Study on purification process of quartz sand beneficiation

I. Introduction

Quartz sand, also known as silica sand, is a common non-metallic mineral raw materials, its wide range of applications. China's quartz sand beneficiation purification and deep processing development and utilization is relatively late, and is mainly used in the construction industry, glass manufacturing, ceramic industry and foundry industry. One common point in these fields is the large demand for quartz sand and low quality of raw materials. For high-quality quartz sand from some producing areas in China, it can basically meet the demand of industrial sand without undergoing beneficiation or purification.

At present, the foreign country's quartz sand beneficiation and purification technology is the most advanced, characterized by large industrial production, professional equipment and high degree of production automation. Its products have been developed to the sixth generation (the total mass fraction of impurities is less than 8×10 ^-6 , transparency). For optical grade). High-purity and ultra-high-purity quartz sand made by beneficiation and purification has been widely used in aerospace, atomic energy technology, laser, optical cable communication, military and other high-tech fields. With the advancement of science and technology, the demand for high-tech silicon will also increase greatly, and the depletion of natural crystal resources has forced people to turn their attention to the replacement of natural crystals - high purity and ultra-high purity quartz sand. Therefore, we actively explore and promote the advancement of quartz sand beneficiation and purification technology, realize the cost of refined quartz sand, high-purity and ultra-high-purity quartz sand, mass industrial production, and make up for the shortage of natural crystal resources to meet the demand for high-tech silicon. Important practical significance.

Second, quartz sand ore dressing purification method

Quartz sand purification is a difficult separation technique to remove small or trace impurities in quartz sand to obtain refined quartz sand or high-purity quartz sand (such as electronic grade products). In recent years, the research on quartz sand purification technology at home and abroad mainly focuses on the following Aspects are carried out:

(1) Washing and grading de-sludge

Grade quartz sand of SiO ₂ as quartz sand tapering degree decreases, the magazine mineral iron grade quality and the like made of aluminum, is the opposite, a phenomenon in nature contains a large amount of clay mineral quartz sand is particularly evident. Therefore, before the selection, the quartz sand ore is water-selected, and the de-sludge is very necessary, and the effect is more obvious. For example, the chemical composition of quartz sand ore in the Malingshan Mine of Suqian, Jiangsu Province is: SiO ₂ 79.38%, Fe ₂ O ₃ 1.68%, AL ₂ O ₃ 11.28%, and its particle size composition -0.1mm grain size content is 27.65%. After pre-selected water washing and fractional de-sludge of the ore, the grade of SiO ₂ increased to 86.36%, Fe ₂ O ₃ decreased to 0.49%, and AL ₂ O ₃ decreased to 6.79%. The effect of impurity removal and purification was significant. Washing and grading de-sludge as a pre-treatment method before ore is selected, and it is also very common in application. However, the removal effect of thin-film iron and blocking impurity minerals existing on the surface of quartz sand is not significant.

(2) scrubbing

Scrubbing is to remove the thin film iron, the bonding and muddy impurity minerals on the surface of the quartz sand by mechanical force and the grinding and peeling force between the sand grains, and to further smash the unassembled mineral aggregates, and then further purify the quartz sand by the classification operation. At present, there are two main methods: bar friction washing 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 forms of the scrubber, followed by process factors, including scrubbing time and scrubbing concentration. The research shows that the scrub concentration of sand mine is the best between 50% and 60%, and to a certain extent, it increases the difficulty of purifying quartz sand. In principle, the scrubbing time should be based on the initial product quality requirements. Long, because of the long time, will increase equipment wear, increase energy consumption and increase the cost of purification. Because the mechanical scrubbing and wiping effect is not ideal for some quartz sand mines, it is more common and relatively mature in China's rod scrubbing industry. For example, if the quartz sand ore in a certain place is washed by water and classified, the quartz sand of +0.3mm or more is subjected to rod grinding. The results show that after grinding and scrubbing, the Fe ₂ O _{3 is} reduced from 0.19% to 0.10%, and the iron is removed. The rate reached 47.4%. We used a high-efficiency and strong scrubbing of quartz sand mine in a certain area of ​​Yunnan, combined with appropriate technology and equipment, and found that the effect is better than that of rod scrubbing. The yield after rod scrubbing is 49%, and the high-efficiency strong scrubbing recovery is added. The rate is 73%. The purpose of dosing is to increase the electric repulsion of the surface of the impurity minerals and quartz particles, and to enhance the separation effect between the impurity minerals and the quartz particles.

