CN1641077A

CN1641077A - Method for preparing aragonite type calcium carbonate whisker

Info

Publication number: CN1641077A
Application number: CN 200410022834
Authority: CN
Inventors: 宋永才
Original assignee: National University of Defense Technology
Current assignee: National University of Defense Technology
Priority date: 2004-01-13
Filing date: 2004-01-13
Publication date: 2005-07-20
Anticipated expiration: 2024-01-13
Also published as: CN1303264C

Abstract

The present invention relates to the preparation process of high purity aragonite type calcium carbonate whisker. The present invention prepares aragonite type calcium carbonate whisker with lime or slaked lime as main material and magnesium salt as crystal salt controlling agent and through a CO2 carbonating process. The process features the repeated use of the magnesium salt solution and the homogeneous replenishment of lime slurry during carbonating reaction. The process has low production cost, less environmental pollution and high calcium carbonate whisker yield, and the prepared calcium carbonate whisker has high purity and high length/diameter ratio. The process is suitable for industrial production of calcium carbonate whisker.

Description

Preparation method of aragonite type calcium carbonate whisker

Technical Field

The invention relates to a method for preparing high-purity aragonite calcium carbonate whiskers.

Background

The whiskers are needle-shaped single crystal materials.Because of complete crystallization, the fiber has extremely high strength, modulus, heat resistance and heat insulation performance, and has better processing performance than short fiber materials when being used as a reinforcing material.

Calcium carbonate micropowder (light calcium carbonate, heavy calcium carbonate and nano powder) is widely used as a filler in the industries of plastics, rubber, printing ink, paper making and the like. The calcium carbonate crystal whisker has the performance of strengthening and toughening, and can be used as a filler to improve the mechanical property, the flame retardant property, the heat resistance and the processability of a plastic product; the strength of the rubber product is improved; the glossiness and the transparency of the ink are improved, and the ink can be used for preparing high-grade paper and friction materials to improve the wear resistance. Therefore, the calcium carbonate whisker has wide application prospect.

The calcium carbonate crystal has three crystal forms of calcite, aragonite and vaterite. At normal temperature and pressure, calcite is in a stable crystal form, and aragonite and vaterite are in metastable crystal forms. Calcite crystals are cubic or spindle shaped, while aragonite crystals are often acicular single crystals. Under appropriate conditions, aragonite crystals grow directionally to form whiskers. Therefore, in the preparation process of the calcium carbonate whisker, the crystallization process must be controlled so that aragonite phase crystals are formed.

Calcium carbonate powder is generally prepared from quicklime or slaked lime as a raw material by a carbonation reaction in a carbon dioxide gas stream, and the calcium carbonate obtained by the reaction is calcite-type crystals. During the preparation of calcium carbonate whisker with lime or slaked lime as material and through carbonating reaction, the preparation condition must be controlled, otherwise, the whisker is not obtained and only micro powder is produced. In the existing research reports, besides controlling the preparation temperature, the stirring speed and the carbon dioxide introduction speed, the addition of seed crystals or the addition of a crystal form control agent is a frequently adopted method. Japanese patents JP63-256514 and JP63-260815 report methods for producing calcium carbonate whiskers using phosphoric acid and a soluble phosphate, but the length of the resulting whiskers is generally less than 10 μm, and Japanese patents JP4-321515, JP4-224110 and US5164172 describe methods for producing calcium carbonate whiskers by adding a calcium hydroxide slurry containing a phosphoric acid or a soluble phosphate under conditions in which an aragonite phase calcium carbonate seed crystal is contained, and calcium carbonate whiskers having a length of more than 20 μm can be produced. In the preparation of calcium carbonate whisker, Mg is a crystal form control agent in another class²⁺Can be obtained without pre-seeding in the presence of ions (such as magnesium salts)High purity and high length-diameter ratio of crystal whisker. MgCl has been reported in the literature (J.Am.Ceram.Soc.Vol.78(7), 1983(1995) literature I) and (J.Ceram.Soc.Jpn., Vol.104, 196(1996))₂Is a crystal form control agent, and calcium carbonate crystal whiskers with the purity of more than 98 percent are prepared by reaction in a lime water solution at the temperature of 80 ℃, the diameter of the crystal whiskers is 0.5 to 1 mu m, and the length-diameter ratio is 20 to 80. In Japanese patent JP2001-354416, in the presence of Mg²⁺Introducing carbon dioxide into the high-concentration slaked lime water suspension to carbonate to obtain the high-purity aragonite phase calcium carbonate crystal whisker, wherein the length of the crystal whisker is 10-20 mu m (document II). The above results illustrate the use of Mg²⁺The crystal form control agent is an effective method for preparing high-purity calcium carbonate crystal whiskers. However, as a method for industrial mass production, the method described in the above document has significant drawbacks. First, according to the results of the previous studies, in Mg²⁺When the ion is used as a crystal form control agent, the reaction principle is shown as the following formula:

