IE50481B1 - Process for the production of magnesium oxide from brine or bittern - Google Patents

Description

The present invention relates to preparing magnesium oxide from brine or bittern containing magnesium chloride.

It has been well known to use MgCl2 with MgO in 5 the molar ratio of MgCl2:MgO of 1:1 to 1:20 in the production of Sorel Cement since as early as 1867.

Since then various research works have been carried out for the production of magnesium oxychloride by adding MgO to aqueous solution of MgCl2.6H2O. In all these processes the molar proportion of MgO was in excess of MgCl2-6H2O.

N.L. Industries Inc.. U.S.A. developed a process of producing MgClj. The brines are concentrated by solar evaporation sodium and potassium salts are removed and the MgCl2 concentration is increased so as to give ultimately anhydrous MgCl.,. However there have been considerable engineering and mechanical difficulties in this process.

Processes have been under development in recent years for the production of magnesium oxide starting from aqueous solutions containing magnesium ions, for example sea water. These methods starting from sea water or other magnesium chloride-containing solution comprise the precipitation during a first stage of magnesium hydroxide and/or magnesium carbonate · For example, German Specification 5 No. 377199 (Kiexmayer) discloses a process in which finely divided solid calcium hydroxide is added to the concentrated magnesium chloride solution obtained as a by-product in the potash industry. Magnesium hydroxide is precipitated, separated from the acconpanying calcium chloride solution, and stirred with fresh magnesium chloride solution. A hard mass is obtained. Dolomite also may be added to the magnesium hydroxide, in which case the solid product may be heated to decompose the magnesium chloride present and convert the calcium carbonate of the dolomite into calcium chloride, which can be removed by leaching to leave a residue of inpure magnesium oxide. This process does not avoid the inconvenience of separating solid magnesium hydroxide from calcium chloride solution, and does notg.ve a pure magnesium oxide product.

In a recent attempt to product Mg(OH)2 directly from sea waterzcalcined dolomite (CaO-MgO) was used as the precipitating agent, which reacts with the magnesium chloride in the sea water according to the reaction: CaO-MgO + MgCl2 + 2H20 = 2Mg(OH)2 + CaClj.

Even though this process gives the advantage of increasing the yield of magnesium hydroxide from a given volume of sea water, it still requires a large amount of dolomite, which one would like to avoid.

More recently the precipitation of Mg(0H)2 from 50482 sea water has been studied using calcium carbide (CaC2). This process proceeds in accordance with the following reaction: MgCl2 + 2H20 + CaC2 = C2H2 + Mg(0H)2 4 CaCl2 5 Although it allows acetylene to ba obtained, it suffers from the disadvantage of requiring the use of a reagent (i.e. calcium carbide) which is costly and not always easily available. Furthermore, whatever method is used for precipitating the magnesium hydroxide from sea water on an industrial scale one major problem remains unsolved, namely the slow precipitation and filtration of the product obtained. Many attempts have been made to increase the speed of deposition and to obtain precipitates which are more easily filterable. Evidently a faster deposition and the formation of a more easily filterable precipitate would have the effect of considerably reducing operating costs. For this purpose, various methods have been tried such as recycling a portion of the slurry precipitated in the precipitation zone or continuously adding flocculating agent without however obtaining completely satisfactory results.

On the other hand although the addition of small quantities of aldehydes to the magnesium brines has enabled a precipitate of better filtering characteristics to be obtained, it has been found that an improvement in the precipitation characteristics is obtained at the expense of purity of the final product because of contamination by the flocculating agents absorbed by the magnesium hydroxide.

U.S. patent no.2.921,835 proposes the use of ammonium carbonate as the precipitating means for the magnesium ions from saline solutions. As the quantity of carbon dioxide is larger than that relative to the stoichiometric composition of ammonium carbonate would have to be used, the operation must be carried out under pressure or at low temperature, in order to obtain good yields with industrially acceptable reaction times.

Further, as the operation should be carried out in the presence of a large excess of carbonated ammonia the recovery of the ammonia is costly.

British patent no.1,434,608 proposes a process which comprises the steps of combining brine or a like aqueous solution containing magnesium ions with a precipitating solution of ammonium carbonate containing NH^ and CO2 in stoichiometric quantities corresponding to the composition of ammonium carbonate, at atmospheric pressure, separating a precipitate of magnesium carbonate and magnesium hydroxide, recovering ammonia from the solution after separation of the precipitate, and recycling the said ammonia to prepare the precipitating solution. This process also suggests that control of the following parameters, i.e. temperature, ratio between the reagents (ammonium carbonate and magnesium ions), and the concentration of the magnesium solutions within certain specified limits, is particularly important in order to obtain a very pure product in satisfactory yields. Thus this prior art process is accompanied by certain limitations which involve (i) the use of ammonium carbonate which is a costly reagent and (ii) the use of special equipment or machinery.

