Equilibrium Constant Of Reaction Research Articles

Density, viscosity, and H2S solubility of N-butylmorpholine bromide iron-based ionic liquids

The density and viscosity of N-butylmorpholine bromide iron-based ionic liquids (rFeCl3/ [Nbmm]Br) with two iron-morpholine ratios (r = 0.8 and 1.0) mol·mol−1 were measured at 303.15–348.15 K and 101.3 kPa. Density and viscosity data were fitted by empirical correlations for temperature. The average relative errors were less than 0.02 % and 2 %, respectively. The density and viscosity decrease with increasing temperature. The density increases with the increase of r, while the viscosity shows the opposite trend. The gas-liquid equilibrium data of H2S in rFeCl3/[Nbmm]Br were measured by the isochoric pressure drop method at temperatures of 303.15–348.15 K, pressures of 0–200 kPa, and r of 0.8 and 1.0 mol·mol−1. The total solubility of H2S increases with decreasing temperature, increasing pressure, and decreasing r. The measured solubility data were fitted by the reaction equilibrium thermodynamic model. Chemical reaction equilibrium constant and the Henry's constant at different temperatures and different r were obtained. The average relative error of model fitting is less than 3 %. The results show that the chemical reaction equilibrium constant and the Henry’s constant both decrease with the increase of r, and decrease of temperature. Effect of molecular structure on reaction equilibrium constants was explained by quantum chemistry calculation. The absorption of H2S in rFeCl3/ [Nbmm]Br at low pressure is dominated by chemical absorption. With the increase of pressure, the proportion of physical absorption continues to increase, and gradually occupies the main part.

Understanding the mechanism for initial deposition under the coupling effect of sodium and calcium during boiler operation: The first-principles study and thermodynamic analysis

During the boiler operation, ash deposition can result in a decrease in boiler efficiency and an enhanced release of pollutants. To relieve these issues, the formation mechanism for initial deposition triggered by the coupling effect of sodium and calcium was investigated by the first-principles study in this paper. The results indicated that the binding of sodium and calcium deposited on Fe3O4(001) surface is non-covalent interaction. Furthermore, |V|/G values of different particles on the surface are less than 2 and closed to 1. So the reactions of sodium and calcium deposited on the Fe3O4(001) are mainly closed-shell interactions accompanied by partial covalent interaction by Atom-in-Molecule theory. Additionally, the position and form of weak interaction also be further clarified by the independent gradient model. The thermodynamic calculation results showed that Gibbs free energy change is more affected to the change of the temperature under the existence of sodium and calcium. The reaction equilibrium constants is larger than 1, indicating that sodium and calcium are easily combined with Fe3O4(001). Moreover, calcium is more likely to promote a positive reaction than sodium.

Density, Viscosity, and Hydrogen Sulfide Solubility of the Triethylamine Hydrochloride Ferric Chloride Ionic Liquid

The density, viscosity, and hydrogen sulfide solubility of the triethylamine hydrochloride ferric chloride ionic liquid (rFeCl3/Et3NHCl) were measured at temperatures of 303.15 to 348.15 K, pressures up to 200 kPa, and iron–amine ratios (r, molar ratio of anhydrous FeCl3 to Et3NHCl) of 0.4 to 1.0 mol·mol–1. Density and viscosity data were respectively fitted with empirical correlations for temperature. The H2S solubility in rFeCl3/Et3NHCl was measured by the isochoric pressure drop method. The absorption of H2S in FeCl3/Et3NHCl contains the physical process and chemical process. The decrease in temperature and iron–amine ratio and the increase in pressure are beneficial to improve the total solubility of H2S. Using the reaction equilibrium thermodynamic model (RETM) to correlate the solubility data, the chemical reaction equilibrium constant and Henry’s constant were obtained. Affected by the molecular molar volume and acidity, Henry’s constant first decreases and then increases with the increase in iron–amine ratio and has a minimum value at 0.6 molar ratio. The reaction equilibrium constant decreases with the rise of iron–amine ratio and the reduction of temperature. The total solubility at low pressure is dominated by chemical absorption. As the pressure increases, the proportion of physical absorption increases.

