755 operational challenges. In all these cases, the existing launder models were upgraded to enhance the recovery of valuable minerals and improve operational parameters by shortening the froth transport distance and decreasing the froth surface area. The results from these cases show up to a 68% decrease in froth surface area (FSA) and an 83% decrease in froth transport distance (FTD) (Metso 2021), which have been proven to correlate with higher recovery of valuable metals (Liu et al. 2022). The metallurgical recovery evaluation was conducted for the Constancia, Kennecott, and Bagdad operations, yielding highly consistent results. In each case, the difference in recovery between the upgraded and baseline configurations was measured over the evaluation period, highlighting changes in recovery rates. The direct comparison of a given line performance before and after modification is challenging due to natural variability in ore type, head grade, flotation feed particle size, tonnage, and reagent dosage. However, since these changes affect both flotation lines equally, a statistical evaluation comparing the performance of one line relative to the other before and after the launder upgrade is feasible. Performance was assessed using chemical assays of 12-hour shift composite samples collected by automated on-line sampling devices from both lines. Instead of focusing only on measuring recovery improvements, the studies of Red Chris, New Afton, and Kennecott examined the effect of center launders on operational flexibility, process controllability, and reduction in operational airflow rates. The consistency of the results was demonstrated by improvements in decreased operational airflow rates, increased froth bed thickness, and enhanced stability of the froth surface area (Metso 2021; Bermudez et al. 2022; Seaman et al. 2021). The smaller froth surface area notably increased froth crowding and successfully eliminated all stagnant froth zones within the cell (Seaman et al. 2021). 4. DISCUSSION Based on the studied case examples, the installation of the center launder upgrade has proven to be a highly efficient way to enhance the recovery of copper and other valuable minerals, as well as to improve operational parameters. It has also been highlighted that installing center launder upgrades may positively affect flotation decarbonization by decreasing the energy intensity of the flotation cell. This section presents these consistent results and provides data on the profitability of the investment, showing payback periods of just a few months. It also discusses further improvements in froth management for large flotation cells by incorporating spider crowders, which aim to enhance the efficiency of the center launder upgrade. 4.1 Performance Improvements Evaluation The results from different retrofits show consistent improvements in metallurgical recoveries as well as in operational parameters. Across the studied retrofits in Constancia, Kennecott Copperton, Bagdad, and Red Chris, the improvements in reducing froth surface area and froth transport distance were very consistent. Reduction in froth surface area in all cases varies between 38% to 48%, whereas the reduction in froth transport distance is on average 69%. These consistent results are presented in Table 5. The significant reductions in froth surface area led to enhancements in froth management by increasing froth crowding over the launder lip and the thickness of the froth bed. A thicker froth bed was looking to improve the selectivity of the operation by restraining gangue recovery and thereby improving the grade of the concentrate (Bermudez et al. 2022). The increased crowding is therefore seen to improve metallurgical performance and froth movement, eliminating stagnant froth zones on top of the cell (Liu et al. 2022; Seaman et al. 2021). When evaluating the similarities among the studied cases, the retrofits from Constancia, Kennecott Copperton, and Bagdad are comparable due to similar processing parameters and conditions. The throughput of these three studies ranges from 90 to 150 ktpd, with all three processing Cu-Mo ore. The number of
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