Method for preparing high-whiteness nano calcium carbonate through rapid calcination at high temperature

Abstract

The invention relates to the technical field of inorganic powder preparation and surface modification, in particular to a method for preparing high-whiteness nano calcium carbonate through rapid calcination at a high temperature. The method comprises the following steps: (1) quickly calcining limestone at high temperature to obtain calcium oxide; (2) adding water into the calcium oxide obtained in the step (1), and digesting to prepare calcium hydroxide slurry; (3) introducing carbon dioxide into the calcium hydroxide slurry obtained in the step (2) to carry out carbonization reaction, and adding a whitening conversion agent into the system in the later period of carbonization to coat nano calcium carbonate; and (4) activating the nano calcium carbonate coated in the step (3), and finally separating to obtain the high-whiteness nano calcium carbonate. In the preparation process of the nano calcium carbonate, the whiteness of the nano calcium carbonate is improved through a high-temperature calcination and chemical coating modification method, preparation and whitening are integrated, the technological process is simple, the applicability is wide, and the cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic powder preparation and surface modification, and in particular to a method for preparing high-whiteness nano calcium carbonate by rapid calcination at high temperature. Background Art

[0002] In recent decades, the domestic market demand for nano calcium carbonate as a new functional material has been growing, but the production process of nano calcium carbonate still has problems such as backward process equipment and unstable product quality. In the production of nano calcium carbonate, the calcination process has a long calcination time, which leads to overburning of the limestone surface and raw burning of the center, which will greatly affect the properties of the prepared nano calcium carbonate. The particle size morphology and particle size distribution of nano calcium carbonate are its important quality indicators, because nano calcium carbonate products with small particle size and uniform distribution have greater demand and higher application value in the market.

[0003] With the development of the national economy and the improvement of people's living standards, the demand for light-colored products is increasing. On the other hand, as my country's downstream industries such as papermaking and toothpaste have higher and higher requirements for the whiteness of high-whiteness nano calcium carbonate, the whiteness of nano calcium carbonate on the market is mostly 90, the output of high-whiteness nano calcium carbonate is low, and the supply and demand are unbalanced. Therefore, it is urgent to improve the whiteness of nano calcium carbonate powder.

[0004] At present, there are physical and chemical methods for whitening in the preparation process of nano calcium carbonate. Common physical methods include mechanical crushing, hand selection and gravity separation. The mechanical crushing method first crushes the raw materials to obtain impurities, and then removes impurities through multiple steps such as manual and color sorting. The process is complicated and the whitening effect is poor. The hand selection method requires the naked eye to observe the color and density of the ore, which is not only inefficient and time-consuming, but also has large subjective differences and uneven product quality. The gravity separation method removes impurities based on the difference in mineral density, and the whiteness can only be improved to a certain extent.

[0005] Hu Qingfu et al. explained in the study of chemical whitening technology of light calcium carbonate (Inorganic Salt Industry, 2008, 40(2), 38-40.) that the widely used chemical whitening methods mainly include oxidation-reduction method and chemical coating method. The oxidation-reduction method uses a strong reducing agent to convert Fe 3+ and its oxides are reduced to Fe 2+, and then remove the impurity Fe through complex reaction, but the added strong reducing agent is very likely to cause side reactions, resulting in excessive consumption of the agent and affecting product quality. Chemical coating methods include mechanical coating and chemical precipitation. The chemical precipitation method has a chemical reaction, which makes the combination tighter and has a better whitening effect. CN200610048062 discloses a method of using mechanical coating and chemical coating to eliminate brucite powder chromophore impurities to improve whiteness, but this method requires a complex mechanical treatment process, cannot achieve in-situ modification, and has a complex process.

[0006] In view of this, it is urgent to develop a method for preparing high-whiteness nano calcium carbonate with low energy consumption, simple process, wide applicability, environmental friendliness and high efficiency. Summary of the invention

[0007] The invention solves the problems existing in the prior art and proposes a method for preparing high-whiteness nano calcium carbonate by rapid calcination at high temperature. The method is characterized in that limestone is rapidly calcined at high temperature to obtain calcium oxide, water is added to digest the calcium oxide to prepare calcium hydroxide slurry, a whitening conversion agent is added to the system in the later stage of the carbonization reaction of calcium hydroxide and carbon dioxide to coat the nano calcium carbonate, and finally the nano calcium carbonate is activated by a modifier and separated to obtain the high-whiteness nano calcium carbonate. The invention significantly reduces the calcination energy consumption, improves the whiteness of the nano calcium carbonate product, and has the advantages of being environmentally friendly, free of hazardous chemicals, and having a simple preparation process.

