How is recovered carbon black manufactured from waste tires

Recovered carbon black (rCB) production from waste tires consists of two major stages: tire pyrolysis (to produce crude char) and char upgrading / dry purification (to convert crude char into commercial rCB). The whole workflow converts scrap tires including large OTR mining tires into pyrolysis oil, syngas and high-quality rCB, as referenced at rcb-mill.com.

Step 1: Waste tire pre-treatment

1. Collection & sorting: End-of-life tires are collected and sorted by type (passenger, truck, OTR tires). Mixed foreign waste, metal and textile contaminants are removed. Consistent feedstock quality stabilizes final rCB properties.
2. Shredding & granulation: Tires are shredded into rubber chips or granules. Steel cords and textile fibers are separated mechanically.

Steel can be recycled separately; textile fiber may be sent for energy recovery.

3. Size screening to get uniform granule size for stable pyrolysis reactor feeding.

Step 2: Oxygen-free pyrolysis (core thermal decomposition)

The tire granules are fed into a closed, oxygen-limited pyrolysis reactor.

• Operating temperature: 450–600 °C, no open combustion.
• The vulcanized rubber polymer thermally breaks down into three products:
  1. Pyrolysis vapor: condensed into valuable pyrolysis oil.
  2. Non-condensable syngas: mostly CO, CH₄, H₂; burned to supply heat for the pyrolysis reactor, reducing external energy consumption.
  3. Solid output: crude pyrolysis char (the precursor for rCB).
• During pyrolysis, original carbon black nanoparticles remain intact, but many aggregates fuse into hard sintered agglomerates. Tire mineral additives (ZnO, silica, CaCO₃) stay inside the char.

Important: Crude char ≠ finished rCB. It contains high ash, tar, sulfur and metal impurities and cannot be directly used for high-end applications.

Step 3: Crude char primary purification

1. Coarse crushing: Break large char lumps from the pyrolysis reactor.
2. Multi-stage high-gradient magnetic separation: Remove iron impurities originating from residual steel cords inside char. This step is critical, especially for battery-grade rCB.
3. Ultra-fine de-agglomeration grinding: Use specialized mills to break the hard sintered agglomerates formed during pyrolysis. Grinding separates fused aggregates without destroying the original nano primary particles.

Step 4: Air classification (dry separation)

Air classifiers separate particles based on density and size:

• Dense mineral-rich ash fractions are rejected.
• Fine carbon aggregates are collected.
  This step reduces ash content and narrows particle size distribution.
  Dry grinding + air classification is the core dry purification line for standard and premium tire-grade rCB.

Step 5: Optional thermal devolatilization (for high-end grades)

For premium tire-grade or battery-grade rCB, the char is treated in an inert atmosphere furnace at 800–900 °C.

• Removes residual tar, PAH and volatile organic deposits coating carbon aggregate surfaces.
• Adjusts surface chemistry and pH value, improves filler-matrix compatibility in rubber and polymers.
• Limitation: cannot remove inorganic minerals such as ZnO and ZnS. Excessively high temperature causes sintering and collapses aggregate pore structure.

Step 6: Optional wet deep purification (only for high-purity battery-grade rCB)

If ultra-low ash and ultra-low sulfur are required for lithium-ion battery conductive additives:

1. Acid leaching dissolves inorganic minerals: ZnO, ZnS, calcium salts.
2. Multiple rinsing with deionized water removes dissolved ions.
3. Low-temperature drying.
   This achieves ash <0.5 wt% and sulfur <0.3 wt%, but adds wastewater treatment and higher production costs.

Step 7: Post-processing and quality control

1. Pelletizing (optional): Fine rCB powder is pelletized to reduce dust and improve flowability for transportation and compounding. Powder rCB is also available.
2. Laboratory QC testing: Test carbon content, ash, DBP oil absorption, BET surface area, PSD, sulfur, heating loss, resistivity and morphology.
3. Packaging and storage in sealed containers to avoid moisture absorption.

Simplified workflow summary

Waste tire → Shredding + steel/textile removal → Oxygen-free pyrolysis → Crude char → Magnetic separation → De-agglomeration grinding → Air classification → Thermal devolatilization (optional) → Wet acid deashing (battery grade only) → Pelletizing → Quality inspection → Finished rCB

Pyrolysis recovers carbon black from tires, but the crude char still has heavy impurities. The value of high-quality rCB mainly comes from advanced dry purification: magnetic separation, de-agglomeration grinding and air classification. Thermal and wet chemical treatments further upgrade rCB for premium tire and battery applications.