The present invention relates to an improved process for the preparation of high purity Mn3O4. More particularly it relates to preparation of Mn304 by oxidation of pure MnO in presence of water at room temperatures below 100°.
Mn304 occurs in nature as the mineral hausmanite. In prior art Mn304 is prepared by oxidation of all oxides and hydroxides of Manganese by heating them in air about 1000°C. The best supported preparation appears to be that of Schomate, JACS, 65, 785 (1943), who heated specially prepared electrolytic Mn02 to 1050°C. Preparation of almost as pure Mn304 have been reported by Millar, JACS, 50, 1875 (1928) and by Southard and Moore, JACS, 64, 1769 (1942) by prolonged ignition of pure MnS04 in air at about 1000°C. Another process of interest is that of Krull, Chem. Erde, 7, 473 (1932) who reduced the precipitated Mn02 in H2 at 200°C. T.E. Moore et al., JACS, 72, 859 (1950) prepared it by the thermal decomposition of manganous sulphate, the final product appearing as a dark purplish red solid. U.S. Patent No. 4,441,778)process for Mn304, wherein a higher oxide of Manganese is reduced by methane at temperatures between 250°C and 550°C in a klin.
U.S. Patent No.3, a wet process comprising of oxidation of an aqueous suspension) hydroxide at elevated temperatures and pressures of 100 to 140°C and from 40 psi to 70 psi

respectively. Laughlin et al.U.S. Patent No.4,812,302 (1989) describe a process for the preparation of high purity Mn3O4, wherein particulate manganese metal, suspended in aqueous solution containing water soluble ammonium salt, is oxidised in the presence of an oxidising agent at a temperature of at least 30°C. However, the reaction does not take place in the absence of the soluble ammonium salt or, if at all, at a very slow rate and in presence of a soluble salt alone a readily filterable product is obtained. The role played by the ammonium salt is not known. Yang Yangnian et al., Appl. Catal. A, 101 (1993) 233 prepared nonstoichiometric Mn304 (i.e. Mn031.33) by decomposition of Mn(OH))2 in air at 130°C for 24 hours. The hydroxide was prepared from an aqueous solution of Mn acetate (A.R.) with con. ammoniak at pH > 9.0. Wang Weisnin et al., Reel. Trav. Chim. Pays Baz, 114 (1995) 22 prepared Mn3O4 by a one step procedure namely by decomposition of Mn(OAc)2.4H20 at 350°C for 0.5 hours followed by crystallisation in a N2 flow at 500°C for 12 hours in order to obtain sharp X-ray diffraction lines.
The above mentioned processes for preparation of Mn3O4 need temperatures in the range of 1000°C while carrying out either oxidation or reduction reaction or need high temperatures and pressures.
Another drawback of the process is that the precursors such as Mn(OAc)2 or Mn particulates are very costly, requiring at the same time use of a catalyst and the reactions are also reported to be slow, taking place over 24 hours.

The object of present invention is therefore to provide a process for the preparation of Mn3O4 in general and of pure ferrite grade in particular at the reduced temperature and requiring no use of precursors.
Accordingly the present invention provides an improved process for the preparation of Mn3O4 which comprises decomposing MnCO3 at 450-500°C in absence of oxidizing agent to obtain MnO pouring MnO into water to make slurry for 1 to 2 hours, separating the Mn3O4 formed in the reaction mixture by known filteration methods, washing the product with water, and drying the product at temperature in the range of 30 to 100°C for time period in the range of 2 to 5 hours to obtain Mn304.
In another embodient of the present invention MnO used for the preparation of is obtained from conventional decomposition of
The invention is descrined herein below with reference to following examples which are illustrative only and should not be construed to limit the scope of the present invention any in manner.

Examples 1 to 10
General Procedure:
Pure MnC03 was decomposed in the laboratory furnace in a steel or ceramic vessel in the atmosphere of pure N2 to obtain MnO and a slurry was prepared in pure water and the slurry was heated to temperature of 100°C or less for 1 to 2 hours, while passing air or oxygen, the reaction mixture was filtered to separate the product formed, the product was washed with pure water and the cake obtained was dried at 100°C to obtain the pure Mn304.
Note: Pure N2 was passed only during the decomposition of MnC03.
Example 1
10.0 gms of pure MnCO3 placed in a ceramic boat was heated in a tube
furnace at 450° for 3 hours in the atmosphere of high purity N2. On
cooling it was poured in deionised water to form a slurry. It was then
filtered on a filter paper washed with deionised water and the filtered
mass on the filter paper was exposed to air in the hot sun for several
hours. The X-ray diffraction (XRD) pattern of the dried product showed
single phase of pureMn3O4
Example 2
5.0 gms of pure MnCO3 placed in a ceramic boat was heated in a tube
furnace at 610°C for 2 hours in an atmosphere of pure N2 to obtain MnO

