1. FINES AND COARSE PARTICLES FLOTATION Froth flotation circuits are complex systems composed of tightly interconnected units and processes. They are meticulously designed to maximize metal recovery and concentrate grade, which requires accurate regulation of operating variables such as reagent addition, air flow, and residence time. However, conventional froth flotation equipment is typically limited to a specific particle size range. For instance, studies indicate that in most copper concentrators, approximately 50% of the copper lost to tailings is associated with particles smaller than 20 µm, while an additional 30–40% is lost with particles coarser than 150 µm (Janishar Anzoom et al., 2024). On one side, Coarse Particle Flotation (CPF) aims to minimize unnecessary energy consumption by reducing excessive grinding of gangue material. In this context, Metso has been developing an alternative to existing fluidized-bed CPF technologies. Metso’s CPF solution (name pending) is based on quiescent pneumatic flotation and integrates flash flotation with particle segregation within the froth, enabling the recovery of even very coarse and poorly liberated particles. This technology has been described by de Avila Carvalho et al. (2024), Emer et al. (2024), de Avila Carvalho et al. (2025) and Kupka et al. (2025). Example 1 Laboratory-scale gangue rejection tests were conducted on five copper feed types from a South American concentrator where a demonstration plant of Metso’s CPF technology is installed. Feed grades ranged from 0.9% to 2.2% Cu, with P80 values between 150 and 500 µm. Coarser particles (+150 µm), which contained 20–50% of the copper after grinding, achieved recoveries of up to 70%, and in the best case nearly 90% of the copper was recovered in only 50% of the mass. The enrichment ratio was significantly higher for the coarse fraction, confirming strong selectivity and effective gangue rejection, whereas finer particles (<150 µm) showed more entrainment. Example 2 Gangue rejection test work was conducted on a copper ore from the Antofagasta region (head grade 0.52% Cu, 65% solids), varying froth depth, reagent regime, and gas velocity. Results showed that 95% copper recovery could be achieved while rejecting 28% of the feed mass, or alternatively 42% of the mass could be rejected at approximately 90% recovery. This demonstrates that with only a 10% copper loss, plant throughput could potentially increase by up to 72%, provided that downstream grinding capacity is appropriately upgraded. These results further confirm the significant opportunity for process intensification and capacity expansion through early-stage gangue rejection. On the other side, the Concorde Cell is a high-intensity pneumatic flotation device designed to recover fine and ultrafine particles through high shear conditions and the generation of very fine bubbles. By significantly enhancing flotation kinetics for these size fractions, the Concorde Cell can produce high-grade concentrates with high stage recoveries at an early point in the flotation circuit. The operating principles of this technology, along with laboratory- and industrial-scale performance results, are reported in Yáñez et al. (2024) and in Kupka et al. (2025). From 1957 to 2020, flotation circuits have largely retained traditional layouts, most commonly Rougher–Cleaner–Cleaner and Rougher–Scavenger–Cleaner configurations, typically
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