阅读说明：本技术 一种粒径可控的硅酸钙的制备方法及由其制备的硅酸钙和用途 (Preparation method of calcium silicate with controllable particle size, calcium silicate prepared by preparation method and application of calcium silicate ) 是由 陈芳芳 曹绍涛 张毅 于 2019-10-29 设计创作，主要内容包括：本发明提供一种粒径可控的硅酸钙的制备方法,所述方法通过将含硅酸根的碱液作辅助液与钙源混合制得混合液后,再在反应温度下将硅酸钠溶液滴入所述混合液中,可达到严格控制硅酸钙粒径的目的,不需要额外添加粒径控制剂,也不需要对产物浆料进行过筛处理,即可解决硅酸钙中大颗粒含量高的问题,同时该方法反应条件温和,操作简单,能耗低；所述方法制得的硅酸钙粒径小且粒径分布均匀,将其应用于造纸填料中,显著降低了现有技术中大颗粒商品对高速纸机的磨损,同时可以很好地改善加填纸张的松厚度,具有较高的工业应用价值。(The invention provides a preparation method of calcium silicate with controllable particle size, the method is to mix alkaline liquor containing silicate radical as auxiliary liquid with calcium source to prepare mixed liquid, then to drop sodium silicate solution into the mixed liquid at reaction temperature, to achieve the aim of strictly controlling the particle size of calcium silicate, without adding additional particle size control agent, and without sieving the product slurry, to solve the problem of high content of large particles in calcium silicate, meanwhile, the method has mild reaction condition, simple operation and low energy consumption; the calcium silicate prepared by the method has small particle size and uniform particle size distribution, is applied to papermaking filler, remarkably reduces the abrasion of large-particle commodities to a high-speed paper machine in the prior art, can well improve the bulk of filled paper, and has higher industrial application value.)

1. A method of preparing calcium silicate having a controlled particle size, said method comprising the steps of:

(1) uniformly mixing alkaline liquor containing silicate radicals serving as auxiliary liquor with a calcium source to obtain mixed liquor;

(2) heating the mixed solution to a reaction temperature;

(3) at the reaction temperature, dripping a sodium silicate solution into the mixed solution to obtain a reaction solution;

(4) and reacting the reaction solution at a reaction temperature, and performing solid-liquid separation and drying to obtain the calcium silicate with controllable particle size.

2. The method according to claim 1, wherein the silicate-containing lye of step (1) is a silicate-containing sodium hydroxide solution or potassium hydroxide solution, preferably a silicate-containing sodium hydroxide solution;

preferably, the alkali concentration in the silicate-containing sodium hydroxide solution is Na₂O is 30-240 g/L, preferably 90-220 g/L;

preferably, the silicate concentration in the silicate-containing sodium hydroxide solution is SiO₂Is 0.01 to 10g/L, preferably 0.4 to 7 g/L;

preferably, the calcium source is any one or a combination of at least two of calcium oxide, calcium-containing alkali or calcium salt, preferably any one or a combination of at least two of lime, lime milk, solid calcium hydroxide, calcium chloride or calcium nitrate, and further preferably lime and/or lime milk;

preferably, the addition amount of lime in the lime milk is 100-200 g per liter, and preferably 130-160 g per liter.

3. The method according to claim 1 or 2, wherein the auxiliary liquid and the calcium source are uniformly mixed under stirring in the step (1) to prepare a mixed liquid;

preferably, the stirring speed is 300-700 r/min, preferably 350-500 r/min.

4. The process according to any one of claims 1 to 3, wherein the reaction temperature in step (2) is 60 to 100 ℃, preferably 85 to 98 ℃;

preferably, the heating mode is electric heating, water bath heating or oil bath heating, and preferably electric heating.

5. The method according to any one of claims 1 to 4, wherein the volume ratio of the sodium silicate solution in the step (3) to the auxiliary liquid in the step (1) is 1 to 6:1, preferably 2 to 4: 1;

preferably, the calcium in the calcium source in step (1) is mixed with the silicon in the sodium silicate solution by CaO: SiO₂The calculated molar ratio is 0.9-1.2, preferably 0.95-1.05;

preferably, the sodium silicate solution is dripped into the mixed solution at a constant speed to obtain a reaction solution;

preferably, the sodium silicate solution is dripped into the mixed solution for 0.5 to 3 hours, preferably for 1.0 to 2.5 hours;

preferably, the sodium silicate solution is an alkali-containing sodium silicate solution;

preferably, the sodium silicate solution is low-grade bauxite or a waste catalyst taking a silicon and aluminum system as a carrier and a product obtained by desiliconizing a reaction product of the waste catalyst under the action of alkali liquor;

preferably, the alkali concentration in the sodium silicate solution is Na₂The O is 20-250 g/L, preferably 35-200 g/L;

preferably, the concentration of silicate in the sodium silicate solution is SiO₂The amount is 15-80 g/L, preferably 25-60 g/L.

