Equilibrium Distribution Coefficients Research Articles

Sampling-rate calibration vs. equilibrium calibration for in vivo solid-phase microextraction: Analysis of neonicotinoids in bananas

In vivo solid-phase microextraction (in vivo SPME) is an emerging fascinating sample pretreatment technique, but its quantitative correction method is different from the traditional correction methods, which has become a bottleneck limiting its development. At present, the sampling-rate calibration and equilibrium calibration are mainly used, however, their characteristics and applicability are not clear. In this study, the sampling-rate calibration and equilibrium calibration were evaluated in the case of the determination of neonicotinoids in bananas by in vivo SPME. The factors that affect the sampling rate (Rs), such as the matrix states, sampling durations, and individual differences were studied, and they all had impacts on Rs. Conversely, the equilibrium distribution coefficient (Kfs) remained constant after extraction equilibrium and the individual differences were smaller. The highest accuracy and precision were achieved by equilibrium calibration, and the relative recoveries were in the range of 83.2 %-104.3 % with the relative standard deviations below 8.1 % compared to a standard QuEChERS-based method. The lower limits of quantification for 4 neonicotinoids in bananas were below 5 ng g−1, lower than the standard method and the maximum residue levels in China and the European Union. This work clarifies the characteristics, rules and performance of the sampling-rate calibration and equilibrium calibration, which is of crucial importance for the development and application of in vivo SPME. The developed method is convenient, sensitive, and accurate for the determination of pesticide residues, which is of great significance to guide the safe use of pesticides in the field and prevent products with excessive pesticide residues from entering the market.

Effect of PWHT on microstructure and mechanical properties of welded joint of a new Fe-Ni-based superalloy

In this study, the effect post weld heat treatment (PWHT) on microstructural evolution and mechanical properties of weld metal of HT700P alloy with Inconel 617 filler metal was investigated. After welding, columnar grain, dendritic microstructure and segregation of Mo, Co and Ti elements related to the equilibrium distribution coefficient were observed in the weld metal. The PWHT was conducted in both direct-aging treatment with different time and solution treatment with different cooling methods. The results showed that direct-aging treatment had a limit impact on homogenization of weld metal, while microstructural homogenization and elemental segregation were significantly improved after solution treatment and massive M6C and M23C6 carbides precipitated at the grain boundaries and interdendritic region of weld metal. It was found that the elongation at 700 °C of welded joints after solution treatment was relatively increased, which was related to the decrease of residual stress and the precipitation of Mo-rich carbides at the grain boundaries. The fracture occurred in the weld metal presented interdendritic fracture characteristics, and the fracture mechanism for stress relaxation cracking was the strong grain interior induced by the precipitation of γ′ phase, leading to the stress concentration and nucleation of cavities at grain boundaries. After solution treatment, the creep lifetime of furnace cooling was much greater than that of water quenching. The superior creep properties of furnace-cooled joint could be attributed to the lower residual stress and the migration of carbon element in the fusion line, which inhibited the nucleation and aggregation of cavities in the partially melted zone.

A crystallization method with significant industrial potential for the separation and enrichment of silver from crude lead

Approximately 60 % of silver is produced through lead smelting systems, where silver is mainly concentrated in crude lead. Silver in crude lead is usually separated and enriched during lead refining processes. However, these methods are disadvantageous owing to their lengthy processes and high energy consumption. In this study, a novel, green, and efficient process for silver separation and enrichment via crystallization was developed. Theoretical analysis showed that the equilibrium distribution coefficient (K0) is less than 1. At 327.50 °C, silver was completely separated in the solid phase, while at 304.10 °C, silver was enriched to 2.5 wt% in the liquid phase. Experimental studies showed that, through crystallization, the silver content in low-silver lead was reduced to 0.0047 wt%, achieving a separation rate of 95.41 %. Concurrently, the silver content in rich-silver lead was enriched to 0.5690 wt% with an enrichment ratio of 7.10, consuming 185 kW·h/t of electricity. The silver content in low-silver lead was found to be lower than the Standard Specification for Refined lead, and the rich-silver lead was used for silver refining. Compared to existing processes, this method can efficiently enrich silver from crude lead in a single step. This study provides a sustainable method for silver recovery from crude lead, offering advantages such as a short process duration, cleanliness, and ease of industrial implementation and promotion. This study offers important theoretical and technological guidance for the extraction of silver from crude lead, ensuring a secure supply of silver for major national projects.