(1)

(2)

(3)

(4)

(5)

(6)

it is known that Mg²⁺Conversion of ions initially with slaked lime to Mg (OH)₂And changed into Mg again in the reaction²⁺Ions, Mg after the preparation of calcium carbonate whisker²⁺The ions are not consumed and are washed away in a subsequent water wash. Due to the use of Mg²⁺When ions such as magnesium salt are used as the crystal form control agent, the dosage of the ions is very large (the initial charge ratio is Mg/Ca is more than 1.4 generally), therefore, a large amount of magnesium salt is not recycled, which causes a large amount of waste and increases the manufacturing cost; secondly, water pollution is caused. While the above documents do not relate to Mg²⁺The problem of recycling of ions is described in the literatureHowever, it is mentionedthat the filtered magnesium salt solution can be returned to use, but no further description is given, and no research example is given.

Secondly, in the first document, the feeding concentration of the adopted slaked lime is 0.25mol/L, and the maximum concentration of the corresponding product calcium carbonate whisker can only reach 0.25mol/L, namely 25g/L, so that the product yield is too low, and the industrial preparation cost is increased. In the second document, therefore, a high-concentration slaked lime suspension (according to its typical example, the feed concentration is 1.1mol/L) is used to achieve a calcium carbonate whisker yield of about 110 g/L. However, under such high concentration conditions, the slaked lime is converted into viscous magnesium hydroxide by the above reaction (1), and the system is in a gel state and hardly works by stirring. Therefore, the calcium carbonate whiskers are prepared with higher yield by the improvement that the document II uses a special stirring blade to carry out high-speed stirring to form different water flow directions during stirring. However, the total reaction time is long (about 30 hours is required for one reaction), and the calcium carbonate whiskers are short (the length of the whiskers is 10-20 μm), so that the requirement of high-efficiency production of high-quality whiskers cannot be met.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a preparation method of the aragonite type calcium carbonate whisker aiming at the defects in the preparation method, so that the prepared aragonite type calcium carbonate whisker has high purity, long length and low manufacturing cost and is suitable for industrial batch production.

The technical scheme for solving the technical problem is that the aragonitecalcium carbonate whisker is prepared by taking quick lime or slaked lime as a raw material and adopting magnesium salt as a crystal form control agent through a carbon dioxide carbonation method, namely, the slaked lime or the quick lime is taken as the raw material and mixed with a magnesium salt solution or a magnesium salt recovery solution according to a proper proportion, carbon dioxide gas is introduced at a certain temperature for carbonation reaction, slaked lime slurry is replenished for many times in the carbonation process, filtration is carried out after the reaction is finished, magnesium salt filtrate containing magnesium ions is recycled, and the calcium carbonate whisker is obtained by washing and drying a filter cake (see a process flow chart in figure 1).

The specific preparation process comprises the following production steps:

(1) adding water into industrial quicklime to digest the industrial quicklime into calcium hydroxide slurry, and carrying out sedimentation classification on the slurry for 1-3 times to remove bottom sedimentation coarse particles and dregs to be used as refined raw material slurry. And adding 5-20 times of water into slaked lime to form slurry, and then performing sedimentation and classification to obtain refined raw material slurry.

