Study Of Dissolution Kinetics Research Articles

Formulation And In Vitro, In Vivo Evaluation of Colon Targeted Drug Delivery System Of 5-Fluorouracil

Colon-targeted drug delivery systems can provide therapeutic benefits including better patient compliance and lower costs. The present investigation is aimed to design a colon specific microbially triggered system using biodegradable co-polymer mixtures. The calibration curves of 5-FU were measured in distilled water, 0.1N HCl and phosphate buffer of pH 6.8 and 7.4 which showed good linearity. Compatibility study of pure drugs, excipients and their physical mixtures were evaluated and passed as per standards. Solubility determination was carried out in different solvents. Satisfactory results were found from evaluation of micromeritic parameters such as flow property, in-vitro dissolution study and kinetic study. The prime focus of the study was to design and evaluate a swelling dependent delayed release system for a colonic delivery of anticancer agent 5-Fluorouracil (5-FU) and further to determine the effects of carboxy polymer (Carbopol 71G-NF) on release behavior of 5-FU from a matrix tablet system containing different amounts of inulin (a biodegradable oligofructose) aiding in enzymatic degradation by colonic microflora. Mixed film coating with a blend of Ethyl cellulose: Eudragit®S-100 (2:1) at coat weight levels of 2%w/w, 4%w/w and 6.0%w/w was carried out respectively, which further retarded the drug release in the initial hours of the in-vitro dissolution profile. Swelling studies were also carried out on uncoated matrix tablet batches. The releases studies with or without rat cecal contents were performed on optimized batches and the samples were analyzed by a validated RP-HPLC method. In-vitro rat cecal study results revealed that complete drug release would occur from the tablets in the human colonic microenvironment. The study revealed an effective site-specific delivery of a hydrophilic chemotherapeutic agent, 5-FU to the colon for the treatment of various local as well as systemic pathologies.

Dissolution kinetics studies of kaolin ore as raw material for mesoporous silica by acid leaching

ABSTRACT The high demand for nanoporous silica materials makes it worthwhile to further explore new, cheap and environmentally friendly resources. In this study, the selective acid dissolution of an indigenous kaolin ore after thermal activation for the preparation of mesoporous silica nanoparticles was reported. Experimental parameters (acid concentration, liquid/solid ratio and temperature) were optimised and resultant solid was characterised by X-ray diffraction; scanning and transmission electron microscopy and nitrogen adsorption–desorption measurements. The products were found to be nanoporous with pore sizes of 0.402 and 0.129 cm3 g–1, with specific surface areas of 45.23 and 16.89 m2 g–1, respectively. The pore development follows the Avrami model with parameter model n values of 0.80 and 0.63, and calculated apparent activation energies of 7.22 and 22.81 kJ mol–1 for hydrochloric and sulphuric acid respectively, suggesting that the leaching activity is controlled by diffusion processes. The products as characterised demonstrated the vast potential of kaolinite in the development of mesopore materials for diverse industrial applications.

Chalcopyrite Leaching in Ammonia-Ammonium Chloride Solutions: Insight into the Dissolution Kinetic Studies

The hydrometallurgical method for processing chalcopyrite ore has gained enormous attention due to the environmental problems emanated by the conventional pyrometallurgical route. Here, hydrometallurgy is considered an alternative that may be more of low-cost and environmentally friendly. Thus, alkaline leaching has been considered an effective, efficient, and acceptable leachant for chalcopyrite ore dissolution. The dissolution behaviour of copper from low-grade chalcopyrite mineral was examined in an ammonia-ammonium chloride media. However, the influence of experimental conditions including alkali concentration, reaction temperature, and particle size was considered. At optimized leaching conditions (o.4 mol/L NH3-NH4Cl; 75 °C; 43 μm), 81.1% dissolution efficiency was achieved within 120 minutes. The dissolution mechanism with estimated activation energy (Ea)of 29.95 kJ/mol is by the proposed diffusion control mechanism. Hence, the dissolution rate was affirmed by analyzing the raw ore and un-leached residue using XRD and SEM-EDS analyses for possible industrial utilities.

Dissolution and Biological Assessment of Cancer-Targeting Nano-ZIF-8 in Zebrafish Embryos.

