What is the quartz sand method?

The reagents used in purification process are as follows: dodecylamine (CHN, AR), sodium dodecyl benzene sulfonate (CHNaO 3 S, AR), hydrochloric acid (HCl, GR), nitric acid (HNO 3 , GR), hydrofluoric acid (HF, GR), sulfuric acid (H 2 SO 4 , AR), sodium hydroxide (NaOH, AR), and manganese dioxide (MnO 2 , AR), all of which were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Ultrapure deionized water with a resistivity of 18.25 MΩ·cm was used in all experiments.

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3.2. Experimental Procedures

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Quartz purification techniques involve several steps: pre-treatment, physical separation methods, chemical treatments, and advanced treatments. Pre-treatment includes crushing, scrubbing, desliming, screening, and grinding [ 31 32 ]. Physical separation methods include radiometric sorting, dense media separation, gravity separation, magnetic-electric separation, and flotation [ 15 17 ]. Chemical treatments involve high-temperature calcination&#;water quenching, and acid leaching [ 18 23 ]. Advanced treatments include chlorination, roasting, and vacuum refining [ 20 ]. Each method corresponds to the characteristics of different impurities, and the characteristics of quartz ore impurities are often used to adopt the corresponding purification methods; combining different methods logically is good strategy for achieving the purpose of purification [ 33 ].

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The purity of vein quartz is usually high, and the main impurities in the raw ore are in the form of a small number of gangue minerals, inclusions, and lattice impurity elements. Therefore, this experiment intends to separate gangue minerals through processes such as grinding, screening, ultrasonic cleaning, and flotation. Additionally, it seeks to break down inclusions and remove impurities by means of calcination&#;water quenching, hot pressing, acid leaching, and high-temperature chlorination [ 15 23 ]. The specific experimental flow chart is shown in Figure 2

Crushing and screening: 1 kg of quartz raw ore was separated into decimeter-scale pieces with a hammer. Subsequently, all quartz fragments were washed and brushed in water to remove any surface contamination, especially clay minerals and iron oxide coatings. Then, the small block of quartz was crushed into quartz sand using a jaw crusher (PE&#;F100 × 125). Standard nylon sieves were used to divide quartz sands into different fractions, with particle sizes of &#;0.425 +0.074 mm (40&#;200 mesh) collected for next experiments. Because the quartz sand crushed by the crusher contains more mechanical entrained iron, and considering the limited laboratory conditions, strong magnets were used to identify the appropriately sized quartz sand particles for magnetic absorption and remove the mechanical iron content. This approach can yield better experimental results when using a strong magnetic separator.

Ultrasonic scrubbing&#;desliming: the prepared &#;0.425 +0.074 mm qualified quartz sand underwent ultrasonic scrubbing&#;desliming: Fixed scrub slurry concentration at 50%, and each scrubbing session lasted for 30 min. The water was replaced every 10 min, and ultrasonic scrubbing is carried out three times, followed by two washes to obtain ultrasonically scrubbed quartz sand.

Flotation: The flotation experiment was carried out using an XFD-12 (0.5 L) flotation machine, with a stirring rate of rpm. In this work, a 100 g quartz sand sample was dispersed in a flotation cell filled with ultrapure deionized water. The flotation temperature was maintained between 50 and 60 °C, and the pH value was adjusted to 2.5 using hydrofluoric acid. After stirring for 2 min, 2 mL dodecylamine (DDA) collector and 2 mL sodium dodecyl benzene sulfonate (SDBS) foaming agent were sequentially added to the cell, air flow rate was 0.25 m3/h, and the first flotation process lasted for about 10 min. Similar to the first flotation, the second flotation experiment was performed with half amount of the DDA and SDBS, and some ultrapure water was also added to maintain the slurry level during the flotation experiment. The pH of the slurry during the whole flotation procedure was adjusted to a fixed value of 2.5. The sink quartz sand was collected and dried.

Calcination&#;water quenching: The flotation quartz sand was calcined at °C for 1 h with calcination heating rate of 10 °C/min in a muffle furnace (KSl-X, KEJING, HeFei, China). The calcined quartz sand was rapidly poured in ultrapure water (18.2 MΩ·CM), cleaned three times using ultrasonic and then dried for further acid leaching experiment.

Acid leaching: 10.0 g of quenched quartz sand was accurately weighed and placed in a polytetrafluoroethylene hydrothermal reactor cleaned with ultrapure water. In the HCl-HF-HNO3 mixed acid system (with a mass ratio of 3:1:1), the liquid/solid ratio was 1:1, the reaction temperature was 80 °C, and the reaction time was 24 h. After the acid leaching process, the quartz sand was ultrasonically cleaned with ultrapure water until reaching a neutral pH and then dried.

2 was precisely measured and placed in a round-bottomed flask. Subsequently, 250 mL of HCL was added to a long-neck funnel and the reaction temperature was carefully controlled at 80 °C. One bubble was generated every second in a H2SO4 drying flask. To begin the process, 8.0 g of acid-leached quartz sand was weighed accurately and heated to a high temperature of °C in a Cl2 atmosphere for 2 h. After completion of the experiment, argon gas was injected to purge any excess Cl2, which was then absorbed by a NaOH solution.

