Ultrafine ground calcium carbonate as well as preparation process and preparation device thereof

Abstract

The invention provides superfine ground calcium carbonate as well as a preparation process and a preparation device thereof. The preparation process comprises the following steps: S1, mixing calcium carbonate dry powder with water to prepare slurry with the solid content of 75-76%, adding a dispersing agent A for size mixing, and performing primary grinding to obtain primary ground slurry; s2, a dispersing agent A is added into the primary grinding slurry for slurry mixing, and then the slurry is subjected to secondary grinding to obtain secondary grinding slurry; s3, adding a dispersing agent B into the secondary grinding slurry, and performing tertiary grinding to obtain tertiary grinding slurry; and S4, uniformly mixing the third-time grinding slurry with a dispersing agent B, performing fourth-time grinding to obtain fourth-time grinding slurry, and storing a finished product. The grinding power of the wet grinding machine is adjusted, and a concentrated grinding dispersing agent adding mode is changed into a mode of adding a small amount of grinding dispersing agents in each section, so that the product viscosity of each device in the grinding process can be well controlled, the product viscosity rising problem is finally controlled, the fluidity is good, and the problems that pipes are easily blocked, the conveying resistance is large, and the flow speed is influenced are effectively solved. And the conveying efficiency is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of ground calcium carbonate, and in particular to ultrafine ground calcium carbonate and a preparation process and a preparation device thereof. Background Art

[0002] Ground Calcium Carbonate (GCC), also known as heavy calcium carbonate, is obtained by directly crushing natural calcium carbonate ore by mechanical methods. GCC, pH = 8.0 ~ 10.0, is suitable for medium (alkaline) papermaking and can be used as a filler and pigment. Heavy calcium carbonate is relatively cheap, has a very high whiteness, can be made into products with high solid content, has low abrasion, stable chemical properties, good fluidity and runnability, porosity and good ink absorption, and improves the gloss of paper.

[0003] Ultrafine ground calcium carbonate is used in paper coatings to effectively improve the gloss of paper, even comparable to porcelain clay, and is expected to replace porcelain clay in the future. In today's market where porcelain clay is in short supply and prices are rising, and ultrafine ground calcium carbonate has abundant raw materials and low production costs, the papermaking industry has begun to show a trend of researching ultrafine ground calcium carbonate to replace porcelain clay.

[0004] At present, the preparation of ultrafine calcium carbonate at home and abroad is all obtained by chemical methods. In domestic paper mills, most of the calcium carbonate obtained by physical grinding is ordinary calcium carbonate. If the original equipment can be upgraded to produce ultrafine ground calcium carbonate, it will save huge production investment costs for the paper mill to rebuild the production line. Although there are attempts to grind ultrafine calcium carbonate in China, that is, 1um particle size reaches 88%-90%; 2um particle size reaches 99%-100%, but the technical bottlenecks in the production process are mostly low output, high viscosity, and high power consumption, especially the viscosity reaches more than 600cps, and the viscosity continues to rise to 1000cps after standing for 8 hours, which makes it extremely difficult to transport products over long distances through pumps. In addition, the high viscosity during the grinding process causes serious loss of grinding zirconium beads, which cannot be solved. Summary of the invention

[0005] In view of this, the present invention provides an ultrafine ground calcium carbonate and a preparation process and a preparation device thereof.

[0006] The technical solution of the present invention is achieved in this way:

[0007] A process for preparing ultrafine ground calcium carbonate comprises the following steps:

[0008] S1. Mixing calcium carbonate powder with water to form a slurry with a solid content of 75%-76%, then adding dispersant A to a slurry preparation tank for slurry preparation, and grinding once to obtain a primary grinding slurry; the primary grinding slurry has a particle size of 2um content of 64%-65% and a viscosity of 40-60cps;

[0009] S2, adding dispersant A to the primary grinding slurry to prepare the slurry, and then grinding the slurry for a second time to obtain a secondary grinding slurry; the secondary grinding slurry has a particle size of 2um content of 74%-76% and a viscosity of 90-120cps;

[0010] S3, adding dispersant B to the secondary grinding slurry, mixing, and grinding for three times to obtain a tertiary grinding slurry; the content of particles with a diameter of 2 um in the tertiary grinding slurry is 94%-96%, and the viscosity is 150-180 cps;

[0011] S4, mixing the thrice-ground slurry with dispersant B again and grinding it for a fourth time to obtain a fourth-ground slurry, and then storing the obtained ultrafine ground calcium carbonate finished product.