Cancer-targeting nanotherapeutics offer promising opportunities for selective delivery of cytotoxic chemotherapeutics to cancer cells. However, the understanding of dissolution behavior and safety profiles of such nanotherapeutics is scarce. In this study, we report the dissolution profile of a cancer-targeting nanotherapeutic, gemcitabine (GEM) encapsulated within RGD-functionalized zeolitic imidazolate framework-8 (GEM⊂RGD@nZIF-8), in dissolution media having pH = 6.0 and 7.4. GEM⊂RGD@nZIF-8 was not only responsive in acidic media (pH = 6.0) but also able to sustain the dissolution rate (57.6%) after 48 h compared to non-targeting nanotherapeutic GEM⊂nZIF-8 (76%). This was reflected by the f2 value of 36.1, which indicated a difference in the dissolution behaviors of GEM⊂RGD@nZIF-8 and GEM⊂nZIF-8 in acidic media compared to those in neutral media (pH = 7.4). A dissolution kinetic study showed that the GEM release mechanism from GEM⊂RGD@nZIF-8 followed the Higuchi model. In comparison to a non-targeting nanotherapeutic, the cancer-targeting nanotherapeutic exhibited an enhanced permeability rate in healthy zebrafish embryos but did not induce lethality to 50% of the embryos (LC50 > 250 μg mL-1) with significantly improved survivability (75%) after 96 h of incubation. Monitoring malformation showed minimal adverse effects with only 8.3% of edema at 62.5 μg mL-1. This study indicates that cancer-targeting GEM⊂RGD@nZIF, with its pH-responsive behavior for sustaining chemotherapeutic dissolution in a physiologically relevant environment and its non-toxicity toward the healthy embryos within the tested concentrations, has considerable potential for use in cancer treatment.

Assessment of a Nigerian chalcopyrite ore dissolution in sulfuric acid medium

ABSTRACT. This paper presents a study of dissolution kinetics of a Nigerian chalcopyrite ore in sulfuric acid lixiviant. The effects of acid concentration, temperature and particle diameter on the dissolution rates of chalcopyrite ore have been examined. The dissolution rates are significantly influenced by increase in temperature, hydrogen ion concentration [H+], and decrease in particle diameter. The experimental data for the dissolution rate have been analyzed with the shrinking core model which shows the rate controlling step for the dissolution of chalcopyrite ore occurs via surface chemical solution. With 4 M H2SO4 solution, about 91.6% of 10 g/L chalcopyrite ore at 80 oC was dissolved within 120 min using -90+75 µm particle diameter. The reaction order with respect to hydrogen ion concentration was found to be 0.57 with correlation coefficient 0.968. The calculated activation energy, (Ea) value of 44.9 kJ/mol for the dissolution process was established. However, the SEM morphology of the residues from leaching process showed that about 8.4% of the initial solid material contained admixtures of Fukuchilite (Cu0.42Fe0.58S2), and elemental sulphur (So) and are formed around the shrinking core of the unreacted material.
 
 KEY WORDS: Chalcopyrite, Sulfuric acid, Dissolution kinetics
 
 Bull. Chem. Soc. Ethiop. 2022, 36(1), 187-196. 
 DOI: https://dx.doi.org/10.4314/bcse.v36i1.15

Autoclave dissolution of platinum metals in hydrochloric acid oxidizing media

The paper provides the results obtained in the study of the features of metallic platinum, rhodium and iridium dissolution in hydrochloric acid solutions under hydrothermal autoclave conditions. Hydrogen peroxide was used as an oxidizing agent. Solid and liquid phases were brought into contact after reaching a predetermined temperature, which is critically important in the study of rhodium black and platinum plate dissolution kinetics due to the high rates of these processes. The concentrations of metals in solutions were determined by atomic absorption spectroscopy and inductively coupled plasma mass spectrometry. The forms of rhodium, iridium, and platinum chlorocomplexes in solutions were determined using the spectrophotometric method. As a result of the experiments, the conditions of platinum plate and rhodium quantitative dissolution (in the form of affined powder and a plate) were determined and it was shown that at 210 °C in 6M hydrochloric acid as a medium with the addition of 5 vol.% hydrogen peroxide, iridium taken in the form of affined powder went into the solution by 50 % within more than 50 h, while the platinum plate dissolved completely at 130 °C in about 120 min. Kinetic data analysis using the shrinking core model showed that rhodium black and affined rhodium and iridium powders dissolve under autoclave conditions in a kinetic mode. The results obtained can be used both in analytical chemistry for the quantitative determination of inert platinum metals and in refining production to improve the technology for processing raw materials containing platinum group metals (PGMs) and to optimize approaches to the synthesis of pure chlorocomplex compounds of PGMs.