A theoretical insight into the mechanism of NO heterogeneous reduction on char surface: The catalytic effect of potassium

In this paper, the catalytic effect of K on the NO heterogeneous reduction over char surface was investigated using the quantum chemistry calculation. The adsorption performance and the detailed reaction pathways were obtained via density function theory before and after potassium decorating. Additionally, the mayer bond order, thermodynamic and kinetic analysis were studied to further clarify the effect of K on the NO-char reaction. The calculation results showed that K can promote the adsorption of NO molecules on char surface. It was found that the reaction energy barriers were reduced with the decoration of K, indicating that K can promote the chemical reaction. Four reaction pathways were obtained based on Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms, and the order of reaction activity was as follows: L-H@K > L-H > E-R@K > E-R. Moreover, thermodynamic analysis showed that the reaction equilibrium constants increased with the addition of K, suggesting that the reaction was more complete and irreversible. From kinetic analysis, the reaction rate constants increased with temperature, and the rate of reactions were more faster in the presence of K, which indicated that K can accelerate the NO heterogeneous reduction. Based on the thermodynamic and kinetic performances, it is concluded that K has a significant promotion on the NO heterogeneous reduction by char. The theoretical results systematically reveal the catalytic mechanism of K on the NO reduction by char, which can make contributions to the clean and efficient utilization of the potassium-containing fuels.

The influence of step potentials upon defect equilibria and defect concentrations inside solid oxide fuel cells

The defect chemical models with semi-empirical equilibrium constants are widely adopted to determine defect concentrations inside solid oxide materials. However, the equilibrium constants are tested under uniform atmosphere, which can not be directly applied to working fuel cells. Step potentials are formed at the electrode/electrolyte interfaces of working fuel cells, resulting from the completely different atmosphere between anode and cathode. In this work, the physically meaningful potential framework of working fuel cells and the strong relationship between charged defects and step potentials are established. One part of the Gibbs energy of electrode reactions is converted into electrical energy and stored in the step potentials. The accurate equilibrium constants of SOFC electrode reactions are corrected by considering the step potentials.

Acid-Base Properties of Cis-Vacant Montmorillonite Edge Surfaces: A Combined First-Principles Molecular Dynamics and Surface Complexation Modeling Approach.

Montmorillonite layer edge surfaces have pH-dependent properties, which arises from the acid-base reactivity of their surface functional groups. Edge surface acidity (with intrinsic reaction equilibrium constant, pKa) is a chemical property that is affected by crystal structure. While a cis-vacant structure predominates in natural montmorillonites, prior molecular-level studies assume a centrosymmetric trans-vacant configuration, which potentially leads to an incorrect prediction of montmorillonite acid-base surface properties. We computed intrinsic acidity constants of the surface sites of a montmorillonite layer with a cis-vacant structure using the first-principles molecular dynamics-based vertical energy gap method. We evaluated pKa values for both non-substituted and Mg-substituted layers on common edge surfaces (i.e., surfaces perpendicular to [010], [01̅0], [110], and [1̅1̅0] crystallographic directions). The functional groups ≡Si(OH), ≡Al(OH2)2/≡Al(OH)(OH2), and ≡SiO(OH)Al sites on surfaces perpendicular to [010] and [01̅0] and ≡Si(OH)U, ≡Si(OH)L, ≡Al(OH2), and ≡Al(OH2)2 on surfaces perpendicular to [110] and [1̅1̅0] determine the proton reactivity of non-substituted cis-vacant edge surfaces. Moreover, the structural OH sites on edge surfaces had extremely high pKa values, which do not show reactivity at a common pH. Meanwhile, Mg2+ substitution results in an increase in pKa values at local or adjacent sites, in which the effect is limited by the distance between the sites. A surface complexation model was built with predicted pKa values, which enabled us to predict surface properties as a function of pH and ionic strength. Edge surface charge of both trans- and cis-vacant models has little dependence on Mg2+ substitutions, but the dependence on the crystal plane orientation is strong. In particular, at pH below 7, edge surfaces are positively or negatively charged depending on their orientation. Implications of these findings on contaminant adsorption by smectites are discussed.

