Process for the preparation of magnesia (MgO)

a technology of magnesia and process, applied in the field of improvement, can solve the problems of deterioration of mechanical properties (e.g., strength and volume stability), adversely affecting the properties of sintered magnesia, and high impurity content of magnesite or

Inactive Publication Date: 2007-09-20
COUNCIL OF SCI & IND RES
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Benefits of technology

[0037]Yet another object is to obtain high yields MgO having purity 99% and very low B2O3 impurity directly upon calcination, useful for refractory applications.

Problems solved by technology

Small quantities of “contaminants” are disadvantageous if they form low-melting eutectics with MgO (e.g., with CMS at 1485° C. or with C2F at 1200° C. because this leads to deterioration of mechanical properties (e.g., strength and volume stability) at high temperatures.
The main drawback of this method is that magnesite ore can have high levels of impurity.
The presence of accompanying, low-melting minerals can adversely affect the properties of the sintered magnesia.
The drawback of this process is that magnesite ores contain varying amount of silica, iron oxide, alumina, and lime as silicates, carbonates, and oxides.
Due to all this, high purity magnesia is difficult to produce by this process and most such magnesia has less than 95% purity.
The main drawback of the process is that the process is very sensitive to the partial pressure of carbon dioxide and to the temperature.
Moreover, the bulk density of the MgO would be too low for refractory applications.
The main drawbacks of the above process are that a supply of freshwater (>40 m3 per tonne MgO) is required to wash the Mg(OH)2 and to produce the milk of lime.
The resulting slurry is difficult to filter and is washed and dewatered in a two-stage vacuum drum filter.
The main drawback is that the spray calcined product needs to be washed to remove unreacted MgCl2 and soluble salts and once again subjected to calcination.
Spray calcination is an energy intensive process and choking up of nozzles can pose a problem.
The problem of spray calcination, however, remains.

Method used

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  • Process for the preparation of magnesia (MgO)
  • Process for the preparation of magnesia (MgO)

Examples

Experimental program
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Effect test

example 1

[0084]200 g of MgCl2.6H2O (0.985 moles) was reacted with 75.53 g of NaOH (1.890 moles). The residue obtained on filtration was washed with water. The mass of the wet cake was 270.65 g. Of this 235.34 g was dried at 110° C. to obtain 77.98 g of dry residue. 60 g of this dry residue was calcined to obtain 22.55 g MgO having>99% purity. The loss on ignition was 62.42% (theoretical LOI=30.88%). The observations from this example are that, even though MgO of high purity is obtainable, this is achieved only through elaborate and tedious washing.

example 2

[0085]250 g of MgCl2.6H2O (1.232 moles) was reacted with 190.8 g of 23.8% (w / w) ammonia solution (2.671 moles) and the slurry was stirred for 15 min and then filtered. Filtration was found to be very facile. The residue was washed with 280 mL of pure water to obtain 152 g wet cake which, on drying at 110° C. yielded a weight of 43.40 g. Of this, 31.83 g was calcined at 900° C. to give 21.13 g of MgO (58.46% yield w.r.t. MgCl2) having>99.31% purity. The loss on ignition was 33.71% (theoretical LOI=30.88%) indicating that the dried material prior to calcinations was essentially pure Mg(OH)2. This example establishes that no complexed form of ammonia exists in the product mixture and that all impurities are therefore of adhering nature. These are expected to be MgCl2, NH3 and NH4Cl besides some minor impurities, if any, which may be present in the solid MgCl2.6H2O. It will be further evident that the major adhering impurities would either be converted into MgO or volatilize away on cal...

example 3

[0086]100 gm of MgCl2.6H2O (AR grade) (0.493 moles) having available MgCl2 content of 46.8 gm was mixed under stirring with 73.44 ml (NH3=23.84% w / w; sp. Gr. 0.91)) of ammonia liquor (0.937 moles) of specific gravity 0.91. The mixture was allowed to stand for two hours. The resultant slurry could be readily filtered by vacuum filtration. Wet cake weighing 51.5 gms and 92 ml of filtrate having specific gravity of 1.12 and chemical composition Ca=ND %, Mg=2.68%, Cl=20.38% was obtained. The wet cake was washed with 50 ml water. The wash filtrate composition is, Ca=ND, Mg=0.83%, Cl=5.44%. The cake was dried at 110 C to obtain dry mass of 43.43 gm which was further calcined at 900 C to obtain 13.78 gm (0.344 moles; 70% yield) of MgO showing purity of 99.35%, CaO=ND and Cl=0.37% and B2O3=0.012%. It will be evident from this example and the powder XRD of FIG. 2 that MgO purity matching that of Example 1 is obtainable if the MgCl2 taken is free of impurity salts as is the case when AR grade...

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Abstract

The present invention provides an improved process for the preparation of MgO of high purity >99% from salt bitterns via intermediate formation of Mg(OH)2 obtained from the reaction of MgCl2 and lime, albeit indirectly, i.e., MgCl2 is first reacted with NH3 in aqueous medium and the slurry is then filtered with ease. The resultant NH4Cl-containing filtrate is then treated with any lime, to regenerate NH3 while the lime itself gets transformed into CaCl2 that is used for desulphatation of bittern so as to recover carnallite and thereafter MgCl2 of desired quality required in the present invention. The crude Mg(OH)2 is dried and calcined directly to produce pure MgO, taking advantage of the fact that adhering impurities in the Mg(OH)2 either volatilize away or get transformed into the desired product, i.e., MgO.

Description

FIELD OF THE INVENTION[0001]The present invention relates to an improved process for the preparation of magnesia (MgO). More particularly, the invention relates to an improved process for the preparation of MgO of high purity from Mg(OH)2 without the need to wash Mg(OH)2 or MgO.BACKGROUND OF THE INVENTION[0002]Magnesia is an important compound that finds application in various industries. Magnesium oxide has the highest melting point of the moderately priced oxides and is therefore an important raw material for refractory bricks and other materials. It is the only material apart from ZrO2 that can withstand long-term heating above 2000° C.[0003]Reference may be made to Ullmann's Encyclpedia, 6th Edition (electronic version) wherein it is stated that: “The increased demands made on refractory materials as a result of higher operating temperatures and shorter tap to tap times in metallurgical furnaces and reactors can only be met by pure, high-density magnesia sinters. Small quantitie...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): B01J29/04
CPCC01F5/08C01F5/20C01P2006/80C01P2002/72C01F11/24
Inventor DAVE, ROHIT HARSHADRAILANGALIA, KAUSHIK JETHALALMOHANDAS, VADAKKE PUTHOOR
Owner COUNCIL OF SCI & IND RES
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