Research On Modification And Quality Improvement Of Low-quality Bentonite And Its Pellets Application

Low-quality bentonite produced in industry usually has the characteristics of low montmorillonite content,calcium-based bentonite,poor physical and chemical properties,and fine particle size of impurity minerals,which is difficult to purify.Therefore,low-quality bentonite can not be used effectively,and it is easy to cause a waste of resources.Bentonite is main binder for iron ore pelletizing process,and has the function of stabilizing the pellet production process and ensuring the quality of pellets.In this study,low-quality bentonite from a certain area in Hubei was used as the research object,was directly modified and applied to pellets on the basis of physical and chemical analysis.The sodium modification study was conducted to improve the physical and chemical properties of the original soil.Then the composite modification study was carried out to prepare the pellet composite binder.Then,the modified soil is optimized for pellet application,compared the application effect of bentonite before and after modification in pellets.Through physical and chemical performance,crystal structure and microstructure was analyzed,and explained the changes in physical and chemical properties of bentonite after modification.The main conclusions are as follows.（1）The optimal sodiumized conditions of the raw bentonite included screw extrusion,2%Na₂CO₃ dosage,26%sodiumized water,2 screw extrusion times and 3d aging time.Optimal sodiumized bentonite（hereinafter collectively referred to as sodiumized soil）.The montmorillonite is made of the aggregated coarse particles transformed into an irregular fine single-layer flake structure.Sodiumized bentonite has obvious fiber characteristics.After sodiumized modification,the water absorption and swelling capacity in 2h are increased from 161.1%and 3.1ml/g to 349.15%and 18.1ml/g.When the proportions are both 1.6%,the drop strength increases from 3.9 times/（0.5m）for the original of soil pellets to 5.5 times/（0.5m）of the sodiumized bentonite.（2）The best modification process is sodiumized and compounded simultaneously.under the condition of screw extrusion.The best compound bentonite is FB-bentonite（hereinafter collectively referred to as composite binder）.The compound bentonite is mainly dispersed with very fine particles,and the specific surface area is large.when the proportion is 1.6%,the drop strength and burst temperature are increased from 3.9times/（0.5m）and 545℃of the original soil pellets to 6.6 times/（0.5m）and 668°C of the composite binder pellets.（3）The ratio of sodiumized soil and composite binder in pellets can be reduced from1.6%of the original soil to below 1.4%and 1.0%respectively.When pellets with a ratio of 1.0%composite binder,Its green ball drop strength and burst temperature are 4.4times/（0.5m）and 644℃,and the compressive strengths of preheating ball and roasting ball are 602.8N and 4172.5N,which can meet the industrial requirements.When the proportion of composite binder in the pellets was reduced from 1.6%to 1.0%,the TFe grade of the roasting pellets increased by 0.36%and the SiO₂ content decreased by 0.4%.Under the condition of burst temperature,the water loss rate of the composite binder pellets was slower than that of the original soil pellets and the sodiumized soil pellets,and the composite binder has a buffer effect on the water evaporation in the pellet.