Conditional Equilibrium Constants Research Articles

Evaluation of Thermodynamic Model of Pd(II) Complex Formation with Isosaccharinic Acid

Palladium-107 is one of the selected radionuclides in the safety assessment of geological disposal of radioactive waste. Although isosaccharinic acid (ISA) forms strong complexes with many elements and enhances element solubility, the thermodynamic evaluation of the complex of Pd with ISA has not been conducted. In this study, the solubility of Pd(OH)2 at pH 8.5–12.5 in the presence of ISA was investigated under inert gas (N2) atmosphere. Furthermore, the coordination state of aqueous Pd and ISA was investigated by X-ray absorption and Fourier transform infrared spectroscopy, respectively. According to experimental results, the number of OH ligands in the mixed complex depends on pH. The thermodynamic model and conditional equilibrium constants of the Pd-ISA complex were estimated by slope analyses of solubility experiments at different pH levels and ionic strengths based on the specific ion interaction theory. Hence, the impact of complexation with ISA on Pd(II) solubility under disposal conditions could be quantified using the proposed thermodynamic models in this study.

Optimization of converting process for matte of oxidized nickel ores and sulfide copper ores joint smelting based on thermodynamic simulation

The paper presents the results obtained in the thermodynamic modeling of converting copper-nickel matte (11.3 wt.% Ni + Cu + + Co, 61.5 wt.% Fe, 25.9 wt.% S) produced by joint smelting of oxidized nickel ore and sulfide copper ore. Calculations were made in the approximation of ideal molecular solutions using the HSC Chemistry software package (Outotec Research Oy, Finland). The possibility of low-iron matte, converter slag and gas phase separation was shown. Estimated conditional equilibrium constants of exchange reactions between low-iron matte and slag (KNi/Fe = 0.004÷0.005, KCo/Fe = 0.056÷0.099) are close to ideal values. Statistical data processing was carried out using the mathematical experiment planning method. The converting temperature (t = 1100÷1300 °C) and iron and sulfur oxidation completeness level (q = 0.9÷1.0) determining the air and flux (SiO2) consumption were chosen as the factors to study. Obtained mathematical models of the process were used for its optimization. It was shown that the best converting performance can be achieved at t = 1150 °С and q = 0.950 when the low-iron matte contains 70.7 wt.% Ni + Cu + Co. At a yield of 8.74 % of the charge mass, the nickel, copper and cobalt recovery rates are 67.9, 97.9 and 9.1 %, respectively. The supposed air consumption (145.1 m3 (under normal conditions) per 100 kg of matte) and SiO2 (34.4 kg per 100 kg of matte) as well as slag yield (89.1 % of the charge mass) are close to working regime parameters. The results of the study confirm the possibility of cost-effective processing of poor copper-nickel matte and after experimental verification they can be used to develop automation flowcharts for converter departments at existing and designed production facilities.

Determination of ambient dissolved metal ligand complexation parameters via kinetics and pseudo-voltammetry experiments

Dissolved chemical speciation of metals in natural waters encompasses a wide range of inorganic and organic compounds including metal organic ligand complexes, ML. Because of the different filters used, “dissolved” speciation can range from simple metal-ligand complexes with an average size of about 0.66 nm (mass of <3 k-daltons) to nanoparticles of 1 to 100 nm to colloidal forms that are 10 to 200–400 nm in size. Strong metal-ligand, ML, complexes are normally considered to be in <1 nm size fraction. Over the last 3 decades, competitive ligand exchange – cathodic stripping voltammetry (CLE-CSV) titrations have been the method of choice to study complexation. These titrations primarily give information on the excess ligands in the sample rather than the actual ligand in MLunknown complexes because they require adding metal to the sample. Thus, metal-ligand CLE-CSV titrations do not provide much information on the actual ligand present in MLunknown. However, pseudovoltammetry provides the thermodynamic stability constant, Ktherm, for Zn, Cu, Cd and Pb as the MLunknown complex is destroyed by reduction at the Hg electrode to form metal(Hg). Pseudovoltammetry does not require the addition of any reagents to the sample, but cannot be performed for ions such as Fe(III) [and Mn(III)] because reduction of the ion results in the reduction of the metal ion in the complex without destroying MLunknown. For these ions, kinetic experiments to recover the metal in the ML complex can provide information on the MLunknown dissociation rate constant, kd, and the conditional equilibrium constant, KcondML′. In these kinetic experiments, a competitive ligand (Lcomp) is added to the sample, and over time the MLcomp complex is measured by CSV. If all the metal in MLunknown is recovered, kd of MLunknown can be determined. If only a portion of the metal in MLunknown is recovered, equilibrium is achieved and KcondML′ as well as kd can be determined in a single experiment; kf can then be calculated. We describe how these methods can be used to determine information on the actual MLunknown complex. We show that 7 thermodynamic, kinetic and speciation parameters (Ktherm, KcondML′, KcondM′L′, kf, kd, αM′, αL′) for MLunknown complexes can be derived from a combination of two of these experiments. The approaches described here are useful to determine these parameters for known ML complexes once a ligand has been isolated by advanced separation methods (e.g., LC-MS) and reacted with a metal of interest.

