Evolution Of Microscopic Characteristics Of Mineral Particles During In-situ Leaching Of Ion-type Rare Earth Ore

Ion-type rare earth ore is an important strategic mineral resource,which is mainly mined by in situ leaching process at present.In the leaching mining process,seepage field and chemical field will be generated between the injected leaching agent and mineral particles at the same time.Under the coupling effect of seepage field and chemical field,the change of microscopic properties of mineral particles will form the leaching blind zone and preferential channel,which will lead to slope instability,soil and water loss and groundwater pollution.In the actual production,the change of micro-interface of mineral particles will lead to the change of seepage in the leaching process,which will affect the dosage of leaching agent and the leaching efficiency of rare earth.Factors such as wettability and adhesion work reflect the physical properties of the solid-liquid interface in the leaching process,which is the macroscopic manifestation of the microcosmic properties such as the interaction between molecules of solid-liquid two phases.The changes of electrical conductivity and impedance reflect the chemical properties such as ion-exchange reaction between solid and liquid two-phase interface.Therefore,by studying the changes of mineral particle microstructure,wettability,adhesion work,electrical conductivity and impedance in the leaching process,this thesis explores the evolution law of mineral particle microscopic characteristics in the leaching process,sorts out the exchange process of leaching liquid cation and rare earth ion in different stages of in-situ leaching,and helps optimize the leaching process,reduce mining costs and reduce mine disasters.It is of great significance to realize green and efficient mining.The results are as follows:（1）The micro-structure changes of fine-grained minerals in the leaching process of ammonium sulfate,magnesium sulfate,calcium chloride and deionized water were investigated.It was found that within 0-1 min,clay minerals first accumulated liquid and then gradually wetted;within 1-10 min,clay minerals expanded and dispersed and generated pore cracks;after 10 min,the structure of clay minerals basically did not change.Different leaching agents have great influence on the microstructure of clay minerals,among which the wetting effect and leaching rate of ammonium sulfate are higher than magnesium sulfate and calcium chloride.（2）The influence of leaching agent on the wettability and adhesion work of rare earth ore was explored,and the wetting kinetics equation was established based on the analysis of leaching agent wetting mechanism of ion-type rare earth ore.It was found that the contact Angle and adhesion work of ammonium sulfate and magnesium sulfate reached the minimum value when the concentration was 0.3 mol/L.Acidic condition is better wettability,more conducive to leaching reaction.The wettability of different leaching agents is as follows:deionized water>ammonium sulfate>magnesium sulfate>calcium chloride,and the order of adhesion work is as follows:deionized water<ammonium sulfate<magnesium sulfate<calcium chloride;（3）The change rule of electrical conductivity in leaching process and the influence of different concentration,p H and flow velocity on leaching rate were explored.According to the change curve of leached rare earth ion(hereinafter referred to as RE³⁺)content and conductivity,the leaching process was divided into wetting stage,leaching stage,equilibrium stage and water top stage.The overall conductivity of leaching process increased slowly and then rapidly,then maintained stable,and finally rapidly declined to 0.The higher the concentration of ammonium sulfate solution,the faster the conductivity rises,and the greater the peak conductivity when it reaches stability.Under acidic conditions,the conductivity is inversely proportional to p H.The higher the initial flow velocity,the faster the conductivity rises.When the concentration of ammonium sulfate is 0.1 mol/L,the leaching efficiency is the highest.When the concentration is greater than 0.2 mol/L,the leaching of rare earth will be inhibited.Acidic environment is more favorable to the substitution reaction of cations and rare earth ions than alkaline environment,but when the p H is lower than 4,it inhibits the leaching of rare earth ions.When the initial flow rate is 1.5 m L/min,the leaching rate is improved and the leaching cycle is reduced.（4）The change of electrochemical impedance during the leaching process of ammonium sulfate under the optimal leaching condition was investigated.It was found that during 30-60 min,the sample was in the unsaturated state,the charge transfer was slow,the solution resistance（R_s）was up to 939Ω,and the charge transfer resistance（R_t）was up to 8310Ω.During 60-90 min,the mineral gradually reaches saturation state,the electrical conductivity increases rapidly,the solution resistance（R_s）decreases rapidly to 135Ω,and the charge transfer resistance decreases rapidly to 23.9Ω.At 90-250 min,the exchange reaction between leaching agent cations and rare earth ions gradually leveled off,the charge migration gradually decreased,the solution resistance（R_s）gradually increased and approached 154Ω,and the charge transfer resistance（R_t）gradually increased and approached 47Ω.After 250 min of deionized water injection,the ion concentration of pore solution gradually decreased.Solution resistance（R_s）increases rapidly to 1330Ω,and charge transfer resistance（R_t）gradually increases to338Ω.There are 62 figures,11 tables and 96 references in this thesis.