Value Of Solubility Product Research Articles

Heavy Metal Content in the Seagrass <i>Zostera marina</i> Linnaeus, 1753 in Voevoda Bay (Amur Bay, Sea of Japan)

Concentrations of heavy metals in live and dead leaves, stems, rhizomes and roots of the seagrass Zostera marina Linnaeus, 1753 were analyzed in the study. On the basis of concentration, the metals were arranged in the following row: Fe Mn Zn Cu Pb Ni Cd. Differences in Fe, Pb, Ni, and Cd for live and dead leaves were revealed. The factor of sediment enrichment in heavy metals from dead leaves was calculated. The enrichment factor for the metals under study changed in the row Cu Pb Zn Ni Mn, and the value of solubility product [–lg(SP)] for sulfides of the above-listed metals changed in the same row.

Thermodynamics of the Eu(III)-Mg-SO4-H2O and Eu(III)-Na-SO4-H2O systems. Part I: solubility experiments and the full dissociation Pitzer model.

The solubility of Eu(III) was investigated under undersaturated conditions in acidic, dilute to concentrated MgSO4 and Na2SO4 solutions at T = (22 ± 2) °C. After attaining equilibrium conditions, solid phases were characterized by a multi-method approach, including X-ray diffraction (XRD), Raman and infrared (IR) spectroscopy, quantitative chemical analysis (ICP-OES) and thermogravimetric analysis (TG-DTA). A total of 45 solubility samples were investigated for the systems Eu2(SO4)3-MgSO4-H2O (19 samples) and Eu2(SO4)3-Na2SO4-H2O (26 samples). Eu2(SO4)3·8H2O(cr) was found to control the solubility of Eu(III) in all investigated MgSO4 solutions, as well as in dilute Na2SO4 systems. The transformation of Eu2(SO4)3·8H2O(cr) into the double salt Na2Eu2(SO4)4·2H2O(cr) was observed at mNa2SO4 > 0.01 mol kg-1. The latter phase is characterized by significantly lower solubility. Based on these experimental solubility measurements, thermodynamic and activity models were proposed based on the Pitzer equations considering the full dissociation of the Eu(III) species in MgSO4 and Na2SO4 aqueous solutions, i.e. deliberately excluding Eu(III)-sulfate complex formation. A combination of the geochemical calculation code PhreeSCALE and the parameter estimation code PEST was used to determine the values of solubility products and binary and ternary specific interaction parameters (β(0)ij, β(1)ij, Cϕij, θik, Ψijk).

A kinetic descriptor to optimize Co-precipitation of Nickel-rich cathode precursors for Lithium-ion batteries

This work proposes a kinetic descriptor, reaction quotient to equilibrium constant ratio ( Q / K ), to optimize co-precipitation of nickel-rich hydroxides. Ammonia concentration of 1.0 M rendered the Q / K close to 1, where the crystals can grow efficiently by Ostwald ripening. The enhanced morphological uniformity and performances of the nickel-rich cathode validate the effectiveness of this methodology. • A descriptor to optimize co-precipitation of precursors for nickel-rich cathodes. • Well-ordered hydroxide particles can grow by Ostwald ripening if Q / K approaches 1. • The enhanced morphology and performances validate the suggested descriptor. Nickel-rich cathodes are advantageous for lithium-ion batteries (LIBs) due to their exceptional energy densities at lower cost. In general, particles' shape and crystal structure greatly influence the electrochemical performances of cathode active materials. In this regard, co-precipitation can afford secondary particles made of highly crystalline primary particles with uniform composition. Auxiliary complexing agent such as ammonia provides sufficient time for the well-ordered nucleation and growth of primary and secondary particles by retarding the hydroxide formation. Herein we suggest the reaction quotient ( Q ) to equilibrium constant ( K ) ratio, as a kinetic descriptor for the effective nucleation and crystal growth of metal hydroxide. Based on the cumulative formation constant and the solubility product values of each metal ion, about 1.0 M NH 3 concentration rendered the Q / K ratio close to 1, which implies balanced precipitation and dissolution of metal hydroxide that provides sufficient time for the crystal growth. In accordance with the theoretical expectation, co-precipitation at 1 M NH 3 rendered particles with uniform shape and size. And the resultant nickel-rich cathode outperformed other samples co-precipitated at different NH 3 concentrations, in terms of significantly higher discharge capacity, cycle stability, and rate capability.

