[Determination of free crystalline silica in the dust containing silicates]

The content of free crystalline silica in dusts containing silicates was investigated using Polezajew's method, the HBF4 method and X-ray diffraction. Polezajew's method was found to give highly increased results (133.4% on the average), and with 5% of quartz in mixture with kaolin--252%. Solution of silicates, when heated, in fluoroboric acid considerably reduces the error of determination. The mean value of SiO2 recovery in mixtures of quartz with kaolin is 102.9% and with 5% of quartz--116. This method is highly precise. The results of determination of crystalline silica content in some mineral raw materials used in ceramic industry approximated the results obtained using X-ray diffraction.