[0012] Furthermore, the dispersant A is sodium polyacrylate; and the dispersant B is sodium polycarboxylate.

[0013] Furthermore, in step S1, the calcium carbonate dry powder has a particle size of 2 um and a content of 25%-35%.

[0014] Furthermore, in step S1 and step S2, the dispersant A is added in an amount of 1.5-6 kg / t of calcium carbonate dry powder.

[0015] Furthermore, in step S2, the dispersant A is added in an amount of 1.5-3 kg / t of calcium carbonate dry powder.

[0016] Furthermore, in steps S3 and S4, the dispersant B is added in an amount of 4-6 kg / t of calcium carbonate dry powder.

[0017] Furthermore, in step S1 and step S2, the pH value during the slurry adjustment process is 9.5-10.5.

[0018] Furthermore, the power of the wet grinder during the grinding process is 200-300 kW, and the grinding time is 50-60 min.

[0019] Furthermore, the dispersant B is added in an amount of 8-9 kg / t of calcium carbonate dry powder.

[0020] Furthermore, the ultrafine ground calcium carbonate product has a 2 um particle size content of 98%-100%, a 1 um particle size content of 88%-90%, and a viscosity of 240-280 cps.

[0021] Ultrafine ground calcium carbonate prepared by the preparation process of the invention.

[0022] The device for preparing ultrafine ground calcium carbonate of the present invention comprises: a first slurry preparation tank, a first pre-storage tank, a first filter, a first wet grinder, a first buffer tank, a second filter, a second slurry preparation tank, a second pre-storage tank, a third filter, a second wet grinder, a first receiving tank, a third wet grinder, a second receiving tank, a fourth wet grinder, a second buffer tank and a finished product tank; the first slurry preparation tank is connected with the first pre-storage tank, the first filter, the first wet grinder, the first buffer tank, the second filter, the second slurry preparation tank, the second pre-storage tank, the third filter, the second wet grinder, the first receiving tank, the third wet grinder, the second receiving tank, the fourth wet grinder and the second buffer tank in sequence through a pipeline, and the second buffer tank is connected with the finished product tank through a pressure screen.

[0023] Furthermore, the first filter, the second filter and the third filter are all ECO-S filters.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention optimizes and transforms equipment, uses a plurality of equipment in series to equally distribute power during the grinding process, so that the power of each grinding equipment does not exceed 300KW, and changes the centralized addition of grinding dispersant into a small amount of addition in each section, so that the viscosity of the product of each equipment during the grinding process can be well controlled, and the problem of increasing product viscosity can be finally controlled. In addition, the ground calcium carbonate of the present invention has good fluidity, and effectively solves the problems of easy pipe blockage in long-distance pump transportation of the product, large transportation resistance affecting the flow rate, and reducing the transportation efficiency.

[0026] The preparation process of the present invention can make the content of particle size 2um in the first grinding slurry be 64%-65%, and the viscosity be 40-60cps; the content of particle size 2um in the second grinding slurry be 74%-76%, and the viscosity be 90-120cps; the content of particle size 2um in the third grinding slurry be 94%-96%, and the viscosity be 150-180cps. The viscosity of each section in the grinding process is ≤300cps, the viscosity is appropriate, the product has good rheological properties, and is suitable for long-distance transportation; and the present invention can also control the particle size of the grinding slurry when the wet grinder is used for grinding in each section, so that the content of 2um particle size in the ultrafine ground calcium carbonate product after the fourth grinding is 98%-100%, and the content of 1um particle size is 88%-90%, thereby greatly improving the quality of the finished product.

[0027] In addition, the ultrafine ground calcium carbonate prepared by the present invention is used in calendered paper. Without using porcelain clay, the glossiness of the calendered paper can reach above 65, which can effectively increase the glossiness of paper, reduce the amount of porcelain clay mining, and protect the social environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a schematic diagram of the structure of the device used for the preparation process of ultrafine ground calcium carbonate.

