Experimental Study On Leaching Of Rare Earth Elements From Coal Gangue In Guizho

Rare earth elements are widely used in electronics,energy,medical,transportation,aerospace,military and other fields.In recent years,due to the increasing demand for rare earths by new technologies and equipment and the continuous development of traditional rare earth mines,many countries have tried to find new sources of rare earths.The content,occurrence state,separation and extraction technology of rare earth elements in coal and coal solid waste have gradually become a research hotspot in the world.This study takes the coal gangue of a coal preparation plant in Bijie,Guizhou as the research object.The content and occurrence characteristics of rare earth elements in coal gangue were studied,and the rare earth elements in coal gangue were pre-enriched and leached.The results show that the content of rare earth elements in the coal gangue used in the test is high,which is 1013.02μg/g.The rare earth elements are mainly distributed in fine-grained carbonaceous mudstone,coal and claystone with good grindability.SEM-EDS and step-by-step leaching tests showed that rare earth elements were mainly present in clay minerals such as kaolinite and a small amount in calcite.Selective grinding-tailing test of coal gangue.When the ball milling time is 8 min,the yield of+2 mm and-2 mm in the grinding products is 24.08%and 75.92%,respectively,and the content of rare earth elements is 176.95μg/g and 1104.93μg/g,respectively.The+2 mm coarse-grained tailing has a certain pre-enrichment effect on rare earth elements.High temperature activation roasting and HCl leaching tests were carried out with-2 mm coal gangue as raw ore.The coal gangue and activator Na₂CO₃ were roasted at 850°C for 3.0 h,and then leached with 4 mol/L HCl at 60°C for 3 h.The leaching rate of rare earth elements was 91.41%.The leaching effect is great.In practice,Na Cl with lower cost can also be considered as an activator.The coal gangue was roasted with Na Cl at 900°C for 2.5 h,and then leached with 4 mol/L hydrochloric acid at 80°C for 3 h.The leaching rate of rare earth elements was 68.88%.When Na₂CO₃ was used as activator,the content of rare earth elements in the final leaching solution was 1010.02μg/g,which was significantly higher than that of the main impurity ions（Si 232.20μg/g,Fe 706.10μg/g,Ca 350.40μg/g）.This provides favorable conditions for the next separation and extraction.The mechanism study shows that high temperature roasting increases the pore size and total pore area of coal gangue,which is beneficial to the infiltration of leaching agent and improves the reaction efficiency.At the same time,the sodium salt activator reacts with minerals such as kaolinite in coal gangue to form soluble salts.At the same time,the sodium salt activator reacts with minerals such as kaolinite in coal gangue to form soluble salts.The combination of aluminum silicon ions and free sodium ions effectively activates rare earth elements.The appropriate calcination temperature makes the activator melt,which leads to the transformation of solid phase and solid phase reaction between coal gangue and activator into solid phase and liquid phase reaction.It enhances the activation effect.