Revealing Preservice Teachers’ Conceptions, Troublesome Knowledge and Threshold Concept of Chemical Equilibrium through Predict Observe Explain Mental Model Diagnostic Test (POE-MMDT)

The purpose of this study is to reveal preservice teacher’ conception of chemical equilibrium concepts which then were further analysed to identify the troublesome knowledge and threshold concept of chemical equilibrium. The participants of this study were 68 preservice chemistry teachers from one of the Teacher Education Institutions in Bandung, Indonesia. Using the descriptive-qualitative design, this research uses a predict-observe-explain mental model diagnostic test consisting of four main questions related to the phenomenon equilibrium process of the decomposition of N2O4 to become NO2. The findings show that most of the preservice teachers’ conceptions about chemical equilibrium are at the level of partial understanding, with five misconceptions has been identified in this study: (1) the reaction in chemical equilibrium is the same as an irreversible reaction; (2) the concentration of reactant and products are the same at equilibrium state; (3) gas with a greater concentration at equilibrium state can be determined from the gas that was first inserted to the container; (4) the concentration ratio at equilibrium is equal with the ratio of the coefficient reaction, and (5) the reactant is the gas which fills the container first. Further analysis shows that there are eight concepts in chemical equilibrium with troublesome knowledge characteristics, namely (1) the concentration of reactants and products in a state of equilibrium; (2) changes in the concentration of reactants and products to a state of equilibrium when starting from any side; (3) reactions that occur in an equilibrium state, (4) chemical equations for equilibrium reaction; (5) the rate of reactions in equilibrium state; (6) the change of reaction rate to reach an equilibrium state; (7) the relationship between Q and K; and (8) the calculation of reactants and products concentration at an equilibrium state. In addition, chemical equilibrium has two threshold concepts: the dynamic characteristic of equilibrium reaction and equilibrium constant. These findings show that the predict-observe-explain instrument has the potential to disclose PSTs’ mental model since it requires the participants to explain the prediction and its corresponding observation result. Besides, this instrument also guides the participants in explaining the macroscopic phenomena, which generates information about their understanding at the submicroscopic and symbolic levels. should be recognised as encompassed by and a form or part of “for all.”

Nucleotide Interaction with Nanocrystalline Ceria Surface

The adsorption of nucleotides on the surface of nanocrystalline cerium dioxide (pHpzc = 6.3) in NaCl solutions was investigated using multi-batch adsorption experiments over a wide range of pH. The obtained results were interpreted as a formation of outer and inner sphere surface complexes with the participation of phosphate moieties. The Basic Stern surface complexation model was applied to obtain quantitative equilibrium reaction constants.

Measurement and model of density, viscosity, and hydrogen sulfide solubility in ferric chloride/trioctylmethylammonium chloride ionic liquid

The density and viscosity of ferric chloride/trioctylmethylammonium chloride ionic liquid (rFeCl3/[A336]Cl) with different molar ratios (r = 0.1–0.8) of FeCl3 to [A336]Cl were measured at temperatures from 313.15 to 358.15 K and atmospheric pressure. The density and viscosity data were fitted by the relevant temperature variation equations, respectively. The variation of density and viscosity with temperature and r was obtained. The solubility of rFeCl3/[A336]Cl to H2S was measured at temperatures from 318.15 to 348.15 K and pressures from 0 to 150 kPa. The effects of temperature, pressure, and r on the solubility of H2S were discussed. The reaction equilibrium thermodynamic model (RETM) was used to fit the H2S solubility data, and the average relative error was less than 1.3%, indicating that the model can relate the solubility data well. And Henry's constant and chemical reaction equilibrium constant were obtained by the RETM fitting. The relationships of Henry's constant and chemical reaction equilibrium constant with temperature and r were analyzed.

