Studies on the Chemical, Physical and Mechanical Properties of Different Iron Ore Pellets Prepared under Different Conditions

Abstract

Bentonite is universally accepted silicate-based binder for iron ore pelletization process. However, it is considered as an impurity due to its high amounts of SiO2 and Al2O3 content and these acidic oxides have an adverse effect on the economy of the iron production. Due to this fact that the focus has been shifted in the use of organic binders to make pelltes but most of the organic binders failed to impart enough mechanical strength in the fired pellets as a result of insufficient slag bonding and thus they did not get widespread application in the industry.
The aim of the present work is to replace bentonite binder by molasses for the pelletization process because molasses is cheaply and abundantly available in the country and is free from the impurities like SiO2 and Al2O3. It may be a potential solution to overcome the insufficient compressive strengths of fired iron ore pellets. The pellet quality not only depending on the binder also infulenced by the iron ore nature associated with their chemical composition and their subsequent heat treatment to pellets. So that that in the present study five hematite iron ore (Essel, OMC, PTA, Kirandul and Bacheli ) samples were used for pelletization process. The resulted iron ore pellets were fired at different temperatures in the range of 1173-1573K for 1-3 hr. The performances of the binders on pellet qualities, such as moisture content in green pellet, green and dried pellet drop number, compressive strengths (green, dry and fired pellet), porosity (dried and fired pellets) and degree of reduction has been investigated.
The results showed that the molasses added iron ore pellets exhibited good green iron ore pellets than those bentonite added iron ore pellets. The drop number values and green pellet compressive strengths of the molasses added iron ore pellets exhibited a high values than the bentonite added iron ore pellets even though molasses added iron ore pellets have lower moisture contents, it is due to the viscous nature of the molasses. The highest values being in the Essel green hematite iron ore pellets followed by OMC, PTA, Kirandul and Bacheli iron ore pellets. The compressive strength of the iron ore pellets increased with increasing firing temperature and time. The most significant affect was observed in their strengths at above the firing temperature of 1373K. The molasses added fired hematite iron ore pellets were found to have slightly higher compressive strength values than those for bentonite added iron ore pellets. The industrially sufficient compressive strength was obtained for the pellets fired at only 1523K with the addition of 4 wt.% Molasses, the firing temperature was lowered by the increasing the addition of .molasses up to 6.0 wt.%. In all the conditions, Bacheli and Kirandul iron ore pellets exhibited a highest compressive strength values than the remaining studied iron ore pellets.
Reduction behaviour of the fired hematite iron ore pellets also studied along with their reduction kinetics. The degree of reduction of fired hematite iron ore pellets were found to decrease with increase of their gangue (mainly SiO2) contents due to the formation of fayalite (Fe2SiO4) phase. The formation of fayalite phase was confirmed through the SEM and XRD analyses. The reduction results were well fitted in a1-(1-α) 1/3 = kt equation. The activation energy values of the studied reduced fired hematite iron ore pellets were calculated to be in the range of 42-120 kJ mol-1 and these activation energy values were comparable to the values of indirect reduction reactions, indicating the present overall reduction to be controlled by the reduction of iron ore by CO gas. The activation energy values of bentonite added reduced iron ore pellets were found to be higher (57-120 kJ mol-1) than those of the molasses added reduced iron ore pellets (42-90 kJ mol-1). The activation energy values of the studied iron ore pellets got increased with rise of their firing temperature and time due to their lower reduction rates