— We have synthesized photocatalytically active manganese-modified titanium dioxide-based materials and studied key features of the formation of the synthesized materials and their physicochemical and photocatalytic properties. Modification of TiO 2 with manganese has been shown to ensure preparation of nanopowders (4.8–2550 nm) with a specific free surface area from 0.56 to 479 m 2 /g. The synthesized powders have high photocatalytic activity (PCA) under illumination with visible light, which exceeds the PCA of unmodified TiO 2 of the same origin and that of Degussa P-25 commercially available titanium dioxide. An increased PCA level is offered by the manganese-modified materials containing both anatase and rutile, without separation of individual manganese phases.

С целью развития технологии переработки эвдиалитового концентрата, основанной на применении метода сорбционной конверсии, исследованы закономерности извлечения металлов из насыщавшихся в процессе сульфокатионитов, а также регенерация сульфокатионита и используемых для десорбции растворов для повторного применения. Приведены составы насыщенных сорбентов, в которых содержатся щелочные (натрий, калий), щелочноземельные и редкоземельные металлы, титан, цирконий (гафний), ниобий (тантал), алюминий, железо, марганец, природные радионуклиды. Исследована десорбция различными растворами. Установлено, что наиболее трудно десорбируется ниобий (тантал). Рекомендовано проводить двухстадийную десорбцию при температуре 20 °С: сначала десорбцию раствором 5 М NaCl, при которой достигается перевод в раствор большинства содержащихся в сорбенте металлов, а затем десорбцию циркония и ниобия раствором 1 М Н2С2О4. Рассмотрены вопросы дальнейшей переработки полученных десорбатов. В соответствии с проведенными ранее исследованиями из десорбатов на основе раствора 5 М NaCl дробной нейтрализацией сначала до рН 4 осаждается и отделяется примесный кек, содержащий торий, железо, алюминий, титан, затем до рН 7.5 - концентрат редкоземельных элементов и, наконец, при рН ≥ 10 - щелочноземельные металлы и марганец. Из десорбатов на основе раствора 1 М Н2С2О4 нейтрализацией NaOH до рН 10 осаждается цирконий (гафний)-ниобиевый концентрат, из которого раствором Na2CO3 выщелачивается цирконий (гафний). Отмечено, что после десорбции раствором 1 М Н2С2О4 получается сорбент в Н+-форме, что позволяет его использовать повторно для разложения эвдиалитового концентрата методом сорбционной конверсии. Показано, что раствор 1 М Н2С2О4 может быть регенерирован методом электродиализа из раствора Na2С2О4, полученного при осаждении коллективного цирконий (гафний)-ниобиевого концентрата. In order to develop the technology of eudialyte concentrate processing based on the use of sorption conversion, the patterns of metal extraction from sulphocationites saturated in the process and the regeneration of sulphocationite and solutions used for desorption for reuse are investigated. The compositions of saturated sorbents containing alkaline metals (sodium, potassium), alkaline earth and rare earth metals, titanium, zirconium (hafnium), niobium (tantalum), aluminium, iron, manganese, natural radionuclides are presented. Desorption with various solutions is investigated. It is found that niobium (tantalum) is most difficult to desorb. It is recommended to carry out two-stage desorption at a temperature of 20 oC: at first, desorption with a 5 M NaCl solution, in which the majority of metals contained in the sorbent are converted into solution, and then desorption of zirconium and niobium with a 1 M Н2С2О4 solution. The issues of further processing of the obtained desorbates are considered. In accordance with previous studies, the impurity cake containing thorium, iron, aluminium, titanium is precipitated and separated from desorbates based on a 5 M NaCl solution through fractional neutralization, initially to pH 4, then the concentrate of rare earth elements is separated by neutralization to pH 7.5, and, finally, at pH ≥ 10, alkaline earth metals and manganese. Zirconium (hafnium) - niobium concentrate is precipitated from desorbates based on 1 M Н2С2О4 solution through neutralization with NaOH to pH 10, and then zirconium (hafnium) is leached from it using Na2CO3 solution. It is stressed that the sorbent in the H+-form is formed after desorption with a 1 M Н2С2О4 solution, which allows using it repeatedly to decompose eudialyte concentrate by sorption conversion. It is shown that the 1 M Н2С2О4 solution can be regenerated by electrodialysis from the Na2С2О4 solution obtained by precipitation of the collective zirconium (hafnium) - niobium concentrate.

Синтезированы фотокаталитически активные материалы на основе титана и марганца. Изучены особенности формирования полученных материалов, их физико-химические и фотокаталитические свойства. Показано, что модифицирование TiO 2 марганцем приводит к получению нанодисперсных порошков (4.8–2550 нм) со свободной удельной поверхностью от 0.56 до 479 м 2 /г. Синтезированные порошки обладают высокой фотокаталитической активностью (ФКА) при облучении видимым светом, превышающей ФКА немодифицированного TiO 2 схожего генезиса и промышленного диоксида титана Р-25 фирмы Degussa. Повышенный уровень ФКА наблюдается для образцов, модифицированных марганцем, одновременно содержащих анатаз и рутил, без обособления отдельных фаз марганца.

