JP2019052065A - Method for producing calcium carbonate - Google Patents

Abstract

To provide a method for producing calcium carbonate that can improve precipitation efficiency of calcium carbonate while suppressing power consumption.SOLUTION: The method has: an elution step for adding quick lime to neutral amino acid-containing aqueous solution containing neutral amino acid, to elute calcium ions; and a precipitation step for introducing carbon dioxide to the neutral amino acid-containing aqueous solution in which calcium ios are eluted in the elution step, to precipitate calcium carbonate. In the precipitation step, introduction of carbon dioxide is stopped at the time when the neutral amino acid-containing aqueous solution has a pH of 7.5 or more and less than 9.0.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a method for producing calcium carbonate for producing calcium carbonate used as a filler in the paper industry and the like.

  Conventionally, as a method for producing calcium carbonate, carbon dioxide is blown into a processing unit (reaction vessel in the literature) by adding a solid substance containing calcium (cement or slag in the literature) to an amino acid-containing aqueous solution to elute calcium ions. A technique for precipitating calcium is known (see, for example, Patent Documents 1 and 2). Amino acids undergo a chelate reaction with calcium, and contact with carbon dioxide gas separates and recovers amino acids from the chelate complex. As a result, the amino acid-containing aqueous solution can be used repeatedly, and the precipitation efficiency of calcium carbonate is difficult to decrease.

  In Patent Document 1, in the case of an amino acid-containing aqueous solution in which the molar ratio of amino acids to the molar ratio of calcium ions contained in a solid material is a constant ratio, acidic amino acids are dissolved in calcium ions (rates of calcium ions contained in solid materials). It is disclosed that the ratio of calcium ions in the aqueous solution is increased. On the other hand, Patent Document 2 focuses on the point that neutral amino acids having an isoelectric point near neutrality have high saturation solubility in water, and increasing the concentration of neutral amino acids contained in a neutral amino acid-containing aqueous solution to increase calcium carbonate. A technique for increasing the deposition efficiency of the is disclosed. Patent Document 2 also states that neutral amino acids may be mixed with acidic amino acids or basic amino acids, or basic amino acids may be mixed with acidic amino acids to adjust the isoelectric point to near neutrality. Have been described.

  Conventionally, as a method for producing calcium carbonate, a technique for causing calcium carbonate to precipitate by reacting slaked lime (calcium hydroxide) and carbon dioxide gas is known (see, for example, Patent Documents 3 to 4).

  In Patent Document 3, a liquid (suspension) containing slaked lime (calcium hydroxide) prepared by slaked quick lime (calcium oxide) with water was supplied to the injector, and the liquid was reduced in pressure by the flow of the liquid. A technique for sucking a gas containing carbon dioxide with an injector and precipitating calcium carbonate is disclosed. In Patent Document 4, a suspension containing a low-solubility lime particle residue (lime screen residue) removed by a lime screen from a slaked lime suspension prepared by slaked quick lime with water is used as an injector. There is disclosed a technique in which calcium carbonate is deposited by sucking a gas containing carbon dioxide with an injector that is supplied and is decompressed by a liquid flow.

International Publication No. 2014/007331 International Publication No. 2014/007332 JP 2011-73891 A JP 2011-73892 A

  In the method for producing calcium carbonate described in Patent Documents 1 and 2, although an amino acid-containing aqueous solution can be used repeatedly, in the case of an acidic amino acid having a low saturated solubility in water as in Patent Document 1, calcium ion There is room for improvement from the viewpoint of elution efficiency. On the other hand, by using a neutral amino acid as in Patent Document 2, the saturation solubility in water can be increased, but further improvement in the precipitation efficiency of calcium carbonate is required.

  In the method for producing calcium carbonate described in Patent Documents 3 and 4, since quick lime is hydrated with water to adjust slaked lime, calcium is used using a chelate reaction of amino acids as in Patent Documents 1 and 2. The amount of calcium ions eluted is extremely small compared with the case of elution of. For this reason, there is room for improvement from the viewpoint of elution efficiency of calcium ions and precipitation efficiency of calcium carbonate. In particular, as in Patent Document 4, a lime screen residue as a starting material is quick calcined once, so that the calcium ion content contained in the lime screen residue is small, and the precipitation efficiency of calcium carbonate is further reduced. End up.

  Furthermore, in order to use the precipitated calcium carbonate as an industrial product, it is ideal to increase the precipitation efficiency of calcium carbonate with low power consumption.

  Thus, a method for producing calcium carbonate that can improve the precipitation efficiency of calcium carbonate while suppressing power consumption is desired.

A feature of the method for producing calcium carbonate is an elution step of adding calcium oxide to an aqueous solution containing neutral amino acids containing neutral amino acids to elute calcium ions,
A precipitation step of precipitating calcium carbonate by introducing carbon dioxide into the neutral amino acid-containing aqueous solution from which the calcium ions have been eluted in the elution step,
In the precipitation step, the introduction of the carbon dioxide gas is stopped when the pH of the neutral amino acid-containing aqueous solution becomes 7.5 or more and less than 9.0.

  In the elution step of the present method, quick lime dissolves in water to form calcium hydroxide, and the hydroxide that has been combined with calcium ions in the process of forming a chelate complex of calcium ions and neutral amino acids contained in the calcium hydroxide. The product ions are dissociated and the pH shifts to the alkali side. In the precipitation step, by introducing carbon dioxide, the pH is lowered to around 7 and calcium carbonate is precipitated.

  In these reaction processes, the present inventors have found that the amount of calcium carbonate deposited is lower than when the pH is lowered to around 7 even when the introduction of carbon dioxide gas is stopped at a predetermined value on the alkali side in the precipitation step. It was found that there was almost no decline. That is, when the pH of the neutral amino acid-containing aqueous solution becomes 7.5 or more and less than 9.0 as in this method, the introduction of carbon dioxide gas is stopped, so that the pH is lowered to around 7 and calcium carbonate is precipitated. Compared with the case of making it, the precipitation amount of the calcium carbonate per unit time can be increased. For this reason, the introduction time of carbon dioxide gas can be shortened, and power consumption can be saved.

  Thus, by adopting this method, it is possible to improve the precipitation efficiency of calcium carbonate while suppressing power consumption.

  Another characteristic method is that the neutral amino acid contains DL-alanine and glycine.

