China Clay for Paper Industry:
External or Free Iron impurities can be removed to an extent by Chemical Leaching method, however they cannot completely clean the kaolin from the free iron though this is the most efficient and aggressive method. Other reagents used for Fe removal from clay are pyrophosphate, oxalate, EDTA and CDB. The steps in beneficiation of China Clay to improve brightness are Size Classification, magnetic Separation, Froth Flotation and Chemical dissolution techniques.
During Size Classification, the iron impurities decrease. As the size decreases, the iron content also decreases. But the titania impurities will not change during size classification. Though there is a significant decrease in the ferrous impurity content during size classification, there will not be any much improvement in the brightness. As the ferrous content in form of Titanioferrous impurities remains unchanged during this process and these impurities impart color to the kaolin.
To be Contd…..
