Simulation of the filtered-tailings stacking operation

Filtered-tailings stacking (FTS), also known as dry stacking, has become an important alternative to conventional tailings dams, especially after recent dam failures in Brazil and the increasing demand for safer disposal methods in mining. However, large-scale implementation of FTS operations remains challenging because of operational bottlenecks, particularly during rainy seasons. This study presents a discrete-event simulation model developed in Arena to evaluate the productivity of an iron ore FTS operation located in Minas Gerais, Brazil. The model incorporates operational variability, equipment performance and rainfall seasonality to reproduce the dynamics of the stacking process. Simulation results showed strong agreement with field observations and identified the drying stage as the main operational bottleneck, representing approximately 83 percent of the total layer construction cycle time. The study evaluated three improvement strategies: (1) sector subdivision, (2) expansion of stacking areas and (3) increasing the daily moisture loss rate. Compared with the baseline scenario, these strategies increased the compacted mass of stacked tailings by up to 12, 50.8 and 29.2 percent, respectively. Although area expansion produced the highest gains, sector subdivision was identified as the most feasible short-term solution because it requires minimal additional investment. Introduction The failures of the tailings dams in Mariana and Brumadinho, Brazil, intensified the search for safer alternatives for tailings disposal in mining operations. In this context, FTS has emerged as a viable and safer solution. In FTS operations, tailings are dewatered until they become compactable solids, reducing environmental risks and the potential for catastrophic failures. However, to ensure stack stability, each embankment layer must be compacted under optimal moisture conditions. The operation’s productivity is directly related to the time required to construct a new layer. The main operational risk associated with the tailings stack is the potential interruption of the entire mining production chain if the stacking capacity cannot keep pace with the continuous tailings generation from the concentration plant. This study evaluated the FTS operation using the discrete-event simulation (DES) technique to predict operational scenarios, identify critical bottlenecks and propose improvements under the challenging conditions of a tropical region. Fig. 1 Operational cycle of filtered-tailings stacking for raising a new layer. Method The proposed method uses the DES technique to model and simulate the filtered-tailings stacking process, incorporating the seasonality of the rainy period. The flow of the stacking operation consists of two macro processes: (1) sector filling and (2) layer treatment. Figure 1 illustrates the complete dynamics of the operational cycle for constructing a new layer. The sector filling process involves generating tailings batches, accumulating them in a temporary stockpile, loading them onto trucks and transporting them to the final disposal sectors. Figure 2 shows the allocation of these areas designated for dry-stack formation, subdivided into sectors. If all sectors are occupied during the layer treatment stage, the trucks redirect the material to intermediate temporary storage sectors that must later be reclaimed, ensuring operational continuity. The layer treatment process includes tailings spreading, natural drying under solar exposure, roller compaction and laboratory testing. The target moisture content for compaction was set at 15 percent. Climatic impacts were modeled using stochastic logic based on three monthly factors (rainfall probability, rainfall intensity and consecutive rainy days), with drying delays added according to rainfall intensity. Simulation experiments The DES model was implemented in Arena software using real fleet data. Table 1 summarizes the probability distributions for the processes. Thirty replications of a one-year operation were performed. The baseline scenario, representing the current operation with 12 sectors, revealed that only 4.2 Mt — 51 percent of the annual tailings generated — are effectively compacted. The time analysis indicated that the drying stage consumes, on average, 155.03 h, which represents 83 percent of the total layer cycle time, confirming it as the primary bottleneck. This study also conducted a sensitivity analysis to evaluate three strategies for improving the productivity of the filtered-tailings stacking operation. The first strategy investigated subdividing the same disposal area (12.70 ha) into a larger number of sectors, testing configurations with 18, 24 and 36 sectors. The results demonstrated that increasing the subdivision of the area into sectors improved the operational efficiency, with a more aggressive subdivision scenario (36 sectors) resulting in a 12 percent increase in compacted mass. This improvement occurs because smaller sectors accelerate operational turnover, allowing the material to be spread earlier and optimizing the available evaporation windows, thereby reducing latency time during the drying stage. Fig. 2 Example of subdivision of stacking areas for the formation of the piles into sectors. The second strategy evaluated the impact of expanding the disposal area by 20, 40 and 60 percent. Among all analyzed scenarios, the 60 percent expansion produced the highest absolute gain, increasing the compacted mass by 50.8 percent. This improvement is associated with a larger available area for simultaneous tailings spreading and drying, thereby significantly reducing operational bottlenecks. However, despite its high productivity potential, this strategy requires substantial capital investment and lengthy environmental licensing procedures, making it a long-term solution. Finally, the third strategy evaluated increasing the daily moisture loss rate by 50 to 150 percent relative to the baseline condition. The results showed productivity gains of up to 29.2 percent, demonstrating the importance of improving drying efficiency in FTS operations. Nevertheless, the gains stabilized at higher drying rates, indicating that rainfall frequency during the wet season imposes a physical limit on further productivity gains. Conclusions This study concludes that FTS operations in tropical regions are primarily limited by natural drying, which is strongly influenced by rainfall variability. Although physical expansion of the stacking area provides the largest capacity gain, it is a long-term strategic decision that requires significant capital expenditure (CAPEX) and involves complex regulatory procedures. In contrast, sector subdivision is the most practical and immediately applicable solution. It can increase the compacted mass by up to 12 percent simply by reconfiguring fleet management and deposition planning. This approach helps reduce drying delays without requiring significant structural investments. Funding The article processing charge for the publication of this research was funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) (ROR identifier: 00x0ma614). References A list of all references is available in the full paper.

Simulation of the filtered-tailings stacking operation

Authored by: Frederico Teixeira Villela Araújo, Aldrin Gustavo Martins, Sílvia Maria Santana Mapa and Marcone Jamilson Freitas Souza

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