Efficient Extraction And Separation Of Rare Earth And Cobalt From The Iron Residue Of The NdFeB Waste

Rare earths are widely used in high-tech fields due to their unique electronic valence and physical and chemical properties.Driven by the high-tech industry and low-carbon economy,the production of Nd Fe B magnets has developed rapidly.At present,about 26%of rare earth is widely used in the production of Nd Fe B magnets.However,about 30%of the waste is produced during the production and processing of Nd Fe B magnets.The oxidation roasting-hydrochloric acid preferential dissolution process is often used in industry.Due to the constraints of insufficient oxidation roasting or harsh leaching conditions,about 0.7%of rare earth elements（REEs）and0.3%of cobalt（Co）remain in the iron residue from Nd Fe B waste.The extraction of valuable elements from waste residue has a great influence on the sustainable utilization of rare earth resources,which can not only alleviate the shortage of rare earth supply,but also reduce the pollution to the environment.In this paper,iron residue from Nd Fe B waste was used as raw materials.Based on the full analysis of the occurrence state of rare earth and cobalt in iron tailings,a green and efficient extraction method was proposed,including the following conclusions.（1）The leaching rate of iron oxide was greatly improved by reducing acid leaching,and the effective extraction of rare earth and cobalt was realized.The rare earth phase mainly exists in the form of intergrowth and is mostly encapsulated in iron oxide in fine particles.Aiming at the phase wrapping characteristics of iron residue,the dissociation of rare earth phase is realized by destroying the structure of iron oxide.Under the optimum conditions,the leaching rates of cobalt,neodymium,praseodymium,cerium and iron were 90.6%,89.1%,77.2%,88.7%and 83.8%,respectively.The kinetics of the leaching process was systematically investigated.The results show that the cobalt and iron elements in the iron tailings of Nd Fe B waste follow chemical control,and the rare earth elements of neodymium,praseodymium and cerium follow diffusion control.（2）The activity of the main phase iron oxide was increased by mechanical activation pretreatment,and the selective extraction of coated rare earth and cobalt was realized.Firstly,the dominant range of Fe³⁺in iron oxide was analyzed by thermodynamics,and it was found that Fe³⁺was stable in low p H and high potential regions.After the insoluble phase iron oxide in iron residue from Nd Fe B waste is activated,the coating of valuable metal oxides is reduced.Secondly,compared with atmospheric acid leaching,mechanical activation combined with pressure leaching can more effectively leach rare earth and cobalt.With the increase of temperature and the decrease of acid concentration,Fe³⁺was partially hydrolyzed to realize the selective leaching of rare earth and cobalt.In addition,the iron residue from Nd Fe B waste after mechanical activation can improve the utilization rate of hydrochloric acid and realize the enrichment of rare earth and cobalt through cyclic leaching.After six cycles,the content of rare earth and cobalt in the solution was effectively improved,which was beneficial to the subsequent extraction and separation.The concentrations of Co,Nd,Pr and Ce ions were 0.96 g·L^-1,1.89 g·L^-1,0.53 g·L^-1 and 0.6 g·L^-1,respectively.（3）Extract and separate cobalt by synthesizing sulfur-modified montmorillonite composites.Firstly,the sulfur-modified montmorillonite composite material was synthesized,which can effectively load sulfur into montmorillonite and realize the directional recognition and extraction of Co²⁺.Under the conditions of Co²⁺concentration of 100 ppm,p H of 8,adsorbent dosage of 3 g/L and adsorption time of10 h,the maximum adsorption capacity of sulfur modified montmorillonite composite material was 90 mg·g^-1,and the extraction rate could reach about 95%.In addition,the adsorption process of Co²⁺by sulfur-modified montmorillonite composites conforms to the quasi-second-order kinetic equation.Based on the above research contents,this paper proposes a process flow for the treatment of iron residue from Nd Fe B waste.The effective extraction of iron,cobalt and rare earth and the recycling of copper powder are realized by copper powder reduction acid leaching.Secondly,mechanochemical pretreatment can realize the selective leaching of rare earth and cobalt,and further cyclic leaching achieves the enrichment of valuable elements.The synthesized modified montmorillonite-sulfur composite material can efficiently extract Co²⁺,and finally realize the separation of rare earth and cobalt.The process can be used as an effective method to recover rare earth and cobalt from iron residue from Nd Fe B waste,which is of great significance to the recycling of rare earth secondary resources.