CA1140730A - Process for producing magnesium oxide from an aqueous magnesium sulphate solution - Google Patents
Process for producing magnesium oxide from an aqueous magnesium sulphate solutionInfo
- Publication number
- CA1140730A CA1140730A CA000327993A CA327993A CA1140730A CA 1140730 A CA1140730 A CA 1140730A CA 000327993 A CA000327993 A CA 000327993A CA 327993 A CA327993 A CA 327993A CA 1140730 A CA1140730 A CA 1140730A
- Authority
- CA
- Canada
- Prior art keywords
- magnesium
- circuit
- sulphate solution
- ammonia gas
- crystals
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 title claims abstract description 68
- 238000000034 method Methods 0.000 title claims abstract description 40
- 229910052943 magnesium sulfate Inorganic materials 0.000 title claims abstract description 36
- 235000019341 magnesium sulphate Nutrition 0.000 title claims abstract description 34
- 239000000395 magnesium oxide Substances 0.000 title claims abstract description 25
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 title claims abstract description 25
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 title claims abstract description 25
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims abstract description 32
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 26
- 239000013078 crystal Substances 0.000 claims abstract description 23
- NEKPCAYWQWRBHN-UHFFFAOYSA-L magnesium;carbonate;trihydrate Chemical compound O.O.O.[Mg+2].[O-]C([O-])=O NEKPCAYWQWRBHN-UHFFFAOYSA-L 0.000 claims abstract description 19
- 229910002092 carbon dioxide Inorganic materials 0.000 claims abstract description 18
- 239000001569 carbon dioxide Substances 0.000 claims abstract description 15
- 239000007858 starting material Substances 0.000 claims abstract description 14
- 239000000391 magnesium silicate Substances 0.000 claims abstract description 8
- 229910052919 magnesium silicate Inorganic materials 0.000 claims abstract description 8
- 235000019792 magnesium silicate Nutrition 0.000 claims abstract description 8
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 6
- HCWCAKKEBCNQJP-UHFFFAOYSA-N magnesium orthosilicate Chemical compound [Mg+2].[Mg+2].[O-][Si]([O-])([O-])[O-] HCWCAKKEBCNQJP-UHFFFAOYSA-N 0.000 claims abstract 4
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 claims description 12
- 238000005406 washing Methods 0.000 claims description 10
- 229910052921 ammonium sulfate Inorganic materials 0.000 claims description 9
- 235000011130 ammonium sulphate Nutrition 0.000 claims description 9
- 239000001166 ammonium sulphate Substances 0.000 claims description 8
- 238000001354 calcination Methods 0.000 claims description 6
- 230000001376 precipitating effect Effects 0.000 claims description 6
- 238000001035 drying Methods 0.000 claims description 5
- 239000010425 asbestos Substances 0.000 claims description 4
- 229910052895 riebeckite Inorganic materials 0.000 claims description 4
- 239000002699 waste material Substances 0.000 claims description 4
- WYTGDNHDOZPMIW-RCBQFDQVSA-N alstonine Natural products C1=CC2=C3C=CC=CC3=NC2=C2N1C[C@H]1[C@H](C)OC=C(C(=O)OC)[C@H]1C2 WYTGDNHDOZPMIW-RCBQFDQVSA-N 0.000 claims description 2
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 claims 1
- 238000001556 precipitation Methods 0.000 abstract description 6
- 239000000243 solution Substances 0.000 description 30
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 7
- 230000009102 absorption Effects 0.000 description 7
- 238000010521 absorption reaction Methods 0.000 description 7
- 229910021653 sulphate ion Inorganic materials 0.000 description 7
- 239000007789 gas Substances 0.000 description 5
- 239000007787 solid Substances 0.000 description 5
- WRUGWIBCXHJTDG-UHFFFAOYSA-L magnesium sulfate heptahydrate Chemical compound O.O.O.O.O.O.O.[Mg+2].[O-]S([O-])(=O)=O WRUGWIBCXHJTDG-UHFFFAOYSA-L 0.000 description 4
- ZADYMNAVLSWLEQ-UHFFFAOYSA-N magnesium;oxygen(2-);silicon(4+) Chemical compound [O-2].[O-2].[O-2].[Mg+2].[Si+4] ZADYMNAVLSWLEQ-UHFFFAOYSA-N 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 229910052564 epsomite Inorganic materials 0.000 description 3
- 238000001704 evaporation Methods 0.000 description 3
- 230000008020 evaporation Effects 0.000 description 3
- 229910052749 magnesium Inorganic materials 0.000 description 3
- 235000001055 magnesium Nutrition 0.000 description 3
- 239000011777 magnesium Substances 0.000 description 3
- 229940091250 magnesium supplement Drugs 0.000 description 3
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 2
- 229910021529 ammonia Inorganic materials 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 150000004679 hydroxides Chemical class 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- -1 iron ions Chemical class 0.000 description 2
- ZLNQQNXFFQJAID-UHFFFAOYSA-L magnesium carbonate Chemical compound [Mg+2].[O-]C([O-])=O ZLNQQNXFFQJAID-UHFFFAOYSA-L 0.000 description 2
