Solubility Of Sulfate Research Articles

Study on the Variation Rule of Solubility of Common Scaling under High Temperature and High Pressure Conditions

Abstract In view of the lack of equipment for direct detection of ion content in formation water under high temperature and high pressure conditions at domestic and overseas until now. In this paper, a static experiment was designed to test the solubility of each ion in the fluid under high temperature and high pressure conditions. The influence of different temperature and pressure on the solubility of scaling was tested by experiments, and the variation rule of the scaling solubility under high temperature and high pressure was comprehensively studied. The results show that: With the increase of temperature, the solubility of barium sulfate in pure water increases first and then decreases; the solubility of strontium sulfate decreases gradually; the solubility of magnesium carbonate increases first and then decreases; the solubility of magnesium carbonate increases first and then decreases; the solubility of calcium carbonate increases first, then decreases and then increases; at the same temperature and pressure, the solubility of four scalings that are barium sulfate, calcium carbonate, strontium sulfate and magnesium carbonate is in the size order of BaSO4<CaCO3<SrSO4<MgCO3.

Determination of morphine sulfate anti-pain drug solubility in supercritical CO2 with machine learning method

Accurate solute solubility measuring and modeling in supercritical carbon dioxide (ScCO2) would address the best working conditions and thermodynamic boundaries for material processing with this type of fluid. Theory- and data-driven methods are two general modeling approaches. Using theory-driven methods, the solubility is estimated based on the principles of thermodynamics, while data-driven methods are developed by training the algorithms. Despite acceptance of each of these methods, more experimental solubility data are still needed to promote modeling performances. In this study, for the first time, solubility of morphine sulfate is determined and modeled by a set of 13 semi-empirical (theory-driven) and random forest (data-driven) models. Using a laboratory system with an ultraviolet-visible (UV-Vis) spectroscopy, the experimental solubilities including 48 data points were obtained at different temperatures (308–338 K) and pressures (12–27 MPa). The minimum (0.806 × 10−5) and maximum (5.902 × 10−5) equilibrium mole fractions were observed at working pressures of 12 and 27 MPa, respectively, both at the same temperature of 338 K. It was indicated that random forest model (with AARD% of 1.29%) had an excellent predictive performance against semi-empirical models (with AARD% from 9.33 to 19.76%). The results showed that solute molecular weight had the highest effect on random forest modeling. Using modeling results from Chrastil and Bartle models, total and vaporization enthalpies of dissolution of morphine sulfate in ScCO2 were found to be 35.12 and 59.04 kJ/mole, respectively.

Dissolved Barium Causes Toxicity to Groundwater Cyclopoida.

Barium (Ba) dissolution and mobilization in groundwater are predominantly controlled by sulfate because of the low solubility of barium sulfate (BaSO4) minerals. Naturally present at low concentrations in groundwater, elevated concentrations of Ba can occur as a result of anthropogenic activities, including use of barite in drill operations, and geogenic sources such as leaching from geological formations. No toxicity data exist for Ba with groundwater organisms (stygofauna) to assess the risk of elevated Ba concentrations. The present study measured Ba toxicity to two stygobiont Cyclopoida species: one collected from Wellington and the other from Somersby, New South Wales, Australia. Toxicity was measured as cyclopoid survival over 2, 4, 7, 14, 21, and 28 days in waters of varying sulfate concentration (<1-100 mg SO4/L). When sulfate was present, dissolved Ba concentrations decreased rapidly in toxicity test solutions forming a BaSO4 precipitate until dissolved sulfate was depleted. Barium in excess of sulfate remained in the dissolved form. The toxicity of Ba to cyclopoids was clearly attributed to dissolved Ba. Precipitated Ba was not toxic to the Wellington cyclopoid species. Toxicity values for dissolved Ba for the Wellington and Somersby cyclopoid species included a (21-day) no-effect concentration of 3.3 mg/L and an effective concentration to cause 5% mortality of 4.8 mg/L (at 21 days). Elevated dissolved Ba concentrations due to anthropogenic and/or biogeochemical processes may pose a risk to groundwater organisms. Further toxicity testing with other stygobiont species is recommended to increase the data available to derive a guideline value for Ba that can be used in contaminant risk assessments for groundwaters. Environ Toxicol Chem 2024;00:1-14. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Preparation and properties of hexafluorosilicic acid series accelerators