Solute Effects on Growth Restriction in Dilute Ferrous Alloys

The effect of dilute solute additions on growth restriction in binary ferrous alloys has been assessed by means of the heuristic growth restriction parameter (β) modelling framework (Fan et al. in Acta Mater. 152, 248–257, 2018). The CALPHAD (CALculation of PHAse Diagrams) methodology (Kaufman and Bernstein in Computer Calculation of Phase Diagrams, 1970) has been used to calculate β values from the liquidus slope m and the equilibrium distribution coefficient k values, at first approximation, in conjunction with the liquid-to-solid fraction to obtain true β values. Critical solute concentrations, below which solidification becomes partitionless, have also been calculated. Among 23 dilute binary ferrous alloy systems investigated, the five most efficient solutes on grain refinement are B, Y, O, S and C. A negative correlation, or inverse relationship, was observed between the true β values and the grain size values obtained from a study on experimental multicomponent dilute ferrous alloy systems (Li et al. in Metall. Mater. Trans. A 49 A, 2235–2247, 2018).

Impurity distribution in preparation of high-purity aluminum by vacuum zone melting

A novel vacuum zone melting process for preparing high-purity Al was proposed. The axial segregation of impurities was investigated by determining the equilibrium distribution coefficient. Theoretical and experimental results showed that impurities (Cu, Si, and Fe) with an equilibrium distribution coefficient k0<1 accumulated in the tail of the Al ingot, while Ti (k0 >1) accumulated at the head end of the ingot. When the molten area moving at 1.5 mm/min and zone melting was performed 15 times, the removal rate of the impurities and the purity of Al were the highest. In the middle of the Al ingot, i.e. 140 mm away from the head end of the sample, the removal rates of Cu, Fe, and Si were higher than 90%, that of Ti was higher than 75%, and the Al content was higher than 99.999%. The purity of the Al samples met the requirements of the commercial 99.999% (5N) high-purity Al standard.

Study of the Thermochemical Effect on the Transport and Structural Characteristics of Heterogeneous Ion-Exchange Membranes by Combining the Cell Model and the Fine-Porous Membrane Model.

For the first time, based on the joint application of the fine-porous and cell models, a theoretical analysis of the changing transport and structural characteristics of heterogeneous polymeric ion-exchange membranes (IEMs) MK-40, MA-40, and MA-41 after exposure to elevated temperatures in water and aggressive media (H2SO4 and NaOH solutions), as well as after long-term processing in electrodialyzers of various types, was carried out. The studied membranes are composites of ion-exchange polymers with polyethylene and nylon reinforcing mesh. The external influences provoke the aging of IEMs and the deterioration of their characteristics. The transport properties of IEMs are quantitatively described using five physicochemical parameters: counterion diffusion and equilibrium distribution coefficients in the membrane, characteristic exchange capacity, which depends on the microporosity of ion-exchanger particles, and macroscopic porosity at a known exchange capacity of IEMs. Calculations of the physicochemical parameters of the membranes were performed according to a specially developed fitting technique using the experimental concentration dependences of integral diffusion permeability and specific electrical conductivity, and their model analogs. This made it possible to identify and evaluate changes in the membrane micro- and macrostructure and examine the process of artificial aging of the IEM polymer material due to the abovementioned external impacts.