[0008] Compared with the prior art, the present invention has the following advantages:

[0009] 1. Realize rapid calcination of limestone and reduce energy consumption.

[0010] 2. In the process of preparing nano calcium carbonate, the whitening conversion agent is directly added to prepare the whitening integrated product, which has a simple process flow and is environmentally friendly.

[0011] 3. Compared with the chemical whitening method, the present invention has simple chemical reagents, does not involve hazardous chemicals, and has a high safety production coefficient.

[0012] 4. The process cost is relatively low and the product added value is high. The high whiteness nano calcium carbonate produced has strong competitiveness and good product benefits. DETAILED DESCRIPTION

[0013] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in the present invention.

[0014] 1. A method for preparing high-whiteness nano calcium carbonate by rapid calcination at high temperature, the method comprising the following steps:

[0015] (1) Rapidly calcining limestone at high temperature to obtain calcium oxide;

[0016] (2) adding water to the calcium oxide obtained in step (1) to prepare a calcium hydroxide slurry;

[0017] (3) introducing carbon dioxide into the calcium hydroxide slurry obtained in step (2) for carbonization reaction, and adding a whitening conversion agent to the system in the later stage of carbonization to coat the nano calcium carbonate;

[0018] (4) activating the nano calcium carbonate obtained by coating in step (3), and finally separating to obtain high whiteness nano calcium carbonate.

[0019] 2. The high temperature calcination as described in claim 1 (1), characterized in that the calcination temperature is 650-1350°C, preferably 850-1100°C; the calcination time is 1 min-3 h, preferably 2 min-2 h.

[0020] 3. The process for preparing the calcium hydroxide slurry according to claim 1 (2), characterized in that the digestion temperature is 30-75° C., preferably 50-65° C.; the ratio of calcium oxide to water is 1:1-1:10, preferably 1:4-1:8;

[0021] The concentration of calcium hydroxide is 4-12%, preferably 6.0-9.0%.

[0022] 4. The carbonization reaction as described in claim 1 (3) is a carbonization reaction process of calcium hydroxide and carbon dioxide, wherein the carbonization temperature is 10-30°C, preferably 15-25°C; the CO2 flow rate is 3-9L / (min·10gCaO), preferably 5-8L / (min·10gCaO); and the stirring speed is 200-1000 rpm, preferably 400-700 rpm.

[0023] 5. The late stage of carbonization as described in claim 1 (3) is 70-98% of the overall carbonization process, preferably 85-95%.

[0024] 6. The whitening conversion agent as described in claim 1 (3) is MgSO4, Mg(NO3)2, MgCl2 and

[0025] One or more of MgAc2, the whitening conversion agent accounts for 0.1-3.5% by weight of nano calcium carbonate,

[0026] Preferably it is 0.5-2.0%.

[0027] 7. The modification process as described in claim 1 (4) is an activation process for the whitened nano-calcium carbonate slurry, the modifier is one or more of sodium stearate, stearic acid, oleic acid and lauric acid, and the weight percentage concentration of the modifier is 0.5-4.0%, preferably 1.0-2.5%; the pH of the modification process system is 6-10, preferably 6.5-8.

[0028] 8. As claimed in claim 1 and 7 (4) wherein the nano calcium carbonate slurry concentration is 5-35wt%, preferably

[0029] 10-25wt%; modification temperature 40-90℃, preferably 55-80℃; constant temperature stirring 40-180min, preferably 50-70min; stirring speed 150-3000 rpm, preferably 300-900 rpm.

[0030] The present invention is described in detail below by way of examples, but the protection scope of the present invention is not limited to the contents described above.

[0031] The following examples all use limestone from Tianjin Juhengda Chemical Co., Ltd. as raw material. After analysis, the limestone composition is CaCO3≥99.0 and the whiteness is 85.