(3) Magnetic separation

The magnetic separation process can remove the weak magnetic impurity minerals such as hematite, limonite and biotite including the continuum particles. Strong magnetic separation usually uses a wet magnetic separator or a high gradient magnetic separator. In general, quartz sand, which is mainly composed of weak magnetic impurities such as limonite, hematite and biotite, can be selected by using a wet magnetic machine at 10,000 Oersted or more; For the main ferromagnetic minerals, it is better to use the weak magnetic machine pair or the medium magnetic machine to select the better. Shangcun Hong. Tian Yuanping used a strong magnetic machine to study the experimental conditions of Seto quartz sand. The results show that the magnetic separation and magnetic field strength have an important effect on the removal of iron. With the increase of the number of magnetic separations, the iron content is gradually reduced. Most of the iron can be removed under the magnetic field strength, but even after the magnetic field strength is increased a lot, the iron removal rate does not change much. In addition, the finer the grain size of the quartz sand, the better the iron removal effect, because the fine-grained quartz sand contains a high amount of iron-containing impurities. When the quartz sand raw sand contains more impurity minerals, it is impossible to purify the quartz sand into high-purity sand by scrubbing, deliming and magnetic separation, in order to further improve the purity of the quartz sand and reduce impurities.

(4) Flotation

Taking into account the serious impact of fluorine-containing wastewater on the environment, in the 1970s, there was a “fluorine-free acid-free floatation method”. For example, in Japan, in the separation of feldspar and quartz, sulfuric acid or hydrochloric acid (PH=2) was used to adjust the slurry. The flotation of high-grade aliphatic amine salt and sodium petroleum sulfonate mixed collector was successful. The fluorine-free and acid-free flotation method is a new process for the separation of quartz feldspar flotation in recent years. Tang Jiaying and others began to study yin and yang in 1984. A new process for flotation separation of ion-mixed collectors. In a natural neutral medium, the difference in the composition of quartz and feldspar is used to rationally mix the ratio of anion-cation collectors, and the feldspar is preferentially floated. The separation of the two. However, the fluorine-free and acid-free flotation method is not as mature as the HF method and the acid method. At present, there is no report on the application of industrial production. The isoelectric point of mica and quartz is similar, and the sorting is difficult. The anion collector is used under acidic conditions. Or it can be floated by two methods of anion-cationic collector under alkaline conditions, and good results can be obtained. In general, after scrubbing, deliming, magnetic separation and flotation, the purity of quartz sand can reach 99.3%-99.9%, which basically meets the demand of industrial sand.

(5) Acid leaching

Acid leaching is the use of quartz insoluble in acid (except HF), and other impurity minerals can be dissolved by acid, so that further purification of quartz can be achieved. Acids commonly used in acid leaching include sulfuric acid, hydrochloric acid, nitric acid and hydrofluoric acid; and reducing agents include sulfurous acid and salts thereof. It is found that the above acids have good removal effects on non-metallic impurity minerals in quartz, but have significant effects on different metal impurities, acid species and their concentrations. It is generally believed that the removal of Fe and Al by various dilute acids Both have significant effects, while the removal of Ti and Cr is effected by acid leaching with more concentrated sulfuric acid, aqua regia or HF. The acid leaching of impurity minerals is usually carried out using a mixed acid of the above-mentioned acid composition, and the HF concentration is generally not more than 10% in consideration of the dissolution of HF on quartz. In addition to the acid concentration, the amount of acid, acid leaching time, temperature and slurry agitation can affect the acid leaching effect of quartz. The control of various factors of acid leaching should be based on the final grade requirements of quartz, to minimize the acid concentration, temperature and dosage, and reduce the acid leaching time to achieve quartz purification at a lower beneficiation cost. In some European and American countries, due to the strict requirements on iron in quartz, the quartz acid leaching purification treatment was studied systematically, and the acid leaching quartz beneficiation and purification plant was established. After the acid leaching of quartz sand, high purity quartz sand with a purity of 99.99% can be obtained.

(6) Microbial leaching

The thinning iron or dip-dyed iron on the surface of quartz sand particles by microorganisms is a newly developed iron removal technology. According to foreign research results, it is indicated that aflatoxin, penicillium, pseudomonas, polymyxin, when bacillus microorganism quartz surface film leaching of iron, achieved good results in which black iron fumagillin leaching best, removal of Fe ₂ O ₃ more than 75% concentrate Fe ₂ The grade of O _{3 is} as low as 0.007%. Moreover, it has been found that the leaching of iron by a culture medium preliminarily cultivated with most bacteria and molds is better, as is the case with other strains due to their soluble metabolites. At present, microbial iron removal is in the laboratory research stage, and the production of large-scale industry still needs further experimental research.

(7) Other purification methods

Due to the different requirements of different quartz sand products for impurity mineral content, some other purification methods are sometimes used for further purification. For example, the electrical difference between quartz and impurity minerals is slightly different, and trace mineral impurities are selected. Hot chlorine The method can remove the gas, liquid phase impurities and impurity minerals in the quartz, and the metal inclusions surface contamination during the process to further purify the quartz sand.

