In Chile, mining has historically been an economic pillar but has also left a significant mark on the landscape and the environment. One of the most troubling legacies is the tailings dams, most of which have been managed using conventional methods.
According to the National Geology and Mining Service (SERNAGEOMIN), as of March 2023, 764 tailings dams were registered in the country, distributed across 10 of Chile’s 16 regions. The Coquimbo Region accounts for more than half of these dams, with 389 deposits, followed by the Atacama Region, with 88 deposits in the Municipality of Copiapó. Of these, approximately 60% are inactive, 22% are abandoned, 16% are in operation, and 2% are under construction.
Improper management of these tailings has led to environmental and human disasters. A tragic example is the collapse of the El Soldado mine tailings dam in 1965, which, following an earthquake, triggered an avalanche of toxic sludge that buried the town of El Cobre, killing at least 200 people.
At the international level, the 2019 Brumadinho disaster in Brazil highlighted the risks of conventional tailings. The collapse of the Córrego do Feijão mine dam released 12 million cubic meters of waste, killing 270 people and leaving 11 others missing. More recently, in February 2025, in Zambia, Africa, the collapse of a tailings dam at a copper mine released 50 million liters of acidic waste into the Kafue River, severely impacting the aquatic ecosystem.
These events underscore the urgent need to review and update tailings management regulations. In Chile, Supreme Decree No. 248, which regulates tailings disposal, has been criticized for being outdated and failing to consider safer technologies such as paste or filtered tailings. The ongoing review of this regulation is an opportunity to align national practices with international standards and ensure safer and more sustainable mining.
Filtered and Paste Tailings: Technical Solutions for Safe and Efficient Mining
Faced with the challenges posed by conventional tailings disposal, filtered tailings and paste tailings technologies are emerging as effective technical solutions for reducing geotechnical risks, minimizing water use, and adapting to Chile’s topographic and seismic conditions.
Filtered tailings are obtained through solid-liquid separation processes, such as vacuum or pressure filtration, which achieve less than 20% residual moisture content. The resulting material has a “wet cake” consistency and is transported by trucks or conveyors to a dry deposit. This type of tailings allows for high water recovery (solids > 85%), minimizes the need for retaining walls, and substantially improves the physical stability of the deposit, making it ideal for small- and medium-scale operations in arid areas or areas with intense seismic activity, as is the case at several sites in northern Chile. The operational capacity of a larger number of filters and investments limits large-scale mining operations.
On the other hand, paste tailings are characterized by a higher solid content than conventional tailings but lower than filtered tailings. They are obtained through high-density thickeners and laminar flow transport through pipelines. This mixture, which flows slowly and can be deposited at controlled slopes, allows for greater consolidation and stability of the deposit, achieving very high densities of 1.6 to 1.8 m3/t, comparable to compacted filtered densities. Although it requires an investment in piping, such as high-pressure pumping stations and rheological control, it is highly efficient for high-tonnage operations, typical of large-scale Chilean mining.
The significant environmental advantage of both technologies over conventional tailings is the elimination of the threatening mass of mud and water with densities of 1.2 to 1.4 m3/t, millions of m3 that cause infiltration into the soil where they are located, are a source of particulate matter when they dry, and present a very high risk in the event of failures such as those mentioned.
Both technologies represent a necessary evolution to address current challenges in mining waste management. They reduce environmental and social risks, improve water efficiency, and optimize land use—key factors in the context of increasing regulatory and climate pressure.
Recommendation for the Chilean Case
In Chile, many mining operations process between 100,000 and 400,000 tons per day, representing capacities up to 20 times greater than those in other regions of the world. These conditions require robust solutions adapted to high tonnage, seismic environments, extreme weather events, and intense rainfall in traditionally arid areas.
Below is a comparative technical recommendation for Chile:
In summary, paste tailings offer greater technical and economic scalability for large-tonnage operations, although they require high-torque thickeners and a hydraulic design for high-viscosity slurries. Filtered tailings, on the other hand, are highly recommended for medium—or small-scale operations, especially in areas with high seismic activity and water scarcity, where water security and recovery are priorities.
Is a Hybrid Solution Viable? Filtration + Paste in a Single Operation
Hybrid solutions can represent an efficient and flexible strategy in contexts with different production lines or processing stages with varying flow rates. For example, a plant could implement mechanical filtration for a portion of the tailings while directing the remainder to a thickened or paste tailings system. This allows:
- To Adjust the design based on pulp variability.
- To Minimize water usage without compromising continuous operation.
- To Reduce costs associated with mass filtration equipment for the entire flow rate.
- To Adapt the disposal strategy to the site’s topography.
Pilot examples and developing operations in both Peru and Canada are exploring this hybrid approach. In Chile, this solution can be especially useful in operations with secondary concentrator plants or those transitioning from a conventional to a more modern design, allowing for gradual implementation without halting production.
Supreme Decree No. 248 and its Update Proposal: A Necessary Step Toward Regulatory Modernization
Supreme Decree No. 248, in force since 2006, regulates the procedures and technical requirements for the Chilean mining industry’s approval, design, construction, operation, and closure of tailings dams. Its primary purpose is to safeguard the safety of people and the environment and establish minimum standards for these facilities’ physical and chemical stability.
However, technological advances, climate change, and increased environmental awareness have made this regulatory framework outdated. In response, the Ministry of Mining presented a proposal for a new regulation on July 2, 2024. The proposal was published in the Official Gazette on July 5 and submitted for public consultation between July and August of the same year. To date, its promulgation has not yet been officially confirmed.
The new text seeks to update and replace DS 248, incorporating more rigorous approaches to risk classification, geotechnical characterization, impact control, and operational planning.
Similarities between both regulations:
- Purpose and application: Both regulate the complete cycle of tailings dams, prioritizing safety and the environment.
- Role of SERNAGEOMIN: It remains the leading authority for review, approval, and oversight.
- Technical definitions: They agree on the key terms, although the proposal expands on them.
Key differences that demonstrate the obsolescence of the DS 248:
The proposal represents a substantial step toward modern and responsible tailings management, aligned with international best practices. While it will require higher technical standards and implementation costs, it will also provide greater safety, transparency, and environmental control—key aspects for the future sustainability of Chilean mining.
Conclusion: Modernizing Tailings Management is a Technical and Ethical Decision
The evidence is clear: water and safety matter and conventional tailings no longer offer sufficient guarantees against the mining industry’s current challenges. Their obsolescence has been demonstrated by both historical accidents in Chile and recent disasters abroad. Added to this is the growing pressure for more sustainable, resilient, and resource-efficient mining.
Technologies such as filtered tailings and paste tailings are now presented as the safest and smartest solutions for waste disposal. Each offers clear advantages depending on the processing volume, the geotechnical and climatic conditions of the environment, and the mining operation model. Furthermore, their implementation significantly reduces environmental risks, water recovery, and operational traceability.
As proposed by the update to Supreme Decree No. 248, regulatory modernization must accompany the implementation of these technologies on the ground. Process Minerals Consulting has the technical expertise to support our clients in this process, from the design and implementation of paste and filtration tailings systems to their operational optimization and adaptation to new regulatory requirements.
We are convinced that the future of Chilean mining will be safer, more efficient, and more responsible… as long as we are willing to take a step toward truly modern tailings management.
