CN104790024A - Preparation method for aragonite calcium carbonate whisker with high length-diameter ratio - Google Patents

Abstract

The invention relates to a method for preparing aragonite calcium carbonate whiskers with high aspect ratio. The specific implementation steps are: adding the prepared 1.0-8.2wt% Ca(OH) ₂ suspension into the carbonization reactor, adding MgCl ₂ into the reactor in the form of an aqueous solution, and controlling the magnesium-calcium ratio R to be 0.6-2.0, The carbonization temperature is 30-85°C. Under the action of stirring, CO ₂ and N ₂ with a flow rate of (5-120) m ³ /(h·m ³ suspension) are mixed and then passed into the bottom of the carbonization reactor. Gas distribution The instrument uses a digital display pH meter to track the whole process of carbonization reaction. Suction filter and wash the slurry after carbonization, dry at 80° C. for 5 hours, and pulverize to obtain whisker calcium carbonate samples. Compared with the existing carbonation method for preparing aragonitic calcium carbonate whiskers, the one-step synthesis of calcium carbonate whiskers with high aspect ratio does not require multi-stage growth, and the operation is simpler; no need for magnesium chloride and calcium hydroxide In the equilibrium stage of the co-heating reaction, the ratio of magnesium to calcium in the reaction slurry is low, and the synthesis efficiency is higher.

Description

A kind of preparation method of high aspect ratio aragonite type calcium carbonate whisker

technical field

The invention belongs to the technical field of inorganic salt materials, and relates to a preparation method of aragonite calcium carbonate whiskers with high aspect ratio.

Background technique

Inorganic whiskers, as a material grown in the form of a single crystal, generally exhibit a needle-like or fibrous shape with a high aspect ratio. The atomic arrangement is highly ordered, the whisker structure is relatively complete, and the internal defects are less, so its strength and modulus are close to the theoretical value of the complete whisker material. It is a high-performance reinforcement and toughening of new composite materials. agent.

At present, a few whiskers such as SiC, SiN, Al ₂ O ₃ , ZnO, potassium titanate, mullite, and aluminum borate have been successfully industrialized, but their large-scale application and development are hindered by their high production costs. A more cost-effective whisker to replace the existing high-priced whisker has become one of the important research goals in the materials industry.

In recent years, with the development of research, the appearance of a new material, calcium carbonate whisker, which is rich in raw materials, low in price and high in performance, has aroused the enthusiasm of many researchers. The preparation of calcium carbonate whisker has become a research hotspot at home and abroad. At present, scholars at home and abroad have done a lot of research on the synthesis of aragonite calcium carbonate whiskers. The main point of the synthesis is to reduce the supersaturation at a certain temperature to inhibit the formation of calcite. In summary, there are the following six methods: (1) Double decomposition method; (2) Ca(HCO ₃ ) ₂ thermal decomposition method; (3) urea hydrolysis method; (4) sol-gel method; (5) carbonation method.

The general principle of the metathesis reaction method is to combine soluble Ca ²⁺ salts (such as CaCl ₂ , Ca(NO ₃ ) _2, etc.) with soluble salts (such as Na ₂ CO ₃ , (NH ₄ ) ₂ CO ₃ A method in which a metathesis reaction occurs at 100°C to obtain calcium carbonate whiskers. Relatively speaking, the solubility of the reactants required by this method is relatively low, and the whisker synthesis speed is relatively slow, so generally it is only used in the laboratory for the production of a small amount of calcium carbonate whiskers. degree, you need to add admixtures to it. In addition because of the inhomogeneous reaction temperature and solubility of this method, it is easy to affect the aspect ratio and the quality of the calcium carbonate whiskers synthesized.

The basic principle of the Ca(HCO ₃ ) ₂ thermal decomposition method is to disperse the relatively high-purity limestone powder in water at 2°C and then introduce CO ₂ gas into it, and control the reaction temperature and the flow rate of carbon dioxide gas to prepare a solution. Then control the temperature of reaction, the rate of heating, the calcium carbonate whisker that the intensity of stirring makes. Compared with other methods, the solubility and temperature of the reactants of this method are easier to control, do not need to add any seed crystals or control agents, and the operation is relatively simple, but the long diameter of the calcium carbonate whiskers prepared by this method The ratio is not so ideal, and the energy consumption is relatively high.