EXTRACTION AND ATOMIC-ABSORPTION DETERMINATION OF TUNGSTEN (VI) WITH 2-HYDROXY-5-T-BUTYLPHENOL-4'-NITROAZOBENZENE

The complexation of tungsten (VI) with an azo compound synthesized from para-tret-butylphenol (2-hydroxy-5-Tr-butylphenol-4-nitro-asobenzene) has been studied spectrophoto¬metrically. The optimum pH values of the solution are 2.0-3.0. The maximum light absorption of the complexes in n-butanol is in the range 460-470nm, and that of the reagent at 360-370; complex formation is accompanied by a bathochromic shift. The spectrophotometric characteristics of the complex have been calculated and the composition of the complex was determined by various methods. Using the equilibrium shift and isomolar series methods it has been found that the W:R ratio is 1:2. By the Sommer method it has been found that during complex formation one proton is released from each reagent molecule. The complex stability constant βk = 9.04·108 and the complex formation reaction equilibrium constant (4.2·104) have been calculated by the method of Komar. The molar absorption coefficient is (3.44.2).104. The graduation diagram is linear at a tungsten concentration of 1.0-10 µg/ml, n-butanol has been used as an extractant. A single extraction with n-butanol 97% of tungsten as a complex is extracted. Methods of extraction-atomic-absorption and extraction-photometric determination of tungsten have been developed and the influence of a number of extraneous ions on the determination of tungsten has been revealed. The correctness of the results obtained has been controlled by analysing the State Standard Alloy Reference Materials

Optimization of converting process for matte of oxidized nickel ores and sulfide copper ores joint smelting based on thermodynamic simulation

The paper presents the results obtained in the thermodynamic modeling of converting copper-nickel matte (11.3 wt.% Ni + Cu + + Co, 61.5 wt.% Fe, 25.9 wt.% S) produced by joint smelting of oxidized nickel ore and sulfide copper ore. Calculations were made in the approximation of ideal molecular solutions using the HSC Chemistry software package (Outotec Research Oy, Finland). The possibility of low-iron matte, converter slag and gas phase separation was shown. Estimated conditional equilibrium constants of exchange reactions between low-iron matte and slag (KNi/Fe = 0.004÷0.005, KCo/Fe = 0.056÷0.099) are close to ideal values. Statistical data processing was carried out using the mathematical experiment planning method. The converting temperature (t = 1100÷1300 °C) and iron and sulfur oxidation completeness level (q = 0.9÷1.0) determining the air and flux (SiO2) consumption were chosen as the factors to study. Obtained mathematical models of the process were used for its optimization. It was shown that the best converting performance can be achieved at t = 1150 °С and q = 0.950 when the low-iron matte contains 70.7 wt.% Ni + Cu + Co. At a yield of 8.74 % of the charge mass, the nickel, copper and cobalt recovery rates are 67.9, 97.9 and 9.1 %, respectively. The supposed air consumption (145.1 m3 (under normal conditions) per 100 kg of matte) and SiO2 (34.4 kg per 100 kg of matte) as well as slag yield (89.1 % of the charge mass) are close to working regime parameters. The results of the study confirm the possibility of cost-effective processing of poor copper-nickel matte and after experimental verification they can be used to develop automation flowcharts for converter departments at existing and designed production facilities.

Study of the structure and properties of SiC ceramics

This paper presents the results of the entropy calculation of the equilibrium constants of chemical reactions at liquid-phase sintering of SiC ceramics with eutectic additives. The composition of the charge for sintering ceramics with nanoadditives forming the liquid phase was determined: MnOnano 1.5 wt. % + Al2O3nano 2 wt. % + SiCµm 94 wt. % + SiO2µm 2.5 wt. %. Possible chemical reactions of liquid-phase sintering of ceramics at a temperature of 1800 °C in a weakly reducing CO medium were established. The values of the change in the Gibbs energy for all possible chemical reactions at a sintering temperature of 1800 °C were calculated by the method of entropy calculation of the equilibrium constants. The elements of the liquid phase and reinforcing additives were determined.The elements of the liquid phase and reinforcing additives were determined. The structure and properties of finished sintered ceramic samples were studied. Microstructural analysis of ceramics indicated its grain structure with an average grain size of ⁓10 µm. The main phase components of the ceramics based on silicon oxide were determined. It was found that the sample consists of three main phases: modification of the ring radical of silicate Si3O6, silicon dioxide SiO2 and anorthoclase (SiAl)O4.