Проанализированы результаты исследований по изменению при термообработке химического состава и структуры модифицированного гидроксида титана. Показано, что при нагревании во всех случаях сначала образуется анатаз, который при повышении температуры или/и продолжительности термообработки переходит в рутил. Температура начала перехода анатаз - рутил зависит от вида модифицирующего компонента. Переход происходит не скачком при определенной температуре, а постепенно в широком интервале температур, при этом одновременно могут существовать оба соединения. При постоянной температуре доля рутила возрастает с увеличением продолжительности термообработки. На основании проведенных исследований заключено, что в присутствии модифицирующих компонентов образцы диоксида титана представляют собой широкие классы нестехиометрических соединений с разной кристаллической структурой и переход анатаз - рутил не является полиморфным превращением I рода, а является следствием протекания различных химических процессов, включающих выделение анионных и/или катионных примесей в газовую или твердую фазу. The results of studies on changes in the chemical composition and structure of doped titanium hydroxide during thermal treatment are analysed. It is shown that anatase is formed at first under heating in all cases, and with further increase in temperature or in the duration of thermal treatment it is transformed into rutile. The temperature of the start of anatase-rutile transition depends on the type of doping component. The transition proceeds not abruptly at a certain temperature but gradually over a wide temperature range, while both compounds can exist simultaneously. At a constant temperature, the proportion of rutile increases with an increase in the duration of thermal treatment. It is concluded on the basis of the conducted studies that the samples of titanium dioxide in the presence of doping components represent the broad classes of non-stoichiometric compounds with different crystal structures, and the transition of anatase to rutile is not a polymorphic transformation of the 1st kind but it is a consequence of various chemical processes involving the release of anionic and/or cationic impurities into the gas or solid phases

The results of studies on changes in the chemical composition and structure of doped titanium hydroxide during thermal treatment are analysed. It is shown that anatase is formed at first under heating in all cases, and with further increase in temperature or in the duration of thermal treatment it is transformed into rutile. The temperature of the start of anatase-rutile transition depends on the type of doping component. The transition proceeds not abruptly at a certain temperature but gradually over a wide temperature range, while both compounds can exist simultaneously. At a constant temperature, the proportion of rutile increases with an increase in the duration of thermal treatment. It is concluded on the basis of the conducted studies that the samples of titanium dioxide in the presence of doping components represent the broad classes of non-stoichiometric compounds with different crystal structures, and the transition of anatase to rutile is not a polymorphic transformation of the 1st kind but it is a consequence of various chemical processes involving the release of anionic and/or cationic impurities into the gas or solid phases.

In order to develop the technology of eudialyte concentrate processing based on the use of sorption conversion, the patterns of metal extraction from sulphocationites saturated in the process and the regeneration of sulphoca-tionite and solutions used for desorption for reuse are investigated. The compositions of saturated sorbents con-taining alkaline metals (sodium, potassium), alkaline earth and rare earth metals, titanium, zirconium (hafnium), niobium (tantalum), aluminium, iron, manganese, natural radionuclides are presented. Desorption with various solutions is investigated. It is found that niobium (tantalum) is most difficult to desorb. It is recommended to carry out two-stage desorption at a temperature of 20 degrees C: at first, with a 5 M NaCl solution, in which the majority of metals contained in the sorbent are converted into solution, and then desorption of zirconium and niobium with a 1 M H2C2O4 solution. The issues of further processing of the obtained desorbates are considered. In accordance with previous studies, the impurity cake containing thorium, iron, aluminium, titanium is precipitated and sepa-rated from desorbates based on a 5 M NaCl solution through fractional neutralization, initially to pH 4, then the concentrate of rare earth elements is separated by neutralization to pH 7.5, and, finally, at pH >= 10, alkaline earth metals and manganese. Zirconium (hafnium) - niobium concentrate is precipitated from desorbates based on 1 M H2C2O4 solution through neutralization with NaOH to pH 10, and then zirconium (hafnium) is leached from it using Na2CO3 solution. It is stressed that the sorbent in the H+-form is formed after desorption with a 1 M H2C2O4 solution, which allows using it repeatedly to decompose eudialyte concentrate by sorption conversion. It is shown that the 1 M H2C2O4 solution can be regenerated by electrodialysis from the Na2C2O4 solution obtained by precipitation of the collective zirconium (hafnium) - niobium concentrate.

We have synthesized photocatalytically active molybdenum-modified titanium dioxide-based materials and studied key features of the formation of the synthesized materials and their physicochemical, adsorptive, and photocatalytic properties. The synthesized composites have high adsorption capacity and photocatalytic activity (PCA), which considerably exceeds the PCA of unmodified TiO2 of the same origin and that of Degussa P-25 commercially available titanium dioxide. The materials in which molybdenum is incorporated into the crystal lattice of anatase offer the highest PCA.

