Apparent Equilibrium Constant Research Articles

Development of a conceptual direct solvent extraction (DSX) route and a flowsheet to produce purified concentrated cobalt and nickel solutions representing sulfuric acid leach liquor of laterite

Direct solvent extraction (DSX) was applied to produce purified concentrated Ni and Co solutions from a synthetic sulfuric liquor containing Ca, Cu, Mg, Mn, and Zn as impurities, which simulates the solution obtained by the sulfation-roasting-leaching process after precipitation of Fe, Al, and Cr. The commercial extractants Versatic 10, Cyanex 272, D2EHPA, TBP were used in 3 solvent extraction circuits. In the first circuit, operated at 40 °C, Versatic 10 (0.5 M) fully extracted Cu, Zn, Ni, and Co in 3 stages at O/A = 2:1, and pH 6.5, leaving remaining Mn (54% was extracted) and most of the Ca and Mg in the raffinate. The co-extracted Ca and Mg were fully scrubbed off the loaded Versatic 10 in 2 stages at O/A = 5:1, and pH 6.5. The other metals were stripped out of the Versatic 10 extract using a synthetic Ni spent electrolyte (60 g/L Ni, 2 M H2SO4) in 2 stages at O/A = 9:1. This loaded strip liquor was subjected to a second circuit with Cyanex 272 (0.64 M) operated at 50 °C. Three stages were required to fully extract Co, Cu, Mn, and Zn (O/A = 2:1, pH 4), whereas the raffinate containing 82 g/L Ni was deemed suitable for electrowinning. The co-extracted Ni(II) was fully scrubbed off the loaded Cyanex 272 in only 1 stage at O/A = 5:1, and pH 4. All Co, Cu, Mn, and Zn were stripped out from the scrubbed loaded Cyanex 272 in 2 stages at O/A = 10:1 using a synthetic Co spent electrolyte (45 g/L Co, 1 M H2SO4). The raffinate containing 58.4 g/L Co was submitted to a third circuit using a D2EHPA (0.6 M) + TBP (0.73 M) synergistic system operated at 50 °C. Zinc(II) was fully extracted by the D2EHPA + TBP system in 2 stages at pH 2 and O/A = 1:3, while Mn(II) and Cu(II) were fully extracted from the Zn-depleted raffinate in 2 stages at pH 3.5 and O/A = 2:1. The raffinate containing 58.3 g/L Co was deemed suitable for electrowinning. Copper(II), Mn(II), and Zn(II) were stripped out from the loaded D2EHPA + TBP in 3 stages at O/A = 2.5:1 using 1 M H2SO4. The real number of moles of extractants involved in the extractions and apparent equilibrium constants were estimated for all circuits. A flowsheet of the purification conceptual route is presented.

Assessment of polystyrene nano plastics effect on human salivary α-amylase structural alteration: Insights from an in vitro and in silico study

The study found that the enzyme activity of human salivary α-amylase (α-AHS) was competitively inhibited by nanoplastic polystyrene (PS-NPs), with a half-inhibitory concentration (IC50) of 92 μg/mL, while the maximum reaction rate (Vmax) remained unchanged at 909 μg/mL•min. An increase in the concentration of PS-NPs led to a quenching of α-AHS fluorescence with a slight red shift, indicating a static mechanism. The binding constant (Ka) and quenching constant (Kq) were calculated to be 2.92 × 1011 M−1 and 1.078 × 1019 M−1• S−1 respectively, with a hill coefficient (n) close to one and an apparent binding equilibrium constant (KA) of 1.54 × 1011 M−1. Molecular docking results suggested that the interaction between α-AHS and PS-NPs involved π-anion interactions between the active site Asp197, Asp300 residues, and van der Waals force interactions affecting the Tyr, Trp, and other residues. Fourier transform infrared (FT-IR) and circular dichroism (CD) analyses revealed conformational changes in α-AHS, including a loss of secondary structure α-helix and β-sheet. The study concludes that the interaction between α-AHS and PS-NPs leads to structural and functional changes in α-AHS, potentially impacting human health. This research provides a foundation for further toxicological analysis of MPs/NPs in the human digestive system.

