Thiosulfate Solution Research Articles

Recovery of gold ions from thiosulfate solution using an electrogenerative process

Traditional zinc powder cementation method for recovering gold ions from thiosulfate solution has the disadvantages such as high consumption of active metal, surface passivation, and co-deposition of copper ions. The key to solving these issues is providing the necessary electrons for the reduction of Au(S2O3)23- while avoiding direct contact between zinc powder and the leaching solution. In this study, a novel electrogenerative device with ion exchange membranes separating the anode and cathode is developed for the recovery of gold ions from thiosulfate solution. The oxidation reaction of zinc electrode occurs in the anode chamber, while the reduction reaction of gold ions occurs on a platinum electrode in the cathode chamber. The optimal experimental conditions for the gold recovery are determined to be using a cation exchange membrane, with the anode solution of 0.08 M ZnSO4, pH = 6, and the cathode solution of 0.10 M Na2S2O3, 5 mM CuSO4, 0.5 M NH3·H2O, pH = 10, with an initial gold concentration of 10 mg/L. It obtains the gold recovery of 99.59 %. Compared the zinc powder cementation method with the similar gold recovery, the electrogenerative process reduces zinc consumption by 67 % and prevents the passivation on the zinc surface caused by copper, oxygen, and sulfur.

Efficient and sustainable recovery of Au(I) from thiosulfate solution by tri-n-butylphosphine functionalized chitosan microspheres with abundant pores

Thiosulfate as a green and environmentally friendly lixiviant has received great attention in the field of gold extraction. However, the problem of gold ion recovery in thiosulfate gold leaching solution has hindered the large-scale application of this technology. Here, tri-n-butylphosphine (TBUP) was used as a functional monomer to prepare an adsorbent (CTS-TBUP) with abundant pores through the ion crosslinking reaction of chitosan, which was used to recover Au(I) from Au[(S2O3)2]3− solution with high efficiency and large capacity. CTS-TBUP exhibited good potential for industrial applications with a gold loading capacity of 46.34 mg/g. CTS-TBUP exhibited a similar gold recovery performance for all pH ranges from 6 to 11, and the adsorption process of Au(I) on CTS-TBUP was well described by pseudo-second-order kinetics and Langmuir isothermal model. The mechanism by which CTS-TBUP adsorbs gold ions involves ligand exchange between TBUP and Au[(S2O3)2]3−. In addition, Au(I) on CTS-TBUP will be reduced to elemental gold by TBUP in CTS-TBUP. The mechanism of Au(I) adsorption by CTS-TBUP was also confirmed by density functional theory calculations, and confirmed the rationality of forming a complex with a coordination ratio of 2:1 between TBUP and Au(I) at the theoretical level. CTS-TBUP has a good affinity for gold ions in thiosulfate solution, which provides a new idea for the preparation of gold adsorbent.

Adsorption behaviors and mechanisms of gold recovery from thiosulfate solution by ion exchange resin

The adsorption behaviors and mechanisms of gold from thiosulfate solution on strong-base anion exchange resin were systematically investigated. The comparison experiment of adsorption ability and selectivity for gold showed that gel Amberlite IRA-400 resin with Type I quaternary ammonium functional group had better adsorption performance. The increases of resin dosage, ammonia concentration and solution pH were favorable to gold adsorption, whereas the rises of cupric and thiosulfate concentrations were disadvantageous to gold loading. Microscopic characterization results indicated that gold was adsorbed in the form of [Au(S2O3)2]3– complex anion by exchanging with the counter ion Cl– in the functional group of the resin. Density functional theory calculation result manifested that gold adsorption was mainly depended on the hydrogen bond and van der Waals force generated between O atom in [Au(S2O3)2]3– and H atom in the quaternary ammonium functional group of the resin.

