WO2007078018A1 - Manufacture method of single phase aragonite precipitated calcium carbonate by controlling calcium ion - Google Patents

Manufacture method of single phase aragonite precipitated calcium carbonate by controlling calcium ion Download PDF

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Publication number
WO2007078018A1
WO2007078018A1 PCT/KR2005/004691 KR2005004691W WO2007078018A1 WO 2007078018 A1 WO2007078018 A1 WO 2007078018A1 KR 2005004691 W KR2005004691 W KR 2005004691W WO 2007078018 A1 WO2007078018 A1 WO 2007078018A1
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Prior art keywords
aqueous solution
aragonite
suspension
calcium hydroxide
manufacture
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PCT/KR2005/004691
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French (fr)
Inventor
Ji-Whan Ahn
Jeong-Hwan Kim
Hyun-Seo Park
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Korea Institute Of Geoscience And Mineral Resources
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Priority to CA2633808A priority Critical patent/CA2633808C/en
Publication of WO2007078018A1 publication Critical patent/WO2007078018A1/en

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    • 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
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C01F11/181—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by control of the carbonation conditions
    • 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
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/30—Three-dimensional structures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/10—Particle morphology extending in one dimension, e.g. needle-like
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/54—Particles characterised by their aspect ratio, i.e. the ratio of sizes in the longest to the shortest dimension

Definitions

  • the present invention is related to the methods of manufacture of single-phase aragonite by controlling calcium ions, particularly, to the methods of manufacture of single-phase aragonite in solution process by controlling the rate of elution of calcium ions in the suspension of calcium hydroxide by adding the highly concentrated aqueous solution of sodium hydroxide to the suspension of calcium hydroxide and adding the aqueous solution of sodium carbonate to the above mixed aqueous solution at a constant rate.
  • calcite which is stable at a room temperature is cubic or spindle shaped
  • meta-stable aragonite is navicular or needle shaped
  • unstable vaterite is spherical mostly.
  • aragonite is of needle shape having a very large aspect ratio, and is expected to be a new functional inorganic material that can grant mechanical and optical functionalities in that it becomes possible to enhance strength, to improve whiteness, and to control opaqueness owing to the complicated surface structure of its needle shape when it is used as an industrial raw material such as the filler for rubber, plastic, paints, or the pigment for paper, etc.
  • the 0.05 [M down-shaped needle shape can increase oil absorption owing to the increase in the specific surface area, and the needle shape having the largest diameter of 50 ⁇ 60 ⁇ m has a superior impact resistance. Therefore, it is expected to have an effect of increasing strength if aragonite is mixed with a conformation control thermoplastic resin or a polypropylene resin as filler.
  • aragonite is in the meta-stable phase existing stably in the temperature range of below 75K under atmosphere, and is precipitated at a temperature higher than 60 ⁇ 80 ° Cdue to a faster rate of crystallization in the range of high temperature compared to that of calcite.
  • Korean Laid-Open Patent No. 2005-0110118 is a method of manufacture of aragonite by adding the aqueous solution of sodium hydroxide to control the concentration of calcium ions in the suspension of calcium hydroxide and supplying the aqueous solution of sodium carbonate at a constant rate. But it is practically difficult to manufacture single-phase aragonite having a large aspect ratio since the aqueous solution of sodium hydroxide having the concentration lower than that of the suspension of calcium hydroxide is used in the above method of manufacture.
  • the present invention is devised in order to solve the above- described problems, and it is an object of the present invention to provide methods of manufacture of single-phase aragonite by controlling calcium ions.
  • the present invention is characterized by adding the suspension of sodium hydroxide to the suspension of calcium hydroxide to control calcium ions, and it is an object of the present invention to provide more highly functional and high-value-added aragonite by improving the single phase, aspect ratio, and production yield of aragonite by using solution process by the homogeneous precipitation reaction of sodium carbonate with the above suspension .
  • the present invention is related to the methods of manufacture of single-phase aragonite by controlling calcium ions, particularly, to the methods of manufacture of single-phase aragonite in the aqueous solution process by controlling the rate of elution of calcium ions in the suspension of calcium hydroxide by adding the highly concentrated aqueous solution of sodium hydroxide to the suspension of calcium hydroxide and adding the aqueous solution of sodium carbonate to the above mixed aqueous solution at a constant rate.
