Efficient Deashing and Desulfurization of Waste-Tire-Derived Carbon Black via Ca-Compound Composite Molten Salt (NaOH–Na ₂ CO ₃ –CaX)

Recovered carbon black (RCB) from waste tire pyrolysis is a promising sustainable alternative to commercial carbon black (CB), but its high-value use is limited by pyrolysis-derived impurities. To address inefficiency and pollution in existing methods, in this work we developed a ternary Ca-compound composite molten salt (MS) system (NaOH-Na₂CO₃-CaX). Effects of temperature (450-550 °C), calcium compound type (CaO, Ca(OH)₂, Ca(PO₃)₂, Ca₃(PO₄)₂), and dosage (10-40 wt %) were systematically investigated. Results demonstrate that within the NaOH-Na₂CO₃-CaO MS system, NaOH-CaO synergy converted ZnS/SiO₂ into soluble Na₂[Zn(OH)₄]/Na₄SiO₄, while sulfur-containing short-chain aliphatic hydrocarbons are converted into Na₂SO₄/Na₂SO₃ and dissolved in the MS. Under optimal conditions (500 °C, 10 wt % CaO), removal efficiencies of 82% for ash and 96% for sulfur were achieved. The treated RCB exhibited a broader pore size distribution, a 7.9% increase in specific surface area, and a 60.3% reduction in the average particle size. This process enables the in situ conversion of pollutants, thereby avoiding the emission of sulfur-containing exhaust gases and the generation of waste acids. The treated RCB demonstrates considerable potential as a substitute for commercial CB, offering an environmentally friendly strategy for waste tire valorization.