# Utilization of Thermal-Activated Coal Gangue to Enhance the Properties of Sandy Soil Composites
## 4 Conclusions  
This study investigates the water-holding capacity and the fertilizer retention capacity of mixed soils obtained by mixing TACG with sandy soil. Some conclusions can be addressed as follows:  
1. Under the action of gangue material, the soil structure of composite sandy soil has been effectively improved, and with the increase in the proportion of gangue, in which the content of low-grain-size components gradually increased, R\({}_{0,25}\) increased significantly compared with the CK treatment, which makes the soil structure more stable [25], stronger erosion resistance, and improves the defects of the sandy soil with excessively coarse mechanical composition and poor texture.
2. With the gradual increase in the proportion of gangue incorporated, the content of fine-grained powdered soil and clay particles in the composite soil gradually increased, which led to a gradual increase in the total specific surface area of the soil particles [26], gradually improving the defects of sandy soil particles that are coarse in composition and small in specific surface area and improving the total holding capacity of the soil particles. Secondly, the gradual increase in the proportion of gangue improves the content of colloid and the mutual adhesion between soil particles in the composite soil, gradually improving the poor adhesion between sandy soil particles, the problem of loose structure, and making it easier to form the agglomerate structure, increasing the effective pore space [27]. Water can be retained in the pore space, enhancing the soil's absorption of water and retention performance.  
3. The application of gangue can increase the adsorption of nitrogen, phosphorus, and potassium nutrients in the soil to different degrees and enhance the fixation capacity of such ions in the soil. Among them, the mixed sandy soil mixed with 10% of 600--treated gangue had the most obvious increase in the adsorption effect of ammonium ions. Taken together, the application of modified gangue increased the content of exchangeable ions in the mixed soil, and by increasing the ratio of soluble state ions/exchangeable state ions in the soil [28], on the basis of mitigating the soluble state ions in the soil that are easy to be lost with water, the soil maintained a higher ionic level for a long period of time, which confirms that the application of activated gangue ash has a better fixing effect on soil fertility.  
Conceptualization, Z.G.; methodology, R.L.; software, Z.G. and A.Z.; validation, W.F. and R.L.; formal analysis, J.L. and A.Z.; investigation, J.L.; resources, W.F. and Z.G.; data curation, J.L., J.Q. and R.Z.; writing--original draft preparation, W.F. and R.L.; writing--review and editing, R.Z., R.L., X.C., J.Q., J.L., Z.G. and J.W.; visualization, W.F. and R.L.; supervision, Z.G. and J.L.; project administration, Z.G. and J.W.; funding acquisition, Z.G., W.F. and J.W. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Key Research and Development Program of Shaanxi (Grant No. 2022 GXLH-01-26), the Shaanxi Provincial State-owned Capital Management Budget for Special Project of Science and Technology Innovation (Demonstration Research on the Manufacturing Technology of Coal Gangue-based Modification Materials for Sandy Soil), and the Technology Innovation Center for Land Engineering and Human Settlements by Shaanxi Land Engineering Construction Group Co., Ltd. and Xi'an Jiaotong University (Nos. 201912131-D4, 201912131-D3, 201912131-D1).  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.  
The authors declare that this study received funding from Technology Innovation Center for Land Engineering and Human Settlements by Shaanxi Land Engineering Construction Group Co., Ltd. The funder was not involved in the study design, collection, analysis, interpretation of data, the writing of this article or the decision to submit it for publication.