Comminution process is an energy-consuming stage in mineral processing where equipment becomes the factor affecting the performance of plant. The common primary grinding technologies used today include Semi-Autogenous Grinding (SAG) and High-Pressure Grinding Rolls (HPGR). In SAG mills, ore rocks along with the grinding media consisting of steel balls are used to break rocks using impact force, whereas HPGR technology uses compression to crush rocks between two rolls rotating against each other. The decision regarding choosing the technology is crucial for dealing with competent rock.
The conventional SAG technology has been the industry standard in mining; however, it is faced with difficulties with competent rocks. SAG mills operate with the rock that cannot be impacted due to its hardness, resulting in the creation of critical size pebbles not able to break apart and move out from the mill. This means that the process requires additional energy consumption without increasing the capacity of milling. Furthermore, using additional grinding media due to hardness of the ore rock is cost-prohibitive and causes additional problems with wear (Both & Dimitrakopoulos, 2022).
However, to overcome the problems related to the SAG process, the use of HPGR in hard rock grinding is now becoming increasingly popular. HPGR not only allows for the effective breaking of the rock, but it can also be described as the process of inter-particulate bed fracturing. This method ensures that particles press against each other when they fall into the space between the rolls when working on competent ore (Rashidi et al., 2017).
There are several reasons why HPGR is better compared to SAG from the energy efficiency and benefits point of view. In comparison with SAG mills, HPGR units utilize significantly lower amounts of specific energy due to losses associated with the movement of heavy masses of steel. Furthermore, high pressures applied by HPGR lead to micro-cracking of the product that weakens the ore’s structure making further ball-milling easier (Saramak & Saramak, 2024).
Such considerations apply to the economic and operating aspects as well. Although the initial investment costs associated with the use of HPGR circuits can be higher due to the necessity to install secondary crushing equipment and more complicated material handling facilities, the operating costs will be reduced for hard ores because of lower power consumption rates, which may reduce up to 10-50% compared to conventional circuits and the absence of expensive primary steel grinding media (Saramak & Saramak, 2024).
In conclusion, it can be recommended to use HPGR rather than traditional SAG milling for hard, competent ores that can become a bottleneck of conventional plants. If a mineral deposit has significant resistance to breakage via impacts and raises energy consumption along with media expenses, then HPGR represents the better choice.
References
Both, C., & Dimitrakopoulos, R. (2022). Utilisation of geometallurgical predictions of processing plant reagents and consumables for production scheduling under uncertainty. International Journal of Mining, Reclamation and Environment, 37, 21–42. https://doi.org/10.1080/17480930.2022.2139350
Rashidi, S., Rajamani, R. K., & Fuerstenau, D. W. (2017). A review of the modeling of high pressure grinding rolls. KONA Powder and Particle Journal, 34, 125–140. https://doi.org/10.14356/kona.2017017
Saramak, D., & Saramak, A. (2024). Review of high-pressure technology in terms of technological and economic benefits achieved in raw materials processing. Mineral Processing and Extractive Metallurgy Review, 45, 991–1004. https://doi.org/10.1080/08827508.2024.2410288
