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Quartz sand is a common non-metallic mineral widely used in the glass, ceramics, metallurgy, casting, and refractory industries. Its main component is quartz (SiO₂), often accompanied by impurity minerals such as mica, feldspar, iron-bearing minerals, and aluminum-bearing minerals.
To meet the requirements of high-purity and high-quality industrial applications, quartz sand must undergo impurity removal and purification. The quartz sand beneficiation process involves removing impurities through methods such as scrubbing and desliming, magnetic separation, gravity separation, flotation, acid leaching (pickling), chlorination roasting, and others. These processes are designed to produce high-purity quartz concentrate with suitable particle size.
This article introduces 6 practical quartz sand impurity removal processes.
Scrubbing and desliming is a primary impurity removal method in quartz sand processing. It utilizes mechanical force and the abrasive interaction between sand particles to eliminate surface impurities such as film iron, bonded clay, and other muddy minerals. The quartz sand is then further purified through classification.
This method is suitable for quartz sand containing a high proportion of clay or mineral mud, as well as for the removal of film iron and adhesive impurities on the surface of quartz particles.
Prior to scrubbing, coarse materials are typically removed using a coarse screen with an aperture of approximately 5 mm. The remaining material is then passed through a 0.5–1.0 mm wet screen equipped with a water spray system to separate quartz sand from clay minerals in a water medium.
Subsequently, fine-grained impurities are discharged from the top overflow as slime using a hydraulic classifier, while the coarser and heavier particles are discharged from the bottom. If necessary, a scrubbing agent may be added to adjust particle size distribution and enhance the dispersion of mineral particles, thereby improving impurity removal efficiency.
This method effectively removes weathered clay and heavy minerals smaller than 0.1 mm and also reduces the iron content, providing a solid foundation for subsequent separation processes.
Magnetic separation is one of the most effective methods for removing iron impurities from quartz sand. It utilizes the magnetic susceptibility differences between quartz and impurity minerals. Magnetic minerals (such as magnetite and hematite) are separated from non-magnetic minerals (such as quartz) using magnetic fields, thereby eliminating magnetic inclusions in the quartz ore and achieving purification.
This method is suitable for removing strongly magnetic impurities, primarily magnetite, as well as weakly magnetic impurities, such as hematite, ilmenite, and biotite, from quartz sand.
For strongly magnetic minerals like magnetite, low- or medium-intensity magnetic separators can be used. Weakly magnetic minerals such as hematite, ilmenite, and biotite require wet high-intensity magnetic separation, with magnetic field strengths reaching 8×10⁵ A/m or higher.
To further remove residual weakly magnetic minerals (e.g., amphibole, pyroxene, and magnetic particles associated with quartz), high-gradient magnetic separators with magnetic field strengths exceeding 12,000 Gauss can be employed for secondary separation.
This process effectively eliminates various magnetic impurities, including intergrowths (conjoined bodies), significantly enhances the purity of quartz sand, and ensures a high recovery rate of concentrate.
Based on the density difference between quartz sand and other minerals, gravity separation utilizes water flow, centrifugal force, and gravity to separate mineral particles of varying densities. A spiral chute is typically employed to achieve the removal of heavy impurities and the purification of quartz sand.
This method is suitable for raw materials containing a certain amount of heavy mineral impurities (relative density > 2.9), such as zircon, hematite, limonite, rutile, barite, and others.
The quartz sand slurry is fed into the top of the spiral chute. Under the combined action of inclined water flow and centrifugal force, the heavier impurity minerals spiral downward along the inner wall of the chute and are discharged from the lower outlet. In contrast, the lighter quartz particles flow toward the outer edge and are carried away with the water from the upper outlet.
This method is simple to operate, offers large processing capacity and high efficiency, and is considered one of the effective techniques for removing heavy mineral impurities from quartz sand.
