Nonequilibrium Extraction Research Articles

Interfacial salt effect induced by competitive adsorption of coexisting ions: A new understanding of the mass transfer selectivity in the near-interface boundary layer

Specific ion effects are known to influence the interfacial behavior of ions in the aqueous phase and thus affect their extraction and separation. There are many studies on enhanced extraction and separation of the target ions based on the specific ion effects. A microscopic level understanding of the competitive mass transfer and selectivity of ions at the interface between heterogeneous phases is crucial importance for the precise control of numerous chemical reaction and separation processes. The conventional salt effect (i.e., background coexisting ions promoting the mass transfer of the target ions) are only observed at higher coexisting ion concentrations. However, the present work reveals an interesting phenomenon: the adsorption enrichment and competitive hydration of coexisting salt cations at the liquid–liquid interface can significantly influence the mass transfer rate of the target rare earth ions in the near-interface boundary layer. Notably, such a distinct interfacial salt effect can promote the separation between coexisting and target ions at lower coexisting ion concentrations, and it cannot be explained by the traditional theory for the salt effect. A thin-layer organic oil film extraction system was employed here as a simplified model experiment to investigate this new interfacial salt effect on the non-equilibrium extraction and separation of target rare earth ions. The results demonstrated that the diffusion rate of the target ions (Er3+) is subject to the local concentration gradient of coexisting salt cations (Mg2+) in the near-interface boundary layer. At the lower bulk concentrations, the Mg2+ ions enriched at the interface would compete for water molecules around the hydration shell of target Er3+ ions, resulting in the dehydration of Er3+ ions. Therefore, an enhanced diffusion rate of Er3+ ions and their adsorption affinity towards the interface were observed. However, at a higher bulk concentration of Mg2+ ions, the diffusion resistance of Er3+ ions increased due to the competitive adsorption and hydration of Mg2+ ions at the interface. The thickness of the organic oil film layer also plays an important role in the diffusion of Er3+ ions. In particular, a thinner oil layer makes it easier to perceive the interfacial salt effect, which enhances the separation between Er3+ and Mg2+ compared to the case of a thicker oil layer. A quantitative correlation between the diffusion rate of Er3+ ions and the concentration of coexisting Mg2+ ions was established to describe the interfacial salt effect. This work highlights the microscopic nature of the salt effect induced by the competitive adsorption kinetics of coexisting ions in the near-interface boundary layer on promoting the extraction and separation of target metal ions. The results will help the development of new approaches to control the separation selectivity and enhance the mass transfer of target metal ions in practical applications.

Non-equilibrium kinetic separation of thulium, yttrium and erbium on the surface of freely rising oil droplets

It is difficult to achieve selective separation and enrichment of different rare earths from high abundance yttrium ores efficiently only dependent on their discrepancy in thermodynamic properties. The present work suggests a new strategy based on non-equilibrium kinetic separation of Er and Tm on the surface of freely rising oil droplets to control the separation order of Y. It is revealed that the mutual separation of Er/Tm is significantly promoted with the separation coefficient of 2.89 during the non-equilibrium extraction with the addition of diethylenetriaminepentaacetic acid (DTPA). The extraction sequence of Tm, Er and Y can be controlled as Tm > Y > Er, thus Y can be selectively enriched during the process of separation of Er and Tm. Such a sequence is subject to the controllable dissociation rates of RE(III)–DTPA complexes and extraction abilities of P507 with the three RE(III) ions. The dissociation rate is dependent on the stabilities of RE(III)–DTPA complexes and follows the sequence of Y(III)–DTPA < Tm(III)–DTPA < Er(III)–DTPA. However, the extraction abilities of the three RE(III) ions follow the sequence of Y(III)–P507<Er(III)–P507<Tm(III)–P507. The competition complexation of DTPA and P507 at the interface of oil droplets results in an obvious change in the separation order of Y from Tm > Er > Y to Tm > Y > Er.

