Effect of quaternary basicity on reduction behavior of iron-bearing dust pellets

The treatment of iron-bearing dusts and sludges by the rotary hearth furnace process has the advantage of sufficient utilization of valuable metals and a high impurity removal rate,but the lower strength of the metallized product needs to be addressed.The effects of quaternary basicity R4(w(CaO+MgO)/w(SiO_(2)+Al_(2)O_(3)))on the reduction behavior and physical and chemical properties of metallized pellets,including phase composition,compressive strength,microstructure and soft melting area,were investigated with FactSage thermodynamic software and experiments.The strength of metallized pellets depended on the gangue composition,such as CaO,MgO,Al_(2)O_(3) and SiO_(2),due to the altered chemical composition,physical phase composition,microscopic morphology and stability of the slag phase.The reduction of carbon-bearing pellets was significantly promoted by suitable basicity.The lower basicity(R_(4)<1.4)facilitated the formation of low melting point iron-containing compounds from SiO_(2) and Al_(2)O_(3) with FeO,resulting in increased liquid phase generation,but lower metallization rate,due to the hindered precipitation and growth of iron grains.Interestingly,the higher basicity(R_(4)>1.8)also increased the amount of liquid phase and improved the strength of the pellets,due to the granular iron crystals bonded into sheets.Notably,the main component of the liquid phase in high-basicity conditions was calcium ferrite.Although the additional amount of liquid phase was beneficial to the strength of the metallized pellets,calcium disilicate was formed at R_(4)=1.6,resulting in a reduction in the compressive strength of the pellets to 1521.9 N/pellet.

Drop strength measurement of green pellet based on drop-rebound mechanism

The construction of blast furnace charge structure based on pellet and the development of short process from non-blast furnace to electric furnace will be an efficient way to accomplish"carbon peak,carbon neutral".Since drop strength is one of the most crucial quality indexes for green pellet,the crack detection in the collision process is an indispensable segment;however,the present crack determination is basically completed manually.Due to a series of problems including high labor intensity and poor detection conditions,it is urgent to develop an accurate,convenient and fast standardized method for drop strength detection.In view of the above issues,combined with plenty of experimental studies,it is found that whether rebound occurs after the collision of green ball can be used as the basis for judging if there are cracks on the surface,and the mechanism of this segment is explained by the energy conversion of collision process that the plastic deformation of the collision is a cumulative process.Each collision will cause a slight displacement of the iron ore particles;until the cumulative displacement exceeds the binding force between the particles,they will slip in a large range,that is,cracks will occur.The drop strength can be detected based on the drop-rebound mechanism determining crack generation during collision process by high-speed cameras,and the method is fully applicable to oxidized pellets with particle size of 8-16 mm though various pellet plasticities and masses increase the difficulty of bounce height monitoring.Based on the drop-rebound mechanism of green pellet,three methods for automatically detecting the drop strength are proposed,which are high-speed camera,photoelectric sensor and pressure sensor methods.