(2) Subjecting the recovered magnesium salt (such as magnesium chloride) to chemical analysis to titrate Mg therein²⁺、Ca²⁺After concentration, according to a certain charge ratio R ([ MgCl]₂]/[Ca(OH)₂]) With hydrogenStirring and mixing the calcium oxide slurry, reacting for 0.5-2 hours at the room temperature-80 ℃ to reach reaction balance, and introducing CO at the reaction temperature of 35-85 DEG C₂The gas is subjected to carbonation reaction, and the flow of the carbon dioxide is kept to be 100-1000 ml min^-1l^-1And the stirring speed is 100-600 rpm (revolutions per minute), and the pH value change of the reaction system is monitored by a pH meter.

(3) When the reaction is carried out for 2-4 hours and the pH value of the system is within the range of 7.0-8.0, calcium hydroxide slurry is uniformly supplemented according to 1-8 times of the original feeding amount, and the supplementing speed is controlled to be 0.04-0.20 mol h^-1l^-1And after the addition is finished, continuing the reaction until the pH value of the system is reduced to be below 7, and finishing the reaction.

(4) Filtering the reaction product, washing the precipitate with water for 2-3 times, and drying at 60-80 deg.C to obtain CaCO₃And (3) a whisker product. The filtrate is recovered for the next preparation.

The raw material is quicklime or slaked lime. And adding a proper amount of water into quick lime to be digested into calcium hydroxide by a dry method, sieving to remove coarse impurities, and adding 5-20 times of water to be vigorously stirred to form calcium hydroxide slurry. Or adding excessive water (5-20 times) into the quick lime to be digested into lime milk by a wet method, and removing bottom sedimentation coarse particles and dregs after 1-3 times of sedimentation and classification of the slurry or the lime milk to be used as raw material slurry for later use. And for slaked lime, adding 5-20 times of water to form slurry, and then performing sedimentation classification to prepare refined raw material slurry, wherein the prepared slurry has uniform and fine particles and has no coarse particles observable by naked eyes. Or preparing quicklime by using limestone as a raw material through mild calcination, and refining to obtain the raw material slurry.

The magnesium salt recovery solution is a filtrate formed after a product is filtered in the process of preparing calcium carbonate whiskers(reference example 1 can be referred to for the first preparation condition). The magnesium salt may be anhydrous MgCl₂Alternatively, hydrated MgCl can be used₂Such as 6H₂O·MgCl₂. The filtrate may be used as it is, or the filtrate may be used as a recovered solution together with a part of the washing solution. Mg in the filtrate²⁺、Ca²⁺The concentration can be titrated by chemical analysis (referring to general Mg²⁺、Ca²⁺Method of analysis of concentration). Then according to a certain charging ratio R ([ MgCl]₂]/[Ca(OH)₂]) Determining the required amount of the recovered solution, if Mg is contained in the recovered solution²⁺If the concentration is higher than the required concentration, water can be added for dilution, if the concentration is lower than the required concentration, the required magnesium salt dosage can be calculated according to the feeding ratio and is complemented, or the recovered liquid can be heated and boiled to remove part of water and then is adjusted to the required concentration.

The charge ratio of the raw materials for the reaction R ([ MgCl]₂]/[Ca(OH)₂]) Can be between 1.0 and 6.0, and less than 1.0, calcite type calcium carbonate particles are easily generated, the content of calcite type calcium carbonate whiskers in the product is reduced, and if the content is more than 6.0, the dosage of magnesium salt is too large, so that unnecessary calcium carbonate particles are generatedWaste and increase in raw material cost. The more suitable feeding ratio is 1.4-4.0.

The reaction temperature of the carbonation is preferably 35-85 ℃, and more preferably 65-80 ℃. The reaction temperature is lower than 35 ℃ and calcium carbonate particles are easily formed, and higher than 85 ℃ causes concentration change due to evaporation of water and causesenergy loss.

The carbon dioxide gas used in the carbonation may be pure carbon dioxide gas or a mixed gas of carbon dioxide and air. The carbon dioxide gas is introduced at a rate determined by the volume of the reactants or the amount of the reactants, as pure CO₂Calculating, the introduction speed is 100-1000 ml min^-1l^-1Preferably, it is preferably 100- min^-1l^-1If the gas mixture is the mixed gas, the amount of the gas mixture can be converted according to the proportion to determine the amount of the gas mixture. The carbon dioxide is introduced at a rate too low to reduce the carbonation reaction rate and lower the production efficiency, and the purity and quality of the reaction product are affected by the introduction rate too high.