  • the aqueous solution of sodium hydroxide having a higher concentration than that of calcium hydroxide contained in the suspension more preferably, to add 3 to 10 mol/L of the aqueous solution of sodium hydroxide with respect to 0.2 to 3 mol/L of the suspension of calcium hydroxide.
  • the present invention provides methods of manufacture of single-phase aragonite through the control of calcium ions comprising the steps of: a) manufacturing 0.2 to 3 mol/L suspension of calcium hydroxide in which calcium hydroxide is dispersed in distilled water; b) manufacturing the mixed solution of the suspension of calcium hydroxide and the aqueous solution of sodium hydroxide by adding 3 to 10 mol/L aqueous solution of sodium hydroxide to the above suspension of calcium hydroxide; and c) manufacturing single-phase aragonite by inserting the aqueous solution of sodium carbonate at a constant rate while stirring the above mixed solution.
  • the present invention is illustrated in more detail below: The flow chart of manufacturing single-phase aragonite according to the present invention is shown in Figure 1, and equipment for manufacturing single-phase aragonite according to the present invention is shown in Figure 2.
  • the processes of manufacturing single- phase aragonite according to the present invention are comprised of the steps of manufacturing the suspension of calcium hydroxide; manufacturing the mixed solution of the suspension of calcium hydroxide and the aqueous solution of sodium hydroxide by mixing the aqueous solution of sodium hydroxide with the above suspension of calcium hydroxide; reacting the aqueous solution by inserting the aqueous solution of sodium carbonate while heating and stirring the above mixed solution; and washing, filtering, and drying.
  • the equipment for the manufacturing of aragonite-type precipitated calcium carbonate according to the present invention is comprised of a reactor (1) in which the suspension of calcium hydroxide and the aqueous solution of sodium carbonate are mixed and stirred; a thermostatic water bath (2) filled with water and equipped with the above reactor and a temperature controlling means so that the inside of the reactor is maintained at a constant temperature; an injection container (7) of the aqueous solution of sodium carbonate connected to a supplying unit inserted into the inside of the above reactor through a pipe extended outside of the reactor from the supplying unit so that the amount of supply of the aqueous solution of sodium carbonate is controlled by means of a flowmeter (8); a stirrer (6) comprised of a rotation axis installed rotatably penetrating the cover of the above reactor and a motor at the outer end of the above rotation axis so that the suspension of calcium hydroxide and carbon dioxide are mixed; and a pH measuring device (4) to which a pH electrode (3) and a thermometer (5) installed inside
  • the aqueous solution of NaOH is added for such control of the concentration. This is to lower the initial concentration of Ca 24 ions by reducing the solubility of calcium hydroxide by the common ion effect.
  • the ions existing in the entire reaction system before adding NaOH include Ca 2+ , OH " , Na + , and CO 3 2" , where OH " ion becomes a common ion if NaOH is added. If a common ion exists in a solution, the initial concentration of Ca 2+ ion is reduced as the ionic product becomes greater than the solubility product and the solubility is reduced.
  • Figure 3 shows changes in the solubility of calcium hydroxide according to the concentration of the aqueous solution of sodium hydroxide in 1.5 M suspension of calcium hydroxide.
  • the solubilities of calcium hydroxide according to temperature in the state that NaOH is not added are shown in terms of dotted lines in order to compare solubilities when NaOH is added and not added.
  • Figure 3 it is seen that the solubility of calcium hydroxide is reduced as the concentration of the aqueous solution of sodium hydroxide in the suspension of calcium hydroxide is increased, which leads to lowering of the concentration of calcium ions, that are the main reaction products, in the reaction solution, and supersaturation, which is greatly affected by the concentration of the reaction products, is also lowered.
  • the aqueous solution of sodium hydroxide having a higher concentration than that of the suspension of calcium hydroxide is used, more concretely, 3 to 10 mol/L aqueous solution of sodium hydroxide with respect to 0.2 to 3 mol/L suspension of calcium hydroxide. If the concentration of the aqueous solution of sodium hydroxide is less than 3 mol/L, it is failed to manufacture single-phase aragonite since calcite is produced; and if it exceeds 10 mol/L, it is not economical since the concentration of calcium ions is reduced exceedingly and the reaction time becomes too long.