Green Aqueous Two-Phase Systems Constructed by Guanidinium Ionic Liquid for Efficient Recovery of Gold(I) from Thiosulfate Solution

Green Aqueous Two-Phase Systems Constructed by Guanidinium Ionic Liquid for Efficient Recovery of Gold(I) from Thiosulfate Solution

Granular polyacrylonitrile with internal 3D channels for gold recovery from thiosulfate solution

Gold recovery technology is an urgent challenge in the industrialisation of thiosulfate-based gold extraction. Current materials used for gold recovery suffer from a lack of wear resistance and small particle size, which makes it difficult to separate the material from thiosulfate solutions. In this study, a cysteamine-functionalised granular polyacrylonitrile (cys-PANG) material containing three-dimensional channels was designed and synthesised. The results indicate that cys-PANG, prepared using a solvent exchange method, has remarkable adsorption capacity for gold, smooth outer surface, well-developed internal pore structure, high wear resistance, and controllable size, making it suitable for gold recovery from thiosulfate pulp. The adsorption of gold in a thiosulfate solution by cys-PANG followed the Freundlich isotherm and pseudo-second-order kinetic adsorption models with minimal pH dependence. Cys-PANG also demonstrated the effective adsorption of gold in a Cu(II)–ethanediamine (en)–S2O32− solution, even in the presence of copper and en interference. Both experimental results and theoretical calculations revealed that the interaction between cys-PANG and gold in the thiosulfate solution is predominantly characterised by charge attraction and ligand exchange mechanisms. Adsorption tests of cys-PANG in actual thiosulfate pulp demonstrated exceptional gold recovery properties and minimal wear even after 14 days of continuous stirring. This study presents a promising alternative methodology for the recovery of gold from thiosulfate pulp.

Dissolution patterns of gold on various structural surfaces in thiosulfate solutions: The effect of interface adsorption on thiosulfate oxidation and gold atom dissociation

Passivation caused by the adsorption and decomposition of thiosulfate on gold surfaces significantly influences the leaching rate of gold. The surface structure often determines the reactivity of an interface. Studying the effects of different surfaces on the decomposition of thiosulfate ions and gold dissolution can provide insights into the passivation formation mechanism. In this study, the oxidation of thiosulfate on different surfaces is investigated using linear voltammetry. The oxidation response of thiosulfate was weaker on granular (1 1 1) and (5 4 1) surfaces than on nanoflakes with (1 1 1) surface. Furthermore, the Tafel test results indicate that the potential for gold dissolution is higher on the granular (1 1 1) and (5 4 1) surfaces, leading to a smaller current value of gold dissolution. Raman spectroscopy indicates that the response signals of the polysulfides and polythionate were stronger on the granular (1 1 1) and (5 4 1) surfaces. The chemical bond changes of thiosulfate adsorbed on different surfaces are studied through molecular simulations based on density functional theory. These results indicate that as the saturation of surface gold atoms decreases, their reaction activity increases, and the bonding effect with thiosulfate ions becomes stronger during adsorption. The changes in the SS bonds in thiosulfate reflect the influence of the different surfaces on their stability. On the (1 1 1) surface, the SS bond changes from the initial 2.102 Å to the adsorbed 2.254 Å, while on the (5 4 1) surface, the SS bond changes to 2.274 Å Although the reaction activity of the granular (1 1 1) and (5 4 1) surfaces is high, the energy barrier for dissociating individual gold atoms from them is higher. The adsorption of sulfur-containing substances on the surface, along with the increased energy barrier for gold dissociation are both factor contributing to the greater difficulty of gold dissolution from granular (1 1 1) and (5 4 1) surfaces.

Acceleration of reaction by glass magnet stirring shortens the time for the determination of dissolved oxygen in seawater by the Winkler method

Dissolved oxygen (DO) is one of the core parameters in ocean investigation among various disciplines. The Winkler method, a classical approach, is extensively employed for DO determination. This method uses the reaction of Mn2+ to I3‐− as a proxy to quantitatively convert DO to iodine, followed by titration with sodium thiosulfate solution. However, this method is time-consuming and laborious due to the shaking and/or re-shaking of the DO bottle after adding the pickling reagents and waiting for the precipitate to settle. In this study, we implemented a stirring operation using a glass-coated magnetic stir bar at 1000 rpm for 1 min to replace the traditional static settling. The precision of DO measurements obtained via manual titration (coefficient of variation, CV < 0.2%) was comparable to that of the traditional method. Conversely, a polytetrafluoroethylene (PTFE) coated magnetic stir bar was unsuitable due to the release of pre-adsorbed oxygen. Comparative experiments conducted during an Indian Ocean cruise demonstrated that the DO measurements obtained using the improved method were in good agreement with those obtained using the traditional method. The coefficient of determination (R2) from the linear regression of the two methods was 0.999, and the ratio of the results averaged 1.00 ± 0.02. Our study also revealed that the combined effect of Mg2+, Ca2+, OH−, and HCO3− increases the settling time after the addition of pickling reagents. Overall, this modification represents a useful and labor-saving advancement in the determination of a classic oceanographic parameter, with potential for widespread adoption by scientists and technicians.

