DETERMINATION OF THE REACTION RATE CONTROLLING RESISTANCE OF GOETHITE IRON ORE REDUCTION USING CO/CO2 GASES FROM WOOD CHARCOAL

Abstract

The quest for suitable reductants for the extraction of iron from ores at minimal energy requirements and maximum degree of metallization is attracting growing researchers’ attention. In the present work, an attempt is made to use non-contact charcoal in the reduction of run-off mine goethite ore at heating temperatures above 570oC. The reduction mechanism adopted is in accordance with Levenspiel’s relations for the shrinking core model. The first stage is concerned with the diffusion of gaseous reactant through the film surrounding the particle to the surface of the solid where Goethite hematite is reduced by CO from wood charcoal to magnetite (3Fe2O3 + CO → 2Fe2O3 + CO2). The second stage involves the penetration of a gaseous reactant through the blanket of ash to the surface of the unreacted core where magnetite is reduced to wustite (Fe3O4 + CO → 3FeO + CO2). The final stage is the reaction of the gaseous reactant with solid at the reaction surface, which is described by the stoichiometry equation where the product consists of fluid and solid (FeO + CO → Fe + CO2). This non-contact charcoal reduction approach is adopted to maximize the benefit of using CO/CO2 gases from charcoal for reduction without the need for beneficiation and concentration. The rate-controlling steps for the reduction kinetics of average particle size 5, 10, 15, and 20 mm at 570, 700, 800, 900, and 1000oC are studied after heat treatment of the ore-wood charcoal in activated carbon reactor at total reduction time of 40 minutes based on literature. Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis are done to investigate the spectrometric phase change and metallic components of the ore sample after reduction, respectively. The average percentage metallic iron content of 56.6, 60.8, and 61.7% and degree of metallization of 91.62, 75.96, and 93.6% are achieved from the SEM/EDX analysis of the reduced ore sample at reduction temperature of 570, 800 and 1000oC, respectively. The sharp drop in the degree of metallization of the reduced ore samples is observed at intermediate temperatures 700, 800, 900oC of the reduction. This indicates the tendency of high carbon deposit at the wustite stage of the reduction process at the least temperature and residence time of 5700C and 10 minutes, respectively. This study demonstrates that diffusion through the ash layer is the controlling resistance of the overall reduction process.