Methods of recovering terbium oxide from a glass

Abstract

A method for recovering Tb.sub.4 O.sub.7 from a glass containing terbium oxide is disclosed, the method including the steps of:I. fusing the glass containing terbium oxide with NaOH to provide a solid fusion product;Ii. slurrying the fusion product of Step I to disperse solid particles of Tb.sub.4 O.sub.7 and any Li.sub.2 SiO.sub.3 present and to dissolve any Al.sub.2 O.sub.3, NaOH and Na.sub.2 SiO.sub.3 to thereby separate the same from the solid particles of Tb.sub.4 O.sub.7 ;Iii. reacting the solid particles of Tb.sub.4 O.sub.7 of Step II with HNO.sub.3 to provide Tb(NO.sub.3).sub.3 ;Iv. reacting the Tb(NO.sub.3)3with oxalic acid to form Tb.sub.2 (C.sub.2 O.sub.4).sub.3 ; andV. firing the Tb.sub.2 (C.sub.2 O.sub.4).sub.3 to form CO.sub.2 and solid Tb.sub.4 O.sub.7 to that is recovered from the glass.

Description

INVENTION

The present invention is directed to recovering Tb.sub.4 O.sub.7 from a glass containing terbium oxide and, more particularly, is directed to recovering Tb.sub.4 O.sub.7 from a glass containing terbium oxide and contaminated with small amounts of platinum.

The present invention provides a convenient and economical method of obtaining Tb.sub.4 O.sub.7, which is costly and often difficult to obtain.

It is an object of the present invention to provide a method of recovering Tb.sub.4 O.sub.7 from a laser glass containing terbium oxide and small contaminating amounts of platinum.

It is an object of the present invention to provide a method of recovering Tb.sub.4 O.sub.7 from a laser glass containing terbium oxide, the method comprising the steps of:

I. fusing the glass containing terbium oxide with NaOH to provide a solid fusion product; Ii. slurrying the fusion product of Step I to disperse solid particles of Tb.sub.4 O.sub.7 and to dissolve any Al.sub.2 O.sub.3, NaOH and Na.sub.2 SiO.sub.3 present in the fusion product to thereby separate from the other ingredients solid particles of Tb.sub.4 O.sub.7 + any Li.sub.2 SiO.sub.3 formed; Iii. reacting the solid particles of Tb.sub.4 O.sub.7 separated from the slurry of Step II with HnO.sub.3 to form Tb(NO.sub.3).sub.3 ; Iv. reacting Tb(NO.sub.3).sub.3 with oxalic acid to form terbium oxalate; and V. firing the terbium oxalate to form solid Tb.sub.4 O.sub.7 and CO.sub.2, which CO.sub.2 volatilizes off as a gas and is separated from the solid Tb.sub.4 O.sub.7.

These and other objects will be apparent from the specification that follows and the appended claims.

The present invention provides an economical and convenient method for recovering Tb.sub.4 O.sub.7 from a glass containing terbium oxide, including glass such as laser glass having contaminating amounts of platinum. The method comprises the steps of:

I. fusing the glass containing terbium oxide with NaOH to provide a solid fusion product; Ii. separating the solid particles of Tb.sub.4 O.sub.7 from any Al.sub.2 O.sub.3, NaOH and Na.sub.2 SiO.sub.3 present by slurrying the fusion product of Step I to provide solid particles of Tb.sub.4 O.sub.7 and any Li.sub.2 SiO.sub.3 present; Iii. reacting the solid particles of Tb.sub.4 O.sub.7 of Step II with HNO.sub.3 to provide terbium nitrate; Iv. reacting terbium nitrate with oxalic acid to form terbium oxalate as a reaction product thereof; and V. firing the terbium oxalate to form CO.sub.2, which is volatilized off as a gas and to form solid Tb.sub.4 O.sub.7 that is recovered. The fusing of Step I is suitably carried out at about 500.degree. C.

The methods of this invention were developed in one preferred embodiment for the recovery of terbium oxide from a laser or Faraday rotator glass having contaminated amounts of platinum, the recovered terbium oxide then being advantageously available for subsequent reuse. The methods of this invention are convenient and advantageous.

In one preferred embodiment of the present invention, the laser glass or light rotating glass for use in a Faraday rotator device is a glass containing about 41% by weight of terbium oxide, the remainder of the composition containing silica, alumina and lithium oxide. A suitable light-rotating glass containing terbium oxide is one of the lithia-silica-terbia systems generally comprising, on a mole basis, about 61-80 mole percent SiO.sub.2, 15-27.5 mole percent Li.sub.2 O, 3-9 mole percent terbium oxide, and optionally, up to about 3 mole percent of R.sub.2 O.sub.3, such as La.sub.2 O.sub.3, Al.sub.2 O.sub.3 or B.sub.2 O.sub.3, and optionally, minor amounts of Na.sub.2 O, K.sub.2 O or CaO, namely, 0-10 Na.sub.2 O, 0-5 K.sub.2 O and 0-5 CaO. The sum of Li.sub.2 O + Na.sub.2 O + K.sub.2 O + CaO should not generally be greater than about 32.5 mole percent.

