Quartz sand, also known as silica sand, is a common non-metallic mineral raw material. After beneficiation and purification, it can be made into high-purity quartz sand, which is widely used in industries such as glass, ceramics, metallurgy, casting, and refractory materials. So, what are the common methods for beneficiation and purification of quartz sand? 

I. Quartz Sand Washing and Desliming Method: The SiO2 grade in quartz decreases as the quartz particle size decreases, while the grades of impurities such as iron and aluminum increase. This phenomenon is particularly pronounced in quartz containing a large amount of clay minerals. Therefore, before beneficiation, it is essential and effective to perform water beneficiation and desliming on the raw quartz ore using equipment such as spiral scrubbers, drum screens, hydrocyclones, desliming buckets, and hydraulic classifiers. Washing and desliming, as a pretreatment method before ore beneficiation, has been used for a long time and is widely adopted. However, its removal effect on thin film iron and adhesive impurities present on the quartz surface is not yet significant. 

II. Quartz Sand Scrubbing Method The scrubbing method primarily utilizes mechanical force and the abrasive force between sand grains to remove thin films of iron, bonded minerals, and clayey impurities from the surface of quartz sand, as well as further break down mineral aggregates that have not yet formed individual particles. This is followed by grading to achieve further purification of the quartz sand. Currently, there are two main methods for quartz sand scrubbing: rod friction scrubbing and mechanical scrubbing. For mechanical scrubbing, the factors affecting the scrubbing effect mainly come from the structural characteristics and configuration of the scrubbing machine, followed by process factors, including scrubbing time and scrubbing concentration. Studies have shown that a scrubbing concentration of 50%-60% yields good results for quartz sand ore, but this also increases the difficulty of quartz beneficiation and purification to some extent. The scrubbing time should, in principle, be based on initially achieving the product quality requirements and should not be too long. Excessive time will increase equipment wear, energy consumption, and beneficiation and purification costs. For some quartz ores, mechanical scrubbing is not ideal; rod milling can be used instead. If necessary, reagents can be added to increase the electrostatic repulsion between the impurity minerals and the quartz particles, enhancing the separation effect. 

III. Quartz Sand Magnetic Separation: Magnetic separation can effectively remove weakly magnetic impurity minerals such as hematite, limonite, and biotite, including intergrowth particles. Strong magnetic separation typically uses wet strong magnetic separators or high-gradient magnetic separators. Generally, for quartz with impurities mainly composed of weakly magnetic minerals such as limonite, hematite, and biotite, wet strong magnetic separators at 10000 Oe or higher can effectively separate them; for strongly magnetic minerals containing mainly magnetite, weak or medium magnetic separators are more effective. Research shows that the number of magnetic separation cycles and the magnetic field strength significantly affect the iron removal effect. With increasing magnetic separation cycles, the iron content gradually decreases, and at a certain magnetic field strength, most of the iron can be removed. However, even with significant increases in magnetic field strength thereafter, the iron removal rate does not change much. Furthermore, the finer the quartz sand particle size, the better the iron removal effect, because fine-grained quartz sand contains a high amount of iron-containing impurities. When the raw quartz sand contains a large amount of impurities, washing, desliming, and magnetic separation alone cannot purify the quartz sand into high-purity sand. 

IV. Quartz Sand Flotation Method. Flotation mainly removes non-magnetic associated impurities such as feldspar and mica from quartz sand. Quartz sand flotation methods mainly include fluorinated flotation and fluorine-free flotation. Fluorinated flotation uses cationic collectors and hydrofluoric acid activators within an acidic pH range. Its disadvantage is that the fluorinated wastewater causes serious environmental pollution and requires treatment before discharge. Fluorine-free flotation utilizes the differences in the structural composition of quartz and feldspar, rationally adjusting the ratio and dosage of the mixed anionic and cationic collectors. Taking advantage of their different zeta potentials, feldspar is preferentially floated out, achieving separation. Generally, after scrubbing, desliming, magnetic separation, and flotation, the purity of quartz can reach 99.3%-99.9%, which basically meets the needs of industrial sand. 

V. Quartz Sand Acid Leaching Method: Acid leaching utilizes the characteristic that quartz is insoluble in acids (except HF), while other impurity minerals can be dissolved by acids, thus achieving further purification of quartz. Commonly used acids for acid leaching include sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid, while reducing agents include sulfurous acid and its salts. Studies have found that the above-mentioned acids have good removal effects on non-metallic impurity minerals in quartz. However, for different metallic impurities, the type and concentration of acid have a significant impact. It is generally believed that various dilute acids have a significant effect on the removal of Fe and Al, while the removal of Ti and Cr requires more concentrated sulfuric acid, aqua regia, or HF for acid leaching treatment. Usually, a mixed acid composed of the above-mentioned acids is used for the acid leaching removal of impurity minerals. Considering the dissolving effect of HF on quartz, the HF concentration generally does not exceed 10%. Besides acid concentration, the amount of acid used, leaching time, temperature, and slurry agitation all affect the quartz acid leaching effect. The control of various factors in acid leaching should be based on the final grade requirements of the quartz, minimizing acid concentration, temperature, and dosage, and reducing leaching time to achieve quartz purification at a lower beneficiation cost. These are five common methods for quartz sand beneficiation and purification. The choice of method depends on various factors such as the quartz sand ore properties, beneficiation plant conditions, and investment budget. It is recommended to first understand the quartz sand itself and, based on the beneficiation test report, select a single or combined process flow to achieve ideal technical and economic benefits.

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