Influence of the textural and structural functions of the Urals carnallite rocks on the kinetics of dissolution processes

В статье показана необходимость исследования кинетики процессов растворения карналлитовых пород Приуралья. Описана методика подготовки образцов и лабораторного изучения скорости растворения. Представлены данные о химическом составе образцов 4-х цветовых разностей карналлитовых пород, текстурно-структурных особенностей, результатов по определению скорости растворения и вещественного состава нерастворимого в воде остатка. Цель исследования заключалась в изучении скорости и процессов растворения в воде при температуре 500С в режиме вынужденной конвекции и оценке влияния текстурно-структурных особенностей карналлитовых пород. Задачами исследования являлись: определение солевого и минерального составов, изучениеструктуры и микровключений в шлифах, проведение экспериментов по кинетикерастворения. При решении поставленных задач использовались следующие методы: АЭС-спектрометрия, петрографический анализ, гидростатический метод, РКФА. Проанализирован фактический материал исследования, сделаны соответствующие выводы. Проведенными исследованиями было показано, что важными факторами, влияющими на кинетику процессов растворения, являются вещественный состав и текстурно-структурные свойства. В работе определена суммарная (массовая) скорость растворения образцов. Железооксидная пленка, оконтуривающая зерна карналлитовых пород, экранирует поверхность растворения, замедляя процесс диффузии. Наличие галита и неравномерное его содержание вызывает колебания скорости растворения изамедляет процесс растворения во времени. Микровключения газов положительно влияют на динамику процесса растворения, усиливая конвекцию и массоперенос. С увеличением гидродинамических параметров растворителя (плотности и вязкости) скорость растворения понижается. Установленные закономерности могут оказывать существенное влияние на процессы, происходящие при скважинной добыче (подземное растворение) и галургической переработке карналлитовых руд. The article shows the need to study the kinetics of the dissolution processes of carnallite rocks of the Permian deposits of the Urals. The technique of preparation of samples, laboratory study of the rate of dissolution in water is described. The data on the chemical composition of samples of 4-color differences of carnallite rocks, textural and structural features, the results of determining the rate of dissolution and the material composition of the water-insoluble residue are presented. The purpose of the study was to study the rate and processes of dissolution in water at a temperature of 500C in the forced convection mode and to assess the influence of the textural and structural features of the carnallite rocks of the Urals. The objectives of the study were: determination of salt and mineral compositions, study of textural and structural features and assessment of the effect of microinclusions on the kinetics of the dissolution process. When solving the tasks, the following methods were used: study of the textural and structural features of carnallite rocks - by the petrographic method; determination of the rate of dissolution and density of samples - by the gravimetric method; determination of the density of brines - pycnometric method; the chemical composition of the initial samples and solutions (brines) was analyzed by AES-spectrometry; the mineral composition of the water-insoluble residue - by X-ray quantitative phase analysis. The factual material of the research is analyzed, the corresponding conclusions are drawn. Studies have shown that important factors affecting the kinetics of dissolution processes are the material composition and textural-structural properties. In this work, the total (mass) rate of dissolution of samples was determined, including the vertical and horizontal components. The iron oxide film outlining the grains of carnallite rocks screens the dissolution surface, slowing down the diffusion process. The presence of halite and its uneven content causes fluctuations during dissolution, slowing down the dissolution process over time. Microinclusions of gases have a positive effect on the dynamics of the dissolution process, enhancing convection and mass transfer. With an increase in the hydrodynamic parameters of the solvent (density and viscosity), the dissolution rate decreases. The research results can be suitable for the organization of mining by underground dissolution and for the processing of carnallite rocks of the Permian deposits of the Urals by the halurgical method.

A New Perspective on Fluorapatite Dissolution in Hydrochloric Acid: Thermodynamic Calculations and Experimental Study

Apatite (Ap) dissolution in diluted acids is well described in the literature, but in technological processes which use more concentrated acids, the reaction is fast, and it is complicated to follow the process kinetics. The relationship between pH change and the apatite dissolution rate depending on HCl concentration was studied by thermodynamic calculations and experiments with synthetic fluorapatite (FAp). On the basis of experimental pH measurements, the kinetics of dissolution was analyzed. The solution composition (P, Ca, F) was determined by wet chemical methods and the solid part was characterized by XRD and FTIR. It was shown that the amount of HCl needed for FAp dissolution depends on acid concentration. FAp dissolution rate cannot be deduced from solubility data of P, Ca or F as the secondary reactions of CaF2 and CaHPO4 formation take place simultaneously. It was found that the Ap dissolution rate can be followed by pH change.

