Recycling Of Rare Earth Elements From Waste Phosphor And The Alkaline Fusion Mechanism

Rare earth elements (REEs) are the important strategic non-renewable resources, known as the "industrial monosodium glutamate", is increasingly widely used. Waste phosphor contains about20%of rare earth oxides (REO). such as Y, Eu, Tb and Ce. So, it is becoming one of the ideal material for recycling REEs. However, the recovery rate is low. and there is no mature industrialized technology now. In this paper, the alkaline fusion mechanism of stable aluminate blue and green phosphors was discussed. Under the guidance of mechanism, dual dissolution by hydrochloric acid (DHA), the method of removing Si and were studied systematically.Stable aluminate blue and green phosphors are neither soluble in acid or alkali, it is the main reason for the low recovery rate at present. So. for increasing the recovery rate of Eu, Tb and Ce in the blue and green phosphors. In this paper, the change of phases and the migration of the rare earth (RE) ions in alkaline fusion process were studied. The mechanism of aluminate phosphor disintegration by alkaline fusion was presented. Sodium ions substitute the RE ions in the mirror plane and magnesium ions in the spinel block successively, which results in more oxygen vacancies and interstitial sodium ions. The unit cell breaks from the mirror plane, and the disintegration is continuing, even after the sodium ions substitute the Mg2+ions in the spinel block. Finally it would be decomposed into NaAl2O3. and RE and alkaline earth metal ions combine with free OH-and CO2into MgO. BaCO3, REO and H:O.For solving the problem of the recovery rate from waste phosphor is about50%by the existing technology, based on the the characteristics of the three primary colors rare earth phosphors, DHA was presented under the guidance of mechanism. The red phosphor Y2O3:Eu3+was leached by HCI first. Then the indissolvable blue and green phosphors were decomposed by alkaline fusion and cleaned by the deironzed water. Y-Eu and Ce-Tb concentrate were obtained after second acidolysis. The results showed that the recovery rate was improved significantly. The total leaching rate of the rare earth elements was increased to94.60%from42.08%by existing method. The leaching rate of Y. Eu. Ce and Tb reached94.60%.90.05%.71.45%. and76.22%. respectively. Also, the hydrochloric acid and flake caustic soda consumption reduced 41.67%and37.5%. The mass of alkaline fusion materials reduced43.18%, it reduced the energy consumption effectively. Y-Eu and Ce-Tb concentrate simplifed the extraction process, so that the benefits can be maximized in the cost reduction. In the pilot test by DHA, the REEs leaching solution was treated by oxalic acid precipitation and calcination. The total recovery of the REEs was increased to85.4%from about50%. And the Y-Eu oxide and Ce-Tb oxide concentrate with the purity92.81%and73.19%were obtained.For reducing the impact of the glass and Silicon aluminum oxide impurities on recycling of REEs from waste phosphor. It was presented that removing the impurities by perorating, physical screening and alkailine leaching. The results showed that the total removal rate of SiO2was72.28%. the leaching rate of REEs was increased to95.37%from83.13%, and the leaching rate of Y, Eu, Ce and Tb reached96.19%,98.99%.78.59%and90.94%, respectively. When the Si element were almost removed, the total leaching rate of the REEs was98.60%, and the leaching rate of Y, Eu. Ce and Tb reached99.06%.97.38%,98.22%, and98.15%, respectively. Three different waste phosphor as raw material were compared, the average recoveries of REEs was92.34%, and the average recoveries of Y, Eu, Ce and Tb reached92.76%,94.60%.79.44%and84.93%. respectively. Waste acid solution and alkaline solution from the recycling REEs process was treated by neutralization and precipitation, the waste water was utilized in closed-loop circulation.In conclusion, in this paper, the alkaline fusion mechanism was clarified for the key decomposition of stable aluminate blue and green phosphors. And an efficient, commercial and environmentally-friendly approach for industrialized REEs recycling from waste phosphor was developed. It would promote reasonable recovery of rare earth resources in China.