Acid-resistant calcium carbonate and preparation method thereof

Abstract

The invention discloses acid-resistant calcium carbonate and a preparation method thereof, and belongs to the technical field of calcium carbonate filler production. According to the invention, industrial waste carbide slag is used as a calcium source, and calcium hydroxide slurry is obtained through impurity removal; then adding sodium polyacrylate and sodium hexametaphosphate, stirring and dispersing, then introducing carbon dioxide for carbonization, adding a surfactant for ultrasonic activation after carbonization, and finally sequentially adding zirconium oxychloride and sodium silicate to prepare the acid-resistant calcium carbonate. The defects of traditional silicon dioxide and titanium dioxide coated calcium carbonate products are overcome, the prepared calcium carbonate product is compact and uniform in coating layer and good in stability, meanwhile, excellent acid resistance and mechanical property are considered, the calcium carbonate can be suitable for more acid environments, and the application range of calcium carbonate is effectively widened.

Description

Technical Field

[0001] The invention belongs to the technical field of calcium carbonate filler production, and specifically relates to acid-resistant calcium carbonate and a preparation method thereof. Background Art

[0002] Calcium carbonate is an important inorganic chemical raw material. With its wide source, low cost, large filling volume and environmental friendliness, it is widely used in many industries such as plastics, rubber, coatings, papermaking, medicine, and food. Calcium carbonate can be dissolved in dilute acetic acid, dilute hydrochloric acid, dilute nitric acid, etc., so it is not suitable for some acidic environments such as architectural paints and coatings, acidic packaging materials, papermaking, etc., thus limiting its scope of application.

[0003] Factors that determine the properties of calcium carbonate include structure, morphology, particle size, etc. For acid resistance, silica is generally used to coat it in the current field. By forming a dense silica protective layer on the surface of calcium carbonate, it plays a role in protecting calcium carbonate in acidic substances, thereby improving the resistance of calcium carbonate to acidic environments. However, in some existing production processes, the conditions for the uniform adsorption of silica to the surface of calcium carbonate are relatively harsh, and the raw material costs involved are high or the processes are relatively complex. The uneven coating layer will lead to serious interface defects (large thickness fluctuations lead to local corrosion channels); at the same time, research on silica-coated calcium carbonate mainly focuses on the coating effect and the acid resistance of the product, and often ignores the improvement of the mechanical properties of the material, resulting in the inability of the manufactured products to be used in some scenarios that have multiple performance requirements such as acid resistance and strength.

[0004] In view of this, in order to expand the application scope of calcium carbonate, it is of great significance to study and prepare a calcium carbonate with excellent acid resistance and mechanical properties. Summary of the invention

[0005] In view of the content of the background technology, the purpose of the present invention is to provide an acid-resistant calcium carbonate and a preparation method thereof. The present invention uses carbide slag as a calcium source, and simultaneously uses sodium polyacrylate, sodium hexametaphosphate, a surfactant, zirconium oxychloride and sodium silicate to sequentially process and construct a composite coating layer, which significantly improves the acid resistance and mechanical properties of the calcium carbonate product, overcomes the shortcomings of traditional silica-coated calcium carbonate, and expands the application range of calcium carbonate.

[0006] In order to achieve the above object, the present invention specifically adopts the following technical solutions: The present invention provides a method for preparing acid-resistant calcium carbonate, comprising the following steps: Step 1: taking carbide slag and subjecting it to impurity removal pretreatment to obtain calcium hydroxide slurry for standby use; Step 2: adding sodium polyacrylate and sodium hexametaphosphate to the obtained calcium hydroxide slurry, stirring at a constant temperature to obtain a dispersion; Step 3: introducing carbon dioxide into the obtained dispersion to carbonize it, and then continuing to add a surfactant, ultrasonicating and stirring to obtain an activated slurry; Step 4: Add zirconium oxychloride and sodium silicate to the activated slurry in sequence, and finally obtain acid-resistant calcium carbonate through spray drying and calcination.

[0007] Furthermore, the calcium hydroxide content of the carbide slag in step 1 is not less than 85%, and the carbide slag is mixed with water and stirred evenly, and then sieved to remove impurities to obtain calcium hydroxide slurry; for carbide slag with more impurities, acid washing, magnetic separation or flotation treatment can be selectively added. The present invention uses carbide slag as a calcium source, effectively utilizes industrial waste, and does not require calcination treatment, which significantly reduces raw material costs and process energy consumption.

