Ionization Equilibrium Research Articles

3D Nonequilibrium Ionization and Spectroscopic Modeling of Coronal Mass Ejections. I. Comparison with Hinode/EIS Observations

Abstract High-resolution EUV spectroscopy provides an informative diagnostic tool for the early evolution of coronal mass ejections (CMEs) since it can directly measure many physical properties of CME plasma close to the Sun that cannot be determined from white-light coronagraphs or narrowband imagers. The Hinode/EUV Imaging Spectrometer (EIS) captured a series of high-resolution EUV spectra of the 2008 April 9 event, also known as the “Cartwheel CME,” during its initial acceleration period. CMEs are inherently dynamic events, driving the plasma from ionization equilibrium, which makes the nonequilibrium ionization (NEI) effects important when analyzing spectral observations. In this work, we performed simulations of the Cartwheel CME using the Alfvén Wave Solar atmosphere Model (AWSoM) to provide insight into the plasma structure and dynamics during the early evolution of this CME. For the first time, we combined self-consistent nonequilibrium charge state calculations in the EUV spectral line synthesis for a CME simulation to account for the plasma departures from ionization equilibrium everywhere in the CME. In this first paper of the series, we compare the simulation results to the EIS observations of this event to assess the quality of the AWSoM predictions. We find that the CME is out of equilibrium, indicating that NEI effects should be considered in the EUV spectral synthesis. Overall, the model reproduces the thermodynamic evolution of the CME in the low solar corona well, as compared to the EIS observations.

Suzaku Observations of the Cold Front in A3667: A Nonequilibrium Ionization State of the Intracluster Medium

Abstract We present a systematic study of the thermodynamic properties of the intracluster medium (ICM), including the plasma conditions in the ICM, in the merging galaxy cluster A3667 using Suzaku. We analyze the X-ray spectra of the ICM between the northwestern and the southeastern radio relics across a prominent cold front in A3667 to search for the ICM in a nonequilibrium ionization (NEI) state. We find that the ICM inside the cold front exhibits an NEI state with an ionization parameter of (2.2 ± 0.4) × 1011 s cm−3 at the 90% confidence level, which is lower than that expected from a collisional ionization equilibrium state of the ICM (i.e., n e t > 1012 s cm−3). The timescale calculated from the ionization parameter of the ICM inside the cold front is 3.9 − 0.8 + 0.7 Myr , which is much shorter than the thermal equilibration timescale. A weak transonic sloshing motion might explain the possibility that the ICM inside the cold front of A3667 is in the NEI state. In addition, the NEI state of the ICM in A3667 seems to be associated with the elongated radio halo bridging the region between the northwestern radio relic and the prominent cold front in A3667 across the cluster center.

Strong signature of right-handed circularly polarized photoionization close to the cyclotron line in the atmosphere of magnetic white dwarfs

Magnetic fields break the symmetry of the interaction of atoms with photons with different polarizations, yielding chirality and anisotropy properties. The dependence of the absorption spectrum on the polarization, a phenomenon known as dichroism, is present in the atmosphere of magnetic white dwarfs. Its evaluation for processes in the continuum spectrum has been elusive so far due to the absence of appropriate ionization equilibrium models and incomplete data on photoionization cross sections. We combined rigorous solutions to the equilibrium of atomic populations with approximate cross sections to calculate the absolute opacity due to photoionization in a magnetized hydrogen gas. We predict a strong right-handed circularly polarized absorption (χ+) formed blueward of the cyclotron resonance for fields from about 14 to several hundred megagauss. In energies lower than the cyclotron fundamental, this absorption shows a deep trough with respect to linear and left-handed circular polarizations that steepens with the field strength. The jump in χ+ is due to the confluence of a large number of photoionization continua produced by right-handed circularly polarized transitions from atomic states with a nonnegative magnetic quantum number toward different Landau levels.