According to another known process magnesium chloride dihydrate is dehydrated by a process in which the dehydration takes place in hydrochloric acid produced from the elements. The heat necessary for the dehydration of the magnesium chloride is supplied by the hydrogen chloride synthesis and by external heating. The hydrogen chloride synthesis is controlled in such a way that only as much hydrogen chloride is produced by synthesis as the water of the magnesium chloride dihydrate can absorb.

In this dehydration reaction the reaction temperature is 300 to 400°C. This process is also not suitable as it involves complicated equipment.

British Patent No.1,426,567 also proposes a process for the production of hydrogen chloride and magnesium oxide from magnesium chloride in the presence of steam at elevated temperature as high as 2000°C, which involves costly and complicated equipment for thermal dissociation of magnesium chloride.

MgO can also be produced by treating MgSO^ solution with SO^ and heating the Mg(HSO3)2 so formed, which also is a costly process.

MgO (magnesium oxide) can also be obtained as the final product of thermal decomposition of numerous magnesium compounds. The conventional industrial processes for producing magnesium oxide include calcining magnesium carbonate or magnesium hydroxide and the thermal decomposition of magnesium chloride or sulphate. The material most commonly used in such a decomposition is magnesite i.e. naturally occurring magnesium carbonate or dolomite which consist essentially of a mixed carbonate of magnesium and calcium. The temperature necessary for rapid decomposition of magnesite is between 600θ0 and 700°C, whereas dolomite decomposes rapidly at temperatures between 700°C and 900°C.

These known processes suffer from the disadvantage of requiring large quantities of the aforesaid minerals, i.e. magnesite and dolomite, as their raw materials, and these may evidently not always be easy to obtain in sufficiently pure form. Processes based on the decomposition of magnesium chloride or magnesium sulphate suffer from the disadvantage of requiring much higher decomposition temperature, i.e. temperatures which range between 1300°C and 1700°C in the case of decomposition of magnesium chloride and temperatures between 1100°C and 1200°C in the case of decomposition of magnesium sulphate. Moreover the decomposition of magnesium sulphate must be generally conducted in a reducing atmosphere containing for example, sulphur, hydrogen sulphide, hydrogen or carbon monoxide with evident disadvantages deriving from the difficulty of operating the process at such high temperature in a very chemically reactive atmosphere which requires the use of special equipment.

Another process is known for obtaining hydrogen chloride and magnesium oxide from solutions or salts containing magnesium chloride in which hydrogen chloride is obtained by dissociation of the magnesium chloride in a flue gas current at a temperature of 1300°C to 140Q°C. Here the hot gas coming out from the dissociating furnace is used to concentrate the magnesium chloridecontaining solution and to dry the magnesium chloride to the dihydrate. This process has the disadvantage that the product hydrogen chloride is present only in dilute form in mixture with water vapour and inert substance. For obtaining pure hydrogen chloride, an expensive purification process is subsequently necessary.

S04S2 The present invention provides refractory grade pure magnesia (MgO) especially suitable for use in the manufacture of basic refractories.

This new process does not suffer from 5 some or all of the aforesaid disadvantages associated with known processes for obtaining magnesium oxide from solutions containing magnesium ions, i.e. brine or bittern.

The new process totally avoids the precipitation 10 of magnesium hydroxide from sea water and therefore the problem of increasing the speed of precipitation and obtaining a more easily filterable precipitate.

The question of precipitation does not arise at all in the process of the present invention as the process results in the formation of a solidified mass which does not require precipitation and subsequent filtration.

Surprisingly it has been found that if a solidified mass obtained by adding calcium and/or magnesium oxide to concentrated magnesium chloride solution is calcined, it is converted into a mixture of magnesium oxide and soluble salts from which pure magnesium oxide may be easily isolated by simple washing out of the soluble salts.

The new process uses the minimum amount of calcined dolomite, calcined calcite/limestone, calcined magnesite, or a combination thereof, with brine or bittern as the source of magnesium ions.

The process of the present invention for the production of magnesium oxide from brine or bittern containing magnesium chloride conprises: a process for the production of magnesium oxide from brine or bittern containing magnesia» chloride by precipitation with an oxide or a source for an oxide of calcium or magnesium which comprises: a) adding to brine or bittern containing magnesium chloride in a concentration of at least 25s Be, as a source of MgO and/or CaO, MgO or calcined magnesite or calcined dolomite or calcined calcite/limestone in such amount that in the case of MgO, or calcined magnesite, the molar ratio of MgO: MgCl2 is in the range 0.66:1 to 0.066:1 or, in the case of calcined dolomite, the molar ratio of MgO + CaO : MgCl^ is in the range of 0.66:1 to 0.05:1, or, in the case of calcined calcite/limestone, the molar ratio of Ca0:Mg&2 is in the range of 0.66:1 to 0.1:1; b) keeping the mixture at a temperatue below 90°C till a solid mass is formed; c) drying and calcining the said solid mass at a temperature up to 1200°C to produce magnesium oxide powder; and d) washing the said magnesium oxide powder obtained to produce pure magnesium oxide powder.