[0008] Furthermore, in step 2, the addition amount of sodium polyacrylate and sodium hexametaphosphate is 0.6%-1% and 0.1%-0.4% of the mass of carbide slag, respectively. The present invention uses sodium polyacrylate and sodium hexametaphosphate to pre-treat the generated calcium hydroxide slurry: the carboxylate of sodium polyacrylate is pre-adsorbed on the surface of calcium hydroxide to prevent particle agglomeration through steric hindrance effect, and the phosphate of sodium hexametaphosphate is pre-adsorbed on the surface of calcium hydroxide to enhance electrostatic repulsion. The appropriate proportion of the two can complement each other to improve the dispersion effect, and can achieve rapid and stable dispersion of the subsequent system, reduce the viscosity of the system, avoid uneven subsequent coating, improve the density of calcium carbonate, and lay a foundation for the construction of the composite coating layer and the improvement of acid resistance.

[0009] Furthermore, after adding sodium polyacrylate and sodium hexametaphosphate in step 2, the pH value needs to be fine-tuned to 10, and the constant temperature stirring temperature is 50-60° C. and the time is 1.5-3 h.

[0010] Furthermore, the conditions for introducing carbon dioxide for carbonization in step three are: the carbon dioxide introduction flow rate is 0.4-0.6 L / min, the carbonization reaction temperature is 20-28°C, and the stirring rate is 250-400 rpm; the introduction of carbon dioxide is stopped when the carbonization reaction is carried out until the conductivity decreases to a constant level.

[0011] Furthermore, the surfactant in step 3 is alkyl dimethyl hydroxypropyl phosphate betaine, and the addition amount thereof is 1%-1.8% of the mass of carbide slag. In the present invention, alkyl dimethyl hydroxypropyl phosphate betaine is added after carbonization to generate calcium carbonate, and the alkyl dimethyl hydroxypropyl phosphate betaine can be fully distributed on the surface of calcium carbonate, and at the same time, it acts as a bridge linking calcium carbonate and subsequent composite coating layer through surface activation and interface enhancement, greatly improving the adhesion of the coating layer, helping to form a uniform coating layer and improving the long-term stability of the calcium carbonate product.

[0012] Furthermore, in step three, the frequency of the ultrasound is 30-40 kHz, the power is 120-200 W, and the time is 10-20 min.

[0013] Furthermore, in step 4, the total amount of zirconium oxychloride and sodium silicate added is 1.5%-3.5% of the mass of carbide slag; and the pH needs to be adjusted to 8-8.5 before adding sodium silicate.

[0014] Furthermore, the mass ratio of zirconium oxychloride to sodium silicate is (0.5-1):(1.5-3).

[0015] Furthermore, the inlet temperature of the spray drying in step 4 is 200°C, the outlet temperature is 80°C, and the calcination temperature is 750-800°C. On the basis of the above, the present invention also uses zirconium oxychloride and sodium silicate to sequentially coat calcium carbonate, and by adjusting the treatment sequence and pH, the coating precursor is fully adsorbed on the surface of calcium carbonate, and finally spray-dried and calcined to form a uniform composite coating layer of zirconium dioxide and silicon dioxide. The combination of the two significantly improves the density, uniformity and stability of the coating layer, reduces the permeability of the acid solution, and significantly improves the bonding strength, which greatly improves the mechanical properties of the calcium carbonate product.

[0016] The present invention also provides acid-resistant calcium carbonate obtained by the preparation method.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The surface of the calcium carbonate prepared by the present invention is fully covered by a composite coating layer of zirconium dioxide and silicon dioxide. The coating layer is dense, uniform and stable. The prepared product has excellent acid resistance and mechanical properties, can be applied to more acidic environments, and effectively expands the application range of calcium carbonate.

[0018] 2. Compared with traditional silicon dioxide and titanium dioxide coated calcium carbonate products and production processes, the raw material cost and process energy consumption of the present invention are significantly reduced, the overall preparation process is simple, and it is suitable for industrial production. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0021] Example 1 A method for preparing acid-resistant calcium carbonate, comprising the following steps: 1. Mix carbide slag and water at a solid-liquid ratio of 1:5 and stir evenly, remove impurities through a 200-mesh sieve to obtain calcium hydroxide slurry (control the solid content to be 15%); add 0.8% sodium polyacrylate and 0.3% sodium hexametaphosphate by weight of carbide slag to the obtained calcium hydroxide slurry, fine-tune the pH to 10, and stir continuously at a constant temperature of 50°C for 2 h to obtain a dispersion for use.

[0022] 2. Continuously introduce carbon dioxide (0.5 L / min) into the dispersion, and continuously stir at 25°C and 300 rpm for carbonization. The conductivity decreases until it remains constant, and the carbonization is terminated. The solid content is adjusted to 20% to obtain a suspension. Sodium hydroxide is added to the suspension to adjust the pH to 10, and 1.2% of the mass of carbide slag alkyl dimethyl hydroxypropyl phosphate betaine is continued to be added. Ultrasonic treatment (35kHz, 160 W) is performed at 60°C for 15 min, and the activated slurry is obtained by stirring and kept warm for use.

