Preparation method of nano calcium carbonate

Abstract

The invention relates to the technical field of carbonate, and discloses a preparation method of nano calcium carbonate. The preparation method comprises the following steps: S1, providing a raw material solution rich in calcium and magnesium ions; s2, carrying out magnesium removal treatment on the raw material solution to obtain a mixed solution; s3, adding an alkaline solution into the mixed solution, introducing carbon dioxide gas with the concentration of 70-90%, and carrying out carbonization reaction to obtain a suspension; s4, adding sodium stearate into the suspension, and carrying out ball milling and mixing to modify calcium carbonate; s5, washing and desalting to obtain active nano calcium carbonate slurry; and S6, dehydrating and drying the active nano calcium carbonate slurry to obtain the nano calcium carbonate. The preparation process is simple in flow, free of calcination and low in energy consumption, the nano calcium carbonate is prepared by recycling the waste liquid produced by refined salt, the raw material cost for preparing the nano calcium carbonate is reduced, and resource regeneration is also realized.

Description

Technical Field

[0001] The invention relates to the field of carbonates, in particular to a method for preparing nano calcium carbonate. Background Art

[0002] Nano calcium carbonate, also known as ultrafine calcium carbonate, is a stable inorganic material with the advantages of large specific surface area, non-toxicity, and good biocompatibility. It is widely used in many fields. The most mature industry for the application of nano calcium carbonate is the plastics industry, which is mainly used in high-end plastic products. It can improve the rheological properties of plastic masterbatch and improve its formability. It can be used as a plastic filler to enhance toughness and reinforcement, improve the bending strength and bending elastic modulus, heat deformation temperature and dimensional stability of plastics, and also give plastics thermal hysteresis. Nano calcium carbonate is used in ink products to show excellent dispersibility and transparency, excellent gloss, excellent ink absorption and high drying properties. Nano calcium carbonate is used as an ink filler in resin-based inks, and has the advantages of good stability, high gloss, no effect on the drying properties of printing inks, and strong adaptability.

[0003] The preparation of traditional nano-calcium carbonate often uses limestone as raw material and is prepared by high-temperature calcination, such as the invention patent with application number 201710681913.8, a method for preparing nano-calcium carbonate, and the invention patent with application number 202211585989.8, a method for preparing nano-calcium carbonate for low-modulus and high-elasticity silicone adhesive. The aforementioned patents have the problems of complex process, high energy consumption and high cost. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a method for preparing nano calcium carbonate which has a simple process, does not require calcination, consumes less energy and can achieve resource regeneration.

[0005] A method for preparing nano calcium carbonate comprises the following steps:

[0006] S1 provides a raw material solution rich in calcium and magnesium ions;

[0007] S2 removes magnesium from the raw material liquid to obtain a mixed liquid;

[0008] S3: adding an alkaline liquid to the mixed liquid, introducing carbon dioxide gas with a concentration of 70% to 90% to perform a carbonization reaction to obtain a suspension;

[0009] S4: adding sodium stearate to the suspension, and mixing by ball milling to modify the calcium carbonate;

[0010] S5 washing and desalting to obtain active nano calcium carbonate slurry;

[0011] S6: the active nano-calcium carbonate slurry is dehydrated and dried to obtain nano-calcium carbonate.

[0012] As a further improvement of the above scheme, the waste liquid generated in the brine purification step of the refined salt production process is used as the raw material liquid. At present, the refined salt production uses sedimentary salt rock formed by evaporation of seawater or lake action as raw material, uses water to dissolve the salt rock-shaped brine, removes calcium and magnesium ions in the brine to form refined brine, and the crystals produced by evaporating the refined brine are refined salt. In the process of removing calcium and magnesium ions from the brine, waste liquid rich in calcium ions will be generated. Based on this, the present invention reuses the waste liquid from the refined salt production to produce nano calcium carbonate, reduces the raw material cost of nano calcium carbonate production, and realizes resource regeneration.

