| Acid in-situ leaching（ISL）is used as an in-situ mining technology to minimize surface disturbance.It has become the main mining method of uranium deposits in China.Uranium leaching migration is difficult to analyze because it occurs in underground seams.In order to optimize the scheme of ISL,it is necessary to predict the leaching migration characteristics and leaching area of uranium.Numerical simulation is an effective means to predict the process of in-situ leaching.It can provide suggestions for optimizing ISL.In this thesis,the reactive transport modelling（RTM）coupled with water-rock reaction of ISL mining is investigated in both theory and practical application.The study on theory includes the influence of main impurity minerals（calcite,pyrite,hematite）and reaction kinetics on uranium leaching.The study on practical application includes taking the field ISL test in Bayan-Uul as an example,a hydrodynamic field-chemical field coupling RTM was constructed to analyze the dynamic migration of uranium.1)Based on batch leaching test,the mechanism of impurity minerals affecting uranium leaching was discussed by reaction path simulation,and the time-space characteristics of impurity minerals influencing uranium leaching chemical field was discussed by reaction transport simulation.The results show that:a)Calcite,hematite,pyrite and uranium minerals compete for acid from strong to weak,in which pyrite dissolves weakly and the generated low-valent sulfur and Fe2+reduce the Eh value of leaching solution to reduce uranium leaching,while hematite affects uranium leaching by consuming acid and promoting pyrite dissolution.b)In time,impurity minerals make the dissolution and migration of uranium lag in different degrees.The cycle of dissolution-precipitation of uranium was prolonged and the leaching rate of uranium was reduced.c)In space,impurity minerals reduce the dissolution range of uranium minerals,increase the precipitation amount of uranium dissolution-precipitation cycle and prolong the leaching time of U（Ⅵ）migration.2)A group of ISL mining units with four injection wells and one production well were taken as an example to compare the results of thermodynamic equilibrium and reaction kinetics of water-rock reaction in the numerical model.The result showed that:a)the test results of uranium leaching are close to those of the reaction kinetic simulation,but quite different from those of thermodynamic equilibrium simulation.The reaction kinetic model can better reflect uranium leaching than thermodynamic equilibrium model.b)At the same time,the thermodynamic equilibrium model compared with the reaction kinetics model of leaching area is larger,more leaching uranium deposit amount,uranium leaching time shorter.It is predicted that the degree of uranium mining in ore-bearing strata and the concentration of leached uranium are higher,short time needed for mining,lead to overestimate the uranium leaching rate and underestimate the mining time.Therefore,reaction kinetics optimizes the expression of water-rock reaction rate than thermodynamic equilibrium,which makes the simulation closer to reality.3)RTM based on field test can reproduce the dynamic evolution of fluid and the dynamic release of uranium in pumping-injecting unit.Simulation result shows that the leaching area of uranium ore is much larger than that of acidification.The pollution plume of uranium and acidic water is larger than that of leaching area of uranium.Sensitivity analysis confirmed that the volume fraction and reaction rate of uranium ore were the main factors of uranium leaching.Fe2+in the leaching ions had a significant negative effect on uranium leaching. |
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