Preparation of Quartzite Reference Materials for Chemical Composition Analysis

At present, quartzitic reference materials are prepared by Brazil, England, Japan, and South Africa but are not in series. The SiO₂ contents in these reference materials are generally above 96% and accurate concentration values are determined for only small number of elements. To date, no quartzitic reference material has been prepared in China, which cannot meet the demand of quartzite exploration and practical applications. In this study, three quartzitic reference materials were developed with samples from representative quartz mining areas, namely Damiao Town, Fengyang County, Anhui Province; Jingyang Town, Datong County, Qinghai Province; and Lingqiu mountain, Qichun County, Hubei Province. The samples were finely crushed to -45 μm with a fluidized bed-type airflow crusher to prevent sample contamination. Homogeneity and stability testing was conducted chiefly by inductively coupled plasma emission spectrometry and mass spectrometry rather than X-ray Fluorescence Spectrometry with tablet sample preparation, which results in the quartzite material being difficult to mould. F values for the variance test were less than the threshold, which indicated a good homogeneity. No significant statistical changes were observed in eight two-year stability tests. The short-term stability analysis in the condition of extreme temperatures and vibration were also consistent. Determined values were certified by 10 laboratories in China with multiple methods. For components without homogeneity and stability tests, values and relative uncertainty of 36 components were obtained by comparing similar elements. The three quartzitic reference materials have been approved as National standard reference materials (GBW 07835, GBW 07836 and GBW 07837), with 92.93%, 95.97% and 99.18% of SiO₂, respectively, as a gradient distributed series. This series of reference materials has the characteristics of uniform grading, narrow diameter distribution (D₂₅-D₇₅ ranged between 4-16 μm), multiple value determined elements, and wide-range distribution of SiO₂ content, which should meet the monitoring requirements of chemical composition analysis of quartzite samples.