CA2373402A1 - Method of production of magnesium and chlorine from magnesium chloride solutions containing ammonium chloride - Google Patents
Method of production of magnesium and chlorine from magnesium chloride solutions containing ammonium chloride Download PDFInfo
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- CA2373402A1 CA2373402A1 CA 2373402 CA2373402A CA2373402A1 CA 2373402 A1 CA2373402 A1 CA 2373402A1 CA 2373402 CA2373402 CA 2373402 CA 2373402 A CA2373402 A CA 2373402A CA 2373402 A1 CA2373402 A1 CA 2373402A1
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Abstract
The method of production of magnesium and chlorine consists of the steps of: dehydrating a feedstock of chlorine-magnesium solution containing ammonia compounds; separating anhydrous magnesium chloride therefrom; and electrolytically decomposing magnesium chloride, so as to produce magnesium and chlorine. In this method an initial chlorine-magnesium solution after decontamination is saturated with ammonium chloride and supplied to a fluidized bed dryer for direct production of substantially solid anhydrous ammonium carnallite with subsequent decomposition thereof to obtain anhydrous magnesium chloride, ammonia and hydrogen chloride. Ammonia and hydrogen chloride are recirculated with exhaust gasses within the process, whereas anhydrous magnesium chloride is supplied to electrolytic cells for production of magnesium and chloride.
Description
METHOD OF PRODUCTION OF MAGNESIUM AND
CHLORINE FROM MAGNESIUM CHLORIDE SOLUTIONS
CONTAINING AMMONIUM CHLORIDE
Field of the Invention The invention relates to the production of magnesium from magnesium chloride solutions, produced by leaching oxygen-containing raw material, such as solutions of lake water, and from magnesium chloride solutions resulting from the underground leaching of chlorine-magnesium salts.
Background of the Invention The method of processing the magnesium chloride solution by evaporation and crystallization of bishofite MgCl2 ~ 6 H20 is well known. In present practices, the solution is dehydrated in multistage dryers, equipped with rakes, and then, the resultant granular product containing MgCl2~(1.25 to 1.5) H20, is fed into electrolytic cells. From the electrolytic chamber anode gases containing chlorine, hydrogen chloride, carbon monoxide and carbon dioxide, are delivered to the regeneration furnace for the production of hydrochloric acid. This process by-product provides an essential component used in the neutralization of magnesium hydroxide (see O. A. I,ebedev, "Production of magnesium by electrolysis."
Metallurav, Moscow, 1988; pages 38-39). The major drawbacks of this method are as follows: substantial losses of magnesium occur by the accumulation thereof in the sludge, which is discarded from the electrolytic cells, and that the electrolytic cells experience a short service life.
Another drawback of this prior art method is that a considerable amount of magnesium oxide is present in the dehydrated magnesium chloride (from 1.5 to 3%). These factors considerably reduce economic feasibility of magnesium chloride production by dehydrating its crystalline hydrates.
The production of (anhydrous) dehydrated magnesium chloride, an essential component in the electrolytic production of magnesium metal by means of dehydration of ammonium carnallite (NHdCI ~ MgC12~6H20), is also known in the art. In this method ammonium carnallite is consecutively heated in multistage dryers in dry air up to 360 ° C. The complete dehydration and decomposition of the ammonia carnallite results in MgCl2 and NH4Cl. This method does not result in hydrolysis (see, M. A. Aydenzon, "Magnesium". MetallurQV, Moscow, 1969;
.°
pages 111-112).
CHLORINE FROM MAGNESIUM CHLORIDE SOLUTIONS
CONTAINING AMMONIUM CHLORIDE
Field of the Invention The invention relates to the production of magnesium from magnesium chloride solutions, produced by leaching oxygen-containing raw material, such as solutions of lake water, and from magnesium chloride solutions resulting from the underground leaching of chlorine-magnesium salts.
Background of the Invention The method of processing the magnesium chloride solution by evaporation and crystallization of bishofite MgCl2 ~ 6 H20 is well known. In present practices, the solution is dehydrated in multistage dryers, equipped with rakes, and then, the resultant granular product containing MgCl2~(1.25 to 1.5) H20, is fed into electrolytic cells. From the electrolytic chamber anode gases containing chlorine, hydrogen chloride, carbon monoxide and carbon dioxide, are delivered to the regeneration furnace for the production of hydrochloric acid. This process by-product provides an essential component used in the neutralization of magnesium hydroxide (see O. A. I,ebedev, "Production of magnesium by electrolysis."
Metallurav, Moscow, 1988; pages 38-39). The major drawbacks of this method are as follows: substantial losses of magnesium occur by the accumulation thereof in the sludge, which is discarded from the electrolytic cells, and that the electrolytic cells experience a short service life.
Another drawback of this prior art method is that a considerable amount of magnesium oxide is present in the dehydrated magnesium chloride (from 1.5 to 3%). These factors considerably reduce economic feasibility of magnesium chloride production by dehydrating its crystalline hydrates.
The production of (anhydrous) dehydrated magnesium chloride, an essential component in the electrolytic production of magnesium metal by means of dehydration of ammonium carnallite (NHdCI ~ MgC12~6H20), is also known in the art. In this method ammonium carnallite is consecutively heated in multistage dryers in dry air up to 360 ° C. The complete dehydration and decomposition of the ammonia carnallite results in MgCl2 and NH4Cl. This method does not result in hydrolysis (see, M. A. Aydenzon, "Magnesium". MetallurQV, Moscow, 1969;
.°
pages 111-112).
