| Ion adsorbed rare earth(RE)ore,also known as weathered crust infiltration rare earth ore is a unique type of rare earth ore found in China.It is mainly deposited in clay minerals such as kaolin and illite,which can be dissociated rare earth ions through academic and biological effects.At present,the rare earth mining usually uses ammonium salt as the leaching agent.Through the in-situ leaching technology,the rare earth cations in the rare earth ore are replaced by the more active cations in the leaching solution,and finally the required rare earth resources are extracted from the collected rare earth mother liquor.On the one hand,in the process of ammonium salt in-situ leaching,high concentration of leaching agent and long-term leaching lead to increasingly prominent environmental problems,including the destruction of vegetation in the mining area,the removal of magnesium and other nutrients from the raw ore soil,a large number of wastewater ammonia nitrogen exceeding the standard,etc.,which makes the ecosystem extremely difficult to treat and repair.On the other hand,due to the continuous injection of leaching solution,the rare earth ore is easily damaged under the condition of water saturation.The strong chemical replacement reaction between the rare earth ions in the rare earth ore and the cations in the leaching solution will inevitably lead to the change of the internal pore structure of the ore.Furthermore,according to the principle of equivalent exchange,to desorb the same amount of rare earth elements,the number of cations of different valence states into the ore is different in multiples Under various influences,the evolution of the secondary pore structure of the rare earth ore may produce different results.The dynamic evolution of the pore structure of the rare earth ore has become the key to good migration and penetration of the leaching solution.Therefore,only by studying the microstructure of rare earth ore bodies in different valence ion exchange processes,can we determine the dynamic evolution rule and mechanism of pore structure of rare earth ore bodies in different valence cation chemical exchange processes,and at the same time provide some basic research theory for the development of new green environmental leaching agentsIn this paper,the dynamic evolution of pore structure of rare earth ore was studied by using NH4+,Mg2+and Al3+as cations in the simulated column leaching experiment.At the same time,scanning electron microscopy and energy dispersive spectroscopy were used to observe and determine the micro area morphology of the sample.The difference of micro morphology and pore structure of the sample in different valence cation leaching process was compared,and the statistical analysis results were used to realize the difference quantification and demonstrate the influence of ion valence on the migration and permeability of the leaching solution.Through the above work,the main findings are as follows:(1)In the indoor simulated leaching test,2%(NH4)2SO4,2%MgSO4 and 2%Al2(SO4)3 solution were used to leach the ore.The leaching process could be divided into four stages:(a)The deionized water saturation stage.The entire column immersion process only had physical percolation,and there was no ion exchange reaction;(b)The main reaction stage.Strong ion exchange occurred at this stage,but the exudation of rare earth ions was behind the ion exchange reaction,and the rare earth ion concentration in the rare earth leachate at this stage was minimal.(c)The ion seepage stage.At this stage,there were still few ion exchange reactions,and the content of rare earth ions in the recovered solution began to increase,and then decreased rapidly after reaching the peak;(d)The tailing stage.At this stage,the ion exchange reaction was weak,the concentration of rare earth ions in the leaching solution was lower than the lowest grade of industrial mining,the concentration of leaching rare earth ions decreased slowly,and there was a certain tailing phenomenon(2)In the whole leaching process,the relationship between the peak value of leaching rare earth concentration(C)is:CAl2(SO4)3>C(NH4)2SO4>CMgsO4,and the relationship between the total mass of leaching rare earth(M)is:MMgSO4>M(NH4)2SO4>MAl2(SO4)3.The effective ion replacement time of the three groups of solution leaching is in the main reaction stage,the time was 2.3-4.3h,and the number of cycles was 2-5 times,and the relationship between the liquid discharge rate(V)during the period was V(NH4)2SO4>V MgSO4>VAl2(SO4)3(3)By using the leaching solution containing cations of different valences,in the main reaction stage,the longitudinal and transverse cross-section NMR inversion images of the three groups of samples shown basically the same rules.Inside the sample,along with the top-down process of ion replacement reaction,the solid fine particles migrated from top to bottom,which was reflected in the stripe black aggregation from top to bottom in the inversion image of the longitudinal section of the sample region.A large black area appeared in the inverse image of the cross section of the corresponding sample.After a large amount of ion exchange reaction was completed,the main body of the inversion image of the vertical and horizontal sections of the sample became bright white.Through observing the samples in the black aggregation area,it could found that the generation of the aggregation area was temporary siltation of fine clay particles during migration,and its main component was clay particles.The amount of fine particles adsorbed on the pore surface of the ammonium sulfate leaching group was relatively small,the amount of fine particles adsorbed on the pore surface of the magnesium sulfate leaching group was relatively large,and a large amount of fine particles were enriched inside the sample of the aluminum sulfate leaching group Particles,which caused a large difference in the pore structure of the three groups of samples.(4)By leaching the ore with the leaching solution containing cations of different valences,from the deionized water saturation stage to the main reaction stage to the mass ion exudation stage,comparing the T2 patterns and pore structure evolution rules of the three groups of samples:On the one hand,the pore structure of the ore evolved dynamically from large pores to small and medium pores.After the ion exchange ended,the pore structure changed in reverse.On the other hand,in terms of the number of large pores and super-large pores in the sample,the ammonium sulfate leaching group had the most,followed by the magnesium sulfate leaching group,and the least was the aluminum sulfate leaching group.The combined effect of the cation valence,the ionic strength of the solution,and the pH of the leaching agent caused the van der Waals gravitational force and the electric double layer repulsion between the fine particles and the pore surface to lose their balance.Those promoted the process of adsorption and analysis of fine particles on the surface of the pores,resulting in a difference in the ratio of different pore radii of the sample during the leaching process,and further the difference in the percolation rate of the leachate.The mechanism could be well analyzed by using the electric double layer theory and the classic DLVO theory.(5)Based on the study of the replacement of different valence cations and rare earth ions in the saturated column immersion process,the evolution of the pore structure of the ore body,and the movement of fine particles.And also through the effect of cation valence of leaching solution on the percolation of leaching solution and pores in the ore body during the chemical replacement process was compared and analyzed,as far as the category of replaceable cations studied in this paper,the optimal ionic valence for the seepage of ore leaching solution is+1,which is NH4+. |
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