In an alternative embodiment of the invention, if the magnesium oxide product is required in the, form of briquettes, the solid mass obtained in step (b), frcm an aqueous mixture of MgO and MgCl2, is dried at a tenperature of up to 200°C; calcined at a maximum temperature of 1200°C and briquetted into desired shapes with the addition of organic or inorganic binder, and fired at above 1400°C preferably at above 1600eC.

Light calcined magnesite is preferably added as source of MgO to the bittern or brine.

When calcined magnesite, is. used the molar ratio of MgO:MgCl2 is usually at least 0.1:1 preferably 0.25:1. In the new process any combination of calcined dolomite, calcined magnesite, and calcined calcite/limestone may be added to the brine or bittern, and the amount of any one of the components of such combination is such that the minimum molar ratio of (a) calcined dolomite to MgCl2 is 0.02:1 (b) calcined calcite to MgCl2 is 0.05:1 and of (c) calcined magnesite to MgCl2 is 0.03:1 When briquettes are made the said binder is added in an amount of preferably up to 3% by wt. of the dried mass. An organic binder may be e.g. dextrine, molasses or sulphite lye, and an inorganic binder may be e.g. sodium chromate or chromic acid.

Optionally chromite or chrome ore is added in addition to the inorganic binder. This method involves the joint grinding and firing of the MgO15 producing material with chromite or chrome ore.

The fired clinker represents an excellent base material for the production of dense basic refractories with high hot strength properties.

The invention is illustrated by the following Examples.

EXAMPLE 1 An aqueous solution of MgCl2.6H20 of a concentration of 27° Be was taken and to it light calcined MgO of grain size below 1mm was added in the molar ratio of MgO: MgCl2 = 1:4. The mixture was stirred from time to time and a solid mass was formed in less than 24 hours. This solid mass was then dried at 110°C and heated inside a furnace at 800°C for 2 hours A fine powder of MgO was obtained and was analysed to have a purity of 99% MgO. The fine powder of MgO was mixed with sulphite lye and pressed and fired at 1600°C. The porosity of the final product (MgO) was found to be 10%.

EXAMPLE 2 An aqueous solution of MgCl2:6H2O of a concentration of 27° Be was taken and to it light calcined MgO of grain size below 1mm was added in such amount that the molar ratio of MgO:MgCl2 was 1:2. The mixture was stirred from time to time when a solid mass was . obtained in less than 24 hours. This solid mass was dried at 110°C and heated inside a furnace at 800°C for 2 hours. A fine powder of MgO was obtained and was analysed to have a purity of 99% MgO. The fine powder of MgO was mixed with sulphite lye and pressed and fired at 1600°C. The porosity of the final product (MgO) was tested and found to be 6%.

EXAMPLE 3 Commercial brine containing MgCl2 of 34°Be was taken and heated to 85°C and light calcined MgO of grain size below lmm was added in the molar ratio MgO:MgCl2=l:10. Then it was stirred from time to time and a solid mass was obtained in less than 24 hours. This solid mass was fired at 800°C.

A fine powder of MgO was obtained with other impurities which was subsequently washed with water to get a purity of 99.5% MgO.

EXAMPLE 4 Commercial brine containing MgCl2 of 34°Be was taken and calcined dolomite of grain size below lmm was added to it in the molar ratio of calcined dolomite:MgCl2 of 0.1:1.

The mixture was stirred from time to time till a solid mass was obtained in less than 24 hours. The solid mass was dried at a temperature of 110-120°C and then taken inside a furnace where it was calcined at a temperature of 900°C for 2 hours.

A fine powder of MgO was· obtained and washed with water. On analysis it was found to possess a purity of 98% MgO.

EXAMPLE 5 Oonmercial brine containing MgCl2 of 34°Be was taken. Light calcined calcite of grain size below 1 mm was added to the brine in the molar ratio of calcined calcite :MgCl2 of 0.17:1. The mixture was stirred from time to time and a solid mass was formed in less than 24 hrs. This solid mass was dried at 110-120°C and then taken inside a furnace where it was calcined at a temperature of 900°C for 2 hours. A fine powder of MgO was obtained which was washed with water. On analysis it was found to possess a purity of 98% MgO. EXAMPLE 6 Commercial brine containing MgCl2 of 34°Be was taken.

