Method for preparing nano calcium carbonate by using fluorite leachate

Abstract

The invention discloses a method for preparing nano calcium carbonate by using fluorite leachate, and belongs to the technical field of hydrometallurgy. According to the method, metallurgical-grade fluorite is subjected to magnetic separation iron removal and hydrochloric acid solution leaching, high-purity fluorite and a calcium chloride solution are obtained, and meanwhile carbon dioxide gas is generated; removing impurities from the calcium chloride solution, reacting the calcium chloride solution with an ammonium carbonate solution to form a calcium carbonate emulsion, aging the calcium carbonate emulsion, filtering and separating to obtain nano calcium carbonate and filtrate; heating the filtrate to generate hydrogen chloride and ammonia gas, absorbing hydrogen chloride by water to form a hydrochloric acid solution, and recycling; ammonia gas and carbon dioxide are absorbed by water to generate an ammonium carbonate solution for recycling. According to the method, the metallurgical-grade fluorite is purified, meanwhile, the nano calcium carbonate product with the high additional value is prepared through the fluorite leaching solution, cyclic utilization of hydrochloric acid, ammonium carbonate and the like can be achieved, and the method has the advantages of being environmentally friendly, capable of saving energy, reducing consumption, simple, efficient and the like and is beneficial to large-scale application and popularization.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for processing fluorite leaching solution, in particular to a method for preparing nano calcium carbonate by using fluorite leaching solution, and belongs to the technical field of metallurgy. BACKGROUND

[0002] The existing known fluorite ore deposits mainly include quartz-fluorite type ore, calcite-fluorite type ore, sulfide-fluorite type ore and fluorite-barite-calcite type ore, etc. Among them, the separation of calcite-fluorite type ore is very difficult, mainly because the original ore mineral composition is complex, the mineral paragenetic relationship is close, the dissemination size is fine, and the floatability of gangue minerals calcite and fluorite is similar, so the separation is very difficult. Chinese patent application (CN111170349 A) discloses an acid leaching purification method suitable for fluorite ore, which specifically discloses that silicate and carbonate minerals in fluorite ore are dissolved in liquid phase by using organic acid solution or inorganic acid solution; the obtained solid phase is fluorite concentrate powder; acid solution is added to the liquid phase to convert calcium ions in the liquid phase into calcium salt precipitate, which is removed, and then the liquid phase is returned for acid recycling. The patent technology achieves the purpose of fluorite purification and realizes the recycling of acid, but the calcium ions are converted into solid waste calcium salt, and the acid gas is also absorbed by alkali liquor to obtain carbonate solid waste, which is not effectively utilized. SUMMARY

[0003] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for preparing nano calcium carbonate by using fluorite leaching solution, which can achieve the purification of metallurgical grade fluorite, prepare high value-added nano calcium carbonate products by using fluorite leaching solution, realize the recycling of hydrochloric acid and ammonium carbonate, and has the advantages of green environmental protection, energy saving and consumption reduction, simplicity and efficiency, which is beneficial to large-scale popularization and application.

[0004] In order to achieve the above technical purpose, the present application provides a method for preparing nano calcium carbonate by using fluorite leaching solution, which comprises the following steps:

[0005] 1) After the metallurgical grade fluorite is removed by magnetic separation, the calcium carbonate impurities are leached by hydrochloric acid solution to obtain high-purity fluorite and calcium chloride solution, and carbon dioxide gas is generated at the same time;

[0006] 2) After the calcium chloride solution is hydrolyzed and impurities are removed, ammonium carbonate solution is added at a rate of 1-5 mL / min at a temperature of 5-35℃, and the reaction is stirred, after the ammonium carbonate solution is added, the reaction mixture is aged for not more than 10 min, and then filtered and separated to obtain nano calcium carbonate and filtrate;

[0007] The concentration of ammonium carbonate in the ammonium carbonate solution is 0.5-2 mol / L;

[0008] The concentration of calcium chloride in the calcium chloride solution is 0.5-2 mol / L;

[0009] 3) the filtrate is heated and decomposed to produce hydrogen chloride and ammonia gas, the hydrogen chloride is absorbed by water to form a hydrochloric acid solution and recycled to step 1); the ammonia gas and the carbon dioxide are absorbed by water to generate an ammonium carbonate solution and recycled to step 2).