Chlorination roasting: Figure 3 illustrates the experimental setup used for chlorination roasting. A 25 g quantity of MnOwas precisely measured and placed in a round-bottomed flask. Subsequently, 250 mL of HCL was added to a long-neck funnel and the reaction temperature was carefully controlled at 80 °C. One bubble was generated every second in a HSOdrying flask. To begin the process, 8.0 g of acid-leached quartz sand was weighed accurately and heated to a high temperature of °C in a Clatmosphere for 2 h. After completion of the experiment, argon gas was injected to purge any excess Cl, which was then absorbed by a NaOH solution.

Silicon dioxide (SiO2) is the main chemical component of quartz sand and high purity quartz sand is defined as having a silicon dioxide content of 99.9% or more. As one of the most important industrial raw materials, quartz can be used in industries such as glass, building materials and plastics. The electronics, aerospace, fibre optic communication and military industries have requirements for the purity of silica sand. This article explains the beneficiation method and process flow of high purity quartz sand.

1.High purity quartz sand beneficiation methods

In industrial production, the purification methods of high purity quartz sand mainly contain physical purification, chemical purification and biological purification.

1.1 Physical purification of high purity quartz sand

Common physical refining methods for high purity quartz include water washing - graded desliming, scrubbing, gravity separation, magnetic separation and flotation, one or a combination of these forms can be used to remove impure minerals from silica sand and achieve refining requirements.

Water washing - Classified desliming/scrubbing

In quartz sand beneficiation, particles below 0.1mm are generally referred to as mineral sludge because the finer the particle size, the lower the silica content and the greater the relative impurity mineral content. The impurity minerals are removed by water washing or scrubbing to improve the concentrate grade.

Gravity separation

Gravity separation mainly uses the difference in density, size and shape of the mineral particles to produce different directions of movement and distribution speeds under the action of water and centrifugal force, thus achieving separation.

Magnetic separation

Magnetic separation is the removal of magnetic minerals such as haematite, brown iron and black mica from minerals by means of magnetic separation equipment, using the magnetic differences between quartz and impurity minerals.

Flotation

Flotation is the use of chemicals and equipment to change the nature of the mineral surface to remove a range of impurities present in the mineral under acidic conditions, separating out high purity quartz sand.

1.2 Chemical purification of high purity quartz sand

Among the chemical purification methods for high purity quartz sand, acid leaching and alkali leaching methods are more effective for the purification of high purity quartz sand.

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Acid leaching

The acids commonly used for acid leaching are mainly sulphuric acid, hydrochloric acid, nitric acid, etc. When the acid concentration is low, it is better to remove impurities such as iron, aluminium and magnesium; when the acid is thicker, it is better to remove impurities such as titanium and chromium.

Alkaline leaching

Alkaline leaching is the use of alkaline solutions, usually sodium hydroxide or sodium carbonate solutions to dissolve aluminosilicate impurities, for the purification of quartz sand.

1.3 Biopurification of high purity quartz sand

The biological purification method of high purity quartz sand is mainly through microbial leaching purification, which is achieved through the physiological properties of microorganisms and their metabolites, after oxidation, dissolution and decomposition.

2. High purity quartz sand process flow

In the beneficiation process, the process flow of high purity quartz sand mainly contains the following links:

2.1 Quartz sand crushing

Generally two-stage crushing process is adopted, firstly coarse crushing by jaw crusher, after crushing, the crushed material is conveyed by belt conveyor to vibrating screen for screening, the unqualified material is sent to cone crusher for fine crushing, the qualified material is conveyed to powder bin.

2.2 Grinding and classification

The main purpose of the grinding process is to grind the raw ore to a certain size and to dissociate the quartz sand from the vein minerals. The classifying equipment cooperates with the grinding equipment to produce quartz sand materials with qualified particle size.

2.3 Magnetic separation

The magnetic separation process uses a wet magnetic separator for primary separation, which is used to remove hematite, limonite, ilmenite and their congeners particles present in the quartz sand.

2.4 Flotation

Flotation removes mica and iron oxide from quartz. The flotation operation is carried out using sulphuric acid as an adjusting agent, sodium petroleum sulphonate as a trapping agent and pine alcohol oil as a foaming agent.

2.5 Acid leaching

After two separations by magnetic separation and flotation, impurities are still present in the quartz in the form of flecks or inclusions. To remove this impurity, acid leaching is required, using a mixture of different acids to remove the different impurities.

2.6 Washing

Soluble impurity residues adhere to the surface of the quartz sand after acid leaching and need to be removed by washing. The washing of the acid-impregnated minerals causes the impurities and residues on the quartz surface to diffuse into the solution, thus completing the cleaning process.

The above mainly describes the beneficiation method and process flow of high purity quartz sand. When building a beneficiation plant, in order to obtain high purity quartz sand, the appropriate beneficiation process should be selected according to the nature of the ore, therefore, it is recommended to tailor the appropriate process solution to obtain high purity quartz sand through beneficiation test analysis.

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