Study on dynamic adsorption characteristics of gangue to heavy metals in goaf and its water purification mechanism under leaching condition

Abstract

Arid and semi-arid mining areas in Western China are faced with the problems of water shortage, large water inflow of mines and high-salinity of mine water. When the broken gangue is backfilled to the goaf by the solid backfilling mining technology, a large number of voids between the blocks is generated, which can store groundwater and purify water quality. In this study, the real void structure of the gangue backfilling body in the goaf was obtained through CT scanning. By using the COMSOL numerical simulation software, a coupling model of Free and Porous Media Flow and Transport of Diluted Species in Porous Media was established. From the mesoscopic void scale, the effects of particle size distribution, inflow velocity and ion concentration on the flow field characteristics, ion migration and dynamic adsorption characteristics of gangue in the leaching column were explored, and the purification mechanism of broken gangue to heavy metals in mine water was revealed. The results show that: (1) The larger the gangue particle size gradation, the larger the void size, the higher the velocity in the void, and the more significant the average flow velocity difference between the void area and the gangue area. With the increase of inflow velocity, the average velocity in the gangue area and void area also increases, but the average flow velocity in the void area is 5.36 times that in the gangue area; (2) Both the larger particle size gradation of gangue, higher inflow velocity and inlet concentration can improve the velocity of the ion migration in gangue leaching column; (3) The greater the inlet concentration, the faster the flow velocity, the higher the total adsorption rate of gangue in the leaching column; (4) Both decreasing the particle size gradation of the gangue and increasing the inlet concentration can increase the total adsorption capacity of gangue in the leaching column; (5) The removal of heavy metals by gangue is the result of physical adsorption, ion exchange and other reactions. The research results can provide theoretical reference and data support for the treatment of high-salinity mine water in mining areas of Western China.