A New Rising Droplet Non-Equilibrium Extraction Strategy for Sequential Separation of Thulium, Yttrium and Erbium

A New Rising Droplet Non-Equilibrium Extraction Strategy for Sequential Separation of Thulium, Yttrium and Erbium

Controlling flow patterns and its evolution behavior in microchannel for intensified separation of rare-earth and Al(III) ions: Hints from the hydrodynamics parameters

Abstract Control of flow patterns and its evolution behavior in microchannel is crucial for microfluidic technology to achieve mass transfer intensification in the micro-scale and selective separation of target ions. In the present work, we found that the non-equilibrium extraction and selective separation behaviors of target metal ions from other co-existing background ions have a close relationship with the change of hydrodynamic parameters of the organic and aqueous two phases and the evolution of flow patterns in microchannel. Taking the separation of Er(III) and Al(III) ions in microchannel as a model system, it is revealed that the transition of the flow patterns from parallel flow to slug flow might originate from the decrease of the linear velocity of two phases flow, the increase of viscosity and the decrease of the interfacial tension between the two phases. The change of those hydrodynamic parameters would result in an obvious increase in specific interfacial areas between the two phases and a decrease in wall film thickness of the slug flow. A higher Capillary number corresponds to a larger specific interfacial area and a higher surface renewal rate between the two phases. Therefore, an intensified separation of Er(III) and Al(III) ions can be attributed to the change of those hydrodynamic parameters in microchannel. The present work highlights a novel approach by controlling the flow patterns of aqueous and organic two phases in microchannel for controllable selective separation of target metal ions.

Study on cut-off characteristics of sub-nanosecond silicon carbide PiN switch

In this paper, a simulation model of [Formula: see text] type PiN high voltage pulse open switch is established. The switch operates in “punch through” mode, with a 4 kA/cm2 cut-off current density and sub-nanosecond cut-off speed. The cut-off process of switch can be divided into three stages, that is, non-equilibrium carriers extraction stage, majority carriers drift stage and charging stage of junction capacitance by change of internal electric field and carrier concentration. Keeping injection current and cut-off current as 20 A and 40 A, the switch cut-off speed and “pedestal” voltage are reciprocally determined. Thus, optimizing the doping concentration and thickness of [Formula: see text] layer is a valid solution for the actual system design.

Sulfur-Enriched Bone Char as Alternative P Fertilizer: Spectroscopic, Wet Chemical, and Yield Response Evaluation

Phosphorus- (P) rich bone char (BC) could be an alternative P fertilizer in sustainable agriculture; however, it has a low P solubility. Therefore, sulfur-enriched BC (BCplus) was tested for chemical composition and fertilization effects in a pot experiment. In BCplus sulfur, concentrations increased from &lt;0.1% to 27% and pH decreased from 8.6 to 5.0. These modifications did not change P solubility in water, neutral ammonium citrate, and citric acid. A pot experiment with annual rye grass (Lolium multiflorum L.) and treatments without P (P0), BC, BCplus and triple superphosphate (TSP) was set up. The cumulative dry matter yield of the BC treatment was similar to P0, and that of BCplus similar to TSP. The plant P uptake was in the order P0 = BC &lt; BCplus &lt; TSP. Consequently, the apparent nutrient recovery efficiency differed significantly between BC (&lt;3%), BCplus (10% to 15%), and TSP (&gt;18%). The tested equilibrium extractions, regularly used to classify mineral P-fertilizers, failed to predict differences in plant yield and P uptake. Therefore, non-equilibrium extraction methods should be tested in combination with pot experiments. Additionally, particle-plant root scale analyses and long-term experiments are necessary to gain insights into fertilizer-plant interactions.

Separation of the Minor Actinides Americium(III) and Curium(III) by Hydrophobic and Hydrophilic BTPhen ligands: Exploiting Differences in their Rates of Extraction and Effective Separations at Equilibrium

ABSTRACTThe complexation and extraction of the adjacent minor actinides Am(III) and Cm(III) by both hydrophobic and hydrophilic pre-organized 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen) ligands has been studied in detail. It has been shown that Am(III) is extracted more rapidly than Cm(III) by the hydrophobic CyMe4–BTPhen ligand into different organic diluents under nonequilibrium extraction conditions, leading to separation factors for Am over Cm (SFAm/Cm) as high as 7.9. Furthermore, the selectivity for Am(III) over Cm(III) can be tuned through careful choice of the extraction conditions (organic diluent, contact time, mixing speed, ligand concentration). This “kinetic” effect is attributed to the higher presumed kinetic lability of the Am(III) aqua complex toward ligand substitution. A dependence of the Am(III)/Cm(III) selectivity on the structure of the alkyl groups attached to the triazine rings is also observed, and BTPhens bearing linear alkyl groups are less able to discriminate between Am(III) and Cm(III) than CyMe4–BTPhen. Under equilibrium extraction conditions, hydrophilic tetrasulfonated BTPhen ligands complex selectively Am(III) over Cm(III) and prevent the extraction of Am(III) from nitric acid by the hydrophobic O-donor ligand N,N,N′,N′-tetraoctyldiglycolamide, giving separation factors for Cm(III) over Am(III) (SFCm/Am) of up to 4.6. These results further underline the utility of the BTPhen ligands for the challenging separation of the chemically similar minor actinides Am(III) and Cm(III).

