Spatiotemporal evolution of U and Th isotopes in a mine effluent highly polluted by Acid Mine Drainage (AMD)

• Published in: Journal of hazardous materials Vol. 447; p. 130782
• Main Authors: Guerrero, J.L., Suárez-Vaz, N., Paz-Gómez, D.C., Pérez-Moreno, S.M., Bolívar, J.P.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 05.04.2023
• Subjects: Acid mine drainage; Conservative behavior; Environmental impact; Th isotopes; U isotopes; U isotopes; Conservative behavior; Acid mine drainage; Th isotopes; Environmental impact
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2023.130782

The spatiotemporal evolution of both U and Th isotopes in a mine effluent highly polluted by acid mine drainage (AMD) was evaluated. The acidic tributary, which born from the outflows of an abandoned sulfide mine, flows into the Odiel River. AMD comprises an important source of natural radionuclides, presenting concentrations of 238U and 232Th, two and four orders of magnitude higher, respectively, than the background values of surface continental waters. These natural radionuclides behave conservatively along the mine effluent (pH < 2.5) throughout the hydrological year. Under AMD conditions uranium is in the hexavalent state U(VI) and the main dissolved species are uranyl sulfate complexes. The polluted tributary has a significant impact on the Odiel River acidifying its waters during the low flow season and increasing up to one order of magnitude the activity concentrations of U and Th isotopes. U presented a conservative behavior in the Odiel River during the low flow season (pH ≈ 3), however it is removed from the liquid phase in the wet season (pH ≈ 6), probably due its coprecipitation/adsorption onto Al-phases. Th shows a high sensitivity to small increases of pH, and it is strongly coprecipitated/adsorbed with or onto Fe-oxyhydroxydizes in the river. [Display omitted] •Acid mine drainage comprises an important source of natural radionuclides.•Conservative behaviour of U and Th isotopes in the mine effluent.•Uranium is in the hexavalent state U(VI) in the form of uranyl sulphate complexes.•Coprecipitation/adsorption of uranium with/onto Al-phases.•Coprecipitation/adsorption of thorium with/onto Fe-oxyhydroxides.