Study on the Purification Effect and Equilibrium Distribution Coefficient of Impurities during Zone Refining of Fluorene

High-purity fluorene is widely used in optoelectronic materials, biology, medicine, and other fields. It is a kind of industrial chemical with high added value. In this paper, zone melting purification technology was used to study the purification effect of fluorene on the zone travel rate, the zone length, the zone passing number, and the zone temperature difference. The concentration distribution of fluorene and the impurities 2-methylbiphenyl, 4-methylbiphenyl, 4-methyldibenzofuran, and dibenzofunan along the moving direction of the melting zone was obtained. A one-pass zone refining model of fluorene was established; the effective distribution coefficients of the four impurities above were obtained via mathematical software fitting; and the equilibrium distribution coefficients were further calculated, which were 0.2441, 0.5850, 0.2377, and 0.3497, respectively. The k0 of all impurities was less than 1. The purification effect of fluorene can be improved by using a larger zone length in the initial zone melting purification process, a smaller zone travel rate in the whole zone melting purification process, multiple zone melting purification processes, and a larger zone temperature difference. After four zone melting purification processes, the purity of fluorene increased from 97.62% to 99.08%, which was nearly 1.5% higher than the initial purity of fluorene. Zone melting purification technology provides a new idea for the preparation of high-purity fluorene.

Modelling and Comparative Analysis of Different Methods of Liquid Membrane Separations.

This article is devoted to a brief review of the modelling of liquid membrane separation methods, such as emulsion, supported liquid membranes, film pertraction, and three-phase and multi-phase extraction. Mathematical models and comparative analyses of liquid membrane separations with different flow modes of contacting liquid phases are presented. A comparison of the processes of conventional and liquid membrane separations is carried out under the following assumptions: mass transfer is described by the traditional mass transfer equation; the equilibrium distribution coefficients of a component passing from one of the phases to another are constant. It is shown that, from the point of view of mass transfer driving forces, emulsion and film pertraction liquid membrane methods have advantages over the conventional conjugated extraction stripping method, when the mass-transfer efficiency of the extraction stage is significantly higher than the efficiency of the stripping stage. The comparison of the supported liquid membrane with conjugated extraction stripping showed that when mass-transfer rates on the extraction and stripping sides are different, the liquid membrane method is more efficient, while when they are equal to each other, both processes demonstrate the same results. The advantages and disadvantages of liquid membrane methods are discussed. The main disadvantages of liquid membrane methods-low throughput and complexity-can be overcome by using modified solvent extraction equipment to carry out liquid membrane separations.

Crystallization of nickel sulfate and its purification process: towards efficient production of nickel-rich cathode materials for lithium-ion batteries.

NiSO4·6H2O is an important salt for the battery-making industry. The extraction of nickel sulfate relies on the hydrometallurgical processing of nickel ores as well as the recycling of nickel-containing products. The last step in hydrometallurgical processing is the crystallization of nickel sulfate. Because of the similar ionic radius and ionic charge between nickel and magnesium ions, magnesium undergoes isomorphous substitution and replaces nickel ions in the crystal lattice structure of NiSO4·6H2O. This poses a challenge as achieving the desired metal salt purity is difficult, resulting in an inferior cathode material for nickel-containing batteries. In this work, the removal of magnesium during the purification process of NiSO4·6H2O crystals via a repulping process was thoroughly investigated. Moreover, the impurity uptake mechanisms of magnesium into NiSO4·6H2O crystals were investigated. The results indicated that repulping NiSO4·6H2O crystals with a saturated NiSO4 solution results in 77% removal of magnesium. Using a second-stage repulping process is less effective with only 26% magnesium removal. The purification efficiency of the two repulping stages was quantified by the equilibrium distribution coefficient, which corroborates the trend of decreased removal of magnesium in the second stage of repulping compared with the first stage. The primary impurity uptake mechanisms of magnesium into NiSO4·6H2O crystals were identified to be surface adsorption and lattice substitution (isomorphous substitution).

EXPERIMENTAL BEHAVIOR OF CRUDE SOYBEAN OIL IN ALCOHOLIC SOLVENTS: MISCIBILITY TEMPERATURE AND CHILLING SEPARATION EFFECTIVENESS

Experimental information about the behavior of crude soybean oil with alcohol solvents, useful in the design of oil extraction and separation processes, is provided. The miscibility temperature of crude soybean oil in ethanol, isopropanol and their mixture (M) at different oil/alcohol ratios (OAR), and both the oil equilibrium distribution coefficients (keq) between formed phases and the amount of oil recovered (OR) from the chilled miscellas were determined. In the analyzed OAR range, the highest miscibility temperatures were 78, 40 and 55 °C for ethanol, isopropanol and M, respectively. Generally, OR and keq changed significantly with the solvent, the chilling temperature and the OAR. By using ethanolic miscellas, a more effective separation was reached, being OR slightly changed with the chilling temperature. The validation of the chilling separation, performed using miscellas obtained from the ethanol extraction of soybean oil, demonstrated that other extracted compounds did not affect the separation yield.