Sensitive determination of plasma protein binding of cationic drugs using mixed-mode solid-phase microextraction

Freely dissolved concentrations are considered to be the most relevant concentration in pharmacology and toxicology, as they represent the active concentration available for interaction with its surroundings. Here, a solid-phase microextraction (SPME) coating that combines octadecyl and propylsulfonic acid groups as strong cation exchange sites, known as C18/SCX or “mixed-mode” SPME, is used to measure freely dissolved concentrations of amitriptyline, amphetamine, diazepam and tramadol to different binding matrices, including bovine serum albumin (BSA), human serum albumin (HSA), human plasma and human whole blood. A potential confounding factor in binding studies is that proteins may sorb to the fiber coating leading to incorrect measurement of protein sorption or changes in uptake kinetics to the fiber coating. Sorption of bovine serum albumin (BSA) was observed and quantified using a Lowry assay. BSA binds to the C18/SCX fiber in small amounts, but large changes in uptake kinetics were not observed. All experiments were performed at equilibrium. In addition, however, the effect of depletion and non-equilibrium extraction on the estimation of protein binding affinities was also studied. Binding affinities to BSA and human serum albumin (HSA) were calculated as log KBSA or log KHSA. These values were very similar to reported literature values. Sampling at either equilibrium or non-equilibrium resulted in similar binding affinities. Furthermore, SPME fibers were used to measure freely dissolved concentrations in undiluted human plasma and whole blood. Analysis of SPME extracts could be performed using HPLC-UV or HPLC with fluorescence detection without prior clean-up of the samples. Measured bound fractions in plasma using this SPME approach were comparable to literature reference values. Bound fractions in whole blood were always higher than in plasma, due to red blood cell partitioning. This work shows the potential of SPME as sampling tool for freely dissolved concentrations, especially for highly protein-bound compounds. Conventional SPME coatings such as polyacrylate (PA) or polydimethylsiloxane (PDMS) might be lacking sensitivity when sampling the small neutral fraction of highly protein-bound positively charged compounds, but the C18/SCX fiber is able to sorb the charged species of organic cations, thereby improving sensitivity for these types of compounds.

The automatic control system of a multi-component nonequilibrium extraction process in the pulse column

The construction of the process dynamic model and the automatic control system of a plant constitute the two major objectives that allow the plant to be controlled in automatic mode. The model selected was the dynamic model of the nonequilibrium extraction process in the pulse column based on the mass transfer diffusion kinetics. The use of the molecular diffusion equation in the calculations is conditioned by the fact that diffusion limits the examined process of mass transfer and allows the kinetic processes of the reaction to be disregarded. For the developed model, spatial-temporal profiles were calculated for the distribution of uranium, nitric acid, plutonium, thorium, and neptunium concentrations throughout the height of the column extractor after a step change in the aqueous phase flow rate. The results of the head column automatic control system (ACS) synthesis are presented for the operation in the first and second cycles of irradiated nuclear fuel extraction purification. Several options for the system were examined, with their structural and parametric syntheses being performed on the basis of the column linear dynamic model. The findings of the research are presented in relation to the ACS with a constant-rate actuating mechanism. Several methods of development of the ACS software and hardware tools were studied for the implementation of the formulated requirements.

A dynamic model of a multicomponent nonequilibrium extraction process in a pulsating column

The main principles of a dynamic model of a nonequilibrium extraction process in a pulsating column are considered. The results of calculating the space-time profiles of the distribution of the U, HNO3, Pu, Th, and Np concentrations along the height of a column extractor at a step change in the aqueous phase flow rate are presented.

Centrifugal extraction of rare earths from wet-process phosphoric acid

Phosphorite ore is a potential resource of rare earths (RE) as well as phosphate; therefore, the recovery of RE from wet-process phosphoric acid (WPA) is promising. This study investigated the influence of rotational speed, extractant concentration, flow ratio and phase contact time on the centrifugal extraction of RE from WPA and the separation of RE from impurities. The results indicate that higher rotational speed, higher extractant concentration and larger flow ratio are beneficial to the extraction of RE and impurities from phosphoric acid. It is found that the phase contact time for efficiently extracting RE and that for iron are of great difference, which provides an effective method for separating RE from iron using the non-equilibrium extraction process in centrifugal contactors. Compared with equilibrium extraction, the separation factor βRE/Fe is enhanced from 0.07 to 17.6.

