ADVANCED MINERALOGICAL ANALYSIS OF QUARTZ-RICH SANDS USED FOR THE INDUSTRIAL PRODUCTION OF GLASS

Glass is a versatile and technologically significant material with widespread applications, making it a critical component of modern industrial economies. Its production relies primarily on silica (SiO₂), which serves as the fundamental structural constituent and is typically sourced from natural deposits such as silica sand or quartz pebbles. The purity of these raw materials is of paramount importance, as the presence of impurities can affect the physical, optical, and chemical properties of the final glass products. This study aims to quantify contaminants present in silica-based raw materials used in glass manufacturing. A comprehensive set of analytical techniques was employed to evaluate the nature and concentration of impurities, both in the raw materials and in the resulting glass products. Particular emphasis was placed on the mineralogical composition of quartz-rich sands, with a focus on identifying heavy minerals and assessing the levels of iron (Fe) and titanium (Ti), which are known to affect the glass quality. The results reveal the presence of various impurity-bearing minerals, including zircon, kyanite, andalusite, tourmaline, epidote, muscovite, rutile, and hematite. These minerals contribute to undesirable coloration and defects in glass, thereby limiting its industrial applicability. Therefore, accurate and efficient identification of such impurities is essential for improving raw material selection and ensuring compliance with product quality standards. Impurities detected in final glass products may originate either from the raw materials or from contamination introduced during various stages of the industrial manufacturing process, including interactions with furnace refractory linings. However, the identification of such inclusions using conventional optical microscopy remains challenging due to their encapsulation within the glass matrix, their variable optical properties, and their often-ambiguous morphology. These limitations make it difficult to reliably determine the origin and nature of the impurities. To address these challenges, this study explores the application of Raman spectroscopy as a rapid and non-destructive technique for the direct identification of mineral inclusions within glass. Due to the inherently low Raman scattering of the glass matrix, spectra from embedded impurities can be effectively acquired by focusing directly on the inclusions using an appropriate excitation source. This method was evaluated through comparison with conventional optical identification carried out by experienced quality control operators. The comparison highlights the limitations of traditional approaches, which rely primarily on visual assessment (e.g., shape and colour) and operator expertise, rather than on definitive chemical and crystallographic information. In addition, granulometric analysis was performed on selected raw material samples to evaluate particle size distribution and to identify the grain-size fractions with the highest purity. Grain fractionation enabled the assessment of impurity distribution across different size classes, providing further insight into the suitability of the raw material for industrial applications. The results indicate that the analysed sand deposits, while not sufficiently pure for high-quality colourless glass production, are suitable for the manufacture of coloured glass. Therefore, this work provides a comprehensive Raman spectral database of the most common impurities encountered in the glass industry, offering a standardized reference for application across different production plants. The proposed methodology enables accurate, in situ, and real-time identification of contaminants, significantly enhancing the ability of operators to detect and distinguish impurities with greater accuracy and efficiency. This approach facilitates improved traceability of contamination sources within the production cycle and supports higher quality control in glass industry.