The stirring speed in the carbonation reaction also has a significant influence on the reaction process. The stirring speed is suitably adjusted depending on the volume and capacity of the reaction slurry. Too low a stirring speed affects the uniformity of the carbonation reaction, and too high a stirring speed also adversely affects the quality of the product. In a 1 liter reaction system, the stirring speed is preferably 100 to 600rpm, more preferably 200 to 400 rpm.

The raw material slurry is supplemented in the reaction process, so that the defect that the reaction is difficult to uniformly react due to overlarge system viscosity caused by the reaction of high-concentration slurry and magnesium salt is avoided, the reaction suspension can uniformly react at a lower viscosity, and the addition amount of the slurry is gradually increased, so that the total reaction yield is increased. The adding process takes uniform adding without influencing the reaction process as a principle, can be added continuously at a constant speed, and can also be added intermittently for multiple times. The replenishing speed is controlled to be 0.04-0.20 mol h^-1l^-1Preferably, calcium carbonate particles are generated due to local unevenness when the supplement is too fast, and the reaction efficiency is affected when the supplement is too slow. The present invention features that magnesium salt solution is recovered and combined with the carbonating reaction to replenish slurry homogeneously, and the replenishing amount is 1-8 times, preferably 3-6 times, of the initial amount. And in the replenishing process, the carbon dioxide gas can be stopped from being introduced, the carbon dioxide gas can be introduced again after the replenishing is finished, or the carbon dioxide gas can be introduced while the slurry is added during carbonation.

The change of the pH value of the system in the reaction process can be used for controlling the reaction process. After the reaction of the slaked lime slurry and the magnesium salt solution is balanced, the pH value of the system is 7.6-9.0, after the carbonation reaction starts, the system is in a uniform reaction at the initial stage of the reaction, and the pH value in the system is slightly reduced. At the end of the reaction, the concentration of calcium ions is rapidly reduced with the growth of calcium carbonate crystals in the suspension, and the pH value is rapidly reduced to 7 or less. The carbonation reaction may be terminated.

Compared with the prior art, the method has the following positive effects:

according to the invention, the filtrate obtained by filtering the reaction product is recycled, so that the manufacturing cost of the calcium carbonate whiskers is reduced, and the pollution of the filtrate for pouring and washing the magnesium salt to water quality is avoided; the method for supplementing the raw material slurry for multiple times in the carbonation reaction avoids the defect of uneven reaction caused by the reaction of high-concentration slurry, and improves the single preparation yield; moreover, the aragonite type calcium carbonate crystal whisker prepared by the method has high purity, and the content of aragonite phase crystal whisker in the product is 93-98%; the length of the crystal whisker is 20-60 mu m, the length-diameter ratio of the crystal whisker is large and can reach 15-40; the yield is high and can reach 93-96%. . Therefore, the invention provides a method for producing calcium carbonate whiskers with high production efficiency, low production cost and high quality of calcium carbonate whiskers, which is suitable for industrial batch production.

Drawings

The invention is further explained below with reference to the drawings of the embodiments.

FIG. 1 is a process flow of the preparation method of aragonite type calcium carbonate whisker

FIG. 2 is a scanning electron micrograph of the calcium carbonate whisker obtained in reference example 2

FIG. 3 is a scanning electron micrograph of the calcium carbonate whisker prepared in example 2

Detailed Description

The following are non-limiting examples of the present invention.

Reference example 1

Adding 15 times of water into industrial slaked lime, stirring at room temperature for 0.5 hour at high speed to form slurry, settling and grading the slurry to remove coarse particles at the bottom to obtain refined raw material slurry, wherein the slurry particles are uniform, fine and have no coarse particles observable by naked eyes. The slurry concentration was measured to be 26.6g/100 g.