Also, in the prior art, there is the method of production of practically anhydrous magnesium chloride as disclosed by the international patent application No. 95/ 11859. According to this document, the dehydration of MgCl2 solutions is provided by mixing such solutions with ethylene glycol, removing water therefrom in rectification columns, and subsequently precipitating magnesium ammoniate crystals (MgCIZ ~ nNH3) from the resulant mixture. The anhydrous ammoniate crystals produced are then washed with methanol, and further processed by drying in the fluidized bed unit. As a result, ammonia and anhydrous magnesium chloride are produced.
This method too has the same essential drawbacks. Some of the organic solvents, such as ethylene glycol used in the dehydration process is removed along with the water from the fractionating columns. This waste water contaminated with ethylene glycol needs to be treated in the fractionating columns. Also, after washing magnesium ammoniate crystals, the used methyl alcohol solvent includes some ethylene glycol from the distillation columns. Here, again, the ethylene glycol needs to be separated from the methyl alcohol in the fractionating columns.
Construction of the organic solvent recovery systems, such as fractionating distillation columns, require considerable capital investments. Furthermore, the fractional distillation required for separating the ethylene glycol from the water and the methyl alcohol requires additional energy consumption.
This method too has the same essential drawbacks. Some of the organic solvents, such as ethylene glycol used in the dehydration process is removed along with the water from the fractionating columns. This waste water contaminated with ethylene glycol needs to be treated in the fractionating columns. Also, after washing magnesium ammoniate crystals, the used methyl alcohol solvent includes some ethylene glycol from the distillation columns. Here, again, the ethylene glycol needs to be separated from the methyl alcohol in the fractionating columns.
Construction of the organic solvent recovery systems, such as fractionating distillation columns, require considerable capital investments. Furthermore, the fractional distillation required for separating the ethylene glycol from the water and the methyl alcohol requires additional energy consumption.
Russian patent RU 2136786, granted to Russian National Aluminium Magnesium Institute, discloses the method utilizing ammonium chloride for the production of magnesium from oxygen-containing raw material or from chlorine-magnesium solutions. According to this patent, the solution of magnesium chloride and ammonium chloride is vaporized, so that during the process, ammonium carnallite crystals are formed. The crystals of ammonium carnallite in turn, are dehydrated in the fluidized bed dryer and is further reduced (decomposed) in the melt of recycled electrolyte of the electrolytic cell.
Dehydrated magnesium chloride is fed to an electrolytic chamber, and the gaseous ammonium chloride released by the process is fed into absorption by the magnesium chloride solutions.
In the process, the exhaust gases resulting from the carnallite dehydration containing hydrogen chloride and ammonium chloride are formed. These gases are treated with condensate resulted from evaporation of magnesium chloride and ammonium chloride solutions. The gasses are then used in the leaching of the initial raw material. In this invention the processes of evaporation and crystallization of ammonium carnallite take place. Additionally, the method of Russian patent RU 2136786 discloses the following steps: using ammonium chloride; thermally decomposing anhydrous ammonium carnallite; and currently therewith isolating anhydrous magnesium chloride.
Accordingly, there is well-established need for a method of production of magnesium and chlorine from magnesium chloride solutions which is capable of reducing the costs of processing of the solutions of magnesium chloride and ammonium chloride. This is accomplished by means of minimizing the process areas where vapor losses occur and where ammonium carnallite crystallizes.
SUMMARY OF THE INVENTION
The invention is used in the production of magnesium from magnesium chloride solutions, which are produced by leaching oxygen-containing raw material into surface water, such as lakes, and from magnesium chloride solutions which are produced by the underground leaching of chlorine-magnesium salts into the water table.
One of the main objects of the invention is to reduce costs during the processing of the solutions of magnesium chloride and ammonium chloride. This is accomplished by minimizing the process areas where vapor losses occur and where ammonium carnallite crystallizes.
The method of producing magnesium and chlorine of the invention includes the following steps: processing of chlorine-magnesium solutions utilizing dehydrated compounds of ammonia; separating anhydrous magnesium chloride and electrolytic decomposition thereof into magnesium and chlorine products;
after decontamination, an initial chlorine-magnesium solution is saturated with ammonium chloride in a spray tower and the resultant solution is fed into the fluidized bed dryer for the direct production of solid anhydrous ammonium carnallite. In preparing the initial chlorine-magnesium solution, the decontamination step entails the removal of certain impurities therefrom, which impurities are known to interfere with further processing. The subsequent decomposition of the anhydrous ammonium carnallite produces anhydrous magnesium chloride, ammonia, and hydrogen chloride. The ammonia and hydrogen chloride are supplied together with exhaust gases to a spray tower;
and the anhydrous magnesium chloride is then fed to the electrolytic cells for the ' production of magnesium and chlorine.
Furthermore, in the method of the invention, the solution of salts is supplied through a dispersing device into the bed of fluidized material.
By circulating the effluent gasses as described heretofore, the solution of salts in the spray towers is heated to a temperature of between 85 to 120 ° C and the water content thereof is reduced to 55 to 65 percent.
