A. M. Kalinkin

Mechanical activation of natural titanite and its influence on the mineral decomposition

Abstract Processes induced by mechanical activation of the natural titanite CaTiSiO 5 using a laboratory agate mechanical mortar and a planetary mill AGO-3 have been studied. Titanite consumes substantial amounts of atmospheric carbon dioxide during prolonged dry grinding in air. Carbonisation of titanite occurs alongside with its amorphyzation. According to FT-IR spectroscopic data CO 2 is present in the ground sample in the form of distorted CO 3 2− groups resulting in the characteristic double band in the 1500–1430 cm −1 region. Previously similar processes were revealed for Ca and Mg containing silicate gangue minerals such as enstatite MgSiO 3 , diopside CaMgSi 2 O 6 , akermanite Ca 2 MgSi 2 O 7 , and wollastonite CaSiO 3 . The CO 2 content in the ground titanite reached 4.0 and 7.0 wt.% after grinding in the laboratory agate mechanical mortar for 36 and 108 h, respectively. The amount of carbon dioxide consumed due to grinding increases with increasing CaO content in the chemical formula of minerals and correlates with Gibbs free energies of reactions of the crystalline minerals with CO 2 . The following sequence concerning carbon dioxide sorption ability was revealed: enstatite

Thermodynamics of phase equilibria of the K2SO4 + Rb2SO4 + H2O system at 25°C

Activities of water in the K2SO4+Rb2SO4+H2O system at 25°C have been measured isopiestically. On the basis of the experimental activities of water ternary parameters of the Pitzer equations have been calculated. According to our data and experimental solubility data from the literature, continous solid solutions between K2SO4 and Rb2SO4 are formed in this system. With the use of the Guggenheim polynomial for simulating excess functions of solid solutions on the basis of the original and literature solubility data, excess Gibbs energies of solid solution formation as well as a solubility diagram have been calculated. Results of the solubility calculation are in good agreement with experimental data.

Effect of mechanical activation of magnesia-ferriferous slags in carbon dioxide on their properties

Effect of the mechanochemical activation of magnesia-ferriferous slags in air and in carbon dioxide on their binding properties and the strength of samples, including those produced in fabrication of slag-alkaline binders was studied. Data on the composition of newly formed substances, furnished by scanning electron microscopy and X-ray fluorescence microanalysis, are presented.

Mechanochemical interaction of alkali metal metasilicates with carbon dioxide: 1. Absorption of CO2 and phase formation

Processes proceeding during the mechanochemical activation of alkali metal metasilicates M2SiO3 (where M is Li, Na, K) are studied in the air and in an atmosphere of carbon dioxide. At the initial stage of activation in a centrifugal planetary mill in an atmosphere of carbon dioxide, the main portion of supplied mechanical energy is expended for grinding and the mechanosorption of CO2 occurs in the regime of cleavage, i.e., on the freshly formed surfaces of particles. As the time of activation increases, the specific surface area becomes constant, which, however, does not substantially affect the rate of interaction between carbon dioxide and silicates. The absorption of CO2 occurs in the regime of friction on the active sites of already formed surfaces and is accompanied by the tribodiffusion of gas molecules into structurally disordered layers of particles. With identical amounts of supplied energy, the CO2/M2SiO3 molar ratio in the samples activated in the medium of carbon dioxide increases in the Li < Na < K series. The main product of mechanically induced interactions between Li2SiO3 and CO2 is the X-ray amorphous carbonate-silicate phase. In the case of sodium and potassium metasilicates, the reaction of mechanochemical substitution occurs to form corresponding carbonates, hydrocarbonates, and amorphous silica. It is shown that the character of mechanochemical interaction between M2SiO3 and CO2 depends on the change in the Gibbs energy of the transformation of silicate into corresponding carbonate, as well as on the melting temperature and the hygroscopicity of silicate.

Mechanosorption of carbon dioxide by Ca- and Mg-containing silicates and alumosilicates. Sorption of CO2 and structure-related chemical changes

The discovery of the unusual ability of Ca- and Mg-containing silicates in certain grinding regimes to absorb carbon dioxide from the environment in amounts comparable to the mass of the ground sample has stimulated interest in the study of mechanochemical effects. The range of objects for studying natural minerals, such as labradorite (CaAl2Si2O8)0.562(NaAlSi3O8)0.438, oligoclase (CaAl2Si2O8)0.148(NaAlSi3O8)0.852, diopside CaMgSi2O6, and akermanite Ca2MgSi2O7, as well as synthetic minerals gehlenite Ca2Al2SiO7 and wollastonite CaSiO3, is expanded to develop the model of deep mechanosorption of CO2 and to derive equations that allow the kinetic analysis of the absorption of carbon dioxide by silicates in the course of mechanochemical activation to be performed. Regularities revealed previously and analogies to the processes that occur upon the dissolution of carbon dioxide in silicate melts, are generalized. Data on the absorption of carbon dioxide by Ca- and Mgcontaining silicates and alumosilicates, depending on the duration of mechanochemical activation in an AGO-2 centrifugal planetary mill in the atmosphere of CO2 at a pressure of 105 Pa, are obtained. Based on the data of X-ray phase analysis and IR spectroscopy, structural chemical changes in minerals and the forms of carbon dioxide in mechanochemically activated samples are discussed. It is shown that the intense penetration of gas molecules in particle bulk and their “dissolution” in structurally disordered silicate matrix in the form of distorted CO32− ions occurs upon mechanosorption.

