While alum shale presents specific environmental challenges due to its content of sulphide minerals and low to moderate concentrations of metals, there are safe, scientifically validated methods for both mining and managing the resulting waste, if operations are conducted under strict environmental controls that follow the permit conditions.
Modern research, innovations and experience show that an important factor for safely mining alum shales lies in preventing oxygen and water from reacting with the sulphide minerals, which otherwise could generate acid rock drainage (ARD) and mobilize metals. Techniques such as dry stack tailings, engineered covers or caps, and liming (adding alkaline material to neutralize acidity) are proven methods used to minimize or eliminate these risks.
Because tailings are the fine, ground-up rock left after metal extraction, some form of storage is always necessary. The most common method worldwide is wet tailings dams, where tailings are mixed with water into a slurry and deposited behind large embankments. This is the cheapest way to handle very large volumes, which is why it dominates globally, in fact, the vast ponds or dams you see when driving past a mine or on satellite images are usually tailings dams. However, wet storage carries significant risks such as catastrophic dam failures, seepage of contaminates into groundwater, and the need for costly, long-term monitoring.
An alternative is dry stacking (filtered tailings), a method suitable for Alum shale uranium mines. Here, the tailings are dewatered into a damp “cake” that is transported, layered, compacted, and sealed. This reduces water use, makes long-term closure easier, and essentially eliminates the risk of dam collapse and groundwater contamination thru seepage. Though the “cake” still must be stored to prevent dust, erosion, or acid formation. Dry stacking is more expensive and technically better suited to small- and medium scale operations.
A practical example is Langøya island in Norway, where the company NOAH is permitted to deposit up to 100,000 tonnes of alum shale with low natural radioactivity each year. The dewatered shale is mixed with alkaline materials to neutralize acid, sealed to keep out oxygen and water, and later capped and restored. Continuous monitoring has shown that emissions remain well within strict safety limits. Similarly, the Terrafame mine in Finland demonstrates that even alum shale can be exploited safely, using controlled bioleaching and water treatment to manage environmental risks.
In summary, tailings storage, whether in wet dams or dry stacks is always required in mining. Wet dams remain the most common method globally because they are cost-effective for huge volumes, while dry stacking is increasingly chosen for its safety and environmental benefits. With proper design, operation, and oversight, both exploitation of alum shale and handling of the waste can be done safely.
- Tailings.info, “Dry Stacking of Tailings (Filtered Tailings)”, https://www.tailings.info/disposal/drystack.htm
- NOAH, Safe handling of natural radioactivity, https://www.noah.no/en/trygg-handtering-av-naturlig-radioaktivitet/
- SveMin, “Hållbar gruvnäring – Fakta och framtid”, https://www.svemin.se/publicerat-material