[0029] In the figure, 1-the first slurry preparation tank, 2-the first pre-storage tank, 3-the first filter, 4-the first wet mill, 5-the first buffer tank, 6-the second filter, 7-the second slurry preparation tank, 8-the second pre-storage tank, 9-the third filter, 10-the second wet mill, 11-the first receiving tank, 12-the third wet mill, 13-the second receiving tank, 14-the fourth wet mill, 15-the second buffer tank, 16-the pressure screen, and 17-the finished product tank. DETAILED DESCRIPTION

[0030] In order to better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0031] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0032] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0033] The bactericide of the present invention is Cide 9350 fungicide, the main ingredients are benzalkonium chloride and glutaraldehyde; molecular formula: mixture; appearance and properties: colorless to light yellow liquid; pH (original solution, 25℃): 2.7~4.5; specific gravity (25℃): 1.09~1.17.

[0034] The device for preparing ultrafine ground calcium carbonate of the present invention comprises a first slurry preparation tank 1, a first pre-storage tank 2, a first filter 3, a first wet grinder 4, a first buffer tank 5, a second filter 6, a second slurry preparation tank 7, a second pre-storage tank 8, a third filter 9, a second wet grinder 10, a first receiving tank 11, a third wet grinder 12, a second receiving tank 13, a fourth wet grinder 14, a first buffer tank 5, a second buffer tank 15, and a finished product tank 17; the first slurry preparation tank 1 is connected with the first pre-storage tank 2, the first filter 3, the first wet grinder 4, the first buffer tank 5, the second filter 6, the second slurry preparation tank 7, the second pre-storage tank 8, the third filter 9, the second wet grinder 10, the first receiving tank 11, the third wet grinder 12, the second receiving tank 13, the fourth wet grinder 14, and the second buffer tank 15 in sequence through a pipeline, and the second buffer tank 15 is connected with the finished product tank 17 through a pressure screen 16.

[0035] Example 1

[0036] The ultrafine ground calcium carbonate preparation process of this embodiment comprises the following steps:

[0037] S1. Add calcium carbonate dry powder with a particle size of 2um and a content of 25% and water into the first slurry preparation tank 1 to mix and prepare a slurry with a solid content of 75%. Prepare 20t, then put 81kg of sodium polyacrylate dispersant A into the first slurry preparation tank 1 for slurry preparation. The slurry viscosity is 40cps and the pH is 10. After slurry preparation, it is transported to the first pre-storage tank 2 through a pipeline. Then, the slurry enters the first filter 3 and the first wet mill 4 from the first pre-storage tank 2 through a pipeline in sequence and is ground for the first time at a power of 300kw for 50min to obtain a first grinding slurry. The particle size of the first grinding slurry is 64%-65%, and the viscosity is 40cps.

[0038] S2, the primary grinding slurry in the first wet mill 4 is transported to the first buffer tank 5 through a pipeline, and a fungicide is continuously added to mix so that the fungicide concentration is 180ppm, and then transported to the second slurry preparation tank 7 through the second filter 6 and 25.05kg of sodium polyacrylate dispersant A is added for slurry preparation, and then the slurry prepared in the second slurry preparation tank 7 is transported to the second pre-storage tank 8 through a pipeline, and then the slurry enters the third filter 9 and the second wet mill 10 from the second pre-storage tank 8 through a pipeline in sequence, and is ground for the second time in the second wet mill 10 at a power of 300kw for 50min to obtain a secondary grinding slurry; the content of particle size 2um in the secondary grinding slurry is 74%-76%, and the viscosity is 90cps;

[0039] S3, the secondary grinding slurry in the second wet grinder 10 is transported to the first receiving tank 11 through a pipeline, and then 121.8 kg of polycarboxylate sodium salt dispersant B is continuously added to the first receiving tank 11 and mixed with the secondary grinding slurry, and then transported to the third wet grinder 12 through a pipeline for a third grinding at a power of 300 kW for 50 minutes to obtain a tertiary grinding slurry; the content of 2 μm particles in the tertiary grinding slurry is 94%-96%, and the viscosity is 150 cps;

[0040] S4, the tertiary grinding slurry in the third wet grinder 12 is transported to the second receiving tank 13 through a pipeline, and then 126.6 kg of sodium polycarboxylate dispersant B is continuously added to the second receiving tank 13 and mixed with the tertiary grinding slurry, and then transported to the fourth wet grinder 14 through a pipeline for the fourth grinding at a power of 300 kW for 50 minutes, and the four grinding slurry obtained in the fourth wet grinder 14 is transported to the second buffer tank 15 through a pipeline, and a bactericide is continuously added to mix so that the concentration of the bactericide is 250 ppm, and then transported to the finished product tank 17 through a pressure screen 16, and then the bactericide is added to the obtained ultrafine ground calcium carbonate finished product according to the dosage ratio of bactericide to ultrafine ground calcium carbonate finished product of 165 ml / T for storage.

