Mineralogy, surface properties and electrokinetic behaviour of kaolin clays from the naturally occurring pegmatite deposits

This paper comprises the research on the surface characteristics, the specific surface area (SSA), the cation exchange capacity (CEC) and the electrophoretic mobility (EPM) of the kaolin clays obtained from different naturally occurring pegmatite and granite deposits worldwide. Particularly the influence of the ancillary minerals on these properties was studied, as well as the diversity in morphological and structural characteristics of kaolinite in samples. The mineral composition and the morphology of the kaolin samples were investigated using X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM), respectively. The SSA was determined by BET method, the CEC by ammonium selective electrode and the surface charge by EPM measurements. The results showed that the surface properties of the kaolin samples were strongly influenced by the presence of ancillary constituents, particularly smectite minerals. Their occurrence, even in trace amounts, significantly increased SSA and CEC values of the investigated samples. Most importantly, EPM measurements revealed that the character of the amphoteric surfaces of the dominant kaolinite mineral in samples was rescinded by the permanent pH-independent siloxane basal charge of smectite. The presence of ancillary smectites, characterized with the higher surface reactivity, hindered the surface properties of the prevailing kaolinite mineral in the kaolin clay deposits.