6. The process according to any one of claims 1 to 5, wherein the reaction time in step (4) is 1 to 10 hours, preferably 3 to 7 hours;

preferably, the drying is vacuum drying, freeze drying or forced air drying, preferably forced air drying;

preferably, the temperature of the vacuum drying or the forced air drying is 70-110 ℃, and preferably 85-105 ℃.

7. The method according to any one of claims 1 to 6, characterized in that the operation of washing the calcium silicate subjected to solid-liquid separation is further included between the solid-liquid separation and the drying operation;

preferably, the washing is washing with clean water;

preferably, the number of washes is at least three.

8. A method according to any one of claims 1 to 7, characterized in that the method comprises the steps of:

(1) uniformly mixing a sodium hydroxide solution containing a silicate radical as an auxiliary solution with a calcium source under the stirring condition of 300-700 r/min to obtain a mixed solution, wherein the alkali concentration in the sodium hydroxide solution containing the silicate radical is Na₂O is 30 to 240g/L, and the silicate concentration is SiO₂Calculated as 0.01-10 g/L;

(2) heating the mixed solution to 60-100 ℃;

(3) adding Na to the alkali concentration for 0.5-3 h at 60-100 DEG C₂O is 20 to 250g/L, and the silicate concentration is SiO₂Dripping 15-80 g/L sodium silicate solution into the mixed solution at a constant speed to obtain a reaction solution, wherein the volume ratio of the sodium silicate solution to the auxiliary solution in the step (1) is 1-6: 1, and the calcium in the calcium source in the step (1) and the silicon in the sodium silicate solution are CaO: SiO₂The calculated molar ratio is 0.9-1.2;

(4) and reacting the reaction liquid at 60-100 ℃ for 1-10 h, performing solid-liquid separation on the prepared calcium silicate and the reaction slurry, washing the calcium silicate subjected to solid-liquid separation at least three times by using clear water, and drying the washed calcium silicate to obtain the calcium silicate with controllable particle size.

9. Calcium silicate produced by the production method according to any one of claims 1 to 8.

10. Use of the calcium silicate according to claim 9 in the field of paper, plastics or rubber, preferably in the field of paper.

Technical Field

The invention relates to the technical field of papermaking fillers, in particular to a preparation method of calcium silicate with controllable particle size, calcium silicate prepared by the preparation method and application of the calcium silicate.

Background

In recent years, the global paper industry has consumed about 3170 million tons of mineral fines per year, of which about 1360 million tons are used for paper filler. The filler was the second largest paper stock second only to pulp fibers, of which 43% was Ground Calcium Carbonate (GCC), 33% was Precipitated Calcium Carbonate (PCC), 12% was kaolin, and 10% was talc. The calcium silicate can also be used as a filler in papermaking, wherein the natural wollastonite has more than 10 years of history of application in the papermaking filler in China and mature application technology, but the application field is limited due to large hardness and high abrasion value. Porous calcium silicate is a new papermaking filler that has emerged in recent years. Research shows that the synthetic porous calcium silicate has a honeycomb structure, large specific surface area, small bulk density, higher retention rate as a filler, and can well improve bulk (bulk) of filled paper and endow the paper with better optical performance. However, due to the influence of factors such as the current synthesis cost and the quality of the synthesized product, no industrial examples for the use of the papermaking filler are reported so far.

Wherein, the particle size and the distribution of the calcium silicate have key influence on the application of the calcium silicate in the papermaking filler, and if fine particles, namely particles with the particle size of less than 1 mu m, have higher content, the filler is easy to run off; if the coarse particle content is high, the forming wire and wet end equipment may be worn and may affect sheet tightness and surface strength when used in high speed paper machines. Therefore, the paper filler usually has a requirement of 325 mesh (45 μm) screen residue content of less than or equal to 0.2 percent. The particle size of existing calcium silicates is generally larger than commercial PCC and GCC, and therefore controlling the particle size of synthetic calcium silicates is one of the keys to achieving industrial application of synthetic calcium silicates in papermaking fillers.