[0041] Example 2

[0042] The ultrafine ground calcium carbonate preparation process of this embodiment comprises the following steps:

[0043] S1, add calcium carbonate dry powder with a particle size of 2um and a content of 25% and water into the first slurry preparation tank 1 to mix and prepare a slurry with a solid content of 75%, prepare 20t, and then put 90kg of sodium polyacrylate dispersant A into the first slurry preparation tank 1 for slurry preparation, the slurry viscosity is 50cps, pH is 9.5, after slurry preparation, it is transported to the first pre-storage tank 2 through a pipeline, and then the slurry enters the first filter 3 and the first wet mill 4 from the first pre-storage tank 2 through a pipeline in sequence and is first ground for 60min at a power of 200kw to obtain a primary grinding slurry, the particle size of the primary grinding slurry is 64%-65%, and the viscosity is 60cps;

[0044] S2, the primary grinding slurry in the first wet mill 4 is transported to the first buffer tank 5 through a pipeline, and a fungicide is continuously added to mix so that the fungicide concentration is 180ppm, and then transported to the second slurry preparation tank 7 through the second filter 6 and 22.5kg of sodium polyacrylate dispersant A is added for slurry preparation, and then the slurry prepared in the second slurry preparation tank 7 is transported to the second pre-storage tank 8 through a pipeline, and then the slurry enters the third filter 9 and the second wet mill 10 from the second pre-storage tank 8 through a pipeline in sequence, and is ground for the second time in the second wet mill 10 at a power of 200kw for 60min to obtain a secondary grinding slurry; the content of 2um particles in the secondary grinding slurry is 74%-76%, and the viscosity is 120cps;

[0045] S3, the secondary grinding slurry in the second wet grinder 10 is transported to the first receiving tank 11 through a pipeline, and then 120 kg of polycarboxylate sodium salt dispersant B is continuously added to the first receiving tank 11 and mixed with the secondary grinding slurry, and then transported to the third wet grinder 12 through a pipeline for a third grinding at a power of 200 kW for 60 minutes to obtain a tertiary grinding slurry; the content of 2 μm particles in the tertiary grinding slurry is 94%-96%, and the viscosity is 180 cps;

[0046] S4, the tertiary grinding slurry in the third wet grinder 12 is transported to the second receiving tank 13 through a pipeline, and then 120 kg of sodium polycarboxylate dispersant B is continuously added to the second receiving tank 13 and mixed with the tertiary grinding slurry, and then transported to the fourth wet grinder 14 through a pipeline for a fourth grinding at a power of 200 kW for 60 minutes, and the four grinding slurry obtained in the fourth wet grinder 14 is transported to the second buffer tank 15 through a pipeline, and a bactericide is continuously added to mix so that the concentration of the bactericide is 250 ppm, and then transported to the finished product tank 17 through a pressure screen 16, and then the bactericide is added to the obtained ultrafine ground calcium carbonate finished product according to the dosage ratio of bactericide to ultrafine ground calcium carbonate finished product of 165 ml / T for storage.

[0047] Example 3

[0048] The ultrafine ground calcium carbonate preparation process of this embodiment comprises the following steps:

[0049] S1. Add calcium carbonate dry powder with a particle size of 2um and a content of 25% and water into the first slurry preparation tank 1 to mix and prepare a slurry with a solid content of 76%. Prepare 20t, then put 82.08kg of sodium polyacrylate dispersant A into the first slurry preparation tank 1 for slurry preparation. The slurry viscosity is 40cps and the pH is 10.5. After slurry preparation, it is transported to the first pre-storage tank 2 through a pipeline. Then, the slurry enters the first filter 3 and the first wet mill 4 from the first pre-storage tank 2 through a pipeline in sequence and is ground for the first time at a power of 300kw for 50min to obtain a first grinding slurry. The particle size of the first grinding slurry is 64%-65%, and the viscosity is 50cps.

