Prereduced iron ore pellets are produced at substantially lower heating temperature. For example, a stock of 1/2-in green (moist) balls was prepared by binding a Minnesota taconite concentrate (consisting of magnetite and analyzing 64.5 pct fe and 8.1 pct sio2) with bentonite clay (0.5-1.5 Wt pct dry basis). These were dried at 230 deg. F, and 500 g of pellets + 200 g of lignite char were charged to a slowly rotating steel drum. This was then inserted into a muffle furnace at 840 deg. F and heated to 1,830 deg. F in 85 min. The contents were sampled for s analysis, after which dolomite (54 pct caco3, 44 pct mgco3) or limestone (96 pct caco3) at a particle size of 10-28 mesh was charged into the drum in an amount of 8 g. Heating was continued for an additional 30 min at 1,830 deg. F. The final desulfurized pellets were analyzed for total fe, fe metal, and s and tested for crushing strength. The results indicate that all of the pellets produced were well reduced, but only the reductants fairly high is s yielded strong pellets (>200 lb crushing load per pellet). With reductants low in s, additional tests showed that heating to approximately 2,060 deg. F would be required to yield pellets with crushing strengths >200 lb. Much of the s absorbed in the sulfurization step was effectively removed during desulfurization. This treatment makes it possible to operate at least 200 deg. F lower than previously. Lower rank (high s) fuels can be employed.
U.S. Pat. 3,574,595; Apr. 13, 1971; Chem. Abstr. 74:144,917E