[0013] As a further improvement of the above scheme, the method for removing magnesium to obtain a mixed solution is specifically performed as follows:

[0014] S21 adds lime emulsion to the raw material liquid, stirs and mixes, and the lime emulsion reacts with the magnesium ions in the raw material liquid, and the magnesium ions are precipitated in the form of a precipitate, which is then filtered and washed to obtain a precipitate a and a reaction liquid;

[0015] S22: adding dilute sulfuric acid to the precipitate, stirring and mixing, and then filtering and washing to obtain a precipitate b and a filtrate, and adding the precipitate b to the reaction solution to obtain a mixed solution.

[0016] As a further improvement of the above scheme, the amount of lime emulsion added is 20% to 40% of the total amount of the raw material liquid, and the mixture is stirred and mixed for 20 to 30 minutes until no precipitation is precipitated and then filtered. The precipitate a is calcium carbonate and magnesium hydroxide, and the precipitate b is calcium carbonate. In the raw material liquid of the present invention, since it is taken from sedimentary salt rock, the Ca in the raw material liquid exists in the form of calcium carbonate and does not participate in the reaction during magnesium removal.

[0017] As a further improvement of the above scheme, the concentration of the dilute sulfuric acid is 2-5 mol / L, and the ratio of the dilute sulfuric acid to the precipitate is 1-2:1, and the mixture is stirred for 30-50 minutes until the precipitate stops dissolving and then filtered. Since calcium carbonate does not react with dilute sulfuric acid, the reaction in the above process is: H2SO4+Mg(OH)2↓→MgSO4+2H2O. Based on the above design, the precipitate a is further separated, so as to retain the calcium content in the raw materials entering the next preparation link to the greatest extent, thereby obtaining the maximum output rate of nano calcium carbonate.

[0018] As a further improvement of the above scheme, the suspension contains calcium carbonate precipitate;

[0019] The method for obtaining the suspension by carbonization reaction is specifically performed as follows:

[0020] S31 prepare an alkaline solution by taking NaCl, Na2SO4 and NaOH;

[0021] S32: adding the alkaline solution to the mixed solution, and stirring for 5 to 10 minutes;

[0022] S33: stirring is continued and carbon dioxide gas is introduced into the solution of S32 for reaction, and the carbon dioxide gas is heated and dispersed before being introduced into the mixed solution;

[0023] S34 When the pH of the solution becomes neutral, the introduction of carbon dioxide is stopped and the reaction is terminated.

[0024] As a further improvement of the above scheme, NaCI, Na2SO4 and NaOH are mixed in a ratio of 1:0.5-2.5:1-1.5 to obtain the alkaline solution, and the amount of the alkaline solution added accounts for 5%-15% of the total amount of the mixed solution. The concentration of the NaCI is 2.5-3.5 mol / L, the concentration of the Na2SO4 is 2-4 mol / L, and the concentration of the NaOH is 1-3 mol / L.

[0025] As a further improvement of the above scheme, the carbon dioxide gas is first heated to 30-35°C by a heater before being charged into the mixed solution, and the carbon dioxide gas fed by the main pipe is diverted through at least six branch pipes and then charged into the solution to participate in the reaction. In the present invention, the carbon dioxide gas is first heated and dispersed before being charged into the mixed solution to increase the movement rate of the carbon dioxide gas molecules, thereby energizing the carbon dioxide, so that the carbon dioxide can better contact with the solution, and improve the quality of the generated calcium carbonate.

[0026] As a further improvement of the above scheme, the carbon dioxide gas is derived from the waste gas generated by boiler combustion. The present invention effectively utilizes the waste gas generated by boiler combustion as the source of carbon dioxide gas, and effectively realizes resource reorganization and utilization. In the carbonization reaction, the lime emulsion and Na2SO4 continue to react to generate CaSO4 precipitation, the introduced carbon dioxide reacts with NaOH to generate Na2CO3, and Na2SO4 and Na2CO3 react to generate CaCO3 precipitation.

