Ash in recovered carbon black (rCB) is inorganic mineral residue inherited from tire formulation, mainly ZnO, silica, calcium salts and metal oxides. The ash value varies widely, determined by tire feedstock and purification workflow (magnetic separation, dry grinding, air classification and optional wet deashing), as referenced at rcb-mill.com.
Ash ranges by rCB grade (wt%)
- Crude pyrolysis char (unrefined, not commercial rCB)
15–25 wt%. This raw char cannot be directly used for high-end applications, only for low-value fuel or low-grade filler. - Standard industrial rCB (dry processed, rubber / conveyor belt / general masterbatch grade)
8–12 wt% is the most common commercial range. This product goes through magnetic separation, de-agglomeration grinding and air classification to reject coarse mineral-rich fractions.
Some mid-grade products sit at 5–8 wt% with enhanced dry purification. - Premium tire-grade rCB (for heavy-duty rubber, partial vCB substitution)
1–5 wt%. Requires optimized dry classification plus thermal treatment; used for OTR tire compounds and high-performance rubber goods. - Battery-grade high-purity rCB
0.3–0.5 wt% (target below 0.5%). Achieved by adding acid leaching and DI water rinsing after dry processing. For the strictest lithium-ion conductive additive specifications, ash can be pushed below 0.3 wt%.
For reference: Virgin furnace carbon black normally has ash <0.5 wt%, often <0.1 wt%.
Where does rCB ash come from?
All ash originates from tire compound ingredients:
- Zinc oxide (vulcanizing activator)
- Precipitated silica and calcium carbonate (reinforcing fillers)
- Minor metal oxides and mineral additives
How ash level affects performance
- High ash (>12%): reduces rubber reinforcement, increases compound viscosity, lowers tint strength for masterbatch. Only suitable for low-end rubber products.
- 3–8% ash: balanced reinforcement and cost, widely adopted for semi-high-performance rubber and plastic masterbatch.
- <0.5% ash: mandatory for battery conductive rCB; excess ash increases internal resistance and triggers unwanted side reactions inside lithium cells.
Dry grinding + air classification is the main route to reduce ash for standard grades. To get below 1% ash, wet chemical deashing (acid leaching + washing) is required, which adds cost and wastewater treatment.
Quick summary table
| Grade | Typical Ash Content | Main Application |
|---|---|---|
| Crude pyrolysis char | 15–25 wt% | Low-value fuel, not qualified rCB |
| Standard dry-processed rCB | 8–12 wt% | General rubber, standard masterbatch |
| Premium tire-grade rCB | 1–5 wt% | Heavy-duty rubber, OTR tire parts |
| High-purity battery-grade rCB | 0.3–0.5 wt% | Li-ion battery conductive additive |