Dependence of the potentiometric response of PEDOT(PSS) on the solubility product of silver salts

The potentiometric response of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) deposited on glassy carbon (GC), i.e. GC/PEDOT(PSS), was studied before and after conditioning in silver nitrate solution. The deposition of silver in the PEDOT(PSS) film was characterized by SEM/EDAX and cyclic voltammetry. The potentiometric response of the Ag-conditioned GC/PEDOT(PSS) electrode was dependent on the nature of the anion present in the calibration solutions. In cases where anions do not form sparingly soluble silver salts, a cationic response was observed for GC/PEDOT(PSS), as expected. However, an anionic response was observed in solutions containing anions (X−) that can form sparingly soluble salts with silver ions (AgX). Furthermore, the measured potentials in X− solutions followed the solubility product values of AgX. The agreement between the experimental and thermodynamic data was excellent. This validates the hypothesis of equilibrium existing between Ag+ ions in the polymer film (due to conditioning) and Ag+ ions in the solution. The Ag-conditioned GC/PEDOT(PSS) electrode covered with a potassium ion-selective membrane (GC/PEDOT(PSS)/K+-ISM) showed a cationic response in KCl solutions with close to Nernstian slope value.

Status of multielement in water of the river Buriganga, Bangladesh: Aquatic chemistry of metal ions in polluted river water

The peripheral rivers of Dhaka city became highly polluted because of industrialization and urbanization to a greater extent in the last few decades. Thus, an attempt has been taken to measure 48 elements in water of the river Buriganga using the ICP-MS method for the first time. Accordingly, it could be the reference values for future research in Bangladesh. Out of the 48 elements, the following metals are given more attention because of their detrimental effects on living organisms and for discussing their aquatic chemistry in polluted water body: Be, Na, Al, Cr, Mn, Fe, Ni, Cu, Zn, Cd, Ba, Hg, Pb, Bi and U. Results revealed that metals’ concentrations in water in the monsoon were less than that of the winter, however, Cr and Fe were found at below detection limits in the winter that is unexpected. Physicochemical parameters of the river water such as pH, dissolved oxygen play vital roles for hydrolysis reactions in the stagnant water body. Hydrolyzed products of metal ions having low values of solubility products ( K sp ), for example, iron(III)hydroxide, chromium(III)hydroxide, phase out through precipitation reactions. This study also detects and quantifies total concentrations of Hg and U in water of the river Buriganga for the first time. PCA and correlation matrix results provided potential sources of the relevant metals. Mechanisms of hydrolysis and precipitation reactions for metal ions in the polluted river water are also discussed.

Synthesis of calcium orthophosphates by chemical precipitation: re-evaluation of the solubility products of hydroxyapatites

For the first time, a linear correlation was found between the specific solubility products of calcium orthophosphates and their molar ratio Ca/P (the correlation coefficient being R2=0.9742). Nevertheless, the values of solubility products of tricalcium phosphate (pKS=26–29), hydroxyapatite (pKS=116.8) and its Ca-deficient forms (pKS~85) cannot be correlated. We proposed to adjust these values of solubility products in accordance with the obtained correlation dependence as follows: pKS is 40, 155 and 114–155 for tricalcium phosphate, hydroxyapatite and Ca-deficient hydroxyapatite, respectively. The calculated solubility diagrams (isotherms) with adjusted solubility products agree reasonably well with the known experimental data, which could not be explained and were not accepted by the scientific community up to the present day. Based on well-known ideas of chemical thermodynamics, we suggested an explanation of the correlation between the specific solubility products of calcium orthophosphates and their molar ratios Ca/P. The developed model of dissolution process is based on a comparison between crystal lattice energy and hydration energy of calcium ions. The experiments on chemical precipitation of orthophosphates were performed at pH 4–10 and at a constant molar ratio Ca/P=1.5; their results showed that only one single metastable form, calcium hydrogen phosphate, is precipitated within the entire pH range at the temperature of 200С. The obtained sediments were isothermally exposed at the temperature of 2500С in a mother solution for 6 hours; such a treatment resulted in a full dehydration of calcium hydrogen phosphate and its partial transformation into a more stable form (hydroxyapatite). The mass fraction of hydroxyapatite increases from 14% to 70% and the degree of crystallinity decreases from 20% to 5% with increasing the value of solution pH. It was concluded that the rate of phase transition from CaHPO4 to Ca10(PO4)6(OH)2 in influenced by the concentration of hydroxide ions that are incorporated into a crystal lattice of hydroxyapatite.

