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The highly alkaline multicomponent systems TiO2–H2SO4–Na2SiO3–NaOH–H2O and TiO2–H2SO4–(NH4)2SO4–Na2SiO3–NaOH–H2O have been studied under conditions of hydrothermal synthesis, which gives new products with specified technical properties. It has been shown that, by a targeted selection of structure-forming components, in particular, titanium compounds, together with optimal parameters of hydrothermal treatment of the formed precursor, one can obtain compounds with given chemical composition and particle size and morphology. It has been found that the rate of structural transformations in the synthesis depends on the phase composition of titanosilicate precursors. Their hydrothermal treatment involves the alkaline and thermal hydrolysis followed by dehydration of the hydrolyzed phases of titanium(IV) and silicon. This is accompanied by the localization of free bonds ensuring the formation of Ti–O–Si–O bridges and their subsequent transformation into new structured species. [ABSTRACT FROM AUTHOR]

Pilot-plant testing of a laboratory technology for producing alkaline titanosilicate sorbent from the current titanium-containing technogenic waste from the enrichment of the Khibiny apatite–nepheline ore shows that this technology can be modeled on an enlarged (pilot-plant) scale. The parameters of the main technological operations in systems of various salt compositions are checked and optimized. For example, in the ammonium sulfate systems, a two-phase precipitate is formed, which consists of phases similar to the minerals zorite and ivanyukite at their weight ratio of about 1 : 0.8–1.0. A one-phase precipitate in the form of ivanukite crystals is formed in the sulfate system. A study of the technical and sorption properties characterized in the tests of sorbents finds that the absorption of the Cs+ cation is due to the substitution for the Na+ cation in the interframework space of the crystal. The Sr2+ cation is also substituted for Na+ and is additionally deposited on the sorbent particles due to the alkaline reaction of its surface. The sorption capacities of powder and granules for Sr2+ are, on average, 170 and 160 mg g–1, respectively; and for Cs+, 275 and 245 mg g–1, respectively. Tests will be continued as pilot batches of the sorbent with stable structure and properties are produced for testing in specialized organizations. [ABSTRACT FROM AUTHOR]

The possibility of using technogenic titanium-containing waste from the enrichment of apatite–nepheline ores to obtain import-substituting functional products, in particular fillers for temperature-controllable sealing agents used in advanced branches of technology (shipbuilding, aircraft, and rocket manufacturing), is examined. The method developed is based on the different solubility of the mineral components contained in the waste in hydrochloric acid medium, which makes it possible to separate titanite from apatite and nepheline by sequential processing at the first stage and to separate the titanosilicate precipitate from titanite (a precursor to obtain a filler) at the second stage. It is shown that the neutralization of the hydrochloric acid effluents formed after the first stage of treatment with ammonia water at pH 7–12 provides almost complete precipitation of the aluminum and calcium in them as hydrophosphate amorphous phases and of the silicon as silica. The phase composition of the precipitate obtained remains almost unchanged during its heat treatment (T = 500°C). There is only a decrease in the specific surface area of the particles, which indicates the compaction of its structure. It is recommended to use the sediment thus obtained as an additive to increase the strength of concrete. [ABSTRACT FROM AUTHOR]

The sorption of 137Cs and 90Sr radionuclides from model and real solutions of various salt compositions has been studied on a synthetic powder and pelletized titanosilicate represented by ivanyukite (SIV), the technology of which was developed at the Kola Science Center, Russian Academy of Sciences. Titanosilicate sorbents successfully recover Cs and Sr from mixed multicomponent solutions in a broad pH range (from 4 to 11) at a salt content of up to 10 g/L with a purification coefficient of more than 200 in the case of powder materials. In the case of a pelletized sorbent, the distribution coefficient Kd decreases due to the partial dissolution (peptization) of silicate binder, which results in a decrease in the effective specific surface of sorbent. When there is no salt background, the sorption of radionuclides by SIV significantly decreases. This fact is caused by the protonation of the sorbent and, consequently, competition between hydrogen ions and radionuclides. The extraction ability of SIV towards 137Cs and 90Sr, as well as 51Cr, 54Mn, and 60Co, in the presence of the salts of other elements in the form of unfiltered suspension allows one to carry out sorption without a preliminary water preparation stage, which is represented by precipitation with iron or aluminum salts. The sorption characteristics of SIV have been compared to the Termoksid-35 ferrocyanide sorbent employed in industry for the recovery of 137Cs. The possibility of using one type of sorbent, SIV, for deactivating liquid radioactive waste (LRW) instead of the conventional purification scheme employed at an enterprise would remarkably facilitate the sorption scheme of processing of LRW. Considering this feature of SIV, one can expect a decrease in the volume of secondary radioactive waste in the form of spent sorbents for subsequent utilization. Verifying the process in dynamic mode has confirmed the effectiveness of SIV for processing LRW. The possibility of utilizing the spent sorbent in the form of ceramic material of SYNROC type possessing high radiation and chemical stability is an important potential advantage of SIV. [ABSTRACT FROM AUTHOR]