Thermodynamic calculations and validation of the competing precipitation behavior of BN and Nb(C,N) in 9CrMoCo heat-resistant steel

In this study, the thermodynamic conditions were calculated for the formation of nitrides in the liquid phase and precipitation in the solid phase of the 9CrMoCo steel matrix. The mutual dependency of BN and Nb(C,N) was demonstrated through thermodynamic calculations and validated experimentally. The equilibrium distribution coefficients for Nb, N, and B at the solid–liquid interface were considered, and the solidification rate (fs) was introduced into the thermodynamic calculation. BN and NbN met the formation conditions when the fs values were 97.96% and 99.04%, respectively. The formation of Nb-containing nitrides was restrained by the formation of BN inclusions in the molten steel, which was confirmed by observing the elemental constituents of the Nb-rich precipitates. N (0.019%) in the solid solution was separated from the BN inclusions at 1523 K and it participated in the precipitation of Nb(C,N) during the subsequent cooling process. Needle-like Nb(C,N) precipitates and particles of Nb(C0.15N0.85) were formed under slow furnace cooling and austempering at 1223 K, respectively. In addition, the secondary precipitation of BN in austenite was restricted by the formation of the Nb(C,N) precipitate during the cooling process after the dissolution of BN inclusions.

Research of High-Purity Lanthanum Prepared by Zone Refining.

In this paper, the purification of lanthanum was studied by using zone-refining technology. The equilibrium distribution coefficient of impurities was calculated using a liquidus slope method to reveal impurities’ distribution properties. Meanwhile, the analysis of impurities’ concentration distribution for Fe and Si has been investigated based on the SPIM model. The calculated findings based on SPIM were found to be in good agreement with the experimental results. In addition, the influence of the zone-refining rate and the number of passes on the purification of lanthanum were studied. It was found that after ten times of zone refining with a zone-refining rate of 5 mm/min, the contents of Fe and Si impurities in metal decreased to 4 and 2 ppm, respectively.

THE REFINING OF TITANIUM BY CRUCIBLELESS ZONE MELTING METHOD

The physical substantiation of titanium refining by crucibleless electron beam zone melting (ZM) method in vacuum was presented. Calculations of the equilibrium, limiting and effective distribution coefficients for impurity elements in the base metal were carried out. The refining of titanium was studied experimentally, and samples with a purity of 99.92 wt.% were received. The total content of impurities was reduced by a factor of 1.5 (from 0.12 to 0.08 wt.%). The concentration of interstitial impurities was significantly reduced (oxygen – by 1.3; carbon – by 2; nitrogen – by 2.5 times). The structure and microhardness were investigated.

Estimating the Equilibrium Distribution of Perfluoroalkyl Acids and 4 of Their Alternatives in Mammals.

Perfluoroalkyl acids (PFAAs) mostly exist as ionic compounds that are of major concern because of their accumulative behavior. The discussion about their risk is ongoing considering the increasing production of structurally similar alternatives. We conducted model calculations based on equilibrium distribution coefficients that allow studying the distribution of PFAAs and their alternatives in various mammalian organs through comparison to empirical measurements in humans and rats. The calculations rely on experimentally determined distribution coefficients of a series of PFAAs and 4 of their alternatives to physiological matrices such as structural proteins, storage lipids, membrane lipids, albumin, and fatty acid binding protein (FABP). The relative sorption capacities in each organ were calculated from the combination of distribution coefficients and physiological data. The calculated distribution of PFAAs and alternatives within the organs showed that albumin and membrane lipids and, to a lesser extent, structural proteins have the highest relative sorption capacities for the compounds. Sorption to FABP is only relevant in the distribution of short-chain PFAAs. Storage lipids play a minor role in the distribution of all studied compounds. Our calculated distribution of PFAAs was evaluated by comparison to reported PFAA concentrations in various organs. Environ Toxicol Chem 2021;40:910-920. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Study on the effective distribution coefficient of impurity separation in the preparation of high purity aluminum

