Abstract
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.
Highlights
The lighting industry has undergone great improvements with the advent of the rare earth phosphors
Phosphors are a mixture of red phosphors, blue phosphors, and green phosphors, in which red phosphors are rare earth oxides, which can be decomposed by hydrometallurgical processes, and Y
HCl is in the form of gas, generated from the decomposition of ammonium chloride, and waste phosphors react with HCl to form rare earth chlorides (Formula (2))
Summary
The lighting industry has undergone great improvements with the advent of the rare earth phosphors. In 2011, about 4800 million fluorescent lamps were disposed [2], and the value of rare earths contained in the waste phosphors was more than 1600 million dollars. If these rare earth elements can be recycled and reused efficiently, it will reduce the exploitation of primary rare earth minerals and build the circular-utilization industrial chain of abandoned rare earths, which will greatly help improve the efficient utilization of rare earth resources. The chemical structures of blue and green powders are in spinel structures [3,4], these chemical structures are so stable that they are difficult to destroy with inorganic acids [5]
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