Study On Fluid Characteristics Of Leaching Solution And Its Percolation In Uranium-bearing Sandstone

Nowadays,the unprecedented prosperity of the world economy depends on the rapid development of the modern industry,and the realization of modernization can not avoid the energy problem,and the solution of the energy problem can not be separated from the development of natural resources.Uranium resource is not only an efficient natural resource,but also an important nuclear fuel for nuclear power stations.At present,in-situ leaching has become the main mining method for the development of uranium resources in China,accounting for50%in 2015,70%in 2017 and 90%in 2020.Among the proven sandstone-type uranium resources in China,low permeability uranium-bearing resources account for more than 50%,and the uranium-bearing sandstone is of low grade,small scale and difficult to exploit.Therefore,in order to solve the practical problems of in-situ leaching mining of low permeability uranium-bearing sandstone and improve the leaching rate of uranium and the recovery efficiency of uranium resources,it is necessary to study the in-situ leaching flow law of low permeability uranium-bearing sandstone.In this paper,through the fluid characteristic test of the leaching solution,the fluid characteristics of the leaching solution were studied and the leaching fluid with different viscosity was prepared,and the horizontal seepage test of the cylindrical rock sample of low permeability uranium-bearing sandstone was carried out accordingly.The fluid characteristics of leaching solution with different viscosity and its percolation law in low permeability uranium-bearing sandstone were analyzed based on percolation mechanics,physicochemical percolation theory and dissolution mechanism.The main research contents and conclusions are as follows:(1)In the process of in-situ leaching of uranium,there is a continuous chemical reaction between the leaching solution and the ore,and the chemical composition of the leaching solution changes accordingly,so the leaching fluid containing uranium is not a simple Newtonian fluid or non-Newtonian fluid.It is a fluid that converts between Newtonian fluid and non-Newtonian fluid with chemical reaction.(2)the experimental study on the fluid characteristics of the leaching solution shows that the concentration of uranium in the leaching solution increases with the increase of the reaction times of the leaching solution,while the viscosity of the leaching solution increases sharply with the increase of the concentration of uranium in the leaching solution,then decreases,and finally increases slowly until it is stable.(3)The experimental results show that during the percolation process with10g/L NH₄HCO₃+10g/L H₂O₂alkaline solution as leaching agent,the osmotic pressure and permeability coefficient increase rapidly at a constant flow rate within6 hours,and this stage is in the unsaturated state of percolation.After 6 hours,the average velocity is basically constant,and the seepage flow enters a saturated state.In this state,the variation curve of permeability coefficient K and osmotic pressure P with time is symmetrical when the permeability coefficient is 1.2×10^-4cm/s and the osmotic pressure is 0.5MPa.(4)The experimental study on the percolation of leaching fluid with different viscosity in low permeability uranium-bearing sandstone shows that the percolation characteristics of leaching fluid with different viscosity in rock samples with roughly the same internal pore structure are basically the same.however,there are regular differences between saturated and unsaturated stages.The higher the viscosity of the leaching fluid is,the slower the seepage enters the saturated state,and at the same time,the seepage pressure of the leaching fluid with high viscosity is greater than that with low viscosity,but the permeability coefficient of the fluid with high viscosity is almost always less than that of the fluid with low viscosity.