Study On Mechanical Activation Of Mixed Rare Earth Concentrate Enhancing Leaching Of Bastnaesite

Rare earth elements,“industrial vitamins”,have unique magnetic,optical and electrical properties,which are widely used in the industrial field.The Bayan Obo rare earth ore is the largest known rare earth ore.The rare earth elements in Bayan Obo rare earth ore are mainly distributed in the bastnaesite and monazite,among which the ratio of the content of bastnaesite and monazite in the concentrate is about 6:4⁹:1.The extraction and smelting processes of rare earth mainly include concentrated sulfuric acid roasting and NaOH decomposition.At present,concentrated sulfuric acid roasting is widely used in industry,but this method produces a lot of acidic waste gas,and the radioactive waste residue containing thorium is difficult to deal with.NaOH decomposition method requires minerals with high grade and less impurities.This method consumes a large amount of caustic soda,and calcium in minerals would enter the precipitation,leading to impurity of rare earth products.In view of these problems,our team proposed a clean and efficient leaching process.In this process,after bastnaesite roasted by oxidation,the element cerium would be oxidized into tetravalent.In the subsequent acid leaching process,the strong oxidation of cerium fluoride would oxidize chloride ion into chlorine gas,so reducing agent has to be added in the acid leaching process.On the basis of this process,the mixed rare earth concentrate was activated mechanically to enhance the extraction of bastnaesite from the concentrate.Through the experiment,the following conclusions can be drawn:The particle size of unactivated rare earth concentrate is larger,and the particle size distribution shows a normal distribution trend.With the increase of the degree of mechanical activation,the particle size of the mixed rare earth concentrate decreases gradually and the particle size distribution does not accord with the normal distribution.By comparing the XRD patterns before and after activation,the characteristic peaks of bastnaesite are enhanced to a certain extent with the increase of mechanical activation degree.The diffraction peak of bastnaesite in the activated concentrate gradually widens,whose the half peak width gradually increases,and the characteristic peak appears a certain degree of deviation.Temperature and mineral size have great influence on hydrochloric acid leaching of bastnaesite from concentrate.The rare earth leaching rate was the highest,reaching 38.09%,under leaching conditions of particle size of concentrate95%distributed below 1.5?m,leaching time 60 min and temperature 90?.The reaction process between hydrochloric acid and bastnaesite in mixed rare earth concentrate:bastnaesite in the mixed rare earth concentrate would firstly reacted with hydrochloric acid to release part of the rare earth elements into the solution;this process would generate the intermediate REOxF,which would continue reacting with hydrochloric acid to release the rare earth elements and fluorine ions into the solution;the solution of fluorine ions reacted with RE³⁺to generate insoluble REF₃ precipitation.The leaching kinetic model of bastnaesite in the mixed rare earth concentrate followed the shrinking model.The kinetic formula could be expressed as 1-3?1-x?2/3+2?1-x?=k₁t.The apparent activation energy of the unactivated concentrate and the concentrate with different activation degrees in the acid leaching process is 62.1,54.8,35.1 and 34.9 kJ/mol,respectively.The leaching process of unactivated concentrate and activation?95%of the particle size distribution under 10?m?were controlled by chemical reaction;The reaction process of activation concentrate?95%of the particle size distribution under 5?m?and activation concentrate?95%of the particle size distribution under 1.5?m?were controlled by chemical reaction and diffusion together,where chemical reaction control procedure played a main role.