[0050] S2, the primary grinding slurry in the first wet mill 4 is transported to the first buffer tank 5 through a pipeline, and a fungicide is continuously added to mix so that the fungicide concentration is 180ppm, and then transported to the second slurry preparation tank 7 through the second filter 6 and 25.38kg of sodium polyacrylate dispersant A is added for slurry preparation, and then the slurry prepared in the second slurry preparation tank 7 is transported to the second pre-storage tank 8 through a pipeline, and then the slurry enters the third filter 9 and the second wet mill 10 from the second pre-storage tank 8 through a pipeline in sequence, and is ground for the second time in the second wet mill 10 at a power of 300kw for 50min to obtain a secondary grinding slurry; the content of 2um particles in the secondary grinding slurry is 74%-76%, and the viscosity is 100cps;

[0051] S3, the secondary grinding slurry in the second wet grinder 10 is transported to the first receiving tank 11 through a pipeline, and then 123.42 kg of polycarboxylate sodium salt dispersant B is continuously added to the first receiving tank 11 and mixed with the secondary grinding slurry, and then transported to the third wet grinder 12 through a pipeline for a third grinding at a power of 300 kw for 50 minutes to obtain a tertiary grinding slurry; the content of 2 um particles in the tertiary grinding slurry is 94%-96%, and the viscosity is 160 cps;

[0052] S4, the tertiary grinding slurry in the third wet grinder 12 is transported to the second receiving tank 13 through a pipeline, and then 128.29 kg of sodium polycarboxylate dispersant B is continuously added to the second receiving tank 13 and mixed with the tertiary grinding slurry, and then transported to the fourth wet grinder 14 through a pipeline for a fourth grinding at a power of 300 kW for 50 minutes, and the four grinding slurry obtained in the fourth wet grinder 14 is transported to the second buffer tank 15 through a pipeline, and a bactericide is continuously added to mix so that the concentration of the bactericide is 250 ppm, and then transported to the finished product tank 17 through a pressure screen 16, and then the bactericide is added to the obtained ultrafine ground calcium carbonate finished product according to the dosage ratio of bactericide to ultrafine ground calcium carbonate finished product of 165 ml / T for storage.

[0053] Comparative Example 1

[0054] This comparative example adjusts the dispersant addition process on the basis of comparative example 1, and dispersant A and dispersant B are added into the first slurry preparation tank 1 at one time for slurry preparation, and the rest is the same as example 1.

[0055] The ultrafine ground calcium carbonate preparation process of this comparative example comprises the following steps:

[0056] S1. Add calcium carbonate dry powder with a particle size of 2um and a content of 25% and water into the first slurry preparation tank 1 to mix and prepare a slurry with a solid content of 75%, prepare 20t, and then put 106.05kg of sodium polyacrylate dispersant A and 248.4kg of polycarboxylate sodium salt dispersant B into the first slurry preparation tank 1 for slurry preparation, the pH is 10, and after slurry preparation, it is transported to the first pre-storage tank 2 through a pipeline, and then the slurry enters the first filter 3 and the first wet mill 4 from the first pre-storage tank 2 through a pipeline in sequence, and is ground for the first time at a power of 300kw for 50min to obtain a primary grinding slurry;

[0057] S2, the primary grinding slurry in the first wet mill 4 is transported to the first buffer tank 5 through a pipeline, and a fungicide is continuously added to mix so that the fungicide concentration is 180ppm, and then transported to the second slurry preparation tank 7 through a second filter 6, and then transported to the second pre-storage tank 8 through a pipeline, and then the slurry enters the third filter 9 and the second wet mill 10 from the second pre-storage tank 8 through a pipeline in sequence, and is ground for the second time in the second wet mill 10 at a power of 300kw to obtain a secondary grinding slurry;

[0058] S3, transporting the secondary grinding slurry in the second wet grinder 10 to the first receiving tank 11 through a pipeline, and then transporting it to the third wet grinder 12 through a pipeline for a third grinding at a power of 300 kW to obtain a tertiary grinding slurry;

[0059] S4, the tertiary grinding slurry in the third wet grinder 12 is transported to the second receiving tank 13 through a pipeline, and then transported to the fourth wet grinder 14 through a pipeline for the fourth grinding at a power of 300kw, and the four grinding slurry obtained in the fourth wet grinder 14 is transported to the second buffer tank 15 through a pipeline, and a bactericide is continuously added to mix so that the concentration of the bactericide is 250ppm, and then transported to the finished product tank 17 through a pressure screen 16, and then the bactericide is added to the obtained ultrafine ground calcium carbonate finished product according to the dosage ratio of bactericide to ultrafine ground calcium carbonate finished product of 165ml / T for storage.