[0027] As a further improvement of the above scheme, the amount of sodium stearate added is 3% to 7% of the total amount of the suspension. The ball milling treatment is carried out in a ball mill, and the ball milling speed is 600 to 800 r / min, and the ball milling time is 10 to 20 min. In the present invention, the addition of sodium stearate plays a role in activating calcium carbonate. Sodium stearate performs surface modification on calcium carbonate, thereby reducing surface energy, improving dispersibility, making the surface lipophilic, and avoiding the agglomeration of calcium carbonate powder. When used in composite materials, the active nano calcium carbonate has good affinity with organisms and high dispersibility, thereby overcoming the problem of calcium carbonate agglomeration affecting material performance.

[0028] As a further improvement of the above scheme, the active nano calcium carbonate slurry is obtained by washing with clean water and filtering through a filter press to remove salt.

[0029] As a further improvement of the above scheme, the dehydration and drying is carried out in a dryer, and the drying temperature is 100-120° C. and the drying time is 4-8 hours.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The raw material of the preparation of the invention is the waste liquid generated in the brine purification step of the refined salt production, and the waste liquid of the refined salt production is reused to prepare nano calcium carbonate, thereby reducing the raw material cost of the nano calcium carbonate production and realizing resource regeneration. The preparation process of the invention has a simple process, does not require calcination, and consumes less energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Shown is a flow chart of a method for preparing nano calcium carbonate provided by the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. Additional aspects and advantages of the present invention will be given in part in the following description, and will become apparent from the following description, or will be understood through the practice of the present invention. It should be understood that the following description is only used to explain the present invention and is not intended to limit the present invention.

[0034] As used herein, the terms "comprises," "including," "contains," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0035] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range limited by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including a range of "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When a numerical range is described in this article, unless otherwise specified, the range is intended to include its end values ​​and all integers and fractions within the range.

[0036] The specific embodiments of the present invention are described in detail below.

[0037] Example 1

[0038] This embodiment provides a method for preparing nano calcium carbonate, which comprises the following steps:

[0039] S1 provides a raw material liquid rich in calcium and magnesium ions, and the raw material liquid is taken from the waste liquid generated in the brine purification step of the refined salt production process. At present, refined salt production uses sedimentary salt rock formed by evaporation of seawater or lake action as raw material, uses water to dissolve salt rock-shaped brine, removes calcium and magnesium ions in the brine to form refined brine, and the crystals produced by evaporating the refined brine are refined salt. In the process of removing calcium and magnesium ions from the aforementioned brine, waste liquid rich in calcium ions will be generated. Based on this, this embodiment reuses the waste liquid from refined salt production to produce nano calcium carbonate, thereby realizing resource regeneration.

[0040] S2 removes magnesium from the raw material liquid to obtain a mixed liquid.

[0041] The method for removing magnesium to obtain a mixed solution, the specific operation is as follows:

[0042] S21 adds lime emulsion to the raw liquid, stirs and mixes, the lime emulsion reacts with the magnesium ions in the raw liquid, the magnesium ions are precipitated in the form of precipitation, and then filtered and washed to obtain precipitate a and reaction liquid, the amount of lime emulsion added accounts for 20% of the total amount of the raw liquid, stirs and mixes for 20 minutes, and then filters until no precipitation is precipitated, and the precipitate a is calcium carbonate and magnesium hydroxide. In this embodiment, the reaction formula of lime emulsion and magnesium ion is: Ca(OH)2+MgSO4→Mg(OH)2↓+CaSO4↓. It should be noted that in the raw liquid of this embodiment, since it is taken from sedimentary salt rock, the Ca in the raw liquid exists in the form of calcium carbonate and does not participate in the reaction during magnesium removal.

[0043] S22: Add 2 mol / L dilute sulfuric acid to the precipitate in a ratio of 1:1, stir and mix for 30 minutes until the precipitate stops dissolving, then filter and wash to obtain a precipitate b and a filtrate, add the precipitate b to the reaction solution to obtain a mixed solution, wherein the precipitate b is calcium carbonate.

