Fourteen kinds of iron ore fines (0.015-0.021 cm diameter) were reduced to iron in a laboratory batch fluidized bed with a 90%CO-10%CO₂ mixture (flow rate: 8 times the minimum fluidization velocity U_mf) at 700-900°C to investigate the relation between sticking behavior and sulfur activity in gas phase of bed during metallization (a_S), which could be evaluated from chemical analysis of sulfur species in exhausted gas, relative to iron/iron sulfide equilibrium.
Values of a_S obtained in all of tests were in the range of 0.01-1. The tests showing middle sulfur activities around 0.1, fell into sticking state soon after initial metallization, accompanied with long iron whiskers at higher temperatures. The tests showing activities other than the above conditions, induced short iron whiskers and porous or plain irons, indicating fluidized state until higher reduction degrees at lower temperatures. These temperature and sulfur activity dependences of product morphologies, which were in nearly agreement with authors' previous researches about abnormal swelling during reduction of iron oxide pellets prepared from reagent, corresponded to a sticking tendency of bed. These results give one reasonable idea by which the ore kind dependence of sticking can be interpreted.