Recovery Of Rare Earth Elements From Tailings Based On Mixed Roasting,Acid Leaching And Ion Exchange

The recycling and utilization of rare earth secondary resources have become one of the environmental hotspots of global concern.Currently,there are practical problems that urgently need to be solved in some process steps for handling these secondary resources,such as serious environmental pollution,strong corrosiveness to equipment,and high energy consumption.Therefore,selecting an economical,green,and efficient recovery process is of great strategic significance for the comprehensive utilization of rare earth resources.This article focuses on the rare earth element recovery process of"mixed roasting-acid leaching-ion exchange".The influence of mixed roasting with sodium carbonate,sodium borate,and sodium formate under different roasting conditions on the leaching efficiency of rare earth elements is explored,and the roasting reaction mechanism is speculated using techniques such as thermogravimetric analysis,electron microscopy-energy spectrum analysis,and X-ray diffraction analysis.The leaching efficiency of rare earth elements in the roasted ore is investigated by using hydrochloric acid leaching under different leaching conditions,and the leaching mechanism is discussed.Enrichment and recovery of rare earth elements in the acid leaching solution are carried out by using 001×7,RS-108,RS-10,and RS-1D resins,and the effects of different cross-linking degrees and types of resins on the adsorption-desorption efficiency and their cyclic regeneration performance are explored.The main research results are as follows:（1）The decomposition of fluocerite（REFCO₃）during the mixed roasting process mainly occurs in two stages.The first stage is its self-oxidation and decomposition at high temperatures,and the second stage is the reaction between the decomposition product of rare earth fluoride（REF₃）and the roasting agent to generate rare earth oxide（RE₂O₃）,which promotes the more complete decomposition of fluocerite.（2）Mixed roasting can effectively improve the leaching efficiency of rare earth elements.When sodium formate（SF）,sodium carbonate（SC）,and sodium borate（SB）are mixed with a solid mass ratio of 0.5:1 and roasted at 400°C for 1 hour,the leaching efficiency of rare earth elements is increased by 16.54-31.28%compared to the oxidation roasting（OR）.Among them,the mixed roasting with sodium formate（SF）has the best effect,and the leaching efficiency of La,Ce,Pr,Nd,Sm,and Y can reach 89.31-93.65%.（3）The concentration of hydrochloric acid,leaching time,and liquid-to-solid ratio are all key factors affecting the leaching efficiency of rare earth elements.When the hydrochloric acid concentration is 3 mol L^-1,the leaching time is 1 hour,and the liquid-to-solid ratio is 20:1,there is a high leaching efficiency for the sodium formate mixed roasted ore,and the leaching efficiency of all elements except for Eu can reach 89.31-93.65%.The leaching process is mainly controlled by the interface transfer and diffusion across the product layer.（4）The main functional group of the 001×7,RS-108,RS-10,and RS-1D resins is the sulfonic group（-SO₃H）.In order to ensure the adsorption efficiency of rare earth elements and the separation effect from impurity elements,using RS-10 and RS-1D resins with a dosage of 0.5g,adsorption time of 1 hour,and shaking speed of 200 rpm,had a high adsorption efficiency（88.31-91.00%）for La,Ce,Pr,and Nd,and a certain separation effect for impurity elements（removal efficiency of Fe,Al,Ca,and Sr reached 65-72%,75-90%,60-62%,and 49-50%,respectively）.When desorbing with 2 mol L^-1ammonium sulfate,RS-10 gel-type resin had a higher desorption efficiency（97.36-99.44%）than other resins,as well as better cycling regeneration performance.According to the summary,the method of"mixed roasting-acid-leaching-ion exchange",which uses sodium formate（SF）mixed with rare earth tailings after roasting,leaching with hydrochloric acid,adsorption with RS-10 gel resin,and finally elution with ammonium sulfate as desorption agent,is effective and feasible to recover rare earth elements from tailings.It can provide reference and new ideas for the sustainable development of rare earth secondary resources.