METHOD OF REMOVING YTTRIUM FROM YTTRIUM-CONTAINING EUROPIUM OXIDE

Abstract

A purifying method of removing yttrium from a yttrium-containing europium oxide, including the steps of (A) dissolving a yttrium-containing europium oxide in a solvent to produce a saturated yttrium-containing europium compound solution; (B) performing a low-temperature recrystallization treatment on the saturated yttrium-containing europium compound solution to produce a europium-containing precipitate; (C) calcining the europium-containing precipitate, followed by dissolving the calcined europium-containing precipitate in an inorganic acid to produce a europium-containing metal functioning as an electrolyte; and (D) performing an electrochemical reduction process on the electrolyte which the europium-containing metal functions as, followed by introducing a precipitant thereto to produce a europium compound. The method removes yttrium from yttrium-containing europium oxide present in phosphor powder to purify europium oxide, thereby recycling, purifying and reusing europium valuable metal to reduce environmental pollution.

Claims

1. A purifying method of removing yttrium from a yttrium-containing europium oxide, comprising the steps of: (A) dissolving a europium oxide in a solvent to produce a saturated yttrium-containing europium compound solution; (B) performing a low-temperature recrystallization treatment on the saturated yttrium-containing europium compound solution to produce a europium-containing precipitate; (C) calcining the europium-containing precipitate, followed by dissolving the calcined europium-containing precipitate in an inorganic acid to produce a europium-containing metal functioning as an electrolyte; and (D) performing an electrochemical reduction process on the electrolyte which the europium-containing metal functions as, followed by introducing a precipitant thereto to produce a europium compound.

2. The purifying method of removing yttrium from a yttrium-containing europium oxide according to claim 1, wherein the saturated yttrium-containing europium compound solution is a saturated yttrium-containing europium nitrate solution.

3. The purifying method of removing yttrium from a yttrium-containing europium oxide according to claim 1, wherein the low-temperature recrystallization treatment cools down the saturated yttrium-containing europium compound solution to 030 C. such that the europium-containing precipitate is produced by recrystallization.

4. The purifying method of removing yttrium from a yttrium-containing europium oxide according to claim 1, wherein, in step (C), the calcination process entails calcining the europium-containing precipitate at 9001100 C. for 12 hours to produce europium oxide.

5. The purifying method of removing yttrium from a yttrium-containing europium oxide according to claim 1, wherein the electrochemical reduction process is performed with a platinum netting cathode and a platinum netting anode, a voltage of 34V, and sample volume mole concentration of 0.30.8M.

6. The purifying method of removing yttrium from a yttrium-containing europium oxide according to claim 1, wherein the precipitant is ammonium sulfate.

7. The purifying method of removing yttrium from a yttrium-containing europium oxide according to claim 1, wherein the europium compound is europium (II) sulfate.

8. The purifying method of removing yttrium from a yttrium-containing europium oxide according to claim 1, wherein, in step (D), the europium compound is filtered and calcined again to produce highly pure yttrium-free europium oxide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a flow chart of a purifying method of removing yttrium from a yttrium-containing europium oxide according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention is hereunder illustrated with specific preferred embodiments so that persons skilled in the art can gain insight into the features and advantages of the present invention.

[0015] The method of the present invention employs techniques, namely high-temperature saturated dissolution, low-temperature recrystallization, electrochemical reduction, and selective precipitation, to remove yttrium from yttrium-containing europium oxide for purification. The method of the present invention is efficient, requires a simple process, incurs low costs, and facilitates mass production. In general, metallic nitrates, including europium nitrate, are readily soluble in water. In this regard, the solubility of europium nitrate in water increases greatly with temperature. Given the high solubility of europium nitrate in water, in the embodiments of the present invention, europium oxide reacts with and thus dissolves in a nitrate at a high temperature until the resultant europium nitrate reaches a saturated state. Then, the europium nitrate is cooled down to lower the solubility of the europium nitrate and thus allow the europium nitrate to precipitate, thereby achieving purification of europium. Finally, the purified europium is oxidized to produce highly pure europium oxide. On the other hand, the embodiments of the present invention entail dissolving yttrium-containing europium oxide in HCl, using Y3+-Eu3+-containing solution as an electrolyte, using platinum as cathode and anode, and introducing a current at a selected voltage; meanwhile, the reaction of Eu3+.fwdarw.Eu2+ occurs, but Y3+ does not undergo any reduction reaction. Afterward, the precipitant, such as ammonium sulfate, is added to the solution to precipitate EuSO.sub.4, wherein neither Y3++ nor Eu3+ precipitates, thereby achieving removal of yttrium.

[0016] Referring to FIG. 1, there is shown a flow chart of a purifying method of removing yttrium from a yttrium-containing europium oxide according to the present invention. As shown in the diagram, the present invention provides a purifying method of removing yttrium from a yttrium-containing europium oxide, comprising the steps of: (A) dissolving a yttrium-containing europium oxide in a solvent to produce a saturated yttrium-containing europium compound solution S101; (B) performing a low-temperature recrystallization treatment on the saturated yttrium-containing europium compound solution to produce a europium-containing precipitate S102; (C) calcining the europium-containing precipitate in an inorganic acid to produce a europium-containing metal functioning as an electrolyte S103; and (D) performing an electrochemical reduction process on the electrolyte which the europium-containing metal functions as, followed by introducing a precipitant thereto to produce a europium compound, wherein the europium compound is filtered and calcined again to produce highly pure europium oxide S104. The saturated yttrium-containing europium compound solution includes a saturated yttrium-containing europium compound solution.