Highly Efficient and Selective Extraction of Gold from Thiosulfate Leaching Solution Using Functionalized Dicationic Ionic Liquids.

Thiosulfate leaching has been regarded as a promising alternative to cyanidation, but it still faces the challenge of the recovery of low content of gold from high concentrations of thiosulfate solutions. Liquid-liquid extraction is a method to address this issue but is still limited by the use of volatile and toxic organic solvents. To overcome this limitation, this work synthesized some functionalized dicationic ionic liquids (DILs) to serve as extraction solvents for the recovery of the gold-thiosulfate complex, [Au(S2O3)2]3-, from thiosulfate solutions. Experimental results indicated that the DILs showed higher extraction rates toward [Au(S2O3)2]3- compared with their monocationic-based counterparts, likely due to the stronger electrostatic interaction between the dications of the ILs and [Au(S2O3)2]3-. The transfer of [Au(S2O3)2]3- from the water phase to the IL phase was identified as an anion exchange and endothermic process. The rate of extraction was limited by the anion exchange process occurring at the IL-water interface. The extraction ability of ILs highly depended on the type of anion; specifically, the ILs with anions that had strong hydrogen-bonding ability exhibited high extraction ability toward [Au(S2O3)2]3-. Finally, DILs proved effective in the recovery of [Au(S2O3)2]3- from an actual gold leaching solution and exhibited high selectivity toward coexisting ions, indicating their potential as environmentally friendly solvents for gold recovery.

Protonated covalent organic frameworks for green and effective recovery of Au(I) from thiosulfate solutions: Performance, DFT calculations, and mechanism insights

The recovery of Au(I) from thiosulfate leaching systems is important to ensure the sustainable use of strategic metal resources. In this study, two ionic covalent-organic frameworks (iCOFs), Tmp-Tpa COF-Cl and Tmp-Tpa COF-SO4, were synthesized through a post-modification strategy guided by theoretical calculations. Acid modification redistributed the surface charge of Tmp-Tpa COF due to the protonation of nitrogen atoms, which enabled the efficient and selective recovery of Au(I) from a thiosulfate solution. The Au(I) adsorption capacities of Tmp-Tpa COF-Cl and Tmp-Tpa COF-SO4 were 69.8 mg/g and 71.3 mg/g, respectively, which were significantly higher than those of previously reported materials. Adsorption equilibrium isotherms and kinetic studies revealed that the adsorption of Au(I) onto iCOFs conformed to the Langmuir and quasi-second-order kinetics model, showing that Au(I) underwent uniform monolayer chemisorption on the surface of the iCOFs. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations indicated that the adsorption of Au(I) onto Tmp-Tpa COF-Cl and Tmp-Tpa COF-SO4 was mainly because acid modification converted –C = N to –C = NH+-, which enhanced the strength of electrostatic attraction and coordination with Au(S2O3)23− complexes. Acidic thiourea rapidly eluted Au(I) adsorbed onto the iCOFs and simultaneously regenerated Tmp-Tpa COF-Cl. Even during the fifth adsorption/desorption cycle, the adsorption and desorption efficiencies of the iCOF still reached 86.6 % and 97.7 %, respectively. In addition, Tmp-Tpa COF prepared by Knoevenagel condensation was inexpensive (less than $50/kg) and did not require the use of organic solvents, enabling large-scale green production. This work provides an innovative method for the efficient, selective, and high-capacity recovery of gold from thiosulfate leachate.

Effectively adsorb Au(S2O3)23- using aminoguanidine as trapping group from thiosulfate solutions.

