Study On The Effect Of Main Symbiotic Minerals On Uranium Migration And Transformation And The Corresponding Kinetic Mechanism In Acid Uranium In-situ Leaching

Acid in-situ leaching uranium mining is a relatively common method of uranium mining.Although it does little harm to the surface,it will have a serious impact on the ore-bearing minerals and groundwater.The study of the effect of main symbiotic minerals on uranium migration and transformation and its kinetic mechanism in in-situ leaching environment is beneficial to the improvement of in-situ leaching uranium production technology by acid method,and enriches its basic theoretical support.It is also of great significance to the prevention and control of uranium pollution in groundwater after the decommissioning of in-situ leaching mine.In this paper,the influence mechanism of minerals on uranium migration and transformation in the process of uranium in-situ leaching was studied by means of batch experiments and spectral analysis,taking the main minerals and uranium-bearing solution of sandstone uranium deposit as the research objects in the context of acid in-situ leaching mine environment.The main research contents and conclusions are as follows:1.By means of batch experiments,the effect of pyrite,the main symbiotic mineral of pitchblende,on the dissolution behavior and mechanism of pitchblende under different environmental conditions is studied.The results show that under the condition of adding oxidizer（0.06 mol/L hydrogen peroxide）,pyrite can promote the leaching of UO₂.The presence of pyrite makes the leaching activation energy of UO₂decrease with the leaching reaction activation energy E_a=42.25 kJ/mol,and the leaching process follows the shrinkage particle model controlled by chemical reaction.The leaching kinetics equation of UO₂in the presence of pyrite is established.The reaction order of pyrite in UO₂leaching is 0.36.However,pyrite itself cannot promote the leaching of UO₂,and it will inhibit the leaching of UO₂in the absence of hydrogen peroxide.2.Based on sampling and analysis of groundwater in an acid in-situ leaching mine in Xinjiang,the variation rules and reasons of groundwater geochemical characteristics in acid in-situ leaching mine are discussed.By means of batch experiments,the immobilization behavior and mechanism of iron secondary minerals on uranium under different environmental conditions are studied with the help of SEM-EDS and XPS.The results show that the presence of Fe³⁺can inhibit the migration of U in groundwater of decommissioned mining area.In the pH range of 2 to 7,with the increase of groundwater pH accompanied by the hydrolysis of Fe³⁺U（Ⅵ）would settle down in two different forms:surface complexes and co-precipitation.In the presence of Fe²⁺,the precipitation mechanism of U（Ⅵ）will be changed.Under the action of Fe²⁺,ferrihydrite will be reduced,dissolved and recrystallized to produce needle iron ore,in which most of U（Ⅵ）will be reduced to U（Ⅴ）and embedded in the lattice structure of needle iron ore.3.The main gangue minerals（feldspar and quartz）and the main clay minerals（kaolinite,montmorillonite and illite）in the mineral-bearing aquifer are modified by using sulfuric acid,and the morphological characteristics and structural changes before and after modification are analyzed by means of SEM,N₂-BET,FT-IR and Zeta potential meter.The results are as follows:（1）The sulfuric acid modification has a significant effect on the structure of the gangue mineral.After acidification,gangue mineral surface becomes more broken,rough and loose,with obvious depressions and pores.The specific surface area of acidified feldspar increases by 1.5 times,while that of acidified quartz increases slightly.The number of functional groups on the surface of acidified minerals increases,and Zeta potential also increases slightly.（2）The sulfuric acid modification has obvious effects on the structure of clay minerals.Acidified kaolinite and acidified montmorillonite have serious edge exfoliation,and the lamellar structure is no longer obvious because of the gelation between layers.After acidification,illite presents a better lamellar structure.The specific surface area of acidified kaolinite and acidified illite increases by 1.57 times and 1.76 times respectively,and the specific surface area of acidified montmorillonite decreases to 0.83times of the original one.The number of functional groups on the surface of acidified kaolinite and acidified illite decreases significantly,while the number of functional groups on the surface of acidified montmorillonite increases.The zeta potential of acidified clay shows a small increase.4.With the help of FT-IR,XPS and other characterization means,the adsorption behavior of uranium containing minerals under different environmental conditions（pH,uranium concentration,temperature,ion concentration,etc.）before and after modification is investigated by means of batch experiments,and the mechanism of action is analyzed.The results show that the adsorption of uranium on acidified acidified rock-forming minerals follows pseudo-second order kinetic equation and Langmuir adsorption model,and is insensitive to ionic strength,indicating that surface complexation and charge-attraction-dominated monolayer adsorption are the main adsorption mechanisms for acidified feldspar and charge-attraction-dominated monolayer adsorption is the main adsorption mechanism for acidified quartz.The adsorption process of uranium by acidified clay minerals follows pseudo-second order kinetic equation.The adsorption of uranium on acidified kaolinite and acidified illite is insensitive to ionic strength and consistent with the Langmuir adsorption model.The adsorption of acidified montmorillonite is strongly influenced by the ionic strength of the solution and consistent with the Freundlich model.The main adsorption mechanisms of acidified kaolinite and acidified illite are charge attraction and surface complexation,and the main adsorption mechanisms of acidified montmorillonite are charge attraction,surface complexation and ion exchange.5.The adsorption rates of acidified feldspar,acidified quartz and acidified illite are all at a low level at pH=2,so there is no obvious influence on uranium recovery in the in-situ leaching process.The adsorption capacity of acidified kaolinite and acidified montmorillonite at pH=2 is 0.29 mg/g and 0.26 mg/g respectively,indicating that the existence of kaolinite and montmorillonite will have a certain influence on uranium recovery.Reasonable change of in-situ leaching environment or secondary mining will effectively improve the recovery rate.When the pH value is in the range of 4 to 6,the adsorption rate of minerals to uranium will increase significantly,thus the acidified minerals will hinder the migration of uranium in groundwater at the decommissioning stage of mining area,which is beneficial to the natural purification of groundwater in the mining area.