Catastrophic Cooling Instability in Optically Thin Plasmas

The solar corona is the prototypical example of a low-density environment heated to high temperatures by external sources. The plasma cools radiatively, and because it is optically thin to this radiation, it becomes possible to model the density, velocity, and temperature structure of the system by modifying the MHD equations to include an energy source term that approximates the local heating and cooling rates. The solutions can be highly inhomogeneous and even multiphase because the well-known linear instability associated with this source term, thermal instability, leads to a catastrophic heating and cooling of the plasma in the nonlinear regime. Here we show that there is a separate, much simpler linear instability accompanying this source term that can rival thermal instability in dynamical importance. The stability criterion is the isochoric one identified by Parker (1953), and we demonstrate that cooling functions derived from collisional ionization equilibrium are highly prone to violating this criterion. If catastrophic cooling instability can act locally in global simulations, then it is an alternative mechanism for forming condensations, and due to its nonequilibrium character, it may be relevant to explaining a host of phenomena associated with the production of cooler gas in hot, low density plasmas.

X-Ray Spectroscopy of the Dwarf Nova Z Chamaeleontis in Quiescence and Outburst Using the XMM-Newton Observatory

We present X-ray spectroscopy of the SU UMa–type dwarf nova Z Chamaeleontis using the European Photon Imaging Camera and reflection grating spectrometer (RGS) instruments on board the XMM-Newton observatory. The quiescent system can be modeled by collisional equilibrium (CIE) or nonequilibrium plasma models, yielding a kT of 8.2–13.0 keV at a luminosity of (5.0–6.0) × 1030 erg s−1. The spectra yield better χν2 using partially covering absorbers of cold and/or photoionized nature. The ionized absorber has an equivalent N H = (3.4–5.9) × 1022 cm−2 and a log(ξ) = 3.5–3.7 with a (50–60)% covering fraction when the VNEI model (XSPEC) is used. The line diagnosis in quiescence shows no resonance lines, with only the forbidden lines of Ne, Mg, and Si detected. The H-like C, O, Ne, and Mg are detected. The strongest line is O viii, with (2.7–4.6) × 10−14 erg s−1 cm−2. The quiescent X-ray-emitting plasma is not collisional and not in ionization equilibrium, which is consistent with hot ADAF-like accretion flows. The line diagnosis in the outburst shows He-like O and Ne, with intercombination lines being the strongest, along with weaker resonance lines. This indicates the plasma is more collisional and denser, but not yet in CIE, revealing ionization timescales of (0.97–1.4) × 1011 s cm−3. The R ratios in the outburst yield electron densities of (7–90) × 1011 cm−3 and the G ratios yield electron temperatures of (2–3) × 106 K. The outburst luminosity is (1.4–2.5) × 1030 erg s−1. The flow is inhomogeneous in density. All detected lines are narrow, with widths limited by the resolution of RGS, yielding Keplerian rotational velocities <1000 km s−1. This is too low for boundary layers, consistent with the nature of ADAF-like hot flows.

Dimensionless Analysis of a Physics-Based Model for Economical Hydroxide Exchange Membrane Carbon Capture