A Dissolution Kinetic Study of Disperse Dye in Supercritical Carbon Dioxide to Design an Efficient Supercritical Dyeing Process

The dissolution behavior of dye in supercritical carbon dioxide influences the overall mass transfer that controls a supercritical dyeing process. Increasing the dissolution rate of the dye leads to shortening of the dyeing process time and can improve the efficiency of the process. Controlling the properties of the carbon dioxide flow is a good method to improve the dissolution rate of dyes. In this study, a dissolution kinetic model was designed by quantitatively analyzing and formulating the dissolution phenomenon of dyes using an in situ UV/Vis spectrometer. Through this model, the dissolution rate was compared by varying the geometric shape of the column containing the dye and the flow rate of carbon dioxide. Moreover, the correlation equation between the Reynolds number and Sherwood number was obtained through mass transfer coefficients derived under various conditions. In order to verify the utility of this equation, it was applied to a scaled-up device and the precise result could be predicted. This study can be useful in the design of dyeing processes and make-up equipment.

MODULATORY EFFECT OF POLYMER TYPE AND CONCENTRATION ON DRUG RELEASE FROM SUSTAINED RELEASE MATRIX TABLETS OF RANOLAZINE: A COMPARATIVE RELEASE KINETIC STUDY

Objective: Ranolazine (RZ), antianginal drug indicated for the treatment of chronic stable angina pectoris, was formulated into sustained-release matrix tablets and optimized to improve patient compliance and achieve controlled release over a certain period.
 Methods: Different formulations were prepared by wet- and melt-granulation techniques. Excipients at different ratios as Eudragit® L100-55, Methocel™ E5, Avicel® PH-101, and carnauba wax powder were used to develop a ternary polymeric matrix system for the controlled delivery of RZ. The prepared formulations were subjected to granulometric and characteristic studies. Comparative dissolution and release kinetic studies of the selected formulation and the reference product, Ranexa® extended-release film-coated tablets, Gilead Sciences, Inc., USA, were further carried out to ensure product similarity.
 Results: The optimum pH-dependent to pH-independent polymers ratio was 1:1.3 (w/w). Extragranular carnauba wax in a concentration of 32.50 mg/tablet (2.50 gm% w/w) was the key excipient in controlling drug release kinetics by forming waxy matrix granules which prevent rapid dissolution. Modulation of the microenvironmental pH using a potent alkalinizing agent was very effective for controlling drug release patterns in different dissolution media from pH 1.2–6.8.
 Conclusion: The release of RZ from the matrix tablets was controlled for a period of 24 h, and thereby expected to provide patient compliance with minimal side effects.

HPLC method development and in vitro dissolution kinetics of amlodipine tablets under biowaiver conditions

A biowaiver means that in vivo bioavailability and/or bioequivalence studies may be waived (not considered necessary for product approval). Instead of conducting expensive and time consuming in vivo studies, a dissolution test could be adopted as the surrogate basis for the decision as to whether the two pharmaceutical products are equivalent. The biowaiver approach based on BCS is intended to replace bioequivalence in vivo studies. The aim of the study was to study dissolution kinetics of amlodipine tablets in order to assess their equivalence under conditions in vitro according to the biowaiver. The study of dissolution kinetics of drugs in the form of amlodipine tablets has been carried out in accordance with the requirements of the “biowaiver” procedure, the recommendations of the SPhU and the WHO requirements in order to assess the possibility of replacing the pharmacokinetic studies in vivo by tests in vitro. The possibility to use the recommendations of the "biowaiver" procedure for the registration of generics amlodipine tablets has been found. The studies conducted have shown that amlodipine can be referred to class І of the biopharmaceutical classification system, i.e. substances with a high biopharmaceutical solubility and a high penetration rate. It will allow conducting comparative studies in vitro to confirm the equivalence of drugs. The evaluated amlodipine drugs fulfill biowaiver criteria for drugs containing BCS Class I active pharmaceutical ingredients. Both drugs are “rapidly dissolving,” both meet the criteria of dissolution profile similarity, f2 (i.e., the dissolution profile of the test product is similar to that of the reference product in pH 1.2, 4.5, and 6.8 buffers using the paddle method at 75 rpm), and both are considered to be in vitro equivalent without in vivo evaluation. The proposed chromatographic methods are simple, rapid and accurate for the determination of amlodipine in pharmaceutical dosage forms and can be used for routine quality control of drugs and in vitro dissolution study.