[0010] In the process of preparing nano calcium carbonate from the fluorite leaching solution, the key is to skillfully construct the circulation path of hydrochloric acid and ammonium carbonate, so that the high-value-added nano calcium carbonate product can be prepared from the fluorite leaching solution, and the generation of other waste salts, waste liquids and waste gases can be avoided, and the fluorite leaching solution can be truly utilized as a resource, thereby reducing the treatment cost.

[0011] The purification of the metallurgical-grade fluorite in the application mainly adopts the technical means of combination of magnetic separation and acid leaching, and through the iron removal process of magnetic separation, the magnetic minerals in the fluorite can be removed, the excessive consumption of acid liquid in the subsequent acid leaching process is avoided, and the subsequent hydrolysis impurity removal pressure is also reduced. The acid leaching adopts hydrochloric acid, and the advantage of hydrochloric acid leaching is that it is conducive to the subsequent construction of the hydrochloric acid circulation path.

[0012] The main ions in the fluorite leaching solution of the application are Ca 2+ , and the main impurity ions are Mn 2+ , Mg 2+ , Fe 3+ , Al 3+ , Pb 2+ , etc. The leaching solution is adjusted by Ca(OH)2 to make most of the metal impurity ions form hydroxide precipitates and be removed, and the remaining is a calcium chloride solution which is used as a calcium source for preparing nano calcium carbonate. The key of the application is to use ammonium carbonate as a carbonic acid source, to generate ammonium chloride by the reaction of ammonium carbonate and calcium chloride solution, and to decompose the ammonium chloride into hydrogen chloride and ammonia gas by high-temperature decomposition, so that the double circulation path of hydrochloric acid and ammonium carbonate can be constructed. The hydrogen chloride can be absorbed to form a hydrochloric acid circulation for the acid leaching process of the metallurgical-grade fluorite, and the ammonia gas and the carbon dioxide generated in the acid leaching process are absorbed together to be converted into ammonium carbonate which is recycled for the preparation process of nano calcium carbonate. Thus, the fluorite leaching solution can be utilized as a resource, and the environment is green and pollution-free.

[0013] The application can obtain nano calcium carbonate with high added value by strictly controlling the concentration, addition rate, reaction temperature and aging time of the ammonium carbonate solution.

[0014] As a preferred scheme, the strength of the magnetic separation is 0.5-1.0T. Through high-gradient magnetic separation, the magnetic minerals can be effectively removed, the acid consumption in the subsequent acid leaching process is reduced, and the introduction amount of iron impurities is also reduced.

[0015] As a preferred scheme, the leaching conditions are as follows: the mass concentration of the hydrochloric acid solution is 5-25%, the liquid-solid ratio is 5-20 L:1 kg, the leaching temperature is 10-35 DEG C, the stirring rate is 100-400 r / min, and the time is 30-40 min. Under the preferred leaching conditions, the removal of the acid-soluble impurities in the fluorite can be realized to obtain a high-purity fluorite product.

[0016] As a preferred scheme, calcium hydroxide is used as the alkali adjusting agent in the hydrolysis impurity removal process to adjust the pH to be in the range of 9.5-10.0. The use of calcium hydroxide as the alkali adjusting agent does not introduce new impurity metal ions, and by adjusting the pH to be in the appropriate range, most of the metal impurity ions such as Mn 2+ , Mg 2+ , Fe 3+ , Al 3+ , Pb 2+ , etc. can form hydroxide precipitates.

[0017] As a preferred scheme, the adding rate of the ammonium carbonate solution is 3-5 mL / min.

[0018] As a preferred scheme, the reaction temperature is 5-25 DEG C.

