FR2597086A1 - PROCESS FOR THE PREPARATION OF HIGH PURITY LITHIUM OXIDE - Google Patents

Abstract

THE SUBJECT OF THE PRESENT INVENTION IS A PROCESS FOR PREPARING HIGH PURE LITHIUM OXIDE. FOLLOWING THE INVENTION, IMPUR LITHIUM OXIDE IS DECOMPOSED AT A TEMPERATURE OF 350 TO 450 C IN AN INERT AND ANHYDROUS ATMOSPHERE TO PRODUCE IMPURE LITHIUM OXIDE, AND THE IMPUR LITHIUM OXIDE OBTAINED UNDER A HEATING PRESSURE THAT IS NOT GREATER THAN 0.2 KPA AT 900 C OR MORE FOR AT LEAST ONE HOUR TO OBTAIN HIGH PURITY LITHIUM OXIDE WITH A PURITY OF 99 OR MORE. SUCH LITHIUM OXIDE IS ESPECIALLY USEFUL FOR THE PREPARATION OF LITHIUM ACCUMULATORS.

Description

"Process for the preparation of high purity lithium oxide."

  The present invention relates to a two-stage process at elevated temperature for preparing lithium oxide of greater than 99% purity from hydrogen peroxide.

  low purity lithium (85 to 95%).

  Lithium oxide specifically contains impurities which originate from the raw materials from which lithium oxide is produced. Lithium oxide specifically contains small amounts of lithium hydroxide or lithium carbonate. The top 10 end uses for lithium oxide are in the preparation of pharmaceuticals, lithium batteries and thermonuclear fusion reactors. On the other hand, in thermonuclear fusion operations, high purity lithium oxide is required insofar as the impurities, in particular lithium hydroxide and lithium carbonate, melt at too low a temperature. For use in a lithium battery, the impurities formed by lithium hydroxide and lithium carbonate are not soluble in the organic solvents used for the

  preparation of lithium batteries.

  A process for the preparation of lithium oxide from lithium peroxide is described by R.O. Bach in US-A-3,321,277. In this process, the lithium peroxide is thermally decomposed into lithium oxide by gentle heating to a temperature of 225 to 250 C in an inert atmosphere, preferably under a vacuum of 133.32 to

666.6 Pa up to 24 hours.

  US-A-2,424,512 issued to R.A. Stauffer, describes a process for recovering lithium oxide from phosphate and silicate ores. In this process, granules are formed with ores and lime, and the granules are heated under reduced pressure less than 133.32 Pa and at a temperature greater than 35 900 ° C, which causes displacement of the lithium oxide by lime. The oxide is separated by distillation and condensed. A.J. Cohen in "Inorganic Synthesis", vol. 5, Ch. 1A, 5 pages 3 to 4, McGraw-Hill, New York (1957), described a process for the preparation of lithium oxide by heating anhydrous lithium hydroxide to about 675C under vacuum

for half an hour.

  US-A-4,221,775 to James A. Anno and Howard 10 H. Bowing describes the preparation of porous lithium oxide from lithium hydroxide having a purity of at least 97%. The lithium hydroxide monohydrate forming the starting product is heated to its melting point to remove water of crystallization and produce anhydrous lithium hydroxide. Further heating of the anhydrous lithium hydroxide above its melting point is then carried out in an inert atmosphere while preventing the conversion of the lithium hydroxide to lithium oxide. The molten anhydrous lithium hydroxide is then cooled to a temperature below its melting point, while being protected by the inert atmosphere to a temperature below 1509C. The cooled lithium hydroxide is then subjected to a pressure not exceeding 0.266 Pa, preferably less than 0.133 Pa, at a temperature of 150 to about 200 ° C and it is maintained at this temperature until the total conversion to

  lithium takes place. The purity of the product is 98.1%.

  A permanent need for a useful process of

  Preparation of high purity Li2O has given rise to a number of processes for the preparation of lithium oxide.

  High purity lithium oxide is required for both the accumulator and smelting industries, but lithium oxide at purities of 99% or higher has not

yet been obtained.

  The present invention thus relates to a process for the preparation of high-purity lithium oxide, characterized in that: (a) impure lithium peroxide is decomposed at a temperature of 350 to 450 ° C., in an anhydrous atmosphere and inert to prepare impure lithium oxide, and (b) heating the impure lithium oxide under a

  pressure which is not more than 0.2 kPa at 900 C or more for at least one hour to obtain high purity lithium oxide 10 with a purity of 99% or more.

  According to other characteristics of the invention: The impure lithium oxide of stage (a) is heated in stage (b) under vacuum at a temperature of 900 ° C.

O1000C.

  The impure lithium oxide of step (a) is heated in step (b) under a pressure which is not greater than

0.1 kPa.