  • the concentration of the above aqueous solution of sodium hydroxide is 5 to 8 mol/L, at which pure aragonite having no calcite practically may be manufactured. Having no calcite practically means that no calcite peaks are shown in the x-ray diffraction pattern of aragonite obtained through washing, filtering, and drying aragonite produced in the above step c) . If it is expressed in terms of a numerical value, it means that the content of calcite is less than about 0.01%.
  • the mixed solution of the suspension of calcium hydroxide and the aqueous solution of sodium hydroxide is heated to 60 to 80 ° C and the aqueous solution of sodium carbonate is inserted to the mixed solution while stirring it. It is preferable that the concentration of the aqueous solution of sodium carbonate is 0.1 to 1 mol/L, more preferably, 0.1 to 0.5 mol/L, and the rate of insert is 1 to 5 ml/minute.
  • the concentration of sodium carbonate is too low or the rate of insert is too low, the reaction may not be progressed well since it takes too long to react or the nucleus is not produced; and if the concentration of sodium carbonate is higher than the above or the rate of insert is higher than the above, the size of crystals is small and it is difficult to manufacture single- phase aragonite since the rate of producing the nucleus is increased.
  • the above reaction temperature is 60 to 80 ° C preferably, 75 to 80 ° C since the production of aragonite is more favorable at a high temperature compared to the production of calcite. That is, if the reaction temperature is lower than 60 ° C it is difficult to manufacture single-phase aragonite due to the production of calcite, and the reaction system may become unstable due to the evaporation of moisture during the reaction if the reaction temperature is higher than 80 ° C
  • Figure 1 is a flow chart of manufacturing aragonite according to the present invention
  • Figure 2 shows equipment for manufacturing aragonite according to the present invention
  • Figure 3 shows changes in the solubility of calcium hydroxide according to each concentration of the aqueous solution of sodium hydroxide according to the present invention
  • Figure 4 shows the x-ray diffraction pattern of aragonite manufactured according to each reaction time in 3 M aqueous solution of sodium hydroxide according to the present invention
  • Figure 5 shows production yields of aragonite manufactured according to each reaction time in 3 M aqueous solution of sodium hydroxide according to the present invention
  • Figure 6 shows the x-ray diffraction pattern of aragonite manufactured according to each reaction time in 5 M aqueous solution of sodium hydroxide according to the present invention
  • Figure 7 shows production yields of aragonite manufactured according to each reaction time in 5 M aqueous solution of sodium hydroxide according to the present invention
  • Figure 8 shows the electron micrographs of aragonite manufactured according to each reaction time in 5 M aqueous solution of sodium hydroxide according to the present invention.
  • Figure 9 shows the x-ray diffraction pattern of aragonite manufactured according to each concentration of the aqueous solution of sodium hydroxide according to the present invention.
  • reactor 2 thermostatic water bath
  • pH electrode 4 pH measuring device 5 : thermometer 6 : stirrer 7 : injection container 8 : flowmeter
  • the equipment for the manufacture of aragonite used in the present invention is a 1-liter heat-resistant glass reactor having a length of 300 mm and a diameter of 150 mm equipped with 5 a jacket and connected to a thermostatic water bath.
  • the thermostatic water bath is equipped with in order to control the temperature of the suspension of calcium hydroxide and a pH measuring device and a thermometer are equipped with inside of the suspension in order to measure the changes in pH and
  • reaction temperature of the suspension of calcium hydroxide 10 reaction temperature of the suspension of calcium hydroxide.
  • the suspension is dispersed in distilled water, a stirrer equipped with a 4-cm-long impeller is used in order to mix the reaction solution and to maintain a homogeneous reaction, and a flowmeter that can inject sodium carbonate at a rate of 3 l ⁇ mL/mminute is used in order to control the rate of insert of sodium carbonate.
  • Aragonite thus manufactured is investigated through x-ray diffraction analysis and electron microscopy after it is washed, filtered, and dried.