[0019] A large number of experiments show that: with the increase of the adding rate of the ammonium carbonate solution, a large number of nano calcium carbonate crystal nuclei can be rapidly generated, and the formation of the vaterite-type nano calcium carbonate is also facilitated, and when the adding rate is higher, the nano calcium carbonate with smaller and uniform particle size can be obtained. Meanwhile, the higher the reaction temperature is, the more the vaterite-type nano calcium carbonate with relatively poor stability tends to be converted into the calcite-type nano calcium carbonate with better stability, and the higher the temperature is, the faster the growth rate of the nano calcium carbonate crystal nucleus is, which can make the particle size of the nano calcium carbonate rapidly increase. Therefore, appropriately increasing the adding rate of the ammonium carbonate solution and controlling the reaction temperature to be lower can be more conducive to obtaining the vaterite-type nano calcium carbonate with smaller and uniform particle size.

[0020] As a preferred scheme, the concentration of the ammonium carbonate in the ammonium carbonate solution is 1.0-2.0 mol / L.

[0021] As a preferred scheme, the concentration of the calcium chloride in the calcium chloride solution is 1.0-2.0 mol / L.

[0022] The greater the concentration of the ammonium carbonate solution and the calcium chloride solution is, the more conducive to forming the vateritic nano calcium carbonate, and when the concentration of the two is low, the main tendency is to form the calcitic nano calcium carbonate, and the greater the concentration of the two is, the more conducive to forming the calcium carbonate with a larger particle size, and the lower the concentration of the two is, the more conducive to forming the calcium carbonate with a smaller particle size, therefore, by strictly controlling the reaction concentration of the ammonium carbonate solution and the calcium chloride solution, the balance of the particle size and the phase can be achieved, and the nano calcium carbonate product with a smaller particle size and mainly in the vateritic form can be obtained.

[0023] As a preferred scheme, the aging time is not more than 5 min. The nano calcium carbonate crystal nucleus realizes the crystal nucleus growth to form the nano calcium carbonate with a required particle size in the aging process, but each crystal form of the nano calcium carbonate has a tendency to transform into a crystal form with higher thermodynamic stability, and the thermodynamically unstable vaterite generally transforms into the stable calcite under general conditions, and the transformation mode mainly includes two modes of dissolution and recrystallization and solid-solid transformation, so that the nano calcium carbonate crystal form transforms from the vaterite to the calcite with the extension of the aging time, which conforms to the nano calcium carbonate crystal form transformation rule. Therefore, it is better to control the aging time to be 1-5 min, so as to obtain the vateritic calcium carbonate with a smaller particle size.

[0024] The filtrate after the precipitation of the calcium carbonate in the application is the ammonium chloride solution, which is heated to reflux, can decompose to produce water vapor, hydrogen chloride and ammonia gas mixed gas, the mixed gas is introduced into a long and inclined placed glass tube, the front section (lower end, mixed gas inlet section) of the glass tube is strongly cooled by an ice salt bath (the temperature is below-20 DEG C), the hydrogen chloride gas and the water vapor condense into hydrochloric acid solution along the reflux of the glass tube, and are collected and returned to the fluorite leaching process by adjusting the concentration. The rear section (upper end, gas outlet section) of the glass tube is cooled by an ice water bath (about 0 DEG C), and the end of the glass tube is connected to a water-filled gas washing bottle, and carbon dioxide gas generated in the acid immersion process is introduced into the gas washing bottle at the same time, so as to promote the absorption of ammonia gas, and obtain the ammonium carbonate solution, which is used for reaction with the calcium chloride solution.

[0025] Compared with the prior art, the technical scheme of the application has the following beneficial technical effects:

[0026] (1) The metallurgical grade fluorite can obtain high-purity fluorite through magnetic separation and hydrochloric acid leaching, and the fluorite leaching solution can obtain high-value nano calcium carbonate through purification and ammonium carbonate conversion, and the raw material of ammonium carbonate and hydrochloric acid can be recycled, so that new solid waste, waste liquid and waste gas are not generated, and the resource utilization of the fluorite leaching solution is realized, and the environment is protected.

[0027] (2) The process conditions for synthesizing the nano calcium carbonate are accurately controlled, so that the high-value nano calcium carbonate with a particle size of 138.2 nm, an average particle size of 2.667 microns and a uniform crystal form can be prepared.

