JP2011051835A - Method for manufacturing high purity calcium carbonate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high purity calcium carbonate containing a small amount of strontium at low cost. <P>SOLUTION: The method for manufacturing high purity calcium carbonate includes: the step of generating slaked lime slurry by contacting quick lime, having at most 200 sec. of an activation degree tu-80 of quick lime (particle diameter of under 3.35 mm) tested by the temperature release by slaking (DIN EN 459-2:2001) with water; the step of separating the water phase containing impurities and slaked lime in the slaked lime slurry; the step of removing precipitation by dissolving separated slaked lime in an aqueous solution of ammonium chloride and/or ammonium nitrate; and the step of precipitating calcium carbonate by contacting a filtrate liquid obtained by removing the precipitation with a carbonate salt or a carbon dioxide. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  [Technical Field] The present invention relates to a method for producing calcium carbonate having an increased purity by reducing the content of strontium in the production of calcium carbonate using limestone as a raw material.

  In recent years, high-purity calcium carbonate has attracted attention as optical component raw materials such as calcium fluoride glass, electronic materials such as ceramic capacitors, phosphor materials such as LEDs, and biological materials such as artificial bones. The calcium carbonate used for such applications is required to have a higher purity than those conventionally used.

  As a conventional purification method of calcium carbonate, limestone is made into water-soluble salts, pH of this solution is adjusted, impurities are removed as hydroxide to obtain a pure calcium salt solution, and carbon dioxide gas is added to this solution. A method of obtaining calcium carbonate by blowing or adding a solution containing carbonate ions to obtain calcium carbonate is generally performed. Although most impurities can be removed by this method, strontium among the impurities is a similar element to calcium and has similar properties. Therefore, it has been difficult to remove strontium by the above method.

As a conventional method for producing high-purity calcium carbonate, quick lime is digested to obtain slaked lime slurry, which is filtered to elute at least a part of strontium into the aqueous phase, and the solid content is dissolved in an aqueous solution of ammonium nitrate or ammonium hydrochloride. There is a method (Patent Document 1) in which carbonic acid gas is blown into a filtrate after removing impurities. In addition, there is a method (Patent Document 2) in which an aqueous solution of calcium salt is reacted under the condition of a CO ₂ / Ca molar ratio of 0.2 to 0.9. A number of methods have been proposed, such as a method in which a dilute aqueous solution having a calcium hydroxide concentration of 0.5% by weight or less and carbon dioxide diluted to 1% by volume or less are reacted at a temperature of 40 to 90 ° C. (Patent Document 3). ing.

  However, both methods have insufficient effects, and it is necessary to repeat the steps to sufficiently improve the purity of calcium carbonate, so that it is difficult to manufacture at an industrial level such as an increase in manufacturing cost. there were.

JP 62-36021 A JP-A-63-156012 JP 2005-206456 A

  An object of the present invention is to provide a method for producing high-purity calcium carbonate having a low strontium content at a low cost.

  The present inventor uses quick lime whose raw material has an activity tu-80 of 200 seconds or less in the digestive fever test (DIN EN 459-2: 2001) within 200 seconds as the raw material limestone. Thus, it has been found that extremely high purity calcium carbonate can be produced easily and inexpensively.

The present invention is a process for producing slaked lime slurry by contacting quick lime with an activity tu-80 of 200 seconds or less in a digestive fever test (DIN EN 459-2: 2001) within 200 seconds with water. ,
Separating the aqueous phase containing impurities in the slaked lime slurry and slaked lime,
Dissolving the separated slaked lime in an aqueous solution of ammonium chloride and / or ammonium nitrate and removing the precipitate;
The present invention provides a method for producing high-purity calcium carbonate, comprising a step of bringing carbonate or carbon dioxide gas into contact with a filtrate obtained by removing the precipitate, thereby precipitating calcium carbonate.

  By using the production method of the present invention, the content of impurities, particularly strontium, is reduced, and high-purity calcium carbonate can be produced at a low cost. Thereby, inexpensive high-purity calcium carbonate can be provided in the fields of optical component raw materials, electronic materials, phosphor materials, and biomaterials.

