Quartz Sand Beneficiation and Purification Process

The primary mineral component of quartz sand is quartz (SiO₂), making it an indispensable key raw material for numerous industrial sectors such as glass, ceramics, foundry, construction materials, chemicals, and electronic information. With technological advancement, particularly the growing demand for high-purity quartz sand (SiO₂ > 99.99%) from high-end industries like photovoltaics, electronic semiconductors, and optical communication, efficient beneficiation and purification processes have become the core link in obtaining high-quality quartz sand. Quartz sand beneficiation is a complex physical and chemical process, whose core objective is the effective removal of various impurity minerals from the raw ore through a series of processes to achieve quartz enrichment and purification.

I. Raw Ore Property Analysis and Pre-treatment

The determination of the beneficiation process flow depends primarily on the mineralogical characteristics of the quartz raw ore. Quartz ores from different mining areas vary greatly in the type, content, disseminated particle size, and occurrence state of impurities.

Impurity Types: Mainly include:

• Mineral Impurities: Such as feldspar, mica, clay, hematite, magnetite, rutile, tourmaline, etc.

• Elemental Impurities: Mainly exist in solid solution within the quartz crystal lattice, such as Al³⁺, Fe³⁺, K⁺, Na⁺, Ca²⁺, Ti⁴⁺, etc.

Dissemination Characteristics: Impurities may exist as independent minerals intergrown with quartz, or as fine inclusions within quartz particles.

Therefore, before beneficiation, detailed chemical analysis, mineral composition analysis, particle size analysis, etc., must be conducted on the raw ore to "customize" the most economical and effective beneficiation flowsheet.

II. Detailed Explanation of Core Quartz Sand Beneficiation Process Flow

A complete quartz sand beneficiation process typically includes the following core stages:

(I) Crushing and Grinding

The purpose is to liberate large quartz raw ore into a particle size suitable for separation, achieving sufficient liberation of quartz from impurity minerals.

• Coarse Crushing: Uses a jaw crusher to break the raw ore into blocks several tens of millimeters in size.

  

• Medium and Fine Crushing: Typically uses a cone crusher or impact crusher to further reduce the material to about 10-20mm.

  

• Grinding: Uses a rod mill or ball mill to grind the crushed product to the fineness required for separation (usually 0.1-0.5mm). Particular attention must be paid to "selective grinding" during this process, i.e., utilizing the hardness difference between quartz and impurity minerals to avoid over-grinding and sliming, creating favorable conditions for subsequent separation.

  

(II) Scrubbing and Desliming

This stage primarily removes film iron on the quartz sand surface, adhesive impurities, and primary slimes.

• Scrubbing: In a scrubbing machine, the high-speed rotation of the impeller generates intense friction and collision between sand grains and between sand grains and the machinery, thereby scouring off surface-adhered impurities. A small amount of reagent (e.g., NaOH) may be added to enhance the scrubbing effect.

• Desliming: The scrubbed pulp enters a hydrocyclone or spiral classifier for desliming. Since fine slime contains large amounts of impurities like Al, Fe, K, and Na, effective desliming is a crucial step for improving quartz purity, especially for reducing aluminum content.

  

(III) Classification

Uides high-frequency vibrating screens or hydrocyclones to separate the ground product into sands of different size fractions. This not only yields products meeting user size requirements but also achieves preliminary enrichment, as certain specific size fractions may have lower impurity content.

(IV) Physical Separation

This is the core stage for removing mineral impurities, employing different separation methods based on differences in the physical properties of the impurity minerals.

• Gravity Separation: Utilizes density differences between quartz and feldspar, mica, etc., for separation. Spiral chutes or shaking tables are commonly used. This method is particularly effective for iron-bearing minerals with significant density differences (e.g., magnetite, hematite) and heavy minerals (e.g., rutile, zircon).

  

• Magnetic Separation: The most common and efficient method for removing iron impurities.

• High-Intensity Magnetic Separation: Uses high-gradient magnetic separators to effectively remove weakly magnetic impurity minerals (e.g., hematite, limonite, biotite, garnet) and iron in middlings. This is an essential step for producing high-quality quartz sand.

• Low-Intensity Magnetic Separation: Mainly used to remove strongly magnetic minerals (e.g., magnetite).

  

• Flotation: The most critical and effective process for separating quartz from feldspar, and also the core technology for preparing high-purity quartz sand. Quartz and feldspar have similar physical and chemical properties, but their surface electrical properties differ under specific pH conditions.