  • the aqueous solution reaction is performed at 75 ° C for 100 minutes by adding 3 M aqueous solution of sodium hydroxide to 1.5 M suspension of calcium hydroxide mixing, and further adding 0.5 M aqueous solution of sodium carbonate at a rate of 5 3 mL/minute.
  • 3 M aqueous solution of sodium hydroxide to 1.5 M suspension of calcium hydroxide mixing
  • 0.5 M aqueous solution of sodium carbonate at a rate of 5 3 mL/minute.
  • Figure 6 shows the x-ray diffraction pattern of the aqueous reaction performed at 75 ° C for 130 minutes by adding 5 M aqueous solution of sodium hydroxide and further adding 0.5 M aqueous solution of sodium carbonate at a rate of 3 mL/minute
  • Figures 7 and 8 show the production yields and electron micrographs of aragonite.
  • FIG 6 it is seen that no calcite is produced, but only aragonite is produced purely. Particularly, at the reaction time of 130 minutes, almost no calcium hydroxide remains, and the content of aragonite is about 98%. It is also seen in the micrographs shown in Figure 8 that single-phase aragonite having the aspect ratio of about 20 is manufactured.
  • Figure 9 is the x-ray diffraction pattern of the case that the concentration of the aqueous solution of sodium hydroxide is changed up to 0 ⁇ 5 mol/L. It is seen that the production yields of aragonite are increased as the concentration of the aqueous solution of sodium hydroxide is increased, and single- phase aragonite having no calcite at all may be manufactured by adding 5 M aqueous solution of sodium hydroxide.
  • the method of manufacture of single-phase aragonite according to the present invention is a method of manufacturing aragonite by adding the highly concentrated aqueous solution of sodium hydroxide into the suspension of calcium hydroxide. This method is advantageous in that it is possible to manufacture highly functional high- value-added single-phase aragonite having no calcite produced with a high yield by controlling calcium ions.

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  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
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  • Inorganic Chemistry (AREA)
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Abstract

The present invention is related to the methods of manufacture of single-phase aragonite by controlling calcium ions, particularly, to the methods of manufacture of single-phase aragonite in the solution process by controlling the rate of elution of calcium ions in the suspension of calcium hydroxide by adding the highly concentrated aqueous solution of sodium hydroxide to the suspension of calcium hydroxide and adding the aqueous solution of sodium carbonate to the above mixed aqueous solution at a constant rate. The method of manufacture of single-phase aragonite according to the present invention is characterized by containing no calcite practically since this method is comprised of the steps of manufacturing a suspension in which calcium hydroxide is dispersed in distilled water; controlling calcium ions in the suspension of calcium hydroxide by adding the aqueous solution of sodium hydroxide to the suspension; and supplying the aqueous solution of sodium carbonate at a constant rate while stirring the suspension of calcium hydroxide.

Description

MENUFACTURE METHOD OF SINGLE PHASE ARAGONITE PRECIPITATED CALCIUM CARBONATE BY CONTROLLING CALCIUM ION
[Technical Field] The present invention is related to the methods of manufacture of single-phase aragonite by controlling calcium ions, particularly, to the methods of manufacture of single-phase aragonite in solution process by controlling the rate of elution of calcium ions in the suspension of calcium hydroxide by adding the highly concentrated aqueous solution of sodium hydroxide to the suspension of calcium hydroxide and adding the aqueous solution of sodium carbonate to the above mixed aqueous solution at a constant rate.
