Study On The Binding Mechanisms And Experiment Of Sodium Lignosulfonate In Pellets

Iron ore pellets are more and more used in iron production because of their advantages of high iron grade and uniform grain size.As one of the indispensable raw materials for pellet preparation,binder has an important influence on pellet quality and production process.At present,most domestic pellet factories use inorganic binder bentonite as binder,but the addition amount is too high which resulted in too many harmful oxides Al₂O₃ and SiO₂ residues in pellets,thus reducing the iron grade of pellets.Compared with bentonite,the use of organic binder can increase the strength of pellet and reduce the addition of binder,and the organic binder can be oxidized or break up to gas to escape from the pellet at high temperature in order to reduce the residual in pellet.However,it will increase the cost of production because the price of organic binder such as carboxymethyl cellulose and modified starchis is higher.In this paper,sodium lignosulfonate?SL?as a by-product of papermaking industry,was used as binder to produce pellets.The study found that:?1?SL is a kind of polymer by using ring network and aromatic structure as the skeleton,which contains a large number of polar groups such as hydroxyl,carboxyl and sulfonic groups.The molecular structure characteristics of the polymer accords with the model of ideal organic binder.The thermal stability of SL is better than organic binder starch.The reticular and benzene-like organic chains in the molecular structure of sodium wood have adhesive properties.A large number of groups,such as carboxyl and sulfonic groups,can adsorb strongly on the surface of iron concentrate.When SL used in pelletizing,the colloidal substance is produced by SL dissolved in water and filled between iron concentrate particles,which is tightly connected to iron concentrate,thus increasing the strength of the pellet.Calcium carbonate in the compound binder can enhance the bonding effect of SL and further improve the strength of the green ball.?2?Infrared and Zeta analysis showed that:CaCO₃ can enhance the adsorption and bonding between SL and iron concentrate.In the composite binder,SL plays a decisive role in the strength of green and dry pellets.CaCO₃ plays an important role in the strength of preheated and roasted pellets.?3?Using the same mass fraction of binder,the green pellets falling strength and compressive strength of SL are better than bentonite pellets.When the amount of binder is 2%,the falling and compressive strength of the SL pellets are12.1times/?0.5cm?^-11 and 17.5N/pellet,respectively,which were much higher than those of bentonite pellets,respectively.It showed that the magnetite in the SL pellets is more fully oxidized.The grade of iron in SL pellets is 1.06%higher than that in bentonite pellets.The gas produced by oxidation or pyrolysis of SL in pellets will escape from the pellets during calcination,which will increase the porosity of the preheated pellets and roasted pellets,and promote the oxidation of Fe₃O₄ into Fe₂O₃in the pellets.When the amount of binder is 2%,The grade of iron in roasted pellets of SL pellets is 1.06 higher than that of bentonite pellets,which obviously improves the grade of iron in pellets.?4?The amount of bentonite can be reduced from 2%to 0.75%by partially replacing bentonite with 0.75%of SL,and 0.75%of CaCO₃ as well as 0.5%of SL can be used as binder to replace bentonite completely.Using 0.5%SL and 0.75%CaCO₃as binder can completely replace bentonite,and the wet pellet drop strength,compressive strength and the compressive strength of dry ball can be completely replaced by bentonite.The compressive strength of wet pellets,dry pellets,preheating pellets and roasted pellets are 4.2times/?0.5m?,11.5N/pellet,23.7N/pellet,522.5N/pellet,2610.3N/pellet,respectively,and the strength of each stage pellets can reach the minimum requirement of production.