210-13 EVALUATION OF INTERNALLY CONSISTENT THERMODYNAMIC DATA FOR LEAD MINERALS AND THEIR SOLUBILITIES

Session: Environmental Geochemistry and Health

Presenting Author:

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Abstract:

Lead continues to contaminate our environment and endanger human health as, for example, the incident at Yellowstone National Park. Geochemical models that are used to interpret or predict lead mobility and toxicological models that are used to understand toxicity require a reliable thermodynamic database for lead species. To identify solubility controls on lead in different aqueous environments, we have revised the extensive thermodynamic data on lead species for internal consistency among different studies and among different types of measurements.

The available thermodynamic data for more than 30 lead minerals, associated aqueous complexes, lead free ion, and solubilities were compiled and compared. To evaluate internal consistency, we have compared results from calorimetry, solubility, electrochemistry, and colligative property data. We utilized the basic thermodynamic equations and we revised aqueous solubilities with PHREEQC for a few systems. Remarkable agreement among different types of measurements was found for Pb²⁺(aq), anglesite, cotunnite, litharge, massicot, cerussite and wulfenite. Minerals that clearly need more studies include minium, scrutinyite, vanadinite, crocoite, stolzite, and a few other rare complex lead minerals. Although there have been substantial studies on the Pb-apatite group minerals, pyromorphite-mimetite, there continue to be areas for improvement.

We included data on activity and osmotic coefficients, solubilities, molar volumes, and heat capacities for lead perchlorate, lead nitrate and lead chloride solutions. Aqueous lead complexes include hydrolysis constants, carbonates, chlorides, fluorides, phosphates and sulfates.

A few key lead species and auxiliary species are below as examples.

Species         C_p/J mol^-1K^-1           S^ꝋ/J K^-1mol^-1      ∆_fH^ꝋ/kJ mol^-1     ∆_fG^ꝋ/kJ mol^-1          logK_sp

Anglesite(s)     103.207                 148.57 ± 0.60     -919.8 ± 0.7      -813.19 ± 0.40       -7.81 ± 0.05

Cerussite(s)     87.07 ± 0.09          125.45 ± 0.20     -703.13 ± 1.23  -627.70 ± 1.24     -13.21 ± 0.10

Cotunnite(s)     77.07                     135.98 ± 2.1      -359.41 ± 0.16   -314.121 ± 0.16   -4.778 ± 0.003

Pb²⁺(aq)          -52.7                        19.56 ± 1.0          0.94 ± 0.25     -24.45 ± 0.05

CO₃^2-(aq)                                         -50.0                -675.23 ± 0.25   -527.9 ± 0.4

SO₄^2-(aq)        -293                           18.5 ± 0.4       -909.34 ± 0.40   -744.0 ± 0.4

Cl^-(aq)             -136.4                        56.6 ± 0.2       -167.080 ± 0.1   -131.2 ± 0.1

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10749

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