Investigation On Preparing Oxidized Pellet With Converter Sludge

The comprehensive utilization of sludge converter has always been a major task for iron and steel plants. Oxidized pellet as a new way to treat converter sludge has broad prospects for development. Depth analysis of improved pellets performance reasons after adding the converter sludge. Study on the mechanism provide theoretical support for preparation of oxide pellets and promote the development of the technology. Research on oxidized pellet treatment method and related theories has great theoretical and practical significance for the promotion of the technology application of iron and steel enterprises.Fundamental characteristic of converter sludge, effect of converter sludge on ballability and drying , preheating system of converter sludge pellet, high temperature roasting consolidation mechanism of converter sludge pellet ,effects of converter sludge on oxidized pellet properties and related mechanism are investigated by the ways of XRD,SEM,EDX and mineral phase microscopic.The study of pellet with converter sludge forming process shows that the optimized ratio of bentonite and converter sludge is 1.5wt% and 7wt%, respectively.The investigation on drying preheating system of pellet with converter sludge shows that effects of on compressive strength and low temperature reduction degradation of converter sludge are larger than the other properties. Drying temperature 580, drying time 40min, preheating temperature 800℃and preheating time 20min is the optimal drying preheating system of analysis by synthesis.Converter sludge can increase oxidation rate of iron ore concentrates and can change the final phases, kirschsteinite are found only in converter sludge pellet. Pellet with converter sludge has the similar with reference pellet with the increase of temperature, such as diffraction maximum offset of magnetite, the main reaction is the oxidation reaction of ferriferous oxide and oxidation reaction is over at 1000℃, quartz exists in the two kinds of pellets.Converter sludge can increase compressive strength. The first reason is that porosity decreases adding converter sludge. The second reason is the main binder phase of pellet with converter sludge is kirschsteinite which is higher compressive strength than fayalite that is the main binder phase of reference pellet. The third reason is that interface of heat transfer and oxygenation has the same promoting speed and pellet with converter sludge has no delamination phenomena.Converter sludge improves reduction property of pellet remarkably. One of the reason is that converter sludge can promote oxidation reaction of iron ore concentrates because of fine grit and high surface energy. Another reason is that converter sludge raises basicity of pellet and change the the binder phase and pore structure. The other reasons are that hematite content of pellet with converter sludge is higher than that of reference pellet, pellet with converter sludge has uniform structure inside and outside while reference pellet has inhomogeneous structure and dense surface structure which is harmful to reducing gas going into inside of pellet. Although the solid phase reaction ray thickness is similar, the pore wall inside the reference pellets is covered by the biner phase fayalite or sosoloid of poor reducibility, however, the biner phase kirschsteinite of pellet with converter sludge does not form coating.Low temperature reduction degradation of pellet with converter sludge is similar with that of reference pellet. However, swell index is increased by converter sludge. Softening start temperature, melting temperature and dropping temperature are raised by converter sludge. Melt interval of converter sludge pellet is narrower than that of reference pellet, which is beneficial to ventilation property of charging.