| Summary: | 碩士 === 國立成功大學 === 資源工程學系碩博士班 === 91 === In Hsiang-Yang area of Taitung county, there is a huge amount of reservation of sericite deposite. The recoverable amount is estimated to be about 15 million tons with a grade of 50%. The annual production at present is about 30000 tons. It is one of the most economically important industrial minerals in Taiwan Province. Sericite is a layered silicate mineral. It has excellent properties in anti-ultraviolet, anti-static, heat resistance, electricity insulation, chemical stability, etc. It is already used in conventional industry, as filler in the manufacturing of electric insulating plate, fire-resistant material, paint and plastics. However, no high-valued application has been discovered until present.
The crystalline structure and chemical composition of sericite is similar to muscovite [KAl2(AlSi3)O10(OH)2]. The thickness of the unit cell is about 20 Å, which falls in nanometer range, making sericite an ideal candidate of nano-material. However, three problems should be solved in order to utilize sericite’s nano-properties. The first is that the natural size of sericite is still large. Size must be reduced to relatively fine range. The second is that the interlayer charge of sericite is high, which makes the exfoliation of sericite difficult. The charge must be reduced. The last is that only 50% of the concentrate is sericite. The other half is pyrophyllite, which must be separated. If the size of sericite can be reduced to nanosize range and specific surface area increased, the properties of insulation, heat-resistance, erosion-resistance, anti -ultraviolet, anti-static, chemical stability and elasticity can all be fully developed. The economic value of sericite can be further increased.
The objectives of this research are to investigate the size reduction limit and crystallinity change of grinding operation; to investigate the hydrothermal reaction conditions on interlayer atom substitution. The results can be used for the future cation exchange and intercalation of sericite.
The grinding of sericite was performed using a stirrer-mill. The original sericite equivalent specific surface area disk diameter of sericite sample is 26.41 μm, after grinding for 48 hr, the size is reduced to 0.12μm. The estimated thichness form this diameter is 40 nm, which is about 2 times of lattice c-axis. Further lengthened grinding to 96 hours, seemed to have no effect on size reduction, a hint of reaching the grinding limit. Sericite samples which have been ground for 12 hr were mixed with different salt solutions. Hydrothermal reactions under 220℃ and 23 atmospheres were carried out to perform interlayer ion substitution experiment. The results showed that the sericite which is amorphous after grinding seems to recover its crystallinity by hydrothermal reaction. Form the observation of X-ray diffraction patterns, the reconstruct ion capability of valence-one ions decreases in the order K+, NH4+, Na+, Li+.
The substitution of K+ will substantially be increased if hydrothermal solutions contain valence-one ions and Al3+ simultaneously. The K+/Na+ substitution was the highest, followed by K+/NH4+ and K+/Li+ substitution. The best condition in this resarch is with 5M valence -one ion and 5 M Al3+, under 220℃, 2 hr reaction time. The substitution of K+ by Na+, NH4+ and Li+ are 63.6%, 52.5% and 39.4% respectively. The decrease in K+ and increase in valence-one ions in sericite has been investigated. The amount of K+ substituted was almost equal to Li+ entering the lattice. It shows Li+ replaces the K+ of sericite and transformd it to Li-mica. On the other hand, the amount of Na+ entering the lattice was higner than the K+ substituted. It shows that Na+ not only transforms some sericite to paragonite (sodium mica) but also some pyrophyllite to paragonite. The transformation percentages of sericite and pyrophyllite are 41.1% and 20.1% respectively under the conditions of 5 M Na+, 5 M Al3+, 220℃ and 2 hr reaction.
|
|---|
