Full-scale Pore Size Distribution Of Uranium-bearing Sandstone And Evolution Of Pore Structure During Acid Leaching

The pore structure of uranium-bearing sandstone contains pore-fracture dual medium,which has strong heterogeneity.This complex characteristic has an important influence on the migration of leaching solution and uranium leaching.Therefore,this paper takes the uranium bearing sandstone of a uranium deposit in Yili Basin as the research object,through literature research,field sampling and data collection,combined with a variety of indoor petrophysical and chemical analysis and acid leaching experiments.The mineral composition,pore size distribution,heterogeneity and the influence of pore types on porosity and permeability of this kind of sandstone are studied.In the process of acid leaching,the evolution characteristics of the micro pore structure of the uranium bearing sandstone and its main controlling factors are analyzed,so as to provide theoretical guidance for improving the uranium leaching rate of the uranium bearing sandstone and making a reasonable,efficient and green mining plan,and provide reference for the analysis of the influence of groundwater on the carbonate rock foundation and tunnel engineering.The main research contents and conclusions are as follows:（1）The full-scale pore size distribution curve of uranium-bearing sandstone was obtained by combining nitrogen adsorption and nuclear magnetic resonance experiments.The intergranular pores of about 60nm and 1μm are the main pore types of the uranium bearing sandstone,which control the porosity,and the cumulative pore volume is positively related to the permeability of the rock.However,the dissolution pore has no obvious correlation with its permeability,but it affects the recovery of sandstone type uranium deposits.（2）Through the analysis of the micro pore heterogeneity and interlayer heterogeneity of sandstone,the variation trend of the relative deviation of different pore structure parameters of sandstone is inconsistent,and the pore morphology is greatly different and variable.The smaller the pore size of sandstone,the stronger the heterogeneity of micro pore.The larger the difference of pore size distribution among sandstones,the stronger the interlayer heterogeneity of uranium bearing sandstone.This kind of heterogeneity leads to the change of permeability in the horizontal direction,which provides a basis for setting well spacing parameters reasonably.（3）The acid leaching experiment of uranium bearing sandstone is carried out.The uranium concentration in the leaching solution of this kind of uranium deposit follows the law of exponential function.Combined with the analysis of porosity change process,the acid leaching process can be divided into three stages.The first and second stages are the deposition plugging controlled by surface chemical reaction,in which the first stage is the main completion stage of uranium replacement accompanied by CaSO₄ saturated precipitation,and the second stage is the precipitation of Fe（OH）₃ and Al（OH）₃.The third stage is physical diffusion controlled micro particle plugging.Through the blocking mechanism and main control factors in different stages,the anti-blocking measures can be accurately formulated.（4）The pore size distribution of each leaching stage was analyzed.In the first stage,a large number of dissolution pores were produced,and the intergranular pores with small pore size were blocked by precipitates,and the connectivity between pores was weakened,which hindered the flow of leaching solution.In the second stage,the number of intergranular pores and dissolution pores increased,and the permeability increased.In the third stage,intergranular pores expand and run through,but some of the dissolution pores are blocked by particles,and the total pore volume is reduced,which eventually slows down the transport speed of solute in the leaching solution and affects the recovery of uranium leachate.