Study On The Influencing Factors Of Fe-oxides Cemented With Kaolinite And Their Suface Properties

Fe and Al oxides are the ones of the most important and active components in red soil, When they cement with clay mineral, The physical and chemical properties of soil are influenced obviously. Through synthesizing different Fe oxides and Fe oxides-kaolinite associations, the influencing factors, such as association ratios, pH, aging time and temperature were investigated, and some of suface chemical properties of the associations were tested, The work is aimed to provide some useful evidences of the mechanism of Fe oxides coated on kaolinite. The main results were as follows:1) Analyzed by XRD patterns and SEM micrographs, purified kaolinite and synthesized goethite, hematite, lepidocrocite had good characterisitic diffraction peaks, without extra peaks of impurities in their XRD patterns, which means the products are pure; The ferrihydrite had no characteristic diffraction peaks because of its amorphous structure; The characteristic diffraction peaks of the associations varified with the ratios between Fe oxides and kaolinite, and kaolinite's peak weakened and Fe oxides' appeared or strengthed with the increasing content of Fe, It was indicated that the products may have coated with Fe oxides in different degree.2) The Fe oxides-kaolinite associations were synthesized by two methods: (1) Synthesize the crytalline associations directly. The XRD pattens and SEM micrographs of associations indicated that the suface of kaolinite was covered with Fe oxides and its contents(35.34%)were close to the theory values, which mean kaolinite's suface was coated with Fe oxides. (2) Synthesize of the intermediate phases from amorphous to crystalline. According to the Fe contents of the products tested by EDS, it was found that Fe contents of amorphous associtions were low, Therefore if coatings of the Fe oxides on kaolinite happened, only small amounts of coatings were formed, which may be caused by the short aging time or low temperature during the synthesis.3) In the process of synthesizing different types of Fe oxides-kaolinite associations, the effects of pH, aging time and Fe content on the association formation were investigated. Under the low pH, Fe oxides had much positive charge and were easy to interact with kaolinite. With the aging time prolonging, amorphous ferrihydrite-kaolinite association transformed to crystalline ones. It was shown that the higher the temperature, the faster the transforming of the associations, and it was not liable to form good coatings. With the lower temperature(not lower than room temperature) and longer aging time, it was favorable for Fe oxides to coat on the kaolinite's surface and bring more coatings. The cementations amounts were increased with the increasing contents of Fe oxides.4) By FT-IR spectroscopy, it could be deduced that the main reaction between Fe...