Thiosulfate gold leaching is one of the most promising green cyanide-free gold extraction processes; however, the difficulty of recovering Au(I) from the leaching system hinders its further development. This study prepared aminoguanidine-functionalized microspheres (AGMs) via a one-step reaction involving nucleophilic substitution between aminoguanidine hydrochloride and chloromethylated polystyrene microspheres and used AGMs to adsorb Au(I) from thiosulfate solutions. Scanning electron microscopy, Brunauer-Emmett-Teller analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to analyze the structure and properties of AGMs. Experiments were designed to investigate the effects of pH, temperature, initial Au(I), and thiosulfate concentrations on the gold adsorption performance of AGMs. Results demonstrated that AGMs can efficiently adsorb Au(I) from thiosulfate solutions in a wide pH range. The adsorption process conforms to the pseudo-second-order kinetic model and Langmuir isotherm model, with a maximum capacity of 22.03kg/t. Acidic thiourea is an effective desorbent, and after four adsorption-desorption cycles, the adsorption rate of Au(I) by AGMs is 78.63%, which shows AGMs have good cyclic application potential. Based on the results of characterization, experiments, and density functional theory calculations, the mechanism for the adsorption of [Au(S2O3)2]3- on AGMs involves anion exchange. Importantly, AGMs exhibited satisfactory adsorption property for Au(I) in practical Cu2+-NH3(en)-S2O32- systems. This study provided experimental reference for the recovery of Au(I) from thiosulfate solution.

Role of Semiconductive Property on Selective Cementation Mechanism of Iron Oxides to Gold in Galvanic Interaction with Zero-Valent Aluminum from Gold–Copper Ammoniacal Thiosulfate Solutions

Iron oxides (hematite, Fe2O3, and magnetite, Fe3O4), previously used as electron mediators in the galvanic system with zero-valent aluminum (ZVAl), have been shown to recover Au upon cementation in Au–Cu ammoniacal thiosulfate media selectively, and this warrants further investigation. This research is focused on investigating the role of the semiconductive properties of metal oxides by performing a cementation experiment by mixing 0.15 g of electron mediators (Fe3O4, Fe2O3, TiO2 (anatase and rutile)) and 0.15 g of zero-valent aluminum powder as an electron donor in various electrochemical experiments. The results revealed that upon the cementation experiment, synthetic Fe2O3 and Fe3O4 were consistently able to selectively recover Au at around 90% and Cu at around 20%. Compared to activated carbon (AC), TiO2, in anatase and rutile forms, obtained selective recovery of gold, but the recovery was utterly insignificant compared to that of iron oxides, obtaining an average of 93% Au and 63% Cu recovery. The electrochemical and surface analysis supports the results obtained upon the cementation process, where TiO2, upon cyclic voltammetry (CV), obtained two reduction peaks centered at −1.0 V and −0.5 V assigned to reducing Au and Cu ions, respectively. Furthermore, various electrochemical impedance spectroscopic analyses revealed that the flat band potential obtained in the Mott–Schottky plot is around −1.0 V and −0.2 V for iron oxides and titanium oxides, respectively, suggesting that the electrons travel from semiconductor interface to electrolyte interface, and electrons are accessible only to Au ions in the electrolyte interface (reduction band edge around −1.0 V). The determination of this selective cementation mechanism is one of a kind. It has been proposed that the semiconductive properties of Fe2O3, Fe3O4, and, by configuring their relative energy band diagram, the travel of electrons from the iron oxide–electrolyte interface facilitate the selective cementation towards Au(S2O3)23+ ions in gold–copper ammoniacal thiosulfate solutions.

Designing and synthesizing functional recognition ligands:regulation affinity of soft S atom towards Au(I) ion in thiosulfate solution

The advancement of fundamental research in adsorption remains a significant hurdle in achieving thiosulfate gold extraction method widespread industrial application. The present study described a design scheme for a functional recognition ligand aimed at adsorption Au(I) in thiosulfate solution, and evaluated its performance as an adsorbent. The soft S atom was selected as the coordinating atom for Au(I) in thiosulfate solution, utilizing a planar conjugated structure to regulate the ligand's configuration and charge distribution, resulting in a new ligand with similar polarizability to Au(I). The newly designed ligand can form a stronger σ−feedback π bond interaction with Au(I) while minimizing ligand steric hindrance. Consequently, the Au(I) recognition was achieved due to the increased Au(I)−complexes' stability. The synthesized ligands−rich adsorbent (TF−O−) and its adsorption mode for Au(I), as determined through characterization and batch adsorption experiments, are in agreement with the theoretical predictions. The gold loading capacity on TF−O− in thiosulfate solution reaches 370.87 mg ∙ g−1 at 25 °C, which is approximately 15 times higher than that of resin and carbon materials. Furthermore, TF−O− has achieved effective anti−anion interference, simple desorption, and efficient regeneration. This study presents a promising design scheme for functional recognition ligand in metallurgical solutions.

