Article

Solubility of Litharge (α-PbO) in Alkaline Media at Elevated Temperatures

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Solubility of Litharge (α-PbO) in Alkaline Media at Elevated Temperatures

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Abstract

An inert, flowing autoclave facility was used to investigate the solubility behavior of α-PbO (litharge, tetragonal) in aqueous solutions of morpholine, ammonia and sodium hydroxide between 38 and 260 ∘C. Lead solubilities increased from about 0.4 mmol-kg−1 at 38 ∘C to about 4.5 mmol-kg−1 at 260 ∘C and were relatively insensitive to the concentration and identity of the reagent used to control the pH. The measured lead solubilities were interpreted using a Pb(II) ion hydroxocomplexing model and thermodynamic functions for these equilibria were obtained from a least-squares analysis of the data. A consistent set of thermodynamic properties for the species Pb(OH)+, Pb(OH)2(aq) and Pb(OH)3− was obtained that will permit accurate lead oxide solubility calculations to be made over broad ranges of temperature and alkalinity.

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... Lead deposition onto magnetite can be due to several mechanisms such as precipitation of lead compounds and adsorption. However, dissolved lead concentrations in feed water are much lower than the solubilities of lead compounds (e.g., PbO, PbSO 4 ) [4,5]. X-ray absorption spectra of lead adsorbed on goethite found that monomeric lead complexes were formed at lead concentrations below 2 × 10 −3 mol·kg −1 and no lead hydroxide precipitation occurred on the surface [6]. ...
... It is noted that Pb(II) will undergo hydrolysis in the solution as pH and temperature change [4,30]. High pH and temperature are favorable for Pb(II) hydrolysis and adsorption due to endothermic effect [7,20]. ...
... It is interesting to examine the linear relationship between adsorption enthalpy change and entropy change, a much debated thermodynamic phenomenon called enthalpy-entropy compensation (EEC) observed in many different systems [39,40]. To confirm the relationship for different ion adsorptions onto magnetite, datasets of ΔH and ΔS for both Pb(II) and SO 4 2− [26] adsorption were shown in Fig. 14. A very good linear relationship was observed between ΔH and ΔS which can be due to the thermodynamic equation ΔH = T ΔS − ΔG where ΔG is a constant and T is a slope as the temperature [40,41]. ...
Article
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The presence of lead in steam generators can cause stress corrosion cracking of steam generator tubing in water-cooled nuclear reactors. The deposition of lead in steam generator is likely due to the adsorption of lead species onto magnetite, a major corrosion product of steam generator components. As adsorption of lead onto magnetite at elevated temperatures is rarely reported and the effect of chloride on lead adsorption on magnetite is also not known well, experiments were performed to study the kinetics and equilibrium of the adsorption of lead onto magnetite under various aqueous chemistry conditions from 298 to 573 K. Lead adsorption had a second-order reaction kinetics with an adsorption rate constant of 0.24 h·μmol·g⁻¹ at 298.0 K and initial lead concentration of 9.70 × 10⁻⁶ mol·kg⁻¹. Adsorption equilibria follow a Freundlich isotherm, and the maximum adsorption capacity at pH 5.3 is between 3.6 and 9.8 μmol·g⁻¹ depending on temperature. Increasing pH (2.7–10.0) increases the adsorption from 2% at pH 2.7 to 100% at pH 5 suggesting that specific adsorption of lead onto magnetite surface is the dominant mechanism with a mean-free energy of adsorption between 14 and 17 kJ·mol⁻¹. Increasing temperature from 298 to 423 K increases lead adsorption from less than 25% to more than 90%. Thermodynamic calculation showed that overall enthalpy change and entropy change of adsorption at initial lead concentration of 10⁻⁵ mol·kg⁻¹and pH 5.2 are 32 kJ·mol⁻¹ and 88 J·K⁻¹·mol⁻¹, respectively, suggesting that increasing entropy plays a dominant role in the ion adsorption on iron oxides. Lead adsorption strongly depend on the pH of solution at the temperature above 423 K. Adsorption percentage does not change with increasing temperature at pH above 5; however, lead desorption occurs at lower pH as temperature increases from 423 to 573 K with enthalpy changes ranging from − 12 to − 60 kJ·mol⁻¹ depending on the pH of the solutions. The presence of chloride in solution can enhance lead adsorption by 5 to 10% which has much less effect on lead transport than pH and temperature changes. Maintaining bulk water pHs greater than 5.3 is favorable to lead (Pb) immobility and mitigating the degradation of steam generator-tubing alloys.
... There are two natural crystalline phases for lead monoxide, i.e., litharge and massicot [21]. Litharge is red, which is denoted as α-PbO with a tetragonal crystal structure, whereas massicot is yellow, denoted as β-PbO with an orthorhombic crystal structure [22]. Litharge is thermodynamically more stable than massicot and hydrous lead(II) oxide [22]. ...
