGr < 0, and dissolves for ΔGr > 0

Summary

Introduction

Vanadium oxides (V-O) have been widely studied during the last three decades [1,2,3,4,5,6,7,8,9,10,11,12], mostly due to their broad applications in catalysis and microelectronics. A simultaneous presence of several species in different degrees of oxidation is characteristic and a number of compounds in the V–O system may coexist. In order to create the complete picture of thermodynamic properties of elemental compounds in different valence states both in aqueous solution and in solid phases, the potential-pH diagrams, so-called Pourbaix diagrams, have to be used.

Results

Conclusion