Simulation of nonequilibrium extraction of rare-earth elements with liquid membranes: I. Generalized mathematical model

A mathematical model adequately describing extraction separation of chemically similar elements under nonequilibrium conditions was developed. Both single-extractor systems and systems of two extractors connected via an organic phase (continuous liquid membrane) were studied. The closed and flow modes of oscillatory extraction were considered. A general study of the properties of the model was performed. The model is capable to reproduce the majority of oscillatory modes described in the literature for chemical oscillators based on the Belousov-Zhabotinskii reaction. The correlations between the characteristic features of the oscillations and some parameters of the system were determined. Regular trends in the effect of the rate constants of the Field-Koros-Noyes mechanism simplified in accordance with the irrevesrsible Oregonator scheme and of the intensity of Ce(IV) interphase exchange on the behavior of the system were revealed. Algorithms were suggested for efficient simulation of some common experimental oscillatory modes.

Simulation of nonequilibrium extraction of rare-earth elements with liquid membranes: II. Comparison of theoretical and experimental data

The influence of the initial Ce(III) concentration on the behavior of oscillatory extraction systems 6 M LiNO3 in H2O-0.5 M TBP in n-decane and 6 M LiNO3 in H2O-0.5 M TBP in benzene was examined, and the experimental data were analyzed by simulation. The experimental data on the Belousov-Zhabotinskii (BZh) reaction in concentrated nitrate solutions in the absence and in the presence of the organic phase were described. The effect of the temperature conditions on the behavior of these systems was examined. The set of the rate constants and activation energies of the reactions of the simplified Field-Koros-Noyes (FKN) mechanism was determined. The effect of adding HNO3 in the course of the process on the characteristics of the oscillatory system was examined. An experimental series on REE separation in a flow system of two extractors connected via a liquid membrane under nonequilibrium conditions provided by the BZh reaction was simulated. A set of rate constants of the reactions of the simplified FKN mechanism, and also of the rate constants of the extraction and back-extraction of REE ions in flow systems was obtained. In all the cases, qualitative agreement between the experimental and calculated time dependences of the behavior of the systems was attained; the quantitative agreement in most cases was also reasonable.

Nonequilibrium extraction of hydrogen sulfide and carbon dioxide from gas, with the formation of aerosols containing reaction products with ammonia and water

Nonequilibrium extraction of hydrogen sulfide and carbon dioxide from gas, with the formation of aerosols containing reaction products with ammonia and water

Kinetics of REE separation by nonequilibrium extraction at oscillating temperature

The effect of periodic oscillations of temperature on the extraction and backwashing in the extraction systems 6 M NaNO3-Nd(NO3)3-Pr(NO3)3-TBP-kerosene and [Nd(NO3)3 · 3TBP]-[Pr(NO3)3 · 3TBP]-kerosene-0.1 M HNO3 was studied. Application of periodic temperature oscillations to the extraction system NaNO3-Nd(NO3)3-Pr(NO3)3-TBP-kerosene-0.1 M HNO3 increased the REE separation factor in a unit consiting of a continuous liquid membrane between two extractors. A mathematical model of nonstationary membrane extraction supplemented by the block of the temperature dependences of the extraction rate constants was developed. The activation energies of the forward and reverse reactions of the extraction and backwashing of Pr and Nd were calculated. For the extraction process of REE separation with a liquid membrane under the effect of periodic temperature oscillations, the following parameters were optimized: frequency and amplitude of temperature oscillations, distribution of the total volume of the organic phase between the extractors, and flow rate of the liquid membrane.

Kinetics of nonequilibrium extractive separation of REEs

A procedure is developed for studying the kinetics of nonequilibrium extraction in multicomponent systems by an example of the system Pr-Nd-NaNO3-TBP-kerosene. A unique experimental setup is designed for measuring kinetic parameters, based on the use of UV-VIS spectrophotometers with flow cells. Software for analysis of the spectra of multicomponent systems is developed.