Billions of tons of CO2 emissions are contributing to the detrimental decline of global climate. International agreements regarding the solution to lower emissions dictate that the abatement of CO2 emitting processes is no longer sufficient; negative emission technologies are needed. Technologies using solid and liquid sorbent to capture CO2 are growing at an impressive pace targeting global capture demands. However, capturing CO2 from ambient air poses significant challenges for existing technologies, primarily due to steep energy and capital costs. Moreover, these approaches often rely on energy sources that inadvertently contribute to CO2 emissions. The rapid development of green energy sources like hydrogen presents an opportunity for a new electrochemically-based CO2 capture method powered by hydrogen. Estimates using experimental data of the Hydroxide Exchange Membrane Carbon Capture (HEMCC) approach predict a fraction of the volume relative to traditional technologies. In this H2-powered process, hydroxides are electrochemically generated at the cathode via the oxygen reduction reaction, which chemically removes CO2 from the air. This produces (bi)carbonates that transport across the hydroxide exchange membrane and accumulate at the anode. As a result, the local pH environment at the anode—where hydrogen oxidation reaction occurs—lowers until CO2 generation becomes thermodynamically favorable, resulting in a concentrated CO2 stream.Experimental validation of the HEMCC device has motivated further research; however, for commercialization, there is a need to increase electron efficiency (CO2/e-)—a proxy for lower hydrogen operating costs. Given the novel nature of this technology, our research aims to understand efficiency limitations to inform experiments. To this end, we have developed a steady-state, one-dimensional numerical model of the HEMCC system (Figure 1a). The model simulates four layers—anode, cathode, membrane, and interlayer—involving multiple parallel processes including ion transport, CO2 kinetics, ionic equilibrium, electrochemical kinetics, and gas transport. Using dimensionless diagnostic metrics provides a structured approach to elucidate key CO2 capture information about this complex model (>50 parameters). The study has determined that electron efficiency limitations can be improved through size optimization of electrodes and membranes as well as increasing ionic resistance (Figure 1b). Additional improvements were found by increasing CO2 transport or CO2 kinetics on the air side. This dimensionless approach has elucidated key variables controlling electron efficiency, enabling an intuition-based optimization for CO2 capture. Using this approach, we demonstrated a cost reduction of $23/tonCO2 compared to the baseline, assuming a H2 price aligning with the DOE H2 shot's target cost of $1/kgH2. However, for a more comprehensive analysis incorporating other operating and capital costs, future work should consider realistic system conditions. Given the potential for decentralization of the HEMCC, future work should leverage the computational efficiency of this numerical model and integrate yearly weather patterns to simulate real-time effects on system performance. In summary, future work should conduct a thorough technoeconomic analysis to assess the feasibility of this technology. Figure 1

Relationship between Molecular Structure and Surface Activity of Ionic Surfactants.

A new model is developed to quantify the surface tension of ionic surfactants from surface affinity and ionization equilibrium. The model successfully predicts two important molecular structure-surface activity factors: the length of single-branch homologues and the nature of counterions. The modeling results also clarify the underlying mechanisms of the two processes. Changing the counterion only affects the ionization, not the affinity. On the other hand, increasing carbon length dramatically increases the affinity while having a small effect on ionization. The modeling framework consistently resolves structure-activity observations, some of which have been reported since the 19th century. The model can be extended for surfactants with more than one ionic state and surfactant/electrolyte mixtures.

Time-dependent metal ionization and the persistence of collisionally excited emission lines in the diffuse ionized gas of star-forming galaxies

ABSTRACT We extend our time-dependent hydrogen ionization simulations of diffuse ionized gas to include metals important for collisional cooling and diagnostic emission lines. The combination of heating from supernovae and time-dependent collisional and photoionization from mid-plane OB stars produces emission line intensities (and emission line ratios) that follow the trends observed in the Milky Way and other edge-on galaxies. The long recombination times in low-density gas result in persistent large volumes of ions with high ionization potentials, such as O iii and Ne iii. In particular, the vertically extended layers of Ne iii in our time-dependent simulations result in [Ne iii] 15 $\mu$m/[Ne ii] 12 $\mu$m emission line ratios in agreement with observations of the edge-on galaxy NGC 891. Simulations adopting ionization equilibrium do not allow for the persistence of ions with high ionization states and therefore cannot reproduce the observed emission lines from low-density gas at high altitudes.

Alkali and alkaline earth ion exchange affinity in ETS-10 toward aqueous lithium separation

