US3164462A - Preparation of thorium metal from the oxide - Google Patents

Description

Jan. 5, 1965 J. B. KNIGHTON ETAL 3,154,462

PREPARATION OF THORIUM METAL FROM THE OXIDE Filed June 24, 1963 4 Sheets-Sheet 1 y f duciz'afr 0/ 7/10 0 Iv YEA/T085 James 5. MVIIITOIV 941.51 VL Mam/menu 00537 K JTEUA/EIVBEKQ Msaey 14 4416 ClY/AD firms vex Jan. 5, 1965 Filed June 24, 1963 ZlL/ Reducaz'orz of 77:0, iv Q Q J. B. KNIGHTON ETAL PREPARATION OF THORIUM METAL FROM THE OXIDE '4 Sheets-Sheet 2 J0 20 .90 90 .5'0 211/ jya fles um ozrcerztratiazz in final /g 111 .IN VENToRS James 5 441/0, 70 ALLEPPH v. 1449811104 Reamer K. STEUNENBIERQ wEsLEy A HuScII/LIT flrromvey Jan. 5, 1965 J. B. KNIGHTON ETAL PREPARATION OF THORIUM METAL FROM THE OXIDE 4 Sheets-Sheet 4 Filed June 24, 1963 INVENTORJ James 5. /fw9 4mm K ne-r A. Snows/vac; Wail-5y 6 z9adulllLbT firm/w y United States Patent ()fifice This invention deals with an improved process ofmaking thorium metal from the oxide, and in particular with the reduction of the oxide with zinc-magnesium alloy while the oxide is dispersed in a molten halide mixture,

In the assignees copending application Ser. No. 219,828, fded on August 24, 1962, by James B. Knighton et al., now abandoned, a process for the reduction of thorium dioxide is covered, according to which the oxide is dispersed in a molten magnesium chloride-calcium fluoride-calcium chloride salt mixture or flux and then reduced with a magnesium-zinc alloy containing by Weight of magnesium. When an inert dry atmosphere Was used in said process, the magnesium cation content of the salt mixture was preferably about rn/o, while with an atmosphere of air themagnesium content could range between 45 and 48 m/ 0.. In said process previously filed, a relatively small quantity of thorium dioxide could be dispersed in the salt mixture, a weight ratio of about 0.0227 for ThO zflux usually being chosen. A magnesium-zinc alloy was obtained in that previous process that contained about 5 w/o of thorium;

Further extensive and thorough studies now revealed that, if a number of critical operating conditions are observed, a higher ratio of thorium dioxide can be used in the flux, and an alloy can be obtained that contains a thorium content of up to 12% by weight.

Thus it was found that a flux consisting of 90 m/o of ride and curve 3 on aconsisting of 90 m/o of mag nesium chloride and 10 m/o of magnesium fluoride;

For each experiment. summarized in FIGURE Z, 68.3

grams of thorium dioxide were dispersed in 300 grams of the respective flux, and 600' grams of magnesium-zinc al.-

loy of various magnesium contents were added. The reaction mass was heated to between 800 and 850 C in an argon atmosphere for'four hours and" mixed during that time at 800 r.p.m. ,The magnesium content of the final magnesium-zinc alloy and the degree of reduction obtained were then plotted'in the diagram of FIGURE 2 about 12.5 grams of magnesium were consumed in each experiment for the reduction of the thorium dioxide.

It is obvious from FIGURE- 2 that flux 1 does not accomplish. an about 100% reduction at all, that flux 2 yields practically a 100% reduction at between 5' and 10% of magnesium in the'final alloy, while flux 3 brings a about a nearly quantitative" reduction with a magnesium I content in the final alloy of between 5 and 15 W/ 0L This is oneof the reasons why theflux consisting of 90 111/0 7 magnesium chloride and l'0 mlo'of magnesium fluoride is preferred; 1 I

I That the magnesium cation concentration in the flux has a' distinct effect on the degree of thorium-dioxide re- 'duction and also'on-the thorium concentration that can be present in the final" alloy is obvious from FIGURE 3.

magnesium fluoride) and 90 m/o-of Cl'" (as magnesium Y chloride with or without calcium chloride). Curve 1 was obtained with a flux containing 10 m/o of calcium fluoride, 15 m/o of magnesium chloride and 75 m/o' of calmagnesium chloride and 10 m/o magnesium fluoride which is the preferred flux, as will be shown later-in order to yield a thorium dioxide reduction of nearly 100%, can contain thorium dioxide in a quantity to yield a weight ratio of up to about 0.2 for ThO zflux. This is shown in FIGURE 1 where the percentages of thorium dioxide reduction are correlated with the weight ratio of the thorium dioxide in the magnesium chloride-magnesium fluoride flux. The operating temperature for the experiments that are summarized in FIGURE 1 was 850 C., and the mass was stirred in a tantalum crucible at 1000 r.p.m. The magnesium content of. the magnesiumzinc reducing alloy there was about 10% by Weight. The reaction in each case was carried out in an argon atmosphere for four hours.