According to the invention optimal drying and dehydration of the salt solution with minimal hydrolysis of magnesium chloride occurs when the content of ammonium chloride in the salt solution is maintained between 40 and 55 percent of the magnesium chloride content in the solution.
There are two embodiments of the invention disclosing decomposition of dehydrated ammonium carnallite. According to the first embodiment, the decomposition occurs in the fluidized bed dryer within the stream of flue gases, that are produced in the special burner where the fuel is combusted together with chlorine gas.
As to the second embodiment, decomposition of the anhydrous ammonium carnallite takes place in the melting unit within the recycled electrolyte.
The decontaminated chlorine-magnesium solutions are initially supplied to the absorber of fluidized bed dryer. Then the solutions are directed to the spray tower associated with the device capable of carrying out decomposition of the anhydrous ammonium carnallite.
In order to compensate the losses of ammonia during the production process, this ingredient is introduced into the salt solution before supplying of the salts to the fluidized bed dryer.
During the decomposition of carnallite in the fluidized bed dryer, the gases remaining in the process effluent after ammonium chloride is absorbed, contain a significant proportion of hydrogen chloride gas, which, in turn, is dissolved in water. The resultant byproduct is an 18 to 20 percent hydrochloric acid.
Brief Description of the Drawings FIG. 1 shows the process diagram of the method of the present invention.
Descriution of the Preferred Embodiment A system for the method of production of magnesium and chlorine of the invention typically consists of spray towers 1, 2, and 3; fluidized bed dryers and 7; a melting unit 5 and electrolytic cells 4.
The initial raw material in the form of a decontaminated solution of magnesium chloride is supplied for spraying in the spray tower 1. Exhaust gases from the fluidized bed dryer 7 containing NH4Cl and HC 1 are also fed into the spray tower 1. As the exhaust gases transfer considerable thermal energy, the aqueous portion of the solution is partially evaporated. Additionally, preliminary saturation of the solution occurs as HC 1 and NH3 are absorbed thereby. This is accompanied by the formation of the dissolved ammonium chloride. The solution from the spray tower 1 is fed for the spray nozzle in the spray tower or absorber 2.
Furthermore, effluent gases from the devices for decomposition of anhydrous ammonium carnallite, namely the melting unit 5 and/or the fluidized bed dryer are fed into the spray tower 2. The solution of salts is heated in the spray towers up to the temperature of 85 to 120° C. Through utilization of the heat of the exhaust gasses from the fluidized bed dryer 6 and melting unit 5, the solutions of salts are evaporated in the spray towers to obtain a water content between 55 and 65 percent.
After the saturation of the solution with ammonium chloride and in order to obtain the required content, this solution containing MgCl2 + NHdCI is supplied to the fluidized bed dryer 7 for evaporation, so as to obtain anhydrous or dehydrated ammonium carnallite.
In the above process, irretrievable losses of ammonia are compensated by adding ammonia or ammoniated solutions into the solution containing magnesium chloride solution, supplied into the fluidized bed dryer 7.
For the purposes of this application, the term spray tower is broadly defined as a chemical processing unit in which a gaseous effluent is absorbed by a sprayed or sprinkled solute. The unit is alternately referred to as an absorber.
In the fluidized bed dryer 7 the feedstock is dehydrated and ammonium carnallite is formed. The fluidized bed dryer 7 contains several chambers.
Initially, through a dispersing device, the solutions are introduced into the first chamber of the fluidized bed dryer for drying, so as to form MgCl2 ~ NH4Cl ~ 6 H20 After ammonium carnallite material moves through the subsequent chambers of the dryer 7, water is removed and the material becomes more substantially dehydrated in the following manner:
MgCI2~NH4Cl ~6 H20 -~ MgCl2. NH4C1 + 6 H20 + NH3 + HC 1 Thus, at the final stage, in the dehydrated or anhydrous ammonium carnallite the water content does not exceed 2 to 6 percent and Mg0 content does not exceed 1.2 to 1.6 percent. In the last chamber the bed temperature is between 180 and 230° C. Compared to the dehydration of bishofite (MgC12~6H20) which is formed when only chlorine-magnesium solution is subjected to the step of drying; the dehydration of the ammonium carnallite is accompanied by a several times lower rate of highly undesirable hydrolysis.
The anhydrous or dehydrated ammonium carnallite is subjected to the thermal decomposition in the fluidized bed dryer 6 or in the melting unit or electrolytic cell 5. This step is accompanied by the formation of anhydrous magnesium chloride with the content of water not exceeding 0.2 percent and gaseous hydrogen chloride and ammonia. Hydrogen chloride and ammonia form ammonium chloride that is collected in the spray tower 2.
According to one embodiment of the invention, the thermal decomposition of dehydrated or anhydrous ammonium carnallite occurs in the fluidized bed dryer 6 as follows:
MgCl2 ~ NH4C1 (solid)-~ MgCl2 (solid) + NH3 (gas) + HC 1(gas) In this condition the bed temperature range is between 340 and 380° C, whereas the stream of gaseous heat transfer medium contains less than 10 g/m3 of water. Substantially solid anhydrous MgCl2 formed in the fluidized bed dryer 6 is delivered to the electrolytic cells 4 for subsequent electrolysis.