Shotcrete technology has been widely used in tunnel engineering, road repair, underground engineering, and other scenarios due to its advantages of simple construction and fast progress. Liquid alkali-free accelerator is a necessary additive used in sprayed concrete, which can quickly set the concrete in a short period of time. Therefore, the development of alkali-free liquid accelerator is of great significance. The purpose of this research is to obtain low-cost and high-performance accelerator products and explore the influence of aluminum sulfate, hexafluorosilicic acid, and other raw materials on performance and stability. The main research results are as follows: (1) The accelerator product with low cost and high performance has been prepared. Its aluminum sulfate content is about 43%, hexafluorosilicic acid content is about 17%, sodium aluminate content is about 21%, the initial setting time is 1′ 15″, the final setting time is 2′ 05″, and the 1-day compressive strength is 9.5 MPa. (2) F ion plays a solubilizing role in the solution, and the appropriate ratio of aluminum sulfate and fluorine ion can greatly enhance the stability of accelerator solution. (3) Under the same cost condition, the influence of aluminum sulfate on the condensation performance is far greater than that of hexafluorosilicic acid and sodium metaaluminate. Subsequent research and development should focus on how to effectively increase the solubility of aluminum sulfate.

The Influence of Different Parameters on the Electro Refining of Copper

The experiments were performed using the acidic electrolyte composed of copper sulphate and sulphuric acid. The electro refining process was carried out at the temperatures of 40, 50, and 650C. On the basis of the experiments performed it was stated that the temperature of the electrolyte has significant influence on the copper consumption as well as the topography of copper deposited on the cathode. The influence of the temperature was explained by the increase in copper sulphate solubility and acceleration of the ions diffusion in the adjacent to the electrodes layer, which in consequence lead to the decrease in the resistances of Cu2+ ions deposition.It was also stated that increase in the current density beside the increase in the production rate causes the decrease in the current efficiency. The addition of gelatin to an electrolyte causes the smoothing the cathode deposit but increase in power consumption consequence of the increasing the resistances of Cu2+ ions deposition and as a result of it the increase in the cell voltage. The topography of the cathode deposit was observed using a metallurgical microscope. It was concluded that the optimum conditions for copper electro refining are: the consumption of the electrolyte- 50 kg Cu/m3, 200 kg H2SO4/m3 and gelatin-10 ppm, the temperature - 650C, current density-250A/m2.

A study of enhancing the solubility of streptomycin sulphate in sorbitol using volumetric, acoustic and viscometric properties

The various molecular interactions present between streptomycin sulphate and sorbitol were evaluated using density (ρ), speed of sound (u) and viscosity (η) studies. All these studies have been obtained at different temperatures (300.15, 305.15, 310.15 ad 315.15) K and at 0.1 MPa pressure. The values obtained from these studies have been utilized to calculate the various thermodynamic parameters such as apparent molar volume (ΦV), apparent molar isentropic compression (ΦK), partial molar volume (ΦVo), partial molar isentropic compression (ΦKo), partial molar expansibility (ΦEo) of solute for SMS in various solutions of sorbitol. The data obtained from viscosity studies have been utilized to determine Falkenhagen coefficient (A), Jones- Dole coefficient (B), dB/dT and viscosity B-coefficient of transfer (Btr). A complete discernment into the physicochemical interactions present in the studied system have been redeemed through the scrutiny of above calculated parameters.

