The existence of iron-containing impurities greatly reduces the use value of quartz sand and affects the quality of products. For example, in glass production, iron-containing impurities will cause great harm to the production and quality of glass, especially in the process of glass melting. thermodynamic properties and light transmittance of glass finished products. Therefore, it is very important to improve the grade of quartz sand and reduce the content of iron in the production process. In actual production, the raw materials are first washed with water to remove the sludge, and then mechanical scrubbing, magnetic separation, flotation, ultrasonic cleaning, acid leaching and other processes are used to remove iron in the quartz sand and improve the use value of the quartz sand.
In some small-scale production enterprises and processing enterprises, this method is used for iron removal, because it is low-cost and simple to operate, but the iron removal rate is relatively low.
2. Magnetic separation for iron removal
The main mineral in quartz sand, quartz, is a diamagnetic substance and cannot be magnetized in a magnetic field. The iron-containing impurity minerals 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, this difference in properties is used to remove these iron-containing impurity minerals in the quartz sand through magnetic separation. In order to achieve the purpose of removing iron-bearing minerals and separating magnetic minerals from non-magnetic minerals, the magnetic force acting on the magnetic minerals must meet the following conditions: the magnetic force acting on the magnetic ore particles is greater than all the mechanical forces acting on the magnetic ore particles. together.
Magnetic separation is divided into dry separation and wet separation. Comparing the two processes of dry separation and wet separation, it is found that the wet strong magnetic separation has the defects of high power consumption of the magnetic separator, easy wear of the medium, large production water consumption, and high operation and maintenance costs. The dry type strong magnetic separation process is easy to operate, and the operation and maintenance costs are lower than those of the wet type.
In the magnetic separation process, the wet strong magnetic separator can remove the weak magnetic impurity minerals such as hematite, limonite and biotite, including conjoined particles, to the greatest extent. Generally speaking, quartz sand containing impurities mainly containing weak magnetic impurity minerals can be selected by using a wet strong magnetic machine at a temperature of more than 10,000 Oersted; for strong magnetic minerals containing impurities mainly magnetite, weak Magnetic machine or medium magnetic machine for selection effect is better. The best use of wet magnetic separator in production can obtain high-quality quartz sand concentrate with Fe2O3 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 strength of the magnetic field has the greatest influence. In addition, the more magnetic separation times, the finer the quartz sand particle size, and the better the iron removal effect.
3. Ultrasonic iron removal
Ultrasound is a high-frequency (frequency greater than 20000Hz) sound wave that relies on the medium to propagate. It has mechanical energy, and will interact with the medium during the propagation process, resulting in mechanical effects, thermal effects and cavitation effects. When ultrasonic waves are emitted in water (or solution), many areas of compression and expansion are created, leading to the formation and collapse of numerous micro-bubbles (cavitation bubbles), a condition known as cavitation. In the process of cavitation, the internal pressure of the liquid undergoes a sudden change, which is accompanied by a shock wave, and the pressure can reach several thousand to tens of thousands of atmospheres. Under the action of this shock wave, the iron-containing impurities adhering to the surface of the particles will fall off the surface of the particles and enter the liquid phase, so as to achieve the purpose of iron removal.
Compared with mechanical scrubbing, ultrasonic iron removal can not only remove impurities on the surface of minerals, but also remove impurities in the cleavage gap of particles, so the iron removal effect is better. Ultrasonic iron removal is still relatively expensive for a cheap resource such as silica sand, and it is still difficult to apply in large-scale concentrators, but it is possible to use in those production fields that require high purity and low dosage.
4. Flotation iron removal
Flotation is mainly used to separate feldspar in quartz sand, and can also be used to remove clay minerals such as mica and secondary iron in quartz sand. The most typical process uses hydrofluoric acid as the activator, and uses amine cationic collectors for flotation under strong acidity (pH? 2~3). In iron flotation, NaOH can be used to inhibit quartz activated by metal ions; in flotation of clay minerals such as feldspar and mica, H2SO4 can not only generate localized adsorption on the surface of the flotated feldspar, reduce the surface negative tortoise, but also activate Feldspar and mica.
There are 3 types of flotation methods:
The first is the fluorine-acid method. This method is widely used because of its good flotation effect, easy control and stable index. However, the erosion effect of fluoride ions on the land and the damage to the ecological environment of Zhoutong are very great.
The second is the fluorine-free and acid method. The biggest advantage of this method is that it avoids 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 mineral processing equipment cannot be ignored. There are higher requirements for flotation equipment.
The third is the fluorine-free and acid-free method. Under natural pH conditions, through the reasonable deployment of anion and cation collectors, a unique high-concentration pulp flotation environment is created to achieve the purpose of preferential flotation of impurity minerals. However, because this method has strict requirements on raw sand treatment and pulp environment, it is not easy to control in production, and it has not been widely used at present. The flotation method is very effective for removing iron in heavy minerals. The silica sand concentrator in the United States uses sodium petroleum sulfonate and kerosene as collectors to separate biotite and iron-bearing ore under acidic conditions, so as to make Fe2O3 The content decreased from 0.12% to 0.18% to 0.06% to 0.065%. The flotation method for iron removal is simple, low in cost and good in effect. This process has played a positive role in expanding the utilization range of quartz sand resources in my country.
5. Acid leaching to remove iron
Acid leaching to remove iron is to use the characteristics that quartz is insoluble in acid (except HF), and impurity minerals containing Fe can be dissolved by acid solution, so that the purpose of removing iron-containing minerals from quartz sand can be achieved. The acid leaching method can not only remove iron-bearing minerals from quartz sand, but also has a good removal effect on non-metallic impurity minerals in quartz.
6. Biological iron removal
The use of microorganisms to remove thin-film iron or impregnated iron on the surface of quartz sand particles is a newly developed iron removal technology, which is currently in the research stage of laboratory and small-scale experiments. According to foreign research results, when microorganisms such as Aspergillus niger, Penicillium, Piriformis, Pseudomonas, Bacillus, Bacillus polymyxa, Pediococcus lactis and other microorganisms leached iron oxide on the quartz surface, all obtained The best results were obtained. Among them, Aspergillus niger bacteria leaching had the best effect of iron removal, the removal rate of Fe2O3 was up to 88.8%, and the grade of Fe2O3 in quartz sand was as low as 0.008%. The study also found that the effect of leaching iron was better with pre-cultivated cultures of bacteria and molds. Anaerobic species decompose iron at a slower rate than aerobic species. Bacterial leaching sensitivities differ for different iron oxide minerals, dissolving iron from limonite more slowly than from goethite, but much faster than from hematite. It is worth pointing out that the final iron content after leaching is not related to the initial iron content before leaching, but to the form of iron in the mineral raw material. Only iron that is not located in the mineral lattice can be removed by this method.