Method of preparing lithium salts

Details Method of preparing lithium salts Method of preparing lithium salts

1997-09-16

2003-04-29

Kumar, Shailendra (Department: 1621)

Chemistry of inorganic compounds

Treating mixture to obtain metal containing compound

Alkali metal

C423S277000, C423S332000, C423S395000, C423S400000, C423S463000, C423S464000, C423S518000, C423S519200, C423S515000, C423S551000, C423S566200, C423S605000, C423S606000, C423S641000, C423S642000, C423S643000, C423S646000, C562S477000, C562S493000, C562S578000, C562S582000, C562S584000, C562S588000, C562S607000, C562S609000

Reexamination Certificate

active

06555078

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to a process for preparing lithium salts, and specifically, to an inexpensive process for preparing lithium salts from low cost lithium chloride and lithium sulfate.
BACKGROUND OF THE INVENTION
Lithium salts have found utility in various applications. For example, lithium nitrate is known for use in ceramics, pyrotechnics, salt baths, heat exchange media, refrigeration systems, rocket propellants and specialized concrete applications. Another useful lithium salt, lithium bromide, is known for use in pharmaceuticals, air conditioning systems, low temperature heat exchange media, drying agent, refrigeration systems, batteries, medicine and as a humectant.
The conventional method of producing many lithium salts is to combine either lithium carbonate or lithium hydroxide with acids containing the desired anion for the lithium salt. For example, the conventional method of producing lithium nitrate is to react lithium carbonate and/or lithium hydroxide with nitric acid. Nevertheless, this process requires high purity raw materials and very expensive plant equipment and metal of construction for the handling of the highly alkaline lithium salts and concentrated nitric acid.
Similarly, the conventional method of producing lithium bromide is to react hydrobromic acid with lithium hydroxide or lithium carbonate. The saturated solution on cooling precipitates lithium bromide monohydrate, which can be dried to the anhydrous salt. Nevertheless, hydrobromic acid is a very irritating colorless gas that fumes strongly in moist air. Furthermore, hydrobromic acid is classified under DOT regulations, as highly corrosive, and highly irritative to eyes, skin and respiratory passages. Therefore, the production of lithium bromide using hydrobromic acid can be quite dangerous.
As described above, the use of highly acidic materials in the formation of lithium salts is undesirable as the materials are generally hazardous and require special equipment. Furthermore, the above processes generally do not produce high yields of the lithium salts being produced and therefore cannot be used where high purity lithium salts are desired. Therefore, there is a need to provide an inexpensive method of increasing the purity of the lithium salts without using highly acidic materials.
SUMMARY OF THE INVENTION
The present invention provides an inexpensive process for the preparation of lithium salts using lithium chloride and lithium sulfate. The process of the invention eliminates the use of highly acidic materials and thus reduces the cost of raw materials and the need for specialized equipment. The process produces lithium salts of desired purity without compromising safety in the production of these salts.
The process of the invention comprises preparing a lithium salt of formula LiX of desired or required purity by reacting a lithium salt selected from lithium chloride, lithium sulfate, and combinations thereof with NaX or KX in an aqueous, semiaqueous and/or organic solution and removing the precipitated solids from the semiaqueous solution to obtain a LiX solution of desired purity. Any combinations of solvents can be used in the invention but preferably the lithium salt and NaX or KX salt are reacted in a semiaqueous solution containing water and an organic solvent. Nevertheless, the semiaqueous reacting step can be preceded by an aqueous reacting step or can be replaced by successive aqueous and organic reacting steps. Typically, the organic solvent in the semiaqueous and organic solutions is selected from aliphatic ketones, aliphatic alcohols, and mixtures thereof. The process of the invention has been found especially useful for producing lithium salts of formula LiX wherein the solubility of LiX in the solution used is greater than the solubility of the sodium or potassium salts produced as by-products in the reacting step.
Use of sulfate salts as part of the starting materials or feed can require a cooling step to precipitate the resultant sodium and/or potassium sulfate salts, such as Na
2
SO
4
.10H
2
O, K
2
SO
4
, KLiSO
4
.H
2
O, NaLiSO
4
.H
2
O, and the like. The use of chloride salts as starting materials or feed can require higher temperatures to reject the resultant sodium salt NaCl and lower temperatures for the resultant potassium salt KCl from aqueous metathesis salting out. To purify LiNO
3
and/or LiBr salt solutions, a solvent step metathesis step can be required for precipitation removal of sodium and/or potassium as chloride and/or sulfate salts.
In a specific embodiment of the invention, the process for preparing a lithium salt of formula LiX having a desired or required purity comprises dissolving lithium chloride, lithium sulfate, or a mixture thereof and a NaX salt, KX salt, or mixture thereof, in an aqueous solution and filtering the solution to remove the precipitated sodium and potassium salts. An aliphatic ketone, an aliphatic alcohol, or a mixture thereof, is then added to the solution to form a semiaqueous solution, and the precipitated sodium and potassium salts are again filtered from the solution. In addition, a monovalent cation sulfate salt can be added to the semiaqueous solution to cause the salting out or precipitation of undesired sodium and potassium salts from the solution thereby purifying the solution. The organic solvent is then removed and the resulting LiX solution of desired purity is recovered. The LiX solution can then be dried where solid LiX salt is desired as the end product or stored and sold in solution.
These and other features and advantages of the present invention will become more readily apparent to those skilled in the art upon consideration of the following detailed description which describes both the preferred and alternative embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention comprises preparing a lithium salt of formula LiX having a desired or required purity by reacting a lithium salt selected from lithium chloride, lithium sulfate, and combinations thereof with NaX or KX in an aqueous, semiaqueous or organic solution and removing the precipitated solids from the solution to obtain a LiX solution of desired purity. Any combination of solvents can be used in accordance with the invention. Preferably, a semiaqueous solution is used containing water and an organic solvent. The reaction can also be initiated in an aqueous solution and then continued in either a semiaqueous or an organic solution to provide the LiX salts of the invention. As used herein, and as will be appreciated by the skilled artisan, the term “salt” unless otherwise specifically defined can refer to a salt provided in solid or liquid form (for example as brine solutions).
The lithium chloride and lithium sulfate salts used in the process are inexpensive and readily available in anhydrous form, hydrated form, or in solution. Typically, the lithium chloride is obtained in purified form as a liquid as well as an anhydrous salt from geothermal brine deposits such as those in Chile and Argentina by selective adsorption and solar evaporation. Lithium sulfate is obtained from spodumene ore by conventional roasting, acid leach and purification steps, and from brine by conventional routes. The NaX or KX salts are also available in anhydrous form, hydrated form, or in solution and can be available as mixtures of NaX and KX. Advantageously, the lithium chloride, lithium sulfate, NaX and KX can be used in liquid and well as solid form. Thus, where the transport of the raw materials is not a concern, the lithium chloride, lithium sulfate, NaX and KX can be used in liquid form and thus do not require drying. As a result, the cost of the raw materials used in the process is reduced.
The process of the invention is preferably initiated by dissolving lithium chloride, lithium sulfate, or a mixture thereof and a NaX salt, KX salt, or a mixture thereof, in an aqueous solution. The dissolution of these reactants occurs by dissolving lithium chloride or lithium sulfate in a NaX or KX solution

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