Release of metals from unprocessed and processed black shale due to natural weathering

• Black shale was mined and processed for recovery of hydrocarbons in Kvarntorp, some 200 km SW of Stockholm, Sweden, during 1942–66. Remains from the mining period is a deposit with 40 Mm³ of crushed shale residues: Unprocessed 3ne-grained shale as well as processed shale. The deposit is still hot; oxidation of sulphides as well as burning of hydrocarbons are still in progress some 50 years a1er closure. Weathering of the shale leads to releases of metal-rich leachates which will increase with time. The release of metals from pristine shale as well as weathered shale (exposed to the atmosphere for 50 years) and two di2erent processed shale residues have been studied using water of di2erent pH as leaching solution, to simulate extreme pH-variations in environmental waters: 3.0 (determined by oxidation of iron sulphides), 5.5 (bu2ered by carbon dioxide), 8.5 (bu2ered by calcite) and 12.5 (bu2ered by calcium hydroxide). Extraction of cationic elements was substantial (several percent of the total content) for Ca and Mg, as well as Ni, Co and U at pH 3, and very high (up to 50–60 %) for anionic elements (V, Mo, As) at pH 12.5. Especially the high-temperature processed shale would be a potential source for As and Mo at high pH. The pH-dependence of the weathering processes should be considered when future remediation (or metal recovery) processes and strategies are designed.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

Nyckelord

Black shale

alum shale

wethering

leaching

Chemistry

Kemi

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