what is the basic process of graphite anode raw material pretreatment

The pretreatment flow is split into two independent technical routes: natural spherical graphite pretreatment and artificial graphite (calcined petroleum coke/needle coke) pretreatment. Pretreatment covers all upstream processes before core purification (acid/alkali leaching) or graphitization, aiming to homogenize particle size, remove bulk impurities, control moisture, expose embedded gangue, and stabilize feed conditions for downstream production.

Part 1: Universal Core Objectives of Pretreatment

1. Remove bulk foreign impurities (rock, refractory fragments, metal chunks, plastic, wood fiber)
2. Crush large lumps into uniform particle size to stabilize grinding and purification efficiency
3. Eliminate raw material batch segregation via homogenization
4. Control moisture within standard range to avoid blocking screens/mills and uneven leaching
5. Remove magnetic iron contamination to lower metal impurity baseline
6. Disperse powder agglomerates for uniform chemical contact in subsequent purification

Part 2: Complete Pretreatment Flow – Natural Flake Graphite Raw Material

Raw feed: Graphite ore / flotation concentrate (C:94–96%, lump/filter cake state)

Step 1: Raw Material Receiving & Pre-Sorting

1. Incoming inspection: Test fixed carbon, ash, Si/Fe impurities, moisture; separate batches by mine source and flotation lot.
2. Manual pre-sorting: Pick out large gangue stones, plastic, wood and refractory blocks.
3. Primary magnetic separation (12000 Gs): Remove steel fragments from mining/conveying equipment.

Step 2: Layered Stacking Homogenization

1. Stack flotation concentrate in horizontal layers ≤50 cm inside sealed silos.
2. Cross-layer vertical reclaiming for ≥24 h to average ash and impurity fluctuation of different batches.
3. Homogenization acceptance: Top/middle/bottom sampling ash deviation ≤±0.01%.

Step 3: Primary Coarse Crushing & Initial Sieving

1. Wet filter cake: Low-iron shredder to break wet agglomerates; dry concentrate: jaw coarse crusher.
2. Initial vibrating screen (8–16 mesh): Dmax ≤2.36 mm, oversize residue ≤3% for re-crushing loop.
3. Secondary magnetic separation after screening to remove crushing wear iron.

Step 4: Pre-Drying (Two-Stage Uniform Drying)

1. Hot nitrogen convection pre-drying: Reduce moisture from 12–35% filter cake to ≤3%.
2. Vacuum deep drying: Final moisture controlled ≤0.5%, eliminate pore bound water; multi-point moisture deviation ≤±0.05%.

Step 5: Jet Milling & Air Classification

1. Feed dried coarse graphite into closed jet mill to produce flake powder D50: 8–15 μm.
2. Multi-stage air classifier to narrow PSD span, remove coarse gangue and ultrafine dust with high impurity enrichment.

Step 6: Spheroidization Shaping

High-speed rotary spheroidizer to grind sharp flake edges into spherical particles; repeated circulation shaping to meet target tap density.

Step 7: Post-Shaping Fine Screening & Final Magnetic Removal

1. 200–400 mesh ultrasonic fine screen to remove oversized coarse gangue clusters.
2. High-gradient magnetic separator for final trace iron removal (Fe ≤10 ppm).

Output of Pretreatment

Uniform spherical graphite powder ready for chemical purification (mixed acid / alkali-acid leaching).

Part 3: Complete Pretreatment Flow – Artificial Graphite Raw Material (Calcined Coke)

Raw feed: Bulk calcined petroleum coke / needle coke (50–200 mm lumps, moisture ≤3%)

Step 1: Incoming Inspection & Batch Classification

Separate coke by calcination furnace batch, volatile content, inherent ash and metal impurities; reject unqualified batches. Pre-sort bulk refractory brick, rock foreign bodies.

Step 2: Raw Coke Homogenization Silo

Layered stacking + cross-cut reclaiming ≥12 h to eliminate batch-to-batch ash fluctuation.

Step 3: Two-Stage Pre-Crushing

1. Primary jaw crusher: Crush 50–200 mm lumps to ≤10 mm.
2. Secondary double roller crusher: Further crush to finished pre-crushed particles Dmax ≤5 mm; main fraction 1–3 mm accounts for 60–75%.
3. Closed loop circulation for oversize >5 mm particles to re-crush.

Step 4: Double-Stage Magnetic Separation + Initial Sieving

1. Post-crushing magnetic separation to remove crusher liner iron powder.
2. 10 mesh linear vibrating screen to eliminate residual hard gangue lumps.

Step 5: Closed Silo Circulation Homogenization

Pre-crushed coke stored in nitrogen-sealed silo with air-lift closed circulation ≥4 cycles, eliminate particle size segregation.

Step 6: Jet Milling Fine Grinding & Classification

Grind coarse coke particles to target D50 10–22 μm; air classification to adjust bimodal particle grading for high tap density.

Step 7: Precision Batching & Dry Mixing

1. Automatic loss-in-weight feeding: Proportion large/small fraction coke powder + solid pitch binder.
2. Low-temperature sealed dry mixer (60–90°C, 30–45 min mixing) to uniformly blend solid raw materials without pitch melting agglomeration.

Output of Pretreatment

Uniform coke-pitch mixed powder ready for high-temperature kneading, granulation and pre-carbonization.

Part 4: Shared Key Pretreatment Control Standards

1. Moisture control: All powder entering downstream core process ≤0.5%
2. Anti-contamination: All contact parts lined with zirconia ceramic / PU / 316L stainless steel, no carbon steel
3. Magnetic impurity limit: Fe ≤10 ppm after full pretreatment
4. Homogenization standard: Impurity deviation between multi-point samples ≤3 ppm
5. Particle size stability: PSD fluctuation D50 ≤±0.6 μm

Part 5: Simplified Process Comparison Summary

1. Natural Graphite Pretreatment
   Raw Ore/Flotation Concentrate → Pre-sorting & magnetic separation → Homogenization stacking → Coarse crushing + initial sieving → Two-stage uniform drying → Jet milling classification → Spheroidization shaping → Fine screening & final magnetic removal → Purification feed
2. Artificial Graphite Pretreatment
   Calcined Coke Lump → Batch classification & pre-sorting → Coke homogenization silo → Two-stage pre-crushing → Magnetic separation + initial sieving → Circulation homogenization silo → Jet milling fine grinding → Batching & dry mixing → Kneading feed