# Application of Waste Tire Carbon for Iron-Containing Dust Reduction in Industrial Processes
## 3 Results
### Optimal Reaction Conditions for Iron Reduction  
Under the same conditions, the reduction pathway of iron oxides with carbon as the temperature increases is as follows: Fe\({}_{2}\)O\({}_{3}\)\(\rightarrow\) Fe\({}_{3}\)O\({}_{4}\)\(\rightarrow\) FeO \(\rightarrow\) MFe [44]. From Figure 6a, it can be seen that when the SMTD / WTC is 1:1, with a protective N\({}_{2}\) flow rate of 50 mL/min and a reduction temperature of 700 \({}^{\circ}\)C, iron oxide is completely reduced to Fe\({}_{3}\)O\({}_{4}\) after 60 min of reaction. When the reduction temperature is raised to 800 \({}^{\circ}\)C, FeO starts to appear. As the temperature increases, the sample is further reduced. At 900 \({}^{\circ}\)C, the FeO content increases and is further reduced to MFe, accompanied by the appearance of sulfides such as FeS and ZnS. According to Table 2, the Ca content in SMTD is 11.75%. At this temperature, CaCO\({}_{3}\) has already decomposed to form CaO, and above 935 \({}^{\circ}\)C, the reaction is represented by Equation (2) [45], consistent with Figure 6(a5), where ZnS is converted to CaS, and the iron phase exists entirely as MFe. The FeS-CaS reaction process is shown in Equations (3)-(5). \[\text{ZnS}+\text{CaO}+\text{C}=\text{Zn}+\text{CaS}+\text{CO} \tag{2}\]  
\[\text{FeO}+\text{C}=\text{Fe}+\text{CO} \tag{3}\]  
\[\text{FeS}+\text{CO}=\text{Fe}+\text{COS} \tag{4}\]  
\[\text{CaO}+\text{COS}=\text{CaS}+\text{CO}_{2} \tag{5}\]  
Figure 6: Reduction of samples under different conditions: (**a**) XRD spectrum of different temperature: (a1) 700 \({}^{\circ}\)C, (a2) 800 \({}^{\circ}\)C, (a3) 900 \({}^{\circ}\)C, (a4) 1000 \({}^{\circ}\)C, (a5) 1100 \({}^{\circ}\)C; (**b**) XRD spectrum of different carbon ratio: (b1) 1:1, (b2) 2:1, (b3) 4:1, (b4) 9:1, (b5) 14:1, (c) XRD spectrum of different oxygen ratio: (c1) 0%, (c2) 2%, (c3) 4%, (c4) 6%, (c5) 8%; (**d**) XRD spectrum of different reaction time: (d1) 15 min, (d2) 30 min, (d3) 45 min, (d4) 60 min, (d5) 90 min; (**e**) GC results of different oxygen ratio. Due to the stability of CaS as a sulfide [46], it remains present even when the reaction temperature increases to 1100 \({}^{\circ}\)C. Additionally, the Al\({}_{0.5}\)Fe\({}_{3}\)Si\({}_{0.5}\) phase (labeled as AlFe\({}_{6}\)Si) found in the reduction residue belongs to the \(\tau\)-phase of the Al-Fe-Si ternary system and is Fe-rich. This ternary phase forms during natural cooling following the reduction reaction. Similarly, [PERSON] et al. [47] also identified this compound with 52% Fe content during the carbothermal reduction of fly ash. The natural cooling process, categorized as a semi-rapid solidification (cooling rate between 10\({}^{0}\)-10\({}^{3}\) K/s), produces dispersed AlFe\({}_{6}\)Si metastable phase particles, which are unstable at high temperatures [48]. Thus, as the reaction temperature increases to 1100 \({}^{\circ}\)C, this phase disappears. Considering both the energy loss and Fe reduction efficiency, 1000 \({}^{\circ}\)C is identified as the optimal reaction temperature. From Figure 6b, it can be seen that when the SMTD/WTC is 1:1 and 2:1, there is little difference in material morphology, with MFe primarily present, along with CaS and AlFe\({}_{6}\)Si. When the mixing ratio is 4:1, unreacted FeO begins to appear. As the ratio increases to 9:1 and 14:1, the FeO phase becomes more pronounced, while the Fe phase weakens. Due to the insufficient amount of C, there is not enough COS to react with MFe, resulting in the disappearance of the CaS and AlFe\({}_{6}\)Si phases. Considering both the reduction effectiveness and resource usage, 2:1 is identified as the optimal mixing ratio. As shown in Figure 6c, it is evident that when the O\({}_{2}\) content is between 0 and 8%, under the same conditions (reaction temperature 900 \({}^{\circ}\)C, reaction time 60 min, mixing ratio 2:1), the XRD patterns of the reaction residues are almost identical, showing no significant differences. The dominant phase is iron, with a small amount of incompletely reduced FeO, accompanied by CaS and AlFe\({}_{6}\)Si phases.