Equilibrium Partition Coefficient Research Articles

Metal directional crystallization: A sustainable green separation method for the purification of bismuth from crude bismuth while enriching lead and silver

In the traditional crude bismuth refining process, the addition of additives to form refining slag and the subsequent removal of impurities via separating the refining slag introduce new impurities while lowering the direct yield of bismuth, thereby restricting the green development of bismuth smelters. In this study, we propose a method that uses directional crystallization of metals to purify crude bismuth and enrich lead and silver. The phase diagram was analyzed using equilibrium partition coefficients, and lead and silver impurities were primarily enriched in the liquid phase during the crystallization of crude bismuth. In addition, we investigated the ground-state structures of the clusters, calculated the average binding energies, and elucidated the tendency of Ag to be enriched with Pb rather than Bi during the directional crystallization of crude bismuth from an atomic perspective. Using small-scale experiments, we determined the optimum process conditions, which were a crystallization separator speed of 4 r/min and a 10° inclination of the crystallization separator toward the horizontal plane. The guided semi-industrial experiments yielded Bi with a purity of 98.08 wt%, bismuth with a direct recovery of 92.49%, and Pb and Ag with removal rates of 95.64% and 90.53%, respectively. The entire process is simple, involves no additives, and effectively avoids the generation of refining slag.

Pseudo-Second-Order Kinetic Equation for Describing the Effect of Sorbent and Sorbate Concentrations.

The sorbent concentration (Cs) effect and sorbate initial concentration (C0) effect are common phenomena observed in the study of adsorption kinetics at solid-liquid interfaces. That is, adsorption rate constants simulated with classical kinetic equations, such as the pseudo-second-order (PSO) model, for a given system vary with Cs and C0. The classical kinetic equations cannot predict or describe the "Cs-effect" and "C0-effect" (called "C-effects" here). In the current work, the dynamic partition coefficient of sorbate between solid and liquid phases (Kt) was used to describe the adsorption kinetic processes. Based on the surface component activity (SCA) model, which assumes the activity coefficients of the surface components (fs) are not equal to unity but rather a function of Cs and the adsorption capacity (or C0) and referring to the classical PSO model, a new kinetic equation was established, called the "SCA-PSO kinetic model", and its two parameters, the intrinsic equilibrium partition coefficient (Ke0) and the intrinsic rate constant (k20), are independent of Cs and C0. In addition, the new model relates Kt and the rate constant (k2) to Cs and C0 via fs, and can thus describe the C-effects. The fs can be estimated from the change of equilibrium partition coefficient (Ke) with Cs and C0. The new model predicts that with the increase of Cs and C0, Ke decreases while k2 increases. Its rationality was confirmed by the literature-reported adsorption kinetic data of heavy metals on inorganic and biomass sorbents with the C-effects.

Gas-to-Particle Partitioning of Products from Ozonolysis of Δ3-Carene and the Effect of Temperature and Relative Humidity.

Formation of oxidized products from Δ3-carene (C10H16) ozonolysis and their gas-to-particle partitioning at three temperatures (0, 10, and 20 °C) under dry conditions (<2% RH) and also at 10 °C under humid (78% RH) conditions were studied using a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) combined with a filter inlet for gases and aerosols (FIGAERO). The Δ3-carene ozonolysis products detected by the FIGAERO-ToF-CIMS were dominated by semivolatile organic compounds (SVOCs). The main effect of increasing temperature or RH on the product distribution was an increase in fragmentation of monomer compounds (from C10 to C7 compounds), potentially via alkoxy scission losing a C3 group. The equilibrium partitioning coefficient estimated according to equilibrium partitioning theory shows that the measured SVOC products distribute more into the SOA phase as the temperature decreases from 20 to 10 and 0 °C and for most products as the RH increases from <2 to 78%. The temperature dependency of the saturation vapor pressure (above an assumed liquid state), derived from the partitioning method, also allows for a direct way to obtain enthalpy of vaporization for the detected species without accessibility of authentic standards of the pure substances. This method can provide physical properties, beneficial for, e.g., atmospheric modeling, of complex multifunctional oxidation products.