[0028] (3) The application can greatly improve the utilization rate of the fluorite leaching solution, and has simple process, low cost, green environmental protection, and is suitable for industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The process flow chart of the application for preparing nano calcium carbonate from fluorite leaching solution.

[0030] Figure 2 XRD diagram of nano calcium carbonate product, a and c are standard cards, and b is the nano calcium carbonate product of example 1 (temperature is 25℃). DETAILED DESCRIPTION

[0031] The application is further described below in combination with the drawings of the specification and specific preferred embodiments, but does not limit the protection scope of the claims of the application.

[0032] The materials and instruments used in the following examples are commercially available reagents.

[0033] The fluorite leaching solution used in the examples of the application is a fluorite concentrate from a certain place in Hunan, which is used for metallurgical preparation of fluoride, and the recycling of the fluorite leaching solution.

[0034] Example 1

[0035] (1) The fluorite concentrate (CaF2 content ≈ 85%, calcium carbonate content ≈ 10%, and iron impurity content ≈ 5%) is subjected to magnetic separation, specifically: the fluorite concentrate is placed in a high gradient magnetic separator, the magnetic separation intensity is 1.0T, the feeding amount is 100g, the time is 10min, and a small amount of magnetic minerals in the fluorite concentrate is removed.

[0036] (2) The fluorite concentrate after magnetic separation is added to a 500ml beaker, concentrated hydrochloric acid is used as the leaching agent, deionized water is added to control the concentration of the leaching hydrochloric acid (10%), the liquid-solid ratio is 10L:1kg, the HCl solution is uniformly added to the beaker, and the acid leaching reaction is carried out at room temperature, the stirring rate is 200 r / min, and the time is 30min. After the reaction is completed, the solid-liquid products are separated by filtration, and the purity of the fluorite after leaching is greater than 99.5%.

[0037] (3) 100mL of the separated liquid is taken and placed in a beaker, the beaker is placed in a magnetic stirrer, the temperature of the magnetic stirrer is controlled at 25℃, a portable pH meter is placed in the beaker to monitor the pH of the leaching solution in real time, Ca(OH)2 powder is uniformly added to the beaker to adjust the pH to 10.0 to precipitate impurity ions, and after the reaction is completed, the solid-liquid products are separated by filtration.

[0038] (4) The filtrate was placed in a magnetic stirrer, and 0.5 mol / L (NH4)2CO3 solution was added to the CaCl2 solution (concentration adjusted to 0.5 mol / L) in step (3) at a rate of 3.6 mL / min to prepare nano calcium carbonate products. The reaction temperature was set to 25°C, 50°C, and 80°C, respectively. After the calcium carbonate emulsion was aged for 10 min, it was filtered and washed. The obtained filter cake was dried in an oven at 60°C for 12 h to obtain a powder sample of nano calcium carbonate. The nano calcium carbonate products prepared at different reaction temperatures are shown in Table 1.

[0039]

[0040] As shown in Table 1, when the reaction temperature was 25°C, the average particle size of the nano calcium carbonate particles was 8.87 μm, and the proportion of vaterite-type calcium carbonate was 70%. When the reaction temperature was increased to 80°C, the average particle size of the nano calcium carbonate particles increased to 23.81 μm, and the proportion of vaterite-type calcium carbonate was 0%. This indicates that the crystal cell size and particle size of the nano calcium carbonate gradually increase with increasing temperature, and the crystal type changes from vaterite to calcite. The above results show that a lower reaction temperature is beneficial to the preparation of vaterite-type nano calcium carbonate products with smaller particle size and uniform distribution.

[0041] (5) The filtrate after the separation of calcium carbonate was heated to release ammonia gas, HCl, and water vapor. The hydrochloric acid solution was recovered by condensation and recycled to step (2). The ammonia gas was reacted with the carbon dioxide to form an ammonium carbonate solution, which was recycled to step (4).

