A ball mill is designed to grind 600 t/h of ore material from feed size of 80% passing 212 m to 80% passing 75 m. The critical speed of the mill is 1200 rev/min. Determine the mill speed, breakage mechanism and mill speed effect on the mill product and liner wear rate when the mill is operated at 60% and 75% of its critical speed. Summary of the possible mill-operating mode against the speed range is provided in the Table below. (10 marks)

300 Mill speed800	Cascading mode
800	Cataracting mode
>1000	Centrifuging mode