Species-Specific, pH-Independent, Standard Redox Potential of Selenocysteine and Selenocysteamine.

Microscopic redox equilibrium constants and standard redox potential values were determined to quantify selenolate-diselenide equilibria of biological significance. The highly composite, codependent acid-base and redox equilibria of selenolates could so far be converted into pH-dependent, apparent parameters (equilibrium constants, redox potentials) only. In this work, the selenolate-diselenide redox equilibria of selenocysteamine and selenocysteine against dithiothreitol were analyzed by quantitative nuclear magnetic resonance (NMR) methods to characterize the interfering acid-base and redox equilibria. The directly obtained, pH-dependent, conditional redox equilibrium constants were then decomposed by our method into pH-independent, microscopic constants, which characterize the two-electron redox transitions of selenocysteamine and selenocysteine. The 12 different, species-specific parameter values show close correlation with the respective selenolate basicities, providing a tool to estimate otherwise inaccessible site-specific selenolate-diselenide redox potentials of related moieties in large peptides and proteins.

Modeling trace metal partitioning and speciation at the sediment-water interface using a chemical equilibrium model

Isotherm adsorption experiments for Pb, Cd and Zn were carried out with coastal sediments from China under oxic sediment-water conditions. The conditional equilibrium constants (Kads) determined from the adsorption isotherms were found to be most strongly correlated with Mn oxides (MnOx) for Pb and Cd, and with particulate organic carbon (POC) for Zn. MnOx and POC were then used as the surrogate metal-binding phases in a sediment-water chemical equilibrium model (SCEM). The apparent equilibrium constants (βsed, Me⁎) of the SCEM were determined to be 109.56±0.41 for Pb (n = 9), 105.25±0.34 for Zn (n = 7), and 106.51±0.29 for Cd (n = 7). The SCEM was then used to predict the free metal ion activities ({Me2+}) in seawaters of Jinzhou Bay, China. The SCEM-predicted {Me2+} compared well with the measured ones for Pb and Zn in seawater. However, the predicted {Cd2+} was higher than measured, which may reflect a detoxification mechanism of marine organisms in Jinzhou Bay seawater. Overall, a model of this kind can be highly useful for predicting {Men+} in the overlying waters based on the surface sediment chemistry, and can contribute to the development of sediment quality guidelines by linking them with the corresponding water quality criteria.

An improved biotic ligand model (BLM) for predicting Co(II)-toxicity to wheat root elongation: The influences of toxic metal speciation and accompanying ions

In order to explore the effects of pH and accompanying ions on divalent cobalt (Co(II)) toxicity to the wheat root elongation, an improved biotic ligand model (BLM) to predict Co(II) toxicity was developed in solution culture. The results showed that the Co(II)-toxicity decreased with the increases of K+, Ca2+ and Mg2+ activities, and the activity of Na+ had no impact on the Co(II)-toxicity. High H+ activity reduced the Co(II)-toxicity by the competitive effect of H+, while low H+ activity affected the toxicity by the change in the type of Co(II) in culture medium. Co2+ and CoOH+ were toxic to wheat root elongation, and Co(OH)2 was not. On the basis of BLM theory, the conditional equilibrium constants for Co2+, CoOH+, H+, Mg2+, Ca2+, K+ were obtained: logKCoBL = 4.65, logKCoOHBL = 6.62, logKHBL = 4.53, logKMgBL = 3.65, logKCaBL = 2.36 and logKKBL = 2.17. Free Co2+ and CoOH+, and the competitions of K+, Mg2+ and Ca2+ were suggested to be considered when developing the Co(II)-BLM.