  In the case of a neutral amino acid-containing aqueous solution in which two or more kinds of neutral amino acids are mixed, the present inventors increase the solubility in water as compared with a neutral amino acid-containing aqueous solution in which one type of neutral amino acid is saturated. I got the knowledge that I can do it. This is presumably because the aqueous solution in which neutral amino acids are dissolved has increased polarity due to ionization of amino groups and carboxyl groups, and other neutral amino acids are easily ionically bonded to water molecules. As a result, other neutral amino acids are further dissolved in the saturated aqueous solution of neutral amino acids, so that the solubility in water can be increased.

  If neutral amino acids are composed of DL-alanine and glycine as in this method, these DL-alanine and glycine are very inexpensive and have high saturated solubility in water compared to other amino acids. Can improve the chelate reaction against calcium ions. As a result, the elution efficiency of calcium ions is increased. Therefore, since more calcium ions are eluted from quicklime, a larger amount of calcium carbonate can be deposited by contacting with the carbon dioxide gas.

  Another characteristic method is that the neutral amino acid contains DL-alanine, threonine, and at least one of glycine, cysteine, serine, lysine hydrochloride and asparagine monohydrate.

  In this method, a synergistic effect is exhibited by mixing at least one of DL-alanine, glycine, cysteine, serine, lysine hydrochloride and asparagine monohydrate with high saturation solubility and threonine with high separation recovery ability. Thus, while increasing the precipitation efficiency of calcium carbonate, the neutral amino acid can be repeatedly used while suppressing the weight loss of the neutral amino acid.

  Another characteristic method is that barium sulfate is added to the neutral amino acid-containing aqueous solution in the precipitation step.

  The present inventors have obtained knowledge that the particle diameter of precipitated calcium carbonate can be refined by adding barium sulfate to a neutral amino acid-containing aqueous solution in the precipitation step. It is presumed that barium sulfate is a substance that is extremely insoluble in water, and that barium sulfate acts as an auxiliary agent that suppresses aggregation of calcium ions separated from the chelate complex during the formation of calcium carbonate. Therefore, according to this method, calcium carbonate having a fine particle size useful as a filler in the paper industry or the like can be precipitated.

  Another characteristic method is that, in the precipitation step, water is added to the neutral amino acid-containing aqueous solution before introducing the carbon dioxide gas.

  As described above, the neutral amino acid concentration can be improved by mixing two or more kinds of neutral amino acids. However, if the neutral amino acid concentration is too high, the chelating action is excessively increased and calcium ions are contained in the precipitation step. There is a risk that it will not be separated from sex amino acids. As in this method, by adding water to the neutral amino acid-containing aqueous solution before introducing carbon dioxide gas, the neutral amino acid concentration in the precipitation process is reduced to reduce the chelating action, so introduction of a small amount of carbon dioxide gas Calcium ions can be reliably separated from neutral amino acids by the amount. Therefore, the precipitation efficiency of calcium carbonate can be improved while suppressing power consumption.

It is a figure which shows a calcium carbonate manufacturing apparatus. It is a block diagram of a control form. It is a figure which shows the nozzle which concerns on another embodiment. It is a figure which shows the experimental result of a 1st Example. It is a figure which shows the experimental result of 2nd Example. It is a figure which shows the experimental result of 2nd Example. It is a figure which shows the experimental result of 2nd Example. It is a figure which shows the experimental result of 2nd Example. It is a figure which shows the experimental result of 2nd Example. It is a figure which shows the experimental result of a 3rd Example. It is a figure which shows the experimental result of 4th Example. It is a figure which shows the experimental result of 5th Example. It is a comparison figure of the particle size distribution of the calcium carbonate in a 6th Example.

  Hereinafter, an embodiment of a method for producing calcium carbonate according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the invention.

(Method for producing calcium carbonate)
The manufacturing method of calcium carbonate in the present embodiment includes an elution step in which quick lime (calcium oxide) is added to a neutral amino acid-containing aqueous solution containing a neutral amino acid to elute calcium ions, and calcium ions are eluted in the elution step. A precipitation step of precipitating calcium carbonate by introducing carbon dioxide into the aqueous solution containing a neutral amino acid, and carbon dioxide gas when the pH of the neutral amino acid-containing aqueous solution becomes 7.5 or more and less than 9.0 in the precipitation step Will be stopped.

  A neutral amino acid-containing aqueous solution means an aqueous solution containing at least a predetermined amount of a neutral amino acid. In particular, the neutral amino acid-containing aqueous solution is preferably an aqueous solution in which two or more neutral amino acids are mixed. The isoelectric point of the neutral amino acid-containing aqueous solution is preferably near neutral (pH = about 4 to 8).

The neutral amino acid means an organic compound having both amino group and carboxyl group functional groups and having an isoelectric point at a pH of about 5 to 7. Specifically, cysteine (Cys), phenylalanine (Phe), threonine (Thr), glutamine (Gln), serine (Ser), hydroxyproline (Hyp), methionine (Met), citrulline (Cit), isoleucine (Ile) , Valine (Val), glycine (Gly), DL-alanine (Ala), proline (Pro), β-alanine (βAla), 4-aminobutyric acid (GABA), histidine (His), ornithine hydrochloride (Orn-HCl) ), Arginine hydrochloride (Arg-HCl), lysine hydrochloride (Lys-HCl), leucine (Leu), asparagine monohydrate (Ans-H ₂ O), tryptophan (Trp), tyrosine (Tyr), glucosamine, etc. It is. In addition, it is not limited to the amino acid mentioned above, You may use N protected amino acids, such as N-acetyl-D-glucosamine, and C protected amino acids.

  In the elution step, a neutral amino acid-containing aqueous solution containing neutral amino acids at a predetermined ratio is prepared. Next, quick lime is added to the prepared neutral amino acid-containing aqueous solution to elute calcium ions into the neutral amino acid-containing aqueous solution.

Specifically, for example, the following elution reaction of calcium ions is assumed.
(1) CaO + H ₂ O → Ca (OH) ₂
(2) 2HL + Ca (OH) ₂ → Ca (HL) ₂ ²⁺ + 2OH ⁻
(3) 2HL + Ca (OH) ₂ → CaL ₂ + 2H ₂ O
Here, L indicates a neutral amino acid ligand.

As can be seen from these formulas (2) and (3), the calcium ion (Ca ²⁺ ) causes a chelate reaction with the carboxyl group or amino group of the amino acid to produce a chelate complex (Ca (HL) ₂ ²⁺ , CaL ₂ ). The At this time, since the hydroxide ions (OH ⁻ ) bonded to the calcium ions are dissociated, the mixed aqueous solution is shifted to the alkali side.