- 239000001095 magnesium carbonate Substances 0.000 description 2
- 235000014380 magnesium carbonate Nutrition 0.000 description 2
- 229910000021 magnesium carbonate Inorganic materials 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000012452 mother liquor Substances 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 239000011343 solid material Substances 0.000 description 2
- 244000228957 Ferula foetida Species 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000002671 adjuvant Substances 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000005755 formation reaction Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000002386 leaching Methods 0.000 description 1
- 229960001708 magnesium carbonate Drugs 0.000 description 1
- 229940031958 magnesium carbonate hydroxide Drugs 0.000 description 1
- VTHJTEIRLNZDEV-UHFFFAOYSA-L magnesium dihydroxide Chemical compound [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 description 1
- 239000000347 magnesium hydroxide Substances 0.000 description 1
- 229910001862 magnesium hydroxide Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000003472 neutralizing effect Effects 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 239000004291 sulphur dioxide Substances 0.000 description 1
- 235000010269 sulphur dioxide Nutrition 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/02—Magnesia
- C01F5/06—Magnesia by thermal decomposition of magnesium compounds
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/02—Magnesia
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/14—Magnesium hydroxide
- C01F5/20—Magnesium hydroxide by precipitation from solutions of magnesium salts with ammonia
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Inorganic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An aqueous magnesium sulphate solution, e.g. from a main process using magnesium silicate as a starting material, is introduced into a circuit with ammonia gas and carbon dioxide to obtain cyrstals of magnesium carbonate trihydrate.
The crystals are then freed, washed, dried and calcinated to obtain magnesium oxide. The produced carbon dioxide can be recycled to the circuit to act as a precipitation agent.
An aqueous magnesium sulphate solution, e.g. from a main process using magnesium silicate as a starting material, is introduced into a circuit with ammonia gas and carbon dioxide to obtain cyrstals of magnesium carbonate trihydrate.
The crystals are then freed, washed, dried and calcinated to obtain magnesium oxide. The produced carbon dioxide can be recycled to the circuit to act as a precipitation agent.
Description
Q~30 This invention relates to a process for producing magnesium oxide from an aqueous magnesium sulphate solution. More particularly, this invention rela~es to a process for producing magnesium oxide from a starting material containing magnesium silicate such as a serpentine or asbestos waste.
Heretofore, it has been proposed to prepare magnesium oxide from materials containing magnesium silicate, for example asbestos or asbestos waste. In such cases, the starting material has been dried, mixed wi~h ammonium sulphate and treated at a temperature between 320C and 380C. The resultant products include a solid comprising magnesium sulphate and ammonia gas. These solids are then leached with acid, whereupon magnesium sulphate and excess ammonium sulphate go into solution. Ammonia gas is then added to increase the p~ and dissolved impurities such as iron ions and precipitated as hydroxides.
After iltration, a clear solution of magnesium sulphate remains containing traces of ammonium sulphate. The solution is then concentrated by evaporation whereupon epsomite (MgS04 7H20) crystalizes out. The epsomite crystals are then separated by centrifuging and the mother liquor, enriched with ammonium sulphate, is returned to the leaching stage. The epsomite crystals are dried and at least partially freed from water of crystalization at a temperature of about 180C. The dehydrated epsomite is then decomposed to magnesium oxide and sulphur-dioxide at about 1,000C.
- 1 - ,;
~1~0~3~31 It is now known to add precipitating a~ents to a magnesium sulphate solution in order to precipitate salts, such as magnesium carbonate trihydrate, basic magnesium carbonate or magnesium hydroxide, which are difficult to dissolve. Admittedly, magnesium carbonate~ and hydroxides are much easier to decompose to magnesium oxide than magnesium sulphate. However, it is di~ficult to obtain an easily filterable and washable precipitate. Usually, only very dilute solutions can be precipitated. If the starting solutions are concentrated, it is difficult to precipitate and separate the solid. Accordingly, dilution is economically impossible, particularly if the solution resulting from the precipitation reaction has to be subsequently freed from the added water by expensive evaporation.