[0060] Comparative Example 2

[0061] The number of grinding times in this comparative example is adjusted on the basis of comparative example 1, and the rest is the same as embodiment 1.

[0062] The ultrafine ground calcium carbonate preparation process of this embodiment comprises the following steps:

[0063] S1. Add calcium carbonate dry powder with a particle size of 2um and a content of 25% and water into the first slurry preparation tank 1 to mix and prepare a slurry with a solid content of 75%. Prepare 20t, then put 126kg of sodium polyacrylate dispersant A into the first slurry preparation tank 1 for slurry preparation, the pH is 10, and after slurry preparation, it is transported to the first pre-storage tank 2 through a pipeline, and then the slurry enters the first filter 3 and the first wet mill 4 from the first pre-storage tank 2 through a pipeline in sequence, and performs the first grinding in the first wet mill 4 at a power of 300kw for 50min to obtain a primary grinding slurry;

[0064] S2, the primary grinding slurry in the first wet mill 4 is transported to the first buffer tank 5 through a pipeline, and a fungicide is continuously added to mix so that the fungicide concentration is 180ppm, and then the mixture is transported to the second slurry preparation tank 7 through the second filter 6, and 248.4kg of sodium polyacrylate dispersant A is added for slurry preparation, and then the slurry prepared in the second slurry preparation tank 7 is transported to the second pre-storage tank 8 through a pipeline, and then the slurry enters the third filter 9 and the second wet mill 10 from the second pre-storage tank 8 through a pipeline in sequence, and the second grinding is carried out in the second wet mill 10 at a power of 300kw for 50min to obtain the secondary grinding slurry;

[0065] S3, the secondary grinding slurry in the second wet grinder 10 is transported to the second buffer tank 15 through a pipeline, and a bactericide is continuously added to mix so that the concentration of the bactericide is 250ppm, and then transported to the finished product tank 17 through a pressure screen 16, and then the bactericide is added to the obtained ultrafine ground calcium carbonate finished product according to the dosage ratio of bactericide to ultrafine ground calcium carbonate finished product of 165ml / T for storage.

[0066] Comparative Example 3

[0067] The grinding powers of the four wet grinders were adjusted, and the rest were the same as in Example 1.

[0068] The ultrafine ground calcium carbonate preparation process of this embodiment comprises the following steps:

[0069] S1. Add calcium carbonate dry powder with a particle size of 2um and a content of 25% and water into the first slurry preparation tank 1 to mix and prepare a slurry with a solid content of 75%. Prepare 20t, then put 81kg of sodium polyacrylate dispersant A into the first slurry preparation tank 1 for slurry preparation. The slurry viscosity is 40cps and the pH is 10. After slurry preparation, it is transported to the first pre-storage tank 2 through a pipeline. Then, the slurry enters the first filter 3 and the first wet mill 4 from the first pre-storage tank 2 through a pipeline in sequence and is first ground in the first wet mill 4 at a power of 600kw for 50min to obtain a first grinding slurry;

[0070] S2, the primary grinding slurry in the first wet mill 4 is transported to the first buffer tank 5 through a pipeline, and a fungicide is continuously added to mix so that the fungicide concentration is 180ppm, and then transported to the second slurry preparation tank 7 through the second filter 6 and 25.05kg of sodium polyacrylate dispersant A is added for slurry preparation, and then the slurry prepared in the second slurry preparation tank 7 is transported to the second pre-storage tank 8 through a pipeline, and then the slurry enters the third filter 9 and the second wet mill 10 from the second pre-storage tank 8 through a pipeline in sequence, and the second grinding is carried out in the second wet mill 10 at a power of 100kw for 50min to obtain the secondary grinding slurry;

[0071] S3, the secondary grinding slurry in the second wet grinder 10 is transported to the first receiving tank 11 through a pipeline, and then 121.8 kg of polycarboxylate sodium salt dispersant B is continuously added to the first receiving tank 11 and mixed with the secondary grinding slurry, and then transported to the third wet grinder 12 through a pipeline to perform a third grinding at a power of 500 kW for 50 min to obtain a tertiary grinding slurry;

[0072] S4, the tertiary grinding slurry in the third wet grinder 12 is transported to the second receiving tank 13 through a pipeline, and then 126.6 kg of sodium polycarboxylate dispersant B is continuously added to the second receiving tank 13 and mixed with the tertiary grinding slurry, and then transported to the fourth wet grinder 14 through a pipeline for the fourth grinding at a power of 200 kW for 50 minutes, and the four grinding slurry obtained in the fourth wet grinder 14 is transported to the second buffer tank 15 through a pipeline, and a bactericide is continuously added to mix so that the concentration of the bactericide is 250 ppm, and then transported to the finished product tank 17 through a pressure screen 16, and then the bactericide is added to the obtained ultrafine ground calcium carbonate finished product according to the dosage ratio of bactericide to ultrafine ground calcium carbonate finished product of 165 ml / T for storage.

