Since these iron-containing impurities in the presence of greatly reducing the value of quartz sand, affect product quality, for example in glass production, the iron impurities have a greater harm to glass production and quality are, especially for glass melting process The thermodynamic properties and the transparency of the finished glass. Therefore, it is very important to increase the grade of quartz sand in the production process to reduce the content of iron. In the actual production, the raw materials are firstly washed with water, and then mechanical scrubbing, magnetic separation, flotation, ultrasonic cleaning, acid leaching and the like are used to remove the iron elements in the quartz sand, thereby improving the use value of the quartz sand.
First, mechanical scrubbing and iron removal
Mechanical scrubbing is the removal of thin film iron from the surface of quartz sand and iron-containing minerals adhering to the surface of quartz sand by mechanical external force and collision and friction of 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 the structural features and configuration forms of the scrubber, followed by the process factors, including scrubbing time and scrubbing concentration. The efficiency of mechanical scrubbing increases with increasing pulp concentration because increasing the slurry concentration increases the probability of collisions between particles. Studies have shown that sand scrubbing concentration is best between 50% and 60%. In principle, the scrubbing time should be based on preliminary product quality requirements and should not be too long. Because time is too long, it will increase equipment wear and tear, resulting in increased energy consumption and improve the beneficiation purification costs. If the drug is applied with high efficiency and strong scrubbing, and the appropriate process and equipment are used, the effect of rod scrubbing will be better, because the dosing can increase the electric repulsion of the surface of the impurity minerals and quartz particles, and enhance the separation of the impurity minerals from the quartz particles. effect. For the rod grinding test of quartz ore with a concentration of +0.3 mm or more in a certain area, Fe 2 O 3 was reduced from 0.19% to 0.10%, and the removal rate of iron was 47.4%. Compared with other iron removal processes, the LT art has the following characteristics: 1) good product quality, can meet the quality requirements of float glass for high quality silica sand; 2) large output. Now some small-scale production and processing companies use this method to remove more iron because it is cheaper and easier to operate, but the iron removal rate is relatively low.
Second, magnetic separation iron
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. In order to separate the magnetic mineral from the non-magnetic mineral for the purpose of removing the iron-containing mineral, the magnetic force acting on the magnetic mineral must satisfy the following conditions: the magnetic force acting on the magnetic ore is greater than all the mechanical forces acting on the magnetic ore. Together.
Magnetic separation is divided into dry selection and wet selection. Taking the production process of Yichang quartz sand mine in Hainan as an example, comparing the two processes of dry selection and wet selection, it is found that the wet magnetic separation has a large magnetic consumption, the medium is easy to wear, the production water consumption is large, and the operation is Defects in high maintenance costs. The dry strong magnetic separation process is easy to operate, and the operation and maintenance costs are lower than the wet type.
In the magnetic separation process, the wet magnetic separator can remove the weak magnetic impurity minerals such as hematite, limonite and biotite including the continuum particles. In general, quartz sand containing impurities mainly composed of weak magnetic impurities can be selected by using a wet magnetic machine above 10,000 Oersted; for a strong magnetic mineral containing magnetite as the main impurity, it is weak. The selection effect of the magnetic machine or the medium magnetic machine is better. In the production, a wet-type strong magnetic separator is used to obtain a high-quality quartz sand concentrate with a Fe 2 O 3 content of 0.036%. The iron removal effect of the wet magnetic separator is affected by parameters such as the amount of feed, the amount of flushing water, and the strength of the magnetic field, among which the magnetic field strength is the most affected. In addition, the more the number of magnetic separations, the finer the grain size of the quartz sand, and the better the iron removal effect.
Third, ultrasonic removal of iron
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. When the treatment time is 10min, the iron removal rate is generally 46% to 70%. In the use of ultrasonic removal of iron should pay attention to the timely removal of waste liquid to prevent the iron removal effect due to secondary adhesion. Ultrasonic cleaning combined with chemical agents (dispersants) can increase the iron removal rate by 5% to 30%. The main reason for the strengthening effect of ultrasonic waves on the agent is that the presence of cavitation contributes to the dispersion of the agent, increases the probability of its action on the surface of the ore particles, and contributes to the dissolution and dispersion of the agent on the surface of the particles. When removing iron by ultrasonic wave, the concentration of pulp should not be too large. Because when the concentration is too large, too many impurities due to desorption can not be removed in time, it will be adsorbed on the surface of the particles again, so that the iron removal effect will decrease. The intensity of the ultrasonic wave also has a certain influence on the iron removal effect of the quartz sand. The stronger the intensity of the ultrasonic wave, the higher the iron removal efficiency.