Accordingly, it is an object of this invention to provide a process for producing magnesium oxide from a magnesium sulphate solution which yields easily filterable and washable magnesium carbonate trihydrate without much water having to be evaporated.
It is another object of the invention to provide a process for producing magnesium oxide from a magnesium sulphate solution which requires a relatively small amount of heat.
It is another object of the invention to provide a relatively simple process for producing magnesium oxide from a starting solution having a high concentration of magnesium sulphate.
Briefly, the invention provides a process for producing magnesium oxide which is comprised of the steps 73~
of generating a ~low of an aqueous magnesium sulphate solution at a concentration of from 15% to 25~ t introducing the flow into a circuit maintained at a temperature from 25 to 45 C and a pH of from 7.5 to 8.5, continuously adding ammonia gas and carbon dioxide to the flow in the circuit to precipitate magnesium carbonate trihydrate, continuously separating at least some of the precipitated magnesium carbonate trihydrate crystals from the ~ircuit and thereafter freeing the separated crystals and then wa~hing, drying and calcinating the crystals to magnesium oxide.
The ammonia gas and carbon dioxide are added to the circuit in approximately stoichiometric proportions relative to the magnesium sulphate solution. In this regard, during calcinating of the magnesium carbonate trihydrate crystals, carbon dioxide is produced. This carbon dioxide can then be introduced into the circuit as a precipitating agentJ
In accordance with the process,the a~nium sulphate solution can be withdrawn from the circuit and then concen-trated and crystalized.
The aqueous magnesium sulphate solution can be obtained from a main process which utilizes a starting material containing magnesium sillicate. In this regard, the main process would be of the type to produce an aqueous magnesium sulphate solution and ammonia gas. This ammonia gas may also be added to the circuit as a precipitating agent while the ammD~ium sulphate which is produced can be added to the starting material of the main process.
Q~73(~
It is to be noted that in the processes for produc-ing magnesium oxide from a material containing magnesium sillicate, ammonia gas was produced and could advan~ageously be used. Secondly, ~here was a use for the by-product ammoniilm sulphate by adding the sulphate to the starting material.
One of the advantages of the process of the invent-ion is that precipitation is continuous with all important parameters remaining unchanged during the precipitation process. The product is therefore of constant composition and quality. Furthermore, the resulting magnesium o~ide has good surface activity because th~ calcination temperatuxe is low.
Still further, the investment and energy cost of the process is about half that of the above described previously known process.
These and other objects and advantages of the invention will become more apparent from the following detailed description and accompanying drawing wherein:
The drawing illustrates a schematic flow diagram of the process according to the invention.
Referring to the drawing, a container 1 contains a supply of magnesium sulphate solution (MgSO4) which is supplied, for example from a main process utili~ing a starting material containing magnesium silicate. Any soluble impurit-ies, such as iron ions are precipitated out by temporarily increasing the pH of the aqueous magnesium sulphate solution.
The concentration of the magnesium sulphate solution is from 15~ to 25% and preferably about 2~%.
A conduit 2 connects the container 1 to a circuit Q~3~
3 in order to supply a flow of aqueous magnesium sulphate solution from the tank into the circuit 3. The amount of circulation within the circuit 3 is about 20 to 200 times the amount in the conduit 2.
The circuit 3 is comprised of an absorption device 4 for introducing carbon dioxide (C02) and ammonia gas (NH3) into the circuit via suitable lines 5, 6. The absorption device 4 may comprise a mixing section in which the two gases are conveyed cocurrently with the aqueous solution.
The circuit 3 also has a holding container 8 having an over-flow line 9 and a discharge line 10 which connects to a separator 11. The separator 11 has a return line 12 which connects to the circuit 3 as well as a discharge line 13 which leads to a washing means 14. The washing means 14 also has a discharge line 15 connected to the circuit 3, an input line 16 for washing water and a discharge line 18 which connects to a drying and decomposition means 20, for example a fluidized bed furnace. This furnace has an outlet line 21 for magnesium oxide.
The overflow line 9 of the holding container 8 leads to an evaporator 22 having a yas outlet line 23 and a fluid outlet line 24 leading to a crystalizer 25. The crystalizer 25 has a vapor discharge line 26 as well as a product discharge line 27.
In accordance with the process, a main process operates on a starting material containing magnesium silicate to produce an aqueous magnesium sulphate solution which is delivered to the container 1 as well as ammonia gas which ~L~14(:~73~
can be charged into the absorption device 4 via the line 6.
