Occurrence Of Rare Earth Elements In Coal Fly Ash And Their Intensified Separation

With the rapid development of the global economy and high-tech industries,the demand for various strategic resources is increasing year by year.As a key strategic metal,rare earth elements play an irreplaceable role in many fields.Research has found that coal often contains a large amount of rare earth elements,and coal type associated rare earth minerals may become an important source to replace traditional rare earth minerals.This article selects fly ash from Hequ Power Plant to study its basic properties,distribution and occurrence characteristics of rare earth elements.Thermodynamic simulation software is used to calculate the mechanism of rare earth transformation and migration during the roasting process,explore the precipitation process of rare earth elements,conduct roasting leaching experiments,study various influencing factors and mechanisms,and explore the precipitation conditions of rare earth elements through simulated precipitation,Finally,the precipitation and enrichment experiment of rare earth elements in the fly ash leaching solution was completed.Through the research of this paper,the existing achievements are as follows:（1）The main components of fly ash in Hequ Power Plant are Si O₂ and Al₂O₃,and the mineral composition is mainly composed of mullite,quartz,and glass phases.Rare earth elements are widely distributed in fine-grained fly ash and relatively enriched in non-magnetic components.（2）Through stepwise chemical extraction experiments,it was found that rare earth elements mainly exist in the glass phase.（3）Through thermodynamic simulation and orthogonal experiments,the optimal conditions for baking sodium carbonate were determined to be a roasting temperature of 900℃,a roasting time of 90minutes,and a ratio of fly ash to sodium carbonate of 1:1.2.（4）Four different leaching methods were used to extract rare earth elements,including water bath leaching,reactor leaching,microwave reactor leaching,and microwave digestion apparatus leaching.The results showed that the optimal conditions for the four leaching methods were leaching temperature of 80℃,leaching time of 30 minutes,acid concentration of 3mol/L,and leaching rates of 79.7%,68.35%,92.69%,and 63.23%,respectively.Through the comparison of leaching experiments,it was found that pressure has a reverse effect on the leaching of rare earth elements,while microwave assistance can improve the leaching rate of rare earth elements.（5）In order to realize the precipitation and separation of rare earth elements in fly ash leaching solution,Ammonium bicarbonate precipitation simulation experiment was carried out to discuss the precipitation process of La,Sm,Al,Fe,Mg,Zr and Sr.The final multi-element precipitation,the simulation results show that when p H=6.9,the precipitation of rare earth elements is basically completed,and more than 99%of rare earth elements are precipitated by Ammonium bicarbonate.（6）Through the precipitation experiment of fly ash leaching solution,it was found that during the impurity removal stage with p H=0-4.5,the proportion of rare earth precipitates was26.48%;PH=4.5-6 is the main precipitation stage of rare earth elements,which accounts for 94.9%of the total rare earth element content after impurity removal,accounting for69.57%of the total rare earth element content.This stage of rare earth element precipitation is basically completed.When p H=6-7.5,the precipitation of rare earth elements is only 0.59%.During the entire precipitation process,the precipitation rate of rare earth elements is 96.61%.This study takes fly ash riched in rare earth elements as raw material,used sodium calcination–microwave leaching to realize the enhanced separation of rare earth key metal elements,discussed the influence mechanism of various influencing factors on activation and leaching effect,determined the key factors of directional control of precipitation process.The results may provide scientific guidance for the efficient development and utilization of coal type rare earth elements.