In the present invention, the burners of the fluidized bed dryer 6 burn hydrocarbon fuel and chlorine from the electrolytic cells 4 provided for the production of magnesium. During the combustion process hydrogen from the fuel combines with chlorine to form hydrogen chloride. With the removal of the °
hydrogen chloride from the process effluent, the flue gases contain only water vapor which is supplied to the burner of the fluidized bed dryer 6 along with air.
This eliminates any special drying of the heat transfer medium and replaces the heating thereof by electrical air heaters or any other heat exchange units.
Since the formed hydrogen chloride is more hygroscopic in nature, (see above) upon entering the fluidized bed it minimizes highly undesirable hydrolysis of the anhydrous magnesium chloride. The content of magnesium oxide in anhydrous magnesium chloride produced by the method of this invention generally does not typically exceed 1.2 percent.
As to the second embodiment of the invention, the decomposition of anhydrous ammonium carnallite (produced in the fluidized bed dryer 7) takes place in the melting unit or electrolytic cell 5 at the temperature of about 660 ° C.
This unit is adapted to receive the melt of recycled electrolyte having a low content of MgCl2 from the electrolytic cells 4. According to this method the heat of recycled electrolyte, having a temperature of about 700 ° C, is mainly used to decompose ammonium carnallite in the following manner:
MgCl2 ~ NH4C1 (solid) -~ MgCl2 (melt) + NH3 (gas) + HC 1 (gas) Thus, formed dehydrated or anhydrous MgCl2 is dissolved in the recycled electrolyte and in the form of the melt delivered for electrolysis in the electrolytic cells 4. However, concurrently with the decomposition of carnallite in the melt, Mg0 is chlorinated in the process by hydrogen chloride. In this step, the final content of MgCl2 in the melt reaches 30 percent (max) and the Mg0 content is less than 0.02 percent. After the step of decomposition, the effluent gases from the melting unit 5 are supplied to the spray tower 2, so as to be absorbed by the MgCl2 solution. The enhanced composition of the melt obtained by the method hereof increases the service life of the graphite anodes of electrolytic cells utilized in the production of magnesium and thereby significantly reduces the operating costs of the electrolytic units.
Because of the presence in the spray tower 2 of the solution saturated with magnesium chloride and ammonium at temperatures exceeding 60 ° C, it is difficult to collect hydrogen chloride. Therefore, hydrogen chloride is released to spray tower 3 irrigated with water at a temperature lower than 40 ° C.
There, water saturated with hydrogen chloride forms hydrochloric acid (HCI) with a concentration from 18 to 20 percent. This hydrochloric acid is available for use in leaching magnesium-oxide containing materials utilized in obtaining of magnesium chloride solutions or for use in producing calcium chloride. ' Example 1. Initially; a decontaminated solution of magnesium chloride and ammonium chloride, containing MgCl2 - 18.8 percent and NH4C1- 10 percent and HCl-4 percent, is supplied through an injector nozzle into the fluidized bed dryer at the rate of 1200 kg/hour. The diameter of the furnace grid was 1.50 m.
'The final temperature in the fluidized bed was 190 and 200 ° C. As a result, 1030 kg of granulated dehydrated product, containing MgCl2 - 60 percent, NH4Cl -31.6 percent, Mg0 - 1.4 percent and HZO - 5.8 percent was produced. In the spray tower, exhaust gases are released into a sprayed magnesium chloride solution.
The liquor of following composition is produced: MgCl2 - 33.0 percent, NH~CI - 2.1 percent HCl - 3.7 percent and H20 - 60.5 percent.
Dehydrated granulated ammonium carnallite is loaded into the fluidized bed dryer with grid diameter of 300mm. The weight of carnallite was 150 kg. The temperature in the bed at the end of the run is 300° C (approx.). The heat transfer medium which was formed by the combustion of 7.5 kg of fuel oil and 26 kg of chlorine, was supplied for a 2.5 hour period to the burner below the furnace grid.
The combustion products under the grid are diluted with free air to raise the heat transfer medium temperature to 650 ° C. Anhydrous magnesium chloride in quantity of 85 kg is produced, having the following composition: MgCl2 - 98.3 percent, Mg0 - 1.0 percent; in which there was no NH4C1 present.
After the decomposition of ammonium carnallite, the gases from the fluidized bed dryer are supplied to the spray tower which is sprayed with the solution from the spray tower of the fluidized bed dryer for the dehydration of chlorine-magnesium solutions with ammonium chloride. The solution, containing MgCl2 - 18.8 percent, NH4C1- 10.9 percent and HCl-4 percent was produced in the spray tower operating at the temperature of 70 ° C (approx. ).
From this unit gases were fed to another absorber, which is operated with water sprayed having a temperature of 40 ° C. From the absorption of simultaneously, the hydrogen chloride gas was absorbed by water, so as to produce hydrochloric acid containing 20 percent of HCI.