The magnesium sulphate solution flows from the container 1 and is introduced into the circuit 3 via the line 2. In addition, carbon dioxide i5 added to the absorption device via the line 5.
The circuit 3 mainly contains ammGnium sulphate (NH4) 2SO4] in aqueous solution with some magnesium sulphate, the absorbed carbon dioxide and ammonia gas and a small percentage of suspended crystals of magnesium carbonate trihydrate(MgCO3-3H2o). The ammonia gas and carbon dioxide are continuously added to the circuit in`approximately stoichiometric proportions relative to the magnesium sulphate solution flowing in from the line 2 in order to precipitate magnesium carbonate trihydrate. The proportions of the two gases are such that the molar ratios are approxi-5 matelyNH3: MgSO4 - 2:1 and CO2: MgSO~ = 1:1 The absorption of the two gases is immediately followed by the known precipitation reaction in which magnesium carbonate trihydrate is formed in accordance with the equasion:
MgS04 + 2NH3 ~ C02 ~ 4H20--b MgC03.3H20 +(NH4)2SO4 The magnesium carbonate trihydrate crystals which were present bafore the reaction are used as nuclei for producing large crystals. This prevents super-saturation in the circuit 3, which could result in spontaneous forma-tion of nuclei and the resulting disadvantageous fine and dendritic crystals.
~L14Q73q:~
The holding container 8 thus receives the magnesium carbonate trihydrate crystals which are still very small and permits the crystals to increase in size~ The larger crystals form a slurry at the bot~om of the container 8 and flow out through the discharge line 10. The remaining contents of the container 8 flows back into the circuit 3.
The circuit also contains suitable means ~not shown) for maintaining the circuit at a temperature at a constant value of from 25 to 45 C. The pressure is atmospheric and the pH is from ~.5 to 8.5.
The magnesium carbonate trihydrate crystals are continuously separated from the holding container 8 via the discharge Line 10 into the separator 11 in which the slurry is separated from the accompanying solution~ To this end, the separator 11 can be a filter or centrifuge. The remaining clear solution is returned through the return line 12 into the circuit 3.
In the process t the optimum concentration of solids in the precipitation system can be obtained by varying the proportion of the two flows in the circuit 3 and in the discharge line 10 in the circuit 3 and the absorption devic~
4. The solid material in the separator 11 which comprises magnesium carbonate trihydrate and mother liquor, flows through the line 13 into the washing means 14. In this regard, the washing means 14 may be in the form of a band filter and a washing means. In any event, the solid material is washed in countexcurrent with a minimum of water,which washing water is supplied through the input line 16. After '73~
~ 8--use, the washing water is supplied through the discharge ~ine 15 to the circuit 3.
The washed solid which consists only of pure magnes-ium carbonate trihydrate and water is conveyed through the discharge line 18 to the drying and decomposition means 20 in which the crystals are dried and decomposed at a temperature not exceeding 800C. During the process, carbon dioxide gas is liberated and conveyed through the line 5 into the absorp-tion device 4 in the circuit 3. The remaining pure magnesium oxide (MgO) flows away through the outlet line 21. As a result of the relatively low calcina~ion temperature, the resulting magnesium oxide has good surface activity. Thus, the magnesium oxide can be used, for example to form briquettes without using a binder and can be subsequently burned into high quality magnesium oxide sinter. Alternatively, the magnesium oxide can be used as an active neutralizing agent or adjuvant for chemical and pharmaceutical purposes.
Excess clear a~nium sulphate solution, still contain-ing small traces of magnesium sulphate, ammonia and carbon dioxide, is withdrawn through the overflow line 9 which opens into the top part o the holding container 8. The solution is evaporated in the evaporator 22 and the resulting vapors are discharged through the gas outlet line 23. The remaining solution flows through the fluid outlet line 24 into the crystali~er 25 in which ammonium sulphate is crystalized by further evaporation. The resulting vapors are discharged through the vapor discharge line 26~ The crystaline ammonium sulphate is withdra~n from the crystalizer 25 through the product discharge line 27.
~I~L40~3~3 g Although the process has been described as being part of a main process, the process canl of course, be used independently for producing magnesium oxide from a starting material consisting of aqueous magnesium sulphate solution, if such a solution is available. In this case, gaseous ammonia must be oktained from an external source. However, it is not then necessary to concentrate or crystalize the ammonium sulphate solution if there is no use for the ~loni~m sulphate.