The basic principle of the urea hydrolysis method is to obtain calcium carbonate whiskers through the chemical reaction of urea and soluble calcium salt system. The preparation method of this method is simple, the conditions are easy to control, and there is no need to add seed crystals or crystal form control agents, but the reaction requires a large amount of urea as a reactant, and the production cost is too high. In addition, the reaction is carried out under high temperature and high pressure, which requires high energy consumption and high risk, so it is difficult to form industrial production.

The sol-gel method is a wet chemical preparation method that can prepare from zero-dimensional to three-dimensional materials. Its basic principle is to convert calcium carbonate into calcium-containing intermediates through a series of steps, and then calcine the intermediates to obtain calcium carbonate whiskers. The reaction process of this method is easy to control, and the prepared product has the characteristics of good uniformity and large aspect ratio. However, compared with other traditional preparation methods, the sol-gel method needs to be reacted at 700 ° C, which requires The requirements for equipment are relatively high, and it is not conducive to industrial production.

The carbonization method is currently the most researched and relatively mature method at home and abroad. Its basic principle is to introduce carbon dioxide into the calcium hydroxide suspension, and prepare aragonitic calcium carbonate whiskers under the action of crystal form control agents (magnesium chloride, phosphoric acid, etc.) or crystal seeds, similar to the industrial synthesis of light calcium carbonate. The gas-liquid method, so it is also called the gas-liquid method. The carbonization method is relatively strict on the reaction temperature control, but because of its low production cost, the raw materials can basically come from the widely existing limestone resources in nature, and its process is simple and easy to operate, which is similar to the traditional method of producing light calcium carbonate. The calcium carbonate whisker has the advantages of high purity and large aspect ratio, and is currently the most likely technology for large-scale industrial production.

Chinese patent (Patent No. ZL201010280862.6) discloses a method for preparing calcium carbonate whiskers with a high aspect ratio. The method utilizes bischofite as a crystal form control agent, recycles the mother liquor, and prepares a whisker with a diameter of Calcium carbonate whiskers with a length of 1.5-3.0 μm and a length of 30-50 μm. This method recycles the mother liquor, which reduces the production cost, but the preparation process needs to be divided into three different stages, using the whiskers from the previous stage as seeds, and relying on multi-stage growth, and the lime slurry needs to be adjusted in each stage And the mass concentration of magnesium chloride solution, operation is comparatively complicated; And the mass concentration of magnesium chloride in the reaction solution is more than 5 times of calcium hydroxide mass concentration. Chinese patent (Patent No. ZL200410022834.9) discloses a method for manufacturing high-purity aragonite calcium carbonate whiskers. In the method, magnesium salt is used as a crystal form control agent. In the process of preparing calcium carbonate whiskers, the magnesium salt solution is reused, and slaked lime slurry is evenly added in the carbonation reaction to prepare aragonite phase whiskers with a content of 95%. Whisker calcium carbonate with a length of 20-60 μm and an aspect ratio of 15-40. However, this method needs to react magnesium salt and calcium hydroxide slurry at room temperature to 80°C for 0.5 to 2 hours to reach a reaction equilibrium, and then introduce carbon dioxide to carry out carbonization reaction. Large, the ratio R of calcium to magnesium is about 4.0, and the cost of raw materials is relatively high. Literature (Acta Inorganic Chemistry, 2008, 24(5): 737-742) in the ordinary gravitational field, using soluble phosphate as the crystal form control agent, for the first time synthesized by one-step carbonization method to obtain a crystal with a length of 23 μm and an aspect ratio of 15.3 Calcium carbonate whisker products, the whisker aragonite phase content is 88.3%, high degree of crystallization, good stability. This method realizes the one-step synthesis of calcium carbonate whiskers, and the process operation is simple, but the content of the aragonite phase of the obtained whiskers is slightly lower, and the aspect ratio is also slightly smaller.

