共沈法を用いた廃蛍光体スラッジからの赤色蛍光体(Y_2O_3 : Eu^<3+>) の合成 [in Japanese] Synthesis of Red Phosphor(Y_2O_3 : Eu^<3+>) from Waste Phosphor Sludge by Coprecipitation Process [in Japanese]
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The coprecipitation behaviors of leaching solution and their sintering conditions have been examined to synthesize red phosphor (Y<sub>2</sub>O<sub>3</sub>:Eu<sup>3+</sup>) from phosphor sludge contained in waste fluorescent lamp. At first, the recovery of rare earth elements and the removal of impurity in the leaching solution were investigated by treatment processes such as hydroxide and oxalate precipitations. The drying process of coprecipitation reaction product was examined by freeze-dry and air-dry. The synthesis behavior of red phosphor (Y<sub>2</sub>O<sub>3</sub>:Eu<sup>3+</sup>) was also investigated by changing some factors such as temperature, time and flux. The experimental results obtained are summarized as follows:<BR>(1) The homogeneous Y and Eu oxalate precipitations were produced by adding oxalic acid into leaching solution under the dispersion using ultrasonic stirring and the desiccation using freeze-dry.<BR>(2) Y and Eu precipitations were sintered at 1,473 K for 144 ks under the addition of 1 % barium borate as a flux. Red phosphor (Y<sub>2</sub>O<sub>3</sub>:Eu<sup>3+</sup>) sintered had crystal size more than 0.2<i>μ</i>m and average particle size of 5-6<i>μ</i>m.<BR>(3) Impurity elements in leaching solution were efficiently removed by hydroxide precipitation process, in which leaching solution was retained at less than pH 5.0 and by oxalate synthesis process, in which oxalic acid was added to use 3 times the molar quantity of Y and Eu hydroxides. In these treatments, recovery of Y and Eu were about 85 %, respectively.<BR>(4) Synthesis process of red phosphor (Y<sub>2</sub>O<sub>3</sub>:Eu<sup>3+</sup>) from waste phosphor sludge contained in fluorescent lamp was established by using simulate leaching solution. On the basis of these treatment methods, rare earth powder of red phosphor was synthesized from waste phosphor sludge.<BR>Luminescence properties of rare earth powder synthesized were in fairly agreement with these of commercial red phosphor. Rare earth powder synthesized in this work may be used substantially as a red phosphor.
Shigen-to-Sozai 118(5), 413-418, 2002-06-25
The Mining and Materials Processing Institute of Japan