... Litharge is red, which is denoted as α-PbO with a tetragonal crystal structure, whereas massicot is yellow, denoted as β-PbO with an orthorhombic crystal structure [22]. Litharge is thermodynamically more stable than massicot and hydrous lead(II) oxide [22]. ...
... Tylecote [25] concluded that litharge was a major corrosion product for land-based lead from archaeological sources. Litharge can also form when nickel-based alloys are subject to stress corrosion owing to trace level concentrations of lead in nuclear reactor coolants under hydrothermal conditions in high temperature environments [22]. ...
Article
Full-text available
In this study, a hydrolysis model for lead, applicable to high ionic strength, is developed based on lead oxide solubilities as a function of ionic strength. Solubility measurements on lead oxide, α-PbO (tetragonal, red), mineral name litharge, as a function of ionic strength were conducted in NaClO4 solutions up to I = 0.45 mol·kg−1, in NaCl solutions up to I = 5.0 mol·kg−1, and in Na2SO4 solutions up to I = 5.4 mol·kg−1, at room temperature (22.5 ± 0.5 °C). The lead hydroxyl species considered in this work include the following,$$ {\text{PbO}}\left( {\text{cr}} \right) \, + {\text{ 2H}}^{ + } \rightleftharpoons {\text{Pb}}^{ 2+ } + {\text{ H}}_{ 2} {\text{O}}\left( {\text{l}} \right) $$ (1) $$ {\text{Pb}}^{ 2+ } + {\text{ H}}_{ 2} {\text{O}}\left( {\text{l}} \right) \rightleftharpoons {\text{PbOH}}^{ + } + {\text{ H}}^{ + } $$ (2) $$ {\text{Pb}}^{ 2+ } + {\text{ 2H}}_{ 2} {\text{O}}\left( {\text{l}} \right) \rightleftharpoons {\text{Pb}}\left( {\text{OH}} \right)_{ 2} \left( {\text{aq}} \right) \, + {\text{ 2H}}^{ + } $$ (3) $$ {\text{Pb}}^{ 2+ } + {\text{ 3H}}_{ 2} {\text{O}}\left( {\text{l}} \right) \rightleftharpoons {\text{Pb(OH}})_{3}^{ - } + 3{\text{H}}^{ + } $$ (4) The equilibrium constants for Reactions (1) and (2) were taken from literature. The equilibrium constants in base 10 logarithmic units for Reactions (3) and (4) are determined in this study as − 17.05 ± 0.10 (2σ) and − 27.99 ± 0.15 (2σ), respectively, with a set of Pitzer parameters describing the interactions with Na+, Cl−, and \( {\text{SO}}_{4}^{2 - } .\) In combination with the parameters from literature including those that have already been published by our group, the solution chemistry of lead in a number of media including NaCl, MgCl2, NaHCO3, Na2CO3, Na2SO4, NaClO4, and their mixtures, can be accurately described in a wide range of ionic strengths.
... For the bulk morphology of TiO 2 :Pb one can see almost flawless coincidence between the XPS Pb 4f 7/2-5/2 core-level spectra of the sample under study and litharge polymorph of lead oxides (␣-PbO or lead monoxide). This tetragonal form of lead oxides is the most thermodynamically stable lead-oxygen polymorph, because the multi-thread processes of lead oxidation-reduction are usually ends with the phase-drop to tetragonal ␣-PbO end-phase [25]. In terms of well-known configuration-curve states model, this phase is representing the most ground state for lead oxides phase-transitions. ...
... But, what might be really expected with the high probability, is the distortion of the newly formed "titanium-to-lead-replaced -oxygen" unit-cell if comparing with the initial one. This kind of distortion occurs due to dissimilarity in the charge states of titanium and lead and as well as due to the differences in normal (not distorted) crystal structure parameters [25]: a = 3.999(5) Å, c = 5.036(8) Å for litharge and a = 4.593(7) Å, c = 2.958(6) Å for rutile. In terms of this, the weak sub-bands located at ∼135 eV and ∼140 eV in the XPS Pb 4f core-level spectra of Pb-implanted TiO 2 might be recognized as a spectral signature of the discussed above lattice distortions. ...
... For the bulk morphology of TiO 2 :Pb one can see almost flawless coincidence between the XPS Pb 4f 7/2-5/2 core-level spectra of the sample under study and litharge polymorph of lead oxides (α-PbO or lead monoxide). This tetragonal form of lead oxides is the most thermodynamically stable lead-oxygen polymorph, because the multi-thread processes of lead oxidation-reduction are usually ends with the phase-drop to tetragonal α-PbO end-phase [25]. In terms of well-known configuration-curve states model, this phase is representing the most ground state for lead oxides phase-transitions. ...
... But, what might be really expected with the high probability, is the distortion of the newly formed "titanium-to-lead-replaced -oxygen" unit-cell if comparing with the initial one. This kind of distortion occurs due to dissimilarity in the charge states of titanium and lead and as well as due to the differences in normal (not distorted) crystal structure parameters [25]: a = 3.999(5) Å, c = 5.036(8) Å for litharge and a = 4.593(7) Å, c = 2.958(6) Å for rutile. In terms of this, the weak sub-bands located at ∼135 eV and ∼140 eV in the XPS Pb 4f core-level spectra of Pb-implanted TiO 2 might be recognized as a spectral signature of the discussed above lattice distortions. ...
