## 3 Results and Discussion  
Effects of Revegetation on the Physicochemical and Geochemical Properties Characteristics of Mining Areas  
The physicochemical and geochemical characteristics of the original smelting slag and tailings, as well as the smelting slag heap and tailing piles after revegetation treatment, were analyzed, including the basic physicochemical properties such as pH, TN, TP, and OM, and the chemical compositions such as Fe\({}_{2}\)O\({}_{3}\), Al\({}_{2}\)O\({}_{3}\), and SiO\({}_{2}\). As shown in Table 2, the untreated original smelting slag and tailings were both alkaline (pH 8.9 and 7.9, respectively). Consistent with the results of other studies [40], the pH values of both smelting slag heaps and tailings piles were significantly reduced after revegetation and showed a gradual decreasing trend with the increase in revegetation time; the pH values of RS5 and RS10 were 6.7 and 5.4, respectively. Related studies have found that plant root exudates, plant apoplasts, and their degradation products may contribute to pH reduction [40; 41], in addition to H\({}^{+}\) produced by nitrification reactions, and the release of H\({}^{+}\) and organic acids promoted by plant rooting activities can also lead to a reduction in environmental pH [42]. The content of TN in the smelting slag heap after revegetation was significantly higher than that in the unremediated slag, and the content of TN increased gradually with the extension of the revegetation time. After 10 years of revegetation, the average TN contents in the RS10 and RT10 areas were 0.95 g/kg and 1.07 g/kg, respectively, which were 2.5 and 5.15 times higher than those in the US (0.38 g/kg) and UT (0.21 g/kg) areas and were close \begin{table}
\begin{tabular}{c c c c c c} \hline
**Category** & _RAC_ & \(I_{geo}\) & EF & ER & _CRS_ & **Degree of Pollution** \\ \hline
1 & \textless{}1\% & \textless{}0 & - & - & 6 & None \\
2 & 1–10\% & 0–1 & \textless{}2 & \textless{}40 & 6–8 & Low \\
3 & 10–30\% & 1–2 & 2–5 & 40–80 & 8–12 & Moderate \\
4 & - & 2–3 & 5–20 & 80–160 & 12–15 & Considerable \\
5 & 30–50\% & 3–4 & 20–40 & 160–320 & 15–20 & High \\
6 & \textless{}50\% & 4–5 & \textgreater{}40 & \textgreater{}320 & 20–24 & Very high \\
7 & - & 5–10 & - & - & 25 & Extremely serious \\ \hline \end{tabular}
\end{table} 
Table 1: Degree of contamination and environmental risk assessment criteria for As and Sb. to the background soils (1.21 g/kg). As a dominant plant in the remediated area, _Miscanthus_ sp. can accumulate phosphorus and nitrogen nutrients in the rhizosphere [43]. In addition, related studies reported that the decomposition of plant litter and organic matter during revegetation [40; 44] and that carbon-sequestering microorganisms in the rhizosphere of plants may also increase the nitrogen content of the surrounding environment [45]. The content of TP also showed a gradual cumulative increase after revegetation, and after 10 years of remediation, the average content of TP in the RS10 and RT10 areas was 0.26 g/kg and 0.36 g/kg, respectively, which were 1.44 and 1.89 times higher compared with that in the US (0.18 g/kg) and UT (0.19 g/kg) and were gradually close to the background soils (0.42 g/kg). Similar to the results of this study, several other research on mining sites have also reported an increase in TP content after remediation [40; 44; 45], which could be attributed to the release of root exudates during revegetation that can accelerate the weathering process of minerals, such as phosphate, and thus release phosphorus [40; 44]. The positive effects of revegetation on the recovery of soil carbon sequestration have been widely reported [46; 47], and the OM content in the tailings area also showed a significant increase in this study, which is presumed to be attributed to the positive impacts of the production and decomposition of the plant litter [46].