Abstract: Aiming at the unclear release mechanism of heavy metal antimony (Sb) from open-pit antimony tailings ponds
in karst mountainous areas driven by rainfall and the difficulty in quantifying environmental risks,a typical antimony tailings
yard in Dushan,Guizhou Province was selected as the research object. The objective is to reveal the response characteristics of
Sb release under different rainfall conditions (rainfall intensity,intermittency) and the geological barrier of underlying carbonate
rocks,so as to provide a theoretical basis for pollution prevention and control of tailings ponds. A self-designed rainfall simulation
device was used to conduct simulated experiments of continuous rainfall (25,50,100 mm/ h),intermittent rainfall (alternating
at 100 mm/ h) and multi-layer leaching (passing through carbonate rocks). Combined with ICP-MS,the dynamic evolution
of Sb concentration in leachate was systematically analyzed,and the release kinetics were fitted by parabolic equation,
exponential function and modified Elovich equation. The results show that Sb release has a significant initial effect,and the cumulative
release amount and release rate of Sb increase significantly with the increase of rainfall intensity. At 100 mm/ h,intermittent
rainfall significantly promotes the activated release of Sb,with a maximum increase of 109. 20 μg/ L in the intermittent period. In the multi-layer leaching experiment,the buffering effect of carbonate rocks can effectively inhibit the migration of Sb,
and the initial release concentration is reduced by 74. 7% compared with single-layer tailings. The release process of Sb presents
an obvious coupling characteristic of diffusion and chemical reaction. Rainfall intensity and intermittent mode are the key
factors driving Sb release from tailings,while carbonate rock strata have significant adsorption,neutralization and control effects
on Sb. The kinetic fitting shows that the modified Elovich equation has the best fitting effect (R2 >0. 959),indicating that Sb
release is controlled by a complex process including diffusion,dissolution and surface reaction rather than a single mechanism.
The research results provide scientific support for ecological restoration and heavy metal pollution control of open-pit tailings in
karst areas.