Quantification of hydroperoxides in liquid fuels: A systematic comparison of titration and absorption methods and their coupling to HPLC

Hydroperoxides are major products in the autoxidation of fuels and play a central role in oxidation kinetics. Their presence affects the oxidation rate, even at low concentrations, and, in turn, the thermal stability of fuels. Standard techniques for the quantification of hydroperoxides (ROOH) in fuels involve the reduction of ROOH by I−, yielding iodine (I2), which can be quantified by titration. The ASTM titration method of ROOH is known to be poorly reproducible and have inadequate lower detection limits and limited dynamic ranges. In this work, several analytical methods for the quantification of hydroperoxides in fuels have been systematically compared for known concentrations of ROOH: titrations of iodine with thiosulfate (ASTM D3703) and triphenylphosphine (TPP) solutions, with colorimetric and potentiometric methods, and quantification of iodine by UV–visible absorption. n-decane was used as a surrogate fuel and tert-butyl hydroperoxide as the ROOH internal standard. Our systematic study shows that the ASTM method based on colorimetric titration using thiosulfate aqueous solution is the least accurate because of the non-miscibility of water and n-decane, which even makes the UV–visible spectroscopy method ineffective. The other titration method proposed in the literature, using TPP dissolved in n-decane as the titrant, does not have this miscibility problem. Potentiometric titration is found to be more reproducible and accurate than colorimetric titration. The UV–visible absorption reaches lower detection limits. We show that the combination of the potentiometric titration of iodine with TPP and UV–visible absorption enables ROOH concentrations to be determined with low detection limits and a large dynamic range. The advantages of iodometry and UV-absorption detection methods have been used to develop a new analytical method based on their coupling in HPLC with a post-column reactor.

Low-temperature one-pot synthesis of tin(II) sulfide nanocrystalline thin films

Photosensitive thin films of tin (II) sulfide with p-type conductivity and a band gap of 1.03 ± 0.09 eV have been obtained within the framework of the principles of «green chemistry» using the one-pot approach. In order to expand the range of sulfidizers used in the technology of deposition of thin nanostructured SnS films by chemical deposition, the efficiency of using sodium thiosulfate solutions is shown. It has been found that thin SnS films with good adhesion to a dielectric substrate and a size of coherent scattering regions of about 30 nm can be obtained as a result of a chemical reaction of the hydrolytic decomposition of thiosulfate ions. The conditions for obtaining SnS are substantiated by the thermodynamic analysis of ionic equilibria. Quantum-chemical calculations show that the p-type conductivity of the synthesized SnS films is most likely due to tin vacancies.

Facile synthesis of a novel covalent triazine framework for recovering gold(i) from thiosulfate solution

CTF-MG as a novel polymer adsorbent was prepared via amine–aldehyde condensation between melamine and glutaraldehyde, and exhibited excellent properties for gold(i) thiosulfate complex formation.

Gold Recovery from Thiosulfate Leaching Solution Using Silicon Powder and Electrochemical Monitoring of Its Process

Gold recycling from Waste Electrical and Electronic Equipment (WEEE) has been actively conducted. We previously reported a noble metal recovery process using aqua regia and electroless displacement deposition onto silicon powder [1,2]. Using silicon powder has such advantages as that noble metals and copper are selectively recovered, and sawdust silicon, that is, industrial waste silicon powder is available to use. Recently, ammonium thiosulfate solution has attracted attention as a safe and low-cost solution for gold leaching [3-6]. In this study, we successfully recovered gold from an ammonium thiosulfate solution by using silicon powder [7,8], and tried to monitor the recovering behavior electrochemically. Since the ammonium thiosulfate leaching solution includes copper ions as oxidizing agent, copper is recovered by silicon powder. Thus, the monitoring was conducted in order to determine the suitable timing for efficiently obtaining pure gold during the process. For experimentation, an ammonium thiosulfate solution containing gold(I) sulfite and copper(II) sulfate was prepared (pH = 13). We immersed a gold wire in the solution and measured the rest potential during the recovery process using silicon powder. The potential of gold wire shifted stepwise toward negative direction at each start and end of gold and copper recovery. The results suggest that the efficient recovery of high-purity gold can be achieved by monitoring the potential of gold.[1] K. Fukuda, S. Yae, N. Fukumuro, S. Sakamoto, and H. Matsuda, ECS Trans., 53(19), 69 (2013). DOI: 10.1149/05319.0069ecst[2] K. Fukuda, N. Fukumuro, S. Sakamoto, and S. Yae, ECS Trans., 61(10), 1 (2014). DOI: 10.1149/06110.0001ecst[3] M.G. Aylmore and D.M. Muir, Miner. Eng., 14, 135 (2001). DOI: 10.1016/s0892-6875(00)00172-2[4] H. Arima, T. Fujita, and W. Yen, Mater. Trans., 43, 485 (2002). DOI: 10.2320/matertrans.43.485[5] S. Syed, Hydrometallurgy, 115-116, 30 (2012). DOI: 10.1016/j.hydromet.2011.12.012[6] B. Xu, W. Kong, Q. Li, Y. Yang, T. Jiang, and X. Liu, Metals, 7, 222 (2017). DOI: 10.3390/met7060222[7] Y. Iwai, Y. Takashima, A. Matsumoto, and S. Yae, Abst. Interfinish2020 20th world congress, P-E2-001 (2021).[8] Y. Takashima, A. Matsumoto, Y. Iwai, S. Arita, and S. Yae, J. Surf. Finish. Jpn., 73, 98 (2022). DOI: 10.4139/sfj.73.98