[0042] Example 2

[0043] (1) The fluorite concentrate (CaF2 content ≈ 85%, calcium carbonate content ≈ 10%, and iron impurity content ≈ 5%) was subjected to magnetic separation. Specifically, the fluorite concentrate was placed in a high-gradient magnetic separator, the magnetic separation intensity was 1.0 T, the feeding amount was 100 g, and the time was 10 min to remove a small amount of magnetic minerals from the fluorite concentrate.

[0044] (2) The fluorite concentrate after magnetic separation was added to a 500 ml beaker, and concentrated hydrochloric acid was used as the leaching agent. Deionized water was added to control the concentration of the leaching hydrochloric acid (10%). The liquid-solid ratio was 10 L:1 kg, and the HCl solution was uniformly added to the beaker at room temperature for acid leaching reaction. The stirring rate was 200 r / min, and the time was 30 min. After the reaction, the solid-liquid products were separated by filtration. The purity of the fluorite after leaching was greater than 99.5%.

[0045] (3) Take 100 mL of the separated liquid and place it in a beaker, and place the beaker in a magnetic stirrer, control the temperature of the magnetic stirrer to be 25°C, place a portable pH meter in the beaker to monitor the pH of the leaching liquid in real time, and uniformly add Ca(OH)2 powder to the beaker to adjust the pH to 10.0 to precipitate impurity ions, and after the reaction is completed, filter and separate the solid-liquid products.

[0046] (4) Place the filtrate in a magnetic stirrer, and according to the stoichiometric ratio of ammonium carbonate and calcium chloride, prepare a 0.5 mol / L (NH4)2CO3 solution, and slowly drop the (NH4)2CO3 solution into the CaCl2 solution (concentration adjusted to 0.5 mol / L) of (3) through a peristaltic pump to prepare a nano calcium carbonate product, and the reaction temperature is set to 25°C, and the titration speed of ammonium carbonate is 1.2 mL / min, 2.4 mL / min, and 3.6 mL / min, respectively. After the calcium carbonate emulsion is aged for 10 min, it is suction filtered and washed, and the obtained filter cake is dried in an oven at 60°C for 12 h to obtain a powdery nano calcium carbonate sample. The nano calcium carbonate products prepared at different titration speeds are shown in Table 2.

[0047]

[0048] As can be seen from Table 2, in Example 2, when the titration speed is 2.4 mL / min and 3.6 mL / min, in addition to the characteristic peaks of calcite at the same position, there are also characteristic peaks of vaterite, and the content of vaterite is 15% and 70%, respectively. Therefore, increasing the titration speed promotes the formation of vaterite-type nano calcium carbonate. Increasing the titration speed of (NH4)2CO3 increases the amount of drop in the same time, and the cell generation rate is fast, which is conducive to the rapid formation of vaterite. When the titration speed is 1.2 mL / min, the nano calcium carbonate particles are relatively large and have serious stacking phenomenon, so a higher titration speed is beneficial to the preparation of nano calcium carbonate with smaller particle size.

[0049] (5) The filtrate after filtering and separating the calcium carbonate is heated to release ammonia gas and HCl and water vapor, the hydrochloric acid solution is recovered by condensation and recycled to step (2); the ammonia gas and the carbon dioxide are reacted to generate an ammonium carbonate solution and recycled to step (4).

[0050] Example 3

[0051] (1) The fluorite concentrate (CaF2 content ≈ 85%, calcium carbonate content ≈ 10%, and iron impurity content ≈ 5%) is subjected to magnetic separation, specifically: the fluorite concentrate is placed in a high gradient magnetic separator, the magnetic separation intensity is 1.0 T, the feeding amount is 100 g, and the time is 10 min, to remove a small amount of magnetic minerals in the fluorite concentrate.

[0052] (2) The magnetically separated fluorite ore is added into a 500 ml beaker, concentrated hydrochloric acid is used as leaching agent, deionized water is added to control the concentration of the leaching hydrochloric acid (10%), the beaker is uniformly added with HCl solution at a liquid-solid ratio of 10L:1 kg, the acid leaching reaction is carried out at room temperature, the stirring rate is 200 r / min, and the time is 30 min. After the reaction is completed, the solid-liquid products are separated by filtration, and the purity of the fluorite after leaching is greater than 99.5%.

