Apparatus and method for making metal chloride salt product

[0001] The United States Government has rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the U.S. Department of Energy (DOE) and The University of Chicago.

[0002] This invention is a method for making metal chlorides by combining Cl₂ with Cd to form CdCl₂ which forms a layer over a pool of liquid Cd and where the CdCl₂ reacts with the metal to form the desired metal chloride.

[0003] There is an ongoing problem concerning the development of a method of producing large quantities of metal chloride in a manner which is not corrosive to the containment vessel. The use of gaseous HCl or Cl₂ as the chlorinating agent results in extensive levels of corrosion in ferrous metal containers and any associated ferrous components. To counter this, the use of non-corrosive reactants forms the basis for the present invention. It is known that CdCl₂ is not a corrosive chlorinating agent for ferrous metals and can be combined with various more active metals to form a corresponding chloride. If CdCl₂ is purchased in its commercial form and then purified, the metal process becomes too expensive and also creates Cd metal waste. Applicants developed an alternate method by combining gaseous chlorine with liquid cadmium to form pure CdCl₂ for use as a chlorinating agent in combination with various metals to produce the desired metal chloride while not creating a large Cd waste residue. This occurs since the Cd is continually recycled in the process.

[0004] Accordingly, it is an object of the present invention to provide a method and apparatus for the production of a metal chloride in volatile CdCl₂, using Cl₂ as the chloride source in a manner which does not result in corrosion of the containment vessel and associate manufacturing apparatus.

[0005] Another object of the invention is to provide a method and apparatus which produces metal chloride at a reasonable cost since corrosion is eliminated and Cl₂, not CdCl₂ is the primary chloride source.

[0006] Additional advantages, objects and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.

[0007] This invention involves a method and apparatus for producing metal chlorides which a free energy of formation more negative than CdCl₂ and which are less volatile than CdCl₂, To produce the CdCl₂, gaseous Cl₂ is introduced into liquid Cd which resides, due to density differences, under upper layer initially of molten of CdCl₂. Since CdCl₂ is insoluble in Cd and of lower density, the CdCl₂ produced by the Cl will rise through the liquid Cd into the upper layer and replenish the CdCl₂ which is consumed in forming the metal chloride. A porous basket containing the metal to be chlorinated is suspended in the upper CdCl₂ layer. The CdCl₂ reacts with the metal, which is added in a controlled manner, to form a metal chloride which is soluble to some degree in the upper molten layer. The Cd which is produced in forming the metal chloride sinks due to density differences and recombines with the Cd pool under the molten salt. To maintain the molten state of the Cd and the upper CdCl₂ layer, the temperature of the reactants is maintained at about 600° C. to about 700° C. during the chlorination process. After the reaction is complete, the upper layer consisting of the metal chloride, the CdCl₂ and small amounts of dissolved Cd metal is separated and removed from the immiscible Cd layer which is left in the chlorination vessel. The removed material is then subjected to a distillation process which separates the more volatile CdCl₂ and Cd from the less volatile product metal chloride. The CdCl₂ and Cd are recycled to the chlorination vessel.

[0010] FIG. 1 depicts a schematic of the apparatus for the chlorinator employed to formulate NdCl₃. As is shown in FIG. 1, the chlorination process is housed in a containment vessel 10. A layer of cadmium, Cd 12 is the base layer within the vessel 10. The upper layer 14 is initially CdCl₂ molten salt. The chlorinator is kept at an operational temperature of approximately 600° C.–700° C. which results in both layers being liquids but which is less than the boiling point of either Cd or CdCl₂. A hollow tube 16, preferably of a ferrous composition, penetrates the liquid salt 14 and terminates within the liquid Cd 12 while the opposing end remains above the surface of the liquid salt. In the preferred embodiment, the end of the tube 16 forms a baffle 18. A corresponding baffle 20 can be built into the container on the side opposing the tube 16. The baffles 18, 20 are arranged so that they slope upwardly to approximately the center of the vessel 10 and terminate so as to create a fixed opening 22 within the liquid Cd 12. A second hollow tube 24, preferably made of quartz, is threaded through the tube 16. The lead end of the second tube 24 extends past the end of the first tube such that it is further into the liquid Cd while the opposing end is connected to a Cl₂ feed 28. The second tube 24 is used to transport a stream of gaseous Cl₂ into the liquid Cd where it combines with the liquid Cd to form CdCl₂. The solubility of Cd in pure CdCl₂ at 600° C. is 15 mol %. This allows the material at the Cl₂ nozzle or orifice to have reactant Cd present; thus, the CdCl₂ pool which forms around the nozzle should never be inert. Since the density, at 600° C. of CdCl₂ is 3.37 while that of Cd is 7.82 and since the solubility of CdCl₂ in Cd is near zero, the CdCl₂ feeds into the overlying salt layer 14. The baffles 18 and 20 serve to direct the flow of the CdCl₂ towards the center of the containment vessel 10. A porous basket 26 containing the metal to be chlorinated in ingot form is submerged in the liquid salt 14. Because Cd has a 2⁺ valence, if the metal to be chlorinated has a 2⁺ valence, one mole of CdCl₂ will produce one mole of the chlorinated metal; similarly if the metal to be chlorinated has a 1⁺ valence, then one mole of CdCl₂ produces 2 moles of the chlorinated metal and if the metal to be chlorinated has a 3⁺ valence, then 3 moles of CdCl₂ produces 2 moles of the chlorinated metal.

