Search

The leaching kinetics of Y and Eu from waste phosphors using a hydrochloric acid (HCl) solution containing hydrogen peroxide (H2O2) were investigated. Characterization of the waste phosphors was performed using XRD to ascertain the phases as (Y0.95Eu0.05)2O3 (red phosphors), (Ce0.67Tb0.33)MgAl11O19 (green phosphors), (Ba0.9Eu0.1)Mg2Al16O27 (blue phosphors), and SiO2 (quartz). The influence of factors such as HCl concentration, addition amount of H2O2, temperature, and reaction time on the leaching performance of Y and Eu was investigated. The maximum leaching recoveries of Y (99.87%) and Eu (88.72%) were obtained at 4 M HCl, 0.2 cm³/g H2O2, 60 °C temperature, and 180 min of reaction time at a liquid-to-solid ratio of 7.5 cm³/g. Leaching kinetic results showed the best fit with the shrinking sphere model (1-(1-x)1/3)=kct), ensuring that the overall leaching process was governed by a chemical control mechanism. Activation energies of 42.35 and 33.28 kJ/mol were acquired for leaching of Y and Eu, respectively, at 40-70 °C, which further supports the proposed chemical control leaching process. [ABSTRACT FROM AUTHOR]

Y2O3:Eu were prepared through precursors synthesized by leaching tests, removing impurities, enrichment of Y and Eu from residual purified liquors, annealing treatment, and high temperature solid-state reaction method, which is the most suitable for large-scale production. The analysis of product shows that the purity is 99.42%. The resultant powders were characterized by X-ray diffraction (XRD), differential thermal analysis (TG-DTA), scanning electron microscope (SEM), and photoluminescence (PL). Compared with the commercial phosphors, the XRD spectrum of the product samples revealed the synthesized particles to have a pure cubic Y2O3:Eu structure without any impurities in the crystalline phase. On the morphology, the Y2O3:Eu particles synthesized by a combustion and high temperature solid state process with sintering aids, were large and uniform. For luminescence property, the emission intensity of Y2O3:Eu phosphors synthesized by combustion process and high temperature solid state process with sintering aids were higher than those without sintering aids, at 1400 °. [ABSTRACT FROM AUTHOR]

Recovering Y and Eu from waste phosphors using chlorination roasting followed by a water leaching process was investigated in this study. Firstly, by chlorination roasting and water leaching, Y and Eu elements present in waste phosphors were efficiently extracted into a leach solution. Secondly, the majority of the impurities in the solution can be removed by adjusting the pH to 4.5 using a Na2S and NH3·H2O solution. Thirdly, the rare earths can be precipitated afterwards by adding a H2C2O4 solution and adjusting the pH to 2.0. Then rare earth oxides (REOs) can be obtained after calcining at 800 °C for 1 h. The characterization study of the waste phosphors and the rare earth oxide products was performed by XRD, XRF, and SEM-EDS analysis to determine the phase and morphological features. Influences of the factors, such as roasting temperatures and time, the addition of ammonium chloride on the roasting of waste phosphors, as well as the pH and the amount of oxalates on the precipitation of Y and Eu, were investigated. The maximum grade (99.84%) of mixed rare earth oxides and recovery rate (87.35%) of Y and Eu were obtained at the optimized conditions. [ABSTRACT FROM AUTHOR]

Waste fluorescent powder contains a large amount of rare earth elements, which have a high value for recovery and utilization. In order to achieve the rapid and efficient leaching of rare earth elements in these waste phosphors, microwave-assisted leaching of rare earth elements Y and Eu from the waste phosphor with hydrochloric acid was studied. The maximum leaching rates of Y (99.84%) and Eu (89.82%) were obtained at 600 W microwave power, 60 min microwave radiation time at 60 °C. The leaching kinetics showed that the microwave leaching process of Y and Eu conforms to the chemical reaction control model, and the apparent activation energy is 25.30 kJ/mol and 24.78 kJ/mol. Compared with the conventional heating method, the microwave leaching process can obviously reduce the reaction activation energy, shorten the reaction time, and achieve the rapid and efficient leaching of rare earth elements in the waste phosphors. [ABSTRACT FROM AUTHOR]