[0032] Example 1

[0033] (1) Using limestone from Tianjin Juhengda Chemical Co., Ltd. as raw material, the limestone was calcined at 1000°C for 3 minutes to obtain CaO;

[0034] (2) the CaO obtained by calcination in (1) was digested at 60°C with a CaO:H2O ratio of 1:5 to prepare 8 wt% Ca(OH)2;

[0035] (3) The calcium hydroxide slurry obtained in (2) was cooled to 18° C., 6 L / (min·10 g CaO) was introduced, and a carbonization reaction was carried out at a stirring speed of 600 rpm.

[0036] (4) When the carbonization reaction in (3) is 95%, 2.5 wt% MgCl2 is added to whiten the nano-calcium carbonate, and when pH = 7.5, ventilation is stopped, and constant temperature stirring is maintained for 15 minutes at a stirring speed of 300 rpm to obtain a whitened nano-calcium carbonate slurry.

[0037] (5) The whitened nano-calcium carbonate slurry obtained in (4) was filtered and separated, and then water was added to make it 20wt%, and 2.5wt% sodium stearate was added for activation. The temperature was 80°C, the stirring speed was 700 rpm, and the activation time was 60min.

[0038] (6) The activated nano-calcium carbonate slurry in (5) was separated and dried at 110° C. to obtain a nano-calcium carbonate product, the whiteness of which is shown in Table 1.

[0039] Example 2

[0040] (1) Using limestone from Tianjin Juhengda Chemical Co., Ltd. as raw material, the limestone was calcined at 1000°C for 3 minutes to obtain CaO;

[0041] (2) the CaO obtained by calcination in (1) was digested at 60°C with a CaO:H2O ratio of 1:5 to prepare 8 wt% Ca(OH)2;

[0042] (3) The calcium hydroxide slurry obtained in (2) was cooled to 18° C., 6 L / (min·10 g CaO) was introduced, and a carbonization reaction was carried out at a stirring speed of 600 rpm.

[0043] (4) When the carbonization reaction in (3) is 95%, 2.0 wt% MgCl2 is added to whiten the nano-calcium carbonate, and when pH = 7.5, ventilation is stopped, and constant temperature stirring is maintained for 15 minutes at a stirring speed of 300 rpm to obtain a whitened nano-calcium carbonate slurry.

[0044] (5) The whitened nano-calcium carbonate slurry obtained in (4) was filtered and separated, and then water was added to make it 20wt%, and 2.5wt% sodium stearate was added for activation. The temperature was 80°C, the stirring speed was 700 rpm, and the activation time was 60min.

[0045] (6) The activated nano-calcium carbonate slurry in (5) was separated and dried at 110° C. to obtain a nano-calcium carbonate product, the whiteness of which is shown in Table 1.

[0046] Example 3

[0047] (1) Using limestone from Tianjin Juhengda Chemical Co., Ltd. as raw material, the limestone was calcined at 1000°C for 3 minutes to obtain CaO;

[0048] (2) the CaO obtained by calcination in (1) was digested at 60°C with a CaO:H2O ratio of 1:5 to prepare 8 wt% Ca(OH)2;

[0049] (3) The calcium hydroxide slurry obtained in (2) was cooled to 18° C., 6 L / (min·10 g CaO) was introduced, and a carbonization reaction was carried out at a stirring speed of 600 rpm.

[0050] (4) When the carbonization reaction in (3) is 95%, 1.5 wt% MgCl2 is added to whiten the nano-calcium carbonate, and when pH = 7.5, ventilation is stopped, and constant temperature stirring is maintained for 15 minutes at a stirring speed of 300 rpm to obtain a whitened nano-calcium carbonate slurry.

[0051] (5) The whitened nano-calcium carbonate slurry obtained in (4) was filtered and separated, and then water was added to make it 20wt%, and 2.5wt% sodium stearate was added for activation. The temperature was 80°C, the stirring speed was 700 rpm, and the activation time was 60min.

[0052] (6) The activated nano-calcium carbonate slurry in (5) was separated and dried at 110° C. to obtain a nano-calcium carbonate product, the whiteness of which is shown in Table 1.

