Characterisation of kaolinite colloidal and flow behaviour via crystallinity measurements

• Hinckley index, calculated from XRD spectra estimates the crystallinity of kaolinite.
• Well crystallised kaolinite has relatively smooth basal planes and a smaller surface area thanpoorly crystallised kaolinite.
• Kaolinite samples of different crystallinity present different surface charge properties.
• Surface charge of well crystallised kaolinite samples represents the charge properties of the extensive smooth basal planes.
• Low crystallinity kaolinite samples present higher suspension yield stresses and viscosities.

This study evaluates the possibility of predicting colloidal and flow behaviour of kaolinite suspensions by measuring kaolinite crystallinity. The Hinckley index of different samples was calculated from XRD spectra as an indicator of the crystallinity. Kaolinite samples with a high Hinckley index showed a defined platy morphology with smooth surfaces of low surface area, whilst progressively roughened basal planes with prevalent broken edges were observed in kaolinite samples of lower Hinckley indices. Despite similarity in the elemental composition, the kaolinite samples present different surface charge properties, likely due to variations in exposed pH dependent edge sites. Poorly crystallised kaolinite samples were characterised by higher yield stresses and viscosities. This study highlights the importance of crystallinity characterisation towards predicting colloidal behaviour and flow characteristics of kaolinite suspensions.

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