Experimental Study On Preparation Of Ultra-fine Iron Concentrate Pellets With High Ratio

Ultra-fine iron concentrate is the product of the gradual exhaustion of high-quality iron ore resources and the continuous development of fine-grinding and deep-processing technology.It shows the characteristics of high iron grade,extremely fine particle size,narrow particle size range,smooth particle surface,and weak hydrophilicity.When ultra-fine iron concentrate is used in pellet production,it causes poor ballability,high amount of bentonite,low pellet quality,and the ratio is usually less than 40%.In the past research on ultra-fine iron concentrate pellets,the improvement of pellet quality by preheating roasting was mainly studied,and the research on the improvement of raw material characteristics and green pellet quality was relatively less.Therefore,the research on the preparation technology of ultra-fine iron concentrate pellet is of great significance for utilization of using"poor,fine,and impurities"iron ore resources,expanding the range of pellet raw materials,improving pellet quality and grade,and reducing pellet production costs.In this paper,a high-grade ultra-fine iron concentrate(concentrate A)was used to carry out research on the preparation of pellets.As the ratio of concentrate A increased from 60%to 100%,the falling strength and bursting temperature of the green pellets are decreased from 4.30 times/(0.5 m)and 455?to 2.10 times/(0.5 m)and 330?,while adding 20%porous sulphuric acid slag can promote the formation of ball and increase the bursting temperature to 405?.The effect of high pressure grinding rolls(HPGR)pretreatment on the properties of pelletizing mixture and the quality of green pellets was studied.The results show that,after HPGR,the content of-0.030 mm in the mixture can be increased to 61.52?85.23%,and the specific surface area can be increased to1540?2064 cm²·g^-1.The use of HPGR can improve the quality of green pellets by adding new surfaces,changing morphology,improving the hydrophilicity,and enriching particle size distribution of the particles,it increases the specific surface area,improve the degree of particle incorporation during pelletization,and increase the capillary force between the particles,improveing the specific surface area,particle incorporation and capillary force of the pelletizing mixture.Under the conditions of bentonite ratio of 1.8%,HPGR speed of 280 r/min,pressure of 1.0 MPa,moisture of8.5%,and ratio of 100%,the green pellet can obtain a compressive strength of 18.52N/P,falling strength of 4.2 times/(0.5 m),and bursting temperature of 385?.Aiming at the problems of high ratio of bentonite and low bursting temperature when high proportion of concentrate A is pelletized,the influence of the addition of bentonite and organic binder(binder B)on the preparation of green pellets was studied.The results show that with the addition of 0.2%binder B,the ratio of bentonite can be reduced from 1.8%to 1.2%,and the green pellets can obtain a compressive strength of18.57 N/P and a falling strength of 6.8 times/(0.5 m),the bursting temperature is 435?,and the drying pellet strength is 90.54 N/P.The binder B is dispersed and filled inside the pellets,enhanced capillary effect,optimized particle bonding,and slowing down the effect of water evaporation during bursting.Binder B starts to decompose at low temperature,increasing the internal voids of the pellets and optimizing vapor pressure diffusion conditions.Experimental research on the oxidation rate and preheating roasting process of pellets showed that the use of HPGR and binder B can increase the strength of the oxidized pellets.The compressive strength of finished pellets is 2890 N/P under the conditions of preheating at 950?for 12 min and roasting at 1220?for 12 min,which meets the requirements of blast furnace smelting.