Thermodynamic Analysis and Reaction of Co3O4 Powder with Pyrolytic Gas Derived from Waste Tires With and Without Waste Polyethylene

Abstract

The present study aimed to investigate the pyrometallurgical reduction behavior of Co3O4 in a flowing atmosphere generated by pyrolysis of waste tires (rubber) with and without waste polyethylene. A thermodynamic model predicted that Co3O4 was reduced to Co by pyrolytic gas agents (mainly H-2, CH4, C6H6) in the temperature range 700-900 K. The experiments were carried out by simultaneously heating the waste and Co3O4 powder to 900 K. The extent of Co3O4 reduction increased with increasing tire-to-Co3O4 ratio. The oxide reduction followed the path Co3O4 > CoO > Co as the rubber content increased, in agreement with the thermodynamic prediction. Co3O4 reduction was incomplete when waste tires only were used. Adding a minor amount of high-density polyethylene to the tires and isothermal holding at 900 K led to the full Co3O4 reduction to Co, owing to increased reducing agent content and reaction time. Conversion of spinel Co3O4 to f.c.c. Co has been discussed in terms of structural and morphological changes.