  As a next step, a neutralizing amino acid-containing aqueous solution after the elution step is brought into contact with a gas containing carbon dioxide to precipitate as calcium carbonate, and a recovery step for collecting the precipitated calcium carbonate is provided. In the precipitation step, a filtrate obtained by filtering the residue in the neutral amino acid-containing aqueous solution after the elution step (hereinafter referred to as “reaction liquid”) is brought into contact with a gas containing carbon dioxide gas. In this embodiment, when the pH of the reaction liquid is 7.5 or more and less than 9.0, preferably 8.0 or more and less than 9.0, and more preferably 8.0 or more and 8.5 or less, the introduction of carbon dioxide gas. Trying to stop.

The gas containing carbon dioxide (CO ₂ ) is not limited to pure carbon dioxide. For example, it is generated when combustion liquid exhaust gas generated when hydrocarbon liquid fuel or solid fuel such as coal or wood is burned, or when quick lime is produced. Calcium carbonate calcined exhaust gas, biogas or the like (hereinafter simply referred to as “exhaust gas”) can be used. When exhaust gas is used as the carbon dioxide gas, dust or the like may be removed by passing through an adsorption filter or the like before contacting with the neutral amino acid-containing aqueous solution. In addition, although a precipitation process can be implemented at arbitrary temperature, since it becomes difficult to melt | dissolve a carbon dioxide gas so that temperature is high, it is preferable to use at 70 degrees C or less.

In the precipitation step, calcium ions and carbon dioxide react to generate and precipitate calcium carbonate. Specifically, the precipitation reaction when carbon dioxide gas is brought into contact with the reaction liquid after the elution reaction represented by the above formulas (2) and (3) is as follows.
(4) CO ₂ + H ₂ O → H ₂ CO ₃
(5) H ₂ CO ₃ → HCO ₃ ⁻ + H ⁺
(6) Ca (HL) ₂ ²⁺ + HCO ₃ ⁻ → CaCO ₃ + 2HL + H ⁺
(7) CaL ₂ + HCO ₃ ⁻ → CaCO ₃ + HL + L ⁻

  When carbon dioxide is brought into contact with the reaction liquid containing the chelate complex in the precipitation process, calcium ions are separated from the chelate complex to produce calcium carbonate, and neutral amino acids are separated from the chelate complex, resulting in the original neutrality. The state of the amino acid-containing aqueous solution is recovered. That is, a neutral amino acid is useful because it acts as a catalyst for separating calcium ions from quicklime to produce calcium carbonate and can be used repeatedly.

  By the way, it is known that the range in which carbon dioxide gas can exhibit a desired buffer capacity is within a range of ± 1.5 with respect to the first acid dissociation constant (pKa1). Therefore, the isoelectric point of the neutral amino acid-containing aqueous solution is preferably within a range of ± 1.5 with respect to the first acid dissociation constant of carbon dioxide gas. This is balanced by the overlapping of the buffer capacity range of carbon dioxide gas (left side in formulas (6) and (7)) and the buffer capacity range of amino acids to be recovered (right side in formulas (6) and (7)), This is because the consumption of carbon dioxide gas and the precipitation of calcium carbonate are promoted.

  The first acid dissociation constant of carbon dioxide is the pH at which the equation (5) is satisfied in the case of carbon dioxide, and pKa1 = 6.35. Therefore, for example, the isoelectric point of the neutral amino acid-containing aqueous solution is preferably in the range of 4.75 to 7.85 (= 6.35 ± 1.5). If the neutral amino acid buffer capacity range is ± 1.5 from the isoelectric point, the neutral amino acid exhibits a certain level of buffer capacity, so that the buffer capacity ranges of carbon dioxide and neutral amino acids overlap. The isoelectric point of the neutral amino acid-containing aqueous solution may be in the range of about 4-8.

  The calcium carbonate precipitated in the precipitation step can be recovered by a known method such as filtration in the subsequent recovery step. The recovered calcium carbonate can be used as a filler in industries such as papermaking, pigments, paints, plastics, rubber, woven and knitted fabrics.

  Further, another quick lime may be added to the neutral amino acid-containing aqueous solution after the recovery step, and a second elution step for eluting calcium ions into the neutral amino acid-containing aqueous solution may be performed, and then the second precipitation step and A recovery step may be performed. That is, using the neutral amino acid-containing aqueous solution used in the first elution step, the second elution step, the precipitation step, and the recovery step are performed, and further the third elution step, the precipitation step, and the recovery step are performed. In addition, a series of processes such as an elution step, a precipitation step, and a recovery step can be repeatedly performed on the same neutral amino acid-containing aqueous solution. At this time, the solid matter added to the neutral amino acid-containing aqueous solution may be the same or different from that used in the previous elution step, and is not particularly limited.

(Calcium carbonate production equipment)
As shown in FIG. 1, the calcium carbonate production apparatus Y in the present embodiment is accommodated in a reaction liquid supply unit A, a reaction tank B in which a reservoir C for the reaction liquid W is formed in the lower part, and an upper part of the reaction tank B. A plurality of nozzles D, a circulation pump Pa for supplying the reaction liquid W stored in the storage section C to the nozzle D, a cooling unit E, a precipitate recovery unit F, a water supply unit G, and a carbon dioxide gas concentration Unit J is provided.

  The calcium carbonate production apparatus Y in the present embodiment reacts the reaction liquid W, which is a neutral amino acid-containing aqueous solution from which calcium ions prepared in the reaction liquid supply unit A are eluted, with a gas containing carbon dioxide gas in the reaction tank B. To precipitate calcium carbonate.

  The reaction liquid supply unit A includes an elution tank 1 for adding calcium oxide to a neutral amino acid-containing aqueous solution to elute calcium ions, a stirring device 2 for stirring the neutral amino acid-containing aqueous solution with a propeller, and a filter 3a. And a first filtration tank 3 that removes a residue composed of impurities, unreacted quicklime, and the like in the aqueous solution from which ions are eluted. Further, the reaction liquid supply unit A is configured such that the residue is removed by the first delivery pipe 4 a for sending the reaction liquid W (suspension) before filtration from the elution tank 1 to the first filtration tank 3 and the first filtration tank 3. And a second delivery pipe 4b for delivering the transparent reaction liquid W from which calcium ions are eluted to the reaction tank B by driving the delivery pump Pb. An electric on-off first on-off valve 4c is disposed at the connection port of the first delivery pipe 4a with the elution tank 1. Furthermore, the reaction liquid supply unit A includes a replenishment pipe 14 that replenishes the elution tank 1 with an aqueous solution containing a neutral amino acid separated from the chelate complex in a reservoir C of the reaction tank B described later. An electrically operated second on-off valve 14a is disposed.

