In the concentration plant, the ore is ground so that impurities can be removed and the iron content raised. The ore is mixed to form a slurry for onward transport to the pelletising plant.
The ore is ground in the concentration plant, which means that impurities can be removed – at the same time as raising the iron content. In order to access and remove impurities, the ore is ground to form a fine concentrate and then mixed with water, making a slurry.
Grinding and separation
In the concentration plant, the ore is finely ground and separated in order to remove impurities contained in the ore, such as silicon, sodium, potassium and phosphorus. Grinding is performed in two or three stages, depending on which ore is being concentrated. Grinding and separation are performed alternately, which ensures that impurities are separated from the slurry and that the iron content is raised, to around 68 per cent.
Through a chemical treatment known as flotation, the ore is further purified, for example of the phosphorus mineral apatite. In the flotation process, a reagent is added to the slurry. The reagent binds the apatite in small air bubbles, which are removed from the slurry as foam.
Additives and filtration
After grinding, separation and flotation, various additives are mixed with the slurry, such as olivine, quartzite, limestone and dolomite – depending on product specification and pellet type. The slurry is then filtered until it achieves a predetermined moisture content.
When the concentration of the ore is complete, it is time for pelletisation.