Continuous ion exchange is a more sustainable alternative to current methods for removing common impurities from lithium sources. In this work, we examine ion-adsorbent interactions for Mg2+ and Ca2+ with microporous titanosilicate ETS-10, an ion exchange solid with promising performance, using experimental and computational (density functional theory, DFT) methods. Ion exchange affinity for Mg2+ and Ca2+ using the Na+-form of ETS-10 are quantified from measured equilibrium isotherms, analyzed using a modified Langmuir isotherm accounting for overall stoichiometric desorption/adsorption in the cation exchange process. The equilibrium constant for ion exchange using Na-ETS-10 is greatest for Ca and decreases in order of Mg, K, and Li, respectively. These differences in ion exchange affinity are consistent with trends in DFT-derived ion exchange energies, which account for hydration and solvation of cations using a thermochemical cycle. These equilibrium constant values and ion exchange energies suggest that exchange of Ca2+, Mg2+, and K+ using Na-ETS-10 is more favorable than that of Li+. Indeed, competitive ion exchange of equimolar aqueous mixtures of Li+ and each of K+, Mg2+, or Ca2+ demonstrate selective uptake of the non-lithium cation into the solid, thereby concentrating Li+ in the aqueous solution while removing impurity cations.

Proton nanomodulators for enhanced Mn2+-mediated chemodynamic therapy of tumors via HCO3− regulation

BackgroundMn2+-mediated chemodynamic therapy (CDT) has been emerged as a promising cancer therapeutic modality that relies heavily on HCO3− level in the system. Although the physiological buffers (H2CO3/HCO3−) provide certain amounts of HCO3−, the acidity of the tumor microenvironment (TME) would seriously affect the HCO3− ionic equilibrium (H2CO3 ⇌ H+ + HCO3−). As a result, HCO3− level in the tumor region is actually insufficient to support effective Mn2+-mediated CDT.ResultsIn this study, a robust nanomodulator MnFe2O4@ZIF-8 (PrSMZ) with the capability of in situ self-regulation HCO3− is presented to enhance therapeutic efficacy of Mn2+-mediated CDT. Under an acidic tumor microenvironment, PrSMZ could act as a proton sponge to shift the HCO3− ionic equilibrium to the positive direction, significantly boosting the generation of the HCO3−. Most importantly, such HCO3− supply capacity of PrSMZ could be finely modulated by its ZIF-8 shell thickness, resulting in a 1000-fold increase in reactive oxygen species (ROS) generation. Enhanced ROS-dependent CDT efficacy is further amplified by a glutathione (GSH)-depletion ability and the photothermal effect inherited from the inner core MnFe2O4 of PrSMZ to exert the remarkable antitumor effect on mouse models.ConclusionsThis work addresses the challenge of insufficient HCO3− in the TME for Mn2+-mediated Fenton catalysts and could provide a promising strategy for designing high-performance Mn2+-mediated CDT agents to treat cancer effectively.

BSC2 modulates AmB resistance via the maintenance of intracellular sodium/potassium ion homeostasis in Saccharomyces cerevisiae

Previous studies on BSC2 have shown that it enhances yeast cell resistance to AmB via antioxidation and induces multidrug resistance by contributing to biofilm formation. Herein, we found that BSC2 overexpression could reverse the sensitivity of pmp3Δ to AmB and help the tested strains restore the intracellular sodium/potassium balance under exposure to AmB. Meanwhile, overexpression of the chitin gene CHS2 could simulate BSC2 to reverse the sensitivity of pmp3Δ and nha1Δ to high salt or AmB. However, BSC2 overexpression in flo11Δ failed to induce AmB resistance, form biofilms, and affect cell wall biogenesis, while CHS2 overexpression compensated the resistance of flo11Δ to AmB. Additionally, BSC2 levels were positively correlated with maintaining cell membrane integrity under exposure to AmB, CAS, or a combination of both. BSC2 overexpression in nha1Δ exhibited a similar function of CHS2, which can compensate for the sensitivity of the mutant to high salt. Altogether, the results demonstrate for the first time that BSC2 may promote ion equilibrium by strengthening cell walls and inhibiting membrane damage in a FLO path-dependent manner, thus enhancing the resistance of yeast cells to AmB. This study also reveals the possible mechanism of antifungal drugs CAS and AmB combined to inhibit fungi.

Immersed boundary method for dynamic simulation of polarizable colloids of arbitrary shape in explicit ion electrolytes.