Apatite-nepheline ores of the Khibiny deposits contain the largest phosphorus-bearing resources in the world, and, at the same time, they contain associated valuable components in the rock-forming minerals -- apatite, nepheline, sphene and titanium magnetite. Intensive development of the Khibiny deposits with production of only apatite concentrate and a small part of nepheline concentrate resulted in the accumulation of over 1.0 billion tons of wastes in tailing storage facilities and dumps during 90 years of JSC Apatit operation. The possibility of increasing the efficiency of the use of the main concentrates of apatite-nepheline ores of the Khibiny deposits and wastes for their processing is considered through the use of technological developments of the FRC KSC RAS, JSC RIFI and JSC Apatit to obtain traditional and new target products. A fundamentally new approach to the problem of sustainable use of natural resources is focused on establishment of the whole production chain in the region, from mining and processing operations to manufacturers of final high technology products (rare-earth products, welding and construction materials, coloring agents and other materials). They also determine the level of industrial technical progress. [ABSTRACT FROM AUTHOR]

Using a titania–silica precursor with the composition SiO2 ∙ TiO2 ∙ хH2O, isolated via hydrochloric acid treatment of a process waste from the dressing of apatite–nepheline ore, we have prepared a hybrid composite containing silica as a matrix for an α-Ti(HPO4)2 ∙ H2O functional filler (STP). The key step of the synthesis process is a solution-phase reaction of the precursor with phosphoric acid. Our results demonstrate that a preferable sequence of steps begins with the mechanical activation of the components of the precursor, with their phase transformations. Using a combination of subsequent heat treatment with phosphoric acid with different concentrations under atmospheric conditions and in an autoclave, we have found conditions for chemical reactions that change the composition and structure of the final product and, accordingly, its sorption activity for cesium and strontium cations. The synthesized hybrid inorganic material can be effectively used to remove radionuclides and heavy nonferrous metal cations from liquid discharges. The proposed technology significantly surpasses known processes in economic and environmental characteristics. [ABSTRACT FROM AUTHOR]

The conditions for the preparation of framework titanosilicates with zorite and ivanyukite structures were studied. The preparation of a gel-like precursor for hydrothermal synthesis is preferably performed from solutions. An excess amount of silicon relative to titanium(IV) and an alkaline medium with pH 10.5–12.5 provide oversaturation of the salt mass in the Na2O–K2O–TiO2–H2SO4–SiO2–H2O system. This makes it possible to regulate phase formation, ensuring the stability of the structure and surface properties of the final products. To inhibit titanium(IV) hydrolysis, the reduction Ti4+ → Ti3+ is performed. This technique leads to the formation of a monophase precipitate. [ABSTRACT FROM AUTHOR]

The structural and morphological changes of titanium dioxide particles in the process of ultrafine fragmentation have been studied by means of the X-ray diffraction analysis and BET method based on N2 adsorption-desorption. The sizes of crystallites and microdeformations that indicated a breakage of their structural order with the formation of new phase fragments similar to brookite have been calculated from broadening of diffraction reflections using the method of approximation applying the pseudo-Voigt function. In the study of the morphology of titanium phase particles, it was determined that nitrogen adsorption was described by the isotherm of the IVa type in the p/p0 range of 0.1–0.95 and by the isotherm of the II type at p/p0 higher than 0.95 after mechanical activation in the presence of surface-active substance (SAS). The hysteresis loop of the samples' isotherms is related to the H3 type, which is characteristic of particles with a lamellar morphology. The porous particle system was represented by mesopores of a diameter varying within the range of 20–50 nm. The total volume of micropores was not higher than 10% of their total volume. A monophase product with a rutile structure and the crystallites' size increase was formed from the activated sample at annealing. The specific surface area of titanium dioxide after annealing varied in the range of 6.5–7.5 m2/g, which is about three times higher than the same value for conventional rutile grades. [ABSTRACT FROM AUTHOR]

