The main purpose of quartz sand beneficiation and purification is to remove iron impurities. The occurrence state of iron impurities in quartz ore determines whether they can be removed by beneficiation and the degree of removal. It is an important basis for drawing up the beneficiation and purification plan and predicting the separation index to understand the iron impurities in which ore phases exist, in what form, content and distribution. According to many years of experience in removing iron from quartz sand, Fodamon engineers today explain as follows:
A. Existing forms of iron impurities in quartz sand
The occurrence forms of iron impurities in quartz sand are relatively complex and diverse, or exist in clay or feldspar and other mineral phases, or attach to the surface of particles in the form of iron oxide and iron ore, or occur in the interior of quartz particles.
(1) It exists in clay minerals
There are many weathered clays in some exposed sedimentary sand deposits. This kind of clay is weathered from feldspar, limestone, shale, etc. The clay is composed of natural hydrous bauxite silicate containing a mixture of mica, quartz, limonite, chlorite, calcite and amphibole. Its grain size is very fine, mainly composed of 10 μ Particle composition below m.
(2) It exists in heavy minerals and magnetic minerals
Heavy minerals refer to minerals with relative density greater than 2.9. Most of these minerals are magnetic or weakly magnetic, and iron is the basic constituent of these minerals. So we can also call them existing in single minerals, such as magnetite, hematite, pyrite, pyrrhotite, ilmenite, chromite, olivine, limonite, limonite, etc.
(3) It exists in light minerals
Light minerals mainly refer to feldspar (usually orthoclase or microcline). Alumina in feldspar is sometimes replaced by iron oxide, and its amount can reach 0.5% – 0.7%. In addition, there are kaolinite, muscovite, calcite, dolomite, etc. Among these light minerals, iron enters the lattice in the form of isomorphism. Because their density is very close to that of quartz, it is quite difficult to separate them.
(4) In thin film iron
The quartz particles in the quartz sand are white in the pure condition and gray, brown, yellow and even red after being polluted. For example, clay can make it gray or yellow, metal minerals and other dark minerals can make it gray, and film iron can make it yellow or red. Most of the things we see are contaminated quartz sand.
In terms of composition, the pollution of quartz particles is mainly iron pollution and mud pollution. The former refers to the pollution of iron oxide or hydroxide on quartz particles. The latter refers to a series of layered aluminosilicate clay mineral pollution.
In terms of causes, it can be divided into primary pollution and secondary pollution. Primary pollution refers to the phenomenon that the surface or interior of a certain mineral is polluted by other minerals caused by mineral dyeing. Mineralization is a phenomenon that a mineral occurs in the interior or surface of other minerals in the form of particles or films during the mineralization process, which is closely related to the mineralization process. There is also the phenomenon that the surface of quartz particles is polluted by other minerals (or ions) due to adsorption, which is called secondary pollution.
The contamination of quartz particles by clay minerals is related to the surface depressions and cracks of quartz and the plasticity of clay. This kind of clay attached to the surface of quartz particles is easier to remove because they are not firmly bonded. However, the iron oxide film on the surface of quartz particles is difficult to remove, which is caused by mineralization. In fact, the so-called thin film iron mainly refers to this situation.
(5) Exists in a continuum or lattice
All kinds of minerals in quartz sand can be basically considered to have been in the state of monomer dissociation, so there is no need for further crushing, but quartz particles and other iron-bearing minerals are still linked together. Most of these conjoined bodies are dark minerals, some of which are wrapped in the interior of quartz particles, some of which are embedded in the edge of quartz particles and become mineral aggregates. The so-called wrapped iron mainly refers to this situation.
B. Six methods of removing iron from quartz sand
- Iron removal by mechanical scrubbing
Mechanical scrubbing is to remove the film iron on the surface of quartz sand and the iron-bearing minerals adhering to the surface of quartz sand by means of mechanical external force and collision and friction between sand particles. At present, the scrubbing technology is mainly rod grinding scrubbing and mechanical scrubbing. For mechanical scrubbing, it is generally believed that the main factors affecting the scrubbing effect are the structural characteristics and configuration form of the scrubbing machine, followed by process factors, including scrubbing time and scrubbing concentration. The efficiency of mechanical scrubbing increases with the increase of slurry concentration, because increasing slurry concentration can increase the probability of collision between particles.
Compared with other iron removal processes, this method has the following characteristics:
1) The product quality is good and can meet the quality requirements of float glass for high-quality silica sand;
2) Large output. At present, some small-scale production and processing enterprises use this method to remove iron more, because it is low in cost and simple in operation, but the iron removal rate is relatively low.
- Iron removal by magnetic separation
Quartz, the main mineral in quartz sand, is an antimagnetic material, which cannot be magnetized in a magnetic field. The impurity minerals containing iron in quartz sand: hematite, limonite, magnetite, goethite, etc. Most of them are magnetic substances that can be magnetized in the magnetic field. In the magnetic separation process, it is to take advantage of this property difference to remove these iron-containing impurity minerals from quartz sand by magnetic separation. In order to remove iron-bearing minerals and separate magnetic minerals from non-magnetic minerals, the magnetic force acting on magnetic minerals must meet the following conditions: the magnetic force acting on magnetic particles is greater than the combined force of all mechanical forces acting on magnetic particles.
