In the state of Santa Catarina, Brazil, coal mining began in the late 19th century and, for decades, occurred without environmental care. The coal in the region has a high sulfur and ash content. To meet the standards of the local thermoelectric plant, the coal needs to be processed to remove pyrite and associated rocks, generating 50%–70% waste. It is estimated that more than 320 million tons of coal waste have already been deposited on the surface. The result is a legacy of immense waste with a high pyrite concentration (12%), representing a major environmental problem in Brazilian mining: there is contamination of soil, surface water and groundwater of three river basins by acid mine drainage (AMD). Although legislation and actions to ameliorate environmental damage have advanced substantially since the 1990s, some areas remain affected. Models indicate that AMD may continue to be generated for more than 500 years, requiring effluent treatment and long-term monitoring of the areas. However, in the 1980s, coal waste was reprocessed to concentrate pyrite for the production of sulfuric acid. This practice was discontinued and it is considered one of the major setbacks in the sector, as it went from a clear circular economy to a linear economy (coal to thermoelectric power).

This study assessed the environmental, economic and social benefits that the use of pyrite would have brought to the southern region of Santa Catarina if pyrite concentration had continued. It used quantitative coal waste production data and pyrite was subjected to gravimetric separation tests performed in the laboratory. The processing products were characterised in terms of the sulfur content (pyritic, organic, sulfate and total) and acid generation potential.

The results showed that pyrite recovery would provide the following advantages: reduce the mass of waste by approximately 10%, and decrease the net acid generation potential and lime consumption in active AMD treatment systems by 60%–70%. In addition, there might have been easier decommissioning of the areas and a better supply of sulfuric acid on the Brazilian market. Finally, the results are discussed in terms of the Brazil’s energy matrix, in which coal has lost strength. At present, the decommissioning of this sector is in progress.

In conclusion, if the region had been seen both as a coal and a sulfide deposit, this transition would have been smoother and would have left less of a legacy of pollution for future generations.

The objective of this study is to analyze the failure mechanisms of the Tailing Storage Facility (TSF) Brunita in NE Spain. The dam collapsed on October 20, 1972, resulting in substantial environmental damage and economic consequences. The forensic analysis employed geological, geotechnical, and geophysical criteria to determine the causes of the flow failure.

Despite extensive research on the dam by various experts, none have confirmed the failure process through numerical modeling. Hence, numerical simulations using the GeoStudio Core software package were conducted in four stages: (1) steady-state infiltration analysis to establish reference conditions prior to heavy rainfall, (2) transient infiltration analysis to account for additional water from heavy rainfall, (3) calculation of safety factors and potential failure surfaces using limit equilibrium methods, and (4) stress-strain analysis to estimate displacements and deformations in potentially unstable zones under variable saturation conditions.

The results indicated that heavy rainfall of 119 L/m² in one week substantially increased pore water pressures, leading to a drastic reduction in shear strength and TSF stability. The failure was primarily triggered by internal erosion (piping) and loss of suction in the tailings. The increased pore water pressure weakened the structural integrity of the dam, making it susceptible to failure under the added stress of the heavy rainfall. The findings demonstrate that the dam needs to remain in unsaturated conditions to ensure its stability. This study underlines the fundamental role of effective drainage systems in maintaining the stability of tailings storage facilities under extreme weather conditions. Proper drainage systems can help manage water infiltration and prevent the build-up of pore water pressure, which is crucial for the long-term stability of such structures. Additionally, the study highlights the importance of continuous monitoring and maintenance of tailings storage facilities to detect and mitigate potential failure mechanisms before they lead to catastrophic events.

In conclusion, the forensic analysis and numerical simulations provided valuable insights into the failure mechanisms of the TSF Brunita. The study emphasizes the need for robust design and maintenance practices to ensure the safety and stability of tailings storage facilities, particularly in regions prone to heavy rainfall. By understanding the factors that contributed to the failure, future incidents can be prevented, thereby protecting both the environment and the communities living near such facilities.

Based on two real scale trials carried out in an abandoned mercury mine waste dump, a solution to prevent and reduce the contamination of water with arsenic (As) and mercury (Hg) is proposed. First, the waste surface is covered with a layer of fly ash preventing 90% of the water to be contaminated. Second, the leachate is treated in filtering channels with fly ash and steel slags to reduce the As concentration in four stages with reduction of 60% in each stage. The results demonstrate the feasibility and usefulness of the proposed solution.