Composition and release rates of chemicals in inkjet fabrics determined by non-targeted screening and targeted analysis

Unveiling composition and release rates of chemicals in chemical-intensive products (CIPs) such as inkjet fabrics that are applied extensively in advertising and publicizing industries, is of importance to sound management of chemicals. This study tentatively identified 212 compounds from 69 inkjet fabric samples using gas chromatograph coupled with quadrupole time-of-flight mass spectrometry (GC-QTOF-MS). Contents of six phthalate esters (PAEs) were quantified to range from 3.0 × 102 mg/kg to 3.1 × 105 mg/kg with GC-MS. Bis(2-ethylhexyl) phthalate was predominantly detected to average 96 g/kg. The inkjet fabrics collected from southern China contained fewer non-intentionally added substances (NIASs) than from northern China. Annual mass release rates (RM) of the 6 PAEs from inkjet fabrics to air were estimated to range from 1.4 × 10−2 kg/year to 2.8 × 104 kg/year in China in 2020, and the mean indoor RM was comparable with the outdoor one. Equilibrium partition coefficients of the compounds between the product and air, ambient temperature, and concentrations of chemicals in the product, are key factors leading to RM with the high variance. The findings indicate that contents of the NIASs in the CIPs should be minimized, and the refining concept should be adopted in design of the CIPs, so as to control the release of chemicals from the CIPs.

A compartment model to predict in vitro finite dose absorption of chemicals by human skin

Dermal uptake is an important and complex exposure route for a wide range of chemicals. Dermal exposure can occur due to occupational settings, pharmaceutical applications, environmental contamination, or consumer product use. The large range of both chemicals and scenarios of interest makes it difficult to perform generalizable experiments, creating a need for a generic model to simulate various scenarios. In this study, a model consisting of a series of four well-mixed compartments, representing the source solution (vehicle), stratum corneum, viable tissue, and receptor fluid, was developed for predicting dermal absorption. The model considers experimental conditions including small applied doses as well as evaporation of the vehicle and chemical. To evaluate the model assumptions, we compare model predictions for a set of 26 chemicals to finite dose in-vitro experiments from a single laboratory using steady-state permeability coefficient and equilibrium partition coefficient data derived from in-vitro experiments of infinite dose exposures to these same chemicals from a different laboratory. We find that the model accurately predicts, to within an order of magnitude, total absorption after 24 h for 19 of these chemicals. In combination with key information on experimental conditions, the model is generalizable and can advance efficient assessment of dermal exposure for chemical risk assessment.

The H content of aubrites: An evaluation of bulk versus in situ methods for quantifying water in meteorites

Aubrites and enstatite chondrites (ECs) are isotopically similar to the Earth and therefore may resemble the primary materials that accreted to form our planet. Recent bulk H elemental and isotopic analyses of ECs and the Norton County aubrite suggest that enstatite-rich materials are H-rich and may represent a significant source of terrestrial water, with measured values of 3000±2000 μg/g H2O and 5300±900 μg/g H2O in the bulk and enstatite fractions of Norton County (Piani et al., Science, 2020). Here, we present a detailed investigation of in situ H2O concentrations in enstatite, diopside, forsterite, and plagioclase from a suite of main group aubrites, including Norton County, and Shallowater. We find that enstatite (4±2 μg/g H2O), diopside (4.8±0.5 μg/g H2O), and forsterite (5±3 μg/g H2O) have similar H2O concentrations, and all are significantly lower than plagioclase (24±3 μg/g H2O). We combine our in situ analyses of H2O contents with equilibrium partition coefficients and bulk mineralogies to estimate the bulk H2O content of our samples. We compare these first order estimates with bulk volatile analyses conducted using sample pyrolysis and find that the previous bulk H2O analyses of aubrites predominantly reflect terrestrial contamination and alteration. If our conclusion that the reported bulk H2O analyses of Norton County primarily reflect terrestrial contamination and alteration extends to bulk analyses of ECs, then EC-like material may not be a significant source of terrestrial water. Our results support the hypothesis that thermal metamorphism, melting, and differentiation leads to efficient desiccation of planetesimals relative to chondrites, and that differentiated planetesimals contributed, at most, trace amounts to Earth's water budget.