Elimination of malachite green from aqueous and saline water by laterite-derived Na-polyferrosialate and polyferrophosphosialate geopolymers: A comparative study

In this study, two laterites (LA)-based geopolymers were synthesized using alkalination (GPAL) and phosphoric acid-activation (GPAC) approaches and applied to scavenge malachite green (MG) dye from aqueous (non-saline) and saline water. The precursor (LA) and geopolymers were characterized by XRF, XRD, TG/DTA SEM, and FTIR techniques. Alkalination and acid-activation resulted in morphologically distinguishable geopolymers with different porosity structures. The dissolution of mineral phases and chemical composition was dependent on the activation medium, resulting in Na-polyferrosialate and polyferrophosphosialate geopolymers for GPAL and GPAC, respectively. The adsorption kinetics data were best described by the pseudo-first-order (PFO) model wherein the adsorption rate, denoted by rate constant (k1), increased with an increase in ionic strength (salinity). The equilibrium data were best modelled by the Sips isotherm. GPAL had a higher maximum adsorption capacity (Qms) than GPAC in both aqueous (non-saline) and saline water. The adsorption capacities were increased in saline solution relative to aqueous solutions without NaCl, from 12.4 to 54.1 mg/g and from 57.1 to 92.0 mg/g for GPAC and GPAL, respectively. The adsorption mechanism entailed electrostatic interactions, hydrogen bonding and hydrophobic interactions. Salinity decreased the solubility of MG and increased the hydrophobic interactions and affinity of MG, implied by apparent equilibrium constant (Ka), resulting in increased adsorption density (Qms). These results indicate that alkaline-based geopolymers are better candidates for scavenging MG dye from water, especially in saline environments.

Energy Status of Stygophilous Amphipod Synurella ambulans as a Promising Biomarker of Environmental Stress in the Hyporheic Zone

The hyporheic zone (HZ) is a sensitive ecotone in river ecosystems because of its biodiversity and susceptibility to human activities. Hyporheic fauna are exposed to multiple stressors that affect the physiology and metabolism of organisms and ultimately ecosystem functioning and biodiversity. This study aimed to quantify adenine nucleotides in the stygophilous freshwater amphipod Synurella ambulans and to evaluate the potential of adenylate energy charge (AEC) as a physiological biomarker of general stress in the HZ of the Sava River at sites with different intensities of environmental and anthropogenic stress. Field studies were conducted seasonally (in December 2018 and April, July, and October 2019) at two sampling sites, one upstream (1-UP) and the other downstream (2-DOWN) of the discharge from the wastewater treatment plant using the standard piston pump. The amphipod population from site 1-UP had significantly higher AEC values than the population from site 2-DOWN in all seasons except summer. Coordinated changes in AEC values with the ATP/ADP ratio indicated differences in energy status between the two populations. However, no changes in the apparent equilibrium constant of adenylate kinase were observed, except in spring at site 1-UP. Multiple linear regression models showed the strongest associations of AEC with Fe and Zn accumulated in amphipods, followed by environmental factors (conductivity, dissolved O2, and concentrations of nitrites and phosphates in the interstitial water). AEC was shown to be a useful index of environmental stress in S. ambulans because it can directly measure the change in available energy and thus the metabolic stress to which the organism is exposed. Finally, seasonal and spatial variations in AEC values reflected ecological status in the HZ.

The kinetics of Ni/Al2O3 and Ni-Fe/Al2O3 catalysts for the CO2 methanation reaction and the reasons for promotion