Compared with mechanical scrubbing, this method not only eliminates mineral surface impurities, but also removes impurities from the cleavage gap of the particles. Therefore, the iron removal effect is better. Ultrasonic iron removal is currently more expensive for the cheaper resources of silica sand. It is still difficult to apply in large-scale concentrators, but it is possible to use those areas where high purity and low dosage are required.
Fourth, flotation and iron removal
The flotation method is mainly used to separate feldspar in quartz sand, and 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 acidity (pH 2-3). Flotation iron, NaOH is used to inhibit metal ion activation quartz gold; flotation feldspar, mica, clay minerals, H 2 SO 4 may be produced not only adsorbed positioned feldspar floating surface, reduce the surface of the negative turtle And can activate feldspar and mica.
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 are 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. Removal flotation occurs in heavy mineral iron works well, concentrator U.S. Silica under acidic conditions employed, petroleum sulfonate, kerosene as collector, separated and biotite containing iron, so that The Fe 2 O 3 content is reduced from 0.12% to 0.18% to 0.06% to 0.065%. The flotation method has simple iron removal process, low cost and good effect. This process has played a positive role in expanding the utilization of quartz sand resources in China.
5. Acid leaching and removing iron
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.
The harmful components of the quartz particles after flotation are connected to the surface in the form of spots or inclusions. To remove this part of the impurities, acid leaching must be carried out. Acids commonly used in acid leaching are sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid. For the removal of Fe, AI, and Mg, the above acids have effects. Studies have found that the removal of iron by hydrochloric acid is better than that of sulfuric acid. In the quartz sand towel, since the harmful component is in the form of a mineral aggregate rather than a pure mineral, the acid leaching effect of the mixed acid leaching is better than that of the single acid. The ratio of various acids and the order of addition also have a large effect on the removal of impurity minerals. The acid concentration should be suitable, the acid concentration is too low, the time is long, the yield is low and the impurity removal effect is not good; the acid concentration is too high, which will not only increase the cost, but also increase the corrosion of the equipment, and also reduce the SiO 2 production. . The acid immersion temperature has a great influence on the removal rate of impurities in quartz. The lower the temperature, the slower the reaction rate and the longer the time required; the higher the temperature, the faster the evaporation of the acid, thereby increasing the amount of acid used. In addition, acid leaching time, mineral particle size and slurry agitation have an effect on the removal effect. When the content of impurities in the product after the first acid leaching is not required, secondary acid leaching and multiple acid leaching may be performed until the content of the impurity iron reaches the requirement.
In general, the use of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid is expensive and has a large environmental impact. Foreign scholar F. Viglio et al. used oxalic acid as a leaching agent to remove iron from quartz sand minerals. This method utilizes the reaction of leather acid with Fe 3+ on the surface of the ore particles to form a complex and dissolve 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 advantage of using oxalic acid to remove iron is that a soluble complex (for example, an iron (III) complex anion) is formed upon leaching, and the complex can be decomposed by both microorganisms and sunlight. In addition, the use of oxalic acid to remove iron has certain requirements on the ore particle size. Generally, the ore is ground to an average particle size of about 20um. After treating the ore for more than 3 hours, the iron removal rate can reach 80% to 100%. After the pickling treatment, SiO 2 obtained purity 99.99%, Fe content <235ppm of high purity quartz sand.
Sixth, biological 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 foreign research results, microorganisms such as Aspergillus, Penicillium, Pseudomonas, Pseudomonas, Bacillus, Bacillus polymyxa, and Lactobacillus have been obtained by immersing iron oxide on quartz surface. The better effect is that the effect of extracting iron by aflatoxin is the best, the removal rate of Fe 2 O 3 is up to 88.8%, and the grade of Fe 2 O 3 in quartz sand is as low as 0.008%. 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. It is worth noting that the final iron content after leaching is independent of the initial iron content prior to leaching, and is related to the form of iron present in the mineral raw material. Only iron that is not in the lattice of the mineral lattice can be removed by this method.
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