Abstract

Tailings Storage Facilities (TSFs) are essential for managing mining waste, exhibiting significant variations in their properties due to the hydraulic filling method, interactions with the atmosphere, and material position within deposit. This short review analyze various zonation models and presents a comprehensive model identifying four distinct zones: dike, discharge, transition, and distal (lagoon). Understanding these zones is crucial for optimizing TSF design, enhancing safety assessments, and ensuring long-term stability and environmental protection.

Keywords:Hydromechanical Behavior; Tailings Storage Facilities; Hydraulic Filling; Geotechnical; Mechanical

Introduction

Tailings Storage Facilities (TSFs) play a vital role in managing mining waste, ensuring environmental safety and structural stability. After valuable materials have been extracted, tailings are typically disposed of in TSFs. Over 98% of TSFs worldwide are constructed using the hydraulic filling method, where slurry deposits are discharged into an impoundment. Consequently, TSFs exhibit significant variations in their physical, mechanical, and hydraulic properties across different zones in perpetuity. In the recent 50 years various researchers have proposed different zonation models for TSFs based on geotechnical, mechanical, and hydraulic properties. Smith [1] identified discharge zone and lagoon based on mechanical resistance. Vick [2] proposed beach and lagoon but did not define specific geotechnical characteristics. Additionally, Bu et al. [3] observed that the stacked waste follows certain deposition pattern, with coarser materials at front and finer at the end of the deposit. Wels et al. [4] defined beach, intermediate, and slimes zones based on geotechnical properties. Morgenstern et al. [5] described predominantly slimes, interbedded slimes, and isolated slimes, focusing on granulometric distribution. Bella [6] categorized dike, beach, and lagoon zones based on mechanical and hydraulic behavior. Each study was based on a specific field site. Only recently, Rodríguez-Pacheco et al. [7,8] compiled more than 70 TSF sites and suggested dike, discharge, transition, and distal zones, integrating geological, geotechnical, hydrogeological, and geophysical data.

Zonation conceptual model

Hence, TSFs constructed using the hydraulic filling method exhibit four distinct zones (Figure 1):
•Dike zone: The main retaining structure, built with compacted tailings or rock, characterized by high shear strength and low permeability
•Discharge Zone: Adjacent to the dike, containing sandy-silty material with high permeability and frequent drying-wetting cycles.
•Transition Zone: Between the discharge zone and lagoon, marked by increasing silt content, moderate permeability, and higher capillary rise.
•Distal Zone (Lagoon): The final deposition area with fine silty-clay materials, lowest permeability, and highest water retention.

In each of these zones, a series of processes and phenomena occur due to interactions with the atmosphere (climate), geological and hydrogeological environments, and the drainage system, which influence many of their properties (Figure 1). A detailed description of these processes can be found in Rodríguez- Pacheco et al. [9].

Key Findings

Two notable trends in the behavior of tailings deposited by hydraulic backfill can be highlighted:
• Decreasing Trend: Several parameters decrease from the dike to the lagoon, including grain size, dry density, effective porosity, friction angle, shear strength, shear wave velocities, Young’s modulus, liquefaction resistance and saturate permeability. This is due to the natural segregation of particles during deposition, where coarser materials settle near the discharge point while finer particles travel further.

• Increasing Trend: Other parameters, such as fine content, specific and volumetric surface of solid particles, total porosity, cohesion, retraction limit, liquid limit, plasticity indices, capillary height, total suction, air and water entre value in water retention curve, ion exchange and sorption capacity increase towards the lagoon. This is caused by the accumulation of finer particles in distal zones, leading to higher water retention and lower drainage capacity (Figure 2).

Conclusion

Understanding the zonation within Tailings Storage Facilities (TSFs) is crucial for optimizing their design and ensuring longterm stability and environmental protection. The comprehensive zonation model, which identifies four distinct zones-dike, discharge, transition, and distal (lagoon)-provides a structured framework for managing TSFs effectively. Key trends, such as the decrease in grain size and increase in fine content from the dike to the lagoon, highlight the importance of considering these variations in safety assessments and maintenance strategies. Continuous monitoring and improved engineering designs are essential to address the dynamic nature of TSFs and to mitigate potential risks associated with their operation.

Funding

This research was funded by the Ministry for Ecological Transition and Demographic Challenges (MITECO), Direccion General de Biodiversidad; TD by PRTR Medida C04.I03 belonging to ’Asesoramiento en actuaciones de restauración de zonas mineras en el entorno del Mar Menor’ Project (J. Butlanska) and “Estudio de las materias primas críticas y estratégicas para la transición ecológica y el suministro de las principales cadenas de valor industrial en España” Project (A.O. Oliva-Gonzalez). This work was also supported by grant PID2022-138197OB-I00 funded by MICIU/AEI/10.13039/501100011033 and by“ERDF/E” (R. Rodriguez-Pacheco).

References

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