Determination and correlation of the solubility of magnesium sulfate in ethanol solutions with different concentrations: Application to the removal of magnesium from zinc electrolytic waste solution

In this study, the solubility of anhydrous magnesium sulfate (MgSO4) in ethanol solutions with concentrations ranging from 10 % to 50 % was determined at 15–50 °C. Next, the results were correlated by using the Apelblat model, polynomial empirical equation, ideal solution equation of state model, and Van’t Hoff–Jouyban–Acree model. The results indicated that all four models exhibited correlation coefficients greater than 97 %, and average relative deviations of 3.82 %, 4.24 %, 3.96 %, and 3.96 %, respectively. Notably, the Apelblat model was found to be more accurate and reliable in correlating the solubility of MgSO4 in ethanol solutions with different concentrations. Further, the Van’t Hoff equation was applied to determine the enthalpy and entropy of dissolution. Herein, a certain amount of anhydrous ethanol was added to the zinc (Zn) electrolytic waste solution (ZEWS) to crystallize Zn2+ and Mg2+ through the solvent crystallization method, with the precipitation rates reaching 20.13 % and 39.38 %, respectively. The concentration of Mg2+ reduced to below 15 g⋅L−1, meeting the quality standard of ZEWS. The XRD, TG, and SEM analyses of the output salt mix crystallization confirmed the primary components to be MgSO4·7H2O and ZnSO4·7H2O, with the morphological features primarily consisting of short rods and some crystal agglomerates. This study shows that the removal of Mg2+ from Zn smelting process can be effectively achieved by the proposed solvent crystallization method.

Evaluation of compatibility between formation and Injection water into the Reservoir Rock

Scale deposition represents a critical challenge encountered in water injection systems. The objective of this study is to assess the compatibility between the candidate smart water and the formation water in an oil reservoir rock sample. To achieve this, water samples were collected and analyzed to evaluate the extent of deposit formation under varying temperature and pressure conditions. Additionally, the study also examined the combined influence of temperature and pressure on deposit formation. The results indicated that as the temperature increased, there was a decrease in the concentration of sulfate in the seawater. Taking into account the low concentration of barium (zero) in seawater and the unchanged strontium concentration, the decrease in sulfate concentration can be attributed to the deposition of calcium sulfate. Contrarily, in various ratios of smart water, the sulfate concentration has shown an increase with rising temperatures. This can be attributed to the transformation of sulfite present in the formation water into sulfate due to the influence of temperature. The presence of a low concentration of barium in the formation water resulted in insignificant changes in sulfate concentration due to the precipitation of barium sulfate. Additionally, despite the high concentration of strontium, strontium sulfate deposition did not occur, possibly due to the solubility product constant. The analysis of different smart water ratios under various pressures at ambient temperature revealed that pressure had a minimal effect on the solubility of sulfate and calcium salts. During the sediment analysis, no evidence of strontium sulfate sediment formation was observed. However, the analysis indicated a high possibility of iron sulfide and iron oxide deposits forming. Ultimately, under the experimental conditions, significant sediment formation was not observed.

SOLUBILITY ENHANCEMENT OF ATAZANAVIR BY HYDROTROPIC SOLUBILIZATION TECHNIQUE

Objective: The present study aims to increase the solubility and dissolution of atazanavir sulfate (ATZ) by employing a hydrotropic solubilization technique. Methods: ATZ is a poorly soluble drug classified under the biopharmaceutical classification system (BCS)-II, which accounts for its poor oral bioavailability. Different hydrotropic agents, such as urea and sodium benzoate and their combinations at different ratios were prepared. The prepared hydrotropes were systematically investigated for compatibility between the drug and excipients using Fourier Transform Infra-Red Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) approaches. Further, in order to understand the conversion from crystalline to amorphous nature, X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) studies were also performed. The formulation of a mixed hydrotropic mixture comprising urea (2.5% w/v) and sodium benzoate (5% w/v) exhibited a 100.35±1.7 % drug release at 0.25 h with higher dissolution efficiency as compared with other batches of individual hydrotrope, mixed hydrotropes as well as pure drug. Results: FTIR studies revealed that there is no incompatibility between the drug and the selected hydrotropes. DSC studies also confirmed the fact that there is no interaction between the drug and the hydrotropes by the disappearance of an endothermic peak. XRD studies revealed that there was a significant reduction in the intensity of peaks, indicating the conversion of crystalline to the amorphous form. The SEM studies indicated that the drug appears crystalline in the shape of an irregular tiny prismatic needle, indicating its crystallinity. At the same time, the hydrotrope mixtures appeared in agglomerated form with a porous nature, which may be accountable for its increase in solubility. The hydrotropes prepared using urea alone exhibited an increase in solubility of 4.42 folds, and the hydrotrope prepared using sodium benzoate alone exhibited an increase in solubility of 3.178 folds; the combination hydrotropes of urea and sodium benzoate exhibited an increase in solubility of 8.78 folds in water as compared to pure drug. The drug release from the mixed hydrotropes obeys zero-order kinetics with diffusion as the main mechanism. Conclusion: The present investigation concluded that the combination of hydrotropes enhanced the solubility of the aqueous soluble drug ATZ. However, in vivo studies are essential to establish its potential effect.