Embodiment

[0017] To verify the effectiveness of the steps of the method of the present invention, experiments are conducted against different criteria and parameters, as shown in Table 1. Embodiments 1, 2, 3 involve dissolving a raw material (yttrium-containing europium oxide) at different temperatures, cooling down it, performing recrystallization on it at different temperatures, and calcining it at a high temperature (around 1000 C.) to turn it into an oxide, wherein the raw material (yttrium-containing europium oxide) has the following constituents: europium oxide (95.00 wt %) and yttrium oxide (5.00 wt %). Embodiment 1 entails producing a saturated europium nitrate solution (saturated yttrium-containing europium compound solution) at 60 C., and then cooling it to 20 C.; and the result shows that the purity of the europium oxide increases from 95.0 wt % to 98.50 wt %, thereby verifying that element purity is increased by high-temperature dissolution and low-temperature crystallization. Embodiment 2 entails producing a saturated europium nitrate solution at 60 C. and then cooling it to 0 C.; and the result shows that the purity of the europium oxide increases from 95.00 wt % to 99.09 wt %, whereas the concentration of impurities decreases significantly. Embodiment 3 entails producing a saturated europium nitrate solution at 80 C. and then cooling it to 0 C.; and the result shows that, in the sample, the europium oxide in Embodiment 3 has higher purity than their counterparts in Embodiments 1, 2. The aforesaid experiments verify that element purity is increased by high-temperature dissolution and low-temperature crystallization.

TABLE-US-00001 TABLE 1 parameters for recrystallization and results Embodi- Embodi- Embodi- ment 1 ment 2 ment 3 dissolution temperature C. 60 60 80 recrystallization temperature C. 20 0 0 europium oxide wt % 98.50 99.09 99.43 yttrium oxide wt % 1.50 0.91 0.57

[0018] The europium-containing precipitate (europium oxide with a purity of 99.09 wt %) of Embodiment 2 is used as a raw material and dissolved in HCl to function as an electrolyte for undergoing electrochemical reduction for 24 hours. Then, ammonium sulfate functions as a precipitant, and the resultant europium (II) sulfate is calcined at a high temperature (around 1000 C.) to form an oxide (the criteria and result are shown in Table 3). Embodiment 4 entails dissolving 100 g of the raw material in HCl, applying a voltage of 4V to it to perform thereon electrochemical reduction, and after 24 hours, introducing to it ammonium sulfate to precipitate europium (II) sulfate, calcining it at a high temperature, measuring its total weight, and performing element analysis; and the result shows that the purity of the europium oxide increases from 99.09 wt % to 99.93%, and the recycling rate is 76.2%. Embodiment 5 uses a lower sample weight but keeps the other parameters unchanged, and its result shows that the purity of the europium oxide increases from 99.09 wt % to 99.98%, which is higher than that of Embodiment 5, and its recycling rate of 85.2 is also higher than that of Embodiment 5. Embodiment 6 changes the applied voltage for electrochemical reduction (decreasing it from 4V to 3V) and thus reduces the reduction current, and in consequence the yield of Eu.sup.2+ decreases, causing the end product of Embodiment 6 to have a lower weight than its counterpart in Embodiment 4, but the purity 99.97% of the europium oxide of Embodiment 6 is higher than the purity 99.93% of the europium oxide of Embodiment 4. The results of Embodiment 4 through Embodiment 6 indicate that the removal of europium oxide is achieved by dissolving yttrium-containing europium oxide in HCl to function as an electrolyte, applying a voltage thereto to perform electrochemical reduction thereon, and introducing a precipitant ammonium sulfate thereto.

TABLE-US-00002 TABLE 3 parameters for electrochemical reduction and results Embodi- Embodi- Embod- ment 4 ment 5 iment 6 sample weight (g) 100 50 100 HCl volume (ml) 400 400 400 applied voltage (V) 4 4 3 yttrium oxide (wt %) 0.07 0.02 0.03 europium oxide (wt %) 99.93 99.98 99.97 product weight (g) 76.2 42.6 61.3 recycling rate (%) 76.2 85.2 61.3

[0019] The main objective of the present invention is to increase the purity of yttrium-containing europium oxide with different criteria, such as dissolution temperature of europium oxide, crystallization temperature of europium nitrate, voltage applied to electrode, duration for applying the voltage, and types of precipitant, to remove yttrium and thus increase the purity of europium oxide. When configured appropriately, the aforesaid voltage and duration for applying the voltage together enables Eu.sup.3+ to be reduced and turned into Eu.sup.2+, without causing Y.sup.3+ to undergo any reduction reaction. This, coupled with the precipitant thus introduced, allows Eu.sup.2+ or Y.sup.3+ to precipitate, thereby effectuating europium purification. The method of the present invention is easy, dispenses with any apparatus characterized by intricate component operation and process, incurs low equipment costs, and thus facilitates mass production. The operation of the method of the present invention produces no waste water, dispenses with back-end waste water treatment facilities, and thus provides a recycling process which is environment-friendly.

[0020] The features and advantages of the present invention are disclosed above by preferred embodiments. The preferred embodiments are not restrictive of the present invention. Any persons skilled in the art can make some changes and modifications to the preferred embodiments without departing from the spirit and scope of the present invention. Accordingly, the legal protection for the present invention should be defined by the appended claims.