## 4 Conclusions and Perspectives  
In this study, we evaluated the sorption effect of sediment DX on Mn(II) in the Daxin manganese mining area and explored the importance of microorganisms on heavy metal sorption. It is confirmed that microorganisms abundant in natural sediments and iron and manganese oxides play a key role in the removal of Mn(II). Due to the uncertainty and continuous dynamic changes of natural systems, the process of heavy metal sorption by soils is extremely complex. In this study, the dynamic process of heavy metal sorption  
Figure 11: Chemical morphology analysis of manganese before and after sorption. where “Absorbent” refers to a sample after a single sorption, and “Repeated times” refers to a sample after six repetitions.  
Figure 12: Proportion of each chemical form of adsorbed manganese after deducting background values.  
was investigated, providing a scientific basis for the in-situ remediation of heavy metal pollution. The main results obtained in this study are as follows.  
1. The sorption capacity of Mn(II) differs greatly among different soil sample types. When the sediment dosage was 10 g:L\({}^{-1}\), DX has a good effect on Mn(II) removal and the final removal rate up to 84.85%. Its sorption performance was much higher than that of LB and XY.
2. The sorption process follows the [PERSON] model (R\({}^{2}\) = 0.994) and [PERSON] model (R\({}^{2}\) = 0.936-0.984). The sorption process is mainly based on multi-molecular layer chemisorption, which is jointly influenced by the adsorbent and adsorbent mass.
3. Environmental factors had a significant effect on the Mn(II) sorption process. In a certain range, the increase of temperature, sediment dosage(4-12 g:L\({}^{-1}\)) and pH were favorable to promote the sorption of Mn(II) by the sediment DX.
4. After five repetitions of sorption, the sorption sites of DX reached basic saturation when the sediment dosage was 10 g:L\({}^{-1}\). Meanwhile, in mixed heavy metal solutions, the presence of Pb\({}^{2+}\), Zn\({}^{2+}\), Cu\({}^{2+}\) and Fe\({}^{2+}\) coexisting cations all inhibited the sorption of Mn(II), especially Zn\({}^{2+}\).
5. Microorganisms played a key role in the process of heavy metal sorption and Fe-Mn oxide generation. The addition of NaN\({}_{3}\) inhibited the activity of microorganisms in the soil, and the content of exchangeable and carbonate-bound manganese increased, while the content of Fe-Mn bound state decreased.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12073368/s1](https://www.mdpi.com/article/10.3390/app12073368/s1)]([https://www.mdpi.com/article/10.3390/app12073368/s1](https://www.mdpi.com/article/10.3390/app12073368/s1)), Figure S1: Air-dried sediment and sieved sediment, Table S1: Relative abundance of 16S rRNA gene sequences classified to genus levels.  
Conceptualization, F.Y. and Y.T.; methodology, F.Y.; software, P.L.; validation, L.J., Y.Y. and F.Y.; formal analysis, F.Y.; investigation, F.Y.; data curation, F.Y.; writing--original draft preparation, F.Y.; writing--review and editing, Y.M. and Y.T. All authors have read and agreed to the published version of the manuscript.  
This study was financially supported by the National Natural Science Foundation of China (No. 51668006); the Foundation of Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control, College of Light Industry and Food Engineering, Guangxi University (No. 2019 KF29); the Innovation Project of Guangxi Graduate Education (No. YCSW2021015 and No. YCBZ2021016).  
Not applicable.  
The authors declare no conflict of interest.