[0044] Since calcium carbonate does not react with dilute sulfuric acid, the reaction in the above process is: H2SO4+Mg(OH)2↓→MgSO4+2H2O. Based on the above design, the precipitate a is further separated to retain the calcium content in the raw materials entering the next preparation stage to the greatest extent, thereby obtaining the maximum output rate of nano calcium carbonate.

[0045] S3: adding alkaline liquid to the mixed solution, introducing carbon dioxide gas with a concentration of 70% to perform a carbonization reaction, and obtaining a suspension containing calcium carbonate precipitate;

[0046] The method for obtaining the suspension by carbonization reaction is specifically performed as follows:

[0047] S31: NaCI, Na2SO4 and NaOH are mixed in a ratio of 1:0.5:1 to obtain the alkaline solution; the concentration of NaCI is 2.5 mol / L, the concentration of Na2SO4 is 2 mol / L, and the concentration of NaOH is 1 mol / L.

[0048] S32: adding alkaline liquid into the mixed liquid, stirring and mixing for 5 minutes, wherein the amount of the alkaline liquid added accounts for 5% of the total amount of the mixed liquid.

[0049] S33 keeps stirring and introduces carbon dioxide gas into the solution of S32 for reaction. The carbon dioxide gas is heated to 30°C by a heater before being charged into the mixed solution. The carbon dioxide gas fed by the main pipe is diverted through at least six branch pipes and then charged into the solution to participate in the reaction. The carbon dioxide gas originates from the exhaust gas generated by boiler combustion. In this embodiment, the carbon dioxide gas is heated and dispersed before being charged into the mixed solution to increase the movement rate of the carbon dioxide gas molecules, thereby energizing the carbon dioxide so that the carbon dioxide can better contact the solution and improve the quality of the generated calcium carbonate. In addition, the exhaust gas generated by boiler combustion is effectively used as the source of carbon dioxide gas, effectively realizing resource reorganization and utilization.

[0050] S34 When the pH of the solution becomes neutral, the introduction of carbon dioxide is stopped and the reaction is terminated.

[0051] In the carbonization reaction to obtain calcium carbonate precipitate in this embodiment, lime emulsion and Na2SO continue to react to generate CaSO4 precipitate, and the introduced carbon dioxide reacts with NaOH to generate Na2CO3. The specific reaction formula involved is as follows:

[0052] Ca(OH)2+Na2SO4→2NaOH+CaSO4↓;

[0053] 2NaOH+CO2→Na2CO3+H2O;

[0054] CaSO4+Na2CO3→CaCO3↓+Na2SO4.

[0055] S4 adds sodium stearate to the suspension, and the calcium carbonate is modified by ball milling. The amount of sodium stearate added accounts for 3% of the total amount of the suspension. The ball milling process is carried out in a ball mill, and the ball milling speed is 600r / min, and the ball milling time is 10min. In this embodiment, the addition of sodium stearate plays a role in activating calcium carbonate. Sodium stearate performs surface modification on calcium carbonate, thereby reducing surface energy, improving dispersibility, making its surface lipophilic, and avoiding the agglomeration of calcium carbonate powder. When used in composite materials, the active nano calcium carbonate has good affinity with organisms and high dispersibility, thereby overcoming the problem of calcium carbonate agglomeration affecting material properties.

[0056] S5 is washed with clean water and filtered through a filter press to remove salt to obtain an active nano calcium carbonate slurry.

[0057] S6: the active nano-calcium carbonate slurry is dehydrated and dried to obtain nano-calcium carbonate. The dehydration and drying is carried out in a dryer at a drying temperature of 100° C. and a drying time of 4 hours.