[0053] Example 4

[0054] (1) Using limestone from Tianjin Juhengda Chemical Co., Ltd. as raw material, the limestone was calcined at 1000°C for 3 minutes to obtain CaO;

[0055] (2) the CaO obtained by calcination in (1) was digested at 60°C with a CaO:H2O ratio of 1:5 to prepare 8 wt% Ca(OH)2;

[0056] (3) The calcium hydroxide slurry obtained in (2) was cooled to 18° C., 6 L / (min·10 g CaO) was introduced, and a carbonization reaction was carried out at a stirring speed of 600 rpm.

[0057] (4) When the carbonization reaction in (3) is 95%, 2.5 wt% MgCl2 is added to whiten the nano-calcium carbonate, and when pH = 7.5, ventilation is stopped, and constant temperature stirring is maintained for 15 minutes at a stirring speed of 300 rpm to obtain a whitened nano-calcium carbonate slurry.

[0058] (5) The whitened nano calcium carbonate slurry obtained in (4) was filtered and separated, and then water was added to make it 20wt%, and 2.5wt% sodium stearate was added for activation. The temperature was 70°C, the stirring speed was 700 rpm, and the activation time was 60min.

[0059] (6) The activated nano-calcium carbonate slurry in (5) was separated and dried at 110° C. to obtain a nano-calcium carbonate product, the whiteness of which is shown in Table 1.

[0060] Example 5

[0061] (1) Using limestone from Tianjin Juhengda Chemical Co., Ltd. as raw material, the limestone was calcined at 950°C for 10 min to obtain CaO;

[0062] (2) the CaO obtained by calcination in (1) was digested at 60°C with a CaO:H2O ratio of 1:5 to prepare 8 wt% Ca(OH)2;

[0063] (3) The calcium hydroxide slurry obtained in (2) was cooled to 18° C., 6 L / (min·10 g CaO) was introduced, and a carbonization reaction was carried out at a stirring speed of 600 rpm.

[0064] (4) When the carbonization reaction in (3) is 95%, 2.5 wt% MgCl2 is added to whiten the nano-calcium carbonate, and when pH = 7.5, ventilation is stopped, and constant temperature stirring is maintained for 15 minutes at a stirring speed of 300 rpm to obtain a whitened nano-calcium carbonate slurry.

[0065] (5) The whitened nano-calcium carbonate slurry obtained in (4) was filtered and separated, and then water was added to make it 20wt%, and 2.5wt% sodium stearate was added for activation. The temperature was 80°C, the stirring speed was 700 rpm, and the activation time was 60min.

[0066] (6) The activated nano-calcium carbonate slurry in (5) was separated and dried at 110° C. to obtain a nano-calcium carbonate product, the whiteness of which is shown in Table 1.

[0067] Example 6

[0068] (1) Using limestone from Tianjin Juhengda Chemical Co., Ltd. as raw material, the limestone was calcined at 950°C for 10 min to obtain CaO;

[0069] (2) the CaO obtained by calcination in (1) was digested at 60°C with a CaO:H2O ratio of 1:5 to prepare 8 wt% Ca(OH)2;

[0070] (3) The calcium hydroxide slurry obtained in (2) was cooled to 18° C., 6 L / (min·10 g CaO) was introduced, and a carbonization reaction was carried out at a stirring speed of 600 rpm.

[0071] (4) When the carbonization reaction in (3) is 95%, 2.5 wt% MgCl2 is added to whiten the nano-calcium carbonate, and when pH = 7.5, ventilation is stopped, and constant temperature stirring is maintained for 15 minutes at a stirring speed of 300 rpm to obtain a whitened nano-calcium carbonate slurry.

[0072] (5) The whitened nano-calcium carbonate slurry obtained in (4) was filtered and separated, and then water was added to make it 20wt%, and 2.5wt% stearic acid was added for activation. The temperature was 80°C, the stirring speed was 700 rpm, and the activation time was 60min.

[0073] (6) The activated nano-calcium carbonate slurry in (5) was separated and dried at 110° C. to obtain a nano-calcium carbonate product, the whiteness of which is shown in Table 1.

