What should be the ideal proportion of ore to grinding media charge for coarse grinding in a ball mill?

Question: What should be the ideal proportion of ore to grinding media charge for coarse grinding in a ball mill?

Reply: Hello,Sir.
achieving coarse grinding in a ball mill is the function of a number of parameters:
1, The mill L/D ratio must be low, for example diam. 9ft x 10ft long.
2, The mill must be of grate discharge configuration as opposed to overflow discharge. This will ensure a steep hydraulic gradient in the mill for rapid passage of the ore through the mill.
3, The mill must be fitted with robust lifter bars to induce increased cateracting of the charge i.e. an increased number of impact events per unit time.
The lifter bar configuration, mill diameter, ball charge level and the critical speed will determine the point of impact of the cateracting particles on the descending side of the rotating mill. Ensure that the charge level is high enough so that the cateracting particles impact upon the toe of the charge and not on the shell liners.

Having said all that, the best type of mill for coarse grinding remains the rod mill. However, this type of mill has become impopular since the advent of SAG Mill/Ball Mill circuits that replaced the standard multi-stage crushing plus Rod Mill/Ball Mill circuits of yesteryear.