Highly efficient and selective extraction of Au(I) from thiosulfate gold-leaching solution using diphenylphosphine

Solvent extraction has the advantages of continuous operation mode and high loading capacity, which has received some attention in the field of thiosulfate gold leaching, but current research results are not satisfactory. In this study, diphenylphosphine (DPP) diluted in benzene was used to extract gold from thiosulfate solution, and its extraction behavior and properties were investigated. The effects of the DPP concentration, pH value, contact time, and sodium thiosulfate concentration on the extraction performance were evaluated. Under the optimal conditions, 0.7 mmol/L DPP showed high gold-extraction efficiency (99%) from 0.2 mol/L S2O32− solution embracing 10 mg/L Au(I) at pH = 10.0 with an aqueous/organic (A/O) ratio of 2. A high A/O ratio (A/O = 15) can be used in the extraction stage to achieve complete recovery of gold ions from solution. In addition, DPP showed high selectivity and recovery ability in Cu–NH3–thiosulfate gold-leaching solution, and the recovery rate was higher than 99%. The mechanism of gold-ion extraction by DPP involving ligand exchange between DPP− and [Au(S2O3)2]3− was confirmed by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy. The P atom in Ph2–P− plays an important role in complexation of gold ions, which was confirmed by density functional theory calculation. The extraction method with low reagent consumption and high recovery rate developed in this study will greatly promote the development of gold leaching with thiosulfate.

Development of quantification methods of a new selective carbonic anhydrase II inhibitor in plasma and blood and study of the pharmacokinetics of its ophthalmic suspension in rats

Introduction: Development of new bioanalytical methods is required for studying the systemic exposure of new selective inhibitor of carbonic anhydrase II, 4-(2-methyl-1,3-oxazole-5-yl)-benzenesulfonamide, and its N-hydroxymetabolite in plasma and in whole blood. The results of the experiment with a single administration of an ophthalmic suspension of the drug are necessary to optimize the subsequent design of a full pharmacokinetic study. Materials and Methods: HPLC-MS/MS method was used to measure a concentration of analytes in plasma and whole blood. Chromatographic separation was performed on the Poroshell 120EC-C18 column (50*3.0 mm, 2.7 µm). Pharmacokinetics was studied on 6 Wistar rats weighing 287.50±18.64 g (Mean±SD). Each animal was instilled with 40 µL of the ophthalmic suspension in concentration of 2% in each eye. Blood samples were collected before administration of the drug and 30 min, 1 h, 1 h 30 min, 2 h, 3 h, 4 h, 6 h, 8 h, 12 h, 24 h, 48 h, and 72 h after administration. Non-compartment approach was used for the evaluation of pharmacokinetic parameters. Results and Discussion: The protein precipitation was chosen for a sample preparation of biological fluids. A solution of ascorbic acid in concentration of 10% was added to plasma, and a solution of sodium thiosulfate in concentration of 10% was added to blood to prevent the degradation of N-hydroxymetabolite of the drug. The analytical range of determination of 4-(2-methyl-1,3-oxazole-5-yl)-benzenesulfonamide and its N-hydroxyderivative in blood was 50-10000 ng/mL and 5-1000 ng/mL, respectively, in plasma – 10-2000 ng/mL and 1-200 ng/mL, respectively. The maximum plasma concentration of the studied drug was 264.32±68.47 ng/mL (Mean±SD) 1.92±0.92 h (Mean±SD) after administration, and its metabolite was 10.43±1.79 ng/mL 2.17±1.13 h after administration. The maximum concentration of the drug in blood reached 8705.23±1301.84 ng/mL (Mean±SD) 1.17±0.52 h (Mean±SD) after administration, and the maximum concentration of N-hydroxymetabolite reached 230.00±69.54 ng/mL (Mean±SD) 1.33±0.41 h (Mean± SD) after administration. Conclusion: The developed methods have been fully validated according to the requirements of Russian and internatonal guidelines and have been successfully used for pharmacokinetic research. It was found that a content of 4-(2-methyl-1,3-oxazole-5-yl)-benzenesulfonamide and its main metabolite in whole blood is significantly higher than in plasma.

