Assessment of soil and groundwater pollution risks from coal gangue backfilling: A case study in Inner Mongolia...

This study evaluates the environmental risks of coal gangue (CG) filling through leaching experiments and numerical simulation methods. The results show that under acidic conditions, the leaching concentration of heavy metals in CG is relatively high, with copper concentration reaching 0.80 mg/L, exceeding Class I discharge standards. Under neutral conditions, the leachate indicators meet national standards. Although the reclaimed soil meets the agricultural land standards, its fertility level is relatively low (soil quality index 0.416), and cadmium, due to its high toxicity coefficient, becomes the primary ecological risk factor. The use of a layered compaction process can effectively control the migration of leachate. Numerical simulations indicate that the maximum migration depth of pollutants is 17 m, with concentrations stabilizing after 2500 days. The high mineralization of groundwater is primarily influenced by the geological background values, and the fluoride contamination plume has a diffusion range of less than 204 m. The study suggests that engineered CG filling reclamation presents controllable environmental risks and resource utilization potential. However, it is important to note that the study has limitations, such as a short monitoring period and uncertainties in the model predictions. It is recommended to conduct long-term field monitoring to comprehensively assess the environmental impact.