0.4L of water is put into a 0.5L three-neck flask,adding 50.8g of magnesium chloride hexahydrate, stirring to dissolve, adding 43.6g of calcium hydroxide slurry into the magnesium chloride solution, adding about 0.07L of water, washing into a bottle, heating while stirring, keeping the temperature at 80 ℃ for reaction for 0.5 hour to obtain a viscous suspension, and introducing 100mL/min of CO₂Controlling the carbonation reaction temperature to be 80 ℃, the stirring rate to be 250rmp, controlling the pH value at the initial reaction stage to be 7.96, slowly reducing the pH value to be 7.85 in the reaction, rapidly reducing the pH value to be 6.84 in the later reaction stage, and stopping the reaction. And filtering the product, adding water, washing for 1-2 times, and drying at the temperature of 60 ℃. Measuring aragonite phase content in the product to 98% with X-ray diffractometer, and observing crystal with scanning electron microscopeThe length of the whisker is 30-40 μm, and the length-diameter ratio is 20-30. The yield was 14.8g (reduced to 29.6g/L) and 95%.

Reference example 2.

Adding appropriate amount of water into industrial quicklime, drying to obtain calcium hydroxide, sieving to remove coarse impurities, adding 20 times of water, stirring to obtain coarse calcium hydroxide slurry, settling for three times, and removing coarse particles to obtain refined calcium hydroxide slurry with a slurry concentration of 32.4%

Taking the filtered filtrate obtained in reference example 1, and determining Mg by chemical titration²⁺Adding 2.0g of magnesium chloride hexahydrate into 0.4L of filtrate at the concentration of 0.48M, placing the filtrate in a 0.5L three-neck flask, stirring, adding 35.7g of refined slurry, adding about 0.08L of water, heating while stirring, keeping the temperature at 80 ℃ for reaction for 0.5 hour, and introducing CO₂The gasis subjected to carbonation reaction, the reaction temperature is controlled to be 80 ℃, and CO is added₂The gas introduction rate was 100mL/min and the stirring rate was 200 rmp. The reaction was stopped when the pH of the system was lowered to 6.80. After the product is filtered, washed and dried, the aragonite phase content is measured to be 95% by an X-ray diffractometer, the length of the whisker is observed to be 5-10 mu m by a scanning electron microscope, and the length-diameter ratio is 10-20.

Example 1.

Taking the same refined calcium hydroxide slurry and recovered filtrate as in reference example 2 as raw materials, taking 0.4L of the filtrate, adding 2.0g of magnesium chloride hexahydrate, placing the mixture in a 0.5L three-neck flask, adding 35.8g of the refined slurry while stirring, adding about 0.08L of water again, heating while stirring, and keeping the temperature at 80 ℃ for 0.5 hIntroducing CO at the same time₂The gas is subjected to carbonation reaction, the reaction temperature is controlled to be 80 ℃, and CO is added₂The gas was introduced at a rate of 100mL/min and the stirring rate was 250 rmp. The pH value of the suspension at the initial stage of the reaction was 8.05, the pH value of the system after 2 hours of the reaction was 7.96, 35.8g of the purified slurry was uniformly added at a rate of about 8.9 g/hour, and the reaction was continued until the pH value of the system was reduced to 6.86, and then the reaction was stopped. And filtering the product, then using the filtrate for the next reaction, adding water into the filter cake, washing the filter cake for 1-2 times, and drying at the temperature of 60-100 ℃ to obtain the calcium carbonate whisker, wherein the content of the aragonite phase whisker in the product is 94%, the length of the whisker is 20-30 mu m by observing through a scanning electron microscope, and the length-diameter ratio is 15-30. The yield was 29.4g (58.8 g/L conversion), 96%.

Example 2.

The preparation process and conditions were the same as in example 1, except that 71.6g of the refined calcium hydroxide slurry was additionally added at a rate of about 8.9 g/hr after 2 hours of carbonation, and the product obtained after the same post-treatment had a content of aragonite phase whiskers of 93%, a length of whiskers as observed by scanning electron microscope of 30 to 40 μm, and an aspect ratio of 20 to 30. The yield was 44.1g (88.2 g/L converted) and 94%.

Example 3.

