Guidelines for Ball Charge to Ball Mills for Wet Grinding of Bauxite

Hi Friends,

In earlier posts, we have discussed many design calculations for various stationary and rotating equipment used in Alumina refinery. We have also covered in Detail design calculations for sizing and motor rating of Ball mill for required grinding output.

The product fineness in the Ball mill is dependent on the size of balls used as grinding media. Here, we will present the basis for working out the estimated quantity of total ball charge to the mill required for wet grinding of Bauxite in Bayer process for alumina production. The figure may vary marginally depending on the hardness or work index of Bauxite to be processed.

Generally, following norms are followed as guidelines-

• Total ball charge is taken as 20 to 25% of total effective mill volume,
• Packing density of balls inside the mill is taken as 55 t0 60%,
• Preferred material of balls is forged Manganese steel,
• Sizes of balls are 100 mm, 80 mm and 50 mm in diameter,
• Mass ratio of ball charge for larger to smaller diameter balls is 54% : 36% : 10%,

Hope, the above guidelines give the clear understanding to arrive at ball charge as grinding media to Ball mill for Bauxite grinding.  To compensate for the ball consumption during grinding, only 100 mm diameter balls are charged to Ball mill periodically, generally half yearly basis or as and when felt necessary, @ about 15 to 20 kg balls per thousand tonnes of dry bauxite processed. However, ball shorting is essentially done at an interval of  three years duration and new balls are added depending on total requirement of grinding media for desired throughput rate and product fineness.

Have you ever seen such unique information in any published document so far? I know, your answer will be - 'No'. Please put your views / suggestions / remarks / comments, if any.

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Thanks and regards.

Kunwar Rajendra