deposit, indicated by the intersection of the solid red lines, corresponds to an Axb of 34.4 and a Bond BMWi of 14.55 kWh/t. A reference ‘shifted properties’ ore is also shown in green, maintaining the Axb of 34.4 but with a Bond BMWi of 16 kWh/t. Figure 40 – Comminution Footprint for 261 Ore Samples Across a Deposit SAG and ball mill dimensions and installed power are selected to handle the 80th percentile of Axb and Bond BMWi, which dictate both the total comminution power required and its allocation between the SAG and ball milling sections (e.g., 52% is required in SAG and 48% is required in ball mill). If a circuit with these mill dimensions processes an ore with different ore properties within the comminution footprint—such as the reference “shifted properties” ore—the overall power requirements and the split between SAG and ball milling will change accordingly. The comminution circuit must then utilize its full operational flexibility to meet the new requirements. If these are not met, as is often the case, the circuit will respond with corresponding changes in throughput, SAG mill power draw, and final grind size. 1.4 Dealing with Variability AG/SAG milling technology has become widely adopted in the minerals processing industry due to its favorable capex/opex balance. A key limitation of AG/SAG mills, however, is their sensitivity to ore competency variability, which can cause fluctuations in mill throughput, power draw, and final grind size, ultimately affecting flotation recovery. There are three complementary approaches to managing ore competency variability, all aimed at improving process stability while maximizing SAG mill power draw: • Process control. The operating flexibility of a SAG mill to accommodate variations in feed hardness and coarseness is inherently limited. In practice, mill operators have only a few variables to adjust in real time, such as mill speed, pulp density, feeders’ selection and speeds. Other parameters, such as ball load, are 0 20 40 60 80 100 120 140 160 180 5 7 9 11 13 15 17 19 21 23 Harder Axb →Softer Softer Bond BMWI, kWh/t → Harder 261 Ore Samples 80th Percentile Shifted Properties
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