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 Co 3 O 4 in a flowing atmosphere generated by pyrolysis of waste tires (rubber) with and without waste polyethylene. A thermodynamic model predicted that Co 3 O 4 was reduced to Co by pyrolytic gas agents (mainly H 2 , CH 4 , C 6 H 6 ) in the temperature range 700–900\xa0K. The experiments were carried out by simultaneously heating the waste and Co 3 O 4 powder to 900\xa0K. The extent of Co 3 O 4 reduction increased with increasing tire-to-Co 3 O 4 ratio. The oxide reduction followed the path Co 3 O 4 \xa0>\xa0CoO\xa0>\xa0Co as the rubber content increased, in agreement with the thermodynamic prediction. Co 3 O 4 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\xa0K led to the full Co 3 O 4 reduction to Co, owing to increased reducing agent content and reaction time. Conversion of spinel Co 3 O 4 to f.c.c. Co has been discussed in terms of structural and morphological changes.