[Background Art]
There are three representative polymorphs of calcium carbonate: calcite which is stable at a room temperature is cubic or spindle shaped, meta-stable aragonite is navicular or needle shaped, and unstable vaterite is spherical mostly. Among them, aragonite is of needle shape having a very large aspect ratio, and is expected to be a new functional inorganic material that can grant mechanical and optical functionalities in that it becomes possible to enhance strength, to improve whiteness, and to control opaqueness owing to the complicated surface structure of its needle shape when it is used as an industrial raw material such as the filler for rubber, plastic, paints, or the pigment for paper, etc. Particularly, the 0.05 [M down-shaped needle shape can increase oil absorption owing to the increase in the specific surface area, and the needle shape having the largest diameter of 50 ~ 60 μm has a superior impact resistance. Therefore, it is expected to have an effect of increasing strength if aragonite is mixed with a conformation control thermoplastic resin or a polypropylene resin as filler. However, aragonite is in the meta-stable phase existing stably in the temperature range of below 75K under atmosphere, and is precipitated at a temperature higher than 60 ~ 80°Cdue to a faster rate of crystallization in the range of high temperature compared to that of calcite. And it may be synthesized at a low-temperature owing to the affects of pH of the reaction solution, ions to be added, concentration of calcium hydroxide, etc., but it is difficult to synthesize single-phase aragonite. Disclosed in Korean Laid-Open Patent No. 2005-0110118 is a method of manufacture of aragonite by adding the aqueous solution of sodium hydroxide to control the concentration of calcium ions in the suspension of calcium hydroxide and supplying the aqueous solution of sodium carbonate at a constant rate. But it is practically difficult to manufacture single-phase aragonite having a large aspect ratio since the aqueous solution of sodium hydroxide having the concentration lower than that of the suspension of calcium hydroxide is used in the above method of manufacture.
[Disclosure]
[Technical problem]
Accordingly, it is an object of the present invention to provide methods of manufacture of single-phase aragonite by adding the highly concentrated aqueous solution of sodium hydroxide in order to control the concentration of calcium ions in the suspension of calcium hydroxide.
The present invention is devised in order to solve the above- described problems, and it is an object of the present invention to provide methods of manufacture of single-phase aragonite by controlling calcium ions. The present invention is characterized by adding the suspension of sodium hydroxide to the suspension of calcium hydroxide to control calcium ions, and it is an object of the present invention to provide more highly functional and high-value-added aragonite by improving the single phase, aspect ratio, and production yield of aragonite by using solution process by the homogeneous precipitation reaction of sodium carbonate with the above suspension .
[Technical solution] As a result of repeating studies in order to manufacture single-phase aragonite, the inventors of the present invention found out that the concentration of calcium ions in the early reaction stage should be lower than the solubility in water in order to manufacture single-phase aragonite. They also learned that it was very effective to increase the concentration of the aqueous solution of sodium hydroxide in order to lower the concentration of calcium ions in the early reaction stage, and completed the present invention from the above findings. Accordingly, the present invention is related to the methods of manufacture of single-phase aragonite by controlling calcium ions, particularly, to the methods of manufacture of single-phase aragonite in the aqueous solution process by controlling the rate of elution of calcium ions in the suspension of calcium hydroxide by adding the highly concentrated aqueous solution of sodium hydroxide to the suspension of calcium hydroxide and adding the aqueous solution of sodium carbonate to the above mixed aqueous solution at a constant rate. In order to manufacture single-phase aragonite with a high yield, which is an object of the present invention, it is preferable to use the aqueous solution of sodium hydroxide having a higher concentration than that of calcium hydroxide contained in the suspension, more preferably, to add 3 to 10 mol/L of the aqueous solution of sodium hydroxide with respect to 0.2 to 3 mol/L of the suspension of calcium hydroxide. And it is possible to manufacture single-phase aragonite having a large aspect ratio by inserting the aqueous solution of sodium carbonate to the mixed solution of the suspension of calcium hydroxide and the aqueous solution of sodium hydroxide at a low rate.
Therefore, the present invention provides methods of manufacture of single-phase aragonite through the control of calcium ions comprising the steps of: a) manufacturing 0.2 to 3 mol/L suspension of calcium hydroxide in which calcium hydroxide is dispersed in distilled water; b) manufacturing the mixed solution of the suspension of calcium hydroxide and the aqueous solution of sodium hydroxide by adding 3 to 10 mol/L aqueous solution of sodium hydroxide to the above suspension of calcium hydroxide; and c) manufacturing single-phase aragonite by inserting the aqueous solution of sodium carbonate at a constant rate while stirring the above mixed solution. It is another object of the present invention to provide needle-shaped single-phase aragonite having a large aspect ratio as it is manufactured according to the above method of manufacture . The present invention is illustrated in more detail below: The flow chart of manufacturing single-phase aragonite according to the present invention is shown in Figure 1, and equipment for manufacturing single-phase aragonite according to the present invention is shown in Figure 2.