Replacing nickel with iron is known to promote supported nickel catalyst for CO2 methanation. This promotion is often attributed to the presence of Ni-Fe alloy. However, the effect of replacing Ni with Fe on a common rate expression of CO2 methanation and the specific causes leading to the promotion are not addressed. To achieve these objectives, we synthesize and characterize an alumina supported Ni, 15NiAl, and two alumina supported Ni-Fe catalysts, 15Ni7FeAl and 15Ni3FeAl. These catalysts contain 15 wt% of Ni or Ni + Fe. In 15Ni7FeAl and 15Ni3FeAl the Ni/Fe ratio = 7 and 3, respectively. Characterization studies reveal the presence of smaller Ni-Fe alloy particles in the reduced and spent 15Ni7FeAl and 15Ni3FeAl catalysts. Other characteristics of the catalysts are also identified. With these catalysts we carry out the CO2 methanation reaction under different operating conditions. The enhancement in rate of CH4 formation, rCH4, while using the two bimetallic supported catalysts strongly depends on the Ni/Fe ratio, reactant partial pressures and temperatures. We modify an existing rate expression to adequately represent the reaction data of the three catalysts. In this rate expression, the surface reaction between molecularly adsorbed reactant gases is the rate-determining-step. As Ni is progressively replaced with Fe in the bimetallic catalysts, the apparent rate constants and equilibrium constants for the adsorption of CO2 and H2 of the rate expression increases, which increases rCH4. Under all operating conditions the 15Ni3FeAl catalyst shows the best rCH4 and the apparent rate constants and equilibrium constants are the largest. It appears that the Ni-Fe alloy increases the number of adsorption-sites and the fractional coverage of adsorbed CO2 and H2, which then results in enhanced rCH4 values.

An efficient fluorescence reversible regulation strategy with single labelled oligonucleotide HEX-OND successively triggered by Hg(II) and Cysteine: The application and mechanism

An efficient fluorescence reversible regulation system with HEX-OND was developed. Then the application potential was explored in probing Hg(II) & Cysteine (Cys) in real samples and the thermodynamic mechanism was further investigated by precise theory analysis combining multiple spectroscopic methods. The results showed that only mere disturbances were observed among 15 and 11 kinds of other substances for the optimal system in detecting Hg(II) & Cys, respectively; The linear ranges of quantification were identified as 1.0 ∼ 14.0 and 2.0 ∼ 20.0 (×10-8 mol/L) with LODs of 8.75 and 14.09 (×10-9 mol/L) for Hg(II) and Cys, respectively; no significant deviations were found in the quantification results of Hg(II) in three traditional Chinese herbs and Cys in two samples between the well-understood methods with ours respectively, showing excellent selectivity, sensitivity, and tremendous application feasibility. The detailed mechanism was further verified as that the introduced Hg(II) forced HEX-OND to transform into the Hairpin structure with the apparent equilibrium association constant of 6.02 ± 0.62 × 1010 L/mol in the bimolecular ratio, leading to the equimolar quencher, consecutive two guanine bases ((G)2), approaching and spontaneously static-quenching the reporter HEX (hexachlorofluorescein) (equilibrium constant, 8.75 ± 1.97 × 107 L/mol) in the Photo-induced Electron Transfer (PET) way that was driven by the Electrostatic Interaction. The additional Cys destructed the equimolar Hairpin structure with the apparent equilibrium constant of 8.87 ± 2.47 × 105 L/mol through breaking one of the formed T-Hg(II)-T mismatches by association with the involved Hg(II), occasioning (G)2 apart from HEX and consequently the fluorescence recovery.

Reaction-assisted separation of acetone from the azeotrope of methanol and acetone

The separation of methanol–acetone azeotrope has been a challenging issue. Methanol in the azeotrope was selectively transformed and removed in this paper. Under mild conditions, 95.5% of methanol was transformed into methyl phenylcarbonate (MPC), phenol and dimethyl carbonate (DMC), while acetone was not converted. The separation process of reaction products was simulated, and 99% of acetone with purity of 99.3 wt% was recovered. The byproducts phenol and DMC were also recovered with purity of 93 and 76 wt%, respectively. Compared to the typical pressure-swing and extractive-distillation schemes, the total number of theoretical stages and heat duty could be reduced by 27.7–38.3% and 48.6–58.4%, approximately. The results of thermodynamic experiments showed that the apparent equilibrium constant (124.4 at 23.1 °C) in the first step was much larger than that (12.9) in the second step, indicating that the intermediate MPC was very stable, and thermodynamic factors originating from the specific coplanar structure of substrate contributed to the high methanol conversion. The transesterification reactions were endothermic and spontaneous due to the positive ΔH and negative ΔG values. The spontaneity of reactions was attributed to the increase of entropy, for which the reason was the more possible spatial distributions of atoms in the products. This paper is beneficial for the separation of alcohols from various aprotic solvents.

Recommendations for performing measurements of apparent equilibrium constants of enzyme-catalyzed reactions and for reporting the results of these measurements.