FeNiSx@MoS2 Heterostructure: A Bioinspired Nonprecious Electrocatalyst for the Hydrogen Evolution Reaction in Acidic and Basic Media

AbstractFeNiSx@MoS2 (INSMS) heterostructure is designed and developed to achieve a structural and functional analogue with biological enzyme active sites that catalyze hydrogen production. A two‐step synthetic method is applied to develop the heterostructure. As‐prepared INSMS integrates FeNiSx (INS) nanosheets on the surface of the MoS2 nanopetals. The electrocatalyst demonstrates robust hydrogen evolution reaction (HER) activity due to the selective decoration of INS nanosheets over MoS2, owing to their different solubility product values. Two different phases of INS nanosheets are formed in INSNS due to the topotactic transition of INS nanosheets, as confirmed by the XRD and HR‐TEM analysis. In the HER, INSMS requires overpotentials of 110 and 155 mV at 10 mA cm−2 with Tafel slope values of 34 and 93 mV dec−1 in acidic and alkaline medium, respectively. This improved electrochemical performance is generated by the modification of the electron‐hole separation at the heterostructure interface and interlinked active edge sites at the interface.

Potential dependence of silver passivation start on the solution composition

Based on the analysis of modern experimental data dedicated to anodic behaviour of silver in solutions containing halide anions, an equation establishing the dependence of the peak-start potential of silver passivation on the potential scan rate, ion halide concentration, and solubility product of silver halide, was obtained. It follows from the proposed equation that the smaller the solubility product value and the potential scan rate are, and the greater the concentration of anion halides is, the anode passivation occurs at a lower potential value. The equation agrees with the experimental data presented in the modern literature rather well. The results can be used in studies aimed at finding the optimal modes of anodic treatment of metals, the development of measures to increase the corrosion resistance of materials, as well as for the quantitative analysis of chlorides, bromides and iodides in solution, including their co-occurrence.

Improving potassium recovery with new solubility product values for K-struvite

Crystallisation of ammonium (NH4) struvite is a viable method of recovering valuable nutrients such as nitrogen and phosphorus from waste waters. Little work has been done on potassium (K) recovery since neither is it an environmental pollutant nor is society facing global potassium shortages. However, potassium is an essential plant macronutrient, worldwide imbalances in nutrient and fertiliser use exist and there is a need for a slow-release potassium fertiliser. The goal of this research was to develop a fundamental understanding of K-struvite formation as the first step in recovering potassium to allow for producing a full complement nitrogen–phosphorus–potassium slow-release fertiliser from waste waters. Specific objectives included determination of solubility product values for K-struvite at 10, 25 and 35°C. By using these values, optimal supersaturation conditions for K-struvite precipitation were modelled using aqueous equilibrium modelling software and subsequently validated by experiment. The new solubility product values confirmed that K-struvite was less soluble than previously reported. This research adds to the body of literature in nutrient recovery by furthering the understanding of K-struvite formation.

A Novel Kinetic Method to Measure Apparent Solubility Product of Bulk Human Enamel.

