# Study on Fluorine Pollution in a Slag Yard
## 6 Conclusions  
In this paper, a large-scale three-dimensional numerical simulation method to investigate the fluorine pollution near a slag yard was implemented. The large-scale three-dimensional numerical simulation method included experimental investigation, laboratory studies of solute transport during absorption of water by soil, and a large-scale three-dimensional numerical simulation of solute transport. Experimental investigations were performed, and the test results showed that the concentrations of fluorine from smelting slag and construction waste soil exceeded the discharge limit of 0.1 kg/m\({}^{3}\) of the China criterion. The key parameters of the materials used for numerical simulation were determined based on the experimental investigation, the laboratory studies, the soil saturation of survey results, and back analyses. A large-scale two-dimensional numerical simulation and a large-scale three-dimensional numerical simulation of solute transport were implemented, and their results were compared to the experimental results. The following conclusions were made.  
(1) The simulation results showed that the clay near the slag had high saturation of approximately 0.9, which was consistent with survey results.  
(2) Comparison of the results showed that the numerical simulation results of solute transport and test results were basically identical. Thus, the numerical simulation results could be used as the basis of groundwater environment evaluation.  
(3) Over 100 years of simulation, the pollution plume from the slag field migrated outward slowly. The dispersion velocity near the groundwater was so large that the fluorine concentration in the groundwater did not increase with time. The final fluorine concentration in the groundwater 100 years after disposal started did not exceed 0.001 kg m\({}^{-3}\), the legislative upper limit of the second-grade water of China. The maximal pollution water range from the slag yard to the south, 52 years after disposal started, was approximately 185 m, and the range 100 years after disposal started was approximately 330 m. The maximal pollution water range from the slag yard to the west, 52 years after disposal started, was approximately 75 m. The range 100 years after disposal started was approximately 135 m. The maximal pollution water range from the slag yard to the east, 52 years after disposal started, was approximately 60 m, and the range 100 years after disposal started was approximately 80 m.  
To compare with the study in the literature, a large-scale three-dimensional numerical simulation of groundwater fluoride concentration was performed, and the maximal fluoride pollution water range was attempted to be determined based on a large-scale three-dimensional numerical simulation of groundwater fluoride concentration for the first time.  
Conceptualization, L.W.; methodology, L.W.; validation, L.W. and S.S.; formal analysis, L.W.; investigation, L.W. and S.S.; resources, S.S.; data curation, L.W. and S.S.; writing--original draft preparation, L.W.; writing--review and editing, L.W.; visualization, L.W.; supervision, C.W.; project administration, C.W., funding acquisition, S.S.  
This research was funded by the National Natural Science Foundation of China, grant number 51074152.  
The author would like to thank for the help from project (51074152) supported by National Natural Science Foundation of China and the help from the project supported by Kunming Prospecting Design Institute of China Nonferrous Metal Industry.  
The authors declare no conflict of interest.