[0053] (3) 100 mL of the separated liquid is taken into a beaker, the beaker is placed in a magnetic stirrer, the temperature of the magnetic stirrer is controlled to be 25°C, a portable pH meter is placed in the beaker to monitor the pH of the leaching liquid in real time, Ca(OH)2 powder is uniformly added into the beaker to adjust the pH to 10.0 so that impurity ions are precipitated, and after the reaction is completed, the solid-liquid products are separated by filtration.

[0054] (4) The filtrate is placed in a magnetic stirrer, 0.5 mol / L of (NH4)2CO3 solution is prepared according to the metering ratio of ammonium carbonate and calcium chloride, the (NH4)2CO3 solution is slowly added into the CaCl2 solution (the concentration is adjusted to 0.5 mol / L) of (3) through a peristaltic pump to prepare a nano calcium carbonate product, and the reaction temperature is set to be 25°C. The titration speed of the ammonium carbonate solution is 3.6 mL / min, the calcium carbonate emulsion is aged for 0 min, 5 min and 10 min, then is suction filtered and washed, the obtained filter cake is dried in a 60°C oven for 12 h to obtain a powdery nano calcium carbonate sample. The nano calcium carbonate products prepared at different aging times are shown in Table 3.

[0055]

[0056] That is, the vaterite-type nano calcium carbonate is converted into calcite-type calcium carbonate with the extension of the aging time. During the formation of the nano calcium carbonate, there is a tendency of conversion from each crystal form to a thermodynamically more stable crystal form, and the thermodynamically unstable vaterite-type calcium carbonate is generally converted into the stable calcite-type calcium carbonate under general conditions, and the conversion mode mainly includes dissolution and recrystallization and solid-solid conversion. Therefore, with the extension of the aging time, the nano calcium carbonate crystal form is converted from the vaterite type to the calcite type, which accords with the crystal form conversion rule of the nano calcium carbonate. To obtain the vaterite-type nano calcium carbonate, the aging time is preferably controlled to be within 10 min.

[0057] (5) The filtrate after the filtration separation of the calcium carbonate is subjected to heating decomposition to release ammonia gas, HCl and water vapor, the hydrochloric acid solution is recovered by condensation and recycled to step (2); the ammonia gas and the carbon dioxide are reacted to generate an ammonium carbonate solution by absorption, and the ammonium carbonate solution is recycled to step (4).

[0058] Example 4

[0059] (1) The fluorite concentrate (CaF2 content ≈ 85%, calcium carbonate content ≈ 10%, iron impurity content ≈ 5%) is subjected to magnetic separation, specifically: the fluorite concentrate is placed in a high gradient magnetic separator, the magnetic separation intensity is 1.0T, the feed is 100g, the time is 10min, and a small amount of magnetic mineral in the fluorite concentrate is removed.

[0060] (2) The fluorite concentrate after magnetic separation is added to a 500ml beaker, concentrated hydrochloric acid is used as the leaching agent, deionized water is added to control the leaching hydrochloric acid concentration (10%), according to the liquid-solid ratio 10L:1kg, the beaker is uniformly added with HCl solution, and the acid leaching reaction is carried out at room temperature, the stirring rate is 200 r / min, and the time is 30min. After the reaction is completed, the solid-liquid products are separated by filtration, and the purity of the fluorite after leaching is greater than 99.5%.

[0061] (3) 100mL of the separated liquid is taken and placed in a beaker, and the beaker is placed in a magnetic stirrer, the temperature of the magnetic stirrer is controlled at 25°C, a portable pH meter is placed in the beaker to monitor the pH of the leaching liquid in real time, Ca(OH)2 powder is uniformly added to the beaker to adjust the pH to 10.0 to precipitate impurity ions, and after the reaction is completed, the solid-liquid products are separated by filtration.

