Mechanism Investigation Of MgCl₂-based Binder In Converter Dry Dedusting Dust And Cold Bonded Pellet

The large amount of dust produced in the converter production process,due to its high TFe and basic oxide content,can be used as a secondary resource for the production of cold solid pellets that are returned to the converter as oxidants,slagging agents,and temperature control agents in the steelmaking process.At present,the cold solid pellets produced by the process of adding binder pressure balls are susceptible to powdering and cracking due to the digestion and expansion of?-CaO present in dedusting dust.Therefore,most binders need to be predigested before used.In addition,the pellets can be produced,and the MgCl₂-based binder can be used to produce high-strength pellets without the need for digestion.This is undoubtedly a more economical and simplified method,but studies on its impact on the pellet strength and pulverization mechanism have rarely been reported.Therefore,the mechanism of MgCl₂-based binder in the converter dry dedusting dust cold bonded pellets is studied.First,the mechanism of strengthening the cold bonded pellets strength by MgC1₂-based binder was studied.The mechanism is mainly divided into two points:The first point is that MgC1₂ and MgO in the MgC1₂-based adhesive form a gas-hardening cementitious material to produce adhesion,and the second is that the deliquescence of MgCl₂ accelerates the transition from Fe²⁺to Fe³⁺,making the pellets are oxidized to form a new phase of consolidation,in which the adhesive force generated by the gas-hard cementitious material is the main force.When these two forces act together,the pellets have high strength.The iron oxide scale not only can achieve the consolidation of the new phase in the pellets,but also plays a key role in ensuring the strength of the pellets.The pellet strength is further improved by adjusting the ratio of MgC1₂,MgO and the iron oxide scale:1.The content of the iron oxide skin is 0 to 15%,and the restrictive link is the change of the Fe state.The strength of the pellet can be increased by increasing the content of the iron oxide skin.2.The content of iron oxide skin is more than 15%.The restrictive link for the increase of the pellet strength is the hydration reaction.The strength of the pellet can be increased by increasing the content of MgO.The ball strength test of MgCl₂-based binders shows that the pressed dry dedusting dust cold bonded pellets have a high strength.The green pellets with moisture<5.5%,after curing 48h dry bulb strength up to 800N,dry pellets moisture<3.5%,there was no chalking and cracking occurred during the pellet curing.The reason for dusting of converter dry dedusting dust cold bonded pellets is due to the high moisture in the pellets of the cold bonded pellets is caused by the digestion reaction inside the pellets,which causes the internal expansion stress of the pellets to be higher than the bonding strength.The low moisture content and pellet strength are the key to controlling the chalking of the pellets.Using water glass and sodium humate as binders,under the premise of not dissolving,the pellets will cause varying degrees of chalking and cracking.At the same time,the water content of cold bonded pellets produced with water glass and sodium humate as binder was more than 7%,while the moisture content of pellets produced with MgCl₂-based binders was less than 5.5%.The thermogravimetry-differential thermal analysis of cold bonded pellets shows that the MgCl₂-based binder is not completely reacted in the cold bonded pellets,and the reaction rate is low.It can be reduced by increasing the reaction ratio of the MgCl₂-based binder to reduce amount of this binder.Based on this,a new type of adhesive M?3%MgCl2-based adhesive+1%dispersant D?was developed,which reduced the amount of MgCl₂-based binder by 25%.