Removal of V and Fe from spent denitrification catalyst by using oxalic acid: Study of dissolution kinetics and toxicity

The selective dissolution of V and Fe from spent denitrification catalyst (SDC) with oxalic acid was investigated to minimise their environmental effects. The dissolution kinetics of different elements from SDC by using 0.1–1.5 mol L−1 oxalic acid concentration was studied at 60 °C–90 °C. V and Fe were preferentially released (65% and 81%) compared with Al, Ti and W within 5 min due to the redox reactions of oxalic acid. The dissolved fractions of Fe, V, Al, W and Ti increased with the increase of oxalic acid concentration and reaction temperature. The dissolution kinetic experiments were analysed and controlled diffusion with n < 0.5 according to the Avrami dissolve reaction model (R2 > 0.92). The Arrhenius parameters of the Ea values of Ti, W, V, Fe and Al from SDC with oxalic acid were 30, 26, 20, 19 and 11 kJ mol−1, respectively. The obtained Avrami equation of V and Fe was successfully used to predict their leaching behaviour in oxalic acid. Toxicity characteristic leaching procedure revealed that the toxicity risk of V and Fe metals from SDC after leaching with oxalic acid decreased to below 5 mg kg−1 residua. Overall, the leaching residua by oxalic acid indicated its safety for the environment.

Dissolution kinetics of calcium vanadates in sulfuric acid: a fundamental study for the vanadium extraction process

AbstractBACKGROUNDThe dissolution behavior of calcium vanadates is vital for the vanadium extraction process, as well as the utilization of calcium vanadates based function materials. Therefore, the dissolution kinetics study of calcium vanadates (CaV2O6, Ca2V2O7, and Ca3V2O8) in sulfuric acid are presented. The effects of stirring speed, solid/liquid ratio, pH, and temperature on the dissolution rate of calcium vanadates were determined. The mineralogical and microstructure of the residue after dissolution are also performed.RESULTSThe results showed that the dissolution rate of calcium vanadates significantly increased with the increase of temperature from 30 to 70 °C. Under the conditions with solid/liquid ratio of 1:150 g mL−1, temperature range of 30 to 70 °C, and pH of 4, the rate of Ca3V2O8 dissolution is the fastest, followed by Ca2V2O7 and CaV2O6, especially at low temperature.CONCLUSIONThe mineralogical analyses results showed that the main products for the dissolution of Ca2V2O7 and Ca3V2O8 are needle‐like CaSO4·0.5H2O, whereas for CaV2O6 are undissolved CaV2O6 and hydrolyzed V2O5. The dissolution kinetics indicate that the dissolution of CaV2O6 follows second‐order pseudo‐homogeneous model, whilst Ca2V2O7 and Ca3V2O8 follow the diffusion through the product or ash layer model. The apparent activation energies for the dissolution of CaV2O6, Ca2V2O7, and Ca3V2O8 were determined as 46.44, 38.72, and 23.50 kJ mol−1, respectively. © 2020 Society of Chemical Industry

Preparation of Deoxycholate-Modified Docetaxel-Cimetidine Complex Chitosan Nanoparticles to Improve Oral Bioavailability.

