Improvement Of Compound Binder And Its Influence On The Pellet Quality Of Aoshan Iron Concentrate

The binder used in the production of pellets in China is mostly bentonite,which is hydrophilic and has a strong bonding effect after expansion in water.This can dramatically improve the balling performance of pellets.However,a high proportion of bentonite can affect the grade of pellet ore,causing adverse effects,including an increase in the coke ratio,carbon emissions,and smelting costs.To reduce the proportion of bentonite added,organic binders and bentonite are used in combination,which can not only reduce the amount of bentonite used but also improve the performance of pellets.Notwithstanding,the addition of organic composite binders will decrease the compressive strength of heated and completed pellets.This paper aims to address the issue of decreased compressive strength in both preheated and finished pellets by utilizing a composite binder of bentonite and organic adhesive during the pelletization process.The experiment employed magnetite concentrate as the feedstock for pelletization,with Indian bentonite serving as the inorganic binder,and carboxymethyl cellulose sodium acting as the organic binder,to investigate the effect of using inorganic binder and composite binder respectively on the performance of pellets.The results of adding inorganic binders separately indicate that when 1%bentonite is added,the drop strength of the pellets is only 1.5 times/(0.5m),the compressive strength is 8.2 N·P-1,the bursting temperature is 550°C,the compressive strength of preheated pellets is 534.5 N·P-1,and the strength of the finished pellets is 3121.2 N·P-1.When 1% bentonite and 0.12% sodium carboxymethyl cellulose are compounded,the ball-making effect is improved,and the performance of the green pellets is greatly improved.In addition the drop strength of the pellets can be increased to 8.0 times/(0.5m),and the compressive strength can be increased to11.3 N·P-1.However,the bursting temperature decreases to 395°C,the compressive strength of preheated pellets decreases to 326.2 N·P-1,and the strength of the finished pellets decreases to 2465.1 N·P-1.Vermiculite was added to organic binders used in the production of balls to increase their strength.Experimental results showed that the addition of 0.03%vermiculite had the best effect,and the compressive strength of both preheated and finished balls was significantly improved.The compressive strength of preheated balls increased from 326.2 N·P-1to 423.1N·P-1,with an increase of 29.7%.At the same time,the strength of finished balls increased from 2465.1 N·P-1to 2764.4 N·P-1,with an increase of 12.1%.The drop strength of the balls reached 6.5 times/(0.5m),the compressive strength was 13.4N·P-1,and the bursting temperature was 362 oC,which met the production requirements for balls.The results of SEM and thermogravimetric analysis indicated that vermiculite expansion could fill the pores in the ball resulting from the high-temperature combustion and volatilization of organic binders.Additionally,vermiculite could participate in high-temperature consolidation reactions similar to those of bentonite,thereby improving the compressive strength of the finished balls.