A biogeochemical study of an abandoned pb-zn mine in the aran valley, spain; Applications of natural attenuation of heavy metals via secondary hydrozincite precipitation

• Autores: Max G. Giannetta
• Directores de la Tesis: Jordi Cama Robert (dir. tes.), Josep Maria Soler Matamala (codir. tes.), M Angels Canals Sabaté (tut. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2022
• Idioma: inglés
• Tribunal Calificador de la Tesis: Mercè Corbella i Cordomí (presid.), Cristina Domènech Ortí (secret.), Eva Marguí Grabulosa (voc.)
• Programa de doctorado: Programa de Doctorado en Ciencias de la Tierra por la Universidad de Barcelona
• Materias:
  • Ciencias de la vida
    • Genética
      • Genética de poblaciones
  • Ciencias de la tierra y del espacio
    • Geoquímica
      • Geoquímica de bajas temperaturas
    • Geología
      • Hidrogeología
    • Hidrología
      • Calidad de las aguas
• Enlaces
  • Tesis en acceso abierto en: TESEO
• Resumen

  • The Aran Valley (Spain) was the site of large-scale mining from the late 19th century until ~1950. Although mining activities ceased over 70 years ago, waters associated with the abandoned mining relics exhibit elevated concentrations of Zn, Cd, and Ni posing a potential health risk. In this study, the largest underground mine in the Aran Valley (Victoria Mine) was chosen to showcase the processes affecting metal mobility. The mine is composed of 15 km of tunnel galleries and the lowermost exhibits a continuous output of water whose composition reflects a flow path through the system.

    Three years of sampling provide a spaciotemporal dataset of the system. Rainwater from the upper catchment flows into the host rock and dissolves ore materials (e.g. pyrite and sphalerite) resulting in elevated Zn, Ni, and Cd concentrations in the mine tunnels. Subsequently, hydrozincite precipitates in the tunnels and polishes the metals to safer levels. Notably, DNA sequencing of local bacteria, bioreactor experiments and geochemical modeling confirm that hydrozincite forms abiotically in the Victoria Mine.

    Characterization of the solids from the mine reveal several distinct morphologies, elemental zonations, and small amounts of smithsonite and calcite. All solids show layering, which is likely a result of variable solute concentrations and precipitation rates. This is hypothesized to be due to rain events, which can change the water residence time in the system.

    Solubility experiments and speciation calculations done using the CrunchFlow code demonstrate that hydrozincite exhibits a range of Keq values. This is presumed to be a result of precursor effects, such that amorphous solids with higher solubilities can form before hydrozincite.

    A CrunchFlow reactive transport model reproduces the measured concentrations and mineral reactions. A Sensitivity analysis of the most relevant parameters is performed to capture a range of behavior expected to occur. The model confirms that changes to flow velocity (i.e. rain events), could be the cause of mineral layering and elemental zonation in hydrozincite. The model also confirms that the natural metal attenuation process is expected to persist through a wide range of system perturbations. Thus, the abandoned mine poses little risk to the neighboring ecosystem.