Effective distribution coefficient (ke) plays an important role in zone melting purification but has never been systematically calculated as an important parameter. A novel analysis method for impurity separation separating from Al using determination of impurities (Si, Fe, Cu, Zn) content and calculation of ke has been investigated. Experimental results show that the impurity separation effect was significantly improved due to the ke closely approximating the equilibrium distribution coefficient (k0) via optimization of purification times and speed of the melting zone. When the times of purification were increased from 15 to 20 times, the ke values of Si, Fe, Cu, and Zn at the sample (No. 3) were 0.603, 0.702, 0.364, and 0.502, respectively. Correspondingly, the removal rate of impurities of Si, Fe, Cu, and Zn increased by 6.25%, 1%, 10.49%, and 27.58%, respectively. The effect on the ke of Cu and Fe is more significant at the sample (No. 3) when the melting zone speed is changed. The removal rates of Fe and Cu in the sample are 99.0% and 94.75% when the melting zone speed was 1/3 mm/min, and, correspondingly, the removal rates of Si and Zn were 81.7% and 88.51%, respectively. The Al content at sample position No. 3 is more than 999994.59 ppm when the sample was purified 15 times at a speed of 0.5 mm/min, which meets the standard of 5N high purity aluminum.

Recovery of rare-earth elements from nitrate solutions using polyethylene glycol 1500

A new extraction system based on polyethylene glycol 1500 and NaNO3 was proposed for the recovery of light rare-earth elements (Ce, La, Nd, Pr, and Sm) from aqueous solutions. The equilibrium distribution coefficients and degrees of extraction of CeIII, LaIII, NdIII, PrIII, and SmIII in the proposed aqueous two-phase system were found. The dependences of the quantitative characteristics of rare-earth element extraction on the temperature, initial metal concentration, and acidity of the medium were obtained. The degree of extraction of the metal ions within one step was shown to exceed 60% at the phase ratio 1:1 without introducing additional complexation agents.

Diffusion kinetic process of heavy metals in lacustrine sediment assessed under different redox conditions by DGT and DIFS model

Different fractions and variations of Mn, Co, Ni, Cu, Cd, Pb, Zn, and Fe in sediment via oxic and anaerobic treatments were investigated using BCR sequential extraction methods, DGT technique, and DIFS model. The results indicated that reducible fraction was the considerable pool apart from residual fraction, suggesting the high desorption potential of heavy metals. The high-resolution DGT measurement indicated that CDGT significantly rose after anaerobic condition and characterized by the relative high R value. Significantly increasing positive fluxes varying from 0.64 to 339.4 μg cm−2 s−1 except Ni suggested that apparent diffusion upward occurred over time from the sediment to the overlying water on anaerobic episode. High proportion of reducible Fe fraction and concurrent reduction of Fe(III) to Fe(II) during anaerobic condition were responsible for the increase of labile metals. The diffusion kinetic parameters including the equilibrium distribution coefficient (Kd), response time (Tc), and rate constant (k1 and k−1) were obtained using DIFS model. These parameters confirmed the partially sustained resupply capacity of heavy metals from solid sediment particle to pore water because of the considerable reducible fractions. Additionally, planar optode (PO) imaging approach demonstrated that low pH accompanied with decreasing dissolved oxygen (DO) concentration on anaerobic condition enhanced the release of labile metal fraction. Generally, anoxia facilitated the reduction of reducible fraction of heavy metals and further strengthened the desorption, resupply and diffusion in the aquatic ecosystems.