As shown in Figure 1, the processes of manufacturing single- phase aragonite according to the present invention are comprised of the steps of manufacturing the suspension of calcium hydroxide; manufacturing the mixed solution of the suspension of calcium hydroxide and the aqueous solution of sodium hydroxide by mixing the aqueous solution of sodium hydroxide with the above suspension of calcium hydroxide; reacting the aqueous solution by inserting the aqueous solution of sodium carbonate while heating and stirring the above mixed solution; and washing, filtering, and drying. Also, the equipment for the manufacturing of aragonite-type precipitated calcium carbonate according to the present invention is comprised of a reactor (1) in which the suspension of calcium hydroxide and the aqueous solution of sodium carbonate are mixed and stirred; a thermostatic water bath (2) filled with water and equipped with the above reactor and a temperature controlling means so that the inside of the reactor is maintained at a constant temperature; an injection container (7) of the aqueous solution of sodium carbonate connected to a supplying unit inserted into the inside of the above reactor through a pipe extended outside of the reactor from the supplying unit so that the amount of supply of the aqueous solution of sodium carbonate is controlled by means of a flowmeter (8); a stirrer (6) comprised of a rotation axis installed rotatably penetrating the cover of the above reactor and a motor at the outer end of the above rotation axis so that the suspension of calcium hydroxide and carbon dioxide are mixed; and a pH measuring device (4) to which a pH electrode (3) and a thermometer (5) installed inside of the above reactor are connected. The methods of manufacture of single-phase aragonite according to the present invention are illustrated more concretely as follows :
As described in the above, it is necessary to control the concentration of calcium ions in the early stage of the reaction in order to manufacture single-phase aragonite. The aqueous solution of NaOH is added for such control of the concentration. This is to lower the initial concentration of Ca24 ions by reducing the solubility of calcium hydroxide by the common ion effect. The ions existing in the entire reaction system before adding NaOH include Ca2+, OH", Na+, and CO3 2", where OH" ion becomes a common ion if NaOH is added. If a common ion exists in a solution, the initial concentration of Ca2+ ion is reduced as the ionic product becomes greater than the solubility product and the solubility is reduced. Figure 3 shows changes in the solubility of calcium hydroxide according to the concentration of the aqueous solution of sodium hydroxide in 1.5 M suspension of calcium hydroxide. The solubilities of calcium hydroxide according to temperature in the state that NaOH is not added are shown in terms of dotted lines in order to compare solubilities when NaOH is added and not added. As shown in Figure 3, it is seen that the solubility of calcium hydroxide is reduced as the concentration of the aqueous solution of sodium hydroxide in the suspension of calcium hydroxide is increased, which leads to lowering of the concentration of calcium ions, that are the main reaction products, in the reaction solution, and supersaturation, which is greatly affected by the concentration of the reaction products, is also lowered. Therefore, in the present invention, the aqueous solution of sodium hydroxide having a higher concentration than that of the suspension of calcium hydroxide is used, more concretely, 3 to 10 mol/L aqueous solution of sodium hydroxide with respect to 0.2 to 3 mol/L suspension of calcium hydroxide. If the concentration of the aqueous solution of sodium hydroxide is less than 3 mol/L, it is failed to manufacture single-phase aragonite since calcite is produced; and if it exceeds 10 mol/L, it is not economical since the concentration of calcium ions is reduced exceedingly and the reaction time becomes too long. It is preferable that the concentration of the above aqueous solution of sodium hydroxide is 5 to 8 mol/L, at which pure aragonite having no calcite practically may be manufactured. Having no calcite practically means that no calcite peaks are shown in the x-ray diffraction pattern of aragonite obtained through washing, filtering, and drying aragonite produced in the above step c) . If it is expressed in terms of a numerical value, it means that the content of calcite is less than about 0.01%.