Purification of High-Purity Tin via Vertical Zone Refining

The present investigation delves into the potential of vertical zone refining as an effective purification technique for achieving high-purity tin (Sn) metal. The utilization of vertical zone refining offers distinct advantages over traditional horizontal zone refining, as it allows for enhanced control over the molten zone and solid–liquid interface, ultimately leading to superior impurity separation efficiency. The present study reveals that the solute partition coefficients (k0) of various impurity elements, such as Zn, Ag, Al, Mg, Ca, Ni, In, Co, Cu, As, Pb, Fe, and Bi, during the vertical zone refining process consistently demonstrate values below one. Notably, the partition coefficient of Sb deviates slightly from the others, being greater than one but approaching one. The authors achieve exceptional levels of purity in both the bottom and middle regions of the rod by subjecting the Sn melt to nine passes of vertical zone refining at a heating temperature of 405 °C and a downward pulling rate of 10 µm/s, resulting in purities exceeding 6N4. Furthermore, by evaluating the effective partition coefficients (keff), it was determined that impurity elements, such as Cu and Bi, closely approach their equilibrium partition coefficients, reaching values of approximately 0.492 and 0.327, respectively. To further enhance the purity of Sn metal and maximize product yield, we propose the utilization of electrolytic refining and vacuum distillation, with particular emphasis on the efficient separation of five specific elements, including Cu, Fe, As, Pb, and Sb. By elucidating these findings, this study not only contributes valuable insights into the efficacy of vertical zone refining as a purification technique for high-purity tin metal, but also offers important recommendations for refining strategies and impurity element separation.

Parameter calculation and result storage for phase-field simulation in α-Mg dendrite growth of Mg-5-wt% Zn alloy

Parameter calculation and result storage, as two necessary steps in phase-field simulation play an important role in ensuring the accuracy of simulation results. A strategy of parameter calculation and result storage is presented for phase-field simulation in α-Mg dendrite growth of Mg-5-wt% Zn alloy under isothermal solidification. Based on the phase diagram and empirical formulas, key parameters of the phase-field model, such as equilibrium partition coefficient k, liquidus slope m, solutal diffusion coefficient in liquid D l, and solutal diffusion coefficient in solid D s, can be obtained. Both structured grid method and structured point method can be used to store simulation results, but using the latter method will reduce about 60% storage space and 37.5% storage time compared with the former. Finally, convergent simulation results of α-Mg dendrite growth are obtained and they are in good agreement with the experimental results about optical micrograph, which verify the accuracy of parameters and stability of storage method.

Thermodynamic characterization of interactions between environmental contaminants and room temperature ionic liquids using static headspace gas chromatography with vacuum ultraviolet detection

Understanding the thermodynamic interactions between an analyte and the sample phase is of paramount importance when choosing a co-solvent in headspace analysis. A sample phase – gas phase equilibrium partition coefficient (Kp) is used fundamentally to describe the distribution of the analyte between the two phases. Kp determinations by headspace gas chromatography (HS-GC) were acquired by two methods: vapor phase calibration (VPC) and phase ratio variation (PRV). Here, we demonstrated a pressurized – loop headspace system in conjunction with gas chromatography vacuum ultraviolet detection (HS-GC-VUV) to directly calculate the concentration of analytes in the gas phase from room temperature ionic liquids (RTILs) sample phases, using pseudo-absolute quantification (PAQ). PAQ, an attribute of VUV detection, allowed for quick determination of Kp and other thermodynamic properties, such as enthalpy (ΔH) and entropy (ΔS) of the system through the use of van't Hoff plots in the temperature range of 70–110 °C. The Kp determinations by PAQ were comparable to those obtained using the VPC method with percent difference ranging from ≤ 1–33%. Kp determinations were made for analytes (cyclohexane, benzene, octane, toluene, chlorobenzene, ethylbenzene, m-,p-, and o-xylene) at the varying temperatures (70–110 °C) using different RTILs (1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][ESO4]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), and tris(2-hydroxyethyl)methylammonium methylsulfate ([MTEOA][MeOSO3])) and (1-ethyl-3-methylimidazolium bis(trisfluoromethanesulfonyl)imide ([EMIM] [NTF2])). The results from the van't Hoff analysis revealed that [EMIM] cation-based RTILs exhibit strong solute-solvent interactions with analytes that have π- electrons.

Computational Prodrug Design Methodology for Liposome Formulability Enhancement of Small-Molecule APIs.