Introduction: Tooth enamel mineral loss is influenced by its solubility product value, which is fundamental to the understanding of de- and remineralization resulting from a carious or erosive challenge. Published pKsp values for human enamel and hydroxyapatite range from 110 to 126 suggesting a heterogeneous nature of enamel solubility. However, this range of values may also result from the variety of methods used, e.g., some authors reporting values for suspensions of enamel powder and others for bulk enamel. The aim of this study was to develop a method to measure the solubility of bulk human enamel under controlled in vitro conditions simulating demineralization behavior of enamel within the oral environment using scanning microradiography (SMR). SMR was used to monitor real-time changes in enamel demineralization rates at increasing calcium concentrations in a caries simulating demineralization solution until the concentration at which thermodynamic equilibrium between enamel and solution was achieved.Method: 2 mm thick caries free erupted human enamel slabs with the natural buccal surfaces exposed were placed in SMR cells exposed to circulating caries-simulating 2.0 L 0.1 M pH = 4.0 acetic acid, at 25°C. SMR was used to continuously measure in real-time the decrease in mineral mass during the demineralization at 5 different points from on each slab. Demineralization rates were calculated from a linear regression curve of projected mineral mass against demineralization time. Changes in the demineralization rates were monitored following a series of successive increases in calcium (and phosphate at hydroxyapatite stoichiometric ratios of Ca:P 1.67) were added to the demineralizing solution, until demineralization ceased. The pH was maintained constant throughout.Results: Demineralization halted when the calcium concentration was ~30 mM. At higher calcium concentrations, mineral deposition (remineralization) occurred. By comparison with results from speciation software calculations for the calcium phosphate ternary system, this result suggests that the bulk solubility product of enamel (pKspBEnamel) under the conditions used is 121.Discussion: The apparent pKspBEnamel under these conditions was higher than many previous reported values, and much closer to those previously reported for HAp. However, this is a bulk value, and does not reflect that enamel is a heterogeneous material, nor the influence of ionic inclusions.

Self-supported CuS nanowire array: an efficient hydrogen-evolving electrode in neutral media

A self-supported copper sulfide (CuS) nanowire array (NWA) of hierarchical and porous structure has been developed on Cu foil via two consecutive liquid-solid reactions at room temperature. The composition, structure and morphology of the as-prepared CuS NWA samples have been systematically investigated by a series of techniques. When applied as cathode for the hydrogen evolution reaction (HER) in neutral solution, the optimized CuS NWA electrode exhibits excellent HER performance with high long-term stability. To achieve current densities of 10 and 100mAcm−2, it requires overpotentials of only ∼97 and ∼226mV, respectively. The excellent catalytic performance of CuS NWA toward HER is attributable to the binder-free electrode construction strategy, the unique porous nanowire array structure, and the small solubility product (Ksp) value of CuS that guarantees the high catalyst stability.

Artifact preservation and post-depositional site-formation processes in an urban setting: a geoarchaeological study of a 19th century neighborhood in Detroit, Michigan, USA

A geoarchaeological study was carried out to assess levels of artifact deterioration occurring in a historic-period urban soil during the 20th century. The study site is a former house-lot in a park created in 1919 by demolition of a residential community in Detroit, Michigan, USA. The results show that despite nearly a century of burial in an urban soil impacted heavily by pollution and other anthropogenic activity, many 19th century artifacts are remarkably well preserved. The observed weathering stability sequence of glass > bone > mortar > plaster > paint is consistent with decreasing solubility product values of the corresponding principal mineral constituent (glass < apatite < portlandite < gypsum < cerrusite). Even severely weathered 19th century nails and mortar can often be distinguished using optical petrographic and SEM-EDAX methods. The excellent state of artifact preservation is attributed to a calcareous soil microenvironment, and artificial compaction which limited the weathering effects of water and oxygen. Artifact preservation was further enhanced by burial beneath a thick biomantle created by the casting activity of an invasive species of earthworm. However, Lumbricus terrestris may now pose the greatest threat to artifact preservation because casting and burrowing activities are decreasing bulk density, and promoting the diffusion of air and water into the soil. Early excavation is recommended to recover artifacts in soils impacted by the combined effects of urban pollution and earthworm burrowing. Anthropogenic microparticles smaller than those normally classified as microartifacts were found to be useful indicators of human occupation.

