Methods Of Rare Earth Recycling And Kinetics Study In Lamps

Rare earth is widely used in new fields due to the special properties,such as luminescent materials,magnetic materials,catalytic material,and polishing materials,and plays an important role in the transition to a green economy.The growing applications of rare earths result in a large number of rare earths containing scrapped products,thus causing a waste of rare earth resources.Rare earth fluorescent lamp is one of the important applications of rare earth luminescent materials.It contains a lot of rare earth metals,which makes it rich secondary resources of rare earth elements.Its recycling not only saves rare earth resources,but also contributes to the environmental protection.Meanwhile,it has important practical significance for the sustainable development of rare earth resources.In this paper,the technology process and the dynamic model of recovering rare earth from waste fluorescent lamps are systematically studied.The research is expected to further improve the rare earth recovery process and provide the relevant theoretical basis for industrial production.The main results are as follows:1.Rare earth is recovered by acid leaching.The effects of acid species,acid concentration,leaching temperature,and leaching speed on the leaching rates of rare earth were studied.The results showed that the waste phosphors were leached by 2mol/L sulfuric acid solutions at the reaction temperature of 80 ?,leaching speed of300 rpm,and leaching time of 2 h.Under this condition,the maximum leaching rate of rare earths was 75.1%,and the leaching rates of Y,Eu,Ce,and Tb were 84.3%,83.2%,23.8%,and 19.3%,respectively.2.The waste phosphors were pretreated by alkali mechanical activation.The effects of milling speed,activation time,and amount of alkali on the leaching rates of rare earth elements were investigated.The optimal conditions in terms of rotational speed,activation time,and Na OH-to-waste mass ratio are 550 rpm,60 min,and 3:1,respectively.Under this condition,the leaching rate of rare earth reached 95.2%,which was increased by 20.1% than acid leaching.Among them,leaching rates of Ce and Tb were 85.0% and 89.8%,respectively.And compared with the acid leaching,the leaching rates of Ce and Tb are significantly increased by ~ 61.2% and ~ 70.5%,respectively.The results show that the alkali activation process can effectively destroy the spinel structure of the blue powder and the green powder and improve the leaching rate of the rare earth.3.The leaching kinetics of inactivated and activated waste phosphors were explored.The results indicated that the leaching process of inactivated and activated waste phosphors were diffusion control and the reaction kinetics followed the shrinking core models.The activation energy of the unactivated sample is 16.4 kJ/mol and the activation energy of the sample decreased to 10.6 k J/mol after the alkali activation.The reduction in activation energy implies that the grinding has a very good activation effect on the waste phosphors.Meanwhile,alkali activation can reduce dependence of leaching process on temperature,accelerate the acid leaching process,and improve the leaching rate of rare earth.4.Study on calcination process of oxalic acid precipitation.The effects of the amount of oxalic acid and the p H value of solution on the precipitation rate and purity were investigated.The optimal conditions in terms of the amount of oxalic acid and the p H value of solution are 15 m L and 1.5,respectively.Under this condition,the precipitation rate of rare earth is 96.4% and the purity is 97.4%.Meanwhile,the effects of different calcination temperature on the properties of the products were investigated.After calcination at 900? for 2 h,the diffraction peaks were sharp and the crystallinity was good.The resulting product is mainly a mixture of four rare earth oxides(Y2O3,Eu3O4,Ce2O3,and Tb4O7).It was analyzed and characterized by scanning electron microscopy(SEM).Test results showed that the final rare earth products are mainly lamellar structure,in which the lamellar crystals are densely packed and tightly bonded.In summary,this study provides an environmentally friendly and economically viable new process,which will contribute to the rational recovery of rare earth secondary resources.