A comparative study of aquifer systems occurring at the Paraná sedimentary basin, Brazil: U-isotopes contribution
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2013-01-01
Autores
Bonotto, Daniel Marcos [UNESP]
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The radioactivity due to 238U and 234U in three aquifer systems occurring within the Paraná sedimentary basin, South America, has been investigated. Uranium is much less dissolved from fractured igneous rocks than from the porous sedimentary rocks as indicated by the U-mobility coefficients between 7. 6 × 10-6 and 1. 2 × 10-3 g cm-3. These values are also compatible with the U preference ratios relative to Na, K, Ca, Mg and SiO2, which showed that U is never preferentially mobilized in the liquid phase during the flow occurring in cracks, fissures, fractures and faults of the igneous basaltic rocks. Experimental dissolution of diabase grains on a time-scale laboratory has demonstrated that the U dissolution appeared to be a two-stage process characterized by linear and second-order kinetics. The U dissolution rate was 8 × 10-16 mol m-2 s-1 that is within the range of 4 × 10-16-3 × 10-14 mol m-2 s-1 estimated for other rock types. The 234U/238U activity ratio of dissolved U in solutions was higher than unity, a typical result expected during the water-rock interactions when preferential 234U-leach from the rock surfaces takes place. Some U-isotopes data allowed estimating 320 ka for the groundwater residence time in a sector of a transect in São Paulo State. A modeling has been also realized considering all U-isotopes data obtained in Bauru (35 samples), Serra Geral (16 samples) and Guarani (29 samples) aquifers. The results indicated that the Bauru aquifer waters may result from the admixture of waters from Guarani (1. 5 %) and Serra Geral (98. 5 %) aquifers. © 2012 Springer-Verlag.
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Groundwater, Paraná sedimentary basin, Uranium isotopes, Activity ratios, Aquifer systems, Aquifer water, Basaltic rocks, Comparative studies, Dissolution rates, Fractures and faults, Groundwater residence time, Liquid Phase, Rock surfaces, Rock types, Second order kinetics, Sedimentary basin, South America, Time-scales, Two-stage process, Water rock interactions, Aquifers, Dissolution, Hydrogeology, Isotopes, Leaching, Nuclear fuels, Settling tanks, Groundwater resources, aquifer pollution, basalt, comparative study, data set, fracture, hydrogeology, igneous rock, metal, radioactivity, sedimentary basin, sedimentary rock, silicate, uranium isotope, water-rock interaction, Brazil, Parana [Brazil], Sao Paulo [Brazil]
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Environmental Earth Sciences, v. 68, n. 5, p. 1405-1418, 2013.