SOLVENT EFFECTS ON THE THERMODYNAMICS OF SOLVATION OF BARIUUM DIPHENYLAMINESULFONATE IN ETHANOL-WATER MIXED SOLVENTS

The aim of this study was to determine the thermodynamic functions, Gibbs energy, enthalpy, and entropy for the solution processes of barium diphenylaminesulfonate in the mixed solvent (ethanol+water) were calculated from solubility values obtained at temperatures ranging from 293.15 K to 308.15 K. The respective thermodynamic, functions for mixing and solvation processes, as well as the activity coefficients for the solute were calculated. The solubility of solutes in mixed solvents depends primarily on the solvation of the solutes or their constituent ions by the components of the solvent mixtures. In this study, the solubility of this barium diphenyla1ninesuifonate in the mixed solvent (ethanol + water by value percent of ethanol= 0, 20, 40, 60, 80, and 100% by volume), was determined at different temperature by the solvent evaporation method. The results enable us to estimate the value of thermodynamic solubility product, Kop(th), of barium diphenylaminesulfonate in the mixed solvent. In addition, Gibbs energy, enthalpy, entropy for the solution processes, and free energies of transfer of barium diphenyla1ninesulfonate units from water to the ethanol solutions were also calculated in order to estimate the contributions of solute-solvent interactions related to ion association are based on changes in the electrostatic properties of the solvent, solute, and ion salvation as itself as on the ionic strength of the medium.

Tungsten solubility in evolved granitic melts: An evaluation of magmatic wolframite

A variety of parameters that potentially control the solubilities of synthetic hubnerite (MnWO4) and ferberite (FeWO4) in haplogranitic melts rich in fluxing compounds have been determined at 200MPa in order to test the hypothesis that wolframite can occur as a magmatic mineral. The melts, considered representative of highly evolved pegmatites, contain 1.1, 1.7 and 2.02wt.% of Li2O, P2O5, and B2O3, respectively. Although the molar Al/(Na+K) ratio is one, if Li is considered to be an alkali element the molar Al/(Na+K+Li) (ASILi) of the melt is 0.88, and the melt is peralkaline. Hubnerite and ferberite solubilities at 800°C are strongly controlled by melt composition. They are much lower in subaluminous melt, (ASILi=1.05), than in peralkaline melt. By contrast, hubnerite and ferberite solubilities are nearly independent of the fluorine content of the melt, for up to 8wt.% F. Hubnerite and ferberite solubilities at 800°C are also nearly independent of oxygen fugacity over a logfO2 range of approximately Ni–NiO−3 to Ni–NiO+2, which implies that the predominant oxidation state of tungsten in the melts is +6, even at moderately reduced conditions. A series of experiments on haplogranitic melt, rich in fluxing compounds, with 0 and 6wt.% F at 850–650°C shows that temperature strongly influences hubnerite solubility, e.g., the solubility product of hubnerite (Ksphub) in the melts with 6wt.% F decreases from 71.0±7.9×10−4mol2/kg2 at 850°C to 4.4±2.3×10−4mol2/kg2 at 650°C.Our experimental results show that ferberite solubilities are much higher than those of hubnerite with the same composition of melt, but the Mn, Fe and W concentrations in natural melt inclusions indicate that these melts were undersaturated with wolframite at 800°C. However, flux-rich melts crystallize at lower temperatures in nature and the occurrence of natural, magmatic wolframite was evaluated by comparing experimental solubility product values extrapolated to 500°C with wolframite activities at these temperatures. Magmatic wolframite is unlikely in flux-rich peralkaline melts but by contrast, flux-rich subaluminous to peraluminous melt inclusions appear to have been saturated with wolframite at approximately 500°C. Because of the strong temperature dependence of wolframite solubility the dominant effect of fluxing compounds is to lower the solidus temperature of the melt.

Solubility and Solubility-Limiting Solid Phase in M(IV)-OH-Dicarboxylate Ternary Aqueous System

The solubilities of thorium and zirconium in the presence of several dicarboxylic acids were investigated as functions of the hydrogen ion concentration (pHc). In the presence of succinic, glutaric, and adipic acids, few Th colloidal species larger than 2 nm were observed, and the apparent solubility appeared to be controlled by thorium-dicarboxylate solid phases. The Th solubility in the presence of fumaric (trans-butenedioic) acid was similar to that in the presence of succinic (butanedioic) acid, whereas no solid phase was observed under pHc 4 in the presence of maleic (cis-butenedioic) acid. In the presence of succinic and glutaric acids, the contributions of Zr colloidal species to the apparent solubility were observed, possibly due to the stronger hydrolysis reaction than that of Th. The solubility product values of Th and Zr dicarboxylates were determined from the analysis of the solubility data.