Thermodynamic model of Ni(II) solubility, hydrolysis and complex formation with ISA

AbstractThe solubility of β–Ni(OH)2(cr) was investigated atT=(22±2)°C in the absence and presence of α-isosaccharinic acid (ISA), the main degradation product of cellulose under alkaline pH conditions. Batch solubility experiments were performed from undersaturation conditions under inert gas (Ar) atmosphere. Solubility experiments in the absence of ISA were conducted in 0.5 and 3.0 M NaCl–NaOH solutions at 7.5≤ pHm≤13 (with pHm=–log10[H+]). XRD analyses of selected solid phases collected after completing the solubility experiments (≈300 days) confirmed that β–Ni(OH)2(cr) remains as solid phase controlling the solubility of Ni(II) in all investigated conditions. Based on the slope analysis (log10[Ni] vs. pHm) of the solubility data and solid phase characterization, the equilibrium reactions β–Ni(OH)2(cr)+2 H+⇔Ni2++2 H2O(l) and β–Ni(OH)2(cr)⇔Ni(OH)2(aq) were identified as controlling the solubility of Ni(II) within the investigated pHmregion. The conditional equilibrium constants determined from the solubility experiments at different ionic strengths were evaluated with the specific ion interaction theory (SIT). In contrast to the current thermodynamic selection in the NEA–TDB, solubility data collected in the present work does not support the formation of the anionic hydrolysis species Ni(OH)3−up to pHm≤13.0. Solubility experiments in the presence of ISA were conducted in 0.5 M NaCl–NaOH–NaISA solutions with 0.01 M≤[NaISA] ≤0.2 M and 9≤ pHm≤13. XRD analyses confirmed that β–Ni(OH)2(cr) is also the solid phase controlling the solubility of Ni(II) in the presence of ISA. Solubility data of all investigated systems can be properly explained with chemical and thermodynamic models including the formation of the complexes NiOHISA(aq), Ni(OH)2ISA−and Ni(OH)3ISA2−. The reported data confirm the low solubility (&lt;10−7M) of Ni(II) in hyperalkaline pH conditions representative of cementitious environments (10≤ pH ≤13), which increases to up to 10−5M in the presence of 0.2 M NaISA. These results significantly improve source term estimations for Ni(II) in environments relevant for the disposal of low and intermediate level radioactive waste (L/ILW). The chemical and thermodynamic models derived in this work can be implemented in geochemical models/calculations, and provide further confidence in the safety analysis of repositories for the disposal of L/ILW.

A new approach to determination of hydration equilibria constants for the case of [Er(EDTA)(H2O)(n)](-) complexes.

Two anionic complexes [Er(EDTA)(H2O)2](-) and [Er(EDTA)(H2O)3](-) were obtained in the form of the following compounds: [C(NH2)3]2[Er(EDTA)(H2O)2]ClO4·6H2O () and Na[Er(EDTA)(H2O)3]·5H2O (), respectively. The UV-vis-NIR absorption spectra of both monocrystals were measured at room temperature and at 4.2 K. The influence of the coordination number changes on intensities of the f-f transitions and the crystal field splitting of (2S+1)LJ multiplets are discussed. The weighted sum of molar absorption coefficients of f-f transitions in the spectra of and was used to reproduce the absorption bands of the Er(3+)-EDTA complex in aqueous solution. This approach allowed us to estimate that the complex in solution exists in 95% as the 8-coordinate [Er(EDTA)(H2O)2](-) species and in 5% as the 9-coordinate [Er(EDTA)(H2O)3](-) ones as well as to calculate the conditional hydration equilibrium constant (Kaqua) of the reaction: [Er(EDTA)(H2O)3](-) ↔ [Er(EDTA)(H2O)2](-) + H2O which is rather difficult to determine by using other methods. The Kaqua value was found to be 19 ± 1.

