Contaminated water, stream sediments and soils close to the abandoned Pinhal do Souto uranium mine, central Portugal

摘要

The Pinhal do Souto mine exploited a quartz vein containing uranium minerals, mainly autunite andtorbernite. This vein intersects a two-mica granite containing 10 ppm U and uraninite. The mine wasexploited underground and produced 93091 kg U3O8 between 1978 and 1989 and was then closed down.Two dumps were left in the mine area and these are partially covered by natural vegetation. Groundwaterand surface water have a similar slightly acid-to-alkaline pH. The 2 2UO is abundant and complexedwith 2 3 CO , under neutral to alkaline pH. Metals and arsenic concentrations in the water increase during thedry season due to the evaporation. Uranium concentration in the water increases (up to 104.42 g/l) in thewet season, because secondary uranium minerals are dissolved and uranium is released into the water. Soilstend to retain a higher concentration of several metals, including U (up to 336.79 mg/kg) than streamsediments (up to 35.68 mg/kg), because vermiculite from the former could adsorb it more easily than couldkaolinite from the latter. The Fe-oxides precipitate retains the highest concentrations of several metals,including U and Th (up to 485.20 and 1053.12 mg/kg, respectively) and the metalloid As, because it is richer in oxyhydroxides and organic matter than stream sediments and soils. The median concentrations of Fe, As,Cd, Pb, Sb, Th, U, W and Zn in soils from this area are higher than in European soils of the FOREGS data.Waters from dry and wet seasons, stream sediments and soils are contaminated and must not be used. Thisarea was compared with another Portuguese abandoned uranium mine area. The former mine caused a lowerenvironmental impact attributable to it having lower sulfide concentration and mineral alteration than in thelatter.