Studies of water quality in the Ouro Preto region, Minas Gerais, Brazil: the release of arsenic to the hydrological system (original) (raw)
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Environmental Monitoring and Assessment, 2011
The Iron Quadrangle has been one of the most important gold production regions in Brazil since the end of the seventeenth century. There, arsenic occurs in close association with sulfide-rich auriferous rocks. The most abundant sulfide minerals are pyrite and arsenopyrite, yet trace metal sulfides occur in subordinate phases as well. Historical mining activities have been responsible for the release of As and trace metals to both aquatic and terrestrial environments close to mining sites in the region. Therefore, this study was aimed to evaluate the distribution and mobility of As, Cd, Co, Cr, Cu, Ni, Pb, and Zn in streams in the southeast portion of the Iron Quadrangle between the municipalities of Ouro Preto and Mariana, the oldest Brazilian Au mining province. Total concentrations of some trace metals and arsenic in water were determined. The four-stage sequential extraction procedure proposed by the commission of the European Communities Bureau of Reference (BCR) was used to investigate the distribution of these elements in stream sediments. Arsenic concentration in water was >10 μg L −1 (maximum limit permitted by Brazilian environmental regulations for water destined for human consumption) at all sampling sites, varying between 36.7 and 68.3 μg L −1 . Sequential extraction in sediments showed high concentrations of As and trace metals associated with easily mobilized fractions.
ARSENIC IN WATER AND SEDIMENT IN THE IRON QUADRANGLE, STATE OF MINAS GERAIS, BRAZIL
Since the end of 17th century, the Iron Quadrangle in the State of Minas Gerais has been known as one of the most famous gold producing regions in Brazil. Gold was initially produced from alluvial placers and oxidation zones and, finally from primary ores in modern times. Total gold production must have exceeded 1300 t in all history. Only in the very famous Morro Velho mine around 600-t gold has been produced since 1834. The gold ore is rich in arsenic with the As/Au ratios ranging from 300 to 3000 among the several deposits deposits. The arsenic in rocks and ores (pyrite, pyrrhotite and arsenopyrite) undergo oxidation during the weathering processes and part of the arsenic is naturally liberated into the environment. Since the tailings produced in the past were discharged directly into drainage until 1980, the amount of arsenic that entered the drainage systems must have exceeded 390000 t in the whole region. In the Iron Quadrangle region, the highest arsenic concentrations in wat...
Environmental Science and Pollution Research, 2016
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Environmental Geology, 2003
The Iron Quadrangle has been the scenery of the most important gold production in Brazil. It is estimated that during the three centuries of gold mining in the Iron Quadrangle, at least 390,000 t of arsenic was discharged into the drainage system. This study presents geochemical data for the three river basins in the region, with focus on surface water and stream sediment monitoring. Samples of primary and oxidized sulfide ores as well as of tailings and groundwater from the major gold mines were also studied. The highest As concentrations in water and stream sediments occur in the vicinity of mining areas. In surface water, up to 300 lg As/l were found whereas the As contents in stream sediments were in the range of 20 to 4,000 mg/kg. The As 3+ /As 5+ concentration ratios obtained for some water samples range from 1.10 )1 to 4.10 )2 . The As mobility associated with ore-deposit weathering could be traced in some closed gold mines by observation of insitu pyrite and arsenopyrite oxida-tion, precipitation of scorodite and gippsite, As adsorption onto goethite, and final liberation of As into underground and surface waters. This process is likely to produce large volumes of mine effluents containing total As and trivalent As up to 1,960 and 60 lg/l, respectively. River sediments and tailings pile samples were submitted to a leaching procedure showing maximal arsenic release from 1 to 4% of the original total As in the samples. There are potential risks for As hazards in some areas induced by, for instance, the dispersion of old tailings by flooding, occupation of poisoned soils for settlements, and occasional consumption of contaminated surface and groundwater.
Environmental science and pollution research international, 2018
Arsenic (As) is a dangerous and carcinogenic element and drinking water is its main pathway of human exposure. Gold mines are widely recognized as important sources of As pollution. This work proposes the assessment of As distribution along watersheds surrounding "Morro do Ouro" gold mine (Paracatu, southeastern Brazil). A balance approach between filtered As fluxes (As < 0.45 μm) and suspended particulate material (AsSPM) in different river segments was applied. Ultrafiltration procedure was used to categorize As into the following classes: particulate > 0.1 μm, colloidal < 0.1 μm to > 10 kDa, dissolved < 10 kDa to > 1 kDa, and truly dissolved < 1 kDa. By applying this approach, arsenic contributions from mining facilities were quantified in order to identify critical fluvial segments and support decision makers in actions of remediation. The mass balance indicated the occurrence of a decreasing gradient from upstream to downstream: (i) of the As conc...