Encapsulation into liposomes is a formulation strategy that can improve efficacy and reduce side effects of active pharmaceutical ingredients (APIs) that exhibit poor biodistribution or pharmacokinetics when administered alone. However, many APIs are unsuitable for liposomal formulations intended for parenteral administration due to their inherent physicochemical properties─lipid bilayer permeability and water-lipid equilibrium partitioning coefficient. Too high permeability results in premature leakage from liposomes, while too low permeability means the API is not able to pass across biological barriers. There are several options for solving this issue: (i) change of the lipid bilayer composition, (ii) addition of a permeability enhancer, or (iii) modification of the chemical structure of the API to design a prodrug. The latter approach was taken in the present work, and the effect of small changes in the molecular structure of the API on its permeation rate across a lipidic bilayer was systematically explored utilizing computer simulations. An in silico methodology for prodrug design based on the COSMOperm approach has been proposed and applied to four APIs (abiraterone, cytarabine, 5-fluorouracil, and paliperidone). It is shown that the addition of aliphatic hydrocarbon chains via ester or amide bonds can render the molecule more lipophilic and increase its permeability by approximately 1 order of magnitude for each 2 carbon atoms added, while the formation of fructose adducts can provide a more hydrophilic character to the molecule and reduce its lipid partitioning. While partitioning was found to depend only on the size and type of the added group, permeability was found to depend also on the added group location. Overall, it has been shown that both permeability and lipid partitioning coefficient can be systematically shifted into the desired liposome formulability window by appropriate group contributions to the parental drug. This can significantly increase the portfolio of APIs for which liposome or lipid nanoparticle formulations become feasible.

Development of an in situ equilibrium polydimethylsiloxane passive sampler for measuring volatile organic compounds in soil vapor

An equilibrium passive sampler made of polydimethylsiloxane (PDMS) fiber was developed to measure volatile organic compounds (VOCs) in soil vapor. Expanded polytetrafluoroethylene (ePTFE) was used to protect PDMS from pollution and direct contact with soil components. For all tested VOCs, equilibrium was reached after 7 days at 5 °C. The equilibrium partition coefficients of VOCs between PDMS, gas, and water were measured at three different temperatures. The analyte concentrations in PDMS exposed to gas and water separately were almost the same, which suggests that Cgas and Cwater in soil pores can be accurately deduced from CPDMS after equilibrium at various temperatures. To evaluate the passive sampler, active sampling measurements were performed simultaneously. Concentrations of VOCs deduced from the passive sampler were consistent with the concentrations measured by active sampling near the 1:1 line. Tests with artificial soils were conducted to observe the effects of soil components on passive sampling. The results suggest that the effect of water saturation can be ignored; in other words, the developed passive sampler can be applied in the vadose zone, which has fluctuating water saturation. With a holder for the sampler made of stainless steel, the developed in situ passive sampler can measure VOCs in contaminated soil vapor. The developed passive sampler was proven to be an alternative for measuring VOCs in soil vapor, which can be helpful for soil risk assessment and for observing the diffusion of VOCs in contaminated sites.

Transport-limited kinetics of phosphate retention on iron-coated sand and practical implications

Iron-coated sand (ICS) is a by-product from drinking water treatment made of sand coated with ferric iron (hydr)oxides. It is considered a suitable material for large-scale measures for phosphate removal from natural and agricultural waters to prevent eutrophication. Previous studies demonstrated that the residence time of water must be very long to reach equilibrium partitioning between phosphate and ICS but specifics for application are missing. First, SEM-EDX images were used to support the conceptual assumption that P adsorption inside the coating is a transport-limited process. Second, a conceptual model of phosphate adsorption was proposed considering two types of sites: one type with fast adsorption kinetics and reaching equilibrium with the percolating solution, and another type for which adsorption is also reversible but described by pseudo-first-order kinetics. The latter is conceived to account for transport-limited adsorption in the interior of the coating while the former fraction of sites is assumed to be easily accessible and located close to the grain surface. Third, the kinetics of phosphate adsorption on ICS were quantitatively determined to describe and predict phosphate retention in filters under various flow conditions. The model was calibrated and validated with long-term column experiments, which lasted for 3500 h to approach equilibrium on the slowly reacting sites. The model reproduced the outflowing phosphate concentrations: the pronounced increase after a few pore volumes and the slow increase over the remaining part of the experiment. The parameterized model was also able to predict the time evolution of phosphate concentrations in the outflow of column experiments with different flow velocities, flow interruption, and in desorption experiments. The equilibrium partition coefficient for the experimental conditions was identified as 28.1 L/g-Fe at pH 6.8 and a phosphate concentration of 1.7 mg-P / L. The optimized first-order mass transfer coefficient for the slow adsorption process was 1.56 10−4 h−1, implying that the slow adsorption process has a time scale of several months. However, based on the parameterized model, the slow adsorption process accounted for 95.5% of the equilibrium adsorption capacity, emphasizing the potential relevance of this process for practical applications. The implications for the design, operation, and lifespan of ICS filters are exemplarily illustrated for different scenarios.

