Silica Minerals represent the group of minerals being composed of silicon and oxygen forming the chemical formula SiO2. Silica can occur in macrocrystalline, crytocrystaline and amorphous form.
Industry predominantly uses the crystalline form of silica, i.e. quartz. Silica is used as granular products containing the particle size range >63 µm. Fine grained silica is used as functional fillers in various applications.
Silicadioxide appears in almost 10 different crystal forms, with quartz, the most abundant representative, crystallizing in the trigonal crystal system.
Quartz is mined from hard rock deposits with the most important representatives being vein deposits or pegmatitic deposits and alluvial deposits. The mineralisation respectively the deposit type, the accessory minerals, impurities occurring together with the quartz in the deposit as well as the intergrowth of the minerals in the ore matrix define the process route.
It is chemically inert, chemically resistant to almost all acids with the exception of hydroflouric acid and soluble in alkaline fluxes.
♦ Process Description
Washing and classifying desliming
The SiO2 grade in quartz sand(silica sand) decreases by quartz sand(silica sand) size becoming finer, so washing and desliming of crude quartz sand(silica sand) is necessary before next step.
Scrubbing
Scrubbing is the way to remove film iron and impurity minerals on the surface of quartz by mechanical force and crush these mineral aggregate. The quartz sand gets further purification by classification. There are two kinds of methods rob scrubbing and mechanical scrubbing.
Flotation
The separation of mica and quartz is difficult, the effective methods: anionic collector in acid condition and anionic - cationic collector in alkaline condition. The purification of quartz sand can reach 99% after scrubbing, desliming, magnetic separation and flotation.
Acid Leaching
Dilute acid had a significant effect on removing iron and aluminum, and concentrated acid for the removal of titanium and chromium, and mixed acid for mineral impurity. Control various factors of acid leaching should be based on quartz final grade requirements, and as far as possible reduce the acid concentration, temperature and dosage to achieve quartz purification.
♦ Case
A quartz sand(silica sand) dressing plant in Yunnan with the main component was quartz sand(silica sand) accounting for 95-97%; siliceous cement accounting for 8-23%, the impurity minerals were hematite, limonite, etc. accounting for about 1-3%. The plant adopted screen classification - dry magnetic separation - dosing strong scrubbing-flotation process, the final indexes: SiO2 ≥ 97.62%, Fe2O3 ≤ 0.24, Al2O3 ≤ 1.11%.The poor indexes seriously affect the production and economic benefit. Therefore, the plant commissioned the Hengyang to reform technology. By dressing tests, Hengyang decided to adopt the screen classification - dry magnetic separation - dosing strong scrubbing - acid leaching process.
After the technical reformation, the purified quartz sand(silica sand) met the quality requirements of silicon powder, and it can be used in ceramic, paint, metal casting industry after the superfine grinding.