  The reaction tank B has a rectangular tube-shaped side wall 5 centered on the axial core X in a vertical orientation, a funnel-shaped upper wall 6 that protrudes upward toward the center, and a funnel-shaped bottom wall 7 that protrudes downward toward the center. And.

  A suction port 1 a that sucks exhaust gas (an example of a gas containing carbon dioxide) is formed in the side wall 5 above the liquid level of the reaction liquid W. An intake duct 4 through which the exhaust gas sucked by the blower 18 passes is connected to the suction port 1a.

  The upper wall 6 is formed with a gas discharge port 2a for discharging the exhaust gas in which the carbon dioxide gas is consumed. A discharge cylinder 7a protrudes downward from the bottom wall 7 and protrudes downward. An electric open / close discharge valve 7b is disposed on the discharge cylinder 7a. Above the reaction tank B, a carbon dioxide concentration sensor 15 that detects the carbon dioxide concentration inside the reaction tank B is disposed. Below the reaction tank B, a float type liquid level sensor 8 for detecting the liquid level of the reaction liquid W stored in the storage unit C, a pH sensor 9 for detecting the pH of the reaction liquid W, and a reaction A calcium ion concentration sensor 10 that detects the calcium ion concentration of the liquid W and a temperature sensor 11 such as a thermistor that detects the temperature of the reaction liquid W are disposed. An oxidation-reduction potentiometer that detects the oxidation-reduction potential of the reaction liquid W may be provided.

  Each nozzle D sprays the reaction liquid W stored in the storage section C from the reaction tank B downward (in a direction perpendicular to the liquid surface of the reaction liquid W) linearly by the driving force of the circulation pump Pa. The posture is set.

  As shown in FIG. 1, each nozzle D has a housing H, and the inner peripheral surface of the housing H has a linear cross-sectional introduction portion H1 into which the reaction liquid W is introduced, and the diameter of the introduction portion H1. The blower outlet H2 having a smaller diameter and having a linear cross section for ejecting the reaction liquid W and the tapered part H3 having a diameter reduced from the introduction part H1 toward the blower outlet H2 have a center line parallel to the axis X. Is formed. As a result, the reaction liquid W introduced into the introduction part H1 is smoothly accelerated by the taper part H3 and ejected linearly from the outlet H2.

  In addition, the plurality of nozzles D includes a high position nozzle Da disposed above the suction port 1a at a position adjacent to the suction port 1a, and a position farther from the suction port 1a than the high position nozzle Da than the high position nozzle Da. The low position nozzle Db disposed below and the middle position nozzle Dc disposed below the high position nozzle Da and above the low position nozzle Db at a position between the high position nozzle Da and the low position nozzle Db. And have. In the present embodiment, the high position nozzle Da, the middle position nozzle Dc, and the low position nozzle Db are arranged in this order as the distance from the suction port 1a increases, but the middle position nozzle Dc and the low position nozzle Db are alternately arranged or randomly. Or any one of the middle position nozzle Dc and the low position nozzle Db may be omitted.

  Moreover, although not shown in figure, the some nozzle D is arrange | positioned in zigzag form in planar view (axial core X direction view). Specifically, when the rows are set in order from the side closer to the suction port 1a, the odd-numbered nozzles D and the even-numbered nozzles D are arranged without overlapping in the flow direction of the air passing through the intake duct 4, The odd-numbered nozzles D and the even-numbered nozzles D are arranged so as to overlap each other. It should be noted that all nozzles D may be arranged in an overlapping grid pattern in the flow direction of the air passing through the intake duct 4 without being arranged in a staggered pattern, or may be arranged randomly without overlapping, in particular. It is not limited.

  Circulation pump Pa is driven by an electric motor whose rotation speed can be controlled by an inverter. In the calcium carbonate production apparatus Y, the reaction liquid W is circulated so that the reaction liquid W is supplied to the nozzle D via the suction pipe 12 and the supply pipe 13 by driving the circulation pump Pa.

  In addition, a replenishment pipe 14 for replenishing the elution tank 1 of the reaction liquid supply unit A with a neutral amino acid-containing aqueous solution separated and recovered from the chelate complex is connected to the joining portion of the suction pipe 12 and the supply pipe 13. A pressure sensor 17 that detects the pressure of the reaction liquid W and a third open / close valve 13a that is electrically open / closed are disposed in the supply pipe 13 downstream of the circulation pump Pa.

  The cooling unit E includes a cooling device 25 and a cooling pipe 26 that is arranged in the liquid of the reaction liquid W in the reservoir C when the refrigerant is supplied from the cooling device 25. In the cooling unit E, liquid or gas is used as the refrigerant.

  The sediment collection unit F collects calcium carbonate that precipitates at the bottom of the reservoir C. The sediment collection unit F includes a second filtration tank 31 that filters and removes calcium carbonate from the reaction liquid W using a filter 31a. The suction pipe 12 is connected to the lower part of the second filtration tank 31.

  The water supply unit G includes a water storage unit 27 that stores water, and a transfer pipe 28 that transfers water from the water storage unit 27 to the storage unit C of the reaction tank B. The carbon dioxide concentration unit J includes a concentration adjuster 29 that adjusts the concentration of carbon dioxide, and a junction pipe 30 that joins the carbon dioxide prepared by the concentration adjuster 29 to the intake duct 4.

(Control form)
As shown in FIG. 2, the calcium carbonate manufacturing apparatus Y is configured to control each unit by a control unit 50 including a microprocessor, a DSP (digital signal processor), and the like. An induction motor or a synchronous motor is used as an electric motor that drives a plurality of pumps, and the control unit 50 includes an inverter circuit that controls the rotation speed of the electric motor by adjusting the frequency of power supplied to the electric motor. Yes. In a configuration using a brushless DC motor as an electric motor, a power control circuit that adjusts power by setting PWM or the like is used.

  Detection signals from the liquid level sensor 8, the pH sensor 9, the calcium ion concentration sensor 10, the temperature sensor 11, the carbon dioxide concentration sensor 15, and the pressure sensor 17 are input to the control unit 50. Further, the control unit 50 includes a stirring device 2, a delivery pump Pb, a blower 18, a circulation pump Pa, a first on-off valve 4c, a second on-off valve 14a, a third on-off valve 13a, and a discharge valve 7b. Control signals are output to the cooling device 25, the water storage unit 27, and the concentration adjuster 29.