Effect of (bio)surfactant type and concentration on the gas-liquid equilibrium partitioning of hydrophobic volatile organic compounds.

The biological removal of hydrophobic volatile organic compounds (VOCs) is limited by their low water solubility and, therefore, low bioavailability. The addition of surfactants is a promising strategy, but to gain understanding and broaden its applicability, its effect on the solubility of hydrophobic VOCs should be investigated. This study evaluates the effect of 2 synthetic surfactants (sodium dodecyl sulfate (SDS) and Tween 80) and 3 biological surfactants (surfactin, rhamnolipid and saponin) on the gas-to-liquid equilibrium partitioning coefficient (KGL) of 7 hydrophobic VOCs at different critical micelle concentrations (CMC). For all VOCs, a decrease in their KGL was observed when a (bio)surfactant was added at 1 and 3 CMC. The highest decrease in KGL (71 - 96%) was observed for all compounds when SDS was added at 3 CMC, whereas the smallest effect was noticed when Tween 80 or surfactin (5.1 - 75%) were added at both concentrations. The results are explained in terms of the (bio)surfactant and VOC physical-chemical properties (e.g. CMC and polarity). This is the first study evaluating the effect of biological surfactants on KGL. These fundamental data are essential to improve the design and modeling of air treatment systems using (bio)surfactants.

Determination of partition coefficients of phthalic acid esters between polydimethylsiloxane and water and its field application to surface waters

Phthalic acid esters (PAEs) or phthalates are endocrine-disrupting chemicals and among the most frequently detected hydrophobic organic pollutants, which can be gradually released from consumer products into the environment (e.g., water). This study measured the equilibrium partition coefficients for 10 selected PAEs, with a wide range of logarithms of the octanol-water partition coefficient (log Kow) from 1.60 to 9.37, between poly(dimethylsiloxane) (PDMS) and water (KPDMSw) using the kinetic permeation method. The desorption rate constant (kd) and KPDMSw for each PAEs were calculated from kinetic data. The experimental log KPDMSw for the PAEs ranges from 0.8 to 5.9, which is linearly correlated with log Kow values up to 8 from the literature (R2 > 0.94); however, it slightly deviated for the PAEs with log Kow values greater than 8. In addition, KPDMSw decreased with the temperature and enthalpy for PAEs partitioning in PDMS-water in an exothermic manner. Furthermore, the effects of dissolved organic matter and ionic strength on the partitioning of PAEs in PDMS were investigated. PDMS was used as a passive sampler to determine the aqueous concentration of plasticizers in river surface water. The results of this study can be used to evaluate the bioavailability and risk of phthalates in real environmental samples.

Passive sampling of diverse pesticides in water by hydrophilic–lipophilic balance sorbent-embedded cellulose acetate membrane: Kinetics, equilibrium partitioning and field application

Pesticides are useful products for agriculture and human life, but they are often released into surface waters and are hazardous to aquatic ecosystems. Pesticides monitoring in surface waters is challenging due to the great variety, ultratrace levels and nonpoint source pollution of pesticides; however, continuous passive sampling may be conducive to solving these problems. This work evaluated the performance of a newly developed passive sampler (hydrophilic–lipophilic balance sorbent-embedded cellulose acetate membrane, HECAM) for six types of currently used/present pesticides. The uptake kinetics and equilibrium partitioning of nineteen pesticides in different dissolved concentrations were studied by dynamic accumulation and equilibrium partitioning experiments, respectively. In the dynamic accumulation experiments, pesticides gradually accumulated in the HECAM and followed a first-order kinetic model. The same type of pesticides had roughly comparable accumulation concentrations. The estimated uptake rate constants ranged from 1.04 to 13.5 L g−1 d−1, and sampling rates ranged from 0.02 to 0.31 L d−1 for the pesticides in the HECAM (size of 2 cm × 3 cm). Pesticide accumulation concentrations in the HECAM increased linearly with increasing dissolved concentrations, which means that varying concentrations can also be monitored by the HECAM. In the equilibrium partitioning experiments, the pesticide partitioning behavior at varying dissolved concentrations can be described by the Freundlich model. The calculated equilibrium partition coefficients (log KD) for pesticides ranged from 3.32 to 4.54, and different pesticide types showed different changes with log Kow. Comparable results were found when estimating chemical equilibrium partition coefficients by the dynamic accumulation and equilibrium partitioning methods. Field deployment of the HECAM in river waters resulted in the detection of four pesticides, and the measured results were comparable to those of active sampling coupled with liquid–liquid extraction. These results suggest that the HECAM would be a promising strategy for simultaneously monitoring diverse pesticides in waters.