[0074] Comparative Example 1

[0075] (1) Using limestone from Tianjin Juhengda Chemical Co., Ltd. as raw material, the limestone was calcined at 1000°C for 3 minutes to obtain CaO;

[0076] (2) the CaO obtained by calcination in (1) was digested at 60°C with a CaO:H2O ratio of 1:5 to prepare 8 wt% Ca(OH)2;

[0077] (3) The calcium hydroxide slurry obtained in (2) was cooled to 18° C., 6 L / (min·10 g CaO) was introduced, and carbonization reaction was carried out at a stirring speed of 600 rpm. Aeration was stopped when pH=7.

[0078] (4) The nano calcium carbonate slurry obtained in (3) was separated and dried at 110°C to obtain a nano calcium carbonate product. The whiteness of the product is shown in Table 1 and the scanning electron microscope (SEM) is shown in Table 1. Figure 1 .

[0079] Table 1

[0080] Example Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example Whiteness(wb) 94.8 94.7 94.5 94.4 94.6 94.2 93.4

[0081] It should be understood that parts not elaborated in detail in this specification belong to the prior art.

[0082] It should be understood that the above description of the preferred embodiment is relatively detailed and cannot be regarded as limiting the scope of patent protection of the present invention. Under the enlightenment of the present invention, ordinary technicians in this field can also make substitutions or modifications without departing from the scope of protection of the claims of the present invention, which all fall within the scope of protection of the present invention. The scope of protection requested for the present invention shall be based on the attached claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 Scanning electron microscope image of nano calcium carbonate prepared using limestone from Tianjin Juhengda Chemical Co., Ltd.

Claims

1. A method for preparing high-whiteness nano calcium carbonate by rapid calcination at high temperature, the method comprising the following steps: (1) Rapidly calcining limestone at high temperature to obtain calcium oxide; (2) adding water to the calcium oxide obtained in step (1) to prepare a calcium hydroxide slurry; (3) introducing carbon dioxide into the calcium hydroxide slurry obtained in step (2) for carbonization reaction, and adding a whitening conversion agent to the system in the later stage of carbonization to coat the nano calcium carbonate; (4) activating the nano calcium carbonate obtained by coating in step (3), and finally separating to obtain high whiteness nano calcium carbonate.

2. The high temperature calcination as described in claim 1 (1), characterized in that The calcination temperature is 650-1350°C, preferably 850-1100°C; the calcination time is 1 min-3 h, preferably 2 min-2 h.

3. The preparation process of the calcium hydroxide slurry as described in claim 1 (2), characterized in that The digestion temperature is 30-75°C, preferably 50-65°C; the ratio of calcium oxide to water is 1:1-1:10, preferably 1:4-1:8; The concentration of calcium hydroxide is 4-12%, preferably 6.0-9.0%.

4. The carbonization reaction as described in claim 1 (3) is a carbonization reaction process of calcium hydroxide and carbon dioxide, wherein the carbonization temperature is 10-30°C, preferably 15-25°C; the CO2 flow rate is 3-9L / (min·10gCaO), preferably 5-8L / (min·10gCaO); and the stirring speed is 200-1000 rpm, preferably 400-700 rpm.

5. The late stage of carbonization as described in claim 1 (3) is 70-98% of the overall carbonization process, preferably 85-95%.

6. The whitening conversion agent as described in claim 1 (3) is one or more of MgSO4, Mg(NO3)2, MgCl2 and MgAc2, and the whitening conversion agent accounts for 0.1-3.5% by weight of the nano-calcium carbonate, preferably 0.5-2.0%.

7. The modification process as described in claim 1 (4) is an activation process for the whitened nano-calcium carbonate slurry, the modifier is one or more of sodium stearate, stearic acid, oleic acid and lauric acid, and the weight percentage concentration of the modifier is 0.5-4.0%, preferably 1.0-2.5%; the pH of the modification process system is 6-10, preferably 6.5-8.

8. As claimed in claims 1 and 7 (4), wherein the nano calcium carbonate slurry concentration is 5-35wt%, preferably 10-25wt%; the modification temperature is 40-90°C, preferably 55-80°C; the constant temperature stirring is 40-180min, preferably 50-70min; the stirring speed is 150-3000 rev / min, preferably 300-900 rev / min.

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