  First, as shown in FIG. 1, a neutral amino acid-containing aqueous solution obtained by mixing a neutral amino acid-containing aqueous solution composed of one kind of amino acid or two or more kinds of neutral amino acids into the elution tank 1 of the reaction liquid supply unit A; Quick lime is added, and the control unit 50 drives the stirring device 2. At this time, the stirring device 2 stirs the neutral amino acid-containing aqueous solution intermittently. Specifically, after stirring the neutral amino acid-containing aqueous solution with the stirring device 2 for a predetermined time (for example, 10 seconds), the operation of stopping the driving of the stirring device 2 for a predetermined time (for example, 5 minutes) is repeatedly executed.

  As shown in the above formula (1), when quick lime is added to the neutral amino acid-containing aqueous solution, the quick lime is first dissolved in water to form calcium hydroxide, as shown in the above formulas (2) and (3). In addition, the calcium hydroxide and the neutral amino acid react to form a chelate complex. If a neutral amino acid containing aqueous solution is stirred with the stirring apparatus 2 of the reaction liquid supply unit A, the dissolution rate until quicklime becomes saturated with respect to water increases. Thereafter, when the stirring of the stirring device 2 is stopped to form a chelate complex and thereby the calcium hydroxide concentration is lowered, if the stirring of the stirring device 2 is restarted, quick lime can be further dissolved in water. That is, by setting the stirring for dissolving quicklime in water to the minimum necessary, calcium ions can be eluted with less power consumption.

  Next, the neutral amino acid-containing aqueous solution from which calcium ions are eluted in the elution tank 1 flows into the first filtration tank 3 by the controller 50 opening the first on-off valve 4c, and the filter 3a of the first filtration tank 3 is opened. Then, the residue is filtered, and then sent out as a filtrate (reaction liquid W) to the inside of the reaction tank B by the driving force of the delivery pump Pb. Then, the reaction liquid W from the reaction liquid supply unit A is stored until the detection value of the liquid level sensor 8 in the storage section C reaches a predetermined value with the discharge valve 7b closed. Subsequently, after the reaction liquid W is stored in the storage part C, the discharge valve 7b and the third on-off valve 13a are opened and the circulation pump Pa is driven. At the time of this driving, the electric power supplied to the circulation pump Pa is set so that the pressure detected by the pressure sensor 17 is maintained at the target value.

  Thus, the reaction liquid W is sent out to the suction pipe 12 and circulates through the supply pipe 13, and then is jetted out from the nozzle D in a straight line. Then, the blower 18 is operated and the exhaust gas is sucked into the reaction tank B from the suction port 1a. At this time, the controller 50 drives the concentration adjuster 29 so that the concentration of the carbon dioxide gas detected by the carbon dioxide concentration sensor 15 becomes a predetermined concentration (for example, 20%) of 5% or more. Instead of exhaust gas, high-concentration carbon dioxide gas may be supplied from a carbon dioxide gas cylinder. In this case, the concentration adjuster 29 can be omitted. In addition, the controller 50 may add a predetermined amount of water from the water reservoir 27 to the reaction liquid W before the exhaust gas is sucked into the reaction tank B from the suction port 1a. Thereby, the neutral amino acid concentration in the precipitation step is reduced to reduce the chelating action, so that calcium ions can be reliably separated from the neutral amino acid with a small amount of carbon dioxide introduced. As a result, since the operation time of the blower 18 and the circulation pump Pa is shortened, power consumption can be saved. Instead of water or together with water, acidic condensed water of exhaust gas may be added to the reaction liquid W in a predetermined amount. In this case, since the pH of the reaction liquid W shifted to the alkali side is lowered as shown in the above formulas (2) and (3), a target pH of 7.5 or more is obtained when carbon dioxide is brought into contact with the reaction liquid W. It can be reached in a short time to less than 9.0.

  In the present embodiment, there are provided a plurality of nozzles D each having an outlet H2 for ejecting the reaction liquid W linearly. As a result, the carbon dioxide gas sucked into the reaction tank B from the suction port 1a is drawn into the storage part C by the reaction liquid W ejected linearly. The carbon dioxide gas becomes fine bubbles below the surface of the reaction liquid W, the reactions shown in the above formulas (4) to (7) are promoted, calcium ions are separated from the chelate complex, and calcium carbonate is generated. At the same time, neutral amino acids are separated from the chelate complex, and the state of the original neutral amino acid-containing aqueous solution is recovered. Thus, since the carbon dioxide gas filled in the reaction tank B by the plurality of nozzles D is drawn into the reaction liquid W all at once, the suction capacity of the carbon dioxide gas can be increased to increase the processing capacity.

  Further, in the present embodiment, the plurality of nozzles D are arranged at a position adjacent to the suction port 1a and above the suction port 1a, and at a position farther from the suction port 1a than the high position nozzle Da. It has a middle position nozzle Dc and a low position nozzle Db arranged below the high position nozzle Da. For this reason, the high-position nozzle Da secures a large amount of contact per unit time between the reaction liquid W and carbon dioxide, and increases the amount of carbon dioxide sucked from the suction port 1a into the reservoir C. Let Then, the middle position nozzle Dc and the low position nozzle Db vigorously mix the reaction liquid W into the reservoir C, further refine the carbon dioxide gas that is drawn, and further increase the contact probability between the carbon dioxide gas and the reaction liquid W. It will be. As a result, the precipitation efficiency of calcium carbonate can be reliably increased.

  Furthermore, in this embodiment, since the several nozzle D is arrange | positioned in zigzag form in planar view, the reaction liquid W contacts the carbon dioxide gas with which the inside of the reaction tank B was filled equally. As a result, the amount of carbon dioxide sucked from the suction port 1a can be further increased.

  The precipitated calcium carbonate is discharged together with the reaction liquid W from the discharge cylinder 7a by its own weight, and the reaction liquid W from which the calcium carbonate has been removed by the second filtration tank 31 is ejected from the nozzle D by the driving force of the circulation pump Pa. On the other hand, the precipitated calcium carbonate is collected from the upper surface of the filter 31 a of the second filtration tank 31.