The processing of anhydrous magnesium chloride, produced by electrolytic decomposition of anhydrous ammonium carnallite is conducted in an electrolytic cell operated at an amperage of 2000 amps and an electrolytic temperature of 700 °
C. The gaps) between the electrodes are 70 mm (approx.), and the average MgCl2 content in the bath is 16 percent. In a pilot test over a 48 day period, the current efficiency was 91 percent with other main characteristics of the cell being similar to those when this cell was used for processing of anhydrous magnesium chloride from the titanium production. This magnesium chloride used in the pilot run was obtained during the reduction of titanium tetrachloride. The quality of the magnesium produced met the highest industry standard for crude magnesium.
Example 2. In this example, the method of production of anhydrous ammonium carnallite is similar to that of Example 1. The anhydrous ammonium carnallite produced hereby is supplied to an electrolytic cell. The bath thereof has a square 300 x 300 mm top and a depth of 500 mm. Into the bath, 30 kg of molten electrolyte, at the temperature of 700 ° C is introduced.
Anhydrous ammonium carnallite is also introduced into the bath at the rate of 30 to 35 kg/hour. After the loading of 18 kg of anhydrous carnallite, 40 kg of the melt is received having a temperature of 660 ° C. The resultant product has a MgCl2 content of 30 percent, with Mg0 being absent therefrom. The melt meets all major standards applicable to the raw materials utilized in electrolysis.
Dehydrated magnesium chloride is fed to an electrolytic chamber, and the gaseous ammonium chloride released by the process is fed into absorption by the magnesium chloride solutions.
In the process, the exhaust gases resulting from the carnallite dehydration containing hydrogen chloride and ammonium chloride are formed. These gases are treated with condensate resulted from evaporation of magnesium chloride and ammonium chloride solutions. The gasses are then used in the leaching of the initial raw material. In this invention the processes of evaporation and crystallization of ammonium carnallite take place. Additionally, the method of Russian patent RU 2136786 discloses the following steps: using ammonium chloride; thermally decomposing anhydrous ammonium carnallite; and currently therewith isolating anhydrous magnesium chloride.
Accordingly, there is well-established need for a method of production of magnesium and chlorine from magnesium chloride solutions which is capable of reducing the costs of processing of the solutions of magnesium chloride and ammonium chloride. This is accomplished by means of minimizing the process areas where vapor losses occur and where ammonium carnallite crystallizes.
SUMMARY OF THE INVENTION
The invention is used in the production of magnesium from magnesium chloride solutions, which are produced by leaching oxygen-containing raw material into surface water, such as lakes, and from magnesium chloride solutions which are produced by the underground leaching of chlorine-magnesium salts into the water table.
One of the main objects of the invention is to reduce costs during the processing of the solutions of magnesium chloride and ammonium chloride. This is accomplished by minimizing the process areas where vapor losses occur and where ammonium carnallite crystallizes.
The method of producing magnesium and chlorine of the invention includes the following steps: processing of chlorine-magnesium solutions utilizing dehydrated compounds of ammonia; separating anhydrous magnesium chloride and electrolytic decomposition thereof into magnesium and chlorine products;
after decontamination, an initial chlorine-magnesium solution is saturated with ammonium chloride in a spray tower and the resultant solution is fed into the fluidized bed dryer for the direct production of solid anhydrous ammonium carnallite. In preparing the initial chlorine-magnesium solution, the decontamination step entails the removal of certain impurities therefrom, which impurities are known to interfere with further processing. The subsequent decomposition of the anhydrous ammonium carnallite produces anhydrous magnesium chloride, ammonia, and hydrogen chloride. The ammonia and hydrogen chloride are supplied together with exhaust gases to a spray tower;
and the anhydrous magnesium chloride is then fed to the electrolytic cells for the ' production of magnesium and chlorine.
Furthermore, in the method of the invention, the solution of salts is supplied through a dispersing device into the bed of fluidized material.
By circulating the effluent gasses as described heretofore, the solution of salts in the spray towers is heated to a temperature of between 85 to 120 ° C and the water content thereof is reduced to 55 to 65 percent.
According to the invention optimal drying and dehydration of the salt solution with minimal hydrolysis of magnesium chloride occurs when the content of ammonium chloride in the salt solution is maintained between 40 and 55 percent of the magnesium chloride content in the solution.
There are two embodiments of the invention disclosing decomposition of dehydrated ammonium carnallite. According to the first embodiment, the decomposition occurs in the fluidized bed dryer within the stream of flue gases, that are produced in the special burner where the fuel is combusted together with chlorine gas.
As to the second embodiment, decomposition of the anhydrous ammonium carnallite takes place in the melting unit within the recycled electrolyte.
The decontaminated chlorine-magnesium solutions are initially supplied to the absorber of fluidized bed dryer. Then the solutions are directed to the spray tower associated with the device capable of carrying out decomposition of the anhydrous ammonium carnallite.
In order to compensate the losses of ammonia during the production process, this ingredient is introduced into the salt solution before supplying of the salts to the fluidized bed dryer.
During the decomposition of carnallite in the fluidized bed dryer, the gases remaining in the process effluent after ammonium chloride is absorbed, contain a significant proportion of hydrogen chloride gas, which, in turn, is dissolved in water. The resultant byproduct is an 18 to 20 percent hydrochloric acid.
Brief Description of the Drawings FIG. 1 shows the process diagram of the method of the present invention.
Descriution of the Preferred Embodiment A system for the method of production of magnesium and chlorine of the invention typically consists of spray towers 1, 2, and 3; fluidized bed dryers and 7; a melting unit 5 and electrolytic cells 4.
