Reprocessing potential and environmental risk of Bielatal tailings material, Altenberg, Germany, were assessed using percussion core samples (7 m depth), analyzed for geochemical, mineralogical composition, particle size, and milieu parameters (pH, Eh, EC). Tin (0.12 wt%) and lithium (0.10 wt%) were valuable elements, while arsenic (0.04 wt%) posed environmental concerns. Tin and lithium were associated with cassiterite and mica phases respectively. Samples were composed of 56% silt, 35% fine sand, and 9% clay, with enrichment of tin, lithium, and arsenic in fine fractions. Weak acidity (pH 6) and low oxidation (Eh 160 mV) suggest minimal acid mine drainage risk.

To combat the climate crisis, more metals are needed to accelerate the pace of replacing fossil-fuel-based technologies with renewable energy sources. Although remining has been researched for several decades, the extent to which it could supplement virgin extraction of critical minerals and metals is currently unknown. Programs under way by the US Geological Survey and the European Union, including the EU’s Critical Raw Materials Act of 2024, will increase our knowledge of remining’s potential.

A review of relevant studies, operations, and planned projects has been conducted to examine remining in four areas: Sampling and geochemical characterization; global, regional, and national estimates of the potential for recovery of valuable minerals; remining examples and technical feasibility; and environmental and health effects. This review provides updated remining estimates and examples in the United States, Europe, Australia, Chile, and China and makes recommendations for better understanding remining’s environmental effects and resource potential.

Remining sources for renewable energy metals (e.g., Co, Ni, REEs, Mn, Li) include legacy and existing mine wastes and associated mine waters, coal mine residues, and byproduct and primary production materials. Current remining operations are largely focusing on gold. Tailings are of greatest interest due to their abundance globally and the fact that they are already crushed and ground, which lowers energy and water use. Pollutant registries in the United States, Europe, and Australia can be used to get a very rough estimate of the amount of renewable energy metals in mine wastes, but reporting improvements are needed to better estimate the metal “reserve” and to determine economic viability. Geochemical characterization methods typically applied at active mines for predicting pollution potential need to be expanded to include methods such as mineral liberation analysis and bench-scale process testing for remined materials.

Of the processing approaches examined for recovery of renewable energy metals from tailings, bioleaching appears to offer the most benefits with the fewest potential downsides. The advantages and challenges of different processing methods will be presented. Best practices specifically designed for remining do not currently exist but are urgently needed to improve resource estimates and avoid adverse effects such as the two tailings dam failures that occurred at remining operations in Romania and South Africa.

Interest in remining is booming due to its potential to increase domestic supply. If properly conducted, remining can also improve circularity and environmental conditions in areas affected by existing and legacy mining activity.

Acidic Mine Waters (AMWs) present a major environmental risk due to their high acidity and transition metal content, which can contaminate water bodies and ecosystems. Traditional treatments, while effective at neutralizing acidity and removing metals, generate hazardous sludge, which creates additional environmental concerns. However, recent advances in sustainable technologies have opened up new opportunities to treat AMW in a more resource-efficient way. By considering AMW as a secondary source of Critical Raw Materials (CRMs), such as Rare Earth Elements (REEs), this approach not only mitigates environmental risks but also addresses the increasing demand for CRMs, essential in high-tech industries.

This study introduces a circular treatment scheme for AMW that integrates selective precipitation and ion exchange to recover valuable REEs, focusing on a sustainable alternative to traditional lime-based treatments. AMW from the Aznalcóllar open-pit mine in Spain was utilized, containing relevant amounts of metals like Al, Fe, Zn (in the order of several mg/L), and a total REEs concentration of 18.6 mg/L. The process began with the removal of Fe and Al through precipitation, followed by the selective removal of Zn as a sulfide. Moreover, a fractionation process was developed to separate heavy and light REEs using two different ion exchange resins, prior to their recovery as oxalates.

The study achieved highly efficient metal removal from the AMW, with Fe and Al being removed more than 99.9% and 90%, respectively. The removal of transition metals (Zn, Cd, Cu) as sulfides also exceeded 99% efficiency. Their removal allowed to maximize REEs uptake in the ion-exchange, with concentration factors for REEs up to 50. The final REE oxalates obtained had purities exceeding 90%, confirming the effectiveness of the combined treatment processes.

This research highlights a promising, sustainable approach for the recovery of valuable REEs from AMW, addressing both environmental hazards and the demand for CRMs. The findings suggest that such a circular treatment strategy could be widely applied to treat mine waters while simultaneously generating economic value from CRM extraction. Moreover, this approach reduces hazardous sludge generation, offering an eco-friendly alternative to conventional mine water treatments, with potential for application in other contaminated water sources worldwide.