The mixed solution of the suspension of calcium hydroxide and the aqueous solution of sodium hydroxide is heated to 60 to 80 °C and the aqueous solution of sodium carbonate is inserted to the mixed solution while stirring it. It is preferable that the concentration of the aqueous solution of sodium carbonate is 0.1 to 1 mol/L, more preferably, 0.1 to 0.5 mol/L, and the rate of insert is 1 to 5 ml/minute. If the concentration of sodium carbonate is too low or the rate of insert is too low, the reaction may not be progressed well since it takes too long to react or the nucleus is not produced; and if the concentration of sodium carbonate is higher than the above or the rate of insert is higher than the above, the size of crystals is small and it is difficult to manufacture single- phase aragonite since the rate of producing the nucleus is increased.
Also, it is preferable that the above reaction temperature is 60 to 80°C preferably, 75 to 80°C since the production of aragonite is more favorable at a high temperature compared to the production of calcite. That is, if the reaction temperature is lower than 60 °C it is difficult to manufacture single-phase aragonite due to the production of calcite, and the reaction system may become unstable due to the evaporation of moisture during the reaction if the reaction temperature is higher than 80°C
[Brief Description of the Drawings]
A more complete appreciation of this invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein:
Figure 1 is a flow chart of manufacturing aragonite according to the present invention; Figure 2 shows equipment for manufacturing aragonite according to the present invention;
Figure 3 shows changes in the solubility of calcium hydroxide according to each concentration of the aqueous solution of sodium hydroxide according to the present invention; Figure 4 shows the x-ray diffraction pattern of aragonite manufactured according to each reaction time in 3 M aqueous solution of sodium hydroxide according to the present invention;
Figure 5 shows production yields of aragonite manufactured according to each reaction time in 3 M aqueous solution of sodium hydroxide according to the present invention; Figure 6 shows the x-ray diffraction pattern of aragonite manufactured according to each reaction time in 5 M aqueous solution of sodium hydroxide according to the present invention;
Figure 7 shows production yields of aragonite manufactured according to each reaction time in 5 M aqueous solution of sodium hydroxide according to the present invention; Figure 8 shows the electron micrographs of aragonite manufactured according to each reaction time in 5 M aqueous solution of sodium hydroxide according to the present invention; and
Figure 9 shows the x-ray diffraction pattern of aragonite manufactured according to each concentration of the aqueous solution of sodium hydroxide according to the present invention.
1 : reactor 2 : thermostatic water bath
3 : pH electrode 4 : pH measuring device 5 : thermometer 6 : stirrer 7 : injection container 8 : flowmeter
[ Mode for invention ]
The present invention is illustrated in terms of a few preferred embodiments of the invention below: [Preferred Embodiment]
The equipment for the manufacture of aragonite used in the present invention is a 1-liter heat-resistant glass reactor having a length of 300 mm and a diameter of 150 mm equipped with 5 a jacket and connected to a thermostatic water bath. The thermostatic water bath is equipped with in order to control the temperature of the suspension of calcium hydroxide and a pH measuring device and a thermometer are equipped with inside of the suspension in order to measure the changes in pH and
10 reaction temperature of the suspension of calcium hydroxide. The suspension is dispersed in distilled water, a stirrer equipped with a 4-cm-long impeller is used in order to mix the reaction solution and to maintain a homogeneous reaction, and a flowmeter that can inject sodium carbonate at a rate of 3 lδ mL/mminute is used in order to control the rate of insert of sodium carbonate. Aragonite thus manufactured is investigated through x-ray diffraction analysis and electron microscopy after it is washed, filtered, and dried.
20 [Preferred Embodiment 1]
The aqueous solution reaction is performed at 75 °C for 100 minutes by adding 3 M aqueous solution of sodium hydroxide to 1.5 M suspension of calcium hydroxide mixing, and further adding 0.5 M aqueous solution of sodium carbonate at a rate of 5 3 mL/minute. As seen in the x-ray diffraction pattern and production yields of aragonite according to the reaction time shown in Figures 4 and 5, it is seen that calcite is not produced any further but only aragonite is produced after 2 minutes.
