The effect of micro-grinding and micro-graphite flotation to upgrade the quality of calcite concentrate, with reference to Kurikka calcite marble deposit, Finland

High purity of calcium carbonate deposits are rare. Even the purest calcite marbles contain accessory minerals, which may degrade the deposit in terms of its suitability for paper pigment application. Most of these impurities could be removed by traditional calcite–silicate flotation to produce quality ground calcium carbonate. However, micro-graphite enclosed by calcite remains un-liberated with the traditional flotation particle size distribution. Further grinding alone simply exposes such graphite on the surface of calcite and reduces the brightness of the concentrate.In Kurikka calcite marble, micro-graphite particles of varying morphology occur along calcite grain boundaries and other crystallographic discontinuities. Due to such submicroscopic graphite particles, the calcite concentrate produced from the Kurikka calcite marble by calcite–silicate flotation gives an average ISO brightness value of 83.7.This study shows the application of micro-grinding followed by micro-graphite flotation to remove such fine-grained graphite. As a result, the quality of the calcite concentrate was upgraded to an average brightness value of 92.3.