Research On The Occurrence Pattern And Rinsing Methods Of Ammonium In Ion-absorbed Rare Earth Tailings

Under the ammonium salt leaching system,in situ leaching of ion-absorbed rare earth has led to long-term excessive levels of ammonia nitrogen in the mine area’s watershed,and effective remediation measures are urgently needed.To avoid potential pollution risks from the treatment of residual ammonium in tailings,a water rinsing method has been proposed.However,this method faces challenges such as low ammonium concentration in the leachate and high water usage.To address these issues,efficient rinsing methods for residual ammonium have been researched.Due to the complex influences of factors such as the pore structure of the ore body,particle surface morphology,and charged state,there are many types of residual ammonium,and the control factors of the slow-release process are different.Therefore,a solute transport theory for the residual ammonium rinsing process has not yet been established.Thus,the study focused on investigating the distribution patterns and slow-release mechanisms of different types of ammonium on tailings surfaces and establishing a solute transport equation for the residual ammonium rinsing process.The study provides certain theoretical guidance for the efficient rinsing of residual ammonium in ion-absorbed rare earth tailings,which is of significant importance in mitigating the ammonia nitrogen pollution problem in ionic rare earth tailings.The main findings and conclusions of the research are summarized as follows:(1)To investigate the residual patterns of ammonium in situ leaching of ion-absorbed rare earth,on the basis of experience,on-site experiments of ion-absorbed rare earth in situ leaching were carried out according to the injection steps.The leaching and ammonium residual patterns at different positions and depths of the ore block were analyzed,and the relationship between ammonium residual and rare earth leaching was discussed.The results showed that under the conditions of experience injection,there were differences in rare earth leaching and ammonium residual at different positions on the mountain.The leaching rate of rare earth in the test block was the highest at the mountain top,followed by the middle section and the injection boundary,while the ammonium residual was higher at the surface of the mountain top and middle section than at the injection boundary.The molar ratio of vertical ammonium residual to rare earth leaching in the ore block far exceeded the equivalent ratio of 3:1 required to satisfy the exchange reaction between the two.(2)Experiments on the adsorption-desorption of ammonium on the surface of rare earth ore under wide concentration thresholds were conducted,and the adsorption-desorption law of ammonium on ion-absorbed rare earth ore was analyzed.The concentration conditions of different types of ammonium formed in the solution were studied,and the concept of the distribution of the double electric layer of multi-ion order on the particle surface was proposed and verified.The main influencing factors of ammonium residual on the particle surface were discussed.The results showed that there exists a critical concentration of ammonium for the formation of different types of ammonium,and the critical concentration for the formation of ammonium through ion exchange and physical adsorption is lower than that for fixed ammonium.The ions of different valences on the surface of ion-absorbed rare earth ore particles were distributed in order of "higher valence inside and lower valence outside",and the exchange of ammonium with each ion was carried out in the order of "outer lower valence first,then inner higher valence".The magnitude of ammonium residual was mainly related to the ζ potential of the particle surface.(3)Based on the double-layer model,the location of different types of ammonium on the particle surface was speculated.The saturation adsorption of ammonium on ion-absorbed rare earth ores and the stepwise desorption experiments of saturated adsorption samples have been carried out sequentially.The changes in the concentrations of ammonium ions and sulfate ions in the solution,as well as the variation in particle surface ζ potential,were analyzed through the rinsing conditions of deionized water and KCl solution.A prediction model for the residual amounts of physically adsorbed and ion-exchanged ammonium on the particle surface during the rinsing process was established,and the interface between physically adsorbed and ion-exchanged ammonium was quantified.The results showed that physically adsorbed ammonium partially exists in the diffusion layer on the particle surface and partially exists within the sliding plane,while ion-exchanged ammonium mainly exists in the outer Helmholtz plane.The interface between physically adsorbed and ion-exchanged ammonium will vary with the concentration of the original solution.(4)The release mechanism of tailings ammonium was investigated with a focus on the physical adsorption and ion exchange states of ammonium.Under the condition of sufficient rinsing water,the release behavior of physically adsorbed ammonium was studied.For ion exchange state ammonium,a release experiment was conducted on ion-absorbed rare earth tailings in the steps of rinsing,sealing,and re-rinsing,and the relationship between ammonium release and its influencing factors was analyzed.Then,the release mechanism of ion exchange state ammonium was revealed.The results showed that both physically adsorbed and ion exchange state ammonium exhibited a release behavior.Ion exchange state ammonium was converted to physically adsorbed ammonium and released into the solution,and its release amount was proportional to time and moisture content.The slow release of ion-exchange ammonium is attributed to the slow outward diffusion of surface metastable equilibrium ions in the double-layer electrochemical potential redistribution process,as well as the restricted diffusion of ions within micro-pores on the particle surface.(5)Through indoor rinsing experiments,the effect of continuous and intermittent rinsing on ammonium removal was compared,and the controlling factors of intermittent rinsing were investigated.A ammonium source-sink model for tailings rinsing was established and relevant parameters were determined to carry out numerical simulation of intermittent rinsing in tailings.The impact of tailings-related parameters on the ammonium rinsing effect of different rinsing methods was analyzed,and the applicable conditions for intermittent rinsing were discussed.The results showed that,under the same rinsing water volume and low water evaporation,intermittent rinsing was more effective in ammonium removal from tailings than continuous rinsing.The main influencing factors of rinsing efficiency were the rinsing time and ammonium concentration in the rinsing solution.The desorption equilibrium constant k and the release factor β in the source-sink model respectively determined the amount and rate of ion desorption.Intermittent rinsing is suitable for situations where the rinsing water volume is the evaluation index and only the total amount of ammonium rinsed out is evaluated.