**5. Magnetic Pretreatment**

Magnetic pretreatment is quite a new method investigated for the reduction in the comminution of iron-rich minerals, especially magnetite. The idea behind the method is that the magnetic pulses generated through a magnetic field may probably change the magnetic dipoles of magnetic minerals and hence introduce microcracks in the rock. This method was proposed in 2016 by J. Yu and his research team [107]. A generator was developed that can create magnetic pulses through a dielectric pipe where coils were mounted. The magnetic field and frequency of the pulses generated were 5.0 T and 0.05 Hz, respectively. The magnetic pulse generator (MPG) was used for the treatment of magnetite ore collected from Dagushan city, Liaoning, China. The representative sample was placed in a plastic container and subjected to magnetic pulse treatment in the MPG for 2.5, 5.0, and 7.5 min using separate samples. The magnetic field intensity of the MPG was kept constant throughout the treatment periods. The pretreated samples and the untreated one (500 g each) were ground for 3 min using a laboratory cone call mill. The energy consumption (measured with a DTZ 119 smart power meter) for grinding untreated and treated samples reflects a 10 W difference, representing 1% energy saving in the grinding process. The PSD analysis performed showed no significant change in the size distribution of products. The improvement in the bond ball mill work index of the treated sample was 0.68% (test sieve size = 74 μm). To sum it up, MPG did not sufficiently weaken the magnetite ore and

there was no significant improvement in the work index. [107]. The magnetic method may provide promising results in future research.

#### **6. Ultrasonic Pretreatment**

The ultrasonic pretreatment of ore uses a three-dimensional acoustic wave (sound wave above 20 kHz) that passes through the ore matrix to create fractures. The velocity of this wave varies as it passes through the ore media, due to the change in grain size or mineralogy, which causes a kind of reflection and refraction at the grain boundaries. The tensile stress caused by this phenomenon creates microcracks or extends the existing cracks in the ore matrix. The use of ultrasonic waves for the fragmentation of particles was reported to have firstly been attempted by Gärtner in 1953 [52]. In 1981, the Energy and Mineral Research (EMR) company with the support of the US Department of Energy (DOE) constructed an ultrasonic device consisting of a rotating roller that had the capacity to treat 4.5–13.6 kg/h of ore, with an energy requirement of 3 kWh/t for 80% of the product finer than 75 μm. At that time, the energy requirement to achieve the same size as that of using a hammer mill was 20 kWh/t. The major disadvantage of the device, when compared to the conventional machine, was that it had a very low comminution capacity. The DOE, US, in 1988 commenced an investigation into the construction of their own ultrasonic device using the previous idea from 1981. The constructed device was used for the treatment of coal, and resulted in little liberation of the samples. Indeed, the device consumed more energy than that of conventional comminution mills [108]. However, this method has been reported to have improved the grindability of copper ores by up to 32% [108]. Gaete-Garretón et Al. (2000) provided a solution to the limitation (small capacity) of the previous ultrasonic devices by incorporating ultrasonic treatment into a high-pressure roller mill with a capacity of 20 t/day [109]. The developed device and ball mill were used separately for the grinding of prepared copper ore feeds. It was reported that 66% energy was saved when compared with the ball mill. A similar idea was developed called the Ultrasonic High-Pressure Roller Press (UHPRP), which was used in the investigation of the grinding characteristic of copper ore [110]. Findings show that 6% energy was saved when compared with samples without ultrasonic treatment [110]. The combination of microwave and ultrasonic pretreatment was investigated for the disintegration of iron from phosphorus gangue. The findings showed that the disintegration and removal of fine particles from the samples were higher for microwave-treated samples compared to the ultrasonically treated one. The combination of the two methods indicated that a 20% improvement in disintegration was achieved during the process [111]. An ultrasonic device has been piloted for the treatment of carbonate ore which improved its liberation and downstream processes [112]. The economic and industrial applications of this method are limited in the literature; hence, further research is still needed.

#### **7. Bio-Milling Pretreatment**

Bio-milling is the process of size reduction in particles using living organisms. Since microorganisms can cause the weathering of rock, researchers have therefore suggested that their use for ore comminution could improve the size reduction process. This has found direct application in the milling of particulate matter in the nano range. The use of fungal biomass for milling chemically synthesized BiMnO3 had been reported [113]. It was discussed that BiMnO3 (150–200 nm) was reduced to <10 nm without any effect on either the crystallinity or phases of the material [113]. Research using this approach for ore comminution energy reduction may find relevance in the future.

#### **8. Ranking of Methods of Ore Pretreatment**

To look for an immediate way forward to reduce comminution energy, Canada Mining Innovation Council (CMIC) ranked both conventional and some emerging technologies based on the responses and analysis of a questionnaire filled in by professionals in the mining sector [114]. Consideration was given to energy reduction, costs, safety, stage of the technology, and downstream benefits. For all these parameters considered for rating the pretreatment methods, 1–5 were used as rating numbers in an ascending order of benefit, except cost. For the cost implication of the methods, the rating five means that the cost is very low, meaning that one is the costliest rating number [114]. Based on the available literature [80,100,107], there are developments in the stages of technologies, which was part of the ranking matrix used by the CMIC; hence, there is a need for updating the ranking of emerging technologies so that research can be channeled toward the proven methods (Table 10).


**Table 10.** Ranking of ore pretreatment methods (\* cement production) [114].