Heretofore, it has been proposed to prepare magnesium oxide from materials containing magnesium silicate, for example asbestos or asbestos waste. In such cases, the starting material has been dried, mixed wi~h ammonium sulphate and treated at a temperature between 320C and 380C. The resultant products include a solid comprising magnesium sulphate and ammonia gas. These solids are then leached with acid, whereupon magnesium sulphate and excess ammonium sulphate go into solution. Ammonia gas is then added to increase the p~ and dissolved impurities such as iron ions and precipitated as hydroxides.
After iltration, a clear solution of magnesium sulphate remains containing traces of ammonium sulphate. The solution is then concentrated by evaporation whereupon epsomite (MgS04 7H20) crystalizes out. The epsomite crystals are then separated by centrifuging and the mother liquor, enriched with ammonium sulphate, is returned to the leaching stage. The epsomite crystals are dried and at least partially freed from water of crystalization at a temperature of about 180C. The dehydrated epsomite is then decomposed to magnesium oxide and sulphur-dioxide at about 1,000C.
- 1 - ,;
~1~0~3~31 It is now known to add precipitating a~ents to a magnesium sulphate solution in order to precipitate salts, such as magnesium carbonate trihydrate, basic magnesium carbonate or magnesium hydroxide, which are difficult to dissolve. Admittedly, magnesium carbonate~ and hydroxides are much easier to decompose to magnesium oxide than magnesium sulphate. However, it is di~ficult to obtain an easily filterable and washable precipitate. Usually, only very dilute solutions can be precipitated. If the starting solutions are concentrated, it is difficult to precipitate and separate the solid. Accordingly, dilution is economically impossible, particularly if the solution resulting from the precipitation reaction has to be subsequently freed from the added water by expensive evaporation.
Accordingly, it is an object of this invention to provide a process for producing magnesium oxide from a magnesium sulphate solution which yields easily filterable and washable magnesium carbonate trihydrate without much water having to be evaporated.
It is another object of the invention to provide a process for producing magnesium oxide from a magnesium sulphate solution which requires a relatively small amount of heat.
It is another object of the invention to provide a relatively simple process for producing magnesium oxide from a starting solution having a high concentration of magnesium sulphate.
Briefly, the invention provides a process for producing magnesium oxide which is comprised of the steps 73~
of generating a ~low of an aqueous magnesium sulphate solution at a concentration of from 15% to 25~ t introducing the flow into a circuit maintained at a temperature from 25 to 45 C and a pH of from 7.5 to 8.5, continuously adding ammonia gas and carbon dioxide to the flow in the circuit to precipitate magnesium carbonate trihydrate, continuously separating at least some of the precipitated magnesium carbonate trihydrate crystals from the ~ircuit and thereafter freeing the separated crystals and then wa~hing, drying and calcinating the crystals to magnesium oxide.
The ammonia gas and carbon dioxide are added to the circuit in approximately stoichiometric proportions relative to the magnesium sulphate solution. In this regard, during calcinating of the magnesium carbonate trihydrate crystals, carbon dioxide is produced. This carbon dioxide can then be introduced into the circuit as a precipitating agentJ
In accordance with the process,the a~nium sulphate solution can be withdrawn from the circuit and then concen-trated and crystalized.
The aqueous magnesium sulphate solution can be obtained from a main process which utilizes a starting material containing magnesium sillicate. In this regard, the main process would be of the type to produce an aqueous magnesium sulphate solution and ammonia gas. This ammonia gas may also be added to the circuit as a precipitating agent while the ammD~ium sulphate which is produced can be added to the starting material of the main process.
Q~73(~
It is to be noted that in the processes for produc-ing magnesium oxide from a material containing magnesium sillicate, ammonia gas was produced and could advan~ageously be used. Secondly, ~here was a use for the by-product ammoniilm sulphate by adding the sulphate to the starting material.
One of the advantages of the process of the invent-ion is that precipitation is continuous with all important parameters remaining unchanged during the precipitation process. The product is therefore of constant composition and quality. Furthermore, the resulting magnesium o~ide has good surface activity because th~ calcination temperatuxe is low.
Still further, the investment and energy cost of the process is about half that of the above described previously known process.
These and other objects and advantages of the invention will become more apparent from the following detailed description and accompanying drawing wherein:
The drawing illustrates a schematic flow diagram of the process according to the invention.
Referring to the drawing, a container 1 contains a supply of magnesium sulphate solution (MgSO4) which is supplied, for example from a main process utili~ing a starting material containing magnesium silicate. Any soluble impurit-ies, such as iron ions are precipitated out by temporarily increasing the pH of the aqueous magnesium sulphate solution.
