Environmental risk assessment of industrial byproduct gypsum utilized for flling abandoned mines

In response to the basic policy of green and low-carbon circular development to solve resource,environmental and ecological problems,gypsum is considered to be a flling material for mine backflling.To explore the potential risks of gypsum to the groundwater environment due to the backflling of abandoned mines,a sequential batch leaching experiment was carried out in this paper,which used three types of industrial waste gypsum,namely,phosphorus gypsum(PG),titanium gypsum(TG)and fue gas desulfurization gypsum(FGDG).COMSOL Multiphysics 5.4 software was used to simulate and solve the migration process of the leached metal elements in the mine foor when these three gypsum types were used as flling materials to observe the concentration distributions and difusion distances of the metal elements from these three gypsum types in the mine foor.The results show that(1)during repeated contact of the three types of industrial waste gypsum with the leaching medium,the pH levels changed,and the changes in pH afected the leaching patterns for the heavy metal elements in the gypsum.(2)Based on the concentrations of the metal elements that were leached from the three types of gypsum,it can be determined that these three types of gypsum are not classifed as hazardous solid wastes,but they cannot be ruled out with regard to their risk to the groundwater environment when they are used as mine flling materials.(3)When the three types of gypsum are used as flling materials,the concentration distributions of the metal elements and their migration distances all exhibit signifcant changes over time.The concentration distributions,difusion rates and migration distances of the metal elements from the diferent gypsum types are afected by their initial concentrations in the leachate.The maximum migration distances of Zn in the foor from the PG,FGDG and TG are 8.2,8.1 and 7.5 m,respectively.