A mixture of light calcined magnesite and light calcined dolomite was added to the said brine in such amount that the molar ratio of calcined dolomite:MgCl2 = 0.03:1 and calcined magnesite:MgCl2 = 0.04:1. The mixture was stirred from time to time and a solid mass was formed in less than 24 hours.

This solid mass was dried at 110-120°C and then 3U4S1 taken inside a furnace where it was calcined at 900°C for 2 hours. A fine powder of MgO was obtained which was washed with water. On analysis, it was found to possess u purity of 98% MgO.

EXAMPLE 7 Commercial brine containing MgCl2 of 34°Be was taken. A mixture of light calcined dolomite and light calcined calcite was added to the said brine in such amount that the molar ratio of calcined dolomite:MgCl2 = 0.03:1 and the molar ratio of calcined calcite::MgCl2 = 0.06:1. The mixture was stirred from time to time and a solid mass was formed in less than 24 hours. The said solid mass was dried at 110-120°C and then calcined in a furnace at 900°C for 2 hours. A fine powder of MgO was obtained which was washed with water.

On analysis, it was found to possess a purity of 98% MgO.

EXAMPLE 8 Commercial brine containing MgCl2 of 34°C was taken A mixture of calcined magnesite and light calcined calcite was added to the said brine in such amount that the molar ratio of calcined magnesite:MgCl2= 0.04:1 and the molar ratio of calcined calcite: MgCl2 = 0.06:1. The mixture was stirred from time to time and a solid mass was formed in less than 24 hours. The said solid mass was dried at 110-120°C and then calcined inside a furnace at a temperature of 900°C for 2 hours. A fine powder of MgO was obtained and washed water.

On analysis, it was found to possess a purity of 98% MgO. 0 4 81

Claims (5)

1. A process for the production of magnesium oxide from brine or bittern containing magnesium chloride by precipitation with an oxide or a source for an oxide of calcium or magnesium which comprises: 5 a) adding to brine or bittern containing magnesium, chloride in a concentration of at least 25°Be, as a source of MgO and/or CaO, MgO or calcined magnesite or calcined dolomite or calcined calcite/limestone in such amount that in the case of MgO or calcined magnesite, the 10 molar ratio of MgOsMgCl^ is in the range of 0.66:1 to 0.066:1 or, in the case of calcined dolomite , the molar ratio of MgO + CaO : MgCl 2 is in the range of 0.66:1 to 0.05:1, or, in the case of calcined calcite/limestone, the molar ratio of CaO:MgCl 2 is in the 15 range of 0.66:1 to 0.1:1; b) keeping the mixture at a temperature below 90°C till a solid mass is formed; c) drying and calcining the said solid mass at a temperature up to 1200°C to produce magnesium oxide 20 powder; and d) washing the said magnesium oxide powder to produce pure magnesium oxide.

2. A process according to claim 1, wherein light calcined magnesite is added as a source of MgO 25 to the brine or bittern.

3. A process according to claim 1 or 2 , wherein calcined magnesite is added to the brine or bittern in a molar ratio of MgO:MgCl 2 of at least » k

4. A process according to claim 3, 30 wherein the said molar ratio is 0.25:1. 5. A process according to claim 1, wherein any combination of calcined dolomite, calcined magnesite and calcined calcite/limestone ia added to the brine or bittern, in auch amount that the minimum molar ratio of: 5 calcined dolomitefo MgCl^ is 0.02:1; of calcined calcite to MgCl 2 is 0.05:1; and of calcined magnesite to MgClj is 0.03:1. 6. Modification of the process according to any one of claims 1 to 5, wherein the solid mass obtained in 10 step ib), from an aqueous mixture of MgO and MgCl 2 , is dried at a temperature up to 200°C, calcined at a maximum temperature of 1200°C, and then briquetted into desired shapes with the addition of organic or inorganic binder, and the briquettes are fired 15 at above 1400 e C. 7. A process according to Claim 6, wherein the said briquettes are fired at above 1600 e C. 8. A process according to claim 6 or 7, wherein the said binder is added in amount of up to 20 3% by weight of the calcined mass. 9. A process according to claim 8, wherein the binder is dextrin, molasses, sulphite lye, sodium chromate or chromic acid. 10. A process according to any of claims 6 to 9, 25 wherein chromite or chrome ore is also added with the binder. 11. A process according to Claim 1 for the production of magnesium oxide from brine or bittern substantially as hereinbefore described in any one of the foregoing Examples.

5. 12. Magnesium oxide whenever produced by a process as claimed in any of the preceding claims. F. R. KELLY & CO.,