The measurement of values of apparent equilibrium constants K' for enzyme-catalyzed reactions involve a substantial number of critical details, neglect of which could lead to systematic errors. Here, interferences, impurities in the substances used, and failure to achieve equilibrium are matters of substantial consequence. Careful reporting of results is of great importance if the results are to have archival value. Thus, attention must be paid to the identification of the substances, specification of the reaction(s), the conditions of reaction, the definition of the equilibrium constant(s) and standard states, the use of standard nomenclature, symbols, and units, and uncertainties. This document contains a general discussion of various aspects of these equilibrium measurements as well as STRENDA (Standards for Reporting Enzymology Data) recommendations regarding the measurements and the reporting of results.

Extraction mechanism of germanium in sulfate solutions using a tertiary amine (N235)-based solvent extraction system

With the increasing demand for germanium in high-technology fields, the recovery of germanium has gained a great deal of attention. In this study, classical methods (including stoichiometry and saturation methods) were combined with spectroscopic methods (FT-IR, NMR, and ESI-MS) to investigate the mechanism of Ge(IV) extraction from a sulfuric acid solution using the tertiary amines (N235) and trioctyl phosphate (TOP) system. The results indicate that Ge(IV) was extracted as a Ge(OH)(HL)3 anion complex, and tartaric acid is coordinated to Ge(IV) via a CO bond from the carboxylate group. The extraction process followed an anion exchange mechanism. TOP participated in the formation of extraction complexes through hydrogen bonds in the form of GeOH⋯OP but did not co-extract germanium with N235. The extracted complex species were Ge(OH)(HL)2L·HN(R1)3 and Ge(OH)(HL)L2·[HN(R1)3]2 (R=C8H17). The apparent equilibrium constants of the extraction reactions Kex were 100.36 and 100.43 at tartaric acid/Ge(IV) ratios of 5 and 3, respectively. The thermodynamic constants for the extraction process were ΔH=−0.457 kJ·mol−1, ΔS=1.176 kJ·mol−1·K−1, and ΔG=−351.081 kJ·mol−1.

A study on the enrichment mechanism of three nitrophenol isomers in environmental water samples by charge transfer supramolecular-mediated hollow fiber liquid-phase microextraction.

To explore the mechanism of extraction and enrichment of three nitrophenol isomers by charge-transfer supramolecular synergistic three-phase microextraction system, a charge transfer supramolecular-mediated hollow fiber liquid-phase microextraction (CTSM-HF-LPME) combined with high-performance liquid chromatography-ultraviolet detector (HPLC-UV) method was established for the determination of real environmental water samples. In this study, the three nitrophenols (NPs) formed charge-transfer supramolecules with electron-rich hollow fibers, which promoted the transport of NPs in the three-phase extraction system and greatly increased the EFs of NPs. The relationships between the EFs of NPs and their solubility, pKa, apparent partition coefficient, equilibrium constant, and structural property parameters were investigated and discussed. At the same time, most of factors affecting the EFs of NPs were investigated and optimized, such as the type of extraction solvent, pH value of sample phase and acceptor phase, extraction time, and stirring speed. Under optimal conditions, the EFs of o-nitrophenol, m-nitrophenol, and p-nitrophenol were 163, 145, and 87, respectively. With good linearity in the range of 5 × 10-7 ~ 1µg/mL, and the limit of detection of 0.1pg/mL, the relative standard deviations of the method precision were lower than 7.4%, and the average recoveries were between 98.6 and 106.4%. This method had good selectivity and sensitivity, satisfactory precision, and accuracy and had been successfully applied to the trace detection of real water samples.

