Silica sand purification process and key equipment for TFT-LCD substrate glass: a cornerstone technology for realizing high-precision displays

Abstract: With the popularization of high-resolution and large-size TFT-LCD displays, the flatness, purity and thermal stability of the core carrier - substrate glass - have put forward nearly demanding requirements. This paper analyzes the special purification process and core equipment of high-purity quartz sand (typical index: SiO₂ ≥ 99.7%, Fe₂O₃ ≤ 0.008%) used in the preparation of TFT-LCD substrate glass, and ElevateSilica, with its targeted in-depth iron removal technology and non-polluting equipment system, provides the industry with a stable and efficient overall solution to help customers breakthrough. ElevateSilica provides stable and efficient overall solutions for the industry with its targeted deep iron removal technology and pollution-free equipment system, helping customers to break through the technological bottleneck of raw materials for base glass.

Stringent requirements: Why is silica sand for TFT-LCD substrate glass so special?

TFT-LCD substrate glass is the carrier of thin film transistor arrays, and its quality directly determines the clarity, brightness and uniformity of the display screen. Quartz sand, which is the main component (about 60%-70%), must meet the following extreme requirements:

1. Extremely high purity (SiO₂ ≥ 99.7%): Trace amounts of impurities can alter the thermal expansion coefficient and viscosity of the glass, creating bands, bubbles or precipitated crystals during high-temperature processing, leading to a decrease in panel yield.

2. Extremely low iron content (Fe₂O₃ ≤ 0.008%): Iron ions will significantly absorb visible light, resulting in yellowing and greening of the glass, seriously affecting the backlight penetration and color reproduction, resulting in a dull and off-color display.

3. Strict particle size distribution: the particle size should be uniform and stable, too coarse or too fine will affect the uniform melting of the compound and homogenization of the glass liquid, which will affect the microscopic flatness of the substrate glass.

4. Excellent chemical stability: The raw material itself needs to be stable to avoid deliquescence or reaction during storage and transportation.

Core purification process: from raw material to high purity silica sand

To meet the above requirements, a combined process based on " physical pretreatment and deep chemical purification " is the most efficient and reliable way to go:

Stage 1: Fine Physical Pretreatment (Pre-enrichment and De-emulsification)

• Objective: Crushing to dissociation size, removing more than 80% of free and magnetic impurities.

• Process Flow:

  1. Multi-stage crushing and grinding: The combination of "Jaw + Cone + High Pressure Roller Mill" realizes energy efficient progressive crushing. Ceramic liners and high alumina zirconium balls are used as the key grinding media to eliminate the introduction of mechanical iron from the source.

  2. Scrubbing and desliming: The thin film of iron and clay minerals on the surface of quartz particles are strongly scrubbed in the scrubber, and the fine sludge of -20μm is removed by the hydrocyclone, which effectively reduces the aluminum and part of the iron.

  3. High gradient magnetic separation: the core physical iron removal process. Adopting high gradient magnetic separator with background field strength up to 1.2T or more, it can efficiently capture and remove hematite, limonite, black mica and other weakly magnetic iron-containing minerals, and initially reduce Fe₂O₃ to below 0.015%.

Stage II: Deep chemical purification (to overcome the "stubborn iron")

• Goal: Remove the "stubborn iron" embedded in the form of micro inclusions or firmly adsorbed on the surface of quartz, so that Fe₂O₃ is stabilized down to below 0.008%.

• Core process: Mild and efficient acid leaching

  • Core technology: Leaching with a specially formulated acid mixture (usually hydrochloric acid-oxalic acid system) at a specific temperature, concentration and reaction time with agitation.

  • ElevateSilica Advantage:

    • Formulation optimization: Organic acids such as oxalic acid have a strong complexing ability for iron, effectively destroying the structure of iron-containing minerals and dissolving them, while being less corrosive to the quartz body, resulting in a high yield.

    • Process enhancement: ultrasonic assistance can be used to produce a "cavitation effect", accelerating the penetration of acid into the micro-cracks and inclusions, greatly improving the efficiency of iron removal.

    • Automatic control: The whole process is carried out in a corrosion-resistant reactor, and the parameters are precisely controlled by a PLC system to ensure batch stability.

Stage 3: Purification and post-treatment (locking purity)

• Objective: Thoroughly remove the acid and dissolved products to obtain clean and dry finished products.

• Process flow:

  1. Countercurrent washing with high-pure water: Use pure water with extremely low conductivity to carry out multi-stage countercurrent washing until the effluent is neutral and the conductivity meets the standard to ensure that there is no residual acid root and metal ions.

  2. Precision Dewatering: High-speed centrifuge or filter press is used for efficient dewatering to form low water content filter cake.

  3. Non-pollution drying and packaging: Drying with clean hot air in special drying equipment and moisture-proof packaging in closed environment to prevent secondary pollution.

Third, the key equipment system: the guarantee of the process landing

The realization of the process depends on reliable equipment. The following is the core equipment developed by ElevateSilica for TFT-LCD silica sand purification line:

1. Non-polluting crushing and grinding system:

   • Equipment: Ceramic liner cone crusher, zirconia media agitator mill.

   • Value: Fundamentally solved the industry problem of "introducing iron pollution in the process".

2. Deep iron removal and magnetic separation system:

   • Equipment: vertical ring high gradient magnetic separator.

   • Value: High field strength and high gradient magnetic media ensure extremely high capture rate of weakly magnetic iron minerals, which is the guarantee of physical iron removal efficiency.

3. Automated pickling and purification system:

   • Equipment: PPH/PVDF composite reactor with heating and stirring function, automatic dosing system.

   • Value: It realizes the precision, safety and environmental protection of the pickling process and ensures the effect and stability of chemical purification.

4. High-purity water washing and wastewater treatment system:

   • Equipment: multi-stage counter-current washing tank, membrane treatment and neutralization system.

   • Value: Ensure the final purity of the product, and at the same time realize the wastewater discharge or recycling, in line with environmental requirements.

Why choose ElevateSilica's solutions?

• Precise process design: We deeply understand the special requirements of TFT-LCD substrate glass for raw materials, and our process solution is directly aimed at the core of "low iron, high purity and homogeneity".

• Perfect match between equipment and process: Our self-developed core equipments are specially designed for high purity material processing, which ensures that the process concept can be transformed into real productivity without any damage.

• Stable product quality: Automated control system and strict quality management ensure that each batch of silica sand can meet the demanding standard of Fe₂O₃ ≤ 0.008%.

• Line Integration and Service: We provide full life cycle service from raw material testing, process package design to line delivery, commissioning and technical training, so that our customers have no worries.

In the increasingly fierce competition in the global display industry, it is crucial to master the upstream core raw material technology, and the purification capability of silica sand for TFT-LCD substrate glass is an important yardstick to measure the competitiveness of an enterprise or even a country in this field, ElevateSilica is willing to work with you with our mature purification process and reliable key equipment, and work together to solidify the foundation of the display industry in China. ElevateSilica is ready to work with you with our mature purification process and reliable key equipment to strengthen the cornerstone of China's display industry, and to contribute to the creation of a clearer and more brilliant visual world.

Welcome to contact us for a technical solution and equipment list for the purification of silica sand for TFT-LCD substrate glass for your raw materials.