# Application of Waste Tire Carbon for Iron-Containing Dust Reduction in Industrial Processes
## 3 Results
### Laaching of Heavy Metals  
The TCLP results are shown in Figure 10, where labels 1 and 2 represent the raw materials and the residues after the reaction, respectively. The effect of different heating methods and raw materials on the leaching levels of various metals varies. The heating method has little effect on the leaching levels of six metals except for Al. After the reduction reaction, the leaching amount of Ca significantly increases, while those of Mg and Zn significantly decrease. The IBD raw materials contain a certain amount of CaCO\({}_{3}\), which exhibits lower leachability under acidic conditions compared to CaO [56]. During the high-temperature carbothermal reduction process, CaCO\({}_{3}\) partially decomposes into more leachable CaO, leading to an overall increase in Ca leaching from the residue. Notably, the SGD-A1 group, with a higher f-CaO content, showed greater Ca leaching than other materials. Mg and Zn can volatilize in metal form during the carbothermic reduction process [57; 58]. A higher reduction degree promotes more complete conversion to their elemental forms, resulting in lower leaching concentrations. Given its higher activity, Mg shows a more pronounced difference in leaching before and after the reaction. For Al, it forms AlFe\({}_{6}\)Si with Fe and Si. Since Fe-Al-Si is a negative deviation system with Fe having the largest negative deviation, it can increase the activity of Al [59]. When the reduction reaction is relatively complete and the Mfe content is high, the activity of Al in the multicomponent system approaches that of metallic Al. However, since the temperature is below 1600 \({}^{\circ}\)C, most of the aluminum phases remain inert, mainly existing in an amorphous form, which has higher solubility than crystalline phases [60; 61]. Consequently, the higher Mfe content in the residue corresponds to increased Al leachability. Figure 10a shows the Al leaching differences before and after reduction and indicates the order of reduction degree as FH > MH > PH. In Figure 10b, the FH2 group, which has the highest Mfe content, exhibits the highest leaching of Al, further confirming this point.  
The leaching level of Mfe is very low, while the leaching amount of FeO increases over time [62]. In Figure 10b, since Fe in CC-A and SGD-A is mostly reduced  
Figure 10: TCLP leaching level of seven kinds of metals from reduced residues: (**a**) heating methods; (**b**) different materials.  
only to FeO, the Fe leaching amount is higher than that in FH2, with the order being CC-A > SGD-A > FH2, which is inverse to the reduction degree of Fe.  
As shown in Table 4, it is worth noting that although the leaching amounts of Cr and Cu in the raw materials are relatively low, their leaching levels in the reduced residues still show a slight increase. Furthermore, the leaching amount of Cr in all experimental groups exceeds the standards [63], with an average post-reduction increase of 117.60%. In contrast, Cu and Zn are within the permissible limits. Therefore, the residues after the reaction still require a further removal of Cr before they can be safely utilized. Given the presence of Al, Si, and Ca in the residue, geopolymerization can be considered after the magnetic separation of Fe. This allows Cr ions to undergo ion exchange with Na+ and Ca2+, leading to their immobilization [64].