The initial raw material in the form of a decontaminated solution of magnesium chloride is supplied for spraying in the spray tower 1. Exhaust gases from the fluidized bed dryer 7 containing NH4Cl and HC 1 are also fed into the spray tower 1. As the exhaust gases transfer considerable thermal energy, the aqueous portion of the solution is partially evaporated. Additionally, preliminary saturation of the solution occurs as HC 1 and NH3 are absorbed thereby. This is accompanied by the formation of the dissolved ammonium chloride. The solution from the spray tower 1 is fed for the spray nozzle in the spray tower or absorber 2.
Furthermore, effluent gases from the devices for decomposition of anhydrous ammonium carnallite, namely the melting unit 5 and/or the fluidized bed dryer are fed into the spray tower 2. The solution of salts is heated in the spray towers up to the temperature of 85 to 120° C. Through utilization of the heat of the exhaust gasses from the fluidized bed dryer 6 and melting unit 5, the solutions of salts are evaporated in the spray towers to obtain a water content between 55 and 65 percent.
After the saturation of the solution with ammonium chloride and in order to obtain the required content, this solution containing MgCl2 + NHdCI is supplied to the fluidized bed dryer 7 for evaporation, so as to obtain anhydrous or dehydrated ammonium carnallite.
In the above process, irretrievable losses of ammonia are compensated by adding ammonia or ammoniated solutions into the solution containing magnesium chloride solution, supplied into the fluidized bed dryer 7.
For the purposes of this application, the term spray tower is broadly defined as a chemical processing unit in which a gaseous effluent is absorbed by a sprayed or sprinkled solute. The unit is alternately referred to as an absorber.
In the fluidized bed dryer 7 the feedstock is dehydrated and ammonium carnallite is formed. The fluidized bed dryer 7 contains several chambers.
Initially, through a dispersing device, the solutions are introduced into the first chamber of the fluidized bed dryer for drying, so as to form MgCl2 ~ NH4Cl ~ 6 H20 After ammonium carnallite material moves through the subsequent chambers of the dryer 7, water is removed and the material becomes more substantially dehydrated in the following manner:
MgCI2~NH4Cl ~6 H20 -~ MgCl2. NH4C1 + 6 H20 + NH3 + HC 1 Thus, at the final stage, in the dehydrated or anhydrous ammonium carnallite the water content does not exceed 2 to 6 percent and Mg0 content does not exceed 1.2 to 1.6 percent. In the last chamber the bed temperature is between 180 and 230° C. Compared to the dehydration of bishofite (MgC12~6H20) which is formed when only chlorine-magnesium solution is subjected to the step of drying; the dehydration of the ammonium carnallite is accompanied by a several times lower rate of highly undesirable hydrolysis.
The anhydrous or dehydrated ammonium carnallite is subjected to the thermal decomposition in the fluidized bed dryer 6 or in the melting unit or electrolytic cell 5. This step is accompanied by the formation of anhydrous magnesium chloride with the content of water not exceeding 0.2 percent and gaseous hydrogen chloride and ammonia. Hydrogen chloride and ammonia form ammonium chloride that is collected in the spray tower 2.
According to one embodiment of the invention, the thermal decomposition of dehydrated or anhydrous ammonium carnallite occurs in the fluidized bed dryer 6 as follows:
MgCl2 ~ NH4C1 (solid)-~ MgCl2 (solid) + NH3 (gas) + HC 1(gas) In this condition the bed temperature range is between 340 and 380° C, whereas the stream of gaseous heat transfer medium contains less than 10 g/m3 of water. Substantially solid anhydrous MgCl2 formed in the fluidized bed dryer 6 is delivered to the electrolytic cells 4 for subsequent electrolysis.
In the present invention, the burners of the fluidized bed dryer 6 burn hydrocarbon fuel and chlorine from the electrolytic cells 4 provided for the production of magnesium. During the combustion process hydrogen from the fuel combines with chlorine to form hydrogen chloride. With the removal of the °
hydrogen chloride from the process effluent, the flue gases contain only water vapor which is supplied to the burner of the fluidized bed dryer 6 along with air.
This eliminates any special drying of the heat transfer medium and replaces the heating thereof by electrical air heaters or any other heat exchange units.
Since the formed hydrogen chloride is more hygroscopic in nature, (see above) upon entering the fluidized bed it minimizes highly undesirable hydrolysis of the anhydrous magnesium chloride. The content of magnesium oxide in anhydrous magnesium chloride produced by the method of this invention generally does not typically exceed 1.2 percent.
As to the second embodiment of the invention, the decomposition of anhydrous ammonium carnallite (produced in the fluidized bed dryer 7) takes place in the melting unit or electrolytic cell 5 at the temperature of about 660 ° C.
