The nature of soil kaolins from Indonesia and Western Australia

Purified soil kaolins from Indonesia and Western Australia were characterized using analytical TEM, XRD, TGA and chemical analysis. The Indonesian kaolins, formed from tuff, consist of a mixture of tubular kaolin crystals with relatively low Fe concentrations and platy kaolin crystals with higher Fe concentrations. Western Australian kaoIins also contained tubular and platy crystals but showed no systematic relationship of crystal morphology with Fe content. The coherently scattering domain (CSD) size of the Indonesian samples (5-6 nm for 001, i.e. c axis dimension) is remarkably consistent and is approximately half of the value for the Western Australian kaolins (9.7-13.4 nm), anti both are much smaller sizes than values for the reference kaolins (15.6-27.8 nm). Coherently scattering domain sizes derived from the Schemer equation are approximately twice the values obtained from the Bertaut-Warren-Averbach Fourier method but the results show the same pattern of variation. For the Indonesian, Western Australian and reference kaolins, the N2-BET surface area ranges 59-88, 44-56 and 5-28 m(2)/g; the dehydroxylation temperatures range 486-499, 484-496 and 520-544degreesC, the mean cation exchange capacities (CEC) are 9.4, 5.0 and 3.5 meq 100 g(-1) and the surface densities of charge range 0.10-0.14, 0.08-0.10 and 0.04-0.12 C/m(2). The properties of the Western Australian kaolins and Indonesian kaolins differ substantially, but kaolins within each group have similar properties. These results suggest that soil kaolin properties may be characteristic of a particular pedoenvironment and that a systematic study of kaolins in different pedoenvironments is required.