  In the present invention, quick lime having an activity tu-80 of 200 seconds or less in quick lime (under 3.35 mm particle diameter) in the digestive fever test (DIN EN 459-2: 2001) is used as a raw material. The more preferable activity tu-80 of quicklime is within 150 seconds, particularly within 70 seconds.

In the digestive fever test, the digestion test is performed with the apparatus described in DIN EN 459: 2001, and the tu value is obtained.
“Conditions for digestive fever test”
Particle size: Use CaO with a particle size adjusted to under 3.35 mm.
Liquid-solid ratio: L / S = 4 (solvent: quicklime = 600 g: 150 g)
Solvent: Distilled water Measurement method: Charge distilled water into a deer bottle (1 L), add CaO while stirring at 300 rpm with a DIN-compliant blade, and record the water temperature.
Tu-80 calculation method: Tu-80 (° C) = (Max temperature-start temperature) x 80% + start temperature
tu-80 (seconds) = time to reach Tu-80

  The quicklime used in the present invention can be produced by firing limestone in an industrial lime firing furnace or the like. As an industrial lime baking furnace, a Beckenbach furnace, a Merz furnace, a qualical furnace, a top furnace, a rotary kiln, an external heat kiln, a tunnel furnace, a box-type electric furnace, or the like can be used.

  The activity tu value of raw apatite is adjusted by selecting the firing conditions. As the firing time is longer and the firing temperature is higher, the crystal diameter is larger and the activity tu value tends to be larger (lower activity). From this viewpoint, the firing time is preferably as short as possible and at a low temperature at which decarboxylation occurs. The specific firing temperature is preferably 800 to 1200 ° C, particularly 900 to 1100 ° C.

  The kind of firing furnace and the residence time of limestone in the firing furnace are adjusted according to the particle size of the limestone. When fine limestone (under 20 mm) is fired, an external heat kiln and a rotary kiln are suitable, and the residence time at the firing temperature is preferably 10 minutes to 2 hours, particularly preferably 15 minutes to 1 hour 30 minutes. In addition, when firing coarse limestone (20-60 mm), a Beckenbach furnace, a Merz furnace, or a qualical furnace is suitable, and the residence time at the firing temperature is 2 to 20 hours, particularly 3 to 10 hours. It is preferable. In the case of firing finer limestone (under 5 mm), a tunnel furnace and a box-type electric furnace are suitable, and the residence time at the firing temperature is preferably 2 to 10 hours, particularly 3 to 5 hours.

Furthermore, from the viewpoint of improving the yield, it is preferable to calcine until the remaining amount of CO ₂ in quicklime is 5% or less, more preferably 3% or less.

  Moreover, when the purity of limestone becomes low, the crystal diameter of quick lime increases due to impurities, and the activity decreases. For this reason, the limestone used preferably has a low impurity content (XRF bead method), and its content is 1.5% or less, more preferably 0.6% or less.

  In the refining process, quick lime is brought into contact with water (digested water and washing water) to produce a slaked lime slurry, but the higher the temperature of the water used in this process, the more easily strontium dissolves in the filtrate. It is preferable to use water of 30 ° C. or higher, more preferably 50 ° C. or higher, particularly 60 to 100 ° C.

  The process which isolate | separates the water phase and the slaked lime which contain the impurity in the produced | generated slaked lime slurry can be performed using a centrifuge, a suction filter, a pressure filter, etc. By this step, at least a part of impurities such as strontium is removed as an aqueous phase.

  Next, the separated slaked lime is dissolved in an aqueous solution of ammonium chloride and / or ammonium nitrate, and the resulting precipitate is removed. Although it does not specifically limit as a density | concentration of the said aqueous solution, The inside of the range of 1-20 weight% is preferable, and the usage-amount is the range from which ammonium chloride and / or ammonium nitrate are 1.0-2.5 equivalent with respect to calcium of the slaked lime to dissolve. Is preferred. The removal of the precipitate can be performed using a centrifuge, a suction filter, a pressure filter, or the like. By this step, remaining impurities such as strontium can be removed.