The existing method for controlling the particle size of calcium silicate mainly controls the particle size of finished calcium silicate by adding a particle size control agent or grinding.

CN104085896B discloses a preparation method of active calcium silicate, which mixes lime milk, fly ash desilication liquid and a particle size control agent for reaction to obtain active calcium silicate slurry, wherein the method can reduce large particles in the active calcium silicate, but the average particle size can only be controlled to be about 20 mu m of D50, and the maximum particle size is about 60-80 mu m, and when the active calcium silicate slurry is applied to a high-speed paper machine in the papermaking process, the slurry causes great abrasion to the high-speed paper machine, and the requirement of the existing papermaking filler on the particle size is difficult to achieve.

Li Tao et al disclose a method of reducing the particle size of calcium silicate fillers by grinding (see "the influence of particle size of calcium silicate fillers on their filling properties in paper", Li Tao et al, university of Shaanxi science and technology, Vol.34, No. 2, pp.30-34). The research shows that the damage degree of the porous structure on the surface of the filler is increased along with the prolonging of the grinding time, the average particle size is reduced, the fine particles are increased, the uniformity of the particle size distribution of the filler is changed, and the damage degree and the average particle size influence the color and the strength of the finished filled paper.

CN103306159B discloses a method for modifying calcium silicate papermaking filler, which comprises the steps of heating the calcium silicate filler to 600-900 ℃, modifying the calcium silicate filler, and strictly controlling the heating rate and the temperature to enable the particle size of final calcium silicate to be 10-20 mu m.

It can be seen that none of the methods currently involved in controlling the calcium silicate particle size meet the paper filler requirements: the particle size and the particle size distribution of the obtained product can not meet the requirements of the existing papermaking filler by selecting a proper particle size control agent, and the grinding and high-temperature modification method greatly increases the energy consumption in the preparation process and increases the production cost.

Therefore, the development of the preparation method of calcium silicate with simple process, low cost and controllable particle size has obvious significance for energy conservation and consumption reduction in the paper industry.

Disclosure of Invention

In view of the problems in the prior art, the invention provides a preparation method of calcium silicate with controllable particle size, which comprises the steps of mixing alkaline liquor containing silicate radicals as auxiliary liquid with a calcium source to prepare a mixed solution, then slowly dropwise adding a sodium silicate solution into the mixed solution at a reaction temperature, and adjusting the molar ratio of silicon to calcium in a reaction system, so that the average particle size of calcium silicate can be obviously reduced, the particle size distribution range is greatly reduced, and the method has mild reaction conditions and low energy consumption; the cut-off particle size of large calcium silicate particles prepared by the method is greatly reduced, the requirement on the content of screen residue can be well met, the abrasion to a forming net and wet-end equipment of a high-speed paper machine can be well reduced by applying the calcium silicate in the papermaking filler, the bulk of filled paper is improved, and the method has high industrial application value.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a process for the preparation of calcium silicate having a controlled particle size, said process comprising the steps of:

(1) uniformly mixing alkaline liquor containing silicate radicals serving as auxiliary liquor with a calcium source to obtain mixed liquor;

(2) heating the mixed solution to a reaction temperature;

(3) at the reaction temperature, dripping a sodium silicate solution into the mixed solution to obtain a reaction solution;

(4) and reacting the reaction solution at a reaction temperature, and performing solid-liquid separation and drying to obtain the calcium silicate with controllable particle size.

According to the preparation method of the calcium silicate with the controllable particle size, provided by the invention, the sodium silicate solution is slowly dripped into the reaction system at the reaction temperature instead of directly mixing the sodium silicate solution with the reaction system, so that the aim of controlling the particle size of the final calcium silicate can be achieved in a reaction control mode, and calcium silicate particles with uniform particle sizes can be obtained without adding a particle size control agent additionally or grinding or high temperature.