Поисковые исследования по гидрометаллургической переработке медьсодержащей руды месторождения Кеншокы-1

The main purpose of these studies was to study the chemical and mineralogical composition of the ore of the Kenshoky-1 deposit with subsequent search experiments on the extraction of copper from ore material by sulfuric acid leaching. During the research it was established that the ore belongs to the type of oxidized cuprous sandstone and along with copper it contains a significant amount of lead and a small amount of zinc. The main minerals of copper and lead in this ore are carbonate – malachite and cerussite. A fairly significant amount of the lead phosphate mineral pyromorphite is present. The main minerals in the waste rock are quartz, orthoclase, and clinochlorine. Iron, according to diffractometric analysis, is bound in clinochlore. The search experiments on copper leaching from the mentioned ore by sulfuric acid solutions showed that even at room temperature and sulfuric acid concentration in the solution of 11.3 g/dm3 extraction of copper in aqueous solution of more than 60% is achieved, and the main technological factors influencing the process of copper leaching are duration, concentration of sulfuric acid in the initial solution, intensity of agitation and the ratio of solid and liquid phases. The concentration of copper in the resulting pregnant solution was, depending on the concentration of sulfuric acid from 6.32 to 10.15 g/dm3 , which is insufficient for further processing of solution by electrolysis, therefore, productive solutions must be additionally saturated with copper by returning pregnant solution to the head of the process. Lead behavior during prospecting studies was not studied, but due to low solubility of lead sulfate in aqueous solutions, the main part of lead should remain in the cake

Biowaiver Monograph for Immediate-Release Solid Oral Dosage Forms: Isavuconazonium Sulfate

A Biopharmaceutics Classification System (BCS)-based biowaiver monograph is presented for isavuconazonium sulfate. A BCS-based biowaiver is a regulatory option to substitute appropriate in vitro data for in vivo bioequivalence studies. Isavuconazonium sulfate is the prodrug of isavuconazole, a broad-spectrum azole antifungal indicated for invasive fungal infections. While the prodrug can be classified as a BCS Class III drug with high solubility but low permeability, the parent drug can be classified as a BCS Class II drug with low solubility but high permeability. Interestingly, the in vivo behavior of both is additive and leads isavuconazonium sulfate to act like a BCS class I drug substance after oral administration. In this work, experimental solubility and dissolution data were evaluated and compared with available literature data to investigate whether it is feasible to approve immediate release solid oral dosage forms containing isavuconazonium sulfate according to official guidance from the FDA, EMA and/or ICH. The risks associated with waiving a prodrug according to the BCS-based biowaiver guidelines are reviewed and discussed, noting that current regulations are quite restrictive on this point. Further, results show high solubility but instability of isavuconazonium sulfate in aqueous media. Although experiments on the dissolution of the capsule contents confirmed ‘very rapid’ dissolution of the active pharmaceutical ingredient (API) isavuconazonium sulfate, its release from the commercial marketed capsule formulation Cresemba is limited by the choice of capsule shell material, providing an additional impediment to approval of generic versions via the BCS-Biowaiver approach.