We develop a computational method for modeling electrostatic interactions of arbitrarily shaped, polarizable objects on colloidal length scales, including colloids/nanoparticles, polymers, and surfactants, dispersed in explicit ion electrolytes and nonionic solvents. Our method computes the nonuniform polarization charge distribution induced in a colloidal particle by both externally applied electric fields and local electric fields arising from other charged objects in the dispersion. This leads to expressions for electrostatic energies, forces, and torques that enable efficient molecular dynamics and Brownian dynamics simulations of colloidal dispersions in electrolytes, which can be harnessed to accurately predict structural and transport properties. We describe an implementation in which colloidal particles are modeled as rigid composites of small spherical beads that tessellate the surface of the particle. The electrostatics calculations are accelerated using a spectrally accurate particle-mesh-Ewald technique implemented on a graphics processing unit and regularized such that the electrostatic calculations are well-defined even for overlapping bodies. We illustrate the effectiveness of this approach with a comprehensive set of calculations: the induced dipole moments and forces for individual, paired, and lattice configurations of spherical colloids in an electric field; the induced dipole moment and torque for anisotropic particles subjected to an electric field; the equilibrium ion distribution in the double layer surrounding charged colloids; the dynamics of charged colloids; and the behavior of ions in the double layer of a polarizable colloid under the influence of an electric field.

Caution for Multidrug Therapy: Significant Baroreflex Afferent Neuroexcitation Coordinated by Multi-Channels/Pumps Under the Threshold Concentration of Yoda1 and Dobutamine Combination

Multi-drug therapies are common in cardiovascular disease intervention; however, io channel/pump coordination has not been tested electrophysiologically. Apparently, inward currents were not elicited by Yoda1/10 nM or Dobutamine/100 nM alone in Ah-type baroreceptor neurons, but were by their combination. To verify this, electroneurography and the whole-cell patch-clamp technique were performed. The results showed that Ah- and C-volley were dramatically increased by the combination at 0.5 V and 5 V, in contrast to A-volley, as consistent with repetitive discharge elicited by step and ramp with markedly reduced current injection/stimulus intensity. Notably, a frequency-dependent action potential (AP) duration was increased with Iberiotoxin-sensitive K+ component. Furthermore, an increased peak in AP measured in phase plots suggested enhanced Na+ influx, cytoplasmic Ca2+ accumulation through reverse mode of Na+/Ca2+ exchanger, and, consequently, functional KCa1.1 up-regulation. Strikingly, the Yoda1- or Dbtm-mediated small/transient Na+/K+-pump currents were robustly increased by their combination, implying a quick ion equilibration that may also be synchronized by hyperpolarization-induced voltage-sag, enabling faster repetitive firing. These novel findings demonstrate multi-channel/pump collaboration together to integrate neurotransmission at the cellular level for baroreflex, providing an afferent explanation in sexual dimorphic blood pressure regulation, and raising the caution regarding the individual drug concentration in multi-drug therapies to optimize efficacy and minimize toxicity.

Modelling stellar irradiances I: the transition regions of FGKM stars

ABSTRACT We employed advanced ionization equilibrium models that we developed in Dufresne et al. (2024), which include charge transfer and density effects, to model UV stellar irradiances for a sample of stars. Our sample includes $\epsilon$ Eridani (K2 V), $\alpha$ Centauri A (G2 V), Procyon (F5 V), and Proxima Centauri (M5.5 Ve). We measured line fluxes from STIS data sets and used O iv and O v as density diagnostics to find the formation pressure of ions in the transition region (TR) and adopted a simple differential emission measure (DEM) modelling. Our findings indicate significant improvements in modelling spectral lines from anomalous ions such as Si iv, C iv, and N v of the Li- and Na-like sequences, which produce the strongest lines in the UV. For example, the Si iv lines were under-predicted by a factor of 5 and now are within 40 per cent the observed fluxes. The improved models allow us to obtain for the first time reliable estimates of some stellar chemical abundances in the TR. We compared our results with available photospheric abundances in the literature and found no evidence for the first ionization potential (FIP) effect in the TR of our stellar sample. Finally, we compared our results with the solar TR that can also be described by photospheric abundances.

