Gas-based Reduction And Melting Separation Technology For Nd Fe B Scrap Recycling

At present,the companies that recycling Nd Fe B Scrap generally extract rare earth by using a serious process that mainly consist of roasting,mill crushing,acid leaching,impurity removal,extraction,sepration,precipitation and calcination.But there are obvious shortcomings,include too much acid and alkali consumption using,heavy environmental pollution,long process,low rare earth recovery rate,high cost,and difficult to use iron slag,the key problem is how to deep separation of rare earth and iron.So it is urgent to find an effective method for removing and recycling iron from Nd Fe B Scrap.On the basis of consulting a large number of literatures and materials,basing by the difference characteristics of rare earth and iron-oxygen binding capacity,the paper carried out a technology study of Nd Fe B Scrap that including gas-based selective reduction,slag metal separation,enrichment and iron separation for finding an effective way to separate Fe and REO in the Nd Fe B Scrap to solving the problem of the existing iron’s affect in the Nd Fe B Scrap and the waste of iron.The research results shows theoretical significance and practical value for the improvement of Nd Fe B Scrap recycling technology.Aiming at the goal of selective reduction of iron and rare earth,gas-based selective reduction theory and experimental research of Nd Fe B Scraps were carried out by basing on the difference characteristics of the binding capacity of rare earth and iron and oxygen.The study also carried out thermodynamic calculation and analyses on the selective reduction of Nd Fe B Scraps.Then carried out fixed bed gas-based selective reduction kinetics and conditions experimental research,explored flash gas-based selective reduction,the results show that:(a)When the reaction temperature is lower than 2000 ℃,CO can only reduct iron oxide to metallic iron,while the earth oxides are not reduced,that proved a good selective reduction effect.(b)The apparent activation energy of the Nd Fe B fixed bed gas-based selective reduction reaction is 1.171 KJ / mol,the reaction is controlled by diffusion.At the reaction temperature of 1000 ℃,the reaction time of 50 min,the material particle size is less than 325 mesh,CO flow rate of 150 m L / min,more than 90% of the iron oxide in the Scrap is reduced to metallic iron,and the residual oxygen in the material is mainly combined with the rare earth,but the metallic iron and rare earth oxidation are intermingled with each other,making it difficult to select by using magnetic the physical method to separate.(c)Flash floating smelting helps to accelerate the gas-solid reaction,making the most of reactions within a few seconds.The reduction products are mainly spherical metal iron,but the surface of the spheres are bonded to each other due to high temperature,leaving unreacted or incompletely reacted oxide in the surface.Aiming at the problem that metallic iron and rare earth oxides are intermixed and difficult to physically seperate of reduction products,a test study on the separation of metal from slag of Nd Fe B Scrap reduction products was carried out.By examining the effects of alkalinity,Fe2O3 and B2O3 content on the melting temperature of rare earth slag,and studying the suitable slag type for slag-gold separation.Then the effects of reaction temperature,separation time,particle size and other parameters on the separation effect of metal iron and rare earth oxide were investigated,and explored the effective separation method of metal iron and rare earth oxide.The results showed that:(a)The REO-Si O2-Al2O3-B2O3 rare earth slag type with a mass ratio of 100: 63: 31: 6 has a melting temperature at only 1200 ℃.(b)Separation of slag and gold under the conditions of reaction temperature 1400 ℃,separation time 2h,and slag type REO-Si O2-Al2O3-B2O3(100: 63: 31: 6)can reduce Nd Fe B Scrap products a good separation of medium metal iron and rare earth slag that achieved the goal of separation and enrichment of iron and rare earth.(c)In the slag-metal separation process,the rare earth oxide part and the slag-forming agent form the compound Na Nd9(Si O4)6O2,and other part of REO is directly dissolved in the slag and form a non-crystalline compound.The rare earth slag contains REO and iron that higher than 57% and lower than 3% seperately,achieves the effective separation of rare earth and iron.(d)The iron nuggets seperated from the slag-metal have a purity of more than 97% iron with no rare earth elements are detected there and contain about 2.5% carbon and trace silicon,which realizes the high value utilization of iron resources in NdFeB scrap.