[0058] Example 2

[0059] This embodiment provides a method for preparing nano calcium carbonate, which comprises the following steps:

[0060] S1 provides a raw material liquid rich in calcium and magnesium ions, and the raw material liquid is taken from the waste liquid generated in the brine purification step of the refined salt production process. At present, refined salt production uses sedimentary salt rock formed by evaporation of seawater or lake action as raw material, uses water to dissolve salt rock-shaped brine, removes calcium and magnesium ions in the brine to form refined brine, and the crystals produced by evaporating the refined brine are refined salt. In the process of removing calcium and magnesium ions from the aforementioned brine, waste liquid rich in calcium ions will be generated. Based on this, this embodiment reuses the waste liquid from refined salt production to produce nano calcium carbonate, thereby realizing resource regeneration.

[0061] S2 removes magnesium from the raw material liquid to obtain a mixed liquid.

[0062] The method for removing magnesium to obtain a mixed solution, the specific operation is as follows:

[0063] S21 adds lime emulsion to the raw liquid, stirs and mixes, and the lime emulsion reacts with the magnesium ions in the raw liquid, and the magnesium ions are precipitated in the form of precipitation, and then filtered and washed to obtain precipitate a and reaction liquid. The amount of lime emulsion added accounts for 30% of the total amount of the raw liquid. Stirring and mixing for 25 minutes, filtering until no precipitation is precipitated, and the precipitate a is calcium carbonate and magnesium hydroxide. In this embodiment, the reaction formula of lime emulsion and magnesium ion is: Ca(OH)2+MgSO4→Mg(OH)2↓+CaSO4↓. It should be noted that in the raw liquid of this embodiment, since it is taken from sedimentary salt rock, the Ca in the raw liquid exists in the form of calcium carbonate and does not participate in the reaction during magnesium removal.

[0064] S22: Add 3 mol / L dilute sulfuric acid to the precipitate in a ratio of 1.5:1, stir and mix for 40 minutes until the precipitate stops dissolving, then filter and wash to obtain a precipitate b and a filtrate, add the precipitate b to the reaction solution to obtain a mixed solution, wherein the precipitate b is calcium carbonate.

[0065] Since calcium carbonate does not react with dilute sulfuric acid, the reaction in the above process is: H2SO4+Mg(OH)2↓→MgSO4+2H2O. Based on the above design, the precipitate a is further separated to retain the calcium content in the raw materials entering the next preparation stage to the greatest extent, thereby obtaining the maximum output rate of nano calcium carbonate.

[0066] S3: adding alkaline liquid to the mixed liquid, introducing carbon dioxide gas with a concentration of 80% to perform a carbonization reaction, and obtaining a suspension containing calcium carbonate precipitate;

[0067] The method for obtaining the suspension by carbonization reaction is specifically performed as follows:

[0068] S31: NaCI, Na2SO4 and NaOH are mixed in a ratio of 1:2:1 to obtain the alkaline solution; the concentration of NaCI is 3 mol / L, the concentration of Na2SO4 is 3 mol / L, and the concentration of NaOH is 2 mol / L.

[0069] S32: adding alkaline liquid into the mixed liquid, stirring and mixing for 8 minutes, wherein the amount of the alkaline liquid added accounts for 10% of the total amount of the mixed liquid.

[0070] S33 keeps stirring and introduces carbon dioxide gas into the solution of S32 for reaction. The carbon dioxide gas is heated to 32°C by a heater before being charged into the mixed solution. The carbon dioxide gas fed by the main pipe is diverted through at least six branch pipes and then charged into the solution to participate in the reaction. The carbon dioxide gas originates from the exhaust gas generated by boiler combustion. In this embodiment, the carbon dioxide gas is heated and dispersed before being charged into the mixed solution to increase the movement rate of the carbon dioxide gas molecules, thereby energizing the carbon dioxide so that the carbon dioxide can better contact the solution and improve the quality of the generated calcium carbonate. In addition, the exhaust gas generated by boiler combustion is effectively used as the source of carbon dioxide gas, effectively realizing resource reorganization and utilization.

