| At present,bentonite is mainly used as binder in the production of iron ore pellets in China.The impurities of Si and Ca in bentonite will reduce the iron grade of the pellets.Therefore,researchers have been looking for new binder to replace bentonite as binder in pellet production.In this work,humic substance-based complex binder,was prepared from lignite mined in Southwest of China.According to the content of free humic acid,Zunyi coal,which was selected from 14 kinds of lignite collected from the Southwest of China,was prepared humic substance-based complex binder by semi-dry method.Under the optimal conditions of 25%Na OH,liquid to solid ratio 1.2:1,extraction temperature 45°C,extraction time 72 h,the extraction rate of humic acid was 41.8%,and the prepared humic substance-based complex binder could be used for the preparation of vanadium-titanium magnetite oxide pellets.The pelletizing results of single iron concentrate show that the strength of green pellets for the three single ores of A,B and C was similar to that of conventional bentonite pellets,when the dosage of humic substance-based complex binder was 0.6%.The pelletization results of mixed iron concentrate showed that the strength of green pellets for mixed iron concentrate could reach the strength of conventional bentonite pellets when the dosage of humic substance-based complex binder was 0.6%.Compared with bentonite as binder,the dosage of humic substance-based complex binder was significantly lower.Through Zeta potential,SEM,FTIR and XPS analysis,it is proved that the action mechanism of humic substance-based complex binder on mineral surface was mainly chemical adsorption.The preheating and roasting test of single iron concentrate pellets was carried out.The results showed that the compressive strength of roasted pellets for A ore and B ore could reach up to 2200 N,when the dosage of binder is 0.6%.For mixed iron concentrate,the roasted pellet strength can also reach 2200 N under optimal condiditons.Compared with bentonite pellets,humic substanc e-based complex binder needs to extend the preheating time to 16 min to make the pellet strength equal to that of bentonite.Under different preheating time,the contents of Fe O in pellets added humic substance-based complex binder and bentonite were analyzed.It was found that the preheating time for the humic substance-based complex binder needed to achieve 16 min,the Fe O content in pellets was below that of bentonite.This also illustrates the humic substance-based complex binder needs to extend the preheating time to16 min to obtain good pellet strength.XRD and SEM-EDS analysis of pellets under different preheating time also proved the above conclusion.The Amplification test for grate-kiln showd that the compressive strengthes for preheated pellet and fired pellet were respectively 405 N and 2385 N,and the the grade of iron increased by 0.95%under the optimal conditions.Compared with bentonite as binder,the strengthes of preheated ball,roasted ball and the drum index were all reduced slightly,but they could meet the requirements of industrial production and improve the grade of iron.For humic substance-based complex binder pellets,because of the low bursting temperature of green balls,it is advisable to use a lower drying air temperature when using belt roasting machine to dry the pellets.To ensure that magnetite can be fully oxidized by properly extending the preheating time to 16 min,satisfactory performance of the finished ball could be obtained.The industrial test shows that the iron grade of vanadium-titanium pellets prepared by F binder was increased by 1.0～1.5%,Si O2 content was lower by 0.5～1.0%,and compressive strength was slightly lower than that of bentonite pellets.The softening interval of pellets produced by F binder was narrower,which is beneficial to the improvement of the air permeability in the furnace.In the third stage of the test,32%organic pellets were used in the blast furnace,and the integrated grade of blast furnace was increased by about 0.5%,the utilization coefficient of blast furnace was increased by 0.279 t/m3·d,the fuel ratio was reduced by 26kg/t,and the iron loss is reduced by 4.6%. |
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