Study On Bentonite-based Composite Binder For Iron Ore Pellets

Binder is an important component of iron ore pellets.At present,the reserves of high-quality bentonite are decreasing.In order to solve the adverse effect of bentonite degradation on the properties of iron ore pellets,metallurgical workers have to constantly look for new binder materials.Among them,the compound of organic matter and bentonite is one of the important technical routes for the development of new binder materials.In this paper,the bentonite with typical low montmorillonite content in East China was used as the base material,which were modified by adding single or multiple organic materials to prepare the iron ore pellet composite binder,and the effect of composite binder was investigated by combining the preparation,drying and preheating of green pellets.Based on the analysis of the effect of composite binder on the preparation,drying and preheating of green pellets,this paper studied the influence of binder types and the amount of additives on the strength,drying strength,bursting temperature and roasting performance of the pellets.Thus,the optimal composition and ratio of composite binder were determined,and the mechanism of composite binder on the properties of iron ore pellets was revealed.According to the research results of pellet performance of single organic materials A,B and C as binder,it can be found that materials A,B and C have positive effects on improving pellet performance,but the preheating and roasting strength are unsatisfactory.Under the condition of the addition amount of 0.25%,the falling strength and compressive strength of the iron ore pellets containing organic material B are 8.3 times and 16.7 N?P^-1,respectively.The bursting temperature is 587?,the drying strength is 65 N?P^-1,and the preheating compressive strength and roasting compressive strength are 118 N?P^-1 and 559 N?P^-1 respectively.According to the test results of the pellet properties of the binder mixed with bentonite and organic material,it is shown that the binder has a good application effect,which is a mixture with a single organic material C with a mass fraction of 4%and a bentonite of 96%.Under the condition that the binder amount was 1.75%,the drop strength and compressive strength of iron ore pellets are 9.5 times and 17.8 N?P^-1 times,respectively.At this time,the bursting temperature reaches 540?,the drying strength is 73 N?P^-1,and the preheating and roasting strength are 554 N?P^-1 and 2852 N?P^-1,respectively.When the amount of binder added is the same as 1.75%,the binder that combines bentonite,organic material B and organic material C with mass fraction of 96%,1%and 3%,respectively,it enjoys better cost performance.Under this condition,the falling strength and compressive strength of iron ore pellets are 11.2 times and 17.5 N?P^-1,respectively,with burst temperature of 583?and drying strength of 75 N?P^-1,and preheating and roasting strength of 643N?P^-1,2983 N?P^-1.The effect mechanism of composite binder on the properties of iron ore pellets is as follows:the presence of organic material B and C anion groups on the surface of bentonite increases the hydration ability and water absorption expansion ability of the binder.Under the action of mechanical grinding,the gelatinous substance formed by hydration of organic material is evenly dispersed and filled between ore particles,and the pellet performance is improved by strengthening the adsorption of iron ore concentrate particles.The volatilization of organic materials at lower temperatures increases the porosity of the green pellets and provides a diffusion channel for the rapid evaporation of water,thus promoting the burst temperature of the green pellets.Compared with the single bentonite binder,the introduction of organic materials would increase the porosity of pellets and reduce the phase production of pellets with low melting point during preheating and roasting,which would have a certain adverse effect on the strength of pellets after roasting.