Magnetic separation is divided into dry separation and wet separation. Comparing dry separation and wet separation, it is found that wet high intensity magnetic separation has the defects of high power consumption of magnetic separator, easy wear of medium, large production water consumption, high operation and maintenance costs. The dry high intensity 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 high intensity magnetic separator can maximally remove hematite, limonite, biotite and other weak magnetic impurity minerals, including connective particles. Generally speaking, quartz sand containing mainly weak magnetic impurity minerals can be selected by using wet high magnetic machine at more than 10000 Ost; For the strong magnetic minerals with magnetite as the main impurity, the weak magnetic machine or medium magnetic machine is better for selection. High quality quartz sand concentrate with Fe2O3 of 0.036% can be obtained by using wet high intensity magnetic separator in production. The iron removal effect of wet high intensity magnetic separator is affected by parameters such as feed volume, flushing water volume, magnetic field strength, etc., of which the magnetic field strength has the greatest impact. In addition, the more magnetic separation times, the finer the grain size of quartz sand, the better the iron removal effect.
- Ultrasonic iron removal
Ultrasonic wave is a kind of high frequency (frequency greater than 20000 Hz) sound wave that depends on the medium. It has mechanical energy and will interact with the medium in the process of propagation, producing mechanical effect, thermal effect and hole effect. When ultrasonic wave is emitted in water (or solution), it will produce many compression and expansion areas, resulting in the formation and rupture of countless microbubbles (cavitation bubbles), which is called cavitation phenomenon. In the process of cavitation, the internal pressure of the liquid changes suddenly, which is accompanied by a shock wave, and its 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 particle surface fall off from the particle surface and enter the liquid phase, thus achieving the purpose of removing iron.
Compared with mechanical scrubbing, ultrasonic iron removal can not only remove the impurities on the mineral surface, but also remove the impurities at the cleavage gap of particles. Therefore, its iron removal effect is better. Ultrasonic iron removal is still relatively expensive for silicon sand, a cheap resource. It is still difficult to apply it in large concentrators, but it is possible to use it in production fields that require high purity and low consumption.
- Flotation iron removal
The flotation method is mainly used to separate feldspar in quartz sand, and also to remove clay minerals such as mica and secondary pig iron in quartz sand. The most typical process is to use hydrofluoric acid as an activator, and use amine cationic collectors for flotation under strong acidity (pH? 2~3). During iron flotation, NaOH can be used to inhibit quartz activated by metal ions; When flotation of feldspar, mica and other clay minerals, H2SO4 can not only produce localized adsorption on the surface of the floated feldspar, reduce the surface negativity, but also activate feldspar and mica.
There are three flotation methods:
The first method is fluorine-acid method. This method is widely used because of its good flotation effect, easy control and stable index. However, fluoride ion has a great impact on soil erosion and the ecological environment of Zhoutong.
The second is fluorine-free and acid-free method. The biggest advantage of this method is to avoid the use of fluoride ions that have destructive effects 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 fluorine-free and acid-free method. Under the natural pH condition, a unique high concentration pulp flotation environment is created through the rational allocation of anionic and cationic collectors to achieve the purpose of preferential flotation of impurity minerals. However, due to the strict requirements on raw sand treatment and pulp environment, this method is not easy to control in production and has not been widely used at present. The flotation method has a good effect on the removal of iron existing in heavy minerals. Under acidic conditions, the U.S. silica sand concentrator uses sodium petroleum sulfonate and kerosene as collectors to separate biotite and iron ore, so that the content of Fe2O3 decreases from 0.12% to 0.18% to 0.06% to 0.065%. The flotation process for iron removal is simple, low cost and good effect. This process has played a positive role in expanding the utilization scope of quartz sand resources in China.
- Iron removal by acid leaching
Iron removal by acid leaching takes advantage of the fact that quartz is insoluble in acid (except HF) and Fe-containing impurity minerals can be dissolved by acid solution, so as to achieve the purpose of removing iron-containing minerals from quartz sand. Acid leaching can not only remove iron minerals from quartz sand, but also remove non-metallic impurities in quartz. - Biological iron removal
Microbial leaching of film iron or disseminated 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 tests. According to the results of foreign research, Aspergillus niger, Penicillium, Trichoderma piriformis, Pseudomonas, Bacillus, Bacillus polymyxa, Micrococcus lactis and other microorganisms have achieved good results in leaching iron oxide on the surface of quartz. Among them, Aspergillus niger has the best effect in removing iron, the removal rate of Fe2O3 is up to 88.8%, and the grade of Fe2O3 in quartz sand is as low as 0.008%. The study also found that the effect of leaching iron from the culture solution pre-cultivated by bacteria and mold is better. The rate of iron decomposition of anaerobic bacteria is slower than that of aerobic bacteria. The bacterial 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 pointing out that the final iron content after leaching is not related to the initial iron content before leaching, but to the existing form of iron in mineral raw materials. Only iron not located in the mineral lattice can be removed by this method.