This unit is adapted to receive the melt of recycled electrolyte having a low content of MgCl2 from the electrolytic cells 4. According to this method the heat of recycled electrolyte, having a temperature of about 700 ° C, is mainly used to decompose ammonium carnallite in the following manner:
MgCl2 ~ NH4C1 (solid) -~ MgCl2 (melt) + NH3 (gas) + HC 1 (gas) Thus, formed dehydrated or anhydrous MgCl2 is dissolved in the recycled electrolyte and in the form of the melt delivered for electrolysis in the electrolytic cells 4. However, concurrently with the decomposition of carnallite in the melt, Mg0 is chlorinated in the process by hydrogen chloride. In this step, the final content of MgCl2 in the melt reaches 30 percent (max) and the Mg0 content is less than 0.02 percent. After the step of decomposition, the effluent gases from the melting unit 5 are supplied to the spray tower 2, so as to be absorbed by the MgCl2 solution. The enhanced composition of the melt obtained by the method hereof increases the service life of the graphite anodes of electrolytic cells utilized in the production of magnesium and thereby significantly reduces the operating costs of the electrolytic units.
Because of the presence in the spray tower 2 of the solution saturated with magnesium chloride and ammonium at temperatures exceeding 60 ° C, it is difficult to collect hydrogen chloride. Therefore, hydrogen chloride is released to spray tower 3 irrigated with water at a temperature lower than 40 ° C.
There, water saturated with hydrogen chloride forms hydrochloric acid (HCI) with a concentration from 18 to 20 percent. This hydrochloric acid is available for use in leaching magnesium-oxide containing materials utilized in obtaining of magnesium chloride solutions or for use in producing calcium chloride. ' Example 1. Initially; a decontaminated solution of magnesium chloride and ammonium chloride, containing MgCl2 - 18.8 percent and NH4C1- 10 percent and HCl-4 percent, is supplied through an injector nozzle into the fluidized bed dryer at the rate of 1200 kg/hour. The diameter of the furnace grid was 1.50 m.
'The final temperature in the fluidized bed was 190 and 200 ° C. As a result, 1030 kg of granulated dehydrated product, containing MgCl2 - 60 percent, NH4Cl -31.6 percent, Mg0 - 1.4 percent and HZO - 5.8 percent was produced. In the spray tower, exhaust gases are released into a sprayed magnesium chloride solution.
The liquor of following composition is produced: MgCl2 - 33.0 percent, NH~CI - 2.1 percent HCl - 3.7 percent and H20 - 60.5 percent.
Dehydrated granulated ammonium carnallite is loaded into the fluidized bed dryer with grid diameter of 300mm. The weight of carnallite was 150 kg. The temperature in the bed at the end of the run is 300° C (approx.). The heat transfer medium which was formed by the combustion of 7.5 kg of fuel oil and 26 kg of chlorine, was supplied for a 2.5 hour period to the burner below the furnace grid.
The combustion products under the grid are diluted with free air to raise the heat transfer medium temperature to 650 ° C. Anhydrous magnesium chloride in quantity of 85 kg is produced, having the following composition: MgCl2 - 98.3 percent, Mg0 - 1.0 percent; in which there was no NH4C1 present.
After the decomposition of ammonium carnallite, the gases from the fluidized bed dryer are supplied to the spray tower which is sprayed with the solution from the spray tower of the fluidized bed dryer for the dehydration of chlorine-magnesium solutions with ammonium chloride. The solution, containing MgCl2 - 18.8 percent, NH4C1- 10.9 percent and HCl-4 percent was produced in the spray tower operating at the temperature of 70 ° C (approx. ).
From this unit gases were fed to another absorber, which is operated with water sprayed having a temperature of 40 ° C. From the absorption of simultaneously, the hydrogen chloride gas was absorbed by water, so as to produce hydrochloric acid containing 20 percent of HCI.
The processing of anhydrous magnesium chloride, produced by electrolytic decomposition of anhydrous ammonium carnallite is conducted in an electrolytic cell operated at an amperage of 2000 amps and an electrolytic temperature of 700 °
C. The gaps) between the electrodes are 70 mm (approx.), and the average MgCl2 content in the bath is 16 percent. In a pilot test over a 48 day period, the current efficiency was 91 percent with other main characteristics of the cell being similar to those when this cell was used for processing of anhydrous magnesium chloride from the titanium production. This magnesium chloride used in the pilot run was obtained during the reduction of titanium tetrachloride. The quality of the magnesium produced met the highest industry standard for crude magnesium.
Example 2. In this example, the method of production of anhydrous ammonium carnallite is similar to that of Example 1. The anhydrous ammonium carnallite produced hereby is supplied to an electrolytic cell. The bath thereof has a square 300 x 300 mm top and a depth of 500 mm. Into the bath, 30 kg of molten electrolyte, at the temperature of 700 ° C is introduced.
Anhydrous ammonium carnallite is also introduced into the bath at the rate of 30 to 35 kg/hour. After the loading of 18 kg of anhydrous carnallite, 40 kg of the melt is received having a temperature of 660 ° C. The resultant product has a MgCl2 content of 30 percent, with Mg0 being absent therefrom. The melt meets all major standards applicable to the raw materials utilized in electrolysis.
Claims (8)
1. The method of production of magnesium and chlorine, comprising the steps of dehydrating a feedstock of chlorine-magnesium solutions having ammonia compounds therewithin; separating anhydrous magnesium chloride therefrom; and electrolytically decomposing magnesium chloride to produce magnesium and chlorine, characterized in that an initial chlorine-magnesium solution after decontamination is saturated with ammonium chloride and supplied to a fluidized bed dryer for direct production of substantially solid anhydrous ammonium carnallite with subsequent decomposition thereof to obtain anhydrous magnesium chloride, ammonia and hydrogen chloride; ammonia and hydrogen chloride are recirculated with exhaust gases within the process, and anhydrous magnesium chloride is supplied to electrolytic cells for production of magnesium and chlorine.
