what is the initial sieving standard for lithium battery graphite anode raw materials

1. Definition of Initial Sieving

Initial sieving refers to the first coarse screening right after raw graphite ore/flotation concentrate incoming and primary crushing, before jet milling, spheroidization and chemical purification.
Core objectives:

1. Remove large gangue rock, wood fiber, plastic debris, metal chunks and oversized uncrushed graphite lumps;
2. Protect downstream jet mills, spheroidizers and filter presses from blockage or abrasion;
3. Stabilize feed particle size for uniform subsequent grinding and purification;
4. Roughly eliminate large magnetic foreign bodies to reduce iron contamination load.

Two raw material systems: natural flake graphite flotation concentrate and artificial graphite petroleum coke raw material, with separate initial sieving standards.

2. Initial Sieving Standard for Natural Flake Graphite (Flotation Concentrate Feed)

2.1 Equipment & Screen Mesh Spec

• Machine: High-frequency linear vibrating screen (wet screen for filter cake; dry vibrating screen for dried flotation powder)
• Primary screen mesh: 8–16 mesh (1.0 mm ~ 2.36 mm)
  • Wet filter cake (moisture 10%–15%): 8 mesh (2.36 mm)
  • Dry flake graphite powder: 12–16 mesh (1.0–1.7 mm)
• Auxiliary secondary fine pre-screen: 60 mesh (250 μm) to remove hard gangue fine gravel mixed in flotation concentrate
• Screen material: 316L stainless steel woven mesh, anti-corrosion, no metal shedding

2.2 Core Control Indexes

1. Oversize residue standard (screen-on material):
   • 8/12 mesh oversize rate ≤3.0% by mass;
   • Oversize components: only rock gangue, no intact graphite flakes; return oversized graphite lumps to coarse crusher for re-crushing.
2. Screening efficiency ≥90%: ≥90% of target feed particles pass through the mesh within single screening cycle
3. Foreign body removal standard:
   • No metal fragments, plastic strips, plant fiber, silica rock in under-screen graphite;
   • Visible foreign impurities per 100 kg feed ≤3 pieces.
4. Feed particle size after initial sieving: All material <1.0 mm, uniform feed for fine crushing/jet mill.

2.3 Wet vs Dry Initial Sieving Differentiation

Wet initial sieving (post flotation filter cake)

• Material state: Moisture 12%–35%
• Screen: 8 mesh heavy-duty wet vibrating screen with spray deionized water flushing
• Standard: No visible hard rock >2 mm on screen oversize; filter cake agglomerates broken fully to pass mesh.

Dry initial sieving (pre-dried flake graphite)

• Material state: Moisture ≤3.0%
• Screen: 12–16 mesh dry vibrating screen with ultrasonic anti-blocking device
• Standard: No static agglomeration blocking mesh; fine graphite loss rate ≤1.5%.

3. Initial Sieving Standard for Artificial Graphite Raw Material (Petroleum Coke/Green Coke)

3.1 Equipment & Mesh

Raw coke lumps 50–200 mm after jaw coarse crushing → initial sieving:

• Screen mesh: 10 mesh (2.0 mm) primary sieve; 40 mesh (380 μm) secondary pre-sieve
• Equipment: Heavy-duty dry vibrating screen, wear-resistant polyurethane screen frame to avoid iron pollution

3.2 Control Standards

1. Oversize >2.0 mm residue ≤2.0%; all oversized coke chunks re-crushed; eliminate refractory stone mixed in coke.
2. Under-screen material fully <2 mm, remove fine coke dust below 380 μm temporarily to control BET of final artificial graphite.
3. No iron, steel slag, refractory brick fragments in undersize coke powder.

4. Mandatory Supporting Technical Standards for Initial Sieving

4.1 Magnetic impurity interlock matching

Permanent magnetic separator installed before initial sieving: remove iron wear debris from crushers; magnetic substance content of under-screen graphite ≤500 ppb.

4.2 Screen quality & anti-contamination rules

1. Mesh aperture tolerance ±0.05 mm, no mesh hole deformation; replace mesh once breakage occurs.
2. All screen contact parts: stainless steel / PU lining, no carbon steel to prevent secondary iron pollution (critical for battery-grade graphite).
3. Ultrasonic vibration system equipped for dry sieving to resolve graphite static agglomeration and mesh blinding.

4.3 Sampling & Testing Frequency

• Offline sampling every 30 minutes to test screen oversize ratio and foreign impurities;
• Daily sieve residue full inspection to count gangue and metal debris quantity.

5. Distinction: Initial Coarse Sieving vs Post-Spheroidization Fine Sieving

Many production lines confuse initial sieving with intermediate fine screening; clear boundary below:

6. Common Unqualified Phenomena & Adjustment Standards

1. Oversize residue >3%: Lower feeding speed, increase screen vibration amplitude, re-crush oversized lumps separately.
2. Mesh blockage (dry sieving): Turn on ultrasonic anti-blocking, reduce feed thickness, control raw material moisture ≤3%.
3. Metal foreign bodies in undersize: Check crusher liner wear, strengthen front-end magnetic separation, replace worn metal equipment parts with ceramic lining.
4. Excessive fine powder loss: Adjust screen inclination angle, reduce vibration frequency.

7. Summary of Unified Initial Sieving Industrial Standard

1. Natural graphite flotation concentrate initial screen: 8–16 mesh, oversize residue ≤3%, screening efficiency ≥90%, no visible metal/rock foreign bodies.
2. Artificial petroleum coke initial screen: 10 mesh primary sieve, oversize ≤2%, remove refractory impurities.
3. All sieving equipment adopts 316L stainless steel mesh + non-magnetic lining to avoid iron contamination; magnetic separation matched upstream.
4. Initial sieving only removes large foreign matter and oversized lumps; precise particle size grading is completed by air classification and fine screening after jet milling/spheroidization.