Comparative studies of the kinetics of dissolution of medicines on the basis of clopidogrel

Generic medicines occupy dominant positions both in the pharmaceutical market of Ukraine and in industrial production by domestic pharmaceutical enterprises. The use of generic drugs in medical practice is of significant medical and social importance for expanding the accessibility of the general population to essential drugs. In Ukraine, more than twenty generic medicines based on clopidogrel, both foreign and domestic, are registered. All generic drugs containing clopidogrel bisulfate must comply with pharmaceutical bisulfate must comply with pharmaceutical equivalence, the kinetics of release of the active pharmaceutical ingredient using the Dissolution test in vitro, and pharmacokinetic parameters in vivo. The aim of the work was to carry out comparative studies of the dissolution kinetics of four samples of generic drugs based on clopidogrel with the dissolution kinetics of the original drug Plavix®, to evaluate the similarity factor of dissolution profiles and to determine the effect of biopharmaceutical factors on the equivalence of generics. Comparative studies of the kinetics of dissolution were carried out by the in vitro method according to the «Dissolution» test using a device with a blade with a rotation speed of 50 rpm, a dissolution medium with a pH value of 2.0 in a volume of 900 ml at a temperature of 37 ± 1 °C. The determination of the quantitative content of clopidogrel, which passed into the dissolution medium, was carried out by the method of adsorption spectrophotometry in the ultraviolet region at a wavelength of about 240 ± 2 nm. Based on the data obtained, the dissolution profiles of the original drug Plavix® and the studied samples of generic drugs were constructed, the similarity of which was assessed by the value of the similarity factor. According to the research results, it was found that one sample of the generic drug proved its equivalence by the in vitro method to Plavix®, and three other samples of generics had differences in dissolution kinetics in comparison with the original drug. Biopharmaceutical factors were analyzed that could affect the dissolution kinetics of the studied generic drugs, from which the physicochemical characteristics of clopidogrel bisulfate, the qualitative and quantitative composition of excipients and the features of the technological process were determined. Thus, on the basis of the comparative studies of the dissolution kinetics of drugs based on clopidogrel, generics were found that did not correspond to the in vitro equivalence according to the Dissolution test to the original drug, which could be due to the influence of a combination of biopharmaceutical factors.

Leaching of Pure Chalcocite with Reject Brine and MnO2 from Manganese Nodules

Chalcocite (Cu2S) has the fastest kinetics of dissolution of Cu in chlorinated media of all copper sulfide minerals. Chalcocite has been identified as having economic interest due to its abundance, although the water necessary for its dissolution is scarce in many regions. In this work, the replacement of fresh water by sea water or by reject brine with high chloride content from desalination plants is analyzed. Additionally, the effect of adding MnO2 from available manganese nodules in vast quantities at the bottom of the sea is studied. Reject brine shows better results than sea water, and the addition of MnO2 to the brine significantly increases the kinetics of chalcocite dissolution in a short time. H2SO4 concentration is found to be irrelevant when working at high concentrations of chloride and MnO2. The best results, 71% Cu extractions in 48 h, are obtained for reject brine, 100 mg of MnO2 per 200 g of mineral and H2SO4 0.5 mol/L. The results are expected to contribute to a sustainable process of dissolution of chalcocite by using the reject brine from desalination plants.

Mechanism, Thermodynamics and Kinetics of Rutile Leaching Process by Sulfuric Acid Reactions

Rutile decomposition by sulfuric acid, including the formation of two salts, Ti(SO4)2/TiOSO4, is thermodynamically modelled. It is shown that TiO2 can spontaneously dissolve in H2SO4 solutions. However, titania is considered as an inert (ballast) phase component of titanium-containing raw materials due to the decelerated separate nature of such chemical transformations. It is concluded that the hampered related kinetics of dissolution can be attributed to the lability of Ti(IV) cations/the specific engineered features of the hierarchical crystalline structure. It is suggested that the breaking of Ti–O–Ti bonds without additional mechanical strains in crystal lattice geometry becomes more advantageous when smaller negative anions/fluoride ions can be used. The analysis of sulfate-fluoride extraction leaching of titanium confirmed that a decrease in the Gibbs energy in the presence of F occurs. It is indicated by kinetic research studies that the addition of corrosive sodium reagent (NaF) reduces the activation by 45 kJ/mol, which results in intensification. A mechanism is proposed for the interactions involving the Ti–O–Ti cleavage on the surface/the H2SO4-induced Ti dioxide degradation on the sites of defects. Moreover, F acts as a homogeneous/heterogeneous bifunctional catalyst.