In general, using magnesium chloride as a seed control agent is superior to other additives. Moreover, the price of magnesium salt is much lower than other crystal form control agents. Therefore, choosing magnesium chloride as the crystal form control agent and simplifying the production process for preparing whisker calcium carbonate by carbonation is of great significance for realizing the industrialization of calcium carbonate whiskers.

Contents of the invention

The purpose of this invention is to provide a kind of preparation method of aragonite type calcium carbonate with low cost and simple process, which is characterized in that it utilizes carbonation method, under the condition that magnesium chloride is the crystal form control agent, one-step method synthesizes high aspect ratio Aragonite calcium carbonate whiskers. The specific implementation is as follows:

1. Put quicklime into distilled water at 60-90°C according to a certain gray-water ratio, seal and stir for digestion for 1-4 hours, pass the obtained Ca(OH) ₂ suspension through a 200-mesh standard sieve, add water to adjust to a certain concentration, and set aside .

2. The prepared mass concentration of 1.0-8.2wt% Ca(OH) ₂ suspension is added to the carbonization reactor, and MgCl ₂ is added to the reactor in the form of an aqueous solution to control the magnesium-calcium ratio R (magnesium chloride and hydroxide Calcium mass ratio) is 0.6-2.0, carbonization temperature is 30-85°C, under stirring, CO ₂ and N ₂ with a flow rate of (5-120) m ³ /(h·m ³ suspension) are mixed Finally, it is passed into the gas distributor at the bottom of the carbonization reaction kettle, and a digital display pH meter is used to track the whole process of carbonization reaction. When the pH of the reaction slurry is 6.5-7.0, the aeration is stopped, and the carbonization reaction ends. Suction filter the carbonized slurry and wash it with deionized water twice, discard the supernatant, and dry at 80° C. for 5 hours to obtain a sample.

The present invention prepares aragonite type calcium carbonate technology compared with existing carbonation method, its outstanding substantive feature and remarkable progress are:

1. Without relying on multi-stage growth, calcium carbonate whiskers with high aspect ratio can be synthesized in one step, and the operation is simpler.

2. There is no need to carry out the co-heating reaction equilibrium stage of magnesium chloride and calcium hydroxide, the ratio of magnesium to calcium is low, and the synthesis efficiency is higher.

Description of drawings

Figure 1 is a scanning electron microscope photo of whisker calcium carbonate

Figure 2 is a statistical distribution diagram of whisker calcium carbonate length and diameter

Figure 3 is the EDS energy spectrum of whisker calcium carbonate

Detailed ways

(1) In the examples, the calculation of the mass fraction of the whisker calcium carbonate aragonite phase. The XRD collection of illustrative plates of contrast sample, calculate the massfraction of calcium carbonate product arsonite phase by formula (1):

$\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; 3.9</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, y is the mass fraction of the arsonite phase in the calcium carbonate product; Ia is the integrated intensity value of the strongest characteristic peak of the arsonite phase in the XRD pattern, and Ic is the integrated intensity value of the strongest characteristic peak of the calcite phase in the XRD pattern.

(2) In an embodiment, the calculation of whisker calcium carbonate aspect ratio. Select SEM photos of different areas, measure the length and median diameter of 100 whiskers, and calculate their aspect ratio.

Example 1

The preparation concentration is (1) 2.0wt%; (2) 2.9wt%; (3) 3.8wt% or (4) 4.7wt% Ca (OH) _Suspension joins in the carbonization reactor, according to magnesium calcium ratio R Add an aqueous solution of magnesium chloride to 1.0, control the carbonization temperature ^to 75°C, apply stirring, and then add CO ₂ with a flow rate of ^{20m 3} /(h·m ³ suspension) and CO After N ₂ is mixed, it is passed into the gas distributor at the bottom of the carbonization reaction kettle, and a digital display pH meter is used to track the whole process of carbonization reaction. When the pH of the reaction slurry is 7, the aeration is stopped, and the carbonization reaction ends. The slurry after carbonization is suction filtered, washed and dried. Calculation of whisker calcium carbonate aragonite phase content and aspect ratio, the results are shown in Table 1.

