**9. Conclusions**

Comminution is an important operation to liberate minerals/ores. It accounts for about 50% to 70% of the total electrical energy required in mining activities. Many methods have been explored to reduce this energy demand. These methods include thermal (via furnace, microwave, and radiofrequency techniques), chemical, electrical, magnetic, ultrasonic, and bio-milling. Thermal pretreatment via furnace showed that improvements in the grindability of some ore can be achieved by up to 45%. Nevertheless, the high energy demand of furnaces, their non-uniform heating, safety issues, and environmental pollution due to their release of process gasses are major concerns. The development of a solar convergence device that can produce high thermal energy to heat ore can be investigated, since solar energy is environmentally friendly and may be cheaper in the long run. Microwave dielectric heating is the most pursued of all methods, with promising results at both laboratory and pilot scale studies. Findings from the former suggested that a 3–92% improvement in the grindability of some ores can be achieved, while the latter shows a maximum of 9% reduction in the grindability of copper ore. In contrast to the microwave, radiofrequency dielectric heating has not produced promising results for some selected rocks. The chemical method has been demonstrated to be appropriate to aid comminution, especially in the cement industry, with an improvement in the grindability of clinker in the range of 7–70%. However, the cost of the chemicals used in the process is still a challenge. The results of studies using electrical and ultrasonic methods showed improvements in grindability of up to 24% and 66%, respectively. The former has been piloted for gold, copper, and iron-related ores, while the latter has been used for carbonate rocks with promising results. For magnetic and bio-milling methods, progress has not been made, as suitable approaches for ore comminution energy reduction have not been found, but these methods may find relevance in the future. To sum up, microwave and electrical pretreatments should be given preferential attention based on their stage of technology, energy reduction, cost, safety, and downstream benefits.

**Author Contributions:** Conceptualization, S.O.A. and H.A.M.A.; methodology, S.O.A.; formal analysis, S.O.A.; investigation, S.O.A.; resources, S.O.A., H.A.M.A.; data curation, S.O.A.; writing—original draft preparation, S.O.A.; writing—review and editing, S.O.A., H.A.M.A.; visualization, H.A.M.A, H.M.A.A.; supervision, H.A.M.A, H.M.A.A.; funding acquisition, H.M.A.A., H.A.M.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project was supported by the Deanship of Scientific Research (DSR), King Abdulaziz University, Jeddah under grant No. (DG-026-306-1441). The authors, therefore, gratefully acknowledge the DSR technical and financial support.

**Acknowledgments:** The authors also acknowledge the contributions of anonymous reviewers that improved this work.

**Conflicts of Interest:** The authors declare no conflict of interest.
