**3.2. Calcination experiments**

Thermogravimetric analysis (TGA) was used to determine the weight loss of raw siderite exposed to temperature and the result is given in **Figure 12**. Calcination experiments of siderite ore were carried at temperatures of 465-500-550-600-650-700-750-800°C. In these experiments; the effects of two different sizes, large (−14 + 4.35 mm) and small (−300 μm), calcination temperatures and duration time on the calcination yields were investigated.

The optimum calcination temperature was determined as 700°C based on the calcination experiments and the TGA graph (**Figure 12**). The weight loss depending on the duration time at 700°C is given in **Figure 13**. In the same graph, the effects of size were also investigated.

In the calcination experiments, weight loss of the siderite ore was found to be 31.01 wt%. According to above graphs, it was found that the CO2 in the siderite was completely removed from the body in terms of weight loss (calcination loss: 31.04%) at the temperature of 700°C and for 15 min and these calcination conditions were selected as a reference conditions and applied in subsequent experiments. No remarkable difference was recorded for the weight loss and magnetic susceptibility balance (**Table 7**) after 15 min at 700°C. It is therefore unnecessary to keep the calcination time longer than 15 min.

Also at this point it was found that the material grain size had no effect on the calcination process (except when it has a heat capacity that is too high to slow the heat transfer too much). The large particle size is also advantageous because it easily provides a comfortable circulation of hot air flow.

heating method, 32.14% weight loss of the siderite was detected. In microwave calcination operation, the siderite ore was mixed with the sucrose (30 wt% by weight of siderite) and the mixture was put into the microwave oven. After 3 min, the temperature of the mixture was detected as 1100°C. In the microwave heating method, sucrose was used as thermal auxiliary to heat siderite ore. The calcination results, showing the weight loss versus time, of the electrical furnace and the microwave furnace are given in **Figure 14**. Apart from the partial reduction in the magnetic susceptibility balance, the microwave oven has no disadvantages over the electri-

Calcination procedures which were carried out using the electrical furnace and the microwave oven were achieved. The results showed that necessary weight losses and high iron content in the calcined samples were obtained and the calcination process in electrical furnace and microwave oven caused the hematite transformation which was provided the magnetic properties. The chemical structure of the raw siderite and the calcined siderite in the electrical furnace and the microwave oven were checked using Rigaku Miniflex 600 XRD (Cu Kα (40 kV, 15 mA, λ: 1.54051 Å). Comparison of the XRD patterns (**Figure 15**) showed that by addition of

**/kg)**

Calcination and Pelletizing of Siderite Ore http://dx.doi.org/10.5772/intechopen.72808 95

cal furnace. On the contrary, higher weight loss was achieved.

**Figure 13.** Calcination graph of raw siderite ore at 700°C.

sucrose the siderite can be calcined by using microwave oven in 3 min.

 465 1708.16 500 17690.50 600 19780.03 700 19530.93 1100 (microwave method) 15410.03

**Table 7.** Magnetic susceptibility balance values.

**Sample no Calcination temperature (°C) Magnetic susceptibility (×10−8 m3**

Calcination experiments were also carried out in a microwave oven. Microwave oven application offers great advantages especially for short heating and calcination time [17]. In microwave

**Figure 12.** Thermogravimetric analysis (TGA) of siderite ore.

**Figure 13.** Calcination graph of raw siderite ore at 700°C.

heating method, 32.14% weight loss of the siderite was detected. In microwave calcination operation, the siderite ore was mixed with the sucrose (30 wt% by weight of siderite) and the mixture was put into the microwave oven. After 3 min, the temperature of the mixture was detected as 1100°C. In the microwave heating method, sucrose was used as thermal auxiliary to heat siderite ore. The calcination results, showing the weight loss versus time, of the electrical furnace and the microwave furnace are given in **Figure 14**. Apart from the partial reduction in the magnetic susceptibility balance, the microwave oven has no disadvantages over the electrical furnace. On the contrary, higher weight loss was achieved.

Calcination procedures which were carried out using the electrical furnace and the microwave oven were achieved. The results showed that necessary weight losses and high iron content in the calcined samples were obtained and the calcination process in electrical furnace and microwave oven caused the hematite transformation which was provided the magnetic properties. The chemical structure of the raw siderite and the calcined siderite in the electrical furnace and the microwave oven were checked using Rigaku Miniflex 600 XRD (Cu Kα (40 kV, 15 mA, λ: 1.54051 Å). Comparison of the XRD patterns (**Figure 15**) showed that by addition of sucrose the siderite can be calcined by using microwave oven in 3 min.


**Table 7.** Magnetic susceptibility balance values.

**Figure 12.** Thermogravimetric analysis (TGA) of siderite ore.

**3.2. Calcination experiments**

94 Iron Ores and Iron Oxide Materials

circulation of hot air flow.

Thermogravimetric analysis (TGA) was used to determine the weight loss of raw siderite exposed to temperature and the result is given in **Figure 12**. Calcination experiments of siderite ore were carried at temperatures of 465-500-550-600-650-700-750-800°C. In these experiments; the effects of two different sizes, large (−14 + 4.35 mm) and small (−300 μm), calcination

The optimum calcination temperature was determined as 700°C based on the calcination experiments and the TGA graph (**Figure 12**). The weight loss depending on the duration time at 700°C is given in **Figure 13**. In the same graph, the effects of size were also investigated.

In the calcination experiments, weight loss of the siderite ore was found to be 31.01 wt%.

from the body in terms of weight loss (calcination loss: 31.04%) at the temperature of 700°C and for 15 min and these calcination conditions were selected as a reference conditions and applied in subsequent experiments. No remarkable difference was recorded for the weight loss and magnetic susceptibility balance (**Table 7**) after 15 min at 700°C. It is therefore unnec-

Also at this point it was found that the material grain size had no effect on the calcination process (except when it has a heat capacity that is too high to slow the heat transfer too much). The large particle size is also advantageous because it easily provides a comfortable

Calcination experiments were also carried out in a microwave oven. Microwave oven application offers great advantages especially for short heating and calcination time [17]. In microwave

in the siderite was completely removed

temperatures and duration time on the calcination yields were investigated.

According to above graphs, it was found that the CO2

essary to keep the calcination time longer than 15 min.

**3.3. Pelletizing experiments**

the proper temperature.

calcined.

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.

Calcination and Pelletizing of Siderite Ore http://dx.doi.org/10.5772/intechopen.72808 97

**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

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 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

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

> 10 12

> 10 12

**Sample type Clay ratio (%)**

Raw siderite (90 min milling) 8

The calcined siderite (60 minutes milling) 8

The calcined siderite (90 minutes milling) 8

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

pellets made with the raw siderite and the calcined siderite.

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

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