The concentration of the magnesium sulphate solution is from 15~ to 25% and preferably about 2~%.
A conduit 2 connects the container 1 to a circuit Q~3~
3 in order to supply a flow of aqueous magnesium sulphate solution from the tank into the circuit 3. The amount of circulation within the circuit 3 is about 20 to 200 times the amount in the conduit 2.
The circuit 3 is comprised of an absorption device 4 for introducing carbon dioxide (C02) and ammonia gas (NH3) into the circuit via suitable lines 5, 6. The absorption device 4 may comprise a mixing section in which the two gases are conveyed cocurrently with the aqueous solution.
The circuit 3 also has a holding container 8 having an over-flow line 9 and a discharge line 10 which connects to a separator 11. The separator 11 has a return line 12 which connects to the circuit 3 as well as a discharge line 13 which leads to a washing means 14. The washing means 14 also has a discharge line 15 connected to the circuit 3, an input line 16 for washing water and a discharge line 18 which connects to a drying and decomposition means 20, for example a fluidized bed furnace. This furnace has an outlet line 21 for magnesium oxide.
The overflow line 9 of the holding container 8 leads to an evaporator 22 having a yas outlet line 23 and a fluid outlet line 24 leading to a crystalizer 25. The crystalizer 25 has a vapor discharge line 26 as well as a product discharge line 27.
In accordance with the process, a main process operates on a starting material containing magnesium silicate to produce an aqueous magnesium sulphate solution which is delivered to the container 1 as well as ammonia gas which ~L~14(:~73~
can be charged into the absorption device 4 via the line 6.
The magnesium sulphate solution flows from the container 1 and is introduced into the circuit 3 via the line 2. In addition, carbon dioxide i5 added to the absorption device via the line 5.
The circuit 3 mainly contains ammGnium sulphate (NH4) 2SO4] in aqueous solution with some magnesium sulphate, the absorbed carbon dioxide and ammonia gas and a small percentage of suspended crystals of magnesium carbonate trihydrate(MgCO3-3H2o). The ammonia gas and carbon dioxide are continuously added to the circuit in`approximately stoichiometric proportions relative to the magnesium sulphate solution flowing in from the line 2 in order to precipitate magnesium carbonate trihydrate. The proportions of the two gases are such that the molar ratios are approxi-5 matelyNH3: MgSO4 - 2:1 and CO2: MgSO~ = 1:1 The absorption of the two gases is immediately followed by the known precipitation reaction in which magnesium carbonate trihydrate is formed in accordance with the equasion:
MgS04 + 2NH3 ~ C02 ~ 4H20--b MgC03.3H20 +(NH4)2SO4 The magnesium carbonate trihydrate crystals which were present bafore the reaction are used as nuclei for producing large crystals. This prevents super-saturation in the circuit 3, which could result in spontaneous forma-tion of nuclei and the resulting disadvantageous fine and dendritic crystals.
~L14Q73q:~
The holding container 8 thus receives the magnesium carbonate trihydrate crystals which are still very small and permits the crystals to increase in size~ The larger crystals form a slurry at the bot~om of the container 8 and flow out through the discharge line 10. The remaining contents of the container 8 flows back into the circuit 3.
The circuit also contains suitable means ~not shown) for maintaining the circuit at a temperature at a constant value of from 25 to 45 C. The pressure is atmospheric and the pH is from ~.5 to 8.5.
The magnesium carbonate trihydrate crystals are continuously separated from the holding container 8 via the discharge Line 10 into the separator 11 in which the slurry is separated from the accompanying solution~ To this end, the separator 11 can be a filter or centrifuge. The remaining clear solution is returned through the return line 12 into the circuit 3.
In the process t the optimum concentration of solids in the precipitation system can be obtained by varying the proportion of the two flows in the circuit 3 and in the discharge line 10 in the circuit 3 and the absorption devic~
4. The solid material in the separator 11 which comprises magnesium carbonate trihydrate and mother liquor, flows through the line 13 into the washing means 14. In this regard, the washing means 14 may be in the form of a band filter and a washing means. In any event, the solid material is washed in countexcurrent with a minimum of water,which washing water is supplied through the input line 16. After '73~
~ 8--use, the washing water is supplied through the discharge ~ine 15 to the circuit 3.