Mathematical modeling the methanol production process for direct CO2 hydrogenation over a gallium (Ga3Ni5) catalyst

Carbon capture and utilization as a raw material for methanol production is a good option for addressing environmental, energy and global warming problems. However, commercial methanol synthesis processes have poor performance due to high water production during the process, oxidation and inactivation of the catalyst, and low CO2 conversion. To overcome these barriers, in this study, an efficient process consisting of Ga3Ni5 catalyst for direct CO2 hydrogenation is modeled. Synthesis equations and reaction rate constants, adsorption equilibrium constants and reaction equilibrium constants were used to model the methanol production process in the vicinity of the Ga3Ni5 catalyst using MATLAB software. In the new process, in order to increase safety and control process costs, the process pressure was reduced from 76.98 bar to 2 bar, on the other hand, the water produced as the poisoning agent of Cu/ZnO/Al2O3 catalyst is significantly ineffective in this configuration. The results show that Ga3Ni5 catalyst increases the conversion rate of carbon dioxide to methanol by about 13.75% compared to Cu/ZnO/Al2O3 catalyst. The proposed catalyst is an active and stable catalyst for methanol production that can compete with the traditional synthesis process.

Effect of tubulin self-association on GTP hydrolysis and nucleotide exchange reactions

We investigated how the self-association of isolated tubulin dimers affects the rate of GTP hydrolysis and the equilibrium of nucleotide exchange. Both reactions are relevant for microtubule (MT) dynamics. We used HPLC to determine the concentrations of GDP and GTP and thereby the GTPase activity of SEC-eluted tubulin dimers in assembly buffer solution, free of glycerol and tubulin aggregates. When GTP hydrolysis was negligible, the nucleotide exchange mechanism was studied by determining the concentrations of tubulin-free and tubulin-bound GTP and GDP. We observed no GTP hydrolysis below the critical conditions for MT assembly (either below the critical tubulin concentration and/or at low temperature), despite the assembly of tubulin 1D curved oligomers and single-rings, showing that their assembly did not involve GTP hydrolysis. Under conditions enabling spontaneous slow MT assembly, a slow pseudo-first-order GTP hydrolysis kinetics was detected, limited by the rate of MT assembly. Cryo-TEM images showed that GTP-tubulin 1D oligomers were curved also at 36 °C. Nucleotide exchange depended on the total tubulin concentration and the molar ratio between tubulin-free GDP and GTP. We used a thermodynamic model of isodesmic tubulin self-association, terminated by the formation of tubulin single-rings to determine the molar fractions of dimers with exposed and buried nucleotide exchangeable sites (E-sites). Our analysis shows that the GDP to GTP exchange reaction equilibrium constant was an order-of-magnitude larger for tubulin dimers with exposed E-sites than for assembled dimers with buried E-sites. This conclusion may have implications on the dynamics at the tip of the MT plus end.

Thermodynamic and kinetic aspects of the solvent-free liquid–liquid synthesis of tailor-made glyceride esters

Direct esterification between glycerol and carboxylic acids allows the design of different glycerides according to predetermined applications. Five carboxylic acids (caprylic, capric, lauric, stearic and oleic) which formed a bi-phasic system with glycerol were tested for esterification in a 1:1 M proportion. Two strategies were pursued: on one hand, homogeneous acid catalysis using sulfuric acid or p-toluenesulfonic acid at 100 °C and on the other hand, reactions catalyzed by immobilized lipase B from Candida antarctica at 65 °C. The selectivity and yield for MG was higher at lower temperature and with the use of the enzyme. Lauric acid was the carboxylic acid with the higher yield and selectivity to MG despite the catalyst used. The decrease in the mutual solubility between the carboxylic acid and glycerol seems to favor MG formation. The rate of reaction decreased with the increase in the molecular weight of the carboxylic acid used and the introduction of one unsaturation. From caprylic to lauric acid, the catalyst performance was: p-toluenesulfonic acid > lipase > sulfuric acid whereas for stearic and oleic acids the lipase was superior. Reactant accumulation at the interface is proposed to explain these results. The thermodynamic UNIFAC model was applied to calculate the initial activity coefficients and molar fractions in each phase. It was demonstrated that the thermodynamic activity of the species is a more convenient representation of the effective concentration for kinetic description of a liquid–liquid system. The equilibrium constant of lipase reaction was calculated with an expression based on the activity of compounds. The equilibrium constant for diglycerides formation decreased with the carbon chain length.

