Abstract
In recent years, there has been an increasing focus on the adverse environmental effects from naturally occurring radioactive materials (NORM). Acid rock drainage (ARD) produced by debris from mining and construction work is a major environmental issue, leading to release of highly acidic water as well as both NORM and stable trace elements. Batch leaching experiments with alum shale demonstrated that exchange of water will increase leaching of elements whose mobility is limited by concentration effects, such as Ba and the extremely radiotoxic, naturally occurring uranium daughter 226Ra. Periods of drying the alum shale in air increased leaching of Li, V, Mo and 226Ra, increasing their mobility in the environment. Acid production from sulphide oxidation did not cause pH values below 6.4 in the 28 weeks experiment. However, exchange of water did lead to reduction of inherent buffer capacity of the alum shale, which increases the risk of ARD as well as likely reducing the time before onset of ARD.
Highlights
Today, the global population growth and increasing rate of con sumption cause rising demands for raw materials
The results demonstrate that the alum shale from Gran is somewhat resistant towards a pH drop, and even with drying periods and exchange of water the buffer capacity was not depleted after 28 weeks
When alum shale debris comes in contact with water, an initial high release of contaminants can be expected, leaching rates are expected to decrease for most elements until an eventual pH drop and onset of acid rock drainage (ARD) that is likely to increase leaching and solubility for a range of elements
Summary
The global population growth and increasing rate of con sumption cause rising demands for raw materials. Many of these raw materials are mined, which often has major environmental conse quences. Rock debris from mining or construction work in certain geological areas can be a major source of naturally occurring radioactive material (NORM) and stable trace elements. Storage conditions for such debris are critical for weathering rates and influence the release of contaminants into the environment. Alum shale contains silicate minerals, sulphides, car bonates and organic matter (kerogen), and is enriched with several trace elements including Ba, V, Mo, Co, Ni, Cu, Zn, Cd, and As, as well as the uranium-series (Falk et al, 2006; Owen et al, 1990; Pabst et al, 2016)
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