a) Consider a binary mixture of galena (specific gravity 7.5) and quartz (s.g. 2.65) particles being classified in water (specific gravity 1). If the quartz particles are 10 mm in diameter, calculate the radius of galena particles for the two minerals to settle at the same time (10 marks) b) Discuss three types of gravity concentrating devices, their areas of application and the operator-controlled variables of each (10 marks) c) A ball mill is designed to grind 600 t/h of ore material from feed size of 80% passing 212 um to 80% passing 75 um. 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 speed5800 Cascading mode 8001000 Centrifuging mode