Determination of the solubility of MgSO4 in the Zinc hydrometallurgy system within the temperature range of 263.15 K–293.15 K

ABSTRACT Solid–liquid equilibrium solubility of magnesium sulphate (MgSO4) is essential for designing and optimising the removal and recovery of magnesium (Mg) from standard zinc (Zn) hydrometallurgy systems via freeze crystallization. In this study, the solubility data of MgSO4 in ternary system MgSO4-H2SO4-H2O and quaternary system MgSO4-ZnSO4-H2SO4-H2O were determined in different zinc sulphate (ZnSO4) concentrations and sulphuric acid (H2SO4) concentrations through the isothermal equilibrium method within the temperature range from 263.15–293.15 K. The results indicated that the solubility of MgSO4 decreased with decreasing temperature and increasing concentrations of H2SO4 and ZnSO4. Furthermore, the modified Apelblat equation was applied to correlate the experimental solubility data, yielding results consistent with the experimental findings. Furthermore, X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy SEM-EDS analysis results indicated that the main phases of the equilibrium solid consist of mixed crystallization products of Zn sulphate heptahydrate (MgSO4·7H2O) and Mg sulphate heptahydrate (ZnSO4·7H2O). The microstructure of the equilibrium solid was affected by the sulphate concentration.

Two steps leaching process for recovery of rare earths from moroccan phosphogypsum

Phosphogypsum (PG), a primary by-product of the wet process phosphoric acid production, poses significant challenges to the fertilizer industry due to its voluminous generation; for each ton of phosphoric acid (P2O5), 5 tons of phosphogypsum are generated. Traditional management practices involving landfill storage or sea discharge are associated with environmental and health risks. As a result, there is an urgent need for innovative management strategies. One promising avenue is the valorization of valuable elements present in PG, notably rare earths elements (REEs). Although previous research has delved into REEs leaching from PG, fully understanding the mechanisms remains a complex endeavor due to the intricacy of the matrix and the variability in impurities concentrations, including that of rare earths. To address this knowledge gap, this study presents a robust two-step hydrometallurgical process that explores the relationship between REEs concentration and their leaching efficiency. Initial experiments focused on optimizing REEs leaching from Moroccan PG, using three agents: nitric acid, hydrochloric acid, and sulfuric acid, under systematic conditions. Subsequent experiments investigated the correlation between REEs concentrations and their leaching efficiency from PG. Three PG samples with deliberate REEs concentration were prepared and subjected to leaching under previously determined optimal conditions. Both nitric and hydrochloric acids demonstrated high leaching efficiencies with results reaching up to 60%. Intriguingly, when the concentration of REEs in PG was adjusted, the leaching efficiency surged to 76% under analogous conditions. This underlines a strong correlation between REEs leaching efficiency and their concentration in PG, with calcium sulfate solubility, emerging as a pivotal factor influencing both variables. Data from these systematic leaching experiments were further utilized for kinetics investigations, revealing that the diffusion of REEs through the product layer dominates as the rate-controlling step. In conclusion, this research bridges critical gaps in understanding the correlation between the concentration of REEs and their leaching from PG and offers insights propelling REEs recovery for potential widespread applications.

Solubilities of individual light rare earth sulfates (lanthanum to europium) in water and H2SO4 solutions (neodymium sulfate)

Rare earth elements (REE) are critical commodities with high accessibility risk due to monopolistic practices of suppliers and increased demand. The REE ores generally require aggressive conditions to dissolve the mineral matrix, and sulfuric acid attack is the most economical preferred treatment route. The main challenge to processing REE resources efficiently is the lack of reliable and recent data regarding the solubility of individual REE sulphates in water as a function of temperature. Therefore, solubilities of light REE sulfates (LaEu) were measured for binary REE2(SO4)3–H2O systems from 25 to 95 °C following both heating and cooling approaches. Additionally, solubility isotherms were determined for the ternary system Nd2(SO4)3–H2SO4–H2O system at 25, 55 and 95 °C from 0.05 to 0.5 M H2SO4. It was found that the solubility of light rare earth sulfates decreases with increasing temperature. Within the light REE series, solubilities increase from La to a local maximum for Pr (by one order of magnitude), followed by a sharp decrease to Nd and Sm. The solubility of Nd2(SO4)3 was moderately improved by the presence of H2SO4, as the solubility values increase by up to 30% in 0.5 M H2SO4 compared to the no acid case. This was explained by the formation of soluble sulfate complexes due to increased concentration of SO42− ions in solution. The increase in solubility resulting from sulfuric acid addition was more significant at higher temperatures, although temperature continued to have a negative overall effect. The nature of the saturating solid phases was determined by XRD analysis on samples collected before and after phase change temperature for Ce, Nd, and Pr sulfates, while only solids collected at 25 and 95 °C were analyzed for the compounds known to form a single type of hydrate over the entire temperature range: usually REE2(SO4)3•8H2O except for La2(SO4)3•9H2O.

