Colloid-borne uranium in an abandoned uranium mine in the stage of flooding


Colloid-borne uranium in an abandoned uranium mine in the stage of flooding

Ulrich, K.-U.; Zänker, H.; Jenk, U.

Abandoned uranium mines which underwent or just undergo flooding may represent a severe source of radioactive contaminants against groundwater, surface water, and the atmosphere. The uranium mines operated until 1990 in Saxony and Thuringia left a total void volume of more than 100 million m3 to be flooded. Prognosis of radionuclide emission via the water path needs detailed knowledge about the hydrological regime of the mine and the speciation of the contaminants. The adsorption of radionuclides on colloidal phases may stimulate or delay their transport and migration. Neglecting the colloidal phases may have the following consequences on environmental hazard prognosis:

a) The radionuclide is fully mobile, i.e. it is not adsorbed onto solid phases: colloidal transport is irrelevant and the model description is correct.
b) The radionuclide is regarded as fully mobile in the model, but it adsorbs on colloids which aggregate and settle (‘natural attenuation’): the prognosis is too pessimistic.
c) The radionuclide is regarded as immobile in the model due to adsorption on the host rock, but in part it adsorbs on colloids which are transported: the prognosis is too optimistic.
Based on their chemical and colloidal composition, mine waters usually range between the following water types:
i) Type ‘acid pore water’ (acid rock or mine drainage, sometimes called ‘yellow boy’): Very acidic (pH 1-3) and usually anoxic waters with a high salt loading.
ii) Type ‘bulk water’: Near-neutral, oxic or suboxic waters with a moderate salt loading, typically represented by gallery or adit water.
Mine flooding is accompanied with a transition of type (i) into type (ii) water, which is crucial for colloid-chemical processes changing the partitioning of heavy metals and radionuclides. Due to pH increase and access of oxygen, colloids of Fe(III) and Al compounds are formed known to adsorb trace metals.
To assess the uranium migration in the stage of flooding and afterwards, we performed neutralization experiments by mixing acid floodwater from an uranium mine with oxic groundwater from an aquifer above the mine and studied the formation and composition of colloids as well as the adsorption of uranium onto these colloids by using spectroscopic methods.

Keywords: mine flooding; acid mine drainage; groundwater; neutralization experiment; uranium mobility; adsorption; colloids; ironoxyhydroxides; ferrihydrite; tangential flow ultrafiltration; XAFS spectroscopy

  • Contribution to external collection
    Qaim, S.M., Coenen, H.H. (Eds.), Advances in Nuclear and Radiochemistry, Extended Abstracts of NRC 6, Schriften des Forschungszentrums Jülich, Reihe Allgemeines und Interdisziplinäres 3(2004), 645-647
  • Lecture (Conference)
    Sixth International Conference on Nuclear and Radiochemistry (NRC 6), 29.08.-03.09.2004, Aachen, Germany

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Publ.-Id: 6052