Reactive separation of gallic acid using trioctylamine in oleyl alcohol and dodecane mixtures: Equilibrium insights, modeling and optimization using RSM and ANN approaches

ABSTRACT The aim of present study is to model and optimize gallic acid (GA) reactive extraction from aqueous solution with trioctylamine (TOA) dissolved in the biocompatible mixture of oleyl alcohol, a modifier and dodecane, an inert diluent using a statistical modeling approach, response surface methodology (RSM) with rotatable central composite design, and artificial neural network (ANN). The optimal values of input parameters for maximum extraction (86%) of GA are found as follows: (i) initial GA concentration ( = 0.387 mol/L); (ii) temperature, T = 26.5°C; (iii) initial TOA concentration ( = 0.049 mol/L); (iv) modifier volume, V = 70% at 101.325 kPa pressure. Predicted responses in terms of extraction degree using RSM and ANN are found to be very close to experimental values. The overall apparent equilibrium constants (K E = 37.24 and 22.38) and stoichiometry of reaction between acid and extractant (m =1.25 and 1.16) are determined considering negligible and 50% physical extraction, respectively. Individual equilibrium constants ( and ) for 1:1 and 2:1 GA:TOA complexes and their concentrations, C11 and C21, respectively, are calculated. Differential evolution approach, a bio-inspired algorithm, is used to investigate the insights of extraction mechanism at the optimum conditions.

Dynamic Liquid-Liquid Interface: Applying a Spinning Interfacial Microreactor to Actively Converge Biphasic Reactants for the Enhanced Interfacial Reaction.

A liquid-liquid interfacial reaction combines reactants with large polarity disparity to achieve greener and more efficient chemistry that is otherwise challenging in traditional single-phase systems. However, current interfacial approaches suffer from the need for a large amount of solvent/reactant/emulsifier and poor reaction performance arising from intrinsic thermodynamic constraints. Herein, we achieve an efficient interfacial reaction by creating a magnetic-responsive, microscale liquid-liquid interface and exploit its dynamic spinning motion to generate vortex-like hydrodynamic flows that rapidly converge biphasic reactants to the point-of-reaction. Notably, the spinning of this functional interface at 800 rpm boosts the reaction efficiency and its apparent equilibrium constant by > 500-fold and 105-fold, respectively, higher than conventional methods that utilize bulk and/or non-dynamic liquid interfaces, even with external mechanical stirring. By driving reaction equilibrium toward favorable product formation, our unique design offers enormous opportunities to realize efficient multiphasic reactions crucial for diverse applications in chemical synthesis, environmental remediation, and even molecular recycling.

Mathematical model and reaction mechanism of molybdenum and tungsten extraction with TRPO from peroxide solution

To understand the behavior of molybdenum and tungsten extracted by tri-alkyl phosphine oxide (TRPO) from peroxide solution, the extraction mechanism was studied by slope method and Raman and FTIR spectroscopy. The empirical formulas of molybdenum and tungsten extraction distribution ratio (DMo and DW) as functions of equilibrium pH, TRPO concentration and temperature were obtained by establishing mathematical models. Furthermore, the reliability of the empirical formula was verified in the H+−W−Mo−H2O2 solution. The results indicate that the calculated values of DMo or DW were consistent with the experimental values. The apparent extraction equilibrium constants of molybdenum and tungsten were =8.51×103 (0.74≤pHe≤1.7), =99.89×103 (1.7<pHe≤4.62) and =2.65×103 (0.92<pHe<2.16) at 20 °C, respectively. The main extraction complex of molybdenum or tungsten was [H2(Mo or W)2O3(O2)4(H2O)2]·2TRPO. These empirical formulas can be used to analyze and estimate the extraction and separation of Mo and W from low molybdenum and tungsten concentration solutions.

Removal of Mg and Ca from Ni-rich sulphate solutions by solvent extraction using cationic and neutral extractants

Selective solvent extraction of Mg and Ca aiming to purify Ni-rich sulfate solutions ([Ni] = 88 g/L, [Mg] = 3.1 g/L, [Ca] = 0.5 g/L) was investigated using the Cyanex 923 + Cyanex 272, and D2EHPA extractive systems (A/O ratio = 1, T = 50 °C). Although Cyanex 923 rejected metals at pH 3–6, a synergistic selective separation of Mg (69%) over Ca (1.2%, βMg/Ca = 179.2) and Ni (5.7%, βMg/Ni = 37.2) was attained at pH 5 with 0.13 M Cyanex 923 + 0.64 M Cyanex 272. Ni crowded out Mg from the loaded organic phase and limited the operation at pH < 5.5. Antagonism on Mg extractions was observed at [Cyanex 923] ≥ 0.25 M + 0.64 M Cyanex 272. Ni was selectively stripped out over Mg, using a dilute 0.031–0.063 M H2SO4, while Mg was stripped out with 0.25 M H2SO4. By contrast, 0.15 M D2EHPA selectively extracted Ca (50.8%) over Mg (2.1%, βCa/Mg = 47.6) and Ni (1.2%, βCa/Ni = 86.4) at pH 3, with Ca being crowded out by Ni at pH > 3. Selective Ni stripping was obtained from the loaded D2EHPA, using a dilute H2SO4 (0.034 M), while Ca and Mg were stripped by H2SO4 or HCl solutions (1 M). The real number of moles of extractants involved in the metal extractions and apparent equilibrium constants were determined for both extractive systems. Moreover, the FTIR spectra were accessed to contemplate the possible coordination compound structures.