  When the liquid temperature detected by the temperature sensor 11 exceeds a target temperature (for example, 10 ° C. ± 5 ° C.), the control unit 50 controls the cooling device 25 so that a low-temperature refrigerant is supplied to the cooling pipe 26. And the rise in the liquid temperature of the reservoir C is suppressed. When the reaction liquid W detected by the pH sensor 9 reaches a target pH of 7.5 or more and less than 9.0 (for example, pH 8.2), the control unit 50 stops driving the blower 18 and generates carbon dioxide. Is stopped, the third on-off valve 13a is closed and the circulation pump Pa is stopped to stop the reaction between the carbon dioxide gas and the neutral amino acid-containing aqueous solution. Moreover, the control part 50 detects the calcium ion concentration of the reaction liquid W in the storage part C of the reaction tank B with the calcium ion concentration sensor 10, and the elution rate (substance amount (mol) of calcium ions in the neutral amino acid-containing aqueous solution) / Amount of calcium ion in quicklime (mole) × 100 (%)) and precipitation rate of calcium carbonate (amount of precipitated calcium carbonate (mole) / amount of change in calcium ion before and after contacting carbon dioxide with reaction liquid W ( Mol) × 100 (%)).

  Next, the control unit 50 opens the second on-off valve 14a to drive the circulation pump Pa, returns the neutral amino acid-containing aqueous solution separated and recovered from the reaction liquid W to the elution tank 1, and the same control is repeatedly executed. Is done.

[Another embodiment]
In addition to the embodiment described above, the following configuration may be used. In addition, the same number and code | symbol are attached | subjected to what has the same function as embodiment mentioned above.

(A) As shown in FIG. 3, the nozzle D includes an outer cylinder Ha and an inner cylinder Hb fixed to the outer cylinder Ha. A fastening mechanism T is constituted by a male screw portion and a nut formed at one end of the inner cylinder Hb, an annular recess Hb1 is formed in a portion adjacent to the male screw portion of the inner cylinder Hb, and a seal member S is provided in the annular recess Hb1. By inserting, one end side of the inner cylinder Hb is fixed to the outer cylinder Ha in a sealed state. The other end side of the inner cylinder Hb has a large-diameter portion Hb2 formed to have a larger diameter than other portions, and an inclined portion Hb3 that decreases in diameter from the large-diameter portion Hb2 toward one end side, The small-diameter portion Hb4 has a smaller diameter than the large-diameter portion Hb2. That is, the large diameter portion Hb2, the inclined portion Hb3, and the small diameter portion Hb4 are arranged in this order from the other end side to the one end side of the inner cylinder Hb.

  An introduction space M1 into which the reaction liquid W is introduced from the supply pipe 13 is formed between the small diameter portion Hb4 of the inner cylinder Hb and the inner surface Ha1 of the outer cylinder Ha, and the inclined portion Hb3 of the inner cylinder Hb and the inner surface Ha1 of the outer cylinder Ha. A constricted space M2 that restricts the flow passage cross-sectional area of the introduction space M1 is formed. A blower outlet M3 is formed between the narrow space H2 and the small diameter portion Hb4 of the inner cylinder Hb and the inner surface Ha1 of the outer cylinder Ha. From such a configuration, the air outlet M3 of the nozzle D is formed in an annular shape between the outer diameter d1 of the small diameter portion Hb4 of the inner cylinder Hb and the inner diameter d2 of the outer cylinder Ha.

  If the air outlet M3 is formed in an annular shape as in the present embodiment, the surface area of the reaction liquid W ejected compared to a general circular hole increases, so the contact area between the reaction liquid W and carbon dioxide gas Can be further enhanced. As a result, the amount of carbon dioxide gas drawn into the reaction liquid W is further increased, and the deposition rate of calcium carbonate can be reliably increased. Further, in the present embodiment, since the constricted space M2 that restricts the flow path cross-sectional area of the introduction space M1 is provided, the flow rate of the reaction liquid W is accelerated and the ejection speed of the reaction liquid W is increased. The amount of C drawn into the interior is surely increased, and the carbon dioxide gas tends to be fine bubbles below the surface of the reaction liquid W.

(B) Although each nozzle D in the above-described embodiment is set in a posture so as to eject the reaction liquid W linearly in a direction perpendicular to the liquid surface of the reaction liquid W stored in the storage unit C, The posture may be set so that the reaction liquid W is ejected linearly from a direction inclined with respect to the liquid level of the reaction liquid W stored in the part C. In addition, each nozzle D may have any ejection form such that the reaction liquid W is ejected with a spread without ejecting the reaction liquid W linearly. That is, the posture of the nozzle D may be set so that the reaction liquid W is ejected from the direction intersecting the liquid level of the reaction liquid W stored in the storage unit C.

[First Example: Example in which two or more amino acids are dissolved until each is saturated]
In this example, in the case of a neutral amino acid-containing aqueous solution in which two or more neutral amino acids are mixed, the solubility in water can be increased as compared with a neutral amino acid-containing aqueous solution in which one neutral amino acid is saturated. Verify what you can do. In this example, DL-alanine as a first neutral amino acid was added to a saturated amount (142 g / L) in 1 L of water set at 10 ° C., and threonine was further saturated as a second neutral amino acid (80 g / L). After addition to L), glycine was added as a third neutral amino acid to a saturation amount (195 g / L). The result is shown in FIG. As shown in FIG. 4, all neutral amino acids were dissolved to saturation and the specific gravity increased. This is presumably because the aqueous solution in which neutral amino acids are dissolved has increased polarity due to ionization of amino groups and carboxyl groups, and other neutral amino acids are easily ionically bonded to water molecules.

[Second Example: Neutral Amino Acids that Increase Calcium Carbonate Precipitation Efficiency]
In this example, a saturated neutral amino acid-containing aqueous solution in which one neutral amino acid or two or more neutral amino acids are mixed and dissolved in water to a saturated amount (each amino acid is dissolved in water to a saturated amount). In addition, the amount of precipitated calcium carbonate is increased and the reusable neutral amino acid is verified. FIG. 5 shows a reaction liquid prepared by adding quick lime at a rate of 100 g / L to water alone or an aqueous solution in which various neutral amino acids and two or more neutral amino acids are mixed. The experimental result of the calcium carbonate precipitation amount (g / L) at the time of making the gas containing a reaction liquid and a carbon dioxide gas contact pH8.2 is shown.