Sulfur nanocomposites with insecticidal effect for the control of Bactericera cockerelli.

The purpose of this research was to synthesize nanocomposites consisting of sulfur nanoparticles coated with eucalyptus and rosemary essential oils to determine the insecticidal effect in the control of nymphs of paratrioza (Bactericera cockerelli (Sulc) (Hemiptera: Triozidae)) in potato crops. A solution of thiosulfate was reduced to elemental sulfur, and the sulfur nanoparticles were coated with eucalyptus and rosemary essential oils with the three concentrations of 0.25%, 0.5%, and 0.75%. The samples were characterized by UV-visible spectroscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and scanning electron microscopy. The insecticidal efficacy of the nanocomposites was evaluated in the entomology laboratory 24, 48, and 72 h after application. Furthermore, efficacy was compared to the commercial insecticide thiamethoxam (0.25%) and a control. The results show that eucalyptus nanocomposites with oil concentrations of 0.25%, 0.5%, and 0.75% and rosemary nanocomposites with an oil concentration of 0.5% have an insecticidal efficacy of 100% for the control of insect nymphs 24 h after application. The insecticidal efficacy of rosemary nanocomposites with oil concentrations of 0.25% and 0.75% increases over time and reaches 100% at 24 and 72 h, respectively. The synthesized nanocomposites are more effective in controlling nymphs of paratrioza than the commercial insecticide thiamethoxam; thus, they could be used for the development of new insecticides.

Oxidation mechanism of pyrite in a thiosulfate solution: electrochemical impedance (EIS) and in situ Raman spectroscopy

Ammoniacal thiosulfate has been used lately as an alternative lixiviant for leaching gold from sulfides ores which are not amenable for cyanidation. However, the oxidation of the sulfide minerals generates products that inhibit the dissolution of gold and can promote the degradation of the leaching solution. The complexity of the ammoniacal thiosulfate leaching system has prevented the unification and clarification of the mechanisms of oxidation of sulfide ores used for gold extraction.In this study, a method combining polarization curves, Electrochemical impedance spectroscopy (EIS), and in situ Raman spectroscopy was implemented to investigate the oxidation process of high-purity pyrite. Pyrite samples were dispersed in carbon paste electrode (CPE-Py). The polarization curves of CPE-Py exhibited an increase in current values for overpotentials greater than 0.1 V, indicating the initiation of mineral oxidation processes. Subsequently, a maximum current was observed initially, followed by subsequent decrease, indicating the occurrence of passivation processes on the electrode surface. Hydrodynamic polarization curves demonstrated that the overpotential at which the passivation process occurs is independent of mass transport, suggesting that the passivation products were formed through solid-state transformation.Impedance spectra revealed that at overpotentials below 0.1 V, a partially resolved capacitive semicircle was observed, which was associated with the resistance encountered when charge was transferred between the solution and the surface layer interface. This resistance decreased as the polarization overpotential increased, implying a decrease in charge transfer kinetics. At higher overpotentials (0.3 V–0.4 V), a second capacitive semicircle appeared, linked to the oxidation of one or several species present in the mineral.In situ Raman spectroscopy was utilized to identify the oxidation species of pyrite in ammonia-thiosulfate ((NH4)2S2O3) leaching solution at a pH = 10.2. The composition of the species varied depending on the applied anodic potential. At low anodic potentials (0.1 V), Fe(OH)2 and thiosulfate (S2O32−) were formed, while at high anodic potentials (0.4 V), iron products such as Fe3O4 and γ-FeOOH, as well as sulfide species including thiosulfate, tetrathionates and sulfates (S2O32−, S4O6−2 and SO42−) were formed.