A kinetic model for the equilibrium dynamics of absorption and scattering processes in four-wave mixing spectroscopy

We construct a kinetic model, analogous to a simple chemical reaction, to describe the spatial propagation of the electromagnetic fields in four-wave mixing spectroscopy in a two-level molecular model, explicitly taking into account the stochastic effects of the solvent. We show that in this case, the nonlinear optics processes (absorption and scattering) along the optical path can be described using an analogy with the kinetic processes that occur in a chemical reaction. A key result is that it is possible to define an apparent equilibrium constant that regulates the competition of the photonic processes that take place, an idea conceptually similar to Einstein’s model for spontaneous emission and how it can be connected to induced emission in atoms and molecules but including an extension to nonlinear optical and relaxation processes. Our model can be generalized to describe a variety of phenomena in nano-photonics and plasmonic systems.

Extraction equilibrium of molybdenum(VI) and tungsten(VI) in aqueous solutions containing hydrogen peroxide by synergistic solvent extraction with TRPO and TBP

The separation of molybdenum from peroxotungstate solution with neutral phosphorus extractant such as trialkyl phosphine oxide (TRPO), tri-butyl phosphate (TBP) is often accompanied by extraction loss of tungsten, which greatly reduces the separation efficiency. To solve the above problems and optimize process, clarifying the reaction equilibrium of extraction is necessary. However, relevant research, especially the TRPO-TBP synergistic system, has not been reported. Here, based on the effect of extractant concentration and equilibrium pH on Mo and W extraction with three extraction systems (TRPO, TBP and TRPO-TBP), the Mo and W distribution equations in the two phases and the stoichiometry of chemical reactions were determined via slope analysis. The apparent extraction equilibrium constants and cumulative protonation constant of [Mo2O3(O2)4]2− were calculated by successive-approximation method. The order of the extraction equilibrium constants is as follows: logKMo-TRPO-H (5.8) > logKMo-TRPO-TBP-H (4.3) > logKMo-TRPO (3.8) > logKW-TRPO (3.7) > logKMo-TRPO-TBP (2.3). The synergistic mechanism of TBP for Mo and W extraction was revealed through Raman, FT-IR and 31P NMR spectroscopy, proposing a synergistic extraction compound TBP·[H2Mo2O3(O2)4·2H2O]·TRPO. The experimental results showed that keeping a higher equilibrium pH (2–2.5) can improve the separation efficiency of W and Mo, which verified the feasibility of optimization measure proposed based on equilibrium data. This study reveals the extraction mechanism of W and Mo in H+-H2O2/TRPO-TBP system, which can provide some reference for the optimization of separation process.

Solubility of N2O and CO2 in nonaqueous blends of 2-(methylamino)ethanol and 2-methoxyethanol

Nonaqueous secondary alkanolamine-based systems, replacing conventional water with 2-alkoxyethanols as cosolvents, have recently attracted much attention for an energy-efficient CO2 capture process. In this work, physical solubility of N2O and CO2 in 2-(methylamino)ethanol (MAE), 2-methoxyethanol (2-ME) and their blends was measured and correlated at temperatures ranging from (283.2 to 333.2) K. Vapor-liquid equilibrium (VLE) data for the CO2 + MAE + 2-ME system at 7.8, 19.4 and 39.1 mass% MAE were also measured in a stirred equilibrium cell at temperatures of (313.2–393.2) K and CO2 partial pressures up to 270 kPa. VLE data were represented by a modified Kent-Eisenberg model with an AARD of 12.6%. The apparent equilibrium constants considering the liquid nonideality were well correlated as a function of temperature, concentration of carbamate product and CO2 loading.

