Tailings are a waste product of primary metal production. Although these metals contribute to the development of modern technology and renewable energy systems, tailings pose significant environmental, economic, and human health risks. Stored behind a dam in tailings storage facilities (TSFs) these waste materials are meant to be isolated from the surrounding environment. However, in the last 120 years at least 350 tailings dam have collapsed, resulting in over 2500 casualties, tens of billions of dollars in financial losses, and severe damage to waterways and the environment. There is a worrying trend of failures becoming more severe and increasing in intensity, and because metal demand is increasing and ore grades are declining, this could potentially become more problematic in the near future.

This study concisely describes the production and disposal of tailings and gives background information on tailings dam failures. Furthermore, it provides a basis for understanding the variations between TSFs across resources categories. Finally, it contributes to the quantification of future copper tailings generation in light of the renewable energy transition. It does so by giving an overview of scientific literature on TSFs, by providing global inventory of TSFs categorized by resource type, and by forecasting the copper tailings production until 2040. Two research question have been answered:

RQ1: To which resources are tailings storage facilities linked?
RQ2: How will the renewable energy transition affect copper tailings production until 2040?

RQ1 presents a comprehensive overview of the resources associated with tailings storage facilities by identifying the primary resources linked to each TSFs. This was done by combining a database on existing TSFs worldwide (GRIDA) with a database that contains mining and mineral processing hubs (USGS MRDS). TSFs have been linked with USGS MRDS hubs by using location data using the geographic information system QGIS and by matching TSFs and mine based on their names. Resource data of TSFs that could not be linked with USGS MRDS data has been manually added by systematically analysis of company websites that own the TSFs, supplemented with scientific literature regarding mining locations, thereby forming the GRIDA+ database.

RQ2 forecasts how the ongoing renewable energy transition will impact copper tailings production up to 2040. Because renewable energy systems use more copper than their fossil equivalents, the energy transition will cause an increase in copper demand. Three IEA energy scenarios (STEPS, SDS, and NZE) have been used as basis for this copper demand. By taking into account the copper recycling rates, ore grades, and smelting efficiency based on scientific literature, this study quantifies the anticipated increase in annual copper tailings production in the period 2020-2040.

This study has identified 27 resource categories linked to TSFs in GRIDA+. The 10 most notable categories are gold, copper, aluminium, lead-zinc, coal, iron, PGE-nickel-chromium, silver, diamond, and manganese. Combined they account for over 90% of TSFs worldwide and 93% of the global tailings volume. Among these categories, the top 3 commodities (copper, gold, and iron) contribute to approximately 74% of the overall tailings volume. Copper accounts for approximately 41% of the total volume reported in the GRIDA+ database, and copper TSFs are among the largest in the world in terms of pond capacity and dam height. The presence of upstream dams in copper TSFs is a cause for concern, as historical data indicates that such dams have a higher likelihood of failure. Additionally, nearly one-third of copper TSFs are inactive, rendering them more susceptible to failure compared to officially closed dams. However, copper TSFs demonstrate relatively favourable performance in terms of stability concerns, the availability of engineering records, and resilience against extreme weather events compared to other resource categories.

The forecasts of the 2040 annual global production indicates that of copper tailings production will grow significantly compared to 2020. The tailings-to-metal ratio of copper will increase from 193:1 to 237:1 and the annual copper demand will increase with 31% to 67%. This will increase the annual copper tailings production with 41% in the STEPS scenario, 47% in the SDS scenario, and 79% in the NZE scenario compared to 2020. In this last scenario the annual tailings production is estimated at 3,740,000,000 m3, which in volume is equivalent to 66% of the annual global crude oil production. Copper tailings is primarily driven by the growing demand for copper and to a lesser extent by the diminishing copper ore quality. Advancements in recycling rates and the possible deterioration of copper smelting efficiency could respectively have a substantial dampening or additional effect on future copper tailings growth.

Because of the expected surge in copper tailings production enhancing tailings storage facility management and improving copper recycling are two important challenges for the future. Converging factors such as increasing mineral demands, diminishing ore grades, advancements in extractive and processing technologies may cause the mining industry to start new mining operations and rapidly upscale existing projects. This puts additional pressure on existing and planned TSFs, leading to additional risks of tailings dam failures. These developments make urgent action necessary in order to prevent future TSF catastrophes and to assure a save, sustainable, and stable supply of copper and other minerals in the future.

Policymakers should adopt measures to limit copper demand and improve copper recycling rates, aim at including the effects of tailings dam failures in Life Cycle Assessments (LCAs) thereby emphasizing the benefits of recycled copper, and enforce a comprehensive industry standard for tailings management.