Certified reference material for ammonium ions in high-purity ammonium chloride: Influence of pH on coulometric titration of ammonium ions with electrogenerated hypobromite

No report has been published concerning reference materials of ammonium chloride in which ammonium ions were accurately determined, though ammonium chloride is widely used as a standard of ammonium ions. In the present paper, accuracy of the coulometric titration of ammonium ions with electrogenerated hypobromite was studied. The authors found that the pH of electrolyte solution significantly affected the accuracy of the assay of ammonium ions. Lower assays were obtained at pH more than 8.5 or less than 8.0: much higher pH values led to evaporation of ammonia and much lower pH ones led to insufficient hypobromite generation or insufficient conditional equilibrium constant of the reaction between ammonium ions and hypobromite. Ammonium ions in ammonium chloride were certified by coulometric titration under an appropriate condition, and chloride ions in it were also certified by gravimetric titration based on standard sodium chloride. The first certified reference material with ammonium assay was developed which enabled more accurate ammonium determination than that before.

A Combined Site‐Specific Metals Sorption and Transport Model for Intact Soil Columns

Simulation of metal attenuation in natural soil environments requires model descriptions of combined sorption and transport processes that are generally transferable to assess potential risk. A non‐electrostatic equilibrium ion exchange and surface complexation model (SCM), developed from batch experiments of Pb and Cd sorption to natural soils, was used to describe coupled transport in undisturbed soil column experiments. The model, based on soil mineral component additivity, was applied to reproduce metal transport without adjustment of sorption reactions or conditional equilibrium constants derived from batch experiments. Good agreement between model results and experimental soil column data for Pb and Cd uptake and release indicates that their transport at two different concentrations and flow rates can be described by sorption equilibria except for Pb at low concentration and slow flow rate. Model simulations were less successful in describing the transport behavior of Ca and Al, and effluent acidic pH, suggesting that additional reactions involving Al are needed. Fluctuations in effluent pH were not well simulated by the model, but model results were within ∼0.25 to 0.5 log units of observed pH. Model results suggest that sorption competition between Pb, Cd, and Ca (from the background electrolyte) was mostly associated with ion exchange sites attributed to weathered illite at acidic pH, with additional adsorption of Pb on hydroxyl sites of extractable Fe‐oxides. Simulations predicted net retention of Pb and Cd by soil columns from −9% to +13% of observed metal retention. This study demonstrates the ability to transfer a relatively small set of equilibrium sorption reactions and constants from batch to hydrodynamic column experiments under a limited set of flow conditions without arbitrary parameter fitting by using soil properties and mineralogy as constraints in model formulation.

Thermodynamic description of Np(VI) solubility, hydrolysis, and redox behavior in dilute to concentrated alkaline NaCl solutions

The solubility of Np(VI) was investigated in carbonate-free NaCl solutions (0.1 M &amp;le; I &amp;le; 5.0 M) at T = 22 &amp;plusmn; 2 &amp;deg;C to derive thermodynamic properties of aqueous species and solid compounds formed under alkaline conditions. The experimentally derived solubility curves can be divided into four main regions: (I) ~7 &amp;le; pHm &amp;le; ~9, showing a steep decrease in Np solubility with a slope (log [Np] vs. pHm) of &amp;ndash;3 or &amp;ndash;2 (depending on NaCl concentration); (II) ~9 &amp;le; pHm &amp;le; ~10.5, with a nearly pH-independent [Np]; (III) ~10.5 &amp;le; pHm &amp;le; ~13.5, showing an increase in the solubility with a well-defined slope of +1. A region (IV) with a slope &amp;ge; +2 was only observed at I &amp;ge; 1.0 M NaCl and pHm &amp;ge; ~13.5. The solubility-controlling solid Np phases were characterized by X-ray diffraction (XRD), quantitative chemical analysis, thermogravimetric analysis and scanning electron microscopy-energy-dispersive spectrometry (SEM-EDS), confirming the presence of anhydrous Na2Np2O7(cr) in regions II and III. The same solid phase was identified in region I except for the system in 0.1 M NaCl, where a NpO2(OH)2&amp;middot;H2O(cr) phase predominates. XRD patterns of this solid phase show a very good agreement with that of metaschoepite (UO3&amp;middot;2H2O), highlighting the similarities between Np(VI) and U(VI) with respect to solid phase formation and structure. Based on the analysis of solubility data, solid phase characterization and chemical analogy with U(VI), the equilibrium reactions 0.5 Na2Np2O7(cr) + 1.5 H2O ⬄ Na+ + NpO2(OH)3 &amp;ndash; and 0.5 Na2Np2O7(cr) + 2.5 H2O ⬄ Na+ + NpO2(OH)4 2&amp;ndash; + H+ were identified as controlling Np(VI) solubility in regions II and III, respectively. The predominance of NpO2 + in the aqueous phase of region I (quantified by UV&amp;ndash;vis/NIR) indicates the reductive dissolution of Np(VI) [either as Na2Np2O7(cr) or NpO2(OH)2&amp;middot;H2O(cr)] to Np(V)aq. Oxidation to Np(VII) can explain the experimental observations in region IV, although it is not included in the chemical and thermodynamic models derived. The conditional equilibrium constants determined from the solubility experiments at different ionic strengths were evaluated with both the specific ion interaction theory (SIT) and Pitzer approaches. Thermodynamic data for aqueous Np(VI) species [NpO2(OH)3 &amp;ndash; and NpO2(OH)4 2&amp;ndash;] and solid compounds [Na2Np2O7(cr) and NpO2(OH)2&amp;middot;H2O(cr)] that are relevant under alkaline conditions were derived. These data are not currently included in the Nuclear Energy Agency-Thermochemical Database (NEA-TDB) compilation.