Tetraspanin 5 orchestrates resilience to salt stress through the regulation of ion and reactive oxygen species homeostasis in rice.

Tetraspanins (TETs) are integral membrane proteins, characterized by four transmembrane domains and a unique signature motif in their large extracellular loop. They form dynamic supramolecular complexes called tetraspanin-enriched microdomains (TEMs), through interactions with partner proteins. In plants, TETs are involved in development, reproduction and immune responses, but their role in defining abiotic stress responses is largely underexplored. We focused on OsTET5, which is differentially expressed under various abiotic stresses and localizes to both plasma membrane and endoplasmic reticulum. Using overexpression and underexpression transgenic lines we demonstrate that OsTET5 contributes to salinity and drought stress tolerance in rice. OsTET5 can interact with itself in yeast, suggesting homomer formation. Immunoblotting of native PAGE of microsomal fraction enriched from OsTET5-Myc transgenic rice lines revealed multimeric complexes containing OsTET5, suggesting the potential formation of TEM complexes. Transcriptome analysis, coupled with quantitative PCR-based validation, of OsTET5-altered transgenic lines unveiled the differential expression patterns of several stress-responsive genes, as well as those coding for transporters under salt stress. Notably, OsTET5 plays a crucial role in maintaining the ionic equilibrium during salinity stress, particularly by preserving an elevated potassium-to-sodium (K+/Na+) ratio. OsTET5 also regulates reactive oxygen species homeostasis, primarily by modulating the gene expression and activities of antioxidant pathway enzymes and proline accumulation. Our comprehensive investigation underscores the multifaceted role of OsTET5 in rice, accentuating its significance in developmental processes and abiotic stress tolerance. These findings open new avenues for potential strategies aimed at enhancing stress resilience and making valuable contributions to global food security.

CHIANTI—An Atomic Database for Emission Lines—Paper. XVIII. Version 11, Advanced Ionization Equilibrium Models: Density and Charge Transfer Effects

Version 11 of the chianti database and software package is presented. Advanced ionization equilibrium models have been added for low charge states of seven elements (C, N, O, Ne, Mg, Si, and S), and represent a significant improvement especially when modeling the solar transition region. The models include the effects of higher electron density and charge transfer on ionization and recombination rates. As an illustration of the difference these models make, a synthetic spectrum is calculated for an electron pressure of 7 × 1015 cm−3 K and compared with an active region observation from HRTS. Increases are seen in factors of 2–5 in the predicted radiances of the strongest lines in the UV from Si iv, C iv, and N v, compared to the previous modeling using the coronal approximation. Much better agreement (within 20%) with the observations is found for the majority of the lines. The new atomic models better equip both those who are studying the transition region and those who are interpreting the emission from higher-density astrophysical and laboratory plasma. In addition to the advanced models, several ion data sets have been added or updated, and data for the radiative recombination energy loss rate have been updated.

A measurement of the escaping ionising efficiency of galaxies at redshift 5

The escaping ionising efficiency from galaxies, $f_ esc ion $, is a crucial ingredient for understanding their contribution to hydrogen reionisation, but both of its components, $f_ esc $ and $ ion $, are extremely difficult to measure. We measured the average escaping ionising efficiency $ esc ion of galaxies at $z=5$ implied by the mean level of ionisation in the intergalactic medium via the Lyman-alpha forest. We used the fact that $ N ion UV f_ esc ion $, the product of the ionising output and the UV density $ UV $, can be calculated from the known average strength of the UV background and the mean free path of ionising photons. These quantities, as well as $ UV $, are robustly measured at $z We calculated the missing factor of $ esc ion at $z=5$ during a convenient epoch after hydrogen reionisation had been completed and the intergalactic medium had reached ionisation equilibrium but before bright quasars began to dominate the ionising photon production. Intuitively, our constraint corresponds to the required escaping ionising production from galaxies in order to avoid over- or under-ionising the Lyman-alpha forest. We obtained a measurement of $ esc ion /$erg $ at $z=5$ when integrating the $ UV $ down to a limiting magnitude $M_ lim =-11$. Our measurement of the escaping ionising efficiency of galaxies is in rough agreement with both observations of early galaxies and with most models.