A suitable glass for a Faraday rotation device is described in U.S. Pat. No. 3,484,152 to Robinson. One suitable terbium oxide-alumina silicate glass, as therein disclosed, is one containing in weight percent about 12% Al.sub.2 O.sub.3, 25% SiO.sub.2, 4% MgO, 1% Pr.sub.2 O.sub.3 and 58% Tb.sub.2 O.sub.3.

In accordance with the specific embodiment of the present invention, the glass containing 61 mole percent SiO.sub.2, 27.5 mole percent Li.sub.2 O, 2.5 mole percent Al.sub.2 O.sub.3 and 9 mole percent Tb.sub.4 O.sub.7 is powdered and fused with NaOH to provide a solid fusion product. The resultant fusion is slurried in water to disperse solid particles of Tb.sub.4 O.sub.7 and Li.sub.2 SiO.sub.3, and to dissolve the alumina, NaOH and Na.sub.2 SiO.sub.3 to thereby separate the latter ingredients from the solid particles of terbium oxide. Thereafter, solid particles of terbium oxide are reacted with HNO.sub.3 to provide Tb (NO.sub.3).sub.3, the insoluble solid products of terbium oxide being reslurried in water and the pH adjusted to 2 with nitric acid. The resulting reaction product is terbium nitrate, which is a soluble salt, and another reaction product is a stable silica salt. Thereafter, the terbium nitrate is reacted with oxalic acid to form Tb.sub.2 (C.sub.2 O.sub.4).sub.3. Thus the oxalic acid forms a complex, insoluble salt with terbium, which is filtered free of the silica. The terbium oxalate is fired in a 1,000.degree. C. furnace to provide the recovered terbium oxide. The terbium oxide is reported as Tb.sub.4 O.sub.7, it generally being a mixture of Tb.sub.2 O.sub.3 and TbO.sub.2.

The resultant recovered terbium oxide was used in a laser glass composition, as above described, to provide a laser glass which was suitable. The resultant laser glass of a lithia-silica-terbia system had a good balance of properties, including a high Verdet constant, good light transmission, good melt properties, high damage threshold, and good forming properties, including a relatively wide working temperature range at approximately log.sub.4 viscosity, being relatively seed-free and easily homogenized.

In accordance with the present invention, it is costly and sometimes difficult to obtain terbium oxide. In the present process, a sometimes scarce material is obtained from glass, which is, as in the case with the light rotating glass, contaminated with platinum, rending it useless. In accordance with the present invention, the glass is fused with sodium hydroxide, which fusion breaks the composition into single components which can be separated from one another. These separations are made by controlling the pH in the subsequent isolation steps.

Claims

1. A method of recovering Tb.sub.4 O.sub.7 from a glass containing terbium oxide, the method comprising the steps of:

I. fusing the glass containing SiO.sub.2, Li.sub.2 O, Al.sub.2 O.sub.3 and terbium oxide with NaOH to provide a solid fusion product;

Ii. slurrying in water the fusion product of Step I to disperse solid particles of Tb.sub.4 O.sub.7 and Li.sub.2 SiO.sub.3 and dissolving the Al.sub.2 O.sub.3, NaOH and Na.sub.2 SiO.sub.3 to thereby separate said Al.sub.2 O.sub.3, NaOH and Na.sub.2 SiO.sub.3 from the solid particles of Tb.sub.4 O.sub.7 ;

Iii. reacting the solid particles of Tb.sub.4 O.sub.7 separated from the slurry of step II with HNO.sub.3 to provide Tb(NO.sub.3).sub.3 ;

Iv. reacting Tb(NO.sub.3).sub.3 with oxalic acid to form Tb.sub.2 (C.sub.2 O.sub.4).sub.3 ; and

V. firing Tb.sub.2 (C.sub.2 O.sub.4).sub.3 to form Tb.sub.4 O.sub.7 and CO.sub.2 to thereby recover solid Tb.sub.4 O.sub.7.

2. A method as defined in claim 1 in which the glass composition is a light rotating glass.

3. A method as defined in claim 1 in which the glass has the following approximate composition:

______________________________________Ingredients Mole Percent______________________________________SiO.sub.2 61 - 80Li.sub.2 O 15 - 27.5Na.sub.2 O 0 - 10K.sub.2 O 0 - 5CaO 0 - 5Al.sub.2 O.sub.3 0 - 3B.sub.2 O.sub.3 0 - 3La.sub.2 O.sub.3 0 - 3Terbium Oxide 3 - 9______________________________________

wherein the sum of Li.sub.2 O + Na.sub.2 O + K.sub.2 O + CaO is no more than about 32.5 mole percent.

4. A method as defined in claim 1 in which the reaction of Step III is at a pH of about 2.

5. A method as defined in claim 1 in which the firing temperature of Step V is about 1,000.degree. C.

6. A method as defined in claim 1 in which the fusing of Step I is at about 500.degree. C.