Quartz sand, also known as silica sand, is a widely used non-metallic mineral material. In quartz sand, the main mineral is quartz, and there are also some other impurities, including iron, hematite, limonite, ilmenite, pyrrhotite, tourmaline, hornblende, biotite and so on. These iron containing impurities are embedded in quartz grains or attached to quartz surfaces. The presence of iron impurities greatly reduces the use value of quartz sand and affects the quality of products.
Quartz sand iron removal method
Quartz, the main mineral in quartz sand, is a diamagnetic substance which cannot be magnetized in a magnetic field. The impurity minerals of iron in quartz sand are hematite, limonite, magnetite, goethite and so on. Most of them are magnetic materials which can be magnetized in magnetic field. In magnetic separation process, the iron impurity minerals in quartz sand can be removed by magnetic separation by using the difference of this property.
2. Ultrasonic removal of iron
Ultrasonic is a kind of high frequency (frequency more than 20000Hz) sound wave, which is transmitted by medium. It has mechanical energy. It can interact with medium in the process of propagation, which produces mechanical effect, thermal effect and cavitation effect. When ultrasonic waves are emitted in water (or solution), many regions of compression and expansion are produced, resulting in the formation and rupture of numerous microbubbles (cavitation bubbles), which are called cavitation. In the process of cavitation, the pressure inside the liquid changes abrupt, and is accompanied by shock waves. The pressure can reach several thousand to tens of thousands of atmospheric pressure. Under the action of this shock wave, the iron impurity adhered to the surface of the particle will fall off the particle surface and enter the liquid phase, thereby achieving the purpose of removing iron. The removal of iron by ultrasonic is mainly the removal of secondary iron thin films (i.e. "thin film iron") on the surface of particles. The iron thin film is firmly bonded and the mechanical scrubbing method used in mineral processing can not be separated. Using ultrasonic technology to treat natural silica sand containing "thin film iron" has the characteristics of short time and high efficiency.
3. Flotation removal of iron
Flotation is mainly used to separate feldspar from quartz sand, but it can also be used to remove mica and other clay minerals and secondary iron in quartz sand. The most typical process is using hydrofluoric acid as an activator and flotation with amine cation collectors under strong acidic conditions (pH2 to 3).
The flotation method can be divided into three kinds:
The first is the fluorine and acid method. This method is widely used because of its good flotation effect, easy control and stable index. However, the erosion of fluorine ions to the land and the damage to the surrounding ecological environment are great.
The second is fluorine free acid method. The greatest advantage of this method is to avoid the use of fluorine ions that have destructive effects on the environment, and the production index is stable, but the corrosion effect of strong acid on mineral processing equipment can not be ignored. There is a high requirement for floatation equipment.
The third is fluorine free and acid free method. Under the natural pH condition, a unique high concentration mineral slurry flotation environment is created by rational distribution of the ion collector of yin and Yang, so as to achieve the priority of flotation of impurities in the mineral. However, because this method has strict requirements for raw sand treatment and pulp environment, it is not easy to control production, and it is not widely used at present.
4. Acid leaching of iron
The acid leaching of iron is the use of quartz insoluble in acid (except HF), and the mineral containing Fe can be dissolved by acid solution, thus the removal of iron containing minerals from quartz sand can be achieved. Acid leaching not only removes iron bearing minerals from quartz sand but also has good removal effect on non metallic impurities in quartz. Generally speaking, the use of sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid is expensive and has great environmental impact. By using the Fe3+ reaction of oxalic acid on the surface of the ore particles, the complex can be dissolved in water to achieve the purpose of removing iron, but in this case the dissolution mechanism of iron is different from the dissolution of iron minerals by inorganic acids. The main advantage of using oxalic acid to remove iron lies in the formation of soluble complex during leaching, which can be decomposed under the action of microorganisms and sunlight.
5. Microorganism removal of iron
The film iron or impregnated iron on the surface of quartz sand particles by microorganism is a newly developed iron removal technology, which is currently in the laboratory and small test stage. According to foreign research results, Aspergillus niger, Penicillium, phaiform fungus and other microorganisms have achieved good results in removing iron oxide from quartz surface. The study also found that the effect of bacteria and mold on the leaching of iron was better. The rate of iron decomposition by anaerobic bacteria is slower than that of aerobic bacteria. The sensitivity of different iron oxide minerals to bacterial leaching is different. The dissolution of iron from limonite is slower than that from goethite, but it is much faster than that from hematite.