| With the attempts and improvements of numerous researchers,the mining of ion-adsorbed rare earth ores has developed from the initial pond leaching and heap leaching to the current in situ leaching,and its mining process is constantly being optimized and updated.The in situ leaching method using ammonium sulfate solution as leaching agent is the most commonly used mining method at present.However,when ammonium sulfate solution is used as leaching agent,the problem of ammonia nitrogen exceeds the standard in the soil and groundwater around the mine area after leaching;meanwhile,the large amount of leaching agent injected makes the water content of the rare earth ore increase after mining,which is prone to natural disasters such as landslide and mudslide.The ammonium sulfate in situ leaching process poses a threat to the safety and ecological environment around the mining area,which in turn hinders the efficient development and utilization of rare earth ore resources in China.The electrokinetic method is widely used in the directional migration of metal ions and drainage consolidation of soils because of its electroosmotic and electromigration phenomena in soils.Therefore,this paper considers the optimization of the leaching process from the perspective of the whole process of rare earth mining,using the adsorption capacity of zeolite to adsorb and intercept the ammonia nitrogen of the leaching solution,exploring the feasibility of the electrokinetic method to promote the leaching of rare earth ions,and also using the electroosmosis phenomenon to drainage consolidation of the high water content rare earth ore after the completion of mining,and exploring the optimization measures of the rare earth mining process to promote the green mining of rare earth ore.In this paper,based on the study of zeolite adsorption characteristics,the effects of zeolite adsorption layer arrangement,liquid-solid ratio and water drenching on the leaching effect of rare earths were investigated by indoor column leaching test;the effects of pH and concentration of leaching agent on the leaching effect of rare earths were investigated by applying electric field on the basis of column leaching test;the effect of electro-osmosis of high water content rare earth ore under different electric potential gradients was investigated by rectangular model test.The effect of electro-osmosis of rare earth ores with high water content at different potential gradients was investigated by rectangular model tests;the leaching of rare earths was simulated and predicted by Comsol numerical simulation software on the basis of indoor tests.The main research results of this paper are as follows:1.The research history and current status of rare earth ore mining are summarized,the basic principles and research progress of electro-osmosis are described,and the main properties of zeolite adsorption materials and their applications in water treatment are summarized.2.The adsorption properties of zeolites were investigated.The adsorption effect of zeolite on ammonia nitrogen and rare earths under different zeolite particle sizes,different zeolite dosing ratios and different solution pH was investigated;the adsorption mechanism of zeolite was described,the adsorption of zeolite on ammonia nitrogen was dominated by unimolecular layer adsorption mode,and the adsorption of zeolite on rare earth ions was dominated by multi-molecular layer inhomogeneous adsorption mode;the adsorption effect of zeolite on ammonia nitrogen was stronger when both ammonia nitrogen and rare earth ions were present in the solution.3.The relationship between rare earth concentration and water output in the column leaching process can be divided into three stages:the first stage,penetration leaching to reach the peak rare earth concentration stage;the second stage,rare earth concentration decreasing stage;the third stage,rare earth complete leaching stage.The relationship between ammonia nitrogen concentration and water output is also divided into three stages with the same nodes:the first stage,the stage of intense ion exchange between ammonium ions and rare earth ions;the second stage,the stage of incomplete utilization of ammonium ions;the third stage,the stage of the end of ion exchange.In the actual project need to eliminate the third stage,improve the second stage of the dragging phenomenon,in order to reduce the cost of column leaching,reduce ammonia nitrogen emissions.4.The arrangement of zeolite adsorption layer can adsorb ammonia nitrogen from the leachate of rare earth ore,and provide data support for in situ treatment of ammonia nitrogen from leachate using zeolite adsorption layer in the in situ leaching process.The zeolite adsorption layer is most effective and easy to construct when it is placed at the bottom of the rare earth mine.By regularly replacing and regenerating the zeolite adsorption layer,the zeolite adsorption layer can continuously adsorb ammonia nitrogen in the effluent during and after the leaching process.5.Electric method has high potential for application in rare earth mining.The dragging phenomenon of the rare earth concentration-output curve at different leaching agent pH was significantly improved when the electric field was applied,and the rare earths in the leach solution were more concentrated.Based on the commonly used 1.5%ammonium sulfate,the leaching rate of rare earths was reduced by 8.6%,15.2%,21.38%and 65.5%when the leaching agent concentration was reduced by 33.3%,50%,66.7%and 83.5%,respectively,and the reduction in leaching rate of rare earths was less than the reduction in leaching agent concentration,and the application of electric field could improve the reduction in leaching rate caused by the reduction in leaching agent concentration.6.For the problem of high water content of rare earth ore,which is easily neglected after the end of rare earth ore mining,the electro-osmosis phenomenon of electric method can be used to drain and consolidate the high water content rare earth ore and reduce the risk of natural disasters such as landslides and mudslides.The electric potential gradient will affect both the cost and dewatering effect of electroosmosis.Elevating the electric potential gradient will improve the dewatering effect,but the energy consumption per unit of water discharged will increase,making the cost higher,and elevating the electric potential gradient cannot infinitely improve the drainage effect of the soil,so it is appropriate to select the appropriate electric potential gradient in the actual project,taking into account the drainage effect and the actual cost.At the same time,choosing the right time to stop electro-osmosis and avoiding the stage of rapid increase of energy consumption coefficient can significantly reduce energy consumption and save engineering period and cost without basically affecting the total drainage volume of electro-osmosis.7.The common effects of three components,namely rare earth ions,ammonium ions and other metal ions,in the leaching process of rare earth ore were considered,and a triple ion exchange model based on the separation factor and kerr selection coefficient was established respectively,and the leaching results of rare earth ore under different factors were simulated and predicted by using Comsol Multiphysics simulation software.The three-ion exchange model based on the kerr selection factor can better simulate the leaching process of rare earths when the zeolite adsorption layer is arranged at the bottom;the simulated results of rare earth leaching rate without electricity at different leaching agent concentrations are compared with the measured rare earth leaching rate results when electricity is applied,which can show that the electric field promotes the leaching of rare earth ions to a certain extent;the leaching effect of the zeolite adsorption layer arranged at the bottom is simulated at different thicknesses.The effect of simulating the leaching of rare earths at different thicknesses of the zeolite adsorption layer at the bottom,increasing the thickness of the zeolite layer will cause a small decrease in the leaching rate of rare earths,but the adsorption effect on the ammonia nitrogen of the leachate is obviously improved. |
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