Taking the same refined calcium hydroxide slurry and recovered filtrate as in example 1 as raw materials, taking 0.8L of the filtrate, adding 4.0g of magnesium chloride hexahydrate, placing in a 1L three-necked flask, adding 71.6g of the refined slurry under stirring, heating under stirring, keeping the temperature at 80 deg.C for 0.5 hr, and introducing CO₂The gas is carbonated, the reaction conditions are controlled as in example 1, 214.8g of refined slurry is uniformly added at a speed of about 17.8 g/h after 2 hours of carbonation reaction, and the reaction is stopped when the pH value of the system is reduced to 6.86 after the reaction is continued. Filtering, washing and drying to obtain the calcium carbonate crystal whisker, wherein the content of the aragonite phase crystal whisker in the product is 93 percent, the length of the crystal whisker is 50-60 mu m by observing through a scanning electron microscope, and the length-diameter ratio is 20-40. The yield was 118.9g (118.9g/L) and 93%.

Comparative example.

0.4L of water was put into a 0.5L three-necked flask, 162.6g of magnesium chloride hexahydrate was added and dissolved by stirring, and the same purified calcium hydroxide slurry 1 as in reference example 1 was added to the magnesium chloride solution39.3g, heating while stirring, keeping the temperature at 80 ℃ for 0.5 hour, reacting to obtain a paste-like extremely viscous liquid, increasing the stirring speed to 600rmp, and still not realizing uniform stirring. Introducing CO at 100mL/min₂Controlling the carbonation reaction temperature to be 80 ℃, the stirring rate to be 600rmp, the pH value at the initial stage of the reaction to be 10.4, slowly reducing the pH value during the reaction, rapidly reducing the pH value to be 6.90 at the later stage of the reaction, and stopping the reaction. And filtering the product, adding water, washing for 1-2 times, and drying at the temperature of 60 ℃. The aragonite phase content in the product is determined to be 30% by an X-ray diffractometer, the length of the whisker is 10-20 μm by observation of a scanning electron microscope, and most of the whisker is calcite type calcium carbonate particles.

The comparison between reference example 1 and reference example 2 shows that the filtrate after the preparation of calcium carbonate whiskers can be recycled, but only fine calcium carbonate whiskers can be obtained by preparing the filtrate under the same conditions by using only the recovered magnesium salt solution. The comparison example shows that if a high-concentration slurry reaction is adopted, the yield and the quality of the product are influenced because the system viscosity is too high and the reaction is not uniform. While examples 1, 2 and 3 show that calcium carbonate whiskers with high aspect ratio can be prepared by recovering the magnesium salt solution and uniformly replenishing slurry in the carbonation reaction, and the whiskers are lengthened with the increase of the amount of the replenished slurry, so that the reaction yield of a single batch is doubled. Therefore, the calcium carbonate crystal whisker with high purity and high length-diameter ratio can be prepared with high yield and low cost by adopting the technology of recovering themagnesium salt solution and uniformly replenishing the slurry in the carbonation reaction.

Claims

1. A process for preparing aragonite-type calcium carbonate whisker includes such steps as mixing lime hydrate or lime with solution of magnesium salt or recovered solution of magnesium salt, introducing carbon dioxide gas for carbonating reaction, supplementing lime hydrate slurry for several times during carbonating reaction, filtering, recovering magnesium salt filtrate containing magnesium ions, washing filter cake with water and baking.

2. The method for preparing aragonite-type calcium carbonate whiskers according to claim 1, characterized by comprising the following production steps:

(1) adding water into industrial quick lime to digest the industrial quick lime into calcium hydroxide slurry, settling and grading the slurry for 1-3 times to remove bottom settled coarse particles and dregs to serve as refined raw material slurry, adding 5-20 times of water into slaked lime to form slurry, and then settling and grading to obtain refined raw material slurry;

(2) the magnesium salt recovery liquid is subjected to chemical analysis to titrate Mg in the magnesium salt recovery liquid²⁺、Ca²⁺After concentration, according to a certain charge ratio R ([ MgCl]₂]/[Ca(OH)₂]) Mixing with calcium hydroxide slurry, reacting at room temperature-80 deg.C for 0.5-2 hr to reach reaction balance, and introducing CO at 35-85 deg.C₂The gas is subjected to carbonation reaction, and the flow of the carbon dioxide is kept to be 100-1000 ml min^-1l^-1The stirring speed is 100-600 rpm, and the pH value change of the reaction system is monitored by a pH meter;

