In the processing plant: comminution
Comminution is the first step when the ore arrives at the processing plant: it is also the largest electricity consumer in the mine – with the mill accounting for much of this. Optimising the mill feed, thus, significantly benefits milling efficiency. For example, the Eccentric Roll Crusher (ERC®) can reduce specific power consumption by 40% compared to a gyratory/jaw crusher in the same application while offering a higher reduction ratio, wider CSS range, and more fines in the product. The resulting mill feed is finer and more uniform, improving grinding efficiency.
Meanwhile, coarse particle flotation increases the particle size at which acceptable flotation is possible. This enables the mill to operate at a coarser grind, which results in significant energy savings per tonne of ROM material processed. The coarseAIR™ Flotation Cell captures particles up to 850µm in sulphide and >1mm in industrial minerals. It is ideal for rougher applications to process a coarse ball mill product. It can also reprocess tailings streams to scavenge valuable coarse particles lost in conventional flotation processes. In some cases, it has been shown to recover more than 60% of the target mineral that would otherwise have been lost to rougher and scavenger tailings.
Regarding the mill itself, SAG mills retain a dominant position as the workhorses of the mineral processing plant. In these mills’ dynamic operating conditions, the speed at which operators can adjust to changes in feed rate, mill speed, and slurry density has a critical impact on mill efficiency. Digital optimisation solutions have a key role to play here. For example, LoadIQ mill scanning technology measures and predicts mill behaviour according to ore properties, trajectory (liner wear), and other main process variables. The smart sensors ensure regular and accurate adjustments to mill loading that increase throughput while reducing energy use.
Switching to lighter-weight composite liners can also significantly influence mill efficiency. Thinner than steel cast liners, composite liners increase the usable volume inside the mill, allowing a higher charge level. They also cut the weight of the liners to about 50% of standard steel cast liners, making it possible to work with a higher ball charge without increasing the total weight of the mill. Both of these benefits result in higher throughput.
Beyond the SAG mill, dry grinding technologies can significantly reduce grinding energy consumption, particularly in more competent ores. High-pressure grinding rolls (HPGR) are well-established in hard-rock grinding applications, with FLS as a leading supplier. Vertical roller mills (VRMs) have been successfully used in other industries for decades. Although commercial applications are currently rare in mining, VRMs are raising interest due to their ability to handle higher moisture content and feed sizes than HPGR. HPGR and VRMs also eliminate the need for grinding media, a significant operating cost and whose manufacture contributes to mining’s Scope 3 emissions.