Solubility Studies of Sulfates of Copper, Zinc and Cobalt in Phosphoric Acid at 30 ºC

Present study reports the isothermal experiments conducted at 30 ºC to ascertain the solubility of copper, zinc and cobalt sulfates in phosphoric acid. The solubility diagram of CuSO4-H3PO4-H2O system is shown to have one branch, this is equivalent to the discharge of copper sulfate pentahydrate into the equilibrium solid phase. The solubility diagrams of zinc and cobalt sulfates have two branches of salt crystallization, corresponding to the release of hexahydrates and monohydrates of zinc and cobalt with increasing phosphoric acid content, saturated solutions in the ZnSO4-H3PO4-H2O and CoSO4-H3PO4-H2O systems become more viscous and denser, reaching a maximum at the transition point, while these indicators in the CuSO4-H3PO4-H2O system only increase.

Fabrication of affinity-based drug delivery systems based on electrospun chitosan sulfate/poly(vinyl alcohol) nanofibrous mats

Benign electrospinning of chitosan in aqueous medium is an open challenge mainly due to its insolubility in neutral pH and inter- and intramolecular hydrogen bonding interactions. Here, we developed a simple and widely-used methodology to improve the chitosan electrospinnability through the sulfation of chitosan and its further mixing with poly(vinyl alcohol) for the first time. The FTIR, 1H NMR and elemental analyses showed the successful sulfation of chitosan. Furthermore, the viscosity and electrical conductivity measurements revealed the high solubility of chitosan sulfate (CS) in aqueous media. In the next step, a uniform electrospun nanofibrous mat of CS/PVA was fabricated with a fiber diameter ranging from 90 to 340 nm. The crosslinked CS/PVA (50/50) nanofibrous mat as the optimum sample showed a swelling ratio of 290 ± 4 % and a high Young's modulus of 3.75 ± 0.10 GPa. Finally, malachite green (MG) as a cationic drug model was loaded into different samples of chitosan film, CS film, and CS/PVA (50/50) nanofibrous mat and its release behavior was studied. The results of these analyses revealed that the CS/PVA (50/50) nanofibrous mat can successfully load higher contents of the MG and also release it in a sustained manner.

Solubility, Crystallization, and Characterization of Cytidine Sulfate.

Cytidine is an important kind of nucleoside that can be applied to drug development and food industry. Cytidine sulfate is one of its popular forms, which is promising as a medicinal intermediate, especially in antiviral and antitumor drugs. Product refining is the key point of industrial development, and crystallization is a significant way of refining. In this work, the solubility of cytidine sulfate in pure water from 278.15 to 328.15 K and in water-ethanol binary solvents at 298.15 K was measured by the UV spectroscopic method. The solubility data were correlated with temperature and solvent composition using the modified Apelblat, van't Hoff, and CNIBS/R-K equations. On this basis, we investigated and compared three crystallization processes, and the coupling method was developed to prepare crystals with a large particle size, concentrated distribution, and high yield and packing density. In addition, the structure and stability of the products were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and dynamic vapor sorption analysis. It was found that cytidine sulfate has only one crystal form in our research process, and the product of coupling crystallization is stable and favorable for industrial development.

Solubility of Barium Sulfate in Water at Elevated Temperatures and Pressures.