Electrospun nanofiber mats as sorbents for polar emerging organic contaminants: Demonstrating tailorable material performance for uptake of neonicotinoid insecticides from water

The number and diversity of chemical contaminants in aquatic environments require versatile technologies for their removal. Here we fabricated various electrospun nanofiber mats (ENMs) and tested their ability to sorb six neonicotinoid insecticides, a model family of small, polar contaminants. ENM formulations were polyacrylonitrile (PAN) or carbon nanofibers (CNF; carbonized from PAN), with additives including carbon nanotubes (CNTs; with and without surface carboxyl groups), the cationic surfactant tetrabutyl ammonium bromide (TBAB), and/or phthalic acid (PTA; a CNF porogen). While sorption on pure PAN ENMs was low [equilibrium partition coefficients (KENM-W) from 0.9 to 1.2 log units (L/kg)], inclusion of CNTs and/or TBAB generally increased uptake in an additive fashion, with carboxylated CNT composites outperforming non-functionalized CNT analogs. CNF ENMs exhibited as much as a tenfold increase relative to PAN for neonicotinoid sorption, which increased with carbonization temperature. Ultimately, the optimal ENM (CNFs with carboxylated-CNTs, PTA, and carbonized at 800 °C) exhibited relatively fast uptake (equilibrium < 1 day without mixing) and surface-area-normalized capacities comparable to other carbonaceous sorbents (e.g., activated carbon). Collectively, this work demonstrates the versatility of electrospinning to produce novel sorbents specifically designed to target emerging chemical classes for applications including water treatment and passive sampling.

Widespread phosphorous excess in olivine, rapid crystal growth, and implications for magma dynamics

Trace element zoning is often used to unravel the crystallization history of phenocrysts in magmatic systems, but interpretation requires quantifying the relative importance of equilibrium versus disequilibrium. Published partition coefficients for phosphorous (P) in olivine vary by more than a factor of ten. After considering kinetic effects, a new equilibrium partition coefficient was extrapolated from a re-examination of natural and experimental systems, indicating that P partition coefficients in olivine are significantly over-estimated. These new partitioning constraints allow us to establish a theoretical P Equilibrium Fractionation Array (PEFA) for mid-ocean ridge basalts (MORBs), revealing that most olivines from MORBs have excess P (2–15 times PEFA) and are thus in disequilibrium. Using an independent case study of natural dendritic olivines, we show that such P enrichments can be explained by diffusion-limited incorporation of P during rapid crystal growth. If growth rate can be related to cooling, the rapid growth rates of olivines have implications for magma system dynamics, such as the size of magma bodies or where crystallization occurs within the body.

Functionalized maghemite nanoparticles for enhanced adsorption of uranium from simulated wastewater and magnetic harvesting