Using X-ray diffraction study of the solid phases formed in an alkaline titanosilicate system with an invariable concentration of components upon process temperature variation in the 180–210°C range and time variation from 1 to 7 days, structural genesis of the solid phases was established. This allowed predicting the final result, consisting in the formation of an ion exchange material as a powder or granules with a high sorption capacity for Cs+ and Sr2+ cations. The formation of granules of the titanosilicate sorbent with a colloidal silicon binder induced agglomeration of particles with partial isolation of their pore system, which decreased the sorption capacity for Cs+ by a factor of 1.5. Simultaneously, the uptake of Sr2+ increased by 10–15% due to the formation of insoluble Sr2+ silicate or hydroxide on the surface with pH of 8.5–9.5. [ABSTRACT FROM AUTHOR]

The metastable structure state of the anatase phase of titanium dioxide has been shown to be a favorable basis for a targeted influence on it with the aim of producing new oxide phases consisting of nanoparticles and, accordingly, having a new combination of properties. Mechanical activation and subsequent annealing of the activated powders result in a sequence of phase transformations (anatase–brookite–rutile), thereby ensuring structural ordering of titanium dioxide. Transformations of the titanium oxide phases have been studied in detail by X-ray diffraction. We have evaluated the crystallite (coherent scattering domain) size and internal strain (ε) from diffraction line broadening by profile fitting with the pseudo-Voigt function. The average particle size was 20 nm after mechanical activation, whereas heat treatment increased it by almost a factor of 2. Similar results have been obtained for internal strain. The pore system of the particles is formed by mesopores. The hysteresis loop observed in nitrogen sorption–desorption isotherms suggests that the titanium dioxide particles have platelike morphology. The results obtained in this study have been used to develop innovative technology of a special grade of titanium dioxide for the preparation of thermally stable glues with dielectric properties and high tensile and shear strength. [ABSTRACT FROM AUTHOR]

Phase formation within the Na2O–TiO2–SiO2–H2SO4–H2O system under hydrothermal treatment was studied in view of the development of new types of sorbents characterized by a framework structure similar to that of ivanyukite (Na4(TiO)4(SiO4)3 · 4–6Н2О). The excess of silicon and sodium related to titanium (III) and (IV) along with an alkaline medium of pH values up to 12 causes the "supersaturation" of the salt mass and controls the formation rate of the sediments by stabilizing the phase composition, structure, and surface conditions. The specificity of interactions between SiO4 tetrahedrons and TiO6 octahedrons in ivanyukite promotes the formation of channels containing Na+ ions and water molecules. This effect combined with the developed mesoporous surface of the grains permits the use of synthetic ivanyukite as an effective ion exchanger. [ABSTRACT FROM AUTHOR]

An important state in the technology of a compositional silicon-containing titanium phosphate adsorbent is studied. The conditions of washing of the adsorbent precursor obtained from a sulfate-containing titanium(IV) solution with an addition of sodium silicate by combining it with orthophosphoric acid are studied in relation to the technical and sorption characteristics of the prepared granulated adsorbent. The washing scheme combining the treatment of precursor by water and alkaline solutions ensures removal of the acidic mother liquor from the precursor while it is still on the filter. The developed washing scheme defines the sequence of applying the washing solutions and their quantities and enables us to control the extent of hydrolysis of the solid phase, limit the loss of amorphous silica from the titanium phosphate matrix, and create a desired pore system on the particle surfaces. By optimizing the washing conditions for the silicon-containing titanium phosphate precursor, we gain better control over the preparation of the target granulated product with the required performance and sorption characteristics. As a result, the technological effectiveness of the process is improved due to shorter process duration and a nearly triple reduction in the required amount of the washing waters. [ABSTRACT FROM AUTHOR]

A study was made of structural, morphological, and chemical transformations in solid-phase systems based on sulfate, oxide, and hydroxide compounds of titanium(IV) under the intense mechanical activation of solid particles. This enabled one to substantiate the phase formation mechanism initiated by the intense homogenization of the reaction mixture, which is accompanied by a decrease in the particle size, deformation of the particle structure, and the formation of a new active surface. The obtained results formed the physicochemical basis for developing an innovative nonwaste technology for producing a new grade of titanium dioxide in the rutile modification from titanium sulfate salt under a program performed by the Roscosmos State Corporation for Space Activities. [ABSTRACT FROM AUTHOR]

The influence of the nature of a silicon-containing component used in synthesis of the composite based on titanium phosphate on its composition and sorption properties has been studied using physicochemical methods of analysis. The relationship between the structural modifications of the silicon-containing phase formed in a solution of titanium(IV) sulfate and the sorption properties of the composite ion exchanger thus obtained has been established. It has been shown that the presence of amorphous silica in the composite sorbent favors an increase in its sorption capacity with respect to nickel cations, which is due to the adsorption processes occurring on the surface of the active dopant. [ABSTRACT FROM AUTHOR]