Influence of fluorine on the solubility of manganotantalite (MnTa 2O 6) and manganocolumbite (MnNb 2O 6) in granitic melts — An experimental study

Solubility experiments of manganotantalite (MnTa 2O 6) and manganocolumbite (MnNb 2O 6) were conducted under nearly fluid-saturated conditions in synthetic haplogranitic (HPG) and natural granitic (NG) melts containing different amounts of fluorine at 800 to 1000 °C and 200 MPa. The experiments were carried out in cold seal pressure vessels (at 800 °C) with water or Ar as a pressure medium and in internally heated pressure vessels (1000 °C) with Ar as a pressure medium. The F contents vary from 0 to 11.43 wt.% in experiments using HPG melts and from 0.61 to 3.78 wt.% in experiments using NG melts. Additionally, the NG melt contains minor amounts of P 2O 5 (0.44 to 0.64 wt.%). In HPG melts (alumina saturation index including Mn (ASI Mn): 0.88 to 0.99) the solubility product values at 800 °C yield log (K sp Ta) and log (K sp Nb) ranging from − 3.36 ± 0.10 to − 2.92 ± 0.10 mol²/kg² and from − 3.01 ± 0.11 to − 2.87 ± 0.06 mol²/kg², respectively. In NG melts the log (K sp Ta) and log (K sp Nb) vary from − 3.00 ± 0.04 to − 2.35 ± 0.13 mol²/kg² and from − 2.83 ± 0.06 to − 2.67 ± 0.18 mol²/kg² at 800 °C, respectively. The solubility products of both MnTa 2O 6 (K sp Ta) and MnNb 2O 6 (K sp Nb) are not significantly affected by the F content for a given melt composition (data are virtually identical within error). The variation of the solubility products observed in this study is rather attributed to the changes in melt structure (e.g. polymerization) and, in particular, to the alumina saturation index. By contrast, there is no evidence for the formation of complexes associating F and Nb and/or Ta. Our results also indicate that the structural changes caused by the incorporation of F in natural water-rich silicate melts are not expected to significantly influence the maximum concentrations of Nb and Ta in granitic or pegmatitic melts coexisting with manganotantalite and manganocolumbite.

Temperature impact assessment on struvite solubility product: A thermodynamic modeling approach

This work addresses the problem of phosphorus recovery from wastewater by struvite precipitation, which is chemically known as magnesium ammonium phosphate hexahydrate MgNH 4PO 4·6H 2O. The struvite solubility product values that are reported in the literature were found to vary significantly, from one solution to another and over the range of the experimental conditions as well. The various factors affecting the struvite solubility include pH, ionic strength and temperature. The struvite solubility product is yet a very important parameter to determine the supersaturation ratio. A thermodynamic model for phosphate precipitation is proposed to determine the phosphate conversion rate and the value of struvite solubility product for a temperature range between 15 and 35 °C. This model is based on numerical equilibrium prediction of the study system Mg–NH 4–PO 4–6H 2O. The mathematical problem is represented by a set of nonlinear equations that turns, to an ill-conditioned system mainly due to the various orders of magnitude of the involved variables. These equations have first been solved by an optimization strategy with a genetic algorithm to perform a preliminary search in the solution space. The procedure helps to identify a good initialization point for the subsequent Newton–Raphson method. A series of experiments were conducted to study the influence of pH and temperature on struvite precipitation and to validate the proposed model.

Nucleation sequence on the cation exchange process between Y0.95Eu0.05PO4 and CePO4 nanorods

Nanorods of Y0.95Eu0.05PO4@CePO4 (Y0.95Eu0.05PO4 phase was nucleated first and then a CePO4 phase was nucleated) and CePO4@Y0.95Eu0.05PO4 (CePO4 phase was nucleated first and then Y0.95Eu0.05PO4 phase was nucleated) were prepared at a relatively low temperature of 140 °C in ethylene glycol medium. Based on XRD, TEM and Raman studies it has been inferred that Y0.95Eu0.05PO4@CePO4 sample consists of a mixture of bigger (length around 800-1000 nm and width around of 80-100 nm) and smaller (length around 70-100 nm and width around 10-20 nm) nanorods, having monoclinic CePO4 and tetragonal YPO4 structure, whereas CePO4@Y0.95Eu0.05PO4 sample consists of mainly small nanorods having a single phase CePO4 structure. From the detailed luminescence studies it has been established that there exists significant incorporation of Y3+/Eu3+ ions in the CePO4 phase in CePO4@Y0.95Eu0.5PO4 sample. This has been attributed to the cation exchange taking place between Ce3+ ions in CePO4 host and Eu3+ and Y3+ ions in solution during the synthesis stage. Unlike this, such an exchange is not possible for Y0.95Eu0.05PO4@CePO4 sample synthesized under identical conditions due to the higher solubility product (Ksp) value of YPO4 compared to CePO4. Incorporation of Eu3+ in the CePO4 lattice of CePO4@Y0.95Eu0.5PO4 sample is confirmed by the significant reduction in the lifetime of 5D0 level of Eu3+ and the luminescence intensity from Eu3+, arising due to the electron transfer between the Ce3+/Ce4+ and Eu3+/Eu2+ species. These results are further supported by the non-radiative decay rates and quantum yields calculated from the emission spectrum.