• Principle: In an acidic (usually using sulfuric acid, hydrofluoric acid) or neutral medium, by adding collectors (e.g., amine cationic collectors), feldspar is selectively and preferentially floated, leaving quartz in the cell, thus achieving separation. This method effectively reduces the Al₂O₃, K₂O, and Na₂O content in quartz.

• Reverse Flotation: Sometimes a reverse flotation process is also used, i.e., floating impurities like mica and iron-bearing minerals.

  

• Electrostatic Separation: Utilizes differences in electrical conductivity between quartz and impurity minerals in a high-voltage electric field. It is effective for removing conductive minerals like titanium-bearing minerals (e.g., rutile) and tourmaline, but has relatively small processing capacity and high requirements for material dryness.

  

(V) Chemical Purification

For impurities existing as inclusions inside quartz crystals, or extremely fine impurities difficult to remove by physical methods, chemical methods must be used.

• Acid Leaching: The physically separated quartz concentrate is reacted with concentrated acids (e.g., hydrochloric acid, sulfuric acid, oxalic acid, hydrofluoric acid) under heating conditions. Acids effectively dissolve impurities containing metallic elements like iron, aluminum, and magnesium. Among them, mixed acids (e.g., HCl + HF) work best, capable of etching the quartz surface, dissolving fine inclusions, and significantly enhancing SiO₂ purity. Acid leaching is an essential step for producing 4N (99.99%) and above high-purity quartz sand.

• High-Temperature Chlorination: Conducted in a high-temperature calcination furnace at about 1000°C, introducing chlorine gas (Cl₂) or hydrogen chloride (HCl) gas. This method is specifically used to remove trace metal impurities (e.g., iron, titanium, lithium) in fluid/gas inclusions and the crystal lattice; these impurities react with chlorine gas to form volatile chlorides that are removed. This is the core technology for preparing ultra-high-purity quartz sand (above 5N grade) used for semiconductor and photovoltaic crucibles.

(VI) Dewatering and Drying

The purified quartz sand slurry needs dewatering treatment.

• Dewatering: Typically uses a high-efficiency thickener for preliminary concentration, followed by filter pressing using a chamber filter press or belt filter press to obtain a filter cake with low moisture content.

• Drying: The filter cake enters a rotary kiln or disc dryer for drying, resulting in a dry quartz sand product with very low moisture content (typically < 0.5%).

  

III. Deep Processing of Quartz Sand and Tailings Treatment

(I) Deep Processing

Depending on the final application, the dried quartz sand can undergo further processing:

• Roasting: Conducted at 800-1000°C, used to remove organic impurities and some volatile impurities, and cause phase transformation of quartz, making it easier to crush.

• Fine Grinding: Uses equipment like Raymond mills, jet mills, etc., to produce quartz powder of different fineness.

(II) Tailings Treatment and Environmental Protection

Tailings (including removed slimes, flotation tailings, etc.) and wastewater generated during the beneficiation process must be properly handled.

• Wastewater Treatment: Beneficiation wastewater, especially from flotation and acid leaching, contains reagents and heavy metal ions. It requires treatment through neutralization, precipitation, flocculation, etc., to achieve recycling or compliant discharge.

• Tailings Disposal: Tailings are transported to tailings storage facilities for safe impoundment, or resource utilization途径 are sought, such as use as construction materials, to achieve green mining and sustainable development.

IV. Example of a Typical Combined Quartz Sand Beneficiation Process Flow

A modern quartz sand beneficiation plant typically involves a combination and optimization of multiple processes. The following is a typical flow example for producing high-purity quartz sand:

Raw Ore → Coarse Crushing → Medium Crushing → Grinding → Scrubbing → Desliming → Classification → High-Intensity Magnetic Separation (remove weakly magnetic iron) → Flotation (separate quartz and feldspar) → Acid Leaching (deep impurity removal) → Dewatering → Drying → High-Purity Quartz Sand Product

For ultra-pure quartz sand with special requirements, a "High-Temperature Chlorination" step is added after acid leaching.

Conclusion

The quartz sand beneficiation process is a systematic engineering project involving multiple disciplines such as comminution, mineralogy, surface chemistry, and fluid mechanics. The selection of the process flow is by no means static; it must be strictly based on the fundamental starting point—"raw ore properties"—and determined through detailed test research. With the continuously increasing quality requirements for quartz sand, beneficiation technology is developing towards greater refinement, high efficiency, intelligence, and greenization. The application of new high-efficiency flotation reagents, large-scale energy-saving equipment, automatic control technology, and wastewater zero-discharge technology will continuously drive the advancement of quartz sand beneficiation processes, providing higher quality and more stable basic material support for high-end manufacturing.