[0023] 3. Slowly add zirconium oxychloride (0.8% by weight of carbide slag) to the activated slurry, and stir the reaction at 60°C for 30 min. Then raise the temperature to 75°C, maintain constant temperature and adjust the pH to 8.5, and then slowly add sodium silicate (pre-dissolved in 5% solution) (2.2% by weight of carbide slag) and continue stirring for 1 h. Finally, spray dry (inlet temperature 200°C, outlet temperature 80°C), and calcine at 780°C for 1 h to obtain an acid-resistant calcium carbonate product.

[0024] Example 2 A method for preparing acid-resistant calcium carbonate, comprising the following steps: 1. Mix carbide slag and water at a solid-liquid ratio of 1:5 and stir evenly, pass through a 200-mesh sieve to remove impurities, and obtain calcium hydroxide slurry (control the solid content to be 15%); add 0.6% sodium polyacrylate and 0.4% sodium hexametaphosphate by mass of carbide slag to the obtained calcium hydroxide slurry, fine-tune the pH to 10, and stir continuously at a constant temperature of 60°C for 2 h to obtain a dispersion for use.

[0025] 2. Continuously introduce carbon dioxide (0.5 L / min) into the dispersion, and continuously stir at 25°C and 300 rpm for carbonization. The conductivity decreases until it remains constant, and the carbonization is terminated. The solid content is adjusted to 20% to obtain a suspension. Sodium hydroxide is added to the suspension to adjust the pH to 10, and 1.8% of the mass of carbide slag alkyl dimethyl hydroxypropyl phosphate betaine is continued to be added. Ultrasonic treatment (35kHz, 160 W) is performed at 60°C for 15 min, and the activated slurry is obtained by stirring and kept warm for use.

[0026] 3. Slowly add zirconium oxychloride (0.5% by weight of carbide slag) to the activated slurry, and stir the reaction at 60°C for 30 min. Then raise the temperature to 75°C, maintain constant temperature and adjust the pH to 8.5, and then slowly add sodium silicate (pre-dissolved in 5% solution) (3% by weight of carbide slag) and continue stirring for 1 h. Finally, spray dry (inlet temperature 200°C, outlet temperature 80°C), and calcine at 780°C for 1 h to obtain an acid-resistant calcium carbonate product.

[0027] Example 3 A method for preparing acid-resistant calcium carbonate, comprising the following steps: 1. Mix carbide slag and water at a solid-liquid ratio of 1:5 and stir evenly, pass through a 200-mesh sieve to remove impurities, and obtain calcium hydroxide slurry (control the solid content to be 15%); add 1% sodium polyacrylate and 0.1% sodium hexametaphosphate by weight of carbide slag to the obtained calcium hydroxide slurry, fine-tune the pH to 10, and stir continuously at a constant temperature of 55°C for 2 h to obtain a dispersion for use.

[0028] 2. Continuously introduce carbon dioxide (0.5 L / min) into the dispersion, and continuously stir at 25°C and 300 rpm for carbonization. The conductivity decreases until it remains constant, and the carbonization is terminated. The solid content is adjusted to 20% to obtain a suspension. Sodium hydroxide is added to the suspension to adjust the pH to 10, and 1% of the mass of carbide slag alkyl dimethyl hydroxypropyl phosphate betaine is added. Ultrasound (35kHz, 160 W) is applied at 60°C for 15 min, and the activated slurry is obtained by stirring and kept warm for use.

[0029] 3. Slowly add zirconium oxychloride (1% by weight of carbide slag) to the activated slurry, and stir the reaction at 60°C for 30 min. Then raise the temperature to 75°C, maintain constant temperature and adjust the pH to 8.5, and then slowly add sodium silicate (pre-dissolved in 5% solution) (1.5% by weight of carbide slag), and continue stirring for 1 h. Finally, spray dry (inlet temperature 200°C, outlet temperature 80°C), and calcine at 780°C for 1 h to obtain an acid-resistant calcium carbonate product.

[0030] Blank control group Commercially available CAH-6350 calcium carbonate.

[0031] Comparative Example 1 Refer to the step parameters of Example 1, except that sodium hexametaphosphate is not added in step 1.

[0032] Comparative Example 2 The step parameters are the same as those of Example 1, except that no ultrasonic treatment is applied in step 2.

[0033] Comparative Example 3 The step parameters are as in Example 1, except that zirconium oxychloride is not added in step 3.