and a slurry was prepared in pure water after cooling the product in current of N2. It was filtered on a filter paper and the filtered mass was exposed to air in hot sun for several hours. The XRD of the dried product showed 2 small MnO peaks besides Mn3O4
Example 3
7 gms of pure MnC03 placed in a ceramic boat was heated in a tube
furnace at 450°C for 1.5 hrs in an atmosphere of pure N2. The sample on
cooling in N2 was treated in a similar manner as in examples 1 and 2.
The XRD showed single pure phase of Mn3O4
Example 4
6 gms of pure MnC03 placed in a ceramic boat was heated in a tube furnace at 450°C for 2.5 hours in an atmosphere of pure N2 and a slurry was prepared in pure water after cooling the product in the current of N2. It was filtered and washed with pure water on a filter paper and the filtered mass was exposed to air in hot sun for several hours. The XRD of the dried product showed peaks of pure Mn3O4 single phase.
Example 5
8 gms of pure MnCO4 placed in a ceramic boat was heated in a tube
furnace at 500°C for 3 hours in an atmosphere of pure N2 and a slurry was
made in pure water after cooling the product in a current of pure N2. The
slurry was filtered and washed with pure water on a filter paper and the

filtered mass was exposed to air in hot sun for several hours. The XRD of the dried product showed 2 peaks of MnO besides those ofMn3O4
Example 6
8 gms of pure MnC03 placed in a ceramic boat was heated in a tube furnace at 600°C for 2 hours in an atmosphere of pure N2 and a slurry was prepared in pure water after cooling the product in a current of pure N2. It was filtered on a filter paper, washed with pure water and the mass was exposed to air in hot sun for several hours. The XRD of the dried product showed 2 peaks of MnO besides those of Mn3O4.
Example 7
9.5 gms of pure MnCO3 placed in a ceramic boat was heated in a tube furnace at 620°C for 3 hours in an atmosphere of pure N2 and a slurry was prepared in pure water after cooling the product in a current of pure N2. It was filtered on a filter paper, washed with pure water and the mass was exposed to air in hot sun for several hours. The XRD of the dried product showed 2 peaks of MnO besides those of Mn304.
Example 8
500 gms of pure MnCO3 placed in a steel container was heated to 620°C for 3 hours in a muffle furnace in a current of pure N2. On cooling in N2 the material was poured into deionised water to make a slurry. The slurry thereafter was heated to boiling for 3 hours while a steady current of air was passed. On filtration and washing with deionised water the product

was dried at 100°C. The XRD showed 2 MnO peaks with reduced intensity besides Mn3O4.
Example 9
500 gms of pure MnCO3 placed in a steel container was heated in a muffle furnace at 5500C for 3 hours in an atmosphere of pure N2. On cooling the product in a current of pure N2, a slurry was made in pure water. The slurry was boiled for 2 hour while passing a slow current of 02. The product was filtered a filter paper and washed with pure water. The mass, thus obtained, was dried in an oven at less than 100°C. The XRD of the dried mass exhibited peaks of only Mn3O4 single phase.
Example 10
500 gms of pure MnCO3 placed in a steel container was heated at 500°C for 3 hours in a muffle furnace in a current of pure N2. On cooling in N2 the material was poured into deionised water to make a slurry. The slurry thereafter was boiled for 1 hour in a steady current of 02. The product was then filtered and washed with deionised water and dried at 100°C. The XRD showed the presence of pure phase of Mn304.


TABLE-1
(Table Removed)
)The main advantages of the process of the present invention are as follows:
1. The process is economically viable in obtaining the product of the
quality required in the ferrite industry, since all the raw materials required
to produce MnO are cheap and abundantly available.
2. The product obtained is free from contamination of any other
phase, or impurities and is easily filterable. The particle size of the
product as obtained before the final step of wet milling is less than 2µ

WE CLAIM :
1. An improved process for the preparation of Mn3O4 which comprises
decomposing MnCO3 at 450-500°C in absence of oxidizing agent to
obtain MnO, pouring MnO into water to make slurry for 1 to 2 hours,
separating the Mn3O4 formed in the reaction mixture by known filteration
methods, washing the product with water, and drying the product at
temperature in the range of 30 to 100°C for time period in the range of 2
to 5 hours.to obtain Mn3O4

2. An improved process for the preparation of Mn3O4 as substantialy
described herein before with reference to examples.