  Phenylalanine (Phe), glutamine (Gln), hydroxyproline (Hyp), methionine (Met), citrulline (Cit), isoleucine (Ile), valine (Val), proline (Pro), β-alanine not shown in FIG. 14 types of (βAla), 4-aminobutyric acid (GABA), histidine (His), ornithine hydrochloride (Orn-HCl), arginine hydrochloride (Arg-HCl), and leucine (Leu), respectively, DL-alanine (Ala) ) And threonine (Thr) -containing saturated neutral amino acid-containing aqueous solution had small precipitated calcium carbonate particles and could not be separated by filtration with a filter paper having a filtration diameter of 1 μm. In order to use calcium carbonate for papermaking, the average particle diameter is preferably larger than 1 μm and not larger than 10 μm. Therefore, these 14 kinds of amino acids have a pH of 8.2 with the reaction liquid and the gas containing carbon dioxide in the precipitation step. Cannot be used when touching up to.

As shown in FIG. 5, DL-alanine (Ala), threonine (Thr) or glycine (Gly) alone, DL-alanine (Ala) and glycine (Gly) or glycine (Gly) and threonine (Thr) were mixed 2 Seed mixing, DL-alanine (Ala) and threonine (Thr), glycine (Gly), cysteine (Cys), serine (Ser), lysine hydrochloride (Lys-HCl) and asparagine monohydrate (Ans-H ₂₎ Oxidized aqueous solution containing three kinds of saturated neutral amino acids mixed with any one of O) was able to significantly increase the amount of precipitated calcium carbonate compared to water alone. On the other hand, the saturated neutral amino acid-containing aqueous solution containing two kinds of glycine (Gly) alone or a mixture of glycine (Gly) and threonine (Thr) had a larger amount of precipitated calcium carbonate than the others, as shown in FIG. As described above, the specific gravity of the saturated neutral amino acid-containing aqueous solution after the precipitation step has decreased more than the specific gravity before the elution step. This is presumed that the amount of precipitation increased due to the neutral amino acid in the solution becoming a compound and precipitated in the calcium carbonate. That is, it was found that a saturated neutral amino acid-containing aqueous solution containing two kinds of glycine (Gly) alone or a mixture of glycine (Gly) and threonine (Thr) is not suitable for repeated use.

From these, DL-alanine (Ala) or threonine (Thr) alone, DL-alanine (Ala) and glycine (Gly) mixed in two kinds, DL-alanine (Ala) and threonine (Thr) into glycine (Gly ), Cysteine (Cys), serine (Ser), lysine hydrochloride (Lys-HCl) and asparagine monohydrate (Ans-H ₂ O) mixed in one of three types of saturated neutral amino acids It was verified that the aqueous solution is effective in increasing the precipitation efficiency because the precipitation amount of calcium carbonate is large and reusability. In particular, a neutral amino acid-containing aqueous solution containing a mixture of DL-alanine (Ala) and glycine (Gly) having the highest precipitation amount is effective.

  FIGS. 7 to 8 show that DL-alanine is added as a first neutral amino acid to a saturated amount (142 g / L) in 1 L of water set at 10 ° C., and threonine is saturated as a second neutral amino acid ( 80 g / L), and then using a saturated neutral amino acid-containing aqueous solution in which glycine is added as a third neutral amino acid to a saturated amount (195 g / L), quick lime is added at a rate of 100 g / L, and the reaction liquid is added. The results of continuous experiments are shown when the reaction liquid from which calcium ions are eluted in the elution step and the gas containing carbon dioxide gas are brought into contact with each other up to pH 8.2. Even if the same saturated neutral amino acid-containing aqueous solution is repeatedly used 5 times, the calcium ion elution amount does not decrease in each elution step, and the calcium carbonate production amount does not decrease in each precipitation step. It was confirmed that the specific gravity of the solution after being collected by filtration did not decrease. Thus, it was confirmed that the neutral amino acid-containing aqueous solution whose specific gravity does not decrease before and after the precipitation step as shown in FIG. 6 can be used repeatedly.

  FIG. 9 shows a neutral amino acid-containing aqueous solution prepared by mixing DL-alanine (Ala) and glycine (Gly) at a concentration of 10% or 50% with respect to their respective saturation amounts in 1 L of water set at 10 ° C. The reaction liquid was prepared by adding quick lime at a rate of 14 g / L and 44 g / L to neutral amino acid-containing aqueous solutions of 10% concentration and 50% concentration, respectively, and the reaction in which calcium ions were eluted in the elution step. The continuous experiment result at the time of making the liquid and the gas containing a carbon dioxide gas contact pH8.2 is shown. Even if the same neutral amino acid-containing aqueous solution is used repeatedly three times, the elution amount of calcium ions does not decrease in each elution step, and the calcium carbonate production amount does not decrease in each precipitation step. It was confirmed that the specific gravity of the solution after the collected calcium carbonate was recovered by filtration did not decrease. Thus, it was confirmed that the neutral amino acid containing aqueous solution which mixed DL-alanine and glycine can be used repeatedly. Moreover, since the neutral amino acid cost per gram of precipitated calcium carbonate is the cheapest when DL-alanine and glycine are mixed as compared with the case of using other amino acids, it is preferable in producing calcium carbonate.

[Third embodiment: Advantage by stopping the introduction of carbon dioxide at pH 8.2]
In this example, the superiority when the introduction of carbon dioxide gas is stopped at pH 7.0 in the precipitation step is verified as compared with the case where the introduction is stopped at pH 7.0. FIG. 10 shows the precipitation time (min), the precipitation amount (g), and the time required to deposit 1 g of calcium carbonate when 200 g of quicklime is added to 200 g of water set at 10 ° C. The experimental result of min / g) is shown. A saturated neutral amino acid-containing aqueous solution in which DL-alanine (Ala) alone, threonine (Thr) alone, DL-alanine (Ala), threonine (Thr), and glycine (Gly) are each dissolved to saturation. It was. On the other hand, about 3 types of mixture of DL-alanine (Ala), threonine (Thr), and cysteine (Cys), it was set as the neutral amino acid containing aqueous solution melt | dissolved at 100%, 100%, and 85% with respect to saturation amount, respectively. . Moreover, about 3 types of mixture of DL-alanine (Ala), threonine (Thr), and cysteine (Ser), it was set as the neutral amino acid containing aqueous solution melt | dissolved at 100%, 100%, and 51% with respect to saturation amount, respectively. .

