Study On Migration And Transformation Of Clay Minerals In Ionic Rare Earth Ore Under Leaching Conditions

Rare earth elements are strategic resources in China,and are widely used in military,electronic,medical,mechanical and other fields.Ion type rare earth is mainly distributed in the south of China,and it's mining not only brings great economic benefits for China,but also brings many environmental problems.In recent years,there are more and more researches on the prevention and control of landslides and the migration and transformation of heavy metals in ion type rare earth mining areas.The spatial distribution and mechanical properties of clay minerals in rare earth mines have become the focus of research.The parent rock of the ion type rare earth ore is mostly granite,and the weathering crust is mainly composed of quartz,feldspar,clay minerals and mica.During the leaching process,due to the effect of the leaching liquid,the feldspar minerals in the weathering crust are continuously weathered and decomposed,and gradually converted into other clay minerals such as kaolinite.Due to the influence of leaching,the mechanical characteristics of the slope soil such as cohesion and internal friction angle change with the migration and transformation of clay minerals.At present,there are few problems in the systematic study of clay mineral migration and microstructure evolution during the leaching process of ion-type rare earth minerals.There are still many problems in the discussion of the formation mechanism of clay mineral structure changes and landslides in rare earth mines.Based on the analysis of the above problems,this paper takes the typical weathering crust section of granite in Longnan City of Ganzhou as the research object,through field sampling,particle size analysis,indoor simulated leaching,with the help of X-ray diffraction(XRD),transmission electron microscopy(TEM)and other modern testing methods,analyzes the regional clay mineral particle size,distribution and mineral migration and transformation of weathering crust section of granite before and after leaching The laws of migration and transformation of clay minerals in ion rare earth ore are revealed.The main understandings are as follows:(1)The analysis of the grain size and mineral composition of the granite weathering crust surface soil layer of the regional rare earth mines shows that the main clay minerals in the rare earth mines are mainly kaolinite and illite,and the content of chlorite and vermiculite is less and unevenly distributed.The distribution characteristics of weathering crust and ore particle size in the surface layer of rare earth mine are obviously controlled by chemical weathering and topography.The overall granular surface soil layer is dominated by fine particles.With the continuous progress of chemical weathering,the coarse-grained feldspar in the weathering crust accelerates to decompose,and the fine particles migrate to the lower part.(2)XRD images show that the characteristic diffraction peak of rare earth ore is 1-10 (?),the highest intensity is quartz d = 3.3532 (?),followed by kaolinite d = 3.2546 (?).Under different leaching conditions,the XRD characteristic diffraction peaks of the samples are almost the same,only slightly different in peak strength and half peak width.The higher the concentration of leaching solution is,the lower the p H is,the more unfavorable it is to the crystallinity of minerals,and it is easier to destroy the crystallinity of minerals,which weakens the XRD characteristic diffraction peak.In the process of leaching,the migration of clay minerals is controlled by the leaching solution and diffuses around.Under the action of the leaching solution,clay minerals will be more dispersed,less cohesive and easier to migrate.Low p H value and high concentration of leaching solution will accelerate its migration.(3)TEM analysis results show that kaolinite stripes of clay minerals are intermittent,and often pinch out and twist,while illite stripes are relatively straight;mixed layer minerals of kaolinite and illite appear,which indicates the transformation between kaolinite and illite.TEM images of simulated leaching show that in the early stage of leaching,pits formed by stripping of rare earth elements can be seen on the surface of clay minerals in the completely weathered layer,while black aggregates can be formed in the transition layer and the moderately weathered layer.Kaolinite transforms to illite in the middle stage of leaching,and illite transforms to kaolinite in the late stage of leaching.Under different leaching conditions,the p H value of 3-4is conducive to the mutual transformation of clay minerals,and the p H value of 4-5 is conducive to the transformation of potassium feldspar to clay minerals.Under the same conditions,the higher the concentration of leaching solution is,the more favorable the formation of kaolinite is,and the lower the concentration of leaching solution is,the more favorable the formation of illite is.(4)The continuous leaching of ionic rare earths has caused the minerals inside the earth quarry of rare earth mines to decompose,break and loosen,reduce the cohesion of the soil,and lead to a sharp drop in anti-sliding capacity.On the other hand,leaching makes clay minerals transform into each other,and different clay minerals have different shear strength and water swelling capacity.The water swelling of clay increases the sliding force.Under the coupling of the two factors,it can promote the instability and sliding of the stope slope after leaching.