(3) when the reaction is carried out for 2-4 hours and the pH value of the system is within the range of 7.0-8.0, calcium hydroxide slurry is uniformly supplemented according to 1-8 times of the original feeding amount, and the supplementing speed is controlled to be 0.04-0.20 mol h^-1l^-1After the replenishment is finished, continuing the reaction until the pH value of the system is reduced to below 7, and finishing the reaction;

3. The method for preparing aragonite-type calcium carbonate whiskers as claimed in claim 1 or 2, characterized in that a proper amount of water is added to quick lime to be slaked into calcium hydroxide by a dry method, then the calcium hydroxide is sieved to remove coarse impurities, 5-20 times of water is added to the mixture to be vigorously stirred to form calcium hydroxide slurry, or 5-20 times of excessive water is added to the quick lime to be digested into lime milk by a wet method, and the slurry or the lime milk is subjected to sedimentation and classification for 1-3 times to remove bottom sedimentation coarse particles and dregs as raw material slurry for later use. And for slaked lime, adding 5-20 times of water to form slurry, and then performing sedimentation classification to prepare refined raw material slurry, wherein the prepared slurry has uniform and fine particles and has no coarse particles observable by naked eyes. Or preparing quicklime by using limestone as a raw material through mild calcination, and refining to obtain the raw material slurry.

4. The process for preparing aragonite-type calcium carbonate whiskers according to claim 1 or 2, wherein the magnesium salt-recovering solution is a filtrate obtained by filtering a product in the process of preparing calcium carbonate whiskers, and the magnesium salt used may be anhydrous MgCl₂Alternatively, hydrated MgCl can be used₂The filtrate can be used directly or after adding part of the washing solution as recovery solution, and Mg in the filtrate²⁺、Ca²⁺The concentration can be titrated by chemical analysis method, and then [ MgCl]is obtained according to a certain charging ratio R₂]/[Ca(OH)₂]Determining the required amount of the recovered solution, if Mg is contained in the recovered solution²⁺If the concentration is higher than the required concentration, water can be added for dilution, if the concentration is lower than the required concentration, the required magnesium salt dosage can be calculated according to the feeding ratio and is complemented, or the recovered liquid can be heated and boiled to remove part of water and then is adjusted to the required concentration.

5. The method for preparing aragonite-type calcium carbonate whiskers as claimed in claim 4, wherein the raw material charge ratio of the reaction is R [ MgCl]₂]/[Ca(OH)₂]Between 1.0 and 6.0.

6. The method for preparing aragonite-type calcium carbonate whiskers as claimed in claim 5, wherein the feed ratio R of the raw materials for reaction is 1.4-4.0.

7. The method for preparing aragonite-type calcium carbonate whiskers according to claim 1 or 2, wherein the reaction temperature of carbonation is 35 to 80 ℃.

8. The process for preparing aragonite-type calcium carbonate whiskers according to claim 1 or 2, characterized in that it is used in carbonationThe carbon dioxide gas may be pure carbon dioxide gas or a mixed gas of carbon dioxide and air. The carbon dioxide gas is introduced at a rate determined by the volume of the reactants or the amount of the reactants, as pure CO₂Calculating, the introduction speed is 100-1000 ml min^-1l^-1Preferably, it is 100-^-1l^-1If the gas mixture is the mixed gas, the amount of the gas mixture can be converted according to the proportion to determine the amount of the gas mixture.

9. The method for preparing aragonite-type calcium carbonate whiskers as claimed in claim 1 or 2, wherein the magnesium salt solution is recovered and combined with the slurry to be uniformly supplemented in the carbonation reaction, the addition amount of the raw slurry in the reaction process is 1-8 times of the initial feeding amount on the principle that the viscosity of the system is increased but the reaction uniformity problem is not caused, and the supplementing speed is 0.04-0.20 mol h^-1l^-1。

10. The method for preparing aragonite-type calcium carbonate whiskers as claimed in claim 1 or 2, wherein the change in the pH of the system during the reaction is used to control the reaction process, the pH of the system is 7.6-9.0 after the reaction equilibrium between the slaked lime slurry and the magnesium salt solution, the system is in a uniform reaction at the initial stage of the reaction after the carbonation reaction, the pH in the system is slightly lowered, and the pH is rapidly lowered to 7 or less at the final stage of the reaction as the calcium carbonate crystals grow in suspension.