A Voltammetric Study on the Adsorption of Cd(II) and Zn(II) on Marine MicroalgaeTetraselmis gracilis(Kylin) Butcher

Proton and metal binding capacities of living cells of the microalgae Tetraselmis gracilis were determined by potentiometric titration and anodic stripping voltammetry, respectively. Binding of Cd(II) and Zn(II) was studied in seawater (pH 8.2) by additions of either single metallic species or binary mixtures. Computation of metal concentrations considered the cell-metal aggregates as slow diffusing. Adsorption capacities and conditional equilibrium constants were 2.9 ± 0.3 µmol g-1 and 6.9 ± 0.3 L g-1 for Cd(II) and 18.5 ± 0.9 µmol g-1 and 8.8 ± 0.2 L g-1 for Zn(II), respectively. For titrations with binary mixtures of Cd(II) and Zn(II), the adsorption capacity of Cd(II) decreased to 0.14 ± 0.01 µmol g-1 and that for Zn(II) to 15.9 ± 1.1 µmol g-1. The results suggest that binding of Zn(II) inhibits that of Cd(II). Under conditions of depleted Zn(II), the alga surface binds Cd(II), a process that can lead to bioaccumulation.

Quantifying Differences in the Impact of Variable Chemistry on Equilibrium Uranium(VI) Adsorption Properties of Aquifer Sediments

Uranium adsorption–desorption on sediment samples collected from the Hanford 300-Area, Richland, WA varied extensively over a range of field-relevant chemical conditions, complicating assessment of possible differences in equilibrium adsorption properties. Adsorption equilibrium was achieved in 500–1000 h although dissolved uranium concentrations increased over thousands of hours owing to changes in aqueous chemical composition driven by sediment-water reactions. A nonelectrostatic surface complexation reaction, >SOH + UO22+ + 2CO32- = >SOUO2(CO3HCO3)2–, provided the best fit to experimental data for each sediment sample resulting in a range of conditional equilibrium constants (logKc) from 21.49 to 21.76. Potential differences in uranium adsorption properties could be assessed in plots based on the generalized mass-action expressions yielding linear trends displaced vertically by differences in logKc values. Using this approach, logKc values for seven sediment samples were not significantly different. However, a significant difference in adsorption properties between one sediment sample and the fines (<0.063 mm) of another could be demonstrated despite the fines requiring a different reaction stoichiometry. Estimates of logKc uncertainty were improved by capturing all data points within experimental errors. The mass-action expression plots demonstrate that applying models outside the range of conditions used in model calibration greatly increases potential errors.

Solubility of tetravalent actinides in alkaline CaCl2solutions and formation of Ca4[An(OH)8]4+complexes: A study of Np(IV) and Pu(IV) under reducing conditions and the systematic trend in the An(IV) series

AbstractThe solubility of Np(IV) and Pu(IV) hydrous oxides was studied at 22±2 °C under reducing conditions in alkaline CaCl2solutions. Redox conditions were adjusted either with 2 mM Na2S2O4or additions of iron powder. In 2.0 and 4.5 M CaCl2and pHc=11–12, the neptunium and plutonium concentrations increase with a slope of +4 (log[An]vs. pHc) as expected for the formation of the complex Ca4[An(OH)8]4+recently identified for Th(IV). At CaCl2concentrations ≤1.0 M this effect is negligible for both Np(IV) and Pu(IV). The conditional equilibrium constants log*Ks,(4,1,8)for the reactionAn(OH)4(am) + 4 H2O + 4 Ca2+⇔ Ca4[An(OH)8]4++ 4 H+are evaluated with the SIT and Pitzer model using the parameters derived from analogous data for Th(IV) in 0.5–4.5 M CaCl2. The log*K°s,(4,1,8)values and the complex formation constants logβ°(4,1,8)follow systematic trends in the series Th(IV), Np(IV) and Pu(IV) which allows the estimation of the corresponding data for U(IV).