Extraction chromatography of 225Ac and lanthanides on N,N-dioctyldiglycolamic acid /1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide solvent impregnated resin

The alpha-emitter 225Ac (t1/2 = 9.92 d) is currently under development for targeted alpha-particle therapy of cancer, and accelerator production of 225Ac via proton irradiation of thorium targets requires robust separations of 225Ac from chemically similar fission product lanthanides. Additionally, the lanthanide elements represent critical components in modern technologies, and radiolanthanides such as 140Nd (t1/2 = 3.37 d) also have potential application in the field of nuclear medicine. The ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][NTf2]), combined with the diglycolamide extractant, N,N-dioctyldiglycolamic acid (DODGAA), was adsorbed on macroporous resin support to produce a solvent impregnated resin (SIR) that was investigated for separations of 225Ac and lanthanides. The equilibrium distribution coefficients (Kd) of the rare earth elements (Sc(III), Y(III), Ln(III)), 225Ac(III), Th(IV), and U(VI) on the prepared DODGAA/[Bmim][NTf2]-SIR were determined from batch adsorption experiments in HCl and HNO3 media. The DODGAA/[Bmim][NTf2]-SIR exhibited preferential uptake of the heavier lanthanide elements while allowing for the separation of the lighter lanthanides. Column separations utilizing the DODGAA/[Bmim][NTf2]-SIR were effective at separating the lighter lanthanides from each other, and separating 225Ac from a mixture of lanthanides, 213Bi, and 225Ra without the need for additional complexing agents.

Kinetically selective preparative chromatography of biologically active substances on polymeric sorbents

A technique of preparative adsorption chromatography, according to which the separation of substances is determined by the effect of kinetic selectivity of sorption (KSS), is discussed. Unlike traditional chromatography methods, in which separation is determined by the difference in the binding strength of the separated components (distribution coefficients), in kinetically selective chromatography, the separation parameters can be controlled by changing the ratios between the distribution coefficients and the sorption rate of components (effective diffusion coefficients). The necessary and sufficient prerequisites for the inversion of the selectivity of sorption of the components of sorption systems are identified, when the order of components coming off the column is reversed and a component with a higher equilibrium distribution coefficient comes out of the column first. The KSS effect consists in the fact that a component with a higher distribution coefficient is more selectively adsorbed before the selectivity inversion point and a component with a lower distribution coefficient is preferably absorbed after the inversion point. The prospects of practical use of kinetically selective chromatography are considered using systems important for biotechnology and pharmaceutics. The use of the KSS effect allowed us to optimize the separation of a number of biologically active substances both in the case of the inversion of sorption selectivity of the separated components and in those cases when the conditions of the inversion of sorption selectivity were not met.

Theoretical Bases and Technology of Steel Exhaustive Metal Desulfurization and Direct Microalloying with Boron Beneath Basic Boron-Containing Slags

Results of theoretical and experimental studies of the physicochemical properties of slags of the CaO–SiO2–B2O3 system containing 15% Al2O3 and 8% MgO lie at the basis for the development of technology for exhaustive desulfurization of metal beneath basic boron-containing slags formed in a steelpouring ladle in a ladle-furnace unit (LFU), and steel direct microalloying with boron. Methods of simplex lattice planning of an experiment, a software complex HSC 6.1 Chemistry (Outokumpu), and the method of electro-vibration viscosimetry are used. Results of thermodynamic modeling of the effect of slag basicity and B2O3 content on sulfur and boron equilibrium distribution coefficient between slag of the oxide system under study and low-carbon metal are presented. The quantitative effect of basicity and B2O3 content on slag viscosity containing 15% Al2O3 and 8% MgO at a temperature of 1600°C and the influence of the slag chemical composition of the oxide system under study on the degree of wear of periclase-carbon refractory material are shown. Results of studying physicochemical properties of slags of the CaO–SiO2–B2O3 system containing 15% Al2O3 and 8% MgO are a basis for developing a ladle slag composition with low viscosity and providing exhaustive metal desulfurization, and direct microalloying of boron steel with low corrosive effect on periclase-carbon refractories. Development of this technology provides, depending on the steel grade, a boron content of 0.001–0.008%, low metal sulfur concentration at 0.004–0.014%, a reduction in manganese ferroalloy consumption from 0.5 kg/ton of steel 08KP to 1.4 kg/ton of steel 09G2S, exclusion of ferroboron and fluorspar additives in the ladle, and achievement of good finished metal product mechanical properties.