According to the invention, the alkali liquor containing silicate radicals is used as the auxiliary liquor, wherein the silicate radicals can interact with a calcium source after being heated to the reaction temperature to form reaction seed nuclei, and the particle size distribution and morphology of the calcium silicate product are controlled; the existence of the alkali liquor can control the reaction rate and slow down the reaction speed to achieve the purpose of preventing the calcium silicate from being overlarge in particle size; therefore, the alkali liquor containing the silicate radicals is used as the auxiliary liquor, so that a better solution environment can be provided for the subsequent dropwise addition of the sodium silicate solution, the controllability of the particle size of calcium silicate particles is further improved, and the particle size distribution span of the calcium silicate particles is reduced, so that the abrasion to a forming net and wet-end equipment of a high-speed paper machine in the papermaking process is better reduced, the bulk of filled paper is improved, and the paper quality is improved.

The solid-liquid separation method of the present invention is not particularly limited, and a solid-liquid separation method known to those skilled in the art may be used, and for example, a centrifugal separation or a filtration operation may be used.

Preferably, the silicate-containing alkali liquor in step (1) is a silicate-containing sodium hydroxide solution or potassium hydroxide solution, preferably a silicate-containing sodium hydroxide solution.

The source of the silicate in the auxiliary liquid is not particularly limited in the present invention, and any silicate known to those skilled in the art can be used, and for example, the silicate can be dissolved in the sodium hydroxide solution, or solid calcium silicate can be added to the sodium hydroxide solution, wherein the solid calcium silicate includes various forms of calcium silicate reagents that can be obtained.

Preferably, the alkali concentration in the silicate-containing sodium hydroxide solution is Na₂O is 30 to 240g/L, and may be, for example, 30g/L, 40g/L, 50g/L, 60g/L, 70g/L, 80g/L, 90g/L, 100g/L, 110g/L, 120g/L, 130g/L, 140g/L, 150g/L, 160g/L, 170g/L, 180g/L, 190g/L, 200g/L, 210g/L, 220g/L, 230g/L or 240g/L, preferably 90 to 220 g/L.

Preferably, the silicate concentration in the silicate-containing sodium hydroxide solution is SiO₂The amount is 0.01 to 10g/L, and may be, for example, 0.01g/L, 0.5g/L, 1g/L, 1.5g/L, 2g/L, 2.5g/L, 3g/L, 3.5g/L, 4g/L, 4.5g/L, 5g/L, 5.5g/L, 6g/L, 6.5g/L, 7g/L, 7.5g/L, 8g/L, 8.5g/L, 9g/L, 9.5g/L or 10g/L, preferably 0.4 to 7 g/L.

Preferably, the calcium source is any one of, or a combination of at least two of, an oxide of calcium, a base containing calcium, or a calcium salt, wherein typical but non-limiting combinations are: a combination of calcium oxide and calcium-containing base, a combination of calcium oxide and calcium salt, a combination of calcium-containing base and calcium salt, preferably any one or a combination of at least two of lime, milk of lime, solid calcium hydroxide, calcium chloride or calcium nitrate, wherein typical but non-limiting combinations are: a combination of lime and milk of lime, a combination of lime and solid calcium hydroxide, a combination of lime and calcium chloride, a combination of milk of lime and solid calcium hydroxide, a combination of milk of lime and calcium chloride, a combination of solid calcium hydroxide and calcium chloride, a combination of calcium chloride and calcium nitrate, further preferably lime and/or milk of lime.

Preferably, the addition amount of lime in the lime milk is 100-200 g per liter, for example, 100g, 110g, 120g, 130g, 140g, 150g, 160g, 170g, 180g, 190g or 200g, preferably 130-160 g per liter.

Preferably, in the step (1), the auxiliary liquid and the calcium source are uniformly mixed under stirring to prepare a mixed liquid.

Preferably, the stirring speed is 300-700 r/min, such as 300r/min, 330r/min, 350r/min, 380r/min, 400r/min, 430r/min, 450r/min, 480r/min, 490r/min, 500r/min, 520r/min, 550r/min, 580r/min, 600r/min, 620r/min, 650r/min, 680r/min or 700r/min, preferably 350-500 r/min.

Preferably, the reaction temperature in step (2) is 60 to 100 ℃, for example, 60 ℃, 62 ℃, 65 ℃, 68 ℃, 70 ℃, 72 ℃, 75 ℃, 78 ℃, 80 ℃, 82 ℃, 85 ℃, 88 ℃, 90 ℃, 92 ℃, 95 ℃, 98 ℃ or 100 ℃, preferably 85 to 98 ℃.

Preferably, the heating mode is electric heating, water bath heating or oil bath heating, and preferably electric heating.