Extraction of Nitric Acid into Alcohol: Kerosene Mixtures

Nitric acid extraction from 0.1 mol/L – 5 mol/L nitric acid into varied volume fractions (5%–100%) of long-chain aliphatic alcohols (1-hexanol, 1-octanol, 2-ethylhexanol, 1-decanol) in alkanes (different kerosenes, n-dodecane, isooctane) was measured. At equal molar alcohol concentration, 1-hexanol, 1-octanol, and 1-decanol extract equal amounts of nitric acid. The amount of nitric acid extracted into 2-ethylhexanol is approxmately half compared to 1-octanol. The alkane does not influence nitric acid extraction. Extraction can accurately be calculated taking into account the formation of a species (HNO3)(ROH)2. Due to the change in diluent properties with alcohol volume fraction, conditional equilibrium constants must be used.

In situ adsorption of mercury, methylmercury and other elements by iron oxyhydroxides and organic matter in lake sediments

Samples of authigenic material, sediment overlying water and oxic surface sediment (0–0.5-cm depth) from a perennially oxygenated lacustrine basin were analysed to investigate which solid phases are important for binding a suite of trace elements (Ag, As, Ca, Cd, Cu, Hg, In, methylmercury (MeHg), Mg, Mo, Pb, Sb and Zn). The authigenic material, which was collected with inert Teflon sheets deployed for several years across the sediment–water interface, contained mainly poorly crystallized Fe oxyhydroxides and natural organic matter, presumably humic substances derived from the watershed. Manganese oxyhydroxides were not present in the collected authigenic material due to the slightly acidic condition (pH = 5.6) of the lake that prevents the formation and recycling of these compounds. Conditional equilibrium constants for the adsorption of cationic (KFe–M) and anionic (KFe–A) trace elements onto the authigenic Fe oxyhydroxides were estimated from their concentrations in the authigenic material and in bottom water samples. These field-derived values of KFe–M and KFe–A were compared with those predicted by the surface complexation model, using laboratory-derived intrinsic adsorption constants and the water composition at the study site. Equilibrium constants (KPOM–M) were also calculated for the adsorption of the cationic trace elements onto the humic substances contained in the diagenetic material. The field-derived values of KPOM–M were compared to those predicted by the speciation code WHAM 6 for the complexation of the trace elements by dissolved humic substances in the lake. Combining the results of the present study with those on the distributions of trace elements in the porewater and solid-phase sediments reported in previous studies at the same site, it was determined whether the trace elements bind preferentially to Fe oxyhydroxides or natural organic matter in oxic sediments. The main inferences are that the anionic trace elements As, Mo and Sb, as well as the cationic metal Pb are preferentially bound to the authigenic Fe oxyhydroxides whereas the other trace elements, and especially Hg and MeHg, are preferentially bound to the humic substances.

TRLFS study on the complexation of Cm(III) with nitrate in the temperature range from 5 to 200 °C

The formation of aqueous Cm(III) nitrate complexes is studied in the temperature range from 5 to 200 °C by time resolved laser fluorescence spectroscopy (TRLFS). The experiments are performed in a custom build high pressure and high temperature fluorescence cell. The complex formation is measured at nitrate concentrations ranging from 0.10 to 4.61 mol/kg H2O. The mono- and dinitrate complexes are quantified by peak deconvolution of the fluorescence spectra and the complexation constants are determined as a function of the temperature. The conditional equilibrium constants are extrapolated to zero ionic strength using the specific ion interaction theory (SIT) and the thermodynamic standard state data (ΔrH°m, ΔrS°m, ΔrG°m, ΔrC°p,m) are determined from the temperature dependence of the equilibrium constants at I=0. The equilibrium constants up to 75 °C are well described by the Van´t Hoff equation (ΔrH°m independent of T and ΔrC°p,m=0). Modelling of the data at higher temperatures requires an extended equation including a term for the heat capacity changes (ΔrC°p,m).

