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Geochemical study of an old mining area in the district of Aveiro, Portugal
2001 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

This study was performed in the district of Aveiro, northern Portugal. The studied old mining area is located around 20 km northeast of the city of Aveiro in the drainage area of the Caima River, a tributary to the Vouga River. There is a long mining history in the area dating back to the time of the Romans. From the middle of the 19th century, coinciding with the start of the industrial revolution, until the first half of the 20th century, mining was an important industry in the area. The main reason why the mines were closed was the heavy pollution of the watercourses in the area. Even if the concentrations are lower today, the watercourses still are polluted by tailings lying exposed at the old mine sites. In order to characterise the affected area, dispersion mechanisms and the mineralogical associations of the metals, the samples were collected in different sampling environments (tailings, stream sediments and water). The tailings samples were collected from two of the mines in the area (Coval da Mó and Palhal). The sediment samples were principally collected downstream the Coval da Mó mine. The water samples were collected in different streams in the area and also from the leachate at the two mines. The sediment and tailings samples were analysed for heavy metals. A sequential selective extraction was also made for some of the samples in order to determine the metal bearing phases. The water samples were analysed for heavy metals and major elements. The results showed very high concentrations of heavy metals in the tailings samples from both the mines. The stream sediments also contained high metal concentrations in many parts of the area. Downstream the Coval da Mó mine high concentrations of Cd (>7 ppm), Pb (>400 ppm) and Zn (>1000 ppm) were found. Co, Cu, Fe, Mn, and Ni also showed elevated values in the sediments. High concentrations of As (>30 ppm) are found in sediments within the whole area, which can be explained by the high As concentrations in the bedrock. The leachate from the tailings showed high metal concentrations from both the mines. In the stream water high concentrations of Pb (>3 ppb) and Zn (>60 ppb) were found. The SSCE shows that many metals, especially Pb, Zn, Cd and Mn, occur in the easily extracted phase. The metals related to this phase are the metals that are most bioavailable and they are also the ones that easily dissolve in the water. Several metals are related to the Fe-oxides in the sediments. If the pH value for some reason is lowered, Fe and the other metals related to the oxides will be dissolved in the water. The study also showed that the dominating dispersion mechanism in the streams is mechanical dispersion.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Dispersion, Geochemistry, Heavy metals, Mines, Portugal, Sediment, SSCE, Tailings, Water
Keyword [sv]
URN: urn:nbn:se:ltu:diva-43466ISRN: LTU-EX--01/230--SELocal ID: 155d9ea6-38d2-4567-a47b-9bd09e6d76b3OAI: diva2:1016698
Subject / course
Student thesis, at least 30 credits
Educational program
Environmental Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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