Estimating Release of Trace Elements from an Area with Historical Open Pit Mining of Alum Shale Using Mass Transport and Element/Sulfate Ratios Calculations

Kristina Åhlgren,Viktor Sjöberg,Mattias Bäckström

doi:10.3390/environments7110100

Abstract

Alum shale was mined for oil and uranium production in Kvarntorp, Sweden, 1942–1966. Remnants such as pit lakes, exposed shale and a 100-meter-high waste deposit with a hot interior affect the surrounding environment, with elevated concentrations of, e.g., Mo, Ni and U in the recipient. Today most pit lakes are circumneutral while one of the lakes is still acidic. All pit lakes show signs of sulfide weathering with elevated sulfate concentrations. Mass transport calculations show that for elements such as uranium and molybdenum the western lake system (lake Söderhavet in particular) contributes the largest part. For sulfate, the two western lakes contribute with a quarter each, the eastern lake Norrtorpssjön about a third and a serpentine pond system receiving water from the waste deposit contributes around 17%. Except for a few elements (e.g., nickel 35%), the Serpentine system (including the waste deposit area) is not a very pronounced point source for metal release compared to the pit lakes. Estimates about future water runoff when the deposit has cooled down suggest only a slight increase in downstream water flow. There could possibly be first flush effects when previous hot areas have been reached by water.

Highlights

Mining can have a long-term impact on the surrounding aquatic systems and deteriorate water quality
Oil and uranium production has affected the environment in Kvarntorp
Downstream water has higher concentrations of these elements than water upstream the Kvarntorp area. Features such as the pit lakes, weathering shale exposures and the waste deposit all affect the downstream water quality, mining and production ceased more than 50 years ago

Summary

Introduction

Mining can have a long-term impact on the surrounding aquatic systems and deteriorate water quality. There are several examples worldwide where coal mines have had negative impact on the environment, and it is often associated with acid rock drainage Mining of black shale can display the same type of problems with acid rock drainage and metal release since black shales in many cases are a source of acidity and trace metals released to the environment It has been shown that black shale alteration is initiated by oxidation of pyrite and organic matter [9]. Soils developed on Cambrian black shales in China have shown increased concentrations of Mo, Ca, Sb, Sn, U, V and Ba [10]. It has been found that from deposits of processed black shale mainly the same metals are dispersed as from acid sulfate soils [11]

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Conclusion