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| Titel |
The effect of remediation on water from a former Portuguese uranium mine area |
| VerfasserIn |
Ana Neiva, Paula Carvalho, Isabel Antunes, António Santos, Marina Cabral-Pinto |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250123427
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| Publikation (Nr.) |
 EGU/EGU2016-2677.pdf |
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| Zusammenfassung |
| The old Senhora das Fontes uranium mine consists of quartz veins containing autunite down
to a depth of 40 m. But below, uraninite, Fe-saleeite and black uranium oxides occur in small
veinlets or forming elongated nodules. The mine was exploited underground and
was closed down in 1971. However, the ores from this mine and two others were
treated by the heap-leach process in this area until 1982. Seven dumps containing
33,800 m3 of material were left in the area. The remediation process was carried
out from May 2010 to January 2011. During this process, the relocation of the
material deposited in dumps took place and was covered with erosion resisting
covers. Groundwater and surface water were collected just before the remediation at
November of 2009 and February 2010, in the wet season, at the beginning of the
remediation, at May and June of 2010, and also after the remediation, at May and June of
2011, in the dry season. Ten wells, four springs and seven streams were chosen to
collect water samples. However, some points were occasionally dry and a total of
113 water samples were obtained. The pH of groundwater and surface water was
acid-to-alkaline, before, at the beginning and after the remediation, but decreased
with the remediation, whereas Eh increased. In general, the uranium concentration
was up to 116 μg/L in groundwater and up to 83 μg/L in surface water, before the
remediation, in the wet season. The uranium water concentration increased up to 272
μg/L and 183 μg/L in the former and the latter, respectively, at the beginning of the
remediation, in the dry season of 2010, due to remobilization of mine dumps and
pyrite and chalcopyrite exposures, which caused the pH decrease. However, the
uranium concentration decreased in groundwater and surface water at the north part
of the mine area, after the remediation, in the dry season of 2011, but increased
in both, particularly in groundwater up to 774 μg/L in the south and southwest
parts of the area, due to remobilization of sulphides that caused metals and As
to migrate to the groundwater flow. Uranium is adsorbed in clay minerals of the
streams. The geochemical modelling indicates that uranium is also adsorbed in
goethite. But after the remediation, the saturation indices of oxyhydroxydes decrease
as pH decreases. After the remediation has finished, Cd, Co, Cr, Ni, Pb, Zn, Cu,
As, Sr and Mn concentrations also decreased in groundwater and surface water at
north of the mine area, supported by the speciation modelling which shows the
decrease of most divalent species. But U, Th, Cd, Al, Li, Pb, Sr and As concentrations
increased in groundwater and surface water located at south and southwest of the mine
area. Groundwater and surface water are contaminated in U, Cd, Cr, Al, Mn, Ni,
Pb, Cu and As before and after the remediation. The contamination increased at
south and southwest of the area, but decreased in the north after the remediation. |
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