[0073] After preparing ultrafine ground calcium carbonate according to the process of Examples 1-3 of the present invention and Comparative Examples 1-3, the finished product was tested for viscosity using a rotary viscometer, and then the viscosity was measured again after standing for 8 hours. The test results are shown in Table 1 below.

[0074] Table 1 Viscosity test of ultrafine ground calcium carbonate

[0075] Viscosity(cps) Viscosity after standing for 8 hours (cps) Example 1 236.8 350.7 Example 2 243.9 363.1 Example 3 240.2 356.3 Comparative Example 1 498.6 839.2 Comparative Example 2 542.5 871.6 Comparative Example 3 326.4 502.8

[0076] The above results show that by adding dispersant A and dispersant B in small amounts multiple times, controlling the power of each wet grinder, and using parallel multiple grinding processes in Examples 1-3 of the present invention, the viscosity of the prepared ultrafine ground calcium carbonate can be effectively controlled, and the viscosity value rises slowly after standing for 8 hours, and the viscosity value is between 350.7 and 363.1 cps, with good rheological properties and high viscosity stability. The viscosity can effectively improve the efficiency of long-distance pump transportation of finished products, avoid problems such as blockage in the pump and increased pumping pressure affecting the flow rate. Compared with Example 1, Comparative Example 1 adds dispersant A and dispersant B to the slurry at one time, but cannot be evenly dispersed, and cannot better control the viscosity of the slurry during the subsequent grinding process, resulting in excessive viscosity of the finished product, and the viscosity reaches 839.2 cps after standing for 8 hours, resulting in increased resistance to long-distance pumping of the ultrafine ground calcium carbonate finished product and reduced flow rate. Compared with Example 1, Comparative Example 2 changed the grinding times, and the grinding was not sufficient, so that dispersant A and dispersant B could not be fully mixed, resulting in an increase in the viscosity of the formed product. Compared with Example 1, Comparative Example 3 changed the power of the four grinders, resulting in uneven viscosity distribution of the ultrafine ground calcium carbonate obtained by grinding at each stage, and the viscosity of the finished product obtained in the later stage changed.

[0077] The ultrafine ground calcium carbonate prepared in Examples 1-3 of the present invention and Comparative Examples 1-3 was tested for particle size distribution by the liquid dispersion method in GB / T19077-2016 / IS013320:2009 Particle size distribution laser diffraction method, and the particle size and distribution characteristics of the tiny particles were measured by the LS-909 laser particle size analyzer (and automatic sampler). The results are shown in Table 1 below.

[0078]

[0079]

[0080] The above results show that the ultrafine ground calcium carbonate product prepared by the process of Examples 1-3 of the present invention has a good particle size, 1um particle size content 88%-90%, 2um particle size content 98%-100%, and can accurately control the ultrafine ground calcium carbonate particle size fineness within the required range. Compared with Example 1, Comparative Example 1 and dispersant A and dispersant B are added simultaneously, but they are not evenly dispersed, and the grinding particle size is uneven during the grinding process, so that the ultrafine ground calcium carbonate content of particle size 1um and 2um is slightly reduced; Compared with Example 1, Comparative Example 2 only adds dispersant A and dispersant B once and grinds twice, the grinding is insufficient, and the ultrafine ground calcium carbonate 1um and 2um contents are reduced to 80.39% and 89.46% respectively; Compared with Example 1, Comparative Example 3 changes the grinding power of four wet grinders, resulting in uneven distribution of ultrafine ground calcium carbonate particles obtained by grinding in each section, and the 1um and 2um contents are reduced to 82.67% and 91.63% respectively.