Thermodynamic Properties of Autunite, Uranyl Hydrogen Phosphate, and Uranyl Orthophosphate from Solubility and Calorimetric Measurements

In this study, we use solubility and drop-solution calorimetry measurements to determine the thermodynamic properties of the uranyl phosphate phases autunite, uranyl hydrogen phosphate, and uranyl orthophosphate. Conducting the solubility measurements from both supersaturated and undersaturated conditions and under different pH conditions rigorously demonstrates attainment of equilibrium and yields well-constrained solubility product values. We use the solubility data and the calorimetry data, respectively, to calculate standard-state Gibbs free energies of formation and standard-state enthalpies of formation for these uranyl phosphate phases. Combining these results allows us also to calculate the standard-state entropy of formation for each mineral phase. The results from this study are part of a combined effort to develop reliable and internally consistent thermodynamic data for environmentally relevant uranyl minerals. Data such as these are required to optimize and quantitatively assess the effect of phosphate amendment remediation technologies for uranium contaminated systems.

Solubility measurements of the uranyl oxide hydrate phases metaschoepite, compreignacite, Na–compreignacite, becquerelite, and clarkeite

The mobility of uranium under oxidizing conditions can only be modeled if the thermodynamic stabilities of the secondary uranyl minerals are known. Toward this end, we synthesized metaschoepite (UO 3(H 2O) 2), becquerelite (Ca(UO 2) 6O 4(OH) 6(H 2O) 8), compreignacite (K 2(UO 2) 6O 4(OH) 6(H 2O) 7), sodium compreignacite (Na 2(UO 2) 6O 4(OH) 6(H 2O) 7), and clarkeite (Na(UO 2)O(OH)) and performed solubility measurements from both undersaturation and supersaturation under controlled-pH conditions. The solubility measurements rigorously constrain the values of the solubility products for these synthetic phases, and consequently the standard-state Gibbs free energies of formation of the phases. The calculated lg solubility product values (lg K sp), with associated 1 σ uncertainties, for metaschoepite, becquerelite, compreignacite, sodium compreignacite, and clarkeite are (5.6 −0.2/+0.1), (40.5 −1.4/+0.2), (35.8 −0.5/+0.3), (39.4 −1.1/+0.7), and (9.4 −0.9/+0.6), respectively. The standard-state Gibbs free energies of formation, with their 2 σ uncertainties, for these same phases are (−1632.2 ± 7.4) kJ · mol −1, (−10305.6 ± 26.5) kJ · mol −1, (−10107.3 ± 21.8) kJ · mol −1, (−10045.6 ±24.5) kJ · mol −1, and (−1635.1 ± 23.4) kJ · mol −1, respectively. Combining our data with previously measured standard-state enthalpies of formation for metaschoepite, becquerelite, sodium compreignacite, and clarkeite yields calculated standard-state entropies of formation, with associated 2 σ uncertainties, of (−532.5 ± 8.1) J · mol −1 · K −1, (−3634.5 ± 29.7) J · mol −1 · K −1, ( −2987.6 ± 28.5) J · mol −1 · K −1, and (−300.5 ± 23.9) J · mol −1 · K −1, respectively. The measurements and associated calculated thermodynamic properties from this study not only describe the stability and solubility at T = 298 K, but also can be used in predictions of uranium mobility through extrapolation of these properties to temperatures and pressures of geologic and environmental interest.