The results of studying of the nitric acid and NaOH + KOH alkalis’ mixture recovery from concentrated solutions in filter-press-type electrodialyzers with anion-exchange, cation-exchange, and bipolar membranes are presented. The necessity of the technological solutions preliminary purification from calcium and boron compounds was established, in order to obtain crystalline boric acid (H3BO3) and gypsum (CaSO4·2H2O). The possibility of obtaining, from purified concentrated salt solutions, acids and alkalis with a concentration of ~300–600 g/L suitable for reuse is shown. This can be provided only by the electrodialysis with anion- and cation-exchange membranes, while electrodialysis with bipolar membranes is complicated by noticeable contamination of both acidic and alkaline solutions with salts.

Photocatalytically active materials based on titania modified with tungsten (5–30 wt %) have been synthesized. Specific features of the formation of these materials and their physicochemical and photocatalytic properties have been described. It has been found that the modification of titania with tungsten provides the formation of nanodispersed powders (7.2–96.7 nm) with a free specific surface area of 6.4–215 m2/g. Using the example of gram-negative bacteria Pseudomonas fluorescens, it has been shown that photocatalysts based on titania modified with tungsten (10–30 wt %) and calcined at 600°C are highly efficient for the photocatalytic inactivation of the microbiota. The highest photocatalytic antibacterial activity has been exhibited by the 600-W-20 sample. Most of the bacteria are inactivated under irradiation with visible light of natural origin at an illuminance (E) of 14 500 lx during the first 20–45 min. Upon the introduction of unmodified titania, the 600-W-5 sample, and a commercial P-25 photocatalyst from Degussa as a photocatalyst, no inhibition of bacterial growth has been detected.

We have synthesized oxide composites based on tungsten-modified titanium dioxide and investigated specific features of their formation and their physicochemical, adsorptive, and photocatalytic properties. The results demonstrate that tungsten modification of TiO2 makes it possible to obtain nanopowders (7.2 to 96.7 nm in particle size) with a free specific surface area from 6.4 to 215 m(2)/g. The synthesized composites have been shown to have considerably higher adsorption capacity and photocatalytic activity (PCA) in comparison to unmodified TiO2 with the same thermal history and Degussa P-25 commercially available titanium dioxide. The materials in which tungsten is incorporated into the crystal lattice of anatase, without tungsten in the form of an individual phase, offer the highest PCA. The electrical conductivity of the composites has been shown to correlate with their PCA.

The oxide composites based on titanium dioxide modified by molybdenum have been synthesized. The peculiarities of the formation of these composites their physico-chemical and photocatalytic properties have been studied. It is shown that the modification of TiO2 with molybdenum provides obtaining nanodispersed powders (from 8.3 to 12.1 nm) with a free specific surface from 279 to 190 m2/g, respectively. It is shown that the synthesized composites have significantly higher photocatalytic activity (PCA) relative to unmodified TiO2 of similar genesis and industrial titanium dioxide P-25 of Degussa by the example of decomposition of various dyes.

The article presents the results of the studies of the physicochemical and photocatalytic properties of titanium dioxide modified with manganese, by the example of decomposition of organic dyes — ferroin and methylene blue. The correlations between the specific surface area and phase composition of the composites with their photocatalytic activity are revealed.

We have synthesized oxide composites based on TiO 2 modified with aliovalent cations, W 6+ , Co 3+ , Cu 2+ , and Fe 3+ , in the range 5–30 wt %. Its deviation from stoichiometry is increased by active generation of Ti 3+ cations during vacuum calcination at temperatures from 500 to 800°C. The photocatalytic activity (PCA) of the composites for dye degradation reactions under illumination with visible light exceeds that of analogous samples calcined in air. The PCA of the synthesized materials is an intricate function of their composition and structure. The highest PCA, which considerably exceeds the PCA of TiO 2 of similar origin and that of the commercially available Degussa P-25 TiO 2 , is offered by the optimal compositions of the W- and Cu-modified samples for ferroin and methylene blue degradation and the Co- and Fe-modified samples for aniline degradation.

The paper describes distillation of hydrofluoric acid from model and process acid fluoride-sulphate solutions. Conditions for the most complete distillation of hydrofluoric acid from fluoride-sulphate solutions were determined and proposed. Fluorosulphonic acid is formed in large amounts, as shown for model solutions containing hydrofluoric and sulphuric acids. Herewith, with increasing the concentration of acids, their interaction degree rises and fluorosulphonic acid is formed, as demonstrated. An increase in the heating temperature of the mixture leads to a substantial increase in acidity due to HSO3F content decrease. The larger the concentration of acids (especially, sulphuric) is, the higher heating temperatures are required to decompose HSO3F, as established. The formation of fluorosulphonic acid may have a significant effect on HF distillation degree, as shown. The energetic and economic cost in the processing of 1 m(3) of process acid fluoride-sulphate solution is calculated with an account of the initial concentration of HF of 78 g/L. Considering sulphuric acid regeneration and having excluded lime content for its neutralization, energy costs for processing of this solution do not exceed 4500 RUB. The findings explain high solubility of lanthanide fluorides compared to their dissolution in monobasic acids, as noted in a series of papers. Our earlier observations of decreasing the concentration of fluorine determinable by potentiometric titration relatively to initially introduced one at pH correction by using sulphuric acid, unlike that with nitric or hydrochloric ones were also explained.