Mechanosorption of carbon dioxide by Ca- and Mg-containing silicates and alumosilicates: Kinetic regularities and correlations with the dissolution of CO2 in silicate melts

The kinetics of the deep mechanosorption of carbon dioxide by natural and synthetic silicates and aluminosilicates (labradorite (CaAl2Si2O8)0.562(NaAlSi3O8)0.438, oligoclase (CaAl2Si2O8)0.148(NaAlSi3O8)0.852, diopside CaMgSi2O6, akermanite Ca2MgSi2O7, gehlenite Ca2Al2SiO7, and wollastonite CaSiO3 in the course of mechanochemical activation in an AGO-2 centrifugal planetary mill at CO2 pressure of 105 Pa is studied. Equations are proposed that make it possible to calculate coefficients of mechanosorption that characterize the ability of CO2 molecules to penetrate into the disordered silicate matrix of minerals under intense mechanical actions with the formation of carbonate ions. Solubilities and diffusion coefficients of CO2 at temperature of 1900 K and pressure of 1500 MPa in silicate melts, the compositions of which coincide with those of studied materials, are calculated using published data. Correlations are revealed between the degree of silicate carbonization upon mechanochemical activation in carbon dioxide and the solubility of carbon dioxide in silicate melts with analogous compositions, as well as between coefficients of mechanosorption and diffusion of CO2 in melts.

Structural transformations of silicates upon prolonged grinding

Structural changes in diopside, CaMgSi2O6, and wollastonite, CaSiO3, upon prolonged (up to 84 h) grinding in a mechanic agate mortar under environmental conditions were studied. X-ray phase analysis and specific surface measurements were used to show that the stage of amorphization of the starting substances under mechanical treatment is followed by the formation of a partially ordered phase whose reflexes correspond to reflexes of α-quartz. Possible mechanisms of the structural transformations were discussed.

Kinetics of two-stage mechanochemical synthesis of calcium zirconate in CaCO3-ZrO2 system

Reaction of formation of calcium zirconate in CaCO3-ZrO3 system at 1:1 molar ratio is studied at 800, 850, and 900°C. Preliminary mechanoactivation of the reagents mixture in the centrifugal planetary mill was used. Obtained conversion data were analyzed using a macrokinetic model of two-stage mechanochemical synthesis applying the Jander and Zhuravlev-Lesokhin-Tempelman equations.

Kinetic and thermodynamic patterns of CaZrO3 formation at sintering zirconium dioxide with calcium carbonate

Experimental data were obtained on the kinetics of formation of calcium zirconate in the system of ZrO2-CaCO3 with a 1:1 molar ratio of the components at 1000, 1100, 1200, and 1300°C. The thermodynamic characteristics of reactions occurring during sintering zirconium dioxide and calcium carbonate were calculated. The changes in specific surface area of zirconium dioxide at heating and its effect on the kinetics of the studied process were investigated. Analysis of experimental data on the degree of CaZrO3 formation was performed using the fundamental equations of the kinetics of solid-state reactions. The best agreement between the calculation and the experiment was obtained for Jander and Zhuravlev-Lesokhin-Tempelman diffusion models.

Mechanochemical interaction of alkali metal metasilicates with carbon dioxide: 2. The influence of thermal treatment on the properties of activated samples

Processes proceeding during the heating of the samples of lithium, sodium, and potassium metasilicates mechanochemically activated in carbon dioxide are studied using thermal analysis, X-ray phase analysis, and IR spectroscopy. Upon the heating of the samples of sodium and potassium metasilicates, the reversal of phases occurs in the sequence according to their appearance during the mechanical treatment in the mill in the atmosphere of carbon dioxide. Hydrocarbonates are first decomposed to neutral carbonates followed by their interaction with silica to form metasilicates. In the course of thermal treatment of lithium sample, the metastable carbonate-silicate phase, which is formed due to the intense mechanosorption of carbon dioxide, is decomposed first. Afterwards, lithium carbonate formed at the final stage of mechanoactivation reacts with SiO2.