There are few measurements of barium sulfate (BaSO4) solubility in water above 373 K available in the literature. BaSO4 solubility data at water saturation pressure are scare. The pressure dependence on BaSO4 solubility has not previously been comprehensively reported for the pressure range 100-350 bar. In this work, an experimental apparatus was designed and built to measure BaSO4 solubility in aqueous solutions under high-pressure (HP), high-temperature (HT) conditions. The solubility of BaSO4 was experimentally determined in pure water over the temperature range from T = (323.1 to 440.1) K and pressures ranging from p = (1 to 350) bar. Most of the measurements were done at water saturation pressure: six data points were done above the saturation pressure (323.1-373.1 K) and 10 experiments were conducted at water saturation (373.1-440.1 K). The reliability of the extended UNIQUAC model and results generated in this work was demonstrated by comparing with the scrutinized experimental data reported in the literature. The model gives a very good agreement with BaSO4 equilibrium solubility data, demonstrating the reliability of the extended UNIQUAC model. The accuracy of the model at high temperature and saturated pressure due to data insufficiencies is discussed.

Solubility measurement and modeling of hydroxychloroquine sulfate (antimalarial medication) in supercritical carbon dioxide

A supercritical fluid, such as supercritical carbon dioxide (scCO2) is increasingly used for the micronization of pharmaceuticals in the recent past. The role of scCO2 as a green solvent in supercritical fluid (SCF) process is decided by the solubility information of the pharmaceutical compound in scCO2. The commonly used SCF processes are the rapid expansion of supercritical solution (RESS) and supercritical antisolvent precipitation (SAS). To implement micronization process, solubility of pharmaceuticals in scCO2 is required. Present study is aimed at both measuring and modeling of solubilities of hydroxychloroquine sulfate (HCQS) in scCO2. Experiments were conducted at various conditions (P = 12 to 27 MPa and T = 308 to 338 K), for the first time. The measured solubilities were found to be ranging between (0.0304 × 10–4 and 0.1459 × 10–4) at 308 K, (0.0627 × 10–4 and 0.3158 × 10–4) at 318 K, (0.0982 × 10–4 and 0.4351 × 10–4) at 328 K, (0.1398 × 10–4 and 0.5515 × 10–4) at 338 K. To expand the usage of the data, various models were tested. For the modelling task existing models (Chrastil, reformulated Chrastil, Méndez-Santiago and Teja (MST), Bartle et al., Reddy-Garlapati, Sodeifian et al., models) and new set of solvate complex models were considered. Among the all models investigated Reddy-Garlapati and new solvate complex models are able to fit the data with the least error. Finally, the total and solvation enthalpies of HCQS in scCO2 were calculated with the help of model constants obtained from Chrastil, reformulated Chrastil and Bartle et al., models.

Solubilities of heavy rare earth sulfates in water (gadolinium to lutetium) and H2SO4 solutions (dysprosium)

Solubilities of rare earth element (REE) sulfates are critical in hydrometallurgical process development for REE extraction, but measurements are notably lacking for heavy REE sulfates. Therefore, solubilities of heavy REE sulfates are measured for binary REE2(SO4)3–H2O systems from 25 to 95 °C for gadolinium through lutetium. Solubility isotherms are also determined for the ternary Dy2(SO4)3–H2SO4–H2O system at 25–95 °C and 0.05–0.5 M H2SO4. Saturating solid phases are identified by X-ray diffraction and thermogravimetric analyses. For all REEs, the octahydrates, REE2(SO4)3•8H2O, are the equilibrium saturating solid phases at 25–95 °C. Solubilities decrease strongly with increasing temperature, indicative of exothermic heats of solution for REE sulfate octahydrates. Within the REE series, solubilities increase markedly (an order of magnitude) from gadolinium through lutetium sulfate. Changes in solubilities are juxtaposed with stability constants for REE sulfate complexes, REESO4+ and REE(SO4)2−. As these species are inner-sphere complexes, water of hydration is released from REE3+ during complex formation which increases water activity. Hence, heavy REEs with larger complex stability constants also display lower solubilities, and vice versa. In sulfuric acid solutions, dysprosium sulfate solubility increases and passes through a maximum with increasing sulfuric acid concentration, as with other REE sulfates. The maximum solubility is postulated to relate to the dissociation constant of bisulfate (HSO4−), which passes through a minimum with increasing sulfuric acid concentration. The formation of bisulfate consumes some free sulfate thereby increasing REE sulfate solubility.