[0071] S34 When the pH of the solution becomes neutral, the introduction of carbon dioxide is stopped and the reaction is terminated.

[0072] In the carbonization reaction to obtain calcium carbonate precipitate in this embodiment, lime emulsion and Na2SO continue to react to generate CaSO4 precipitate, and the introduced carbon dioxide reacts with NaOH to generate Na2CO3. The specific reaction formula involved is as follows:

[0073] Ca(OH)2+Na2SO4→2NaOH+CaSO4↓;

[0074] 2NaOH+CO2→Na2CO3+H2O;

[0075] CaSO4+Na2CO3→CaCO3↓+Na2SO4.

[0076] S4 adds sodium stearate to the suspension, and the calcium carbonate is modified by ball milling. The amount of sodium stearate added accounts for 5% of the total amount of the suspension. The ball milling process is carried out in a ball mill, and the ball milling speed is 700r / min, and the ball milling time is 15min. In this embodiment, the addition of sodium stearate plays a role in activating calcium carbonate. Sodium stearate performs surface modification on calcium carbonate, thereby reducing surface energy, improving dispersibility, making its surface lipophilic, and avoiding the agglomeration of calcium carbonate powder. When used in composite materials, the active nano calcium carbonate has good affinity with organisms and high dispersibility, thereby overcoming the problem of calcium carbonate agglomeration affecting material properties.

[0077] S5 is washed with clean water and filtered through a filter press to remove salt to obtain an active nano calcium carbonate slurry.

[0078] S6: the active nano-calcium carbonate slurry is dehydrated and dried to obtain nano-calcium carbonate. The dehydration and drying is carried out in a dryer at a drying temperature of 110° C. and a drying time of 6 hours.

[0079] Example 3

[0080] This embodiment provides a method for preparing nano calcium carbonate, which comprises the following steps:

[0081] S1 provides a raw material liquid rich in calcium and magnesium ions, and the raw material liquid is taken from the waste liquid generated in the brine purification step of the refined salt production process. At present, refined salt production uses sedimentary salt rock formed by evaporation of seawater or lake action as raw material, uses water to dissolve salt rock-shaped brine, removes calcium and magnesium ions in the brine to form refined brine, and the crystals produced by evaporating the refined brine are refined salt. In the process of removing calcium and magnesium ions from the aforementioned brine, waste liquid rich in calcium ions will be generated. Based on this, this embodiment reuses the waste liquid from refined salt production to produce nano calcium carbonate, thereby realizing resource regeneration.

[0082] S2 removes magnesium from the raw material liquid to obtain a mixed liquid.

[0083] The method for removing magnesium to obtain a mixed solution, the specific operation is as follows:

[0084] S21 adds lime emulsion to the raw liquid, stirs and mixes, and the lime emulsion reacts with the magnesium ions in the raw liquid, and the magnesium ions are precipitated in the form of precipitation, and then filtered and washed to obtain precipitate a and reaction liquid. The amount of lime emulsion added accounts for 40% of the total amount of the raw liquid. Stirring and mixing for 30 minutes, filtering until no precipitation is precipitated, and the precipitate a is calcium carbonate and magnesium hydroxide. In this embodiment, the reaction formula of lime emulsion and magnesium ion is: Ca(OH)2+MgSO4→Mg(OH)2↓+CaSO4↓. It should be noted that in the raw liquid of this embodiment, since it is taken from sedimentary salt rock, the Ca in the raw liquid exists in the form of calcium carbonate and does not participate in the reaction during magnesium removal.

[0085] S22: Add 5 mol / L dilute sulfuric acid to the precipitate in a ratio of 2:1, stir and mix for 50 minutes until the precipitate stops dissolving, then filter and wash to obtain a precipitate b and a filtrate, add the precipitate b to the reaction solution to obtain a mixed solution, wherein the precipitate b is calcium carbonate.

