Our plant has four cement mills (closed circuit with first generation separator) - we use about 20 per cent slag, the output is 100tph ,the dimension of every mill is 15.5 x 4.4, the liners in the first chamber are lifting and in second chamber classifier. Are there any ways to increase mill production? How about for a raw mill?

There are numerous ways to increase the production from your cement mills. In the short term use of grinding aids combined with optimisation of the ball charge and drafting would be the best method. Longer term (and at greater cost) you could upgrade the separators to third generation or install a roll press to pre-crush the clinker ahead of the mills. With regard to raw mills you can again use grinding aids or install pre-grinding equipment.

We are using synthesised calcium sulphate anhydrite from a nearby aluminium plant. This calcium sulphate (96 per cent purity) is fine in form and free from moisture. In addition to CaSO₄ this material contains 2.0 per cent CaF₂. Can calcium sulphate be used as an alternative retarder for the natural gypsum? Your expert opinion on the solubility of this synthetic calcium sulphate anhydrite is appreciated.

The solubility of anhydrite varies dependent on the temperature history to which it has been subjected. However, I am sure this will be a good material to use as a set-controlling additive in your cement. You may need to use it in combination with your natural gypsum or you may be able to replace your natural gypsum with 100 per cent of this material. The only way to find out will be to conduct trials with the synthetic CaSO₄.