title: Neutralisation of an acidic pit lake by alkaline waste products.
abstract: A former open pit where black shale (alum shale) was excavated during 1942-1965 has been water filled since 1966. The water chemistry was dominated by calcium and sulphate and had a pH of 3.2-3.4 until 1997-1998, when pH was gradually increasing. This was due to the intrusion of leachates from alkaline cement waste deposited close to the lake. A stable pH of around 7.5 was obtained after 6-7 years. The chemistry of the pit lake has changed due to the neutralisation. Concentrations of some dissolved metals, notably zinc and nickel, have gone down, as a result of adsorption/co-precipitation on solid phases (most likely iron and aluminium hydroxides), while other metals, notably uranium and molybdenum, are present at elevated levels. Uranium concentration is reaching a minimum of around pH 6.5 and is increasing at higher pH, which may indicate a formation of neutral and anionic uranyl carbonate species at high pH (and total carbonate levels around 1 mM). Weathering of the water-exposed shale is still in progress.
authors.affiliation: Man-Technology-Environment Research Centre, Örebro University, 70182, Örebro, Sweden, bert.allard@oru.se.
authors.forename: Bert
authors.initials: B
authors.lastname: Allard
authors.forename: Mattias
authors.initials: M
authors.lastname: Bäckström
authors.forename: Stefan
authors.initials: S
authors.lastname: Karlsson
authors.forename: Anja
authors.initials: A
authors.lastname: Grawunder
mesh_terms: D000468:Alkalies / Q000032:analysis*; D000534:Alum Compounds / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods / Q000706:statistics & numerical data*; D006863:Hydrogen-Ion Concentration; D060106:Lakes / Q000737:chemistry*; D019216:Metals, Heavy / Q000032:analysis*; D008906:Mining; D013548:Sweden; D014501:Uranium / Q000032:analysis; D014866:Waste Products; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D000468:Alkalies; D000534:Alum Compounds; D019216:Metals, Heavy; D014866:Waste Products; D014874:Water Pollutants, Chemical; D014501:Uranium
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