Preferably, the volume ratio of the sodium silicate solution in the step (3) to the auxiliary liquid in the step (1) is 1-6: 1, and may be, for example, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.8:1, 4:1, 4.2:1, 4.5:1, 4.8:1, 5:1, 5.2:1, 5.5:1, 5.8:1 or 6:1, preferably 2-4: 1.

Preferably, the calcium in the calcium source in step (1) is mixed with the silicon in the sodium silicate solution by CaO: SiO₂The molar ratio is 0.9 to 1.2, and may be, for example, 0.9, 0.92, 0.95, 0.98, 1.0, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18 or 1.2, and preferably 0.95 to 1.05.

Preferably, the sodium silicate solution is dripped into the mixed solution at a constant speed to obtain a reaction solution.

The invention has no special limit on the dropping speed of the sodium silicate solution, and for reaction systems with different scales, under the condition of keeping the volume ratio of the sodium silicate solution to the auxiliary liquid, the span of the volume range of the sodium silicate solution to be dropped is large, and the limitation on the dropping speed of the sodium silicate can hardly adapt to the reaction systems with different scales.

Preferably, the sodium silicate solution is dripped into the mixed solution for 0.5 to 3 hours, for example, 0.5 hour, 0.8 hour, 1.0 hour, 1.2 hour, 1.3 hour, 1.5 hour, 1.8 hour, 2.0 hour, 2.2 hour, 2.5 hour, 2.8 hour or 3.0 hour, preferably 1.0 to 2.5 hours.

According to the invention, the sodium silicate solution is slowly dripped into the mixed solution within 0.5-3 h instead of being poured into the reaction system at one time, so that the growth rate of the molar ratio of silicon to calcium in the reaction system is controlled to a certain extent, the particle size formed by calcium silicate in the reaction is further controlled, the particle size distribution range is greatly reduced, the particle size of large particles is greatly reduced, and the quality of paper products is finally improved.

Preferably, the sodium silicate solution is an alkali-containing sodium silicate solution.

The source of sodium silicate in the present invention is not particularly limited, and sources of sodium silicate well known to those skilled in the art may be used, for example, sodium silicate solutions formulated with commercially available technical grade water glass or sodium silicate nonahydrate, or low-grade bauxite (the A/S ratio can be as low as-1: namely the bauxite with the aluminum-silicon ratio being lower than 3 and being as low as about 1, wherein the A/S ratio refers to the mass percentage of alumina and silicon dioxide in the bauxite ore and is one of the most main standards for measuring the quality of the bauxite, generally, ores with the A/S ratio being lower than 3 can not be directly smelted by a wet method and need to be subjected to desiliconization treatment), high-alumina fly ash, coal gangue, nepheline, waste catalysts using silicon/aluminum systems as carriers or reaction products thereof and the like which are obtained by desiliconizing under the action of alkali liquor can be used as sodium silicate solution.

Preferably, the sodium silicate solution is low-grade bauxite (the A/S ratio is lower than 3 and can be as low as-1), a waste catalyst taking a silicon/aluminum system as a carrier or a sodium silicate solution obtained by desiliconizing a reaction product of the waste catalyst under the action of alkali liquor.

According to the preparation method of calcium silicate provided by the invention, the industrial byproduct sodium silicate solution is preferably adopted, so that the preparation method is connected with a system of the byproduct sodium silicate solution, sodium silicate is converted into high-value filler calcium silicate, the production cost is saved, and the industrial popularization is facilitated.

Preferably, the alkali concentration in the sodium silicate solution is Na₂The amount of O is 20 to 250g/L, and may be, for example, 20g/L, 30g/L, 40g/L, 50g/L, 60g/L, 70g/L, 80g/L, 90g/L, 100g/L, 110g/L, 120g/L, 130g/L, 140g/L, 150g/L, 160g/L, 170g/L, 180g/L, 190g/L, 200g/L, 210g/L, 220g/L, 230g/L, 240g/L or 250g/L, preferably 35 to 200 g/L.

Preferably, the concentration of silicate in the sodium silicate solution is SiO₂The concentration is 15 to 80g/L, for example, 15g/L, 20g/L, 25g/L, 30g/L, 35g/L, 40g/L, 45g/L, 50g/L, 55g/L, 60g/L, 65g/L, 70g/L, 75g/L or 80g/L, preferably 25 to 60 g/L.

