Impurities removal process for high-purity silica production from diatomite

This study presents a novel chemical process for the extraction of high purity silica from diatomite. The process involves leaching of raw diatomite with acid prior to alkali extraction, solubilization of treated diatomite with alkali solution to form sodium silicate solution, and precipitation of silica gel by adding sulfuric acid. Besides, the process includes washing of silica gel with hot solution of 6 M hydrochloric acid for three hours. The morphology and the chemical composition of the raw diatomite, the derivative products, and the final purified silica were determined by scanning electron microscopy, X-ray fluorescence, X-ray diffraction, and inductively coupled-plasma optical emission spectroscopy. The results indicate that raw diatomite contains over 80 wt% of amorphous micro-porous silica (SiO2) with particle size, 10–35 μm. We were able to enrich the content of silica in diatomite to 90.2 wt% by step-wise acid leaching. Moreover, in this study, boron (B) was removed from silica slurry using mannitol as a complexing compound. The elimination ratio of boron based on this method was about 70%. Incorporation of mannitol in the final stage of the acid washing of silica gel led to a silica product with lower B content. The final purified silica is 99.99 wt% (four nines) pure.