The Quantitative Phase Analysis Of Montmorillonite In Bentonite

Montmorillonite content is the most important indicator to evaluate the quality of bentonite. There are many quantitative phase analysis methods to determine montmo- rillonite content in bentonite, but the precise determination of montmorillonite content in bentonite has been always a difficult task owing to the complex composition and structure of montmorillonite.In this paper, author use Methylene blue absorption, powder X-ray diffraction quantitative phase analysis (Rietveld quantitative phase analysis, calibration curve method and the matrix flushing method) and chemical composition analysis to determine montmorillonite content in bentonite. Then compare quantitative analysis results to examine the advantages and disadvantages of each method.The results show that the chemical composition analysis can calculate montmori- llonite content of bentonite with chemical analysis of atomic percent content of each element, this method is comparative intuitional. Owing to the calculation of silicon content of montmorillonite is an approximate calculation by basing on some assumptions, the calculated final result also is an approximation of montmorillonite content, which is the experimental results confirmed.Methylene blue absorption is a simple method, but its empirical formula can only use in a certain range, and its accuracy is not enough to distinguish the disparity of montmorillonites with similar content.Because there is no suitable sample of pure montmorillonite, the calibration curve method and matrix flushing method can’t determine montmorillonite content in bentonite directly. But it is feasible to determine content of impurities in bentonite then calculate the content of montmorillonite. The two methods have high demands on sample preparation and testing conditions, and the quantitative results usually higher than really value due to samples may contain other crystal impurities or amorphous impurities.Using free software named Fullprof with Rietveld quantitative phase analysis can do the quantitative analysis of bentonite. This method of quantitative analysis is more complicated, but tolerance can be reduced better because of many factors have been considered. By evaluating the reliability factor R and comparing with other quantitative analysis methods, it is showed the Rietveld quantitative phase analysis has higher reliability, better accuracy and applicability.