I. G. Gorichev

Influence of oxalic acid on the dissolution kinetics of manganese oxide

The kinetics and electrochemical processes of the dissolution of manganese oxides with various oxidation states in sulfuric acid solutions containing oxalate ion additives is studied under variable conditions (concentration, pH, temperature). The parameters favoring a higher degree of the dissolution of manganese oxides in acidic media are determined. The optimal conditions are found for the dissolution of manganese oxides in acidic media in the presence of oxalate ions. The mechanism proposed for the dissolution of manganese oxides in sulfuric acid solutions containing oxalic acid is based on the results of kinetic and electrochemical studies. The steps of the dissolution mechanism are discussed.

Interaction of manganese(IV) oxide with aqueous solutions of citric and sulfuric acids

The kinetic laws of the dissolution of manganese(IV) oxide using citric acid are studied as functions of the temperature and pH of a solution and the concentration of citric acid. The following kinetic parameters of the dissolution are calculated: the reaction rate, the reaction order with respect to citrate ions (n = 0.6), and the activation energy (Ea = 47.4 kJ/mol). The optimum conditions favoring an increase in the leaching intensity and economical consumption of the reactants are experimentally determined.

Kinetics of dissolution of cobalt oxides in acidic media

The kinetics of dissolution of cobalt oxides Co2O3 and Co3O4 in aqueous solutions of acids (H2SO4, EDTA) is experimentally studied. Dissolution rate W increases with the temperature or the EDTA concentration. The reaction orders of dissolution for hydrogen ions in sulfuric acid and EDTA (dlogW/dpH = 0.5 ± 0.1) and for anions (dlogW/dlog[An−] = 0.5 ± 0.1) are determined. A specific feature of the dissolution kinetics in EDTA is a maximum in the dissolution rate of the cobalt oxides at pH −1. The activation energy of the process Ea is 70 kJ/mol in H2SO4 and 60 kJ/mol in EDTA. The modeling of the process shows that the CoOH+ ion is a surface particle controlling the dissolution rate in mineral acids and the CoHY− ion, in the complexone.

Stimulating effect of phosphate ions on the dissolution kinetics of iron oxides in an acidic medium

The dissolution kinetics of iron oxides FeO, Fe2O3, and Fe3O4 in orthophosphoric acid is studied. The dependence of the rate of Fe2O3 (iron(III) oxide) dissolution on the nature of inorganic acids is examined. The values of the stationary potential in a magnetite electrode-orthophosphoric acid solution system are determined. It is established from the experimental results that the stimulating effect of phosphate ions is related to their influence on the potential at the oxide/solution interface.

Methods for calculating the kinetic parameters of carbonate decomposition from thermal analysis data

A procedure is proposed for an analysis of the data on the decomposition of inorganic carbonates (MgCO3, CaCO3, SrCO3, MnCO3, CoCO3) on the basis of results of thermogravimetric studies. The activation energy and the rate constant for carbonate decomposition are calculated taking into account the main points of the heterogeneous reaction kinetics. A comparative analysis of the obtained results is performed.

Kinetics of the dissolution of cobalt, nickel, and iron oxides in sulfuric acid

The modeling of dissolution of cobalt, nickel, and iron oxides in sulfuric acid shows that the rate-determining step of the dissolution is the passage of oxide complexes formed on the surface of oxide particles to a solution. A system analysis of the dissolution curves (α-τ) of the oxides is developed to calculate the kinetic parameters (

Dissolution mechanism of aluminum hydroxides in acid media

n_{H^ + }

Calculation of parameters of an electrical double layer at the magnetite/solution interface from potentiometric titration data on magnetite suspension

,Ea). Cobalt oxide Co3O4 dissolves in H2SO4 more rapidly than nickel and iron oxides (Ni2O3 and Fe2O3).

Study and simulation of the adsorption of dihydrogen phosphate ions on magnetite as a function of pH

The effects of the concentration, temperature, and potential at the hydroxide/electrolyte interface on the aluminum hydroxide dissolution in sulfuric, hydrochloric, and perchloric acids are studied. The limiting stage of the aluminum hydroxide dissolution in the acids is found to be the transition of the complexes that form on the aluminum hydroxide surface from the solid phase into the solution. The results of the calculation of the acid-base equilibrium constants at the oxide (hydroxide)/solution interface using the experimental data on the potentiometric titration of Al2O3 and AlOOH suspensions are analyzed. A mechanism is proposed for the dissolution of aluminum hydroxides in acid media.

Adsorption of dichromate ions on the red mud surface

A three-layer model of an electrical double layer at magnetite/aqueous 0.001–1 mol/L KCl solution interfaces has been considered in a pH range of 3.5–9.5. A procedure has been proposed for determining the constants of equilibrium reactions and the parameters of electrical double layers from the acid–base potentiometric titration data of magnetite suspensions in the solutions taking into account the generation of a surface charge. The determination of these constants and the parameters of the electrical double layer is based on the use of the point of zero charge. Software has been developed and used for calculating the main parameters of the electrical double layer within the framework of the three-layer model and the Graham–Parsons concepts.