Preferably, the reaction time in step (4) is 1 to 10 hours, such as 1.0 hour, 1.5 hours, 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, 6.0 hours, 6.5 hours, 7.0 hours, 7.5 hours, 8.0 hours, 8.5 hours, 9.0 hours, 9.5 hours or 10.0 hours, preferably 3 to 7 hours.

Preferably, the drying is by vacuum drying, freeze drying or forced air drying, preferably forced air drying.

Preferably, the temperature of the vacuum drying or the forced air drying is 70 to 110 ℃, for example, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃ or 110 ℃, preferably 85 to 105 ℃.

Preferably, the operation of washing the calcium silicate subjected to solid-liquid separation is further included between the solid-liquid separation and the drying operation.

Preferably, the washing is washing with clean water.

Preferably, the number of washes is at least three.

As a preferred technical scheme of the invention, the method comprises the following steps:

(1) taking a sodium hydroxide solution containing the silicate radicals as an auxiliary solution, and uniformly mixing the sodium hydroxide solution containing the silicate radicals and a calcium source under the stirring condition of 300-700 r/min to obtain a mixed solution, wherein the alkali concentration in the sodium hydroxide solution containing the silicate radicals is Na₂O is 30 to 240g/L, and the silicate concentration is SiO₂Calculated as 0.01-10 g/L;

(2) heating the mixed solution to 60-100 ℃;

(3) adding Na to the alkali concentration for 0.5-3 h at 60-100 DEG C₂O is 20 to 250g/L, and the silicate concentration is SiO₂Dripping 15-80 g/L sodium silicate solution into the mixed solution at a constant speed to obtain a reaction solution, wherein the volume ratio of the sodium silicate solution to the auxiliary solution in the step (1) is 1-6: 1, and the calcium in the calcium source in the step (1) and the silicon in the sodium silicate solution are CaO: SiO₂The calculated molar ratio is 0.9-1.2;

(4) and reacting the reaction liquid at 60-100 ℃ for 1-10 h, performing solid-liquid separation on the prepared calcium silicate and the reaction slurry, washing the calcium silicate subjected to solid-liquid separation at least three times by using clear water, and drying the washed calcium silicate to obtain the calcium silicate with controllable particle size.

In a second aspect, the present invention provides calcium silicate produced by the method of the first aspect.

The calcium silicate provided by the second aspect of the invention is prepared by the method provided by the first aspect of the invention, the prepared calcium silicate has small particle size and uniform distribution, the problem of high content of large particles in the existing calcium silicate is solved, and the product has high application value.

In a third aspect, the present invention provides the use of calcium silicate according to the second aspect in the paper, plastic or rubber sector, preferably in the paper sector.

The calcium silicate provided by the second aspect of the invention has uniform particle size and excellent performance, can be better applied to the field of papermaking, plastics or rubber, and when the calcium silicate is applied to papermaking filler, the calcium silicate not only can reduce the abrasion problem of a forming net and wet-end equipment of a high-speed paper machine, but also can well improve the bulk of filled paper, and the lifting amount of the bulk is increased along with the increase of the filling amount; on the basis of basically not changing the tensile index (tensile index), the paper is filled by at least 15 percent higher than the commercial calcium silicate (wollastonite) or calcium silicate products with larger particle sizes reported in the literature as fillers; meanwhile, the addition of the papermaking filler can reduce the usage amount of wood fibers in the papermaking process, reduce the production cost and achieve the purpose of environmental protection, and the papermaking filler has higher economic and practical values.

Compared with the prior art, the invention has at least the following beneficial effects:

(1) according to the preparation method of the calcium silicate, the alkaline liquor containing the silicate radicals is used as the auxiliary liquid and the reaction process is controlled, no additional particle size control agent is needed, and the product slurry is not needed to be screened, so that the problem of high content of large particles in the calcium silicate can be solved, the content of the prepared calcium silicate particles D50 is 10.36-12.76 mu m, the content of the calcium silicate particles larger than or equal to 45 mu m is lower than 0.18%, the abrasion to a forming net and wet-end equipment of a high-speed paper machine can be reduced, and the requirement that the content of 325-mesh (45 mu m) screen residue in papermaking filler is less than or equal to 0.2% is well met;

(2) the preparation method of the calcium silicate provided by the invention is simple to operate, mild in reaction conditions, free of special operation equipment and strong in operability;

(3) the preparation method of calcium silicate provided by the invention can be connected with a system of a byproduct sodium silicate solution to convert sodium silicate into high-value filler calcium silicate, so that the production cost is saved, the industrial popularization is convenient to realize, and the preparation method has higher industrial application value;

(4) the calcium silicate prepared by the preparation method provided by the invention has small particle size and uniform particle size distribution, the distribution Span of the calcium silicate is less than or equal to 1.58, and the calcium silicate is at least 15% higher than a calcium silicate commodity (wollastonite) sold in the market or a calcium silicate product with larger particle size reported in literature as a filler and filled paper on the basis of basically not changing the tensile index (tensile index) of the paper, so that the use of wood is reduced, the environment is protected, and the preparation method has higher economic and practical values.