The washed solid which consists only of pure magnes-ium carbonate trihydrate and water is conveyed through the discharge line 18 to the drying and decomposition means 20 in which the crystals are dried and decomposed at a temperature not exceeding 800C. During the process, carbon dioxide gas is liberated and conveyed through the line 5 into the absorp-tion device 4 in the circuit 3. The remaining pure magnesium oxide (MgO) flows away through the outlet line 21. As a result of the relatively low calcina~ion temperature, the resulting magnesium oxide has good surface activity. Thus, the magnesium oxide can be used, for example to form briquettes without using a binder and can be subsequently burned into high quality magnesium oxide sinter. Alternatively, the magnesium oxide can be used as an active neutralizing agent or adjuvant for chemical and pharmaceutical purposes.
Excess clear a~nium sulphate solution, still contain-ing small traces of magnesium sulphate, ammonia and carbon dioxide, is withdrawn through the overflow line 9 which opens into the top part o the holding container 8. The solution is evaporated in the evaporator 22 and the resulting vapors are discharged through the gas outlet line 23. The remaining solution flows through the fluid outlet line 24 into the crystali~er 25 in which ammonium sulphate is crystalized by further evaporation. The resulting vapors are discharged through the vapor discharge line 26~ The crystaline ammonium sulphate is withdra~n from the crystalizer 25 through the product discharge line 27.
~I~L40~3~3 g Although the process has been described as being part of a main process, the process canl of course, be used independently for producing magnesium oxide from a starting material consisting of aqueous magnesium sulphate solution, if such a solution is available. In this case, gaseous ammonia must be oktained from an external source. However, it is not then necessary to concentrate or crystalize the ammonium sulphate solution if there is no use for the ~loni~m sulphate.
Claims (9)
1. A process for producing magnesium oxide compri-sing the steps of generating a flow of an aqueous magnesium sulphate solution at a concentration of from 15% to 25%;
introducing said flow into a circuit maintained at a temperature of from 25° to 45° C and a pH of from 7.5 to 8.5;
continuously adding ammonia gas and carbon dioxide in approximately stiochiometric proportions relative to said solution to said flow in said circuit to precipitate magnesium carbonate trihydrate;
continuously separating at least some of the precipitated magnesium carbonate trihydrate crystals from the circuit; and thereafter freeing the separated crystals and then washing, drying and calcinating the crystals to magnesium oxide.
introducing said flow into a circuit maintained at a temperature of from 25° to 45° C and a pH of from 7.5 to 8.5;
continuously adding ammonia gas and carbon dioxide in approximately stiochiometric proportions relative to said solution to said flow in said circuit to precipitate magnesium carbonate trihydrate;
continuously separating at least some of the precipitated magnesium carbonate trihydrate crystals from the circuit; and thereafter freeing the separated crystals and then washing, drying and calcinating the crystals to magnesium oxide.
2. A process as set forth in claim 1 which further comprises the steps of withdrawing ammonium sulphate solution from said circuit, and then concentrating and crystallizing the ammonium sulphate solution.
3. A process as set forth in claim 1 wherein during calcinating of the magnesium carbonate trihydrate crystals carbon dioxide is produced and introduced into said circuit as a precipitating agent.
4. A process as set forth in claim 1 wherein the flow of aqueous magnesium sulphate solution is generated in a main process from a starting material containing magnesium silicate wherein the main process produces the aqueous magnesium sulphate solution and ammonia gas.
5. A process as set forth in claim 4 wherein the silicate is one of a serpentine waste and asbestos waste.
6. A process as set forth in claim 2 wherein the flow of aqueous magnesium sulphate solution is generated in main process from a starting material containing magnesium silicate wherein the main process produces the aqueous magnesium sulphate solution and ammonia gas,
7. A process as set forth in claim 6 wherein the ammonia gas produced in the main process is added to said circuit as a precipitating agent and the produced ammonium sulphate is added to the starting material.
8. A process of producing magnesium oxide comprising the steps of producing an aqueous magnesium sulphate solution and ammonia gas from a starting material containing magnesium silicate;
introducing the aqueous magnesium sulphate solution at a concentration of 15% to 25% into a circuit maintained at a temperature of from 25° to 45°C and a pH
of from 7.5 to 8.5;
continuously adding ammonia gas and carbon dioxide in approximately stoichiometric proportions relative to said solution to said flow in said circuit to precipitate magnesium carbonate trihydrate;
continuously separating at least some of the precipitated magnesium carbonate trihydrate crystals from the circuit; and thereafter freeing the separated crystals and then washing, drying and calcinating the crystals to magnesium oxide.
introducing the aqueous magnesium sulphate solution at a concentration of 15% to 25% into a circuit maintained at a temperature of from 25° to 45°C and a pH
of from 7.5 to 8.5;
continuously adding ammonia gas and carbon dioxide in approximately stoichiometric proportions relative to said solution to said flow in said circuit to precipitate magnesium carbonate trihydrate;
continuously separating at least some of the precipitated magnesium carbonate trihydrate crystals from the circuit; and thereafter freeing the separated crystals and then washing, drying and calcinating the crystals to magnesium oxide.
