I would like to know how to estimate the quantity of grinding media of each size required for a ball mill using the data mill size, number of chambers and type of material to be ground. Kindly explain me what formula is to be used.

The total quantity of media required for each chamber is determined by calculating the internal volume of the chambers. A rule of thumb is to change the first chamber to 30 per cent of this volume and the second chamber to 27 per cent. You can use 4.6t/m₃ as the density of grinding media. As for the individual ball size gradings this has to be determined by conducting a series of axial tests in the mill while you are building up the media charge.

Are there any recognised ways to increase raw mill production?

The first stage is to maximise the output with the existing mill. You should conduct axial tests and recirculating load tests to make sure that the ball charge and lining are optimal. The next stage might be to conduct trials with grinding aids to try to boost the output of the mill by up to 15 per cent. Beyond that you will need to consider modifications to the milling circuit by adding further equipment. There are two options to do that:
1. Add a pregrinding facility such as a hammer mill or roll press, or
2. Add a regrind mill. Adding further equipment will be significantly more expensive than introducing grinding aids but has the potential to boost the output to higher levels.