Maghemite (γ-Fe2O3) nanoparticles (MNPs) were functionalized with 3-aminopropyltriethoxysilane (APTES) to give APTES@Fe2O3 (AMNP) which was then reacted with diethylenetriamine-pentaacetic acid (DTPA) to give a nanohybrid DTPA-APTES@Fe2O3 (DAMNP). Nano-isothermal titration calorimetry shows that DTPA complexation with uranyl ions in water is exothermic and has a stoichiometry of two DTPA to three uranyl ions. Density functional theory calculations indicate the possibility of several complexes between DTPA and UO22+ with different stoichiometries. Interactions between uranyl ions and DAMNP functional groups are revealed by X-photoelectron and Fourier transform infrared spectroscopies. Spherical aberration-corrected Scanning Transmission Electron Microscopy visualizes uranium on the particle surface. Adsorbent performance metrics were evaluated by batch adsorption studies under different conditions of pH, initial uranium concentration and contact time, and the results expressed in terms of equilibrium adsorption capacities (qe) and partition coefficients (PC). By either criterion, performance increases from MNP to AMNP to DAMNP, with the maximum uptake at pH 5.5 in all cases: MNP, qe = 63 mg g−1, PC = 127 mg g−1 mM−1; AMNP, qe = 165 mg g−1, PC = 584 mg g−1 mM−1; DAMNP, qe = 249 mg g−1, PC = 2318 mg g−1 mM−1 (at 25 °C; initial U concentration 0.63 mM; 5 mg adsorbent in 10 mL of solution; contact time, 3 h). The pH maximum is related to the predominance of mono- and di-cationic uranium species. Uptake by DAMNPs follows a pseudo-first-order or pseudo-second-order kinetic model and fits a variety of adsorption models. The maximum adsorption capacity for DAMNPs is higher than for other functionalized magnetic nanohybrids. This adsorbent can be regenerated and recycled for at least 10 cycles with less than 10% loss in activity, and shows high selectivity. These findings suggest that DAMNP could be a promising adsorbent for the recovery of uranium from nuclear wastewaters.

Preferential sorption of polysaccharides on mackinawite: A chemometrics approach

Marine sediments represent the most important sink for natural organic matter (NOM) across geological time spans. Strong associations between minerals, including iron oxides, and organic matter reaching the seafloor play a fundamental role in this preservation and have been known for some decades. Despite the importance of this protective mechanism in the balances of the global carbon budget, very little is known about the affinity of NOM for reduced iron species such as mackinawite (FeS) in the anoxic layers of sediment. In this study, equilibrium partition coefficients (Kd) for three types of NOM (soil extract, corn leaf extract and plankton extract) on FeS were determined through batch sorption experiments. Models were then built via multiple linear regression (MLR) and partial least squares regression (PLSR) in order to predict sorption Kd’s based on the chemical characteristics of the NOM. Investigation of the PLSR regression coefficients indicates that functional groups characteristic of polysaccharides are the greatest positive predictors of NOM sorption onto FeS at marine sediment porewater pH. This conclusion was independently verified by analyses of NOM FTIR spectra pre- and post-sorption. PLSR outperformed MLR with a lower root mean square error of prediction (RMSEP) of 53.4 L/kg compared to 64.0 L/kg. To our knowledge, this research presents a novel machine-learning approach to the quantitative modelling of NOM sorption to minerals found in anoxic marine environments.

Study of the evolution mechanisms of Fe-rich phases in Al-Si-Fe alloys with Mn modification using synchrotron X-ray imaging

The plate-like Fe-rich intermetallics phases in the recycled Al-Si alloys significantly deteriorate the mechanical properties. In this study, the effect of Mn addition on Fe-rich phases formation and the properties of the Al-7Si-1.2Fe alloys were systematically studied by optical microscopy, scanning electron microscopy, differential scanning calorimetry, thermodynamic calculations, synchrotron X-ray radiography and tomography. The results show that with the addition of Mn, the two-dimensional (2D) morphology of the Fe-rich phase change from plate-like to Chinese-script and star-like. The synchrotron X-ray tomography results indicate that the three-dimensional (3D) morphology of Fe-rich phases change from interconnected plate-like to separated hollow polyhedron with increasing Mn content. The in-situ synchrotron X-ray radiography results reveal that the formation temperature, size, and area fraction of the primary Fe-rich phase in the Al-7Si-1.2Fe-1.09Mn alloy gradually decreased, but the number density increased as the cooling rate increased. The thermodynamic calculation results indicate that β-Al 5 FeSi could be eliminated when the Mn content exceeded 1.06%, which was consistent with the experimental results. However, excessive Mn addition caused the formation of large primary Fe-rich phases, resulting in a significant reduction in the elongation of the alloys. Reducing the equilibrium partition coefficient difference of Mn and Fe and reducing the formation of primary Fe-rich phases with high Mn/Fe ratios are good strategies to neutralize the negative effect of Fe-rich phases. • Suitable Mn content added to Al-Si-Fe alloys to improved properties are obtained. • 3D morphology of Fe-rich phases with different Mn content are presented. • In-situ observation the nucleation and growth of Fe-rich phases during solidification.