The slaked lime is carbonated by bringing carbonate or carbon dioxide gas into contact with the filtrate obtained by removing the precipitate, thereby precipitating calcium carbonate. Examples of carbonates include sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, ammonium carbonate, ammonium hydrogen carbonate, etc., among which ammonium carbonate and ammonium hydrogen carbonate that do not contain metals as impurities. Etc. are preferred. As the carbon dioxide gas, carbon dioxide gas generated in a manufacturing process of a commercially available CO ₂ cylinder or quicklime can be used.

  The high purity calcium carbonate produced by carbonation is dried after separation. The dried calcium carbonate is pulverized to adjust the particle size as necessary.

  Hereinafter, examples will be described in more detail.

Example 1
Limestone (5 mm under) was fired at 1000 ° C. for 5 hours in a box-type electric furnace to obtain 30 g of quick lime. This quicklime was poured into 300 mL of hot water at 70 ° C. to prepare a slaked lime slurry. The obtained slaked lime slurry was centrifuged to separate the filtrate and slaked lime, and then washed again by adding 300 mL of 70 ° C. hot water to the slaked lime.
Next, slaked lime was dissolved in 425 mL of a 13.5 wt% ammonium chloride aqueous solution, and the insoluble matter was filtered off. Finally, 700 mL of a 6 wt% ammonium carbonate aqueous solution was added to the resulting calcium chloride solution to perform carbonation.
The produced calcium carbonate was separated by filtration and dried at 105 ° C. for 2 hours to obtain high-purity calcium carbonate. The raw material limestone was analyzed by the XRD beet method, and the generated calcium carbonate was analyzed by ICP-MASS. Moreover, digestion fever was measured by the method based on DIN EN 459-2: 2001, and tu value of quicklime was calculated | required. The test results are shown in Table 1.

Example 2
Limestone (50-30 mm) was calcined in a qualical furnace (reaction temperature 1000-1100 ° C., residence time 5 hours), and calcium carbonate was purified by the same method as in Example 1 except that the obtained quicklime was used. . The test results are shown in Table 1.

Example 3
Quick lime was baked and calcium carbonate was purified by the same method as in Example 1 except that 13.5 wt% ammonium nitrate aqueous solution was used instead of 425 mL of 13.5 wt% ammonium chloride aqueous solution. The test results are shown in Table 1.

Example 4
Calcium carbonate was purified by the same method as in Example 1 except that the same limestone (5 mm under) as in Example 1 was fired at 1100 ° C. for 3 hours in a box-type electric furnace and the obtained quicklime was used. The test results are shown in Table 1.

Comparative Example 1
The same limestone (5 mm under) as in Example 1 was calcined at 1200 ° C. for 7 hours in a box-type electric furnace, and calcium carbonate was purified by the same method as in Example 1 except that the obtained quicklime was used. The test results are shown in Table 1.

Comparative Example 2
Calcium carbonate was purified by the same method as in Example 1 except that the same limestone (5 mm under) as in Example 1 was fired at 1200 ° C. for 3 hours in a box-type electric furnace and the obtained quicklime was used. The test results are shown in Table 1.

Claims (2)

A process of generating slaked lime slurry by contacting quick lime with a water activity of tu-80 within 200 seconds in the digestive fever test (DIN EN 459-2: 2001), with an activity tu-80 within 200 seconds,
A step of separating the slaked lime from the aqueous phase containing impurities in the slaked lime slurry,
Dissolving the separated slaked lime in an aqueous solution of ammonium chloride and / or ammonium nitrate and removing the precipitate;
A method for producing high-purity calcium carbonate, comprising a step of bringing carbonate or carbon dioxide gas into contact with a filtrate obtained by removing the precipitate, thereby precipitating calcium carbonate.   High purity calcium carbonate obtained by the method according to claim 1.