**3.3. Pelletizing experiments**

**Figure 14.** The weight loss versus time obtained from the electrical furnace and the microwave oven.

96 Iron Ores and Iron Oxide Materials

**Figure 15.** XRD patterns of the raw and the calcined siderite.

The green pellets were obtained by pelletizing machine which has a disc diameter of 60 cm and an angle of 50° and operated at a speed of 20 rpm. Pellets were produced by adding bentonite in proportions of 8, 10, 12% by weight into the raw and calcined ore. The mixture conditions are given in **Table 8**. The best pellet strength results were obtained for the calcined siderite sample with 10% bentonite addition which had been subjected to 90 min in mill.

**Figure 16** indicates the raw pellets which were obtained from the raw and calcined siderite.

Examples of product pellets which were obtained using the electrical chamber furnace are given in **Figure 17**. After heating process, there was no visual difference observed between the pellets made with the raw siderite and the calcined siderite.

The SEM images belonging to the pellets obtained by mixing the siderite and 10 wt% bentonite are given in **Figure 18**. Trigonal crystals were observed in the SEM images, indicating the recrystallized hematite minerals. It can be said that the pellet heating process is performed at the proper temperature.

The resulting product pellets were subjected to a compressive strength test at a constant loading rate of 10 mm/min according to ISO/TC 102/SC 3 ISO 4700: 2015 coded standards of the International Organization for Standardization. The data obtained in the test result are presented in **Table 9**. According to the results, the pellets with the highest compressive strength obtained from the raw material added with 10% bentonite and milled for 90 min after being calcined.

The compressive strengths of the obtained pellets are shown on the graph in **Figure 19**. As it can be seen in the graph pellets obtained from calcined ores have more strength than that obtained from uncalcined ore. The improvements in the milling parameters of the calcined


**Table 8.** Raw materials and clay rates used in pelletizing.

**Figure 16.** The pellets obtained from the raw and calcined siderite.

siderite ore was further reduced the size distribution in the raw material, making it possible to do more durable pellets. The smaller the size distribution in a raw material, the more resistant the pellets to be obtained from it [18].

The most basic way to increase the specific surface area is milling operation. In the previous sections, we have mentioned that grinding is not a very economical process in terms of both machineequipment and energy costs, and that work should be done in large grain sizes as possible. For this reason, in order to investigate the possibility of using large grain size materials for pellet production, an urea (30% by weight) was added into the raw siderite with the size of the −150 + 75 μm, which cannot be pelletized by conventional methods. The mixture was put into the microwave oven with a frequency of 900 W for 5 min. The photo of the pellets is given in **Figure 20**.

The pellets which were obtained by this method had very high porosity. It is very advantageous to use large-sized material as pellet raw material. For example, with the aid of a sieve to be used after grinding, the product can be divided into two different fractions. The small size fractions may be fed to the conventional pelletizing plant and the large size may be fed into the microwave pelletizing plant.

**Figure 18.** SEM images of the pellets.

**Sample type and grinding time Clay ratio (%) Density (g/cm3**

**Table 9.** Pellet compression strengths according to pellet diameters and clay rate.

Raw siderite 90 min 8 4.05 129 146 153 179 199

Calcined siderite 60 min 8 4.38 139 147 156 168 189

Calcined siderite 90 min 8 3.86 155 159 164 169 198

**) Pellet diameter (mm)**

10 3.77 155 164 179 191 211 12 3.52 139 152 160 167 200

10 4.28 159 162 166 176 205 12 4.06 149 154 165 182 213

 3.84 174 190 192 200 207 3.84 199 215 225 232 268 3.81 149 183 205 230 258 3.75 142 144 146 156 171

**9 10 11 12 13**

Calcination and Pelletizing of Siderite Ore http://dx.doi.org/10.5772/intechopen.72808 99