[0011] The metal to be chlorinated may be an alkali, alkaline earth, rare earth, actinide or TRU metal with the chloride thereof having free energy of formation more negative than CdCl₂.

[0012] Since the reactions to produce CdCl₂ and the chlorinated metal are both exothermic, the rate of Cl₂ addition and metal addition have to be controlled. The cooling rate of the vessel should be designed to match the selected total heat production rate of ≦1 KW, as is depicted in FIG. 1, this value was selected so as to maintain the temperature of the interior of the vessel and its contents at about 600° C.–700° C.

[0013] The porous basket 26 which receives the metal ingots to be chlorinated from the stationary chute 30 is rotated in the salt causing mixing which is necessary to scrub off the formed metal chloride and Cd, reaction products, from the metal surface. The metal chloride dissolves in the CdCl₂ or may form a separate phase or combine with the CdCl₂ depending on the particular metal chloride product. For valence 1, 2, 3 in the metal (M), the reaction with CdCl₂ is (x)M+(y)CdCl₂→(x)MCl_(2y/x)+yCd with (x,y) being (2,1), (1,1), (2,3) respectively. At the reaction temperature, the metal feed is a solid. As its salt is formed by the reaction with CdCl₂, the metal product chloride dissolves (is liquified) in the liquid metal chloride—CdCl₂ mixture. This mixture grows richer in the metal chloride as the as the metal chloride dissolves until it is saturated. At saturation, a solid precipitate forms, the precipitated solid is either a metal chloride or a metal chloride—CdCl₂ compound. In any case the solid will remain with the salt phase since its density is considerably less than the Cd metal phase.

[0014] The other product of the reaction is Cd liquid metal which will be suspended as immiscible drops in the liquid salt, since the salt is under agitation from the rotation of the basket 26. When rotation ceases, the droplets settle out under gravitational force and recombine with the lower layer. The cadmium metal is substantially insoluble in the salt, CdCl₂ and is more dense causing the Cd to sink and recombine with the Cd layer positioned under the molten salt layer 14. The Cl₂ feed may be halted prior to consumption of all of the metal in the basket 26 in order to give a lower level of CdCl₂ in the product salt, metal chloride if desired.

[0015] After the reaction is complete, the salt layer consisting of the metal chloride, CdCl₂, possibly precipitated salt solids, and residual dissolved Cd is removed and the components are separated by distillation using the differences in boiling points, representative examples of which are set out in Table 1. The CdCl₂ and Cd distillate are recycled to the chlorinator.

[0016]

	TABLE 1
		° C.	° C.	g/cm3
	G.	M.P.	B.P.	Density
	LiCl	605	1325	2.07
	NdCl3	784	1600	4.13
	CdCl2	568	960	4.05
	Cd	321	765	8.64
	UCl3	842	1410	5.5
	CeCl3	842	1727	3.92
	LaCl3	860	1000	3.84
	PuCl3	760	1650	5.7
	YCl3	721	1507	2.67
	BaCl2	963	1560	3.9

[0017] The invention, as stated above is useful for chlorinating a wide variety of metals, the limiting factor being that the free energy of formation of the chloride of the selected metal be more negative than CdCl₂, otherwise the chlorination of the metal and reduction of the CdCl₂ will not be thermodynamically driven. Table 1 is representative only, all values being readily available to one of ordinary skill in the art. Although relative motion between the metal in the porous basket 26 and the salt 14 is shown as rotation of the basket, any mechanism known to those of ordinary skill may be used to provide relative movement between the salt 14 and the metal in the basket 26. The chlorination reactions will be exothermic as is the chlorination of Cd, so that a limiting factor is total heat removal rate from the system to maintain the reactants within a suitable temperature range, such as but not necessarily from about 600° C. to about 700° C. The heat removal (loss) rate from the chlorinator matches the heat input rate of the chlorination reactions.

[0018] For instance, it would be undesirable for the salt temperature to exceed the boiling point of Cd (765°), unless the system was pressurized, but these operational details are within the skill of the art. In addition, the BP boiling point, of the metal chloride should be greater than that of the CdCl₂ or Cd to allow for the separation of the metal chloride a distillation process.

[0019] While there has been disclosed what is considered to be the preferred embodiment of the present intention, it is understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.