Docetaxel (DTX) was effective in the treatment of neoplasm but could only be administered intravenously with the poor oral bioavailability owing to its undesirable solubility, remarkably metabolic conversion, and other factors. Cimetidine (CMD), a classic CYP3A4 isozyme inhibitor, had exhibited a wide range of inhibition on the metabolism of many drugs. The aim of this study was to construct the novel docetaxel-cimetidine (DTX-CMD) complex and the chitosan-deoxycholate nanoparticles based on it to confirm whether this formulation could show advantages in terms of solubility, dissolution rate, small intestinal absorption, and oral bioavailability in comparison with the pure drug. The solid-state characterization was carried out by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), and simultaneous DSC-TGA (SDT). Dissolution rate and kinetic solubility study were determined by evaluating the amount of DTX in distilled water and phosphate buffer solution (pH = 7.4), respectively. And small intestinal absorption and pharmacokinetics study were conducted in rats. The results of this study demonstrated that we successfully constructed DTX-CMD complex and its chitosan-deoxycholate nanoparticles. Furthermore, the DTX-CMD complex increased the solubility of DTX by 2.3-fold and 2.1-fold in distilled water and phosphate buffer solution, respectively. The ultimate accumulative amount of DTX-CMD complex nanoparticles through rat small intestinal in 2h was approximately 4.9-fold and the oral bioavailability of the novel nanoparticles was enhanced 2.8-fold, compared with the pure DTX. The superior properties of the complex nanoparticles could both improve oral bioavailability and provide much more feasibility for other formulations of DTX.

Study on the dissolution kinetics of NaCl in environmentally friendly drilling fluids containing glycerin

The oil well drilling process in the pre-salt layer faces some challenges including the salt dissolution on the drilling muds. The dissolution may be harmful to mechanical processes and drastically change fluid properties. With the increasing research for less aggressive fluids, glycerin from biodiesel production meets technical, economic and environmental requirements for fluids formulation. The aim of this work is the study of dissolution kinetics of NaCl in drilling fluids containing glycerin. Experimental dynamic salt concentration profiles in the liquid phase were obtained in a stirred tank. These data were used to evaluate the mass transfer coefficient in different rotation rates and salt concentrations. The mathematical model simulated the process by the application of the mass conservation equations applied on fluid and solid phases. Through experimental analysis and parameter estimation, the kinetics dissolution was evaluated for two types of glycerin, different rotation speeds and salt concentrations.

Amine decorated 2d hexagonal and 3d cubic mesoporous silica nanoparticles: A comprehensive dissolution kinetic study in simulated and biorelevant media

Highly ordered Bexarotene (BXR) encapsulated mesoporous silica nanoparticles in particular bare and amine functionalized MCM-41 and MCM-48 were designed employing a novel impregnation solvent evaporation strategy. The outcomes unveiled successful synthesis of mesoporous assembly having 2 D hexagonal and 3 D cubic framework for MCM-41 and MCM-48 respectively withholding large surface area, optimum pore size, pore volume along with uniform particle size distribution. Additionally, SXRD and TEM findings divulged retention of characteristic mesoporous features regardless of surface modification and drug incorporation. Eventually the release profile and release kinetics results in different dissolution media demonstrated complete drug release in simulated intestinal fluid (SIF) within 75 min and 45 min from BXR-41 and BXR-48 along with 3.33 and 5 fold increment in dissolution profile. Furthermore, lack of any interaction between gelatin of hard capsule shell and amine group in presence of enzyme were justified from the indistinguishable release pattern in enzyme free and enzyme enriched SIF media. The divergent release pattern in fed and fasted state condition having a higher release in former media strongly directs towards taking medicine after meal. Finally the release kinetics study exhibited Weibull and Higuchi model as a best fit models for bare and amine coated BXR nanoparticles respectively.

Crystal Dissolution Kinetics Studied by a Combination of Monte Carlo and Voronoi Methods