[0034] Test example The calcium carbonate samples obtained in the above Examples 1-3 and the blank control group and Comparative Examples 1-4 were subjected to performance tests (HG / T3249.1-2013; the acid resistance test method is to immerse the sample in acetic acid with pH=4.5 and hydrochloric acid with pH=1 for a certain period of time and measure the dissolution rate; the mechanical property test is to prepare a composite material according to the formula: 60 parts of PBAT, 40 parts of calcium carbonate sample, 2 parts of KH550, 2.5 parts of epoxidized soybean oil, 0.3 parts of antioxidant 168, and 0.4 parts of DCP cross-linking agent, and then test the impact strength and tensile strength respectively), and the results are shown in Table 1.

[0035] Table 1 Calcium carbonate performance test results

[0036] It can be seen from the test results of Table 1 that the calcium carbonate samples prepared by Examples 1-3 of the present invention have the characteristics of high whiteness, excellent acid resistance, high impact strength and tensile strength, and the acid resistance and mechanical properties are significantly improved compared to ordinary calcium carbonate. According to the test results of Comparative Example 1, its acid resistance and mechanical properties have both decreased, which may be due to the lack of complementary dispersion of sodium polyacrylate and sodium hexametaphosphate, which in turn affects the uniformity of the coating layer. According to the test results of Comparative Example 2, its acid resistance and mechanical properties have also decreased, indicating that the alkyl dimethyl hydroxypropyl phosphate betaine selected by the present invention can cooperate with ultrasonic action to strengthen surface activation and interface enhancement. According to the test results of Comparative Example 3, the composite coating layer of zirconium dioxide and silicon dioxide of the present invention is significantly improved in acid resistance and mechanical properties compared to single silicon dioxide coating. The present invention effectively overcomes the shortcomings of existing coated calcium carbonate products, while taking into account excellent acid resistance and mechanical properties, can be applied to more acidic environments, and has good market competitiveness.

[0037] The embodiments described above only express several preferred embodiments of the present invention, and the descriptions thereof are relatively specific and detailed, but are not intended to limit the present invention. It should be noted that for those skilled in the art, the present invention may also have various changes and modifications, and any modifications, equivalent substitutions, improvements, etc. made within the concept and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing an acid-resistant calcium carbonate, characterized in that: The steps include: Step 1: taking carbide slag and subjecting it to impurity removal pretreatment to obtain calcium hydroxide slurry for standby use; Step 2: adding sodium polyacrylate and sodium hexametaphosphate to the obtained calcium hydroxide slurry, stirring at a constant temperature to obtain a dispersion; Step 3: introducing carbon dioxide into the obtained dispersion to carbonize it, and then continuing to add a surfactant, ultrasonicating and stirring to obtain an activated slurry; Step 4: Add zirconium oxychloride and sodium silicate to the activated slurry in sequence, and finally obtain acid-resistant calcium carbonate through spray drying and calcination.

2. The preparation method of acid-resistant calcium carbonate according to claim 1, wherein In step 2, the addition amounts of sodium polyacrylate and sodium hexametaphosphate are 0.6%-1% and 0.1%-0.4% of the mass of carbide slag respectively.

3. The preparation method of acid-resistant calcium carbonate according to claim 1, characterized in that, Step 2: After adding sodium polyacrylate and sodium hexametaphosphate, the pH value needs to be fine-tuned to 10, and the constant temperature stirring temperature is 50-60° C. and the time is 1.5-3 h.

4. The preparation method of acid-resistant calcium carbonate according to claim 1, characterized in that The conditions for carbonization by introducing carbon dioxide in step 3 are: a carbon dioxide introduction flow rate of 0.4-0.6 L / min, a carbonization reaction temperature of 20-28° C., and a stirring rate of 250-400 rpm; the introduction of carbon dioxide is stopped when the carbonization reaction is carried out until the conductivity decreases to a constant level.

5. The preparation method of acid-resistant calcium carbonate according to claim 1, characterized in that, The surfactant in step 3 is alkyl dimethyl hydroxypropyl phosphate betaine, and its addition amount is 1%-1.8% of the mass of calcium carbide slag.

6. The preparation method of acid-resistant calcium carbonate according to claim 1, characterized in that, The ultrasound in step 3 has a frequency of 30-40 kHz, a power of 120-200 W, and a time of 10-20 min.

7. The preparation method of acid-resistant calcium carbonate according to claim 1, characterized in that, In step 4, the total amount of zirconium oxychloride and sodium silicate added is 1.5%-3.5% of the mass of carbide slag.

8. The method for preparing acid-resistant calcium carbonate according to claim 7, wherein The mass ratio of zirconium oxychloride to sodium silicate is (0.5-1):(1.5-3).

9. The preparation method of acid-resistant calcium carbonate according to claim 1, characterized in that, In step 4, the inlet temperature of the spray drying is 200°C, the outlet temperature is 80°C, and the calcination temperature is 750-800°C.

10. The acid-resistant calcium carbonate obtained by the preparation method as described in any one of claims 1 to 9.

Images