Study On Dissolution Effect Of Phosphogypsum Leachate On Karst Fissures Under Concentrated Recharge And Discharge Conditions

Guizhou has accumulated a huge amount of waste slag such as phosphogypsum and gangue.In the case of improper anti-seepage measures in tailings reservoirs,it is easy to cause large-scale underground pollution problems.In this paper,the dissolution mechanism of phosphogypsum acid wastewater on fissures by using the acid leaching water of phosphogypsum tailings reservoir as the dissolution reaction carrier.Combined with the characteristics of karst aqueous medium in Guizhou,using the self-designed centralized recharge and discharge single fissure test device,and fully studying the water transport characteristics of fissures under different hydrodynamic conditions and different gap widths.Combined with the three-dimensional laser scanning system,the morphological characterization of rock surface before and after dissolution was quantitatively analyzed,the influence of leaching water on carbonate rock dissolution and related relationship laws were revealed,and a kinetic model for controlling carbonate rock dissolution reaction was established,which provided theoretical and experimental basis for the study of carbonate rock dissolution mechanism under acidic wastewater conditions,the analysis of the impact of acid water failure of foundation in karst area,and acid wastewater treatment.The main conclusions were as follows:(1)The results of the dispersion test under the condition of concentrated recharge and discharge show that the fissure water flow under the condition of centralized recharge and discharge is non-uniform flow,and the water flow profile of the fissure from recharge to discharge shows an"anti-equilibrium"state.There is a retention zone(relatively stationary zone)in the water flow of the fissure,and the tracer migration is non-Fickian phenomena,resulting in obvious tailing phenomena of the tracer penetration curve.(2)By analyzing the relationship between Ca O content,Mg O content and Ca O/Mg O ratio and dissolution amount per unit area of carbonate rock slab after phosphogypsum acid liquid dissolution erosion,it was obtained:there was a negative correlation between Ca O,Mg O and Ca O/Mg O on the surface of carbonate rock slab and the amount of dissolution.(3)By analyzing the difference in dissolution amount per unit area under different conditions,it was obtained that the dissolution amount per unit area of carbonate fracture under the same hydrodynamic conditions gradually decreased with the increase of gap width;However,the dissolution amount per unit area of carbonate fracture under the same gap width showed a trend of first increasing and then decreasing with the enhancement of hydrodynamic conditions.(4)The change of conductivity and p H of phosphogypsum leaching water before and after the analysis of carbonate rock dissolution found that with the dissolution reaction,H~+decreased,p H value increased,and conductivity decreased.(5)By analyzing the relationship between the surface roughness of carbonate fissures and the hydrodynamic conditions and fissure characteristics,it is concluded that there is a positive correlation between the root mean square slope and the amount of dissolution per unit area under different hydrodynamic and gap width conditions,and the root mean square slope parameter can accurately characterize the dissolution degree of carbonate fissures.