Characteristics of soil kaolin on various parent materials in Thailand

摘要

The nature of kaolin in Thai soils developed on sandstone, shale/limestone, granite and basalt has been investigated. Mineralogical, chemical and morphological properties of kaolins were determined using X-ray diffraction, transmission electron microscopy, and chemical analysis. Clay concentrates from Thai soils consist of >70% kaolin group minerals with minor amounts of inhibited vermiculite, illite, interstratified clay mineral, gibbsite, quartz and anatase. Soil kaolins exhibit a wide range of crystal sizes, (0.02-0.83 mu rn, median 0.02 mu m) with a variety of morphologies including euhedral platy crystals, laths and tubes. Euhedral hexagonal platy crystals predominate in soils derived from sandstone, lath-shaped crystals in soils derived from basalt and anhedral crystals in soils on shale/limestone.There are considerable variations in other soil kaolin properties, d(001) ranged from 0.7121-0.7275 nm, coherently scattering domain size (CSD001) 10.3-43.7 nm, Hughes and Brown crystallinity index (HB) 4.1-11.7, specific surface area 34-76 m~2/g and cation exchange capacity 4.2-13.9 cmol/kg. Kaolin in soils on sandstone has the highest value of HB index and largest crystal size, in contrast to kaolin in soils on basalt which has the lowest values of crystallinity index and crystal size. The CEC of soilkaolin (median 9.4 cmol/kg) did not differ systematically between parent materials but was much higher than values for reference mineral kaolin (3.2 cmol/kg). The median value of structural Fe_20_3 in soil kaolin is 1.84% being highest for soils developed on basalt (median 2.67%) and lowest for soils on shale/limestone (1.39).