[Preferred Embodiment 2]
Figure 6 shows the x-ray diffraction pattern of the aqueous reaction performed at 75 °C for 130 minutes by adding 5 M aqueous solution of sodium hydroxide and further adding 0.5 M aqueous solution of sodium carbonate at a rate of 3 mL/minute, and Figures 7 and 8 show the production yields and electron micrographs of aragonite. As shown in Figure 6, it is seen that no calcite is produced, but only aragonite is produced purely. Particularly, at the reaction time of 130 minutes, almost no calcium hydroxide remains, and the content of aragonite is about 98%. It is also seen in the micrographs shown in Figure 8 that single-phase aragonite having the aspect ratio of about 20 is manufactured.
[Preferred Embodiment 3]
Figure 9 is the x-ray diffraction pattern of the case that the concentration of the aqueous solution of sodium hydroxide is changed up to 0 ~ 5 mol/L. It is seen that the production yields of aragonite are increased as the concentration of the aqueous solution of sodium hydroxide is increased, and single- phase aragonite having no calcite at all may be manufactured by adding 5 M aqueous solution of sodium hydroxide.
[industrial Applicability] As described in the above, the method of manufacture of single-phase aragonite according to the present invention is a method of manufacturing aragonite by adding the highly concentrated aqueous solution of sodium hydroxide into the suspension of calcium hydroxide. This method is advantageous in that it is possible to manufacture highly functional high- value-added single-phase aragonite having no calcite produced with a high yield by controlling calcium ions.
While certain present preferred embodiments of the invention have been shown and described, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

[Claims]
1. A method of manufacture of single-phase aragonite by controlling calcium ions comprising the steps of: manufacturing 0.2 to 3 mol/L suspension of calcium hydroxide in which calcium hydroxide is dispersed in distilled water; manufacturing a mixed solution by adding 3 to 10 mol/L aqueous solution of sodium hydroxide to said suspension of calcium hydroxide; and manufacturing single-phase aragonite by inserting the aqueous solution of sodium carbonate to said mixed solution at a constant rate while stirring said mixed solution.
2. The method of manufacture of single-phase aragonite by controlling calcium ions in Claim 1, characterized by that the concentration of said aqueous solution of sodium carbonate is 0.1 to 1 mol/L, and the rate of insert of said aqueous solution of sodium carbonate is 1 to 5 ml/minute.
3. The method of manufacture of single-phase aragonite by controlling calcium ions in Claim 2, characterized by that the reaction temperature in said step of manufacturing single- phase aragonite is 60 to 80 °C
4. The method of manufacture of single-phase aragonite by controlling calcium ions in Claim 3, characterized by that the concentration of said aqueous solution of sodium hydroxide is 5 to 8 mol/L.
5. Single-phase aragonite characterized by having no calcite contained practically as said single-phase aragonite is manufactured according to a method of manufacture comprising the steps of: manufacturing 0.2 to 3 mol/L suspension of calcium hydroxide in which calcium hydroxide is dispersed in distilled water; manufacturing a mixed solution by adding 5 to 8 mol/L aqueous solution of sodium hydroxide to said suspension of calcium hydroxide; and manufacturing single-phase aragonite by inserting 0.1 to 0.5 mol/L aqueous solution of sodium carbonate to said mixed solution at a rate of 1 to 5 mL/minute while stirring said mixed solution at 75 to 80 °C
6. The single-phase aragonite in Claim 5, characterized by that said single-phase aragonite shows no calcite peaks in the x-ray diffraction pattern.
PCT/KR2005/004691 2005-12-31 2005-12-31 Manufacture method of single phase aragonite precipitated calcium carbonate by controlling calcium ion WO2007078018A1 (en)

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JP7382091B1 (en) 2022-10-07 2023-11-16 白石工業株式会社 Calcium carbonate production method, calcium carbonate and paper making filler

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KR20050110118A (en) * 2004-05-18 2005-11-23 한국지질자원연구원 Manufacturing method of aragonite precipitated calcium carbonate by homogeneous precipitation of ca(oh)2 and naco3 solution reaction

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US20030049194A1 (en) * 2000-01-18 2003-03-13 Haruo Konno Method for producing calcium carbonate
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JP7382091B1 (en) 2022-10-07 2023-11-16 白石工業株式会社 Calcium carbonate production method, calcium carbonate and paper making filler
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