Drawings

FIG. 1 is a graph of the particle size distribution of calcium silicate produced by the method provided in example 1 of the present invention.

FIG. 2 is a scanning electron micrograph of calcium silicate prepared by the method provided in example 1 of the present invention at a magnification of 1000.

FIG. 3 is a scanning electron micrograph of calcium silicate prepared by the method of example 1 of the present invention at a magnification of 8000.

FIG. 4 is a scanning electron micrograph of calcium silicate produced by the method of example 1 of the present invention at a magnification of 20000.

Detailed Description

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.

The present invention is described in further detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.

First, an embodiment

Example 1

This example provides a method of preparing calcium silicate, comprising the steps of:

(1) taking 0.1L of sodium hydroxide solution containing silicate radicals as auxiliary solution, and uniformly mixing the auxiliary solution with lime under the stirring condition of 400r/min to obtain mixed solution, wherein the alkali concentration in the sodium hydroxide solution containing silicate radicals is Na₂The O content is 96g/L, and the silicate concentration is SiO₂Calculated as 0.53 g/L;

(2) heating the mixed solution to 96 ℃;

(3) 0.2L of alkali in Na concentration is added at 96 ℃ over 1h₂The O content is 96g/L, and the silicate concentration is SiO₂Sodium silicate solution of 36g/L is dripped into the solution at a constant speedObtaining a reaction solution in the mixed solution; wherein the sodium silicate solution is obtained by desiliconizing pretreatment of low-grade bauxite (A/S ratio-2) under the action of alkali liquor, and the calcium in the lime and the silicon in the sodium silicate solution in the step (1) are mixed by CaO: SiO₂The calculated molar ratio is 1.05;

(4) reacting the reaction liquid at 96 ℃ for 2h, filtering the prepared calcium silicate and the reaction slurry by using a vacuum suction filter, washing the filtered calcium silicate for three times by using clean water, and carrying out forced air drying on the washed calcium silicate at 100 ℃ to obtain the calcium silicate with controllable particle size.

The calcium silicate prepared in this example was subjected to a particle size test using a malvern Mastersizer-2000 laser particle sizer, and the results are shown in fig. 1, and it can be seen from fig. 1 that the calcium silicate D50 prepared in this example is 11.45 μm, the maximum particle size is only 45.7 μm, the content of calcium silicate particles greater than or equal to 45 μm is 0.17 wt%, the particle size distribution is uniform, and the application prospect is good.

The calcium silicate prepared by the embodiment is subjected to shape scanning by using a scanning electron microscope, and the result is shown in fig. 2-4, and as can be seen from fig. 2, the calcium silicate prepared by the embodiment has uniform particle size and can better meet the requirement of papermaking filler; as can be seen from FIG. 3, the calcium silicate prepared by the embodiment has a porous structure, high sphericity and high industrial application value; from the morphological analysis of fig. 4, it can be seen that calcium silicate particles are grown by foil-like calcium silicate in clusters, and such a growth reduces the content of fine calcium silicate particles and the agglomeration phenomenon between calcium silicate particles, thereby reducing the particle size distribution Span of the final calcium silicate particles.

