Study On The Influence Of Magnesium-containing Solvent On Quality Of Ultra-fine Mineral Pellet

With the proportion of pellets increasing and the shortage of rich ore growing,more and more high grade by beneficiation and fine grinding is used for pellet production.However,the reflowing temperature of ordinary pellets is relatively low.Adding magnesium-containing solvent is good for improving the metallurgical performance of pellets and can also reduce the burden of the sintered ore on magnesium oxide(MgO).Therefore,it is of great importance to study the ultrafine mineral magnesium pellets.In the current paper,the influence of magnesium-containing solvent on the quality,preheat,roasting and metallurgical properties of ultra-fine pellets was investigated.The high-grade Australian ultra-fine iron ore was selected as ironcontaining raw materials.The coarse-grained domestic slag was used to adjust the size of raw materials.The magnesium ball and light burning dolomite were used as the magnesium-containing flux.The action mechanism of MgO on the pellet was analyzed using SEM-EDS and phase diagram.The results showed that the compressive strength of the produced pellet decreased in case of both magnesia and pulverized dolomite as the flux.Compared with magnesium-containing pellets,the longer produced time(more than 25 min),larger compressive strength(more than 30 N/unit),and lower burst temperature(less than 350 oC)were needed for ultra-fine ore pellets.MgO had a negative effect on the pellet strength after preheating and calcination,but both met the production requirements(preheat pellet strength >400 N/unit,roasting pellet strength > 4000 N/unit).The strength of ultra-fine ore pellets after roasting were larger than ordinary magnesium-containing pellets.According to the analysis of SEM-EDS and phase diagram,MgO,ferrous oxide(FeO),and iron oxide(Fe2O3)were solid solution.They hindered the oxidation of magnetite and the aggregation of hematite so that the pellet strength decreased.MgO was beneficial to improve the metallurgical properties of pellets.When the content of MgO increased from 0.52% to 1.5%,the degree of agglomeration(RI)of the magnesium ball increased from 73.69% to 74.92%.The low temperature reduction pulverization index(RDI+6.3mm)increased from 81.46% to 95.14%.The reduction index(RSI)decreased from 17.20% to 13.82%.The agglomeration degree(RI)of the pulverized dolomite increased from 73.69% to 75.61%.The low temperature reduction pulverization The index(RDI+6.3mm)increased from 81.46% to 92.61% and the reduction index(RSI)increased from 17.20% to 25.46%.It was because that calcium oxide(CaO)in lightly burnt dolomite was favorable for the growth of the iron whisker in a specific direction and increased the internal stress of pellets,resulting in the pellet volume expanding in the specific direction.The mineral phase showed that the main compositions of the pelletized slag phase were fermented olivine and magnesium ferrite,and the melting point of the high melting point slag phase increased with increasing the content of MgO.The experimental results showed a good agreement with those obtained from industrialtrails.Although the compressive strength of roasting pellets was lower than that of industrialtrails,the strength was larger than 3600 N/unit and it still met the requirements of large blast furnace(usually more than 2500 N/unit).