Spectral studies on the interaction of yttrium ion with the ligands of phenolic groups: N, N′-Ethylenebis[2-( o-hydroxyphenolic)glycine] and N, N′-di(2-hydroxybenzyl)ethylenediamine- N, N′-diacetic acid

The interactions of yttrium with N, N′-ethylenebis[2-( o-hydroxyphenolic)glycine] (EHPG) and N, N′-di(2-hydroxybenzyl)ethylenediamine- N, N′-diacetic acid (HBED) are investigated by using UV difference and fluorescence spectra methods in 0.1 M N-2-hydroxyethylpiperazine- N-2-ethanesulfonic acid (Hepes) at pH 7.4. Yttrium binding produces two UV difference peaks near 240 and 294 nm, respectively, that both are the characteristic of phenolic groups binding to yttrium. The molar extinction coefficient of Y-EHPG and Y-HBED are (15.7 ± 0.40) × 10 3, (15.8 ± 0.80) × 10 3 cm −1 M −1 at 240 nm, respectively. Using EDTA as a competitor the obtained conditional equilibrium constants of the complexes are log K Y-EHPG = 15.07 ± 0.32 and log K Y-HBED = 15.18 ± 0.26, respectively. However, the effects of yttrium binding on the fluorescence intensity of EHPG and HBED are quite different, the former showing a decrease but the latter an increase.

Sorption of palladium(II), rhodium(III), and platinum(IV) on Fe 3O 4 nanoparticles

The adsorption of palladium(II), rhodium(III), and platinum(IV) from diluted hydrochloric acid solutions onto Fe 3O 4 nanoparticles has been investigated. The parameters studied include the contact time and the concentrations of metals and other solutes such as H + and chloride. The equilibrium time was reached in less than 20 min for all metals. The maximum loading capacity of Fe 3O 4 nanoparticles for Pd(II), Rh(III), and Pt(IV) was determined to be 0.103, 0.149, and 0.068 mmol g −1, respectively. A sorption mechanism for Pd(II), Rh(III), and Pt(IV) has been proposed and their conditional adsorption equilibrium constants have been determined to be log K = 1.72 , 1.69, and 1.84, respectively. Different compositions of eluting solution were tested for the recovery of Pt(IV), Pd(II), and Rh(III) from Fe 3O 4 nanoparticles. It was found that 0.5 mol L −1 HNO 3 can elute all of the metal ions simultaneously, while 1 mol L −1 NaHSO 3 was an effective eluting solution for Rh(III), and 0.5 mol L −1 NaClO 4 for Pt(IV). In competitive adsorption, the nanoparticles showed stronger affinity for Rh(III) than for Pd(II) and Pt(IV).

UV and fluorescence spectral changes induced by neodymium binding of N,N′-ethylenebis[2-(o-hydroxyphenolic)glycine] and N,N′-di(2-hydroxybenzyl)ethylenediamine-N,N′ diacetic acid

In 0.01M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (Hepes), pH 7.4 and room temperature, the binding of neodymium to N,N′-ethylenebis[2-(o-hydroxyphenolic)glycine] (EHPG), or N,N′-di(2-hydroxybenzyl)ethylenediamine-N,N′ diacetic acid (HBED) had been studied from 210 to 330nm by means of difference UV spectra. Two peaks at 240 and 292nm appear in difference UV spectra after neodymium binding to EHPG or HBED. The 1:1 stable complex can be confirmed from spectral titration curves. The molar extinction coefficient of Nd–EHPG and Nd–HBED complexes are ΔɛNd–EHPG=(12.93±0.21)×103cm−1M−1, ΔɛNd–HBED=(14.45±0.51)×105cm−1M−1 at 240nm, respectively. Using EDTA as a competitor, the conditional equilibrium constants of the complexes are logKNd–EHPG=11.89±0.09 and logKNd–HBED=12.19±0.15, respectively. At the same conditions, fluorescence measurements show that neodymium binding to EHPG leads to a quenching of the fluorescence of EHPG at near 310nm. However, there is no obvious fluorescence change of HBED at 318nm with the binding of neodymium to HBED.