| Summary: | Effect of water immersion at different times (from 1/2 h to 24 h) on raw and expanded vermiculite from Uganda was investigated. The expansion was carried out by electrical heating at different temperatures and by irradiation with microwaves. After, the expansibility (k) and the water absorption content (WA) were obtained and the samples were characterized. The elemental and mineral composition was determined by X-ray fluorescence and X-ray diffraction, respectively; the thermal behavior by thermal gravimetric analyses; and the textural parameters by BET. The expansibility of Ugandan vermiculite is relatively lower than the other commercial vermiculites due basically to its lower K<sub>2</sub>O content (0.36%) and higher water content (about 20%). The water absorption capacity of samples significantly increased with the increase in heating temperature. The maximum WA content, about 130 mg/g, was obtained at 900 °C for 24 h. The loss of water during the expansion process in the Ugandan vermiculite caused loss of structural order and crystallinity. Moreover, in the samples expanded and subsequently immersed in water, the structural order and crystallinity increased with increasing WA values. Specific surface area and porosity hardly vary with temperature and are practically independent of vermiculite purity. Expanded commercial vermiculites could be a suitable hygroscopic material, given its efficient water absorption. Microwave expanded commercial vermiculites, in this case, would not be recommended.
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