Example 2

The prepared concentration is 2.0wt% Ca(OH) ₂ suspensions are added in the carbonization reactor, and the magnesium chloride aqueous solution is added as 1.0 according to the ratio R of magnesium to calcium, and the carbonization temperature is controlled to be (1) 55° C.; (2) 65° C.; (3) ) 75°C or (4) 85°C, apply agitation, and then mix CO ₂ with a flow rate of 20m ³ /(h·m ³ suspension) and N ₂ with a flow rate of 40m ³ /(h·m ³ suspension) Finally, it is passed into the gas distributor at the bottom of the carbonization reaction kettle, and a digital display pH meter is used to track the whole process of carbonization reaction. When the pH of the reaction slurry is 7, the aeration is stopped, and the carbonization reaction ends. The slurry after carbonization is suction filtered, washed and dried. Calculation of whisker calcium carbonate aragonite phase content and aspect ratio, the results are shown in Table 1.

Example 3

The preparation concentration is 2.0wt% Ca (OH) ₂ suspensions are added in the carbonization reactor, according to magnesium calcium ratio (1) R=0.8; (2) R=1.0; (3) R=1.2 or (4) R =1.4 Add magnesium chloride aqueous solution, control the carbonization temperature to 75°C, apply stirring, and then add 20m ³ /(h·m ³ suspension) of CO ₂ and flow rate of 40m ³ /(h·m ³ suspension) N ₂ After mixing, it is passed into the gas distributor at the bottom of the carbonization reaction kettle, and a digital display pH meter is used to track the whole process of carbonization reaction. When the pH of the reaction slurry is 7, the aeration is stopped, and the carbonization reaction ends. The slurry after carbonization is suction filtered, washed and dried. Calculation of whisker calcium carbonate aragonite phase content and aspect ratio, the results are shown in Table 1.

Table 1

Claims (7)

1. A preparation method of high aspect ratio aragonite calcium carbonate whiskers. The specific steps are: (1) Put quicklime into hot water for digestion according to the ratio of gray to water of 1:4~5, pass through a 200-mesh standard sieve, add water to adjust to a certain concentration, and set aside. (2) Add the prepared Ca(OH) ₂ suspension into the carbonization reactor, add a crystal form control agent, mix CO ₂ and N ₂ and pass it into the gas distributor at the bottom of the carbonization reactor for carbonization reaction. Use a digital display pH meter to track the whole process of the carbonization reaction. When the pH of the reaction slurry is 6.5-7.0, stop the ventilation and the carbonization reaction ends. (3) Suction filter and wash the slurry after the carbonization is completed, repeat twice, dry at 80° C. for 5 hours, and pulverize to obtain the desired whisker calcium carbonate sample. 2. The method according to claim 1, characterized in that: the temperature of the hot water for digestion in the step (1) is 60-90° C., and the digestion time is 4 hours. 3. The method according to claim 2, characterized in that: said step (1) the concentration of the Ca(OH) ₂ suspension is 1.0-8.2 wt%. 4. The method according to claim 3, characterized in that: the crystal form control agent added in the step (2) is magnesium chloride, and the ratio R of magnesium to calcium is 0.6-2.0. 5. The method according to claim 4, characterized in that: in the step (2), magnesium chloride is added to the calcium hydroxide suspension, and the carbonization reaction is carried out without co-heating reaction equilibrium. 6. The method according to claim 5, characterized in that: the carbonization reaction process in the step (2) requires a circulating water bath to control the carbonization temperature and apply stirring. Wherein the carbonization temperature is 30-85°C. 7. The method according to claim 6, characterized in that: in the step (2), the flow rate of CO ₂ fed into the gas distributor during the carbonization reaction is (5-120)m ³ /(h·m ³ suspension), the flow rate of N ₂ is (5-120) m ³ /(h·m ³ suspension).