Multi-cationic molten salt electrolyte of high-performance sodium liquid metal battery for grid storage

Multi-cationic molten chloride salt mixtures such as LiCl–KCl–NaCl are promising molten salt electrolytes for sodium liquid metal batteries (Na-LMBs). In this work, the melting temperature of LiCl–KCl–NaCl was determined with Differential Scanning Calorimetry (DSC), assisted by FactSage™ simulation and confirmed by a melting point apparatus OptiMelt™. It is founded that the eutectic LiCl–KCl–NaCl can be considered as a pseudo-binary system with LiCl–KCl eutectic (59.2–40.8 mol.%) as the solvent and NaCl as the solute. When NaCl is not more than 9 mol.%, the eutectic LiCl–KCl–NaCl salt mixture has a melting temperature of ∼350 °C as that of LiCl–KCl eutectic. In addition, the exchange reactions between anode Na metal with LiCl–KCl–NaCl molten salt electrolyte were studied at the temperature of 400–500 °C quantitatively. The equilibrium constants of the exchange reactions were determined by chemical analysis on the salt and metal phases with Ion Chromatography (IC). A one ampere-hour (Ah) Na-LMB test cell shows promising energy storage performance. Moreover, the phenomena in the cell test can be explained convincingly, combining the results of exchange reactions and the pseudo-binary-system theory. The findings on the multi-cationic molten salt electrolytes for Na-LMBs in this work could support further development of other liquid metal batteries.

Three-component 1,1,3,3-tetramethylguanidine based CO2-binding organic liquids: Statistical solvent design and thermodynamic modeling of CO2 solubility by LJ-Global TPT2 EoS

In this study, three-component CO2-binding organic liquids (CO2BOLs) are introduced for high pressure CO2 absorption. The non-aqueous, green solvents consist of a superbase (1,1,3,3-tetramethylguanidine (TMG)), a tertiary alkanolamine (Dimethylethanolamine (DMEA), Diethylethanolamine (DEEA) and N-methyldiethanolamine (MDEA)) and an alcohol (MeOH, n-BuOH, sec‑BuOH, tert‑BuOH and 1-HexOH). The best combination of solvent components was determined to be the TMG/DMEA/n-BuOH BOL (molar ration:1/1/1) based on both CO2 loading (αeq= 0.431 mol CO2/mol solvent) and absorption rate (αR= 0.225 mol CO2/mol solvent within 20 min) by implementing screening experiments. The mixture design approach was applied for the design of experiments, modeling and investigating the effect of components’ proportion on αeq and αR at the constant temperature of 35.0 °C and initial CO2 pressure of 25.0 bar. The highest αeq (0.573 mol CO2/mol BOL) and αR (0.362 mol CO2/mol solvent) were obtained using TMG/n-butanol (1/1) and DMEA BOLs, respectively. The CO2 solubility data in the two-component BOLs: TMG/n-BuOH, TMG/DMEA and DMEA/n-BuOH as well as the three-component TMG/DMEA/n-BuOH BOL were gathered at 25.0, 35.0 and 45.0 °C and the pressures up to 35.0 bar using equimolar solvent mixtures. The LJ-Global TPT2 EoS was used in the simultaneous VLE and chemical equilibrium calculation algorithm for the thermodynamic modeling of CO2 solubility in the BOLs. The AAD% in the modeling of TMG/n-BuOH, TMG/DMEA, DMEA/n-BuOH and TMG/DMEA/n-BuOH BOLs were calculated to be 11.5%, 12.4%, 10.5 and 12.9%, respectively. The enthalpies of CO2 absorption in BOLs and the speciation of the system components were predicted from reaction equilibrium constants and using LJ-Global TPT2 EoS.

