Feasibility of safe and effective CRM recovery from tailings storage facilities

Old mine waste could become a key resource for the future. Large volumes of metals remain in tailings storage facilities, materials once considered uneconomical but now classified as critical for the green transition. Researchers are now exploring how these resources can be recovered in a safe, efficient and economically viable way, despite the technical challenges posed by water-saturated deposits.

Metal and mineral mining generate large volumes of waste known as tailings – the portion of ore that is not economically recoverable at the time of extraction. Tailings are typically stored in tailings storage facilities (TSFs), which can cover several square kilometres and reach heights of several tens of metres. The composition of deposited tailings reflects historic fluctuations in metal prices, refining processes and technical developments, because price changes dictate how much material is deemed waste versus a viable resource.

In many TSFs, there are minerals that were previously left unrecovered due to economic or technological constraints. Some of these are classified today as “critical raw materials (CRMs)” or “strategic raw materials (SRMs)”. Consequently, the material already lying in place is essentially a preconcentrated resource that could be reprocessed. Such re-processing is in line with EU’s Critical Raw Materials Act (CRMA).

Extracting minerals from existing deposits poses distinct technical challenges that must be resolved before production can commence. Unlike conventional hard rock mining, which relies on drilling and blasting, recovery from tailings deposits is more like “digging out” the material. Although this may appear simpler, TSFs consist of water saturated tailings that normally cannot be excavated below a depth of a few meters. Deeper walls of excavation will start to collapse and material might liquefy. In geotechnical engineering, conventional reinforcement techniques (e.g., diaphragm walls, sheet piles etc.) are employed for deep excavations in urban areas, but applying comparable methods to stabilize tailings deposits has not yet been demonstrated as possible and cost-effective. The stabilization process is time-consuming and will set limits for continuous extraction from the deposit.

Recent discussion among Swedish mine companies have highlighted the growing interest in re-mining of tailings through excavations. While the concept is regarded as a promising route to access critical minerals, a safe and cost-effective excavation methodology has not yet been identified. In terms of safety, both dam stability (perimeter embankment dams) and the work environment (close to the excavation pits) must be considered.

Therefore, developing safe, efficient, and economically viable excavation or mining methods for reprocessing tailings from TSFs is a prerequisite for scaling up secondary resource recovery, i.e re-mining. This research aims to investigate and optimise such methods, addressing geotechnical stability, water management, and extraction efficiency, thereby enabling industrial scale reclamation of tailings as a sustainable source of critical raw materials.

The aim is to conduct a t project that serves as a first step feasibility study for the safe, economical, and scalable extraction methods of critical raw materials from existing, water-saturated tailings storage facilities in Sweden. This project will:

1. Map the current international state-of-the-art in tailings re-processing, excavations and corresponding geotechnical stabilization
2. Translate that knowledge to the Swedish regulatory, geological, and industrial context
3. Validate selected concepts through laboratory and small-scale field trials, focusing on excavation in water-saturated, loosely deposited tailings

The outcome will be a clear set of recommendations and a validated methodological framework that can serve as a base for a larger multi-year research programme.