Thermodynamics and Reduction of Bi₂O₃ in Waste Tire-Derived Atmosphere

Abstract

The present study aimed to investigate reduction behavior of Bi₂O₃ in the gaseous atmosphere generated by the pyrolysis of waste tires. Thermodynamic analysis carried out in the Bi-O-C-H-S-Ar system predicted that Bi₂O₃ could be reduced to Bi in the temperature range 700–900 K. Bi₂O₃ reduction experiments were carried out as a function of reactant mass ratio ($m_{\text{tire}} /m_{{{\text{Bi}}_{ 2} {\text{O}}_{ 3} }}$ = 0–10) and temperature (600–900 K). The extent of tire pyrolysis increased as the temperature was raised to 900 K. The degree of Bi₂O₃ reduction increased with increasing tire pyrolysis, while the waste pyrolysis process controlled Bi₂O₃ reduction. The oxide reduction was incomplete, when only waste tires were used. Adding a minor amount of waste high-density polyethylene to the tires sufficed for full Bi₂O₃ reduction at 900 K. The reduction reactions and a model for the morphological evolution are presented. Large Bi shots formed owing to the coalescence of the liquid Bi droplets at the reduction temperature.