Tunable Ferroionic Properties in CeO2/BaTiO3 Heterostructures.

Ferroionic materials combine ferroelectric properties and spontaneous polarization with ionic phenomena of fast charge recombination and electrodic functionalities. In this paper, we propose the concept of tunable polarization in CeO2-δ (ceria) thin (5 nm) films induced by built-in remnant polarization of a BaTiO3 (BTO) ferroelectric thin film interface, which is buried under the ceria layer. Upward and downward fixed polarizations at the BTO thin film (10 nm) are achieved by the lattice termination engineering of the SrO or TiO2 terminated Nb:SrTiO3 (NSTO or STN) substrate. We find that the ceria layer punctually replicates the polarization of the BTO interface via a dynamic reconfiguration of its intrinsic defects, i.e., oxygen vacancies and small polarons. Tunable oxidative or reducing properties (redox) also arise at the surface from the built-in polarization. Opposite polarities at the ceria termination tune the chemo-physical dynamics toward water molecule adsorbates. The inversion of the surface potential leads to a modulation of the water adsorption-desorption equilibrium and water ionization (splitting) redox overpotentials within ±400 mV at room temperature, depending on the ceria termination's charges. Such tunability opens up the perspectives of using ferroionics for wireless electrochemically enhanced catalysis.

Plasma diagnostics of supernova remnant 3C 400.2 by Suzaku observations

Abstract We report on the results of plasma diagnostics of the supernova remnant (SNR) 3C 400.2, which has been reported to have a recombining plasma by previous studies. For careful background estimation, we simultaneously fitted spectra extracted from the SNR and background regions and evaluated the SNR emission contaminating the background-region spectrum as well as the background emission in the source-region spectrum. The SNR emission is explained by the collisional ionization equilibrium plasma originating from the interstellar medium and the ionizing plasma originating from the ejecta, in contrast to previous studies. In addition, we found an unidentified X-ray source near the SNR, Suzaku J1937.4$+$1718, which is accompanied by an emission line at $\sim$4.4 keV with a $2.8\sigma$ confidence level. Because there is no striking atomic line at the energy in the rest frame, Suzaku J1937.4$+$1718 could be an extragalactic object with a redshifted Fe line.

COMPETITIVE ADSORPTION OF Fe2+, Pb2+, AND Zn2+ IONS FROM MULTI-METAL ION SOLUTION ON AMMONIUM OXALATE MODIFIED KAOLINITE CLAY

The competitive adsorption of Fe2+, Pb2+, and Zn2+ ions from mixed multi-metal aqueous solution on ammonium oxalate-modified kaolinite clay (AOK) was studied to determine the competitive influence of the metal ions on the adsorption of other metal ions. The kaolinite clay was modified by treating it with 0.2 M of ammonium oxalate solution at 50 oC. The adsorption of the metal ions was carried out using initial concentrations of 20, 35, and 50 mg L-1 in both the single and multi-metal ion solutions. The results revealed that at a low concentration of 20 mg L-1, the adsorption capacity for the uptake of the metal ions on AOK is non-competitive. At higher adsorbate concentrations of 35 and 50 mg L-1, the single to multi-metal ions equilibrium adsorption capacity ratio value obtained was less than 1. This indicated an antagonistic effect on competing for the adsorption site in the following order: Pb2+ (9.9 mg g-1) &gt; Fe2+ (3.85 mg g-1) &gt; Zn2+ (2.85 mg g-1). The outcome revealed that ammonium oxalate-modified kaolinite is a potential adsorbent for remediation of multi-heavy metal-laden wastewater with preferentially higher affinity for Pb2+ ions than other metal ions.