  As shown in FIG. 10, in the case of all neutral amino acid-containing aqueous solutions, when the introduction of carbon dioxide gas was stopped at pH 8.2, the amount of precipitated calcium carbonate slightly decreased. However, the deposition time could be greatly shortened. As a result, when the introduction of carbon dioxide gas is stopped at pH 8.2, the time required to deposit 1 g of calcium carbonate is shortened by about 2/3 to 1/4 times when the introduction of carbon dioxide gas is stopped at pH 8.2. It becomes possible. Therefore, it was verified that stopping the introduction of carbon dioxide gas when the pH reached about 8 leads to a reduction in power consumption.

[Fourth Example: Examining the upper limit of pH at which introduction of carbon dioxide is stopped]
In this embodiment, the upper limit value of pH at which the introduction of carbon dioxide gas is stopped is verified. In FIG. 11, 983 g (54.6 g / L) of quicklime is added to 18 L of water set at 10 ° C. to prepare a reaction liquid, and the pH at which the introduction of carbon dioxide gas is stopped in the precipitation step is 8.0 to 9.0. The experimental results of the precipitation time (minutes), the precipitation amount (g), and the time (minute / g) required to precipitate 1 g of calcium carbonate are shown. In addition, about 3 types of mixture of DL-alanine (Ala), threonine (Thr), and cysteine (Cys), it was set as the neutral amino acid containing aqueous solution melt | dissolved in 100%, 10%, and 30% with respect to saturation amount, respectively. .

  As shown in FIG. 11, when the introduction of carbon dioxide gas was stopped at a pH of less than 9.0, it was possible to shorten the time required to precipitate 1 g of calcium carbonate while securing an appropriate amount of precipitated calcium carbonate. . In particular, when the introduction of carbon dioxide gas is stopped at pH 8.3, it is preferable from the viewpoint of the precipitation efficiency that the precipitation amount of calcium carbonate is large and the introduction of carbon dioxide gas is stopped at pH 8.0 or more and 8.5 or less. Verified.

[Fifth Example: Calcium ion elution and power consumption when stirring intermittently]
In this example, compared with the case where the neutral amino acid-containing aqueous solution to which quicklime is added is continuously stirred, the amount of calcium ions eluted can be increased with less power consumption when intermittently stirred. Validate the points. FIG. 12 shows the experimental results of the elution amount and power consumption when continuously stirring and intermittently stirring when the same amount of quicklime is added to the same neutral amino acid-containing aqueous solution. .

  In the case of intermittent stirring, the neutral amino acid-containing aqueous solution was stirred for 10 seconds and then left (cured) for 5 minutes, and this combination of intermittent operations was repeated 3 or 6 times. When the combination of intermittent operation was repeated 6 times, the calcium ion elution amount was 1.5 times that in the case of continuous stirring for 60 seconds with the same power consumption. Moreover, in order to stir the equivalent amount of elution, continuous stirring for about 300 seconds is necessary, and the amount of power consumption has increased about five times. From these, after increasing the dissolution rate until quicklime is saturated with water by stirring, the stirring is stopped until a chelate complex is formed, and stirring is resumed when the calcium hydroxide concentration decreases. In other words, it was verified that calcium carbonate can be efficiently produced while securing a calcium ion elution amount with low power consumption.

[Sixth embodiment: auxiliary agent for atomizing calcium carbonate]
In this example, quick lime was added at a rate of 55 g / L to a neutral amino acid-containing aqueous solution in which DL-alanine was mixed at 142 g / L, threonine at 6 g / L, and glycine at a rate of 43.9 g / L. Of the particle size distribution of calcium carbonate with and without the addition of the auxiliary barium sulfate at a rate of 8 g / L in an experiment in which the reaction liquid was brought into contact with a gas containing carbon dioxide up to pH 8.2. Verify the difference. FIG. 13 shows the result of measuring the particle size distribution of calcium carbonate deposited by a wet laser diffraction / scattering method.

  The upper part of FIG. 13 shows the measurement results when no auxiliary agent was added. The particle size distribution of calcium carbonate was 17.825 μm to 89.337 μm, and the average particle size was 43.162 μm. It is thought that the average particle diameter of calcium carbonate became a large value due to secondary aggregates of primary particles. The middle part of FIG. 13 shows the measurement results when 8 g / L of barium sulfate is added as an auxiliary before blowing a gas containing carbon dioxide in the precipitation step. The particle size distribution of calcium carbonate was 0.283 μm to 12.619 μm, and the average diameter was 3.650 μm. The lower part of FIG. 13 shows the measurement results when 8 g / L of barium sulfate is added as an auxiliary after the introduction of the gas containing carbon dioxide gas in the precipitation step. The particle size distribution of calcium carbonate was 0.283 μm to 8.934 μm, and the average diameter was 2.622 μm. Thus, the particle diameter of the precipitated calcium carbonate was able to be refined | miniaturized by adding barium sulfate to the neutral amino acid containing aqueous solution in a precipitation process. This is presumably because barium sulfate is a very insoluble substance in water, and barium sulfate acted as an auxiliary agent to suppress aggregation of calcium ions separated from the chelate complex during the formation of calcium carbonate. Therefore, calcium carbonate having a fine particle size useful as a filler in the paper industry can be deposited.

  INDUSTRIAL APPLICABILITY The present invention can be used for a calcium carbonate manufacturing method for manufacturing calcium carbonate used as a filler in the paper industry and the like.

Claims (5)

An elution step of adding calcium oxide to a neutral amino acid-containing aqueous solution containing a neutral amino acid to elute calcium ions;
A precipitation step of precipitating calcium carbonate by introducing carbon dioxide into the neutral amino acid-containing aqueous solution from which the calcium ions have been eluted in the elution step,
The method for producing calcium carbonate, wherein in the precipitation step, the introduction of the carbon dioxide gas is stopped when the pH of the neutral amino acid-containing aqueous solution becomes 7.5 or more and less than 9.0.   The method for producing calcium carbonate according to claim 1, wherein the neutral amino acid contains DL-alanine and glycine.   The method for producing calcium carbonate according to claim 1, wherein the neutral amino acid contains DL-alanine, threonine, and at least one of glycine, cysteine, serine, lysine hydrochloride and asparagine monohydrate.   The manufacturing method of the calcium carbonate as described in any one of Claim 1 to 3 which adds a barium sulfate to the said neutral amino acid containing aqueous solution in the said precipitation process.   The said precipitation process WHEREIN: The manufacturing method of the calcium carbonate as described in any one of Claim 2 to 4 which adds water to the said neutral amino acid containing aqueous solution before introduce | transducing the said carbon dioxide gas.

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