The flotation method is mainly applied when scrubbing, washing, desliming, magnetic separation, and other processes fail to achieve satisfactory results. Based on the differences in the physicochemical properties of mineral particles, flotation separates minerals by utilizing the adhesion of particles to air bubbles. This allows for the effective removal of mica, feldspar, and impurity minerals containing iron, phosphorus, and other elements associated with quartz, thereby improving the purity of quartz sand.
Flotation is primarily used to remove feldspar, mica, and various non-magnetic associated impurities in quartz sand.
Quartz sand flotation purification generally adopts a three-stage flotation process to sequentially remove different types of impurities.
· In the first stage, iron-bearing fine mud is floated from the slurry using specific reagents under neutral or weakly acidic conditions.
· In the second stage, cationic collectors are used to float mica and mica–quartz intergrowths under pH 3–4 conditions.
· In the third stage, either fluorine flotation or non-fluorine flotation is employed to remove feldspar and its intergrowths under acidic conditions.
Fluorine flotation typically uses hydrofluoric acid as an activator and cationic collectors to preferentially float feldspar. However, fluorine-containing wastewater must be strictly treated to minimize environmental impact.
In non-fluorine flotation, feldspar is selectively floated in an acidic medium (hydrochloric acid or sulfuric acid) using a mixture of anionic and cationic collectors (such as dodecyl sulfonate and dodecylamine). This separation is based on the difference in zeta potential between quartz and feldspar.
Quartz can be purified based on the property that impurity minerals can be dissolved by acid treatment.
This method is suitable for quartz sand containing various metallic impurities such as iron (Fe), aluminum (Al), magnesium (Mg), titanium (Ti), chromium (Cr), etc., especially when high-purity quartz is required.
Pickling is generally classified into single-acid and mixed-acid treatment. Common acid reagents include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃), and hydrofluoric acid (HF).
Dilute acids (e.g., HCl, HNO₃) are effective for removing soluble impurities such as Fe, Al, and Mg.
Concentrated sulfuric acid and hydrofluoric acid are used to dissolve more stable and insoluble impurities such as Ti and Cr.
Industrial practice has shown that a combination of multiple acids significantly improves the purification effect of quartz sand.
However, the pickling process generates a large amount of acid-containing wastewater, which may contain hydrogen ions, fluoride ions, suspended solids, and heavy metal ions. Fluoride-containing wastewater is particularly challenging to treat. The effective removal of fluoride ions is key to pickling wastewater treatment. If not properly handled, this can lead to serious environmental pollution risks.
At high temperatures (1200–1500°C), chlorine gas (Cl₂) is introduced. The metal impurities react with chlorine to form volatile metal chlorides, which evaporate due to their low boiling points and are removed from the system, achieving purification.
Chlorination roasting is a critical step in the purification of ultra-pure quartz sand, used to remove residual non-volatile metal oxides such as Fe₂O₃, Al₂O₃, TiO₂, etc.
Prior to chlorination, quartz sand should undergo a series of pre-treatment steps, including:
crushing,magnetic separation,gravity separation,flotation, and acid leaching (e.g., with HCl and HF)to remove most of the metallic impurities and convert the remaining ones into oxides.
The raw material particle size should be controlled within 0.1–1 mm to ensure sufficient contact and reaction with chlorine gas.
The chlorination reaction is conducted in a rotary kiln with the following conditions:
Temperature: 1200–1500°C (adjusted based on specific impurities; e.g., higher temperature for Ti removal)
Chlorine concentration: 10–30% Cl₂ (mixed with inert gas such as N₂ or Ar) to prevent explosion
Reaction time: 1–4 hours to ensure complete reaction
After the reaction, tail gas is absorbed in an alkaline solution. The resulting ultrapure quartz concentrate is rapidly cooled by inert gas (e.g., N₂) to prevent re-adsorption of impurities. Finally, ultrapure water rinsing is used to remove residual chloride ions (Cl⁻) on the quartz surface.
Conclusion
Xinhai Mining has extensive experience in quartz processing and has undertaken numerous quartz sand beneficiation, purification, and impurity removal projects. If you have a project in this field and are looking for a contractor or need to purchase quartz sand processing equipment, please feel free to contact us!
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