Analysis of the Biochemical Reaction Status by Real-Time Monitoring Molecular Diffusion Behaviors Using a Transistor Biosensor Integrated with a Microfluidic Channel.

Traditional methods of monitoring biochemical reactions measure certain detectable reagents or products while assuming that the undetectable species follow the stoichiometry of the reactions. Here, based upon the metal-oxide thin-film transistor (TFT) biosensor, we develop a real-time molecular diffusion model to benchmark the concentration of the reagents and products. Using the nicotinamide adenine dinucleotide (NADH)–oxaloacetic acid with the enzyme of malate dehydrogenase as an example, mixtures of different reagent concentrations were characterized to extract the ratio of remaining concentrations between NAD+ and NADH. We can thus obtain the apparent equilibrium constant of the reaction, (8.06 ± 0.61) × 104. Because the whole analysis was conducted using a TFT sensor fabricated using a semiconductor process, our approach has the advantages of exploring biochemical reaction kinetics in a massively parallel manner.

Sorption Recovery of Platinum Metals from Production Solutions of Sulfate-Chloride Leaching of Chromite Wastes

This paper discusses the scientific rationale for methods of platinum metals sorption centralization from saturated solutions with a high content of macrocomponents. Methods of sorption centralization of platinum and iridium using local anionites such as AH-31, AB-17-8, Purolite S985 are described. The sorbents used were conditioned to remove organic and mineral impurities. The sorption isotherms of platinum group metals 1/EC=f(1/Cp) at a temperature of 20 °C and a duration of 24 h were plotted. The data on the sorption recovery of platinum and iridium from individual and combined sulfate-chloride solutions were determined. Isotherms of iridium sorption from sulfate-chloride solution are formed. Results of the apparent sorption equilibrium constant and values of standard Gibbs energy (ΔG, kJ/mol) of ion exchange for sorption of platinum and iridium from individual and combined sulfate-chloride solutions are presented. Linearized isotherms and kinetic curves of joint sorption of platinum and iridium from sulfate-chloride solution are described. Comparative sorption of the platinum-group metals (PGM) by anionites AB-17-8 and Purolite S985 from sulfate-chloride solutions is shown. The sorption diagram of platinum and iridium from sulfate-chloride product solutions is presented. It has been revealed that complete recovery is achieved using chelation ion-exchange resin Purolite S985, with recovery of Pt up to 95% and Ir more than 73%. The sorption process is accompanied by intradiffusion constraints that are confirmed by the analysis of kinetic curves using Schmukler and Boyd–Adams models.

Revaluating solvent extraction equilibria of trivalent rare earths with EHEHPA (PC-88A) using Alstad equation

The equilibria associated with the solvent extraction of trivalent rare earth elements (REEs) with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHEHPA) have been previously studied by many researchers because of the industrial importance of REEs. However, quantitative analysis has been limited to relatively low concentrations of EHEHPA because of the nonideal characteristics of the organic phase. In the present paper, we used an empirical equation to correct the nonideality of the organic phase and calculated extraction equilibrium constants for some trivalent REEs (La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, and Y) that are particularly important in RE recycling from end-of-life products and in-plant scraps. Calculations based on use of EHEHPA in a nonpolar diluent and a nitrate medium were used to systematically investigate equilibria at a constant ionic strength of 1 mol/L, temperature of 298 K, EHEHPA dimeric concentrations that ranged from 0.04 to 0.33 mol/L, and a range of pHs. Apparent extraction equilibrium constants that reproduced the distribution ratios of the REEs with good accuracy were obtained. Further experiments at higher EHEHPA concentrations revealed that the empirical equation was effective up to an EHEHPA dimer concentration of 0.5 mol/L, which is significantly higher than the upper bound for the conventional dimer model. Separation factors defined as the ratios of the distribution ratios of two REEs were calculated from the extraction equilibrium constants for the possible pairs of REEs and compared critically with literature values. Differences in the separation factors depended on the measurement conditions and were most pronounced when the difference in atomic numbers of the REEs was large. The results are expected to facilitate designing processes for the separation and purification of REEs.