Mobilisation of metals and metalloids from historical smelting slag dumps, Rio Tinto, Spain

Lottermoser, B.G. (2004) Mobilisation of metals and metalloids from historical smelting slag dumps, Rio Tinto, Spain. In: Proceedings of 14th Annual Goldschmidt Conference (68) A437-A437. From: 14th Annual Goldschmidt Conference, 5-11 June 2004, Copenhagen, Denmark.

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While the chemistry and mineralogy of sulfidic, AMD producing wastes have been studied in great detail, few studies have focused on smelting residues commonly present at historic mine sites. This is despite the fact that historical base metal smelting slags contain elevated levels of heavy metals and metalloids and are subject to contemporaneous weathering processes thereby releasing elements to ground and surface waters. This work reports the chemistry and mineralogy of slag deposits (3 Mt) at the historic Rio Tinto smelter site, southwest Spain.

The microcrystalline slags contain primary slag phases, relict flux, ore and furnace materials and secondary weathering related minerals. Common primary slag phases are glass, Zn-rich fayalite and Zn-rich hedenbergite/augite. The slag materials contain wt% concentrations of Zn, major (ie. 1000 - 10000 ppm) Cu and Pb, minor (ie. 100 - 1000 ppm) Co, Sb and Sn, and traces (ie. <100 ppm) of Ag, As, Bi, Cd, Mo, Ni, TI and W. The slags have been subject to weathering since dumping in the 19th and 20th century, and a series of mineral efflorescences has been observed. They most commonly occur as powdery or cemented salt precipitates at seepage points and as solid aggregates in protected overhangs facing the Rio Tinto river. Mineral salts include gypsum, epsomite and copiapite as well as a series of minor phases such as roemerite, bloedite and hexahydrite. The mineral mixtures contain variable metal concentrations, including major Cu and Zn, minor As and Co, and traces of Cd, Ni and Pb.

Rio Tinto slags have high concentrations of metals and metalloids in the order of Zn>Cu>Pb>Sb>Co>As>Ni. In contrast, the mineral salt mixtures have metal concentrations in the order of Zn>Cu>As>Co>Ni>Sb. Such distinctly different relative concentrations of elements in the two sample media collected from the weathered slag dumps can be related to the different mobility of elements in surface environments. For example, Sb displays a reduced mobility possibly due to the formation of insoluble precipitates, coprecipitation and adsorption in the slag dump. Thus, weathering of siliceous smelting slags is accompanied by the preferential mobilisation of some trace elements (ie. As, Co) into pore and seepage waters. Evaporation of the saline, metalliferous seepage waters emanating from the siliceous slag dumps causes the precipitation of secondary minerals. These minerals temporarily store metals, metalloids and sulfate until redissolution during the next rainfall. The Rio Tinto slag dumps represent long-term sources of metals and metalloid pollutants to local ground and surface waters.

Item ID: 8165
Item Type: Conference Item (Abstract / Summary)
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Geochemica et Cosmochimica Acta: Special Supplement Abstracts of the 14th Annual V.M. Goldschmidt Conference

Date Deposited: 09 Sep 2010 01:21
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040202 Inorganic Geochemistry @ 100%
SEO Codes: 84 MINERAL RESOURCES (excl. Energy Resources) > 8498 Environmentally Sustainable Mineral Resource Activities > 849899 Environmentally Sustainable Mineral Resource Activities not elsewhere classified @ 100%
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