(Invited) Ligand Exchange at Chalcogenide and Perovskite Nanocrystal Surfaces Examined Via Isothermal Titration Calorimetry

I will describe our group’s efforts to quantify ligand association and exchange reactions on semiconductor nanocrystal (NC) surfaces via isothermal titration calorimetry (ITC). ITC provides a direct thermal measurement of reaction progress. As shown in earlier work by our group and others examining ligand exchange on chalcogenide and pnictide quantum dots, ITC is able to access the enthalpy change of reaction, equivalency, and effective equilibrium constants, including in cases that are challenging to resolve by NMR alone. Here, we will describe the extension of this approach to ligand exchange reactions on halide perovskite NCs, and to ligand exchange on chalcogenide NCs in aqueous solution. Such advances are needed to contribute a quantitative description of NC surface chemistry toward applications such as advanced optoelectronic devices, bioimaging probes, and photocatalysis.

Reactive extraction of gallic acid using tri-n-octylamine in a biocompatible mixture of diluents

The present study is an approach to develop a biocompatible extraction system using tri-n-octylamine (TOA), with a modifier, 1-decanol and inert diluent, n-dodecane for the recovery of gallic acid (GA) from aqueous solution. The effects of GA concentration, modifier volume ratio, solvent polarity and pH of aqueous solution on reactive extraction of GA, are examined. With optimized extraction system of 20% TOA with 40% 1-decanol and 40% n-dodecane, further investigations are carried out for the determination of reaction stoichiometry ( m = 1.53 – 2.02), equilibrium constants (K E = 20.30 – 83.23) and thermodynamics (∆H o = -94,385.86 J.mol –1 , ∆S o = -267.51 J.mol –1 .K –1 and ∆G o = -14,627.83 to -6602.54 J.mol –1 .K –1 ) in the range of GA concentrations (0.00294 kmol.m –3 – 0.04703 kmol.m –3 ) at different temperature (298.15 K – 328.15 K) using a bio-inspired, population based genetic algorithm, differential evolution (DE). At the temperature 298.15 K, maximum distribution of GA in organic phase is found as 81%.

Stability and structure of platinum sulfide complexes in hydrothermal fluids

Knowledge of the chemical speciation of platinum and the solubility of Pt-bearing minerals in hydrothermal fluids is required to assess Pt transport, remobilization and concentration in the Earth’s crust. In this study, we combined PtS(s) solubility measurements in a hydrothermal reactor allowing fluid sampling, in situ X-ray absorption spectroscopy, and first-principles molecular dynamics simulations to systematically investigate the structure, composition and stability of Pt sulfide complexes in model aqueous H2S-bearing solutions up to 300 °C and 600 bar. The results demonstrate that tetrahydrosulfide, PtII(HS)42–, is the major Pt-bearing complex in aqueous solutions saturated with PtS(s) over a wide range of dissolved hydrogen sulfide concentrations, from < 0.2 to ∼ 2 molal. The equilibrium constants of the dissolution reaction of PtS(s) generated in this study, PtS(s) + 3 H2S(aq) = Pt(HS)42– + 2 H+ (β4), are described by the equation log10β4 = 0.9 × 1000/T(K) – 19.7 (± 0.5) over the temperature range 25–300 °C and pressure range Psat–600 bar. Furthermore, the stepwise formation constants of four PtII-HS complexes, Pt(HS)+, Pt(HS)20, Pt(HS)3–, and Pt(HS)42–, were estimated, for the first time, from molecular dynamics simulations. The generated constants indicate that the maximum solubility of platinum in the form of Pt(HS)42– in reduced H2S-dominated hydrothermal fluids at moderate temperatures (≤ 350 °C) is close to 1 ppb Pt at near-neutral pH of 6–8 and hydrogen sulfide concentrations of 0.1 molal. Although this solubility is much greater than that of Pt-Cl, Pt-OH and Pt-SO4 complexes at such conditions, it is yet too low to account for significant Pt transport in most shallow-crust hydrothermal settings, characterized by the presence of both sulfide and sulfate. Complexes with S-bearing ligands, very likely other than H2S/HS–, such as S3–, would be required to account for Pt hydrothermal mobility. Our results provide a basis for more systematic future studies, using combined approaches, of the role of hydrothermal fluids in the behavior of platinum group elements in nature.