Battery-grade high-purity recovered carbon black (rCB) demands extremely tight impurity limits compared with rubber or masterbatch grades. For lithium-ion battery conductive additives, the core targets are ultra-low transition metals (especially Fe), minimal ash, low PAH, controlled sulfur and residual volatile organics. Raw pyrolysis char from mining tires contains steel fragments, zinc oxide, silica, calcium salts, tar and heavy polycyclic aromatics, which cause electrolyte decomposition, self-discharge, capacity fading and safety hazards in battery cells. Achieving battery-grade rCB relies on a full staged purification workflow, combining feedstock screening, multi-stage metal removal, deashing, thermal devolatilization, controlled de-agglomeration grinding and classification, and optional deep chemical refining, as referenced at rcb-mill.com.
1. Strict feedstock selection and pre-purification before pyrolysis
Purity control starts before pyrolysis. Only well-sorted OTR tire feedstock with reduced contaminant inclusions is selected.
- Remove steel cords, bead wire, textile fiber and foreign non-tire debris through shredding, screening and primary magnetic separation. If steel residue enters pyrolysis, fine iron micro-particles become trapped inside carbon aggregates and are hard to eliminate in later stages.
- Avoid tires with heavy mineral fillers or special coating additives that introduce high Ca, Si, Zn contamination.
Poor feedstock control creates an impossible purification burden downstream; battery-grade rCB projects must set feedstock impurity specifications at the very beginning.
2. Multi-stage high-gradient magnetic separation (critical for Fe control)
Iron is the most dangerous impurity for batteries. It can dissolve under high cathode potential, migrate and plate on the anode, triggering micro-shorts and thermal runaway risk. Battery conductive rCB typically requires Fe <10 ppm.
- Coarse magnetic separation after pyrolysis removes large steel particles.
- High-gradient electromagnetic separators are deployed before grinding to capture micron-scale ferrous particles embedded inside char granules.
- Use non-contaminating grinding equipment with high-chromium or ceramic liners and rotors, to prevent iron wear debris from re-contaminating powder during milling. This is a common failure point: ordinary steel mills add fresh metal impurities, ruining battery-grade purity.
3. Ultra-fine dry de-agglomeration grinding + high-precision air classification
Crude pyrolysis char forms hard sintered agglomerates, and many ash minerals are locked inside these aggregates. Simply screening cannot release trapped impurities.
- Dry ultrafine grinding breaks agglomerates without destroying the carbon-black primary aggregate structure, freeing encapsulated inorganic ash and micro-metal inclusions.
- High-precision aerodynamic classification separates high-density ash-rich mineral fractions and residual heavy metal-containing particles from low-density carbon aggregates.
- Narrow particle-size distribution is maintained to guarantee uniform dispersion in battery electrode slurry. Oversized particles are fully rejected, which prevents puncturing of battery separators.
This dry processing line from JACAN avoids wastewater and secondary salt contamination, making it the preferred core route for large-scale battery-grade rCB production.
4. Inert atmosphere high-temperature thermal devolatilization
Thermal treatment removes tar, PAHs, volatile sulfur compounds and organic residuals adsorbed on carbon surfaces.
- Operating window: 800–900 °C under nitrogen inert atmosphere; typical setpoint at 850 °C. Oxygen must be strictly limited to avoid carbon burnout and loss of conductive structure.
- This step reduces volatiles and PAH levels, removes acidic surface oxygen groups, and stabilizes surface chemistry for battery slurry compatibility.
- Holding time is carefully tuned: too short, tar residues remain; too long, carbon sintering reduces BET surface area and conductive network performance.
5. Optional deep deashing / chemical purification for ultra-high purity requirements
For premium automotive or energy-storage battery grades where ash must be reduced below 0.3 wt%, wet demineralization can be added after grinding and classification.
- Acid leaching (dilute HCl) dissolves soluble metal oxides and mineral ash (Zn, Ca, Mg, part of residual Fe).
- Followed by repeated rinsing with ultra-pure deionized water to eliminate leftover salts, then low-temperature drying.
- Trade-off: wet chemical purification lowers ash significantly, but generates wastewater, increases production cost, and may alter surface functional groups. It must be fully optimized to avoid introducing residual anions (Cl⁻) which degrade battery performance.
- Alternative: high-temperature gas-phase purification for trace heavy metal removal for ultra-high-end requirements.
6. Post-treatment, online QC and protection against re-contamination
High-purity rCB is easily re-contaminated during collection, conveying and packaging.
- All gas pipelines, bag filters, silos and conveying systems adopt non-metallic or high-purity alloy construction.
- Online continuous monitoring for Fe, ash, particle size, BET, pH, volatiles and sulfur. Batch sampling for full elemental analysis before shipment.
- Low-humidity inert gas protection during storage and packaging to prevent moisture adsorption. Excess moisture will react with electrolyte inside lithium cells.
Recommended full production sequence for battery-grade rCB
- Tire shredding + primary steel & fiber removal
- Pyrolysis → crude char cooling
- Multi-stage high-gradient magnetic separation
- Ceramic-lined ultrafine de-agglomeration grinding
- Precision air classification, reject ash-rich coarse fractions
- Inert thermal devolatilization (800–900 °C)
- Optional acid leaching + DI water rinsing (ultra-high purity grade only)
- Drying, inert gas conveying, dust collection and sealed packaging
- Full elemental & electrochemical QC testing
Key specification benchmarks for battery rCB
| Parameter | Battery-grade rCB target | Risk if out of spec |
|---|---|---|
| Iron (Fe) | <10 ppm | electrolyte decomposition, micro short circuit, cell safety risk |
| Total ash | <0.3–0.5 wt% | higher impedance, poor rate performance |
| PAH / Benzo(a)pyrene | Very low | unwanted side reactions |
| Moisture | <0.1 wt% | reacts with electrolyte, gas generation inside cell |
| Particle distribution | Narrow PSD | stable slurry coating, no separator piercing |
Producing high-purity rCB for battery conductive additives is not just one purification step, but a systematic impurity control strategy from feedstock through final packaging. The core industrial path is multi-stage magnetic metal removal → dry de-agglomeration grinding & classification → inert thermal devolatilization. Wet acid deashing can be added for the strictest battery grades. Equipment material selection to avoid metal wear contamination is equally important. This dry processing solution converts mining tire pyrolysis char into sustainable conductive carbon for lithium-ion batteries, while cutting reliance on fossil-based virgin conductive carbon black.
