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A geochemical survey in Peti Lake, Minas Gerais, Brasil
2002 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

This project is a part of a collaboration project between a German research centre in Magdeburg, Germany and the Brasilian department of geology in Ouro Preto, Brasil. The project was performed in Minas Gerais, Brasil, September through November 2001. The main purpose of this project is to make a general geochemical study of Peti Lake, situated in the recently explored Santa Bárbara district, in the old, active mining area of Quadrilátero Ferríferro of Minas Gerais. The fourth largest gold mine of Brasil, São Bento mine and other smaller gold mines are situated within this district and are potential sources of contamination for Peti Lake. The area is covered by laterite soils formed by weathering of the bedrock. The laterites often contain naturally high levels of certain elements such as Ni, Cr, Co and Cu, which also often are related to mining activities. The geochemical investigation will give a first insight into the status of the water, sediment and pore water and serve as a base for further limnological investigations in the area. This will be the groundwork for assessing the environmental state of Peti Lake. To study the distribution of pollutants in the lake, samples from the water column and the sediments were taken at three sampling stations where pore water also was extracted for analyses. Two of the sampling stations, Peti A and B, were located at the inflow of the two major river inflows to study the contribution from each river. The third sampling station, Peti C, was located further downstream in the lake to study the contribution from both rivers. To investigate the spread of different elements throughout the lake, surface sediments were collected at 27 stations evenly spread with a distance of approximately 500 meters between neighboring stations. The results from the water column show a very high concentration of Fe and Mn in the lower part of the water column while the concentration of other analyzed elements are low. There is also a rather distinct stratification in Peti A and B while Peti C shows little or no signs of stratification. This indicates that the two rivers are contributing with water of different character compared to the lake water and that the water column has not been mixed for a while. These stratification layers can be looked upon as boundary zones between oxic and anoxic conditions where the dissolution and subsequent reoxidation of Fe and Mn oxidhydroxides control many other elements. The Fe- and Mn concentration is high in both the solid phase of the sediment and in the pore water. The concentrations of Ni, Cr, Hg, As, Sb and Cu in the sediments were between moderately high to very high according to the Swedish Environmental Protection Agency. Concentrations of other analyzed elements are low. The minerals found in the sediments were weathering minerals and therefore most likely originated from the surrounding laterite soils. The high concentrations of Ni and Cr are likely to be a contribution from the laterite soils while As, Sb and Cu are believed to be high due to mining activity since natural accumulation of these elements in laterite soils is not expected. The pollution of Peti Lake water is not extensive, but for some elements high concentrations occur in the sediments. If the conditions in the lake are changed, a release of these elements to the water column is a possible scenario.

Place, publisher, year, edition, pages
2002.
Keyword [en]
Technology, geochemistry, water, sediment, porewater, Brasil, Minas, Gerais, Iron Quadrangle
Keyword [sv]
Teknik
Identifiers
URN: urn:nbn:se:ltu:diva-42516ISRN: LTU-EX--02/356--SELocal ID: 084ab1c2-741c-44e1-87b5-75ba5b525444OAI: oai:DiVA.org:ltu-42516DiVA: diva2:1015739
Subject / course
Student thesis, at least 30 credits
Educational program
Environmental Engineering, master's level
Examiners
Note
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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