Fine grinding of limestone and dolomite for the paper industry

Abstract

Calcium carbonate can replace kaolin as filler and pigment for some kinds of paper. Calcium carbonate can be produced domestically at a lower price than imported kaolin. Domestic materials have to be cleaned by means of flotation to remove silicates and iron-bearing minerals. After flotation, the carbonate concentrate will have to be ground to 50 to 90% - 2 microns for various applications where a specified particle size distribution is required. Different kinds of fine grinding equipment have been tested for this purpose. Mills tested include attrition mills, annular ball mills and vibro-energy mills. It has been found that the attrition mill produces a wide particle size distribution and a product with a large specific surface area. On the other hand, the vibro-energy mill produces a steep particle size distribution and a product with a smaller specific surface area. The paper will also describe classification experiments with small hydrocyclones to produce a steep particle size distribution. The vibro-energy mill has been tested in detail and the influence of various parameters such as frequency, amplitude, solids concentration, media filling and lead angle has been investigated.