Kinetic Monte Carlo (kMC) methods have been used extensively for the study of crystal dissolution kinetics and surface reactivity. A current restriction of kMC simulation calculations is their limitation in spatial system size. Here, we explore a new and very fast method for the calculation of the reaction kinetics of a dissolving crystal, capable of being used for much larger systems. This method includes a geometrical approach, the Voronoi distance map, to generate the surface morphology, including etch pit evolution, and calculation of reaction rate maps and rate spectra in an efficient way, at a calculation time that was about 1/180 of the time required for a kMC simulation of the same system size at one million removed atoms. We calculate Voronoi distance maps that are based on a distance metric corresponding to the crystal lattice, weighted additively in relation to stochastic etch pit depths. We also show how Voronoi distance maps can be effectively parameterized by kMC simulation results. The resulting temporal sequences of Voronoi maps provide kinetic information. By comparing temporal sequences of kMC simulation and Voronoi distance maps of identical etch pit distributions, we demonstrate the opportunity of making specific predictions about the dissolution reaction kinetics, based on rate maps and rate spectra. The dissolution of an initially flat Kossel crystal surface served as an example to show that a sequence of Voronoi calculations can predict dissolution kinetics based on the information about the distribution of screw defects. The results confirm that a geometrical relationship exists between the material flux from the surface at a certain point and the distance (or, when considering anisotropy, a function of distance) to the nearest defect. In this study, for the sake of comparability, the calculations are made using input parameters directly derived from the kMC models operating at the atomic scale. We show that, using values of v(rpit) and weighting factors obtained by kMC, the resulting surface morphologies and material flux are almost identical. This implies that discrete Voronoi calculations of starting and end points of the dissolution are sufficient to calculate material flux maps, without the time-consuming overhead of computing the interim reactions at the atomic-scale. This opens a promising new venue to efficiently upscale full-atomic kMC models to the continuum macroscopic level where reactive transport and Lattice Boltzmann calculations can be applied.

Dissolution kinetics of CeO2 powders with different morphologies and analogy to PuO2 dissolution

Several CeO2 powders with different morphologies were synthetized thanks to four different processes (two at the laboratory by sol-gel and oxalic routes and two commercial powders). These powders were divided into five batches each and calcined at several temperatures. Thus, twenty different powders were made, each possessing different structural or morphological properties. After a thorough characterization of the 20 powders, this work is dedicated to the study of their dissolution in nitric acid using the same experimental conditions to exhibit the morphology effect on dissolution kinetics. Significant differences in dissolution kinetics were observed meaning that the morphology of the powders was found to be a key parameter that has to be considered in studies of dissolution kinetics. The effect of the morphological parameters on dissolution kinetics was quantified and a kinetics law was established and then, applied with success to PuO2 dissolution.

FORMULATION AND EVALUATION OF PECTIN-CALCIUM CHLORIDE BEADS OF AZATHIOPRINE FOR COLON TARGETED DRUG DELIVERY SYSTEM

Objective: Calcium pectinate is an insoluble hydrophilic material used for sustained release delivery. The objective of the study was formulation and evaluation pectin-calcium chloride beads of azathioprine.Methods: Calibration curves of azathioprine were prepared in 0.1N HCl solution (pH-1.2) and phosphate buffer (pH-6.8 and pH-7.4). Fourier transform infrared spectroscopy and differential scanning calorimetry was used to determine compatibility between azathioprine and excipients. Formulation and optimization of calcium-pectinate beads were performed. The coating of the optimized batch was performed with eudragit S100. Micrometric properties, scanning electron microscopy, in vitro azathioprine release, and stability study was performed. Dissolution kinetic study was assessed for various kinetics models of the optimized batch. The Wilcoxon test followed by the Dunnett’s multiple comparison tests were performed between uncoated and coated beads in vitro dissolution profile of optimized batch in 0.1N HCl after 2 h.Results: Fourier transform infrared spectroscopy and differential scanning calorimetry had identical peaks with that of pure azathioprine in compatibility study. Scanning electron microscopy of an uncoated optimized batch of beads indicated the smooth and uniform surface of prepared beads. Eudragit S100 coating was decreased release of azathioprine release in 0.1N HCl after 2 h (p = 0.049, q = 3.533). Korsmeyer/Peppa's model was applied with release exponent higher than 1. In vitro percentage cumulative azathioprine release was identical before and after stability study.Conclusion: Calcium pectinate beads of azathioprine, a multi-particulate dosage form using pH-dependent approaches were prepared.