2. The method of claim 1, wherein the fluidized bed dryer is formed with a bed of fluidized material and a solution of salts is supplied through a dispersing device into the bed of fluidized material.
3. The method of claim 1, further comprising heating of the solution of salts in spray towers up to the temperature of 85 to 120° C; and by utilizing the heat of the exhaust gases from the steps of dehydration and decomposition, said solutions of salts are evaporated to obtain a water content of between 55 and percent.
4. The method of claim 1, wherein the decomposition of anhydrous ammonium carnalite is conducted in a fluidized bed dryer in a stream of gaseous heat transfer medium produced by burning of a combusting hydrocarbon fuel together with chlorine.
5. The method of claims 1, wherein the decomposition of anhydrous ammonium carnalite is conducted in a recycled liquid electrolyte.
6. The method of claim 1, wherein said decontaminated chlorine-magnesium solutions are initially supplied into a first spray tower associated with a fluidized bed dehydration dryer and then said solution is directed to a second spray tower associated with an arrangement for decomposition of said anhydrous ammonium carnallite.
7. The method of claim 6, wherein ammonia is introduced into a solution of salts produced in said second spray tower to compensate the losses of ammonium chloride.
8. The method of claim 1, wherein after the absorption of ammonium chloride forming a part of the gases released from dryers provided for dehydration and decomposition of carnallite, said gases are supplied into a spray tower, to be sprinkled with water, so as to produce hydrochloric acid containing at least percent of HCl.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| RU2001105602A RU2200704C2 (en) | 2001-02-27 | 2001-02-27 | Method for production of magnesium and chlorine from ammonium chloride- containing magnesium chloride solution |
| RU2001105602 | 2001-02-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2373402A1 true CA2373402A1 (en) | 2002-08-27 |
Family
ID=20246646
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2373402 Abandoned CA2373402A1 (en) | 2001-02-27 | 2002-02-26 | Method of production of magnesium and chlorine from magnesium chloride solutions containing ammonium chloride |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2373402A1 (en) |
| RU (1) | RU2200704C2 (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102534196A (en) * | 2010-12-14 | 2012-07-04 | 贵阳铝镁设计研究院有限公司 | Chlorination process for pressing magnesite into balls through light burning dry method |
| CN104278293A (en) * | 2013-07-12 | 2015-01-14 | 中国科学院过程工程研究所 | K3NaMgCl6 as well as preparation method and application thereof |
| CN105236446A (en) * | 2015-11-24 | 2016-01-13 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for recycling waste hydrochloric acid |
| CN113008726A (en) * | 2021-04-09 | 2021-06-22 | 河北大有镁业有限责任公司 | Device and method for determining components of ammonium carnallite dehydrated material |
| CN113044862A (en) * | 2021-04-09 | 2021-06-29 | 河北大有镁业有限责任公司 | Method for dehydrating different ammonium carnallite materials by utilizing synergistic coupling effect of different ammonium carnallite materials |
| CN113479917A (en) * | 2021-08-02 | 2021-10-08 | 青海盐湖工业股份有限公司 | Method and system for preparing anhydrous magnesium chloride |
-
2001
- 2001-02-27 RU RU2001105602A patent/RU2200704C2/en not_active IP Right Cessation
-
2002
- 2002-02-26 CA CA 2373402 patent/CA2373402A1/en not_active Abandoned
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102534196A (en) * | 2010-12-14 | 2012-07-04 | 贵阳铝镁设计研究院有限公司 | Chlorination process for pressing magnesite into balls through light burning dry method |
| CN104278293A (en) * | 2013-07-12 | 2015-01-14 | 中国科学院过程工程研究所 | K3NaMgCl6 as well as preparation method and application thereof |
| CN105236446A (en) * | 2015-11-24 | 2016-01-13 | 攀钢集团攀枝花钢铁研究院有限公司 | Method for recycling waste hydrochloric acid |
| CN113008726A (en) * | 2021-04-09 | 2021-06-22 | 河北大有镁业有限责任公司 | Device and method for determining components of ammonium carnallite dehydrated material |
| CN113044862A (en) * | 2021-04-09 | 2021-06-29 | 河北大有镁业有限责任公司 | Method for dehydrating different ammonium carnallite materials by utilizing synergistic coupling effect of different ammonium carnallite materials |
| CN113044862B (en) * | 2021-04-09 | 2022-07-08 | 河北大有镁业有限责任公司 | Method for dehydrating different ammonium carnallite materials by utilizing synergistic coupling effect of different ammonium carnallite materials |
| CN113008726B (en) * | 2021-04-09 | 2023-04-25 | 河北大有镁业有限责任公司 | Determination device and method for ammonium carnallite dehydration material components |
| CN113479917A (en) * | 2021-08-02 | 2021-10-08 | 青海盐湖工业股份有限公司 | Method and system for preparing anhydrous magnesium chloride |
Also Published As
| Publication number | Publication date |
|---|---|
| RU2200704C2 (en) | 2003-03-20 |
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