Environmental Earth Sciences, 2007
In the city of Ouro Preto (MG), water catchment for public supply originates from superficial drainage, springs, old abandoned mines and some driven wells. In the rocks of the region, As is originally found in gold-enriched sulphide-bearing mineral deposits. The weathering process introduces As into the hydrological system by dissolution of this element into the leachate. Measurement of the As content in the groundwater of some catchments was carried out during 1 year and these measurements demonstrated high As content—up to 224 μg L−1 of As(V)—during the rainy season (the maximum concentration limit according to World Health Organization is 10 μg L−1). Lower values were observed during the dry season and in some sampling stations, As was not even detected. The As concentration variability during 1 year shows a strict and direct relationship to seasonal and hydrological conditions. For city authorities, responsible for public water supply, it is necessary to perform a complete inventory of the water sources used and constantly monitor the As content in the water.
Heavy metals in stream sediments from copper and gold mining areas in southern Brazil
Journal of Geochemical Exploration, 1997
This work is part of a research effort which is intended to identify natural and anthropogenic sources for metal contamination in gold and copper mining areas of the Camaqu~ River Basin, located in the shield region of the Rio Grande do Sul state. This particular study area is located in the upper Camaqu~ River Basin, where gold, copper and marble occurs. Stream bed sediments were collected during four sampling periods, between 1992 and 1994. Total Fe, Mn, Cu, Zn, Pb and Hg concentrations as well as TOC contents were determined in the silt-clay fraction of all collected samples. Sequential e~tfactions were performed in some selected samples to evaluate geochemical phase associations and potential metal mobilities. A general increase in metal concentrations was observed in more recent sampling periods for Mn, Fe and Cu, e~pecially in the copper mining area. Two groups of metals, Cu-Fe and Hg-Pb-Zn-Mn, presented some similarities in spatial distributions, but exhibited different geochemic behaviors in the gold and copper mining areas. l~eywords: sediments; heavy metals; mines: environmental geology: fluvial environment * Corresponding author. by a complex variety of lithologies including schists, granitic-gneisses, volcano-sedimentary and molassic sedimentary rocks (DNPM, 1989). The predominant human activities are cattle raising, agriculture (rice crops), and mining of gold, copper and marble. Copper and gold exploitations began, in the upper Camaqu~ River Basin, during the last century and continued into the early nineteen hundreds. However, interest into past, present and future environmental impacts has only recently appeared . In the period of time during which the sampling of this study was conducted, only the copper mine was going on, while 0375-6742/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. t'II S0375-6742(96)00074-X
Rem: Revista Escola de Minas, 2015
A regional study on the arsenic concentration in surface waters and stream sediments, with a density of one sample every 13 km2, was carried out for the first time in the Quadrilátero Ferrífero (Brazil). The region was divided into 3rd order catchment basins, in which 512 areas were sampled. The arsenic concentration was determined in waters and stream sediments after partial digestion with the aid of ICP-OES. The arsenic values found in surface waters ranged from 57.70 to 414 µg.L-1, while for stream sediments, arsenic concentrations ranged from 0.63 to 1691 mg.kg-1, and from the 512 sampling points, 135 (26%) had arsenic concentrations above the limit of detection, which was 0.63 mg.kg-1. It was also found that 106 3rd order catchment basins had values above the third quartile, (5.09 mg.kg-1). The results show that high concentrations of this element are strongly related to the presence of Nova Lima rocks that contain minerals rich in arsenic. However, the anthropogenic influence ...
Environmental Geology, 2003
This paper describes the geochemistry of water and sediment samples downstream from two iron mines in the Gualaxo do Norte River basin, north of Mariana city, Minas Gerais state, Brazil. Electric conductivity, total dissolved solids, pH, E h , Na, K, Ca, Mg and trace elements (Fe, Mn, Al, Cd, Ni, Cr, Zn, As, Pb, Co, Sb, Cu, Mo, Rb, Sr, Ti, V, Y, Zr and Ba) have been analysed in water and sediments. The observed Na anomalies are mainly associated with the iron mine processing plants. Enriched concentrations of iron and manganese were only observed in rudimentary gold exploitation areas (prospectors) and where supergenic alteration of the banded iron formation has occurred. Iron and manganese background values are in some places higher than the limits established by Brazilian legislation. Mn, As, Sb and Ba anomalies have been observed in sediments. Their main source is associated with the sulphide-rich mineral deposits in the spring of the Gualaxo do Norte River and not directly related to the present iron exploitation in the region. Background values are proposed for the studied region.