Quartz sand, also known as silica sand, a wide range of applications of non-metallic mineral raw materials. Quartz sand, quartz is the main mineral, also often contain some other mineral impurities, wherein the impurity elements are iron-containing minerals: goethite, hematite, limonite, titanium, iron, pyrrhotite, electrical Stone , hornblende, biotite, etc. These iron-containing impurities are either embedded in the quartz particles or attached to the quartz surface. The presence of these iron-containing impurities greatly reduces the use value of quartz sand and affects the quality of the product.
Quartz sand removal method
Mechanical scrubbing
Mechanical scrubbing is the removal of iron from the surface of quartz sand and iron-containing minerals adhering to the surface of quartz sand by means of mechanical external force and collision and friction between sand particles. Currently, scrubbing techniques are primarily rod scrubbing and mechanical scrubbing. For mechanical scrubbing, it is generally believed that the factors affecting the scrubbing effect are mainly from the structural features and configuration of the scrubber, followed by the process factors, including scrubbing time and scrubbing concentration.
Magnetic separation
Quartz, the main mineral in quartz sand, is a diamagnetic substance that cannot be magnetized in a magnetic field. The impurity minerals containing iron in quartz sand: hematite, limonite, magnetite, goethite, etc., most of which are magnetic substances that can be magnetized in a magnetic field. In the magnetic separation process, the difference in this property is utilized to remove these iron-containing impurity minerals in the quartz sand by magnetic separation.
Ultrasonic iron removal
Ultrasonic waves are high-frequency (frequency greater than 20,000 Hz) sound waves that rely on the medium to propagate. They have mechanical energy that interacts with the medium during propagation to produce mechanical, thermal, and cavitation effects. When ultrasonic waves are emitted in water (or solution), many areas of compression and expansion occur, resulting in the formation and rupture of numerous microbubbles (cavitation bubbles), a condition known as cavitation. During the cavitation process, the internal pressure of the liquid is abruptly accompanied by a shock wave with a pressure of several thousand to several tens of thousands of atmospheres. Under the action of the shock wave, the iron-containing impurities adhering to the surface of the particles are detached from the surface of the particles and enter the liquid phase, thereby achieving the purpose of removing iron. Ultrasonic iron removal is primarily a secondary iron film (ie, "thin film iron") that removes the surface of the particles. The iron film is firmly bonded and the mechanical scrubbing method used in the beneficiation cannot be separated. The use of ultrasonic technology to treat natural silica sand containing "thin film iron" has the characteristics of short time and high efficiency.
Flotation iron removal
The flotation method is mainly used to separate feldspar in quartz sand, but it can also be used to remove clay minerals such as mica in quartz sand and secondary iron. The most typical process is to use hydrofluoric acid as an activator to perform flotation using an amine cation collector under strong acidic conditions (pH 2 to 3).
The flotation method can be divided into three types: the first one is a fluorine acid method. This method is widely used because of its good flotation effect, easy control, and stable index. However, the erosive effect of fluoride ions on the land and the damage to the surrounding ecological environment is great.
The second is a fluorine-free acid method. The biggest advantage of this method is to avoid the use of fluoride ions that have a destructive effect on the environment, and the production index is stable, but the corrosive effect of strong acid on the beneficiation equipment cannot be ignored. There are high requirements for flotation equipment .
The third is a fluorine-free and acid-free method. Under the natural pH condition, a unique high-concentration slurry flotation environment is created by rationally blending the anion-cation collector to achieve the purpose of preferential flotation of impurity minerals. However, due to the strict requirements of the original sand treatment and slurry environment, the production is not easy to control and has not been widely used.
Acid leaching
Acid leaching removes iron by utilizing quartz insoluble in acid (except HF), and impurities containing Fe can be dissolved by acid, so that the purpose of removing iron-containing minerals from quartz sand can be achieved. The acid leaching method not only removes iron-containing minerals from quartz sand, but also has a good removal effect on non-metallic impurity minerals in quartz. In general, the use of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid is expensive and has a large environmental impact. The oxalic acid is reacted with Fe3+ on the surface of the ore particles to form a complex and then dissolved in water to achieve the purpose of removing iron. However, the dissolution mechanism of iron in this case is different from the dissolution of iron mineral by inorganic acid. The main advantage of using oxalic acid to remove iron is that a soluble complex is formed upon leaching, and the complex can be decomposed under the action of microorganisms and sunlight.
Microbial iron removal
Thin film iron or dip-dyed iron on the surface of quartz sand particles by microorganisms is a newly developed iron removal technology, and is currently in the research stage of laboratory and small experiments. According to the results of foreign research, microorganisms such as Aspergillus, Penicillium, and Pear-like bacteria have achieved good results when the iron oxide on the surface of quartz is impregnated. The study also found that the effect of leaching iron with bacteria and mold pre-cultured culture fluid is better. Anaerobic strains decompose iron at a slower rate than aerobic species. The leaching sensitivity of different iron oxide minerals is different. The dissolution of iron from limonite is slower than that from goethite, but much faster than that from hematite.
Conclusion
Different industries in China have different requirements for the content of SiO2 and iron in quartz sand. Different methods of removing iron can be selected according to the use of quartz sand, the content of SiO2 in quartzite , and the size of the production enterprise. The mechanical scrubbing and iron removal technology is simple, the production volume is large, but the iron removal rate is low. Magnetic separation method Iron removal and flotation method have a wide range of applications in iron removal, which are suitable for large-scale production and have good iron removal effect. Ultrasonic iron removal is suitable for production enterprises with high purity requirements and low dosage. The acid leaching method has high cost and high complexity, but high purity quartz sand can be obtained by acid leaching. This method is suitable for high purity quartz sand products. Microbial iron removal technology is still not perfect, and it is still in the experimental stage.
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