[0086] Since calcium carbonate does not react with dilute sulfuric acid, the reaction in the above process is: H2SO4+Mg(OH)2↓→MgSO4+2H2O. Based on the above design, the precipitate a is further separated to retain the calcium content in the raw materials entering the next preparation stage to the greatest extent, thereby obtaining the maximum output rate of nano calcium carbonate.

[0087] S3: adding alkaline liquid to the mixed liquid, introducing carbon dioxide gas with a concentration of 90% to perform a carbonization reaction, and obtaining a suspension containing calcium carbonate precipitate;

[0088] The method for obtaining the suspension by carbonization reaction is specifically performed as follows:

[0089] S31: NaCI, Na2SO4 and NaOH are mixed in a ratio of 1:2.5:1.5 to obtain the alkaline solution; the concentration of NaCI is 3.5 mol / L, the concentration of Na2SO4 is 4 mol / L, and the concentration of NaOH is 3 mol / L.

[0090] S32: adding alkaline liquid into the mixed liquid, stirring and mixing for 10 minutes, wherein the amount of the alkaline liquid added accounts for 15% of the total amount of the mixed liquid.

[0091] S33 keeps stirring and introduces carbon dioxide gas into the solution of S32 for reaction. The carbon dioxide gas is heated to 35°C by a heater before being charged into the mixed solution. The carbon dioxide gas fed by the main pipe is diverted through at least six branch pipes and then charged into the solution to participate in the reaction. The carbon dioxide gas originates from the exhaust gas generated by boiler combustion. In this embodiment, the carbon dioxide gas is heated and dispersed before being charged into the mixed solution to increase the movement rate of the carbon dioxide gas molecules, thereby energizing the carbon dioxide so that the carbon dioxide can better contact the solution and improve the quality of the generated calcium carbonate. In addition, the exhaust gas generated by boiler combustion is effectively used as the source of carbon dioxide gas, effectively realizing resource reorganization and utilization.

[0092] S34 When the pH of the solution becomes neutral, the introduction of carbon dioxide is stopped and the reaction is terminated.

[0093] In the carbonization reaction to obtain calcium carbonate precipitate in this embodiment, lime emulsion and Na2SO continue to react to generate CaSO4 precipitate, and the introduced carbon dioxide reacts with NaOH to generate Na2CO3. The specific reaction formula involved is as follows:

[0094] Ca(OH)2+Na2SO4→2NaOH+CaSO4↓;

[0095] 2NaOH+CO2→Na2CO3+H2O;

[0096] CaSO4+Na2CO3→CaCO3↓+Na2SO4.

[0097] S4 adds sodium stearate to the suspension, and the calcium carbonate is modified by ball milling. The amount of sodium stearate added accounts for 7% of the total amount of the suspension. The ball milling process is carried out in a ball mill, and the ball milling speed is 800r / min, and the ball milling time is 20min. In this embodiment, the addition of sodium stearate plays a role in activating calcium carbonate. Sodium stearate performs surface modification on calcium carbonate, thereby reducing surface energy, improving dispersibility, making its surface lipophilic, and avoiding the agglomeration of calcium carbonate powder. When used in composite materials, the active nano calcium carbonate has good affinity with organisms and high dispersibility, thereby overcoming the problem of calcium carbonate agglomeration affecting material properties.

[0098] S5 is washed with clean water and filtered through a filter press to remove salt to obtain an active nano calcium carbonate slurry.

[0099] S6: the active nano-calcium carbonate slurry is dehydrated and dried to obtain nano-calcium carbonate. The dehydration and drying is carried out in a dryer at a drying temperature of 120° C. and a drying time of 8 hours.

[0100] The above embodiments are merely preferred implementations of the present invention. Any simple modification, amendment and substitution of the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing nano calcium carbonate, characterized in that, The following steps are involved: S1 provides a raw material solution rich in calcium and magnesium ions; S2 removes magnesium from the raw material liquid to obtain a mixed liquid; S3: adding an alkaline liquid to the mixed liquid, introducing carbon dioxide gas with a concentration of 70% to 90% to perform a carbonization reaction to obtain a suspension; S4: adding sodium stearate to the suspension, and mixing by ball milling to modify the calcium carbonate; S5 washing and desalting to obtain active nano calcium carbonate slurry; S6: the active nano-calcium carbonate slurry is dehydrated and dried to obtain nano-calcium carbonate.