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The results of combined experimental and theoretical study of substitutional and clustering effects in the structure of Pb-doped TiO2-hosts (bulk ceramics and thin-film morphologies) are presented. Pb-doping of the bulk and thin-film titanium dioxide was made with the help of pulsed ion-implantation without posterior tempering (Electronic Structure Modulation Mode). The X-ray photoelectron spectroscopy (XPS) qualification of core-levels and valence bands and Density-Functional Theory (DFT) calculations were employed in order to study the yielded electronic structure of Pb-ion modulated TiO2 host-matrices. The combined XPS-and-DFT analysis has agreed definitely with the scenario of the implantation stimulated appearance of PbO-like structures in the bulk morphology of TiO2:Pb, whereas in thin-film morphology the PbO2-like structure becomes dominating, essentially contributing weak O/Pb bonding (PbxOy defect clusters). The crucial role of the oxygen hollow-type vacancies for the process of Pb-impurity "insertion" into the structure of bulk TiO2 was pointed out employing DFT-based theoretical background. Both experiment and theory established clearly the final electronic structure re-arrangement of the bulk and thin-film morphologies of TiO2 because of the Pb-modulated deformation and shift of the initial Valence Base-Band Width about 1 eV up.
... At 35°C, however, lead release maintained a relative constant rate during the course of the experiments. The enhanced rate of lead release can be attributed to the higher solubility of lead stabilizer, such as PbO, at a higher temperature (Sue et al. 1999;Ziemniak et al. 2005). ...
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Unplasticized polyvinyl chloride (uPVC) pipes have been used in the premise plumbing system due to their high strength, long-term durability, and low cost. uPVC pipes, however, may contain lead due to the use of lead compounds as the stabilizer during the manufacturing process. The release of lead from three locally purchased uPVC pipes was investigated in this study. The effects of various water quality parameters including pH value, temperature, and type of disinfectant on the rate of lead release were examined. The elemental mapping obtained using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) confirmed the presence of lead on the inner surfaces of the uPVC pipes and their surface lead weight percentages were determined. The leachable lead concentration for each pipe was determined using high strength acidic EDTA solutions (pH 4, EDTA = 100 mg/L). Lead leaching experiments using tap water and reconstituted tape water under static conditions showed that the rate of lead release increased with the decreasing pH value and increasing temperature. In the presence of monochloramine, lead release was faster than that in the presence of free chlorine.
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Most algorithms for the least-squares estimation of non-linear parameters have centered about either of two approaches. On the one hand, the model may be expanded as a Taylor series and corrections to the several parameters calculated at each iteration on the assumption of local linearity. On the other hand, various modifications of the method of steepest-descent have been used. Both methods not infrequently run aground, the Taylor series method because of divergence of the successive iterates, the steepest-descent (or gradient) methods because of agonizingly slow convergence after the first few iterations. In this paper a maximum neighborhood method is developed which, in effect, performs an optimum interpolation between the Taylor series method and the gradient method, the interpolation being based upon the maximum neighborhood in which the truncated Taylor series gives an adequate representation of the nonlinear model. The results are extended to the problem of solving a set of nonlinear algebraic e
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Correlations among experimentally determined standard partial molal thermodynamic properties of inorganic aqueous species at 25 degrees C and 1 bar allow estimates of these properties for numerous monatomic cations and anions, polyatomic anions, oxyanions, acid oxyanions, neutral oxy-acid species, dissolved gases, and hydroxide complexes of metal cations. Combined with correlations among parameters in the revised Helgeson-Kirkham-Flowers (HKF) equation of state (Shock et al., 1992), these estimates permit predictions of standard partial molal volumes, heat capacities, and entropies, as well as apparent standard partial molal enthalpies and Gibbs free energies of formation to 1000 degrees C and 5 kb for hundreds of inorganic aqueous species of interest in geochemistry. Data and parameters for more than 300 inorganic aqueous species are presented. Close agreement between calculated and experimentally determined equilibrium constants for acid dissociation reactions and cation hydrolysis reactions supports the generality and validity of these predictive methods. These data facilitate the calculation of the speciation of major, minor, and trace elements in hydrothermal and metamorphic fluids throughout most of the crust of the Earth.
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