Non-equilibrium chemical potential and polymer extraction from a porous matrix

The influence of a flow on the transfer of a polymer solution from a porous matrix to a flowing fluid is analysed. Since the flow modifies the free energy of the solution, through stretching and orientation of the macromolecules, the thermodynamic driving force for polymer transport is modified with respect to that of a quiescent fluid. The consequences of this modification for the extraction of a polymer from a porous matrix are explored in detail, and the formal results are explicitly illustrated by means of a specific solution. For the particular example analysed here, of possible interest in oil extraction or in microfluidic problems, the non-equilibrium effects may yield a reduction of the order of 10% of the extraction rate.

Response Characteristics of a Reversible Electrochemical Sensor for the Polyion Protamine

We describe here in detail the first reversible electrochemical sensors for the polyion protamine. Potentiometric sensors were proposed in recent years, mainly for the determination of the polyions heparin and protamine. Such potentiometric polyion sensors functioned on the nonequilibrium extraction of polyions into a hydrophobic membrane phase via ion pairing with lipophilic ion exchangers. This made it difficult to design sensors that operate in a truly reversible fashion. The reversible sensors described here utilize the same basic response mechanism as their potentiometric counterparts, but the processes of extraction and ion stripping are now fully controlled electrochemically. Spontaneous polyion extraction is avoided by using membranes containing highly lipophilic electrolytes that possess no ion-exchange properties. Reversible extraction of polyions is induced if a constant current pulse of fixed duration is applied across the membrane, followed by a baseline potential pulse. The key theoretical response principles of this new class of polyion sensors are discussed here and compared to those of its classical potentiometric counterpart. The electrochemical sensing system is characterized in terms of optimal working conditions, membrane composition, selectivity, and influence of sample stirring and organic-phase diffusion coefficient on the response characteristics. Excellent potential stability and reversibility of the sensors are observed, and measurements of heparin concentration in whole blood samples via protamine titration are demonstrated.

STRIPPING OF Zn(II), Cu(II), Co(II), AND Cd(II) FROM DEHPA USING EDTA IN A HOLLOW-FIBER MEMBRANE MODULE

The equilibrium behavior of liquid-liquid extraction of Zn(II), Cu(II), Co(II), and Cd(II) from DEHPA (di(2-ethylhexyl)phosphoric acid) with EDTA (ethylenediamine-tetraacetic acid) was studied. A concentration of 0.003M EDTA was able to extract simultaneously 83, 70, 88 and 54% of the cadmium, cobalt, copper and zinc, respectively at a pH between 1.6 and 1.8. The non-equilibrium liquid-liquid extraction behavior was studied using a polysulfonic hollow fiber membrane module with 1 mm ID and 5,000 molecular weight cut-off. The aqueous feed solution and EDTA was passed through the tubeside of the two membrane modules, and the organic DEHPA solution was circulated through the shellside. The optimum flow rate for the organic solution was 77ml/min and that of the aqueous feed and strip solutions were 78ml/min. The shellside pressure was maintained at 1.0–1.2 psig and that of the tubeside was kept at atmospheric pressure so that a stable organic interface was achieved. Under these conditions, 77, 63, 93, and 56% of cadmium, cobalt, copper and zinc were extracted from DEHPA, respectively.

NONDISPERSIVE LIQUID-LIQUID EXTRACTION OF Zn(II), Cu(II), Co(II), AND Cd(II) FROM DILUTE SOLUTION WITH DEHPA IN A HOLLOW-FIBER MEMBRANE MODULE

The ability to concentrate dilute aqueous solutions containing metals is desirable both from the standpoint of waste volume reduction and increased ease of concentration measurement. The first challenge in designing a liquid-liquid extraction (LLE) system to concentrate metals is to find an organic system that can be used to simultaneously remove a number of metals. The goal of this work was to find a LLE system that extracts zinc, copper, cadmium and cobalt simultaneously. In the LLE extraction experiments, nearly 100% extraction of all four metals (Zn(II), Cu(II), Cd(II) and Co(II) at about 25 ppm initially) was achieved when all of them were extracted simultaneously using 0.3 mol/L DEHPA in n-heptane. The extraction order observed as the pH of the aqueous solution increased was Zn(II) > Co(II) > Cu(II) > Cd(II). Based on these results, a polysulfone Hollow Fiber Contained Liquid Membrane (HFCLM) system was designed and operated to study the nonequilibrium extraction of all four metals via nondispersive LLE. The aqueous and organic streams were operated at 100% recycle. Interference effects between the four metal ions are discussed.