[0081] Without using porcelain clay, the ultrafine ground calcium carbonate prepared in Example 1 of the present invention is added to the calendered paper base paper of model GAD157, the calendered paper base paper is composed of base paper, coating and starch glue in a mass ratio of 96:58:3; the base paper is composed of NBKP bleached sulfate coniferous pulp (lion): LBKP bleached sulfate broadleaf pulp (Lion): BCTMP bleached chemical thermomechanical pulp (Jingui 75L) in a mass ratio of 10:78:12; the coating formula is composed of ultrafine ground calcium carbonate and adhesive in a mass ratio of 9:10; the adhesive is composed of latex and starch in a mass ratio of 8:2. The glossiness of the paper is measured at a measuring angle of 75° using a photoelectric detector of model code 224, and the experimental results are shown in Table 3 below.

[0082] Table 3 Glossiness measurement of calendered paper

[0083]

[0084]

[0085] From the above results, it can be seen that the ultrafine ground calcium carbonate prepared by the present invention can be used in the manufacture of calendered paper, and the glossiness of the paper can be 65 or above, and the paper performance is good. It shows that the ultrafine ground calcium carbonate of the present invention can partially or completely replace the use of porcelain clay, thereby reducing the amount of porcelain clay mining and protecting the social environment.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for preparing ultrafine ground calcium carbonate, characterized in that: The following steps are involved: S1. Mixing calcium carbonate powder with water to form a slurry with a solid content of 75%-76%, then adding dispersant A to a slurry preparation tank for slurry preparation, and grinding once to obtain a primary grinding slurry; the primary grinding slurry has a particle size of 2um content of 64%-65% and a viscosity of 40-60cps; S2, adding dispersant A to the primary grinding slurry to prepare the slurry, and then grinding the slurry for a second time to obtain a secondary grinding slurry; the secondary grinding slurry has a particle size of 2um content of 74%-76% and a viscosity of 90-120cps; S3, adding dispersant B to the secondary grinding slurry, mixing, and grinding for three times to obtain a tertiary grinding slurry; the content of particles with a diameter of 2 um in the tertiary grinding slurry is 94%-96%, and the viscosity is 150-180 cps; S4, mixing the thrice-ground slurry with dispersant B again and grinding it for a fourth time to obtain a fourth-ground slurry, and then storing the obtained ultrafine ground calcium carbonate finished product.

2. The process for preparing ultrafine ground calcium carbonate according to claim 1, wherein: The dispersant A is sodium polyacrylate; the dispersant B is sodium polycarboxylate.

3. The process for preparing ultrafine ground calcium carbonate according to claim 1, wherein: In step S1, the calcium carbonate dry powder has a particle size of 2 um and a content of 25%-35%.

4. The process for preparing ultrafine ground calcium carbonate according to claim 1, wherein: In step S1 and step S2, the dispersant A is added in an amount of 1.5-6 kg / t of calcium carbonate dry powder by mass.

5. The process for preparing ultrafine ground calcium carbonate according to claim 1, wherein: In step S1 and step S2, the pH value during the slurry adjustment process is 9.5-10.

5.

6. The process for preparing ultrafine ground calcium carbonate according to claim 1, wherein: During the grinding process, the power of the wet grinder is 200-300kw, and the grinding time is 50-60min.

7. The process for preparing ultrafine ground calcium carbonate according to claim 1, wherein: In step S3 and step S4, the dispersant B is added in an amount of 8-9 kg / t of calcium carbonate dry powder.

8. The process for preparing ultrafine ground calcium carbonate according to claim 1, wherein: The ultrafine ground calcium carbonate product has a 2um particle size content of 98%-100%, a 1um particle size content of 88%-90%, and a viscosity of 240-280cps.

9. The ultrafine ground calcium carbonate prepared by the preparation technology described in any one of claims 1 to 8.

10. The process for preparing ultrafine ground calcium carbonate according to any one of claims 1 to 8, characterized in that: The device for preparing ultrafine ground calcium carbonate includes: a first slurry preparation tank, a first pre-storage tank, a first filter, a first wet grinder, a first buffer tank, a second filter, a second slurry preparation tank, a second pre-storage tank, a third filter, a second wet grinder, a first receiving tank, a third wet grinder, a second receiving tank, a fourth wet grinder, a second buffer tank, and a finished product tank; the first slurry preparation tank is connected to the first pre-storage tank, the first filter, the first wet grinder, the first buffer tank, the second filter, the second slurry preparation tank, the second pre-storage tank, the third filter, the second wet grinder, the first receiving tank, the third wet grinder, the second receiving tank, the fourth wet grinder, and the second buffer tank in sequence through a pipeline, and the second buffer tank is connected to the finished product tank through a pressure screen.

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