The treatment of thousands of uranium waste drums in Mendoza stands as a reference case in a context where nuclear energy is re-emerging on the medium-term horizon.
By Panorama Minero
The remediation of the Sierra Pintada Mining Complex in San Rafael addresses one of the most complex environmental legacies in Argentine mining: thousands of uranium waste drums accumulated over decades of operation, as well as large volumes of water in contact with mineralized material. This is not a superficial cleanup or a one-off project; it is a large-scale industrial intervention, requiring the controlled treatment of approximately 5,200 200-liter drums, each containing residual uranium, under strict technical and regulatory standards.
A Drum-by-Drum Approach
The challenge lies not only in the total volume of material but in the individualized nature of the process. Each drum must be handled, opened, and treated under controlled conditions, with no operational shortcuts, in a framework that prioritizes radiological safety, chemical stability, and the permanent containment of the waste. That sheer number—thousands of drums—explains why Sierra Pintada’s remediation cannot be artificially accelerated or simplified: it is, quite literally, a drum-by-drum operation.
The approved process for these solid wastes reflects this approach. Drums are transported to the treatment plant, where specialized equipment ensures safe opening. The contained material is washed with quarry water, and residual uranium is recovered through ion-exchange resin columns, a selective technology that avoids aggressive mineral dissolution. Once uranium is extracted, the remaining solids are neutralized with lime to reduce reactivity, and the generated effluents are directed to the final disposal system. There is no acid leaching or sulfuric acid use: the technical design deliberately excludes such processes, prioritizing geochemical stability and long-term environmental control.
The Other Major Liability: Quarry Water
In parallel, remediation addresses another significant liability: quarry water accumulated in old pits due to rainfall and groundwater infiltration in contact with mineralized zones. This water is treated in multiple stages—first to recover uranium using specific resins, and then to manage associated elements such as radium and arsenic. Once treated and clarified, water is reused onsite under controlled and monitored conditions, completing a closed-loop system with no external discharges.
All resulting material—neutralized solids and treated effluents—is finally contained in a final disposal dam designed with multiple protective barriers, geomembranes, drainage systems, and natural isolation layers. This is not an ancillary component but a central piece of remediation engineering, ensuring long-term containment and preventing any future migration of contaminants.
Current Stage of Remediation
Currently, Sierra Pintada remediation is in an early-to-mid operational stage. The project has fully completed the administrative and environmental phases—Environmental Impact Declaration granted and auditing schemes defined—and is actively executing priority works, commissioning plants and systems, and initiating the treatment of liabilities. However, it has not yet reached a full-scale, sustained mass processing regime for all waste. Progress is incremental, stage-validated, and continuously monitored, without artificial acceleration, a standard practice in nuclear remediation projects of this complexity.
This approach, implemented by the National Atomic Energy Commission (CNEA) and subject to permanent auditing, marks a turning point compared to previous decades. Sierra Pintada, long synonymous with unresolved environmental liabilities, is now an active, technically demanding, and necessarily gradual process, where progress is measured more by the consolidation of facilities, plants, and control systems than by quick closure announcements.
The Weight of Mining History
This context highlights the historical significance of the complex. Sierra Pintada was Argentina’s last major operating uranium deposit, producing nearly 1,600 tonnes of uranium between 1975 and 1997, supplying the national nuclear program. Its closure left a legacy now being addressed with environmental engineering tools that were either unavailable or not required at the time.
The ongoing remediation not only addresses this legacy but also sets a technical benchmark for any future uranium-related discussions in Mendoza and across Argentina. Before new projects are considered, the province is executing one of the sector’s most complex tasks: dismantling, treating, and containing thousands of uranium drums individually, under public oversight and long-term criteria.
In this sense, Sierra Pintada’s remediation goes beyond the environmental liability itself. The process aligns with the global and national resurgence of nuclear energy, where uranium regains strategic relevance as a key input for low-emission, high-power-density energy matrices. Argentina continues to maintain nuclear projects at various planning and development stages, needing a review not only of future resource availability but also of the environmental and social standards under which those resources could be eventually utilized.
Mendoza and Emerging Evaluation Models
Mendoza is fully part of this scenario. In addition to concentrating a substantial portion of the country’s identified uranium resources; the province is reappearing on the exploratory radar with initiatives that propose production models different from historical ones. Among them is the El Corcovo project, promoted by Blue Sky Uranium, currently under analysis and evaluation with a view toward potential in-situ recovery (ISR) production—a method that, if implemented, would imply an operational and environmental logic entirely different from conventional mining, which generated Sierra Pintada’s liabilities.
In this context, the ongoing remediation serves as an indispensable reference case. Not only does it directly address past impacts, but it also establishes a technical, regulatory, and social baseline for any future uranium development in Mendoza.