Hydrometallurgical Processing of a Nigerian Galena Ore in Nitric Acid: Characterization and Dissolution Kinetics

The physico-chemical characterization and dissolution kinetics study of a Nigerian galena ore in nitric acid has been undertaken. The effects of acid concentration, temperature, particle size, stirring speed and solid/liquid ratio on the leaching of galena were investigated. The X-ray fluorescence data showed that the galena ore used in the study exists mainly as PbS. Lead (Pb) was detected as the major metal for galena with metals such as Na, Ca, Fe, Zn, Al and Mg occurring as minor elements. The XRD analysis also confirmed the originality of the galena ore as it revealed that galena exists mainly as lead sulphide (PbS). The Fourier transform infrared (FTIR) analysis also supported the XRF and XRD analysis by revealing the presence of sulphur in the ore. The scanning electron micrograph (SEM) analysis revealed a high level of crystallinity of the ore. Results of the leaching studies showed that galena dissolution in nitric acid (HNO3) increases with increasing concentration of nitric acid, temperature and stirring rate, and decreases with increasing particle diameter and solid/liquid ratio. In 10 M HNO3 at a temperature of 90°C using 75 μm particle diameter with solid/liquid ratio of 20 g/L and stirring speed of 540 rpm, about 84.5% of galena was dissolved in 150 minutes. The values of activation energy, order of reaction and Arrhenius constant calculated at the conditions above for galena were 27.01 KJ/mol, 0.93, 26.71 s-1 respectively. The mechanism of dissolution of galena was established to follow the shrinking core model for the diffusion controlled mechanism, with surface chemical reaction as the rate controlling step for the leaching process. Finally, the XRD analysis of the post-leaching residue revealed the presence of gahnite and anglesite.

An experimental study of dolomite dissolution kinetics at conditions relevant to CO 2 geological storage

The kinetics of dolomite dissolution have been experimentally investigated under subsurface conditions characteristic of the Rotliegend gas fields in the NE of The Netherlands. Experiments were performed in closed, stirred, batch reactors at far from equilibrium conditions, with dolomite powders of different grain sizes. The experiments were repeated for all grain sizes at 25°C and an experiment was also conducted in deionized water. The rates were derived from the measured concentrations of Mg 2+ or Ca 2+ released from dolomite dissolution and were normalized by the surface area of the minerals at each time interval. Regression of the rates with the pH resulted in the kinetic rate constants of: log k 1 = −8.16 ± 0.06 at 25°C and log k 2 = −7.61 ± 0.05 at 100°C (300 – 350 μm), log k 3 = −7.88 ± 0.20 at 25°C, log k 4 = −7.45 at 100°C (75 – 100 μm), log k 5 = −6.62 ± 0.50 at 25°C and log k 6 = −5.96 ± 1 at 100°C (20 – 25 μm). The results obtained in this study indicate that in an acidic regime the dissolution of dolomite in brine is a factor of 2 faster than in deionized water. It was also shown that the dissolution rates, when normalized by surface area, increase with decreasing grain size.

A comparative in vitro release study of raloxifene encapsulated ordered MCM-41 and MCM-48 nanoparticles: A dissolution kinetics study in simulated and biorelevant media

The objective of the present study was to compare the release profile of model drug raloxifene (RLX) from highly ordered MCM-41 and MCM-48 mesoporous silica nanoparticles in simulated and biorelevant dissolution media aiming solubility enhancement of RLX. An effect of 2D hexagonal pattern of MCM-41 and the 3D cubic arrangement of MCM-48 on in vitro RLX release profile in different simulated and biorelevant dissolution media was investigated. MCM-41 and MCM-48 nanoparticles with different crystalline arrangement were synthesized, loaded with RLX and characterized by various techniques. Mesoporous structure of nanoparticle with higher surface area was confirmed by detailed characterization. An assessment of dissolution profile of RLX, marketed formulation (Ralista®), RLX loaded MCM-41 and MCM-48 nanoparticles showed higher percentage cumulative RLX release from MCM-48 nanoparticle with 4.4 and 1.6 time increment with respect to plain RLX and marketed formulation respectively. This could be attributed to a high loading and entrapment efficiency, large surface area and 3D cubic arrangement of the parent moiety. A comprehensive dissolution kinetics study gave Weibull model to be a best fit dissolution model for adopted dissolution media. An identical dissolution profile in fasted and fed state condition suggesting that the formulation could be administered before or after meal.