Example 2

This example provides a method of preparing calcium silicate, comprising the steps of:

(1) taking 0.3L of a silicate radical-containing sodium hydroxide solution as an auxiliary solution, and uniformly mixing the auxiliary solution and a calcium hydroxide reagent under the stirring condition of 300r/min to obtain a mixed solution, wherein the auxiliary solution is a silicate radical-containing sodium hydroxide solution prepared by a commercially available sodium silicate reagent, and the alkali concentration in the silicate radical-containing sodium hydroxide solution is Na₂O is 80g/L, and the concentration of silicate is SiO₂The weight is 4.8 g/L;

(2) heating the mixed solution to 90 ℃;

(3) 1L of alkali in Na concentration at 90 ℃ over 2h₂The content of O in the solution is 37.2g/L, and the concentration of silicate is SiO₂Dripping 36g/L sodium silicate solution into the mixed solution at a constant speed to obtain reaction solution; wherein the sodium silicate solution is prepared from a commercially available sodium silicate nonahydrate reagent, and the calcium in the calcium hydroxide reagent and the silicon in the sodium silicate solution in the step (1) are mixed by CaO and SiO₂The calculated molar ratio is 1.05;

(4) reacting the reaction liquid at 90 ℃ for 2h, filtering the prepared calcium silicate and the reaction slurry by using a vacuum suction filter, washing the filtered calcium silicate for three times by using clean water, and carrying out forced air drying on the washed calcium silicate at 105 ℃ to obtain the calcium silicate with controllable particle size.

Example 3

This example provides a method of preparing calcium silicate, comprising the steps of:

(1) taking 0.1L of sodium hydroxide solution containing silicate radicals as auxiliary solution, and uniformly mixing the auxiliary solution with lime under the stirring condition of 400r/min to obtain mixed solution, wherein the alkali concentration in the sodium hydroxide solution containing silicate radicals is Na₂Calculated as O, is 220g/L, and the concentration of silicate is SiO₂Calculated as 0.6 g/L;

(2) heating the mixed solution to 80 ℃;

(3) 0.2L of alkali in Na concentration is added at 80 ℃ for 1h₂O is 25g/L, and the concentration of silicate is SiO₂Dripping 78g/L sodium silicate solution into the mixed solution at a constant speed to obtain reaction solution; wherein the sodium silicate solution is prepared from commercially available water glass, and the calcium in the lime and the silicon in the sodium silicate solution in the step (1) are CaO, SiO₂The calculated molar ratio is 1.05;

(4) reacting the reaction liquid at 80 ℃ for 3h, filtering the prepared calcium silicate and the reaction slurry by using a vacuum suction filter, washing the filtered calcium silicate for three times by using clean water, and drying the washed calcium silicate in vacuum under the conditions that the vacuum degree is 0.1kPa and the temperature is 70 ℃ to obtain the calcium silicate with controllable particle size.

Example 4

This example provides a method of preparing calcium silicate, comprising the steps of:

(1) 0.06L of silicate radical-containing sodium hydroxide solution is used as auxiliary liquid to be uniformly mixed with lime milk under the stirring condition of 500r/min to obtain mixed liquid, wherein the alkali concentration in the silicate radical-containing sodium hydroxide solution is Na₂Calculated as O, is 115g/L, and the concentration of silicate is SiO₂The amount is 0.07g/L, and the addition amount of lime in the lime milk is 100g per liter;

(2) heating the mixed solution to 98 ℃;

(3) 0.2L of alkali in Na concentration is added at 98 ℃ for 0.6h₂The O content is 96g/L, and the silicate concentration is SiO₂Dripping 37g/L sodium silicate solution into the mixed solution at a constant speed to obtain reaction solution; wherein the sodium silicate solution is obtained by leaching and desiliconizing fly ash with alkali liquor, and the calcium in the lime milk and the silicon in the sodium silicate solution in the step (1) are CaO: SiO₂The calculated molar ratio is 1.2;

(4) reacting the reaction liquid at 98 ℃ for 2h, centrifugally separating the prepared calcium silicate and the reaction slurry by using a centrifugal machine, washing the filtered calcium silicate for three times by using clear water, and carrying out forced air drying on the washed calcium silicate at 110 ℃ to obtain the calcium silicate with controllable particle size.

Example 5

This example provides a method of preparing calcium silicate, comprising the steps of:

(1) taking 0.1L of sodium hydroxide solution containing silicate radicals as auxiliary solution, and uniformly mixing the auxiliary solution with calcium nitrate under the stirring condition of 700r/min to obtain mixed solution, wherein the alkali concentration in the sodium hydroxide solution containing silicate radicals is Na₂Calculated as O, 240g/L and the concentration of silicate groups is SiO₂The weight is 10 g/L;

(2) heating the mixed solution to 100 ℃;

(3) 0.6L of alkali in Na concentration is added at 100 ℃ for 0.5h₂O is 250g/L, and the concentration of silicate isSiO₂Dripping 80g/L sodium silicate solution into the mixed solution