2. The preparation method of nano calcium carbonate according to claim 1, characterized in that, The waste liquid generated in the brine purification step of the refined salt production process is used as the raw material liquid.

3. The preparation method of nano calcium carbonate according to claim 1, characterized in that, The method for removing magnesium to obtain a mixed solution, the specific operation is as follows: S21 adds lime emulsion to the raw material liquid, stirs and mixes, and the lime emulsion reacts with the magnesium ions in the raw material liquid, and the magnesium ions are precipitated in the form of a precipitate, which is then filtered and washed to obtain a precipitate a and a reaction liquid; S22: adding dilute sulfuric acid to the precipitate, stirring and mixing, and then filtering and washing to obtain a precipitate b and a filtrate, and adding the precipitate b to the reaction solution to obtain a mixed solution.

4. The preparation method of nano calcium carbonate according to claim 3, characterized in that, The amount of lime emulsion added is 20% to 40% of the total amount of the raw material liquid, and the mixture is stirred and mixed for 20 to 30 minutes until no precipitation is formed, and then filtered; The precipitate a is calcium carbonate and magnesium hydroxide, and the precipitate b is calcium carbonate.

5. The preparation method of nano calcium carbonate according to claim 4, characterized in that, The concentration of the dilute sulfuric acid is 2-5 mol / L, and the ratio of the dilute sulfuric acid to the precipitate is 1-2:

1. The mixture is stirred and mixed for 30-50 minutes until the precipitate stops dissolving and then filtered.

6. The preparation method of nano calcium carbonate according to claim 1, characterized in that, The suspension contains calcium carbonate precipitate; The method for obtaining the suspension by carbonization reaction is specifically performed as follows: S31 prepare an alkaline solution by taking NaCl, Na2SO4 and NaOH; S32: adding the alkaline solution to the mixed solution, and stirring for 5 to 10 minutes; S33: stirring is continued and carbon dioxide gas is introduced into the solution of S32 for reaction, and the carbon dioxide gas is heated and dispersed before being introduced into the mixed solution; S34 When the pH of the solution becomes neutral, the introduction of carbon dioxide is stopped and the reaction is terminated.

7. The preparation method of nano calcium carbonate according to claim 6, characterized in that, NaCl, Na2SO4 and NaOH are mixed in a ratio of 1:0.5-2.5:1-1.5 to obtain the alkaline solution, wherein the amount of the alkaline solution added accounts for 5%-15% of the total amount of the mixed solution; The concentration of NaCl is 2.5-3.5 mol / L, the concentration of Na2SO4 is 2-4 mol / L, and the concentration of NaOH is 1-3 mol / L.

8. The preparation method of nano calcium carbonate according to claim 7, characterized in that, The carbon dioxide gas is heated to 30-35°C by a heater before being charged into the mixed solution. The carbon dioxide gas fed from the main pipe is divided through at least six branch pipes and then charged into the solution to participate in the reaction. The carbon dioxide gas is derived from exhaust gas generated by boiler combustion.

9. The preparation method of nano calcium carbonate according to claim 1, characterized in that, The amount of sodium stearate added is 3% to 7% of the total amount of the suspension; The ball milling treatment is carried out in a ball mill, and the ball milling speed is 600-800 r / min, and the ball milling time is 10-20 min.

10. The preparation method of nano calcium carbonate according to claim 1, characterized in that, Wash with clean water, and filter through a filter press to remove salt, to obtain active nano calcium carbonate slurry; The dehydration and drying is carried out in a dryer, and the drying temperature is 100-120° C. and the drying time is 4-8 hours.

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