[0062] (4) According to the stoichiometric ratio of ammonium carbonate and calcium chloride, 0.5mol / L, 1mol / L and 2mol / L (NH4)2CO3 solution is slowly added to the CaCl2 solution (the concentration is adjusted to 0.5mol / L, 1mol / L and 2mol / L respectively) in (3) by peristaltic pump to prepare nano calcium carbonate products, and the reaction temperature is set to 25°C. The titration speed of ammonium carbonate solution is 3.6mL / min, the calcium carbonate emulsion is aged for 10min, then it is suction filtered and washed, the obtained filter cake is dried in a 60°C oven for 12h to obtain a powdery nano calcium carbonate sample. The nano calcium carbonate products prepared at different aging times are shown in Table 4.

[0063]

[0064] When the reaction concentration is 0.5 mol / L and 1 mol / L, the nano calcium carbonate is a mixture of calcite type and vaterite type, and the relative content is 70% vaterite + 30% calcite and 90% vaterite + 10% calcite respectively. When the concentration increases to 2 mol / L, the nano calcium carbonate is pure vaterite type. The above shows that the reaction concentration has a significant effect on the crystal type of nano calcium carbonate, and the crystal type is converted to vaterite as the reaction concentration increases. Therefore, lower concentration is more conducive to the formation of calcite type nano calcium carbonate with small particle size, and higher concentration is more conducive to the formation of vaterite type nano calcium carbonate product with larger particle size.

[0065] (5) The filtrate after filtering and separating calcium carbonate is heated to release ammonia gas, HCl and water vapor, the hydrochloric acid solution is recovered by condensation and recycled to step (2); the ammonia gas and the carbon dioxide are reacted to generate ammonium carbonate solution and recycled to step (4).

Claims

1. A method for preparing nano-calcium carbonate using fluorite leachate, characterized in that: Includes the following steps: 1) After removing iron from metallurgical grade fluorite by magnetic separation, calcium carbonate impurities are leached out with hydrochloric acid solution to obtain high-purity fluorite and calcium chloride solution, while carbon dioxide gas is generated at the same time. 2) After the calcium chloride solution is decontaminated by water, ammonium carbonate solution is added at a rate of 1-5 mL / min and stirred at 5-35℃. After the ammonium carbonate solution is completely added, the reaction mixture is aged for no more than 10 minutes, filtered and separated to obtain nano-calcium carbonate and filtrate. The concentration of ammonium carbonate in the ammonium carbonate solution is 0.5~2 mol / L; The concentration of calcium chloride in the calcium chloride solution is 0.5~2 mol / L; 3) The filtrate is heated and decomposed to produce hydrogen chloride and ammonia. The hydrogen chloride is absorbed by water to form hydrochloric acid solution and is recycled to step 1); the ammonia and carbon dioxide are absorbed by water to form ammonium carbonate solution and are recycled to step 2).

2. The method for preparing nano-calcium carbonate using fluorite leachate according to claim 1, characterized in that: The intensity of the magnetic separation is 0.5~1.0T.

3. The method for preparing nano-calcium carbonate using fluorite leachate according to claim 1, characterized in that: The leaching conditions are as follows: the mass concentration of hydrochloric acid solution is 5-25%, the liquid-to-solid ratio is 5-20 L:1 kg, the leaching temperature is 10-35℃, the stirring rate is 100-400 r / min, and the time is 30-40 min.

4. The method for preparing nano-calcium carbonate using fluorite leachate according to claim 1, characterized in that: In the process of decontamination by water, calcium hydroxide is used as an alkali regulator to adjust the pH to the range of 9.5 to 10.

0.

5. The method for preparing nano-calcium carbonate using fluorite leachate according to claim 1, characterized in that: The ammonium carbonate solution is added at a rate of 3-5 mL / min.

6. The method for preparing nano-calcium carbonate using fluorite leachate according to claim 1, characterized in that: The reaction temperature is 5~25℃.

7. The method for preparing nano-calcium carbonate using fluorite leachate according to claim 1, characterized in that: The concentration of ammonium carbonate in the ammonium carbonate solution is 1.0~2.0 mol / L; The concentration of calcium chloride in the calcium chloride solution is 1.0~2.0 mol / L.

8. The method for preparing nano-calcium carbonate using fluorite leachate according to claim 1, characterized in that: The aging time shall not exceed 5 minutes.

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