Third, quartz sand beneficiation purification process research

Quartz sand beneficiation purification process has many processes. Generally, it depends on the type, content, occurrence state and product quality requirements of impurities in quartz sand. The common quartz sand beneficiation purification process is as follows:

(1) Scrubbing---grading and de-sludge

Quartz sand In the process of weathering sedimentation and mineralization, a large number of clay minerals and iron form cement or adhesion minerals on the surface of quartz. The scrubbing---grading and deliming process to remove clay impurity minerals, muddy iron and part of thin film iron is a common process for the purification of such quartz sand. For example, the Sichuan Jiangjin quartz sandstone mine used this process to reduce -0.1mm fine mud and iron, which increased the silica from 85.4% to 97.4%, and the ferric oxide decreased from 0.63% to 0.165%. The process is generally used as a pretreatment process before the raw sand is selected, and the muddy impurity mineral is effectively removed.

(2) Scrubbing - Desliming - Magnetic Separation

In general, common impurity minerals such as limestone, tourmaline , hematite and biotite, such as limonite, tourmaline , hematite and biotite, can only be removed by magnetic separation process and actually produced. The wet magnetic machine is often used for sorting, and the magnetic field strength is about 13,000 oersted. In some places, after the silt-sanded silica sand was rubbed and eluted, the sand contained 0.36% of ferric oxide. The SHP-500 wet-type magnetic machine was used to purify the above-mentioned scrubbed elution sand, and the content of ferric oxide was 0.16. %.

(3) Rod scrubbing-de-sludge---magnetic separation-flotation---acid leaching

After the quartz sand ore is separated by scrubbing, magnetic separation and flotation, the lower impurity mineral particles (including monomers and aggregates) are basically removed, and the purity of the silica can generally reach 99.5%-99.9%. It can basically meet most industrial uses of quartz sand. However, as an ultra-high-purity quartz sand, it is necessary to perform acid leaching treatment on impurities on the surface of quartz particles in the form of spots and inclusions. According to different industrial uses, different impurity minerals (Fe, AL, Requirements for Ti and Cr), mixed acid leaching treatment with different concentrations and ratios. For example, the quartz content of a quartzite ore in Hunchun is 99.76%, containing fine inclusions, mainly impurity minerals such as Fe, AL, Ti, etc. It exists in the form of clay minerals and iron oxides. After the rod scrub-de-sludge---magnetic separation---flotation---acid leaching process, high-purity quartz sand having a silica content of 99.99% or more is obtained.

(4) Dosing and high-efficiency strong scrubbing - graded desilting - magnetic separation

After a detailed and in-depth experimental study on the purification of a quartz sandstone mine in Yunnan, we first creatively used the new purification process of high-efficiency and strong scrubbing, graded desilting-magnetic separation, and achieved success. The process is to improve the structure of the existing scrubbing equipment, optimize the technical parameters, remove more than 80% of the impurities iron and aluminum ore by high-efficiency strong scrubbing and fractional de-slurry, magnetic separation is mainly to remove iron-containing impurity minerals. . After treatment by the process silica obtained ≥99.8%, ferric oxide ≤0.023%, aluminum oxide ≤0.05%, titanium oxide ≤0.02% high refined quartz sand, reaching an optical glass Sand requirements, and the yield of concentrate is as high as 73%, while the rod scrub yield is only 49% and the silica recovery is 72.8%. Further re-selection and acid leaching treatment can obtain high-purity quartz sand with silica ≥99.9%, ferric oxide ≤0.005%, aluminum oxide ≤0.05%, and titanium dioxide ≤0.02%. Adopted, overcomes the shortcomings of iron secondary pollution caused by rod scrubbing, and low yield.

Fourth, the conclusion

(1) Quartz sand beneficiation purification method and process flow are generally determined by the following points: a; the occurrence state of impurity minerals in the raw sand; b the ore dressing cost of the purification process; c the industrial use of the fine sand product.

(2) For the fine sand quartz sand for general industrial use, choose a simple process as much as possible to reduce the purification cost. It is recommended to use the scrubbing-de-sludge-magnetic separation process to meet the quality requirements of the spirit.

(3) For high-purity and ultra-high-purity quartz sand as high-tech sand, it is necessary to further purify quartz sand by flotation and acid leaching. The quality requirements of high-purity and ultra-high-purity quartz sand are generally ≥99.99% for silica and less than 1×10 ^{-5 for} ferric oxide. The purification process must not only strictly control the selection conditions, but also the requirements for the corresponding purification equipment. It is also stricter to prevent secondary pollution.

(IV) For the first time, we used the new high-efficiency strong scrubbing-grading-magnetic separation process, and succeeded in the beneficiation and purification of quartz sandstone in Yunnan, overcoming the iron secondary pollution caused by rod scrubbing. , low yield and other shortcomings. This process is of great significance for realizing the low-cost, high-efficiency purification and impurity removal of quartz sand.

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