Influence of mineral and organic acids on the structural, morphological and packing properties of silica sand

Abstract High-purity silica has seen a growing demand in today’s market, especially for high-tech uses like semiconductors, optical glass, advanced ceramics and in the aerospace sector. Sulfuric acid, along with a mix of oxalic acid and hydrofluoric acid (HF), works well to remove iron impurities. Researchers studied different conditions by changing acid concentration, reaction time, temperature and the ratios of the oxalic acid and HF mixture. For sandy substrates, a higher pulp density of about 50% was manageable. The best temperature for effective iron removal was found to be 60 °C. When treating with the oxalic acid and HF mixture, the iron concentration measured at 32–34 ppm in the processed sand. As a result, recycling studies were done under both sets of conditions. After recycling, the iron concentrations varied between 22 and 34 ppm. Measurements like grain diameter, packing density, and water displacement showed that the highest etching and size reduction happened in samples treated with oxalic acid and HF, though these samples had lower porosity. In contrast, the samples treated with sulfuric acid had higher porosity and showed more cracks. The XRD, SEM and optical microscopy images indicate that the oxalic acid and HF treated sample are attacked by acid making the surface smoother and clearer. There is reduction in the grain size. For sulfuric acid treated sand sample there is enough cleaning of surface and negligible reduction in grain size however crack formation is visible on its surface.