  The impure lithium oxide from step (a) is heated in step (b) under a pressure of 0.1 kPa; An important feature of the process of the present invention is the removal of active oxygen and moisture during heating at low temperatures during the first step of the process. This reduces corrosion of the crucible material, product degradation and sintering, and improves the loading in the crucible of a higher quality material to about 90 to 95% lithium oxide, containing only hydroxide. lithium and lithium carbonate as impurities. With reduced impurity contents at elevated temperatures, problems due to corrosion of the crucibles and sintering of the product are reduced or eliminated. Under the operating conditions of the present invention, the product is obtained in the form of an unsintered friable powder which can be easily removed from its container. In the first step of the process, 85 to 95% purity lithium peroxide is decomposed at temperatures of 350 to about 450 C to produce impure lithium oxide containing residual amounts of carbonate as impurities. lithium and hydroxide

  lithium. Temperatures above 450 ° C are avoided since the lithium hydroxide melts at around 450 ° C and causes the product to sinter. Temperatures below 350 ° C are not used since lithium peroxide 10 decomposes very slowly below 350 C.

  In the first step, the lithium peroxide is heated under an inert atmosphere such as argon, nitrogen, helium, neon or krypton in an inert container which may be aluminum, stainless steel, 15 alumina, nickel, thermal or high temperature glass, or other materials inert to lithium compounds at high temperatures. It is important that water is removed from the process. It is useful

  but no need to remove oxygen.

  The lithium oxide produced in the first step, containing significant amounts of up to 20% or more of lithium carbonate and lithium hydroxide as impurities, is heated to about 900 ° C or more under average vacuum preferably in a crucible which may be a rotary or vibrating crucible, a crucible vibrated by ultrasound or other crucibles provided with any device for agitation or vibration. Useful crucibles are made of alumina, magnesia, graphite, metal or metal coated with an inert film or coating at elevated temperature. Temperatures below 900C can be used, but low purity lithium oxide is obtained. Higher temperatures, below the melting point of lithium oxide, can be used and a finely powdered product is obtained. Temperatures above 1000 C are not necessary to prepare the required product of the present invention, heating to about 900 to about 1000 C is thus suitable and preferred. It is possible to heat up to 1200 ° C.-1300 ° C. but at these high temperatures, the attack of the crucible by the lithium oxide produced, is increased in an unsatisfactory manner. The second step of the process of the present invention is carried out under a medium vacuum. Average vacuum is required to remove oxygen and assist in the removal of decomposition products from the small amounts of lithium carbonate and / or lithium hydroxide present in the lithium peroxide forming the starting material of the first step. The vacuum provided by commercially available vacuum ovens capable of providing a vacuum of about 0.2 kPa or more is suitable. A preferred vacuum is

about 0.1 kPa or less.

  Lithium carbonate and lithium hydroxide decompose at temperatures of 800 to 1000 C to produce litiium oxide and water or lithium oxide and carbon dioxide. This conversion can be partially carried out in an inert atmosphere at 900 C or more and at atmospheric pressure, but it takes place completely at 900 C or more under vacuum. At temperatures above 1000 ° C, the attack of the crucible by lithium-based compounds is greater than at lower temperatures. The attack on the crucible is avoided since it is not desirable to have materials from the crucible

in the lithium oxide produced.

  Surprisingly compared to the prior art, the process of the present invention for the preparation of high purity lithium oxide, implements operating conditions which do not require any particular original apparatus, or unusual operating conditions for produce lithium oxide having purities that have no

not previously obtained.

  The following examples illustrate the

present invention.

Example!

  450 g of a 90% dry lithium peroxide sample containing 8% lithium hydroxide and 2% lithium carbonate were introduced into an aluminum container. The sample was then heated under an argon atmosphere under anhydrous non-oxidizing conditions at 425 C for two hours. The product from the first heating step comprising 300 g of 85% lithium oxide and containing 12% lithium hydroxide and 3% lithium carbonate was placed in a high purity alumina crucible (99%) and heated to 950C under a vacuum of about 0.1 kPa for two hours. Analysis revealed that the product (270 g) was 99.97% lithium oxide. The product was mainly in the form of a fine powder which contained a few small pieces of product. Comparison Example A Example 1 was repeated using a heating temperature of 850C during the vacuum heating of the second step. The purity of the lithium oxide produced was

97%.

  Comparison example B Example 1 was repeated except that

  did not use a vacuum during the second step when heating to 950 C and that the heating was carried out under an atmosphere of argon. The purity of the lithium oxide was 30%.

  Comparison example C We tried a one-step process at 900C under vacuum

  presence of argon but the decomposition of the peroxide was so violent that both the product and the reagent were violently ejected from the crucible.

Claims (4)

  1. A process for the preparation of high purity lithium oxide, characterized in that: (a) impure lithium peroxide is decomposed at a temperature of 350 to 450 ° C., in an anhydrous and inert atmosphere to prepare the oxide of impure lithium, and (b) heating the impure lithium oxide under a pressure of not more than 0.2 kPa at 900 C or more for at least one hour to obtain lithium oxide   of high purity with a purity of 99% or more.   2. Method according to claim 1, characterized in that the impure lithium oxide of step (a) is heated in step (b) under vacuum at a temperature of 900 C at 1000oC. 3. Method according to claim 2, characterized in that the impure lithium oxide of step (a) is heated in step (b) under a pressure which is not greater than 0.1 kPa.   4. Method according to claim 3, characterized in   that the impure lithium oxide of step (a) is heated in step (b) under a pressure of 0.1 kPa.