Thermal Treatment of Waste Tire Fly Ash with Polyvinyl Chloride: Selective Leaching of Zinc with Water

Thermal treatment of waste tire fly ash (TFA) with poly(vinyl chloride) (PVC) at temperatures ranging from 160 to 300 °C has been examined for the recovery of metals from TFA in a subsequent leaching process. Thermogravimetric and differential thermal analyses showed that TFA absorbs hydrogen chloride (HCl) released from PVC. X-ray diffraction measurements also indicated that crystalline ZnO contained in TFA converts into chlorides when the mixtures of TFA and PVC are heat-treated at 180 °C or higher temperatures. By heating the mixture (TFA/PVC = 1.5 by weight) at 250 °C for 1 h, the percentage of dechlorinated PVC reaches more than 95%, and more than 90% of the Zn originally contained in TFA is leached from the residue with water. On the other hand, the leaching of Fe in TFA is much suppressed. Compared to a conventional acid-leaching process, satisfactory Zn leaching and selectivity in metal leaching from TFA were realized. This selectivity for Zn is reasonably explained by a difference in the reactivity of metal compounds in TFA with HCl from a thermodynamic viewpoint.