KINETICS ASPECT OF HYDROCHEMICAL FLUORINATION OF SILICON-CONTAINING INDUSTRIAL WASTE

Предложен способ получения высокодисперсного аморфного кремнезема из отходов обогащения низкотитанистых ванадий содержащих титаномагнетитов АО «ЕВРАЗ Качканарский ГОК» - хвостов мокрой магнитной сепарации. Применение раствора гидрофторида аммония ( NHHF) позволяет практически селективно извлечь кремний в раствор в виде гексафторосиликата аммония. Степень извлечения кремния раствором 1,0 - 2,5 мас.% NHHF за 6 часов составляет 46%. Диффузионный процесс выщелачивания кремния из ХММС описывается кинетическим уравнением 1 -(1 -а) = 0,0043• exp(-5230/RT)-г . Аморфный кремнезем SiO, полученный золь- гель методом из фторидного кремнийсодержащего раствора, имеет высокоразвитую поверхность S = 320 м/г, рассчитанный из средней плотности «белой сажи» размер частиц составляет d = 10 нм. Увеличение концентрации NHHF до 20 мас.% приводит к повышению растворимости кремния, а также других компонентов хвостов мокрой магнитной сепарации, которые являются нежелательными примесями в конечном продукте SiO. В целом показана перспективность гидрохимического выщелачивания кремнийсодержащих промышленных отходов - хвостов мокрой магнитной сепарации слабыми растворами гидрофторида аммония для синтеза чистого аморфного SiO. A method for producing amorphous silica from the enrichment wastes of low-titanium vanadium containing titanomagnetites of JSC «EVRAZ ZSMK» - wet magnetic separation tailings is proposed. The use of a NHHF solution makes it possible to practically selectively extract silicon into the solution in the form of ammonium hexafluorosilicate. The extraction of silicon with 1,0 - 2,5 wt.% NHHF solution for 6 hours reached 46%. The diffusion process of the silicon extraction is described by the kinetic equation 1 - (1 - a) = 0,0043 • exp(-5230 / RT)• t . Amorphous silica obtained by the sol-gel method from a fluoride silicon-containing solution has a highly developed surface 320 m/g, the particle size calculated from the average density of «white carbon black» is of 10 nm. The increase in concentration to 20 wt. % NHHF leads to the rise of the silicon solubility and of other tailings components, which are unwanted impurities in the final product. In general, it is shown that the hydrochemical leaching of silicon-containing industrial waste - tailings with weak solutions of ammonium hydrofluoride is promising for the synthesis of pure amorphous silica.

PHASE FORMATION PROCESSES AT LOW-TEMPERATURE FLUORINATION OF ZIRCONIUM SILICATE

Zirconium silicate ceramics is widely used in different fields of engineering. One of the most actual problem of zircon ceramics is the requiring of high temperatures for its sintering. Perspective method for activation of silicate materials with the aim of intensification of synthesis and sintering processes is the low-temperature fluoridation with the ammonium hydrofluoride. In accordance with that, processes occurring during the interaction of plasma dissociated zircon and natural zircon with ammonium hydrodifluoride were studied. It was established that plasma dissociated zircon actively interacts with ammonium hydrofluoride in the solid phase. Natural zircon because of its chemical inertness reacts with ammonium hydrofluoride only when latter melts. The main product of fluorinating is ammonium hexafluorosilicate. By-products are ammonium hexafluorozirconate and ammonium heptafluorozirconate. Their quantity increases with the content of ammonium hydrofluoride in mixtures. Kinetic equation of reaction between zircon and ammonium hydrofluoride is k×τ = 1-(1-α)1/n. Activation energy of plasma dissociated zircon and natural zircon fluorinating reactions are 13.9 and 32.7 kJ/mol, respectively. Order of reactions (n) are 2.0 and 1.5, respectively. Thermal treatment of fluorinated materials at 400 °C leads to ammonium hexafluorosilicate sublimation and thermal dissociation of ammonium fluorozirconates to zirconium fluoride and fluorozirconate intermediates. It was established that low-temperature fluoridation of zircon makes possible to regulate chemical composition of minerals. Materials obtained by ammonium hydrofluoride treatment of plasma dissociated and natural zircon can be potentialy used in the functional zircon and zirconia-zircon ceramics technology.

Phase formation processes in natural magnesium silicates of various structures by their ammonium fluoride treatment

The processes of forsterite, enstatite and talc treatment by ammonium fluoride have been studied. The phaseformation processes occurring during firing of fluorinated minerals were studied. It was established that structural silica of minerals reacts with ammonium hydrodifluoride with the formation of ammonium hexafluorosilicate. The sublimation of ammonium hexafluorosilicate leads to remove structural silica from minerals with partial destruction of their structure. The firing of fluorinated minerals leads to their structural transformation with the formation of magnesium nesosilicates and fluoronesosilicates.

EFFECT OF AMMONIUM HEXAFLUOROSILICATE ON INHIBITING GROWTH OF VEILLONELLA PARVULA

Objectives: This study analyzes the effects of ammonium hexafluorosilicate (AHF) on Veillonella parvula.Methods: In this in vitro study, solutions of NaF (25%, 50%, and 100%), AHF (25%, 50%, and 100%), and SDF (38%) were applied to solid mediumcultures of V. parvula and Streptococcus mutans. The disc diffusion method was used for testing bacterial sensitivity.Results: AHF was less effective than SDF but more effective than NaF for inhibiting growth of bacteria.Conclusions: AHF could be effective for inhibiting the growth of V. parvula without the side effects of SDF.

Measuring the Remineralization Potential of Different Agents with Quantitative Light-Induced Fluorescence Digital Biluminator

Background The aim of this study was to investigate the effectiveness of different remineralization agents by quantitative light-induced fluorescence digital Biluminator™ (QLF-D). Methods Artificial caries lesions were created, and the teeth were divided according to the tested materials: (i) distilled water, (ii) acidulated phosphate fluoride (APF), (iii) Curodont Repair (CR), (iv) ammonium hexafluorosilicate (SiF) and (v) ammonium hexafluorosilicate plus cetylpyridinium chloride (SiF + CPC). After treatment procedures, each of the samples was placed in artificial saliva. After demineralization and 1 and 4 weeks of remineralization procedures, fluorescence loss and lesion areas were measured with QLF-D. Data were statistically analyzed (α = 0.05). Results The fluorescence values of the demineralized enamel specimens treated with the various agents differed significantly compared with pretreatment values for both 1 and 4 weeks (p<0.05). At 4 weeks, the highest fluorescence gain was calculated in the CR, APF and SiF groups compared with the control (p<0.05). Conclusions APF, SiF and CR groups yielded greater remineralization ability than SiF + CPC and control groups.

Improved high-temperature hydrothermal stability of Cu-SSZ-13 by an ammonium hexafluorosilicate treatment

Cu-SSZ-13 catalysts were treated with ammonium hexafluorosilicate (AHFS) to improve their hydrothermal stabilities.