## 3 Results and Discussions
### Effect of Operating Variables  
#### 3.2.1 Sorption Performance and Equilibrium Time  
The effect of contact time on the sorption of Mn(II) by DX, LB, and XY samples is shown in Figure 2. The sorption capacities of Mn(II) varied greatly among samples, and the final sorption effect of each experimental group was DX (4.42 mg\(\cdot\)g\({}^{-1}\)) > LB (2.99 mg\(\cdot\)g\({}^{-1}\)) > XY (0.63 mg\(\cdot\)g\({}^{-1}\)). The final Mn(II) removal rate of DX was as high as 84.85%, and its  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Temperature** & **pH** & **DO** & **Conductivity** & **Turbidity** & **NH\({}_{4}\)\({}^{+}\)** & **TP (mg\(\cdot\)L\({}^{-1}\))** & **Mn(II)** \\ (\({}^{\circ}\)C) & **pH** & **(mg\(\cdot\)L\({}^{-1}\))** & **(\(\mu\)s)** & **(NTU)** & **(mg\(\cdot\)L\({}^{-1}\))** & **TP (mg\(\cdot\)L\({}^{-1}\))** & **(mg\(\cdot\)L\({}^{-1}\))** \\ \hline
22.6 & 7.3 & 6.6 & 832 & 2.61 & 14.3 & 0.05 & 3.85 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic water quality of streams at sampling sites in manganese mining areas.  
Figure 1: Analysis of Daxin sediment properties. Soil texture classification (**a**); microbial community composition (**b**).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Organic Matter** & **pH** & **CEC** & **Moisture** & **SiO2 (\%)** & **Al2O3 (\%)** & **CaO (\%)** & **MnO (\%)** & **Fe2O3 (\%)** \\ (g/kg) & **pH** & **(cmol\(\cdot\)kg\({}^{-1}\))** & **(cmol\(\cdot\)kg\({}^{-1}\))** & **(cmol\(\cdot\)kg\({}^{-1}\))** & **(cmol\(\cdot\)kg\({}^{-1}\))** & **(cm\(\cdot\)kg\({}^{-1}\))** & **(cm\(\cdot\)kg\({}^{-1}\))** & **(cm\(\cdot\)kg\({}^{-1}\))** \\ \hline
28.5 & 7.62 & 14.21 & 46.38 & 48.4 & 6.38 & 6.08 & 5.28 & 4.86 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Basic physicochemical properties of sediments in the manganese mining areas.  
sorption performance was much higher than that of LB and XY. In particular, the DX river sediment was loaded with manganese for a long time, and the abundance of Mn-containing microorganisms and Fe-Mn oxides were both at a high level. In addition, the sorption of heavy metal Mn(II) showed a similar trend for each soil sample. During the transient sorption stage (0-60 min), the adsorbent provided more adsorbable sites, and the sorption reaction could occur freely [33]. The contribution of this stage to the sorption of heavy metals Mn(II) was more significant, and more than 90% of manganese was adsorbed. In particular, the sorption rates of DX, LB and XY in the first 5 min of the sorption process were as high as 56.96%, 35.86% and 12.24%, respectively. Next, the gradual sorption phase (60-420 min) controlled the Mn(II) sorption rate by intra-particle diffusion in the soil particles. As the sorption reaction continues, the sorption rate decreases until the sorption sites are filled with Mn(II), finally reaching equilibrium after 720 min. During the diffusion of free Mn(II) from the surface to the interior of soil particles, complex precipitates are continuously formed on the surface and inside the soil particles, which is also an important reason for the decrease in Mn(II) concentration [34]. Preliminary results showed that DX was specific for Mn(II) sorption, so the DX was used in the subsequent experiments, and the sorption time was set to 12 h to ensure the sorption equilibrium.