**Compressive strength (kgf)**

**Figure 17.** The products pellets.

**Figure 18.** SEM images of the pellets.

siderite ore was further reduced the size distribution in the raw material, making it possible to do more durable pellets. The smaller the size distribution in a raw material, the more resistant

The most basic way to increase the specific surface area is milling operation. In the previous sections, we have mentioned that grinding is not a very economical process in terms of both machineequipment and energy costs, and that work should be done in large grain sizes as possible. For this reason, in order to investigate the possibility of using large grain size materials for pellet production, an urea (30% by weight) was added into the raw siderite with the size of the −150 + 75 μm, which cannot be pelletized by conventional methods. The mixture was put into the microwave oven with a frequency of 900 W for 5 min. The photo of the pellets is given in **Figure 20**.

The pellets which were obtained by this method had very high porosity. It is very advantageous to use large-sized material as pellet raw material. For example, with the aid of a sieve to be used after grinding, the product can be divided into two different fractions. The small size fractions may be fed to the conventional pelletizing plant and the large size may be fed

the pellets to be obtained from it [18].

98 Iron Ores and Iron Oxide Materials

**Figure 16.** The pellets obtained from the raw and calcined siderite.

into the microwave pelletizing plant.

**Figure 17.** The products pellets.


**Table 9.** Pellet compression strengths according to pellet diameters and clay rate.

by adding different bentonite ratios (8, 9, 10, 11, 12%) to the raw siderite and the calcined siderite which were milled for 90 and 60 min, respectively. The raw pellets were heated at a temperature of 1300°C which is the recrystallization temperature of hematite. Recrystallization was confirmed by SEM images and the process was confirmed to be successful. The product pellets were tested for compressive strength. The highest level of pellet strength was determined from the material obtained by grinding calcined siderite for 90 min. This pellet, which has a maximum strength value of 268 kgf, has an average durability of 28% higher than the pellet made of the raw siderite.

Calcination and Pelletizing of Siderite Ore http://dx.doi.org/10.5772/intechopen.72808 101

**1.** Calcination treatment caused big difference in the grinding behaviours of the ore. It has been found that the milling of the ore after calcination is much easier than the raw siderite. **2.** The 31.01% weight loss material that was obtained from the calcination process with the conventional heating method will have great benefits from cost of transportation both in

**3.** It has been determined that the most suitable calcination process for siderite ore is to be

**5.** The raw siderite was treated by microwave radiation (P: 900 W, f: 2.45 GHz) but neither

**6.** The addition of the 30 wt% sucrose into the raw siderite before the irradiation of microwave increased the temperature up to 1100°C in a 3 min. The XRD result showed that the calcination was successfully accomplished in 3 min by microwave. However, in terms of magnetic susceptibility balance, microwave-derived calcined siderite has lower values of

**7.** Pellets obtained from calcined ores have more strength than that obtained from uncalcined ore. The highest compressive strength was obtained with addition of 10% bentonite and ground for 90 min. The highest compressive strength of this pellet is determined as 268 kgf.

**8.** As it is known, the strength of the pellets, which are blast furnace charging materials, determines the charge amount of the furnaces. The material charge to the blast furnaces is such that the pellets at the bottom end are not broken. More durable pellets were obtained

**9.** Pellets with the addition of 30 wt% urea admixture into the coarse size of −150 + 75 μm the siderite ore were obtained using microwave. This method is promising in terms of the

This research was supported by Inonu University with the project numbers of 2015/54 and

**4.** The calcination process increased the Fe content from 37.25 to 55.61%.

The results obtained in this study are listed below:

the plant and outside of the plant.

carried out at 700°C for 15 min.

heating nor weight loss was detected.

about 23% than the conventional method.

in the present study.

**Acknowledgements**

2016/120.

reducing the grinding costs.

This pellet is about 28% more durable than the others.

**Figure 19.** The effects of the bentonite ratio on the compressive strength of the pellets.

**Figure 20.** 30% by weight urea-added pellet obtained by microwave irradiation.