9. A process as set forth in claim 8 wherein the produced ammonia gas is added to said circuit as a precipita-ting agent and the produced ammonium sulphate is added to the starting material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CH3128/79-8 | 1979-04-04 | ||
| CH312879A CH640200A5 (en) | 1979-04-04 | 1979-04-04 | Process for producing magnesium oxide from an aqueous magnesium sulphate solution |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1140730A true CA1140730A (en) | 1983-02-08 |
Family
ID=4249211
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000327993A Expired CA1140730A (en) | 1979-04-04 | 1979-05-22 | Process for producing magnesium oxide from an aqueous magnesium sulphate solution |
Country Status (5)
| Country | Link |
|---|---|
| AT (1) | AT376635B (en) |
| CA (1) | CA1140730A (en) |
| CH (1) | CH640200A5 (en) |
| DE (1) | DE2914662C2 (en) |
| IT (1) | IT1141267B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103130250A (en) * | 2011-11-22 | 2013-06-05 | 北京化工大学 | Method for preparing active magnesium oxide |
| WO2015154196A1 (en) * | 2014-04-10 | 2015-10-15 | Karnalyte Resources Inc. | Process for producing high grade hydromagnesite and magnesium oxide |
| US9346683B2 (en) | 2007-04-02 | 2016-05-24 | Kyowa Chemical Industry Co., Ltd. | Carbonate radical-containing magnesium hydroxide particle and manufacturing method thereof |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103449482B (en) * | 2012-06-01 | 2015-12-16 | 中国科学院过程工程研究所 | A kind of method utilizing serpentine to prepare magnesium oxide, nickel, cobalt and white carbon black |
| CN103496723B (en) * | 2013-09-06 | 2015-02-11 | 中国矿业大学(北京) | Method for improving leaching rate of magnesium oxide in serpentine ammonium salt roasting product |
| CN107915242A (en) * | 2017-05-30 | 2018-04-17 | 张旭 | Asbestos tailings prepare method of magnesium oxide |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2921835A (en) * | 1957-03-15 | 1960-01-19 | Alfred M Thomsen | Method of processing magnesium bearing brines |
| IT956869B (en) * | 1972-06-27 | 1973-10-10 | Ente Minerario Siciliano | PROCEDURE FOR THE PREPARATION OF MAGNESIUM OXIDE STARTING FROM WATER SOLUTIONS CONTAINING MAGNESIUM IONS |
-
1979
- 1979-04-04 CH CH312879A patent/CH640200A5/en not_active IP Right Cessation
- 1979-04-11 DE DE2914662A patent/DE2914662C2/en not_active Expired
- 1979-04-18 AT AT0290379A patent/AT376635B/en not_active IP Right Cessation
- 1979-05-22 CA CA000327993A patent/CA1140730A/en not_active Expired
-
1980
- 1980-04-01 IT IT21095/80A patent/IT1141267B/en active
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9346683B2 (en) | 2007-04-02 | 2016-05-24 | Kyowa Chemical Industry Co., Ltd. | Carbonate radical-containing magnesium hydroxide particle and manufacturing method thereof |
| CN103130250A (en) * | 2011-11-22 | 2013-06-05 | 北京化工大学 | Method for preparing active magnesium oxide |
| CN103130250B (en) * | 2011-11-22 | 2014-12-03 | 北京化工大学 | Method for preparing active magnesium oxide |
| WO2015154196A1 (en) * | 2014-04-10 | 2015-10-15 | Karnalyte Resources Inc. | Process for producing high grade hydromagnesite and magnesium oxide |
| US10364156B2 (en) * | 2014-04-10 | 2019-07-30 | Karnalyte Resources Inc. | Process for producing high grade hydromagnesite and magnesium oxide |
Also Published As
| Publication number | Publication date |
|---|---|
| DE2914662C2 (en) | 1984-09-27 |
| AT376635B (en) | 1984-12-10 |
| ATA290379A (en) | 1984-05-15 |
| IT8021095A0 (en) | 1980-04-01 |
| IT1141267B (en) | 1986-10-01 |
| DE2914662A1 (en) | 1980-10-09 |
| CH640200A5 (en) | 1983-12-30 |
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