Looking at the diagram of FIGURE 1, it will be noted that a sharp drop of the curve to yields of below 100% occurs at T hO rflux weight ratios slightly above 0.2;

It was furthermore discovered that the magnesium content of the magnesium-zinc reducing agent had a pro nounced effect on the degree ofthorium dioxide reduction and that there is a relatively narrow range for the magnesium concentration at which an about quantitative reduction is attained. This is illustrated in FIGURE 2 where three diflerent sets of data are plotted for three diflerent flux mixtures. The abscissa shows the magnesi-.- urn concentrations of the final alloy in weight percent, while on the ordinate the degree of reduction of the thorium dioxide in weight percent is plotted. Y

the degree of reduction.

cium chloride; curve 2 with a flux containing 10 m/o of calcium fluoride, 20 m/o of magnesium chloride and g 70 m/o of calcium chloride; curve 3-with one containing 10 m/o of calcium fluoride, 25 m/o of. magnesium chloride and 65 m/o of calcium chloride; and 'curve4 ments previously described. In FIGURE 3 the thorium concentrations of thevariousfinal alloys are plotted Tak-.

against the degrees of thorium dioxidereduction. ing each curve for each flux separately, it will be noted that in each case an attempted'iricrease of thorium concentration inthe final meta'l'brought about a decrease of' Proceeding now from one curve to the next following curve which shows the higher magusing the flux-containing magnesium cations onlyand it j. i also shows that at a higherthorium-concentration the reduction is markedly,decreased;fsome thorium dioxide remaining in the flux as such. 7 g

It was finally'also ascertained that the solubility of thorium in the zinc-magnesium alloy is improved by an increase of the magnesium concentration in the alloy and also by an increase in temperature. This is shown in FIGURE 4 where the thorium solubility in the alloy is Curve 1 of FIGURE 2 is based on a flux composition consisting of m/o of calcium chloride, 30 m/o of magnesium chloride and 10 m/o of calcium fluoride; curve 2 correlated with the magnesium concentration; It is shown there that a higher thorium concentrationis possible in the alloy with the higher magnesium concentration. and at a higher temperature.

temperature of between 825 and 875;C., the weight ratio of ThO :flux ranging up to 0.2; adding an excess of a m 'ag- Patented Jan. 5 19 nesium-zinc alloy containing between 5 and 15% by weight of magnesium to the solution formed, whereby thorium dioxide is reduced to the metal and the latter is dissolved in the excess alloy to form a final alloy, said thorium dioxide being dispersed in the flux in a quantity so as to yield a thorium content of up to 12% by weight in the final alloy; and separating a thorium-depleted flux from a thorium-magnesium-zinc alloy.

In the following an example is given for illustrative purposes.

Example Thorium dioxide, 54.6 grams, was dispersed in a tantalum crucible in 300 grams of molten flux containing 10 m/o of magnesium fluoride and 90 m/o of magnesium chloride. To the solution formed there were added 41.9 grams of magnesium and 320 grams of zinc. The reaction mixture was maintained at 850 C. for four hours under an argon atmosphere and stirred with a tantalum paddle at 1000 r.p.m.

The reaction mixture was then allowed to settle and cool, and the salt was separated from the metal by mechanical means. Both phases were analyzed for their thorium content. It was found that the reduction has been 98.4%

While the process has been primarily described using thorium dioxide as the starting material, it has been found that thorium tetrafluoride can be substituted therefor and that, in fact, with the latter a still higher thorium concentration in the alloy can be obtained.

It will be understood that the invention is not to be 4} limited to the details given herein but that it may be modified Within the scope of the appended claim.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

A process of reducing thorium dioxide to thorium metal comprising dispersing thorium dioxide in a molten flux consisting of 90 m/o of magnesium chloride and 10 m/o of magnesium fluoride in an inert atmosphere and at a temperature of between 825 and 875 C., the weight ratio of ThO :fluX ranging up to 0.2; adding an exces of a magnesium-zine alloy containing between 10 and 15 by weight of magnesium to the solution formed, whereby thorium dioxide is reduced to the metal and the latter is dissolved in the excess alloy to form a final alloy, whereby a final thorium-zinc-magnesium alloy is obtained containing about 12% by weight of thorium; and separating a thorium-depleted flux from a thorium-magnesiumzinc alloy.

Transactions of the American NuclearSociety, vol. 24, No.2, November 1961, pp. 352-353;

CARL D. QUARFORTH, Primary Examiner. REUBEN EPSTEIN, Examiner.

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