How to Avoid Contamination During the Quartz Grinding Process

Quartz has a Mohs hardness of 7 and strong abrasive properties. When crushed and ground, friction and impact between quartz and equipment linings/grinding media easily introduce iron, aluminum, titanium, zirconium and other foreign impurities, which seriously disqualify high-purity, photovoltaic and semiconductor-grade silica. Based on the anti-pollution processing technology from quartz-mill.com, this article summarizes systematic anti-contamination solutions covering equipment material selection, full-process closed design, pretreatment control, operation management and post-grinding protection.

1. Adopt Non-Metallic, Anti-Abrasive Lining & Grinding Media (Core Measure)

The primary source of contamination is wear from metal alloy contact parts. All material-contact components must replace steel/stainless steel with inert hard non-metal materials.

1.1 Coarse & Medium Crushing Equipment

• Jaw crusher, roller crusher, hammer crusher: Inner cavity lined with silicon carbide (SiC) or high-purity fused corundum; ban cast iron and manganese steel liners.
• Feeding chutes, transfer pipelines: PTFE, quartz block or alumina lining to prevent iron scrap peeling off.

1.2 Ultrafine Grinding Host Matching Materials

1. Vertical roller mill for mass production
   Grinding rollers, grinding rings, classifier impellers: integral corundum or silicon carbide casting, no metal matrix exposed.
2. Wet bead mill
   Cylinder lining: thick PTFE or alumina; grinding beads: high-purity quartz beads or yttrium-stabilized zirconia beads (ordinary zirconia beads will release Zr impurities for electronic-grade silica). Never use steel beads.
3. Fluidized bed jet mill (for 5N ultra-high-purity silica)
   Grinding chamber, classifier housing, cyclone inner wall: fully lined with fused quartz or high-purity alumina; only pure nitrogen or compressed air as grinding power, zero solid media contact.

1.3 Auxiliary Equipment

Hydrocyclones, scrubbing tanks, flotation cells, storage silos: PP, PVC or PTFE anti-corrosion lining to avoid metal ion dissolution.

2. Strict Raw Ore Pre-Purification Before Grinding

Impurity gangue in raw ore will accelerate equipment wear and cause cross-contamination during grinding. Complete physical separation before feeding materials into grinding units:

1. Attrition scrubbing + desliming to remove clay, surface iron/titanium oxide films;
2. High-gradient magnetic separation to eliminate free iron, ilmenite and mechanical iron from mining and crushing;
3. Reverse flotation to remove feldspar, mica and aluminum-rich silicate gangue.
   Clean low-impurity quartz sand reduces abrasive mixed minerals, slowing liner wear and lowering exogenous pollution baseline.

3. Full-Sealed Negative Pressure Production Line to Block External Dust Pollution

Open grinding allows workshop dust containing iron, aluminum and soil clay to mix into finished powder. Full closed negative pressure layout is mandatory:

1. All feeding, grinding, classification, conveying and collecting sections form an airtight system with no open gaps;
2. Negative pressure induced draft prevents outward powder leakage and stops external metal dust from entering equipment;
3. Pulse dust collectors adopt PTFE filter bags without metal fiber fillers; all dust recovery pipelines use non-metallic linings.
   For semiconductor-grade workshops, grinding systems are placed in Class 1000–Class 100 cleanrooms to isolate atmospheric particulate impurities.

4. Optimize Grinding Process Parameters to Reduce Liner Wear

Excessive grinding load accelerates material impact and friction, increasing wear debris generation:

1. Stable and low-speed uniform feeding; avoid over-feeding which causes material accumulation and intense extrusion wear;
2. Control grinding pressure of vertical roller mills within the rated range; over-high hydraulic pressure sharpens abrasion of corundum rollers;
3. For closed-circuit grinding systems, match air volume and classifier speed reasonably to prevent coarse particles from repeatedly hitting liners;
4. Control grinding temperature properly: high temperature softens partial linings and accelerates wear. Cool down circulating air for long-time continuous production.

5. Standardized Equipment Maintenance & Cleaning Management

Residual old powder, worn fragments and mixed foreign materials from maintenance are hidden pollution sources:

1. Regular inspection of liners, rollers, beads and nozzles; replace worn parts before peeling occurs;
2. Before switching batches of different purity grades, thoroughly clean the entire grinding line: flush with pure quartz sand for 30–60 minutes to sweep residual powder and wear debris;
3. Maintenance tools cannot be steel files, iron brushes or metal scrapers; use quartz brushes, plastic shovels and ceramic cleaning tools only;
4. Avoid mixing different raw ore batches in silos; set independent closed stock bins for purified quartz sand and finished ultrafine powder.

6. Separate Dry and Wet Processing Lines to Prevent Cross-Contamination

Do not share grinding equipment for ordinary industrial silica and electronic high-purity silica:

• Dedicated independent jet mill production line for semiconductor-grade powder;
• Separate vertical mill lines for glass/ceramic silica and photovoltaic silica;
• Wet bead mill slurry pipelines, filter presses and drying ovens are exclusively used for high-purity products and forbidden to process low-grade quartz containing lots of iron and feldspar.

7. Anti-Contamination Post-Treatment After Grinding

Even if grinding avoids pollution, subsequent drying, screening and packaging may introduce impurities:

1. Drying kiln inner wall: quartz or alumina refractory lining; heating tubes are wrapped with high-purity quartz sleeves to prevent metal oxidation peeling;
2. Vibrating screens: all-ceramic screen frame and nylon screen cloth, no metal wire mesh;
3. Finished product conveying: air slide pipes lined with SiC; avoid metal screw conveyors;
4. Packaging: double-layer inert gas-filled aluminum foil bags, stored in plastic ton barrels instead of iron drums; isolate finished powder from metal storage frames.

8. Real-Time Purity Monitoring to Trace Pollution Sources

Set regular sampling and testing links to discover abnormal contamination early:

1. Take powder samples at the classifier outlet every hour; test iron and aluminum content via XRF rapid detection;
2. Once impurity content rises sharply, immediately check liner wear, raw ore quality and sealing system;
3. For electronic-grade ultrafine powder, periodic ICP-MS testing to track ppb-level metal pollution indicators.

Contamination in quartz grinding mainly comes from equipment wear, external dust, raw gangue mixing and cross-batch pollution. A complete anti-pollution system includes:

1. Full non-metallic contact parts to eliminate liner/media wear pollution fundamentally;
2. Pre-scrubbing, magnetic separation and flotation to purify feedstock;
3. Negative pressure closed production to isolate external dust;
4. Optimized process parameters and standardized equipment cleaning maintenance;
5. Dedicated independent production lines and cleanroom post-processing packaging.
   This matched anti-contamination grinding scheme from quartz-mill.com effectively controls Fe, Al, Ti, Zr impurities, ensuring finished ultrafine silica meets glass, photovoltaic and strict semiconductor-grade purity standards.