Physical and chemical methods of analysis were used to study the effect of chemical modification of titanium phosphates on their sorption properties, depending on the chemical composition of a composite and nature of a modifier. The dependence of exchange capacity of the materials on the degree of their crystallinity was determined. [ABSTRACT FROM AUTHOR]

The sulfuric acid method of dissolving metallic waste containing rare-earth elements and iron with the obtainment of a sulfate rare-earth concentrate and an iron-containing solution is described. The distribution of the components into solid and liquid reaction products has been studied. The conditions of the conversion of rare-earth sulfate elements into hydroxide and fluoride compounds have been found. The principal possibility of utilizing iron-containing sulfuric acid filtrates with the obtainment of iron oxide pigments of a wide range of colors, catalysts, and coating components of welding electrodes is shown. [ABSTRACT FROM AUTHOR]

The rate of titanium (IV) extraction from sphene concentrate by its treatment with sulfuric acid solutions was determined. The sulfatization conditions to form stable titanium (IV) sulfate solutions suitable for preparing crystal substances—titanyl sulfate and ammonium titanyl sulfate—were found. The kinetics of the crystallization was studied. The phase composition of the titanium salts was established, and the content of impurities was determined by using X-ray analysis. It was shown that the technology for producing titanium salts is simple, which makes it possible to prepare in a few operations the precursors for the synthesis of hard-to-get expensive titanium-containing materials. [ABSTRACT FROM AUTHOR]

The structural characteristics of cleaved mica are studied. Cleavage of phlogopite and muscovite is shown to be accompanied by the deformation of their crystal lattices. The structural charge emerging as a result amounts to 90–95% of the total charge of the mica surface. The acid–base properties of the surfaces of these minerals are studied by the method of potentiometric titration. As is shown using constant capacitance surface complexation model, only deprotonation reactions are characteristic for muscovite, whereas phlogopite undergoes also ion-exchange reactions. The corresponding constants of acid–base equilibrium are determined. [ABSTRACT FROM AUTHOR]

The kinetic properties of the sorbent with respect to cadmium and cobalt ions from dilute solutions have been studied in detail. To determine the limiting stage in the general mechanism of sorption, models of external and internal diffusion, as well as models of pseudo-first and pseudo-second order reactions were used. It is shown that, in the initial period of sorption time, the total rate is controlled by the mechanism of film diffusion. It has been established that when the sorbent is 99% saturated, internal diffusion in the pores is the limiting stage. It has been shown that the chemical interaction between the dissolved substances and the sorbent surface is most adequately described by the pseudo-second order reaction model. The efficiency of the sorbent was confirmed during the sorption of cadmium and cobalt ions in the presence of a high concentration of calcium ions. [ABSTRACT FROM AUTHOR]

The hydrolysis of titanium(IV) sulfate during boiling in the presence of silica gel particles is considered. The scenario of solid-phase formation involves the sedimentation of hydrated titanium(IV) onto reactive silica gel particles; and individual phases of silicon(IV) and titanium(IV) hydroxides are formed. The quantitative ratio between the phases of the hydrated composition dictates the properties of its thermolysis products. Composition-property diagrams are plotted to determine the optimum parameters at which the titanium silicate product has high pigment properties. [ABSTRACT FROM AUTHOR]

The possibility to synthesize titanium phosphate from crystalline titanium salts has been shown for the first time. Optimal synthesis conditions have been found to provide preparation of monophase product of composition Ti(HPO4)2 · H2O or TiO(OH)H2PO4 · 2H2O by heterogeneous reaction of titanium-containing precursors with phosphoric acid. The process has been found to proceed for 3–5 h at stoichiometric consumption of the components and provides more environmentally benign and profitable conditions as compared with the known methods of synthesis. [ABSTRACT FROM AUTHOR]

The effect of temperature and the cesium concentration in the external solution on the sorption capacity of titanium phosphate obtained upon the heterogeneous interaction of the (NH4)2TiO(SO4)2 · H2O crystalline salt with phosphoric acid is studied. Sorption on titanium phosphate is shown to be best described by the Langmuir isotherm. When describing the sorption kinetics of solutions, it is necessary to consider both the possibility of diffusion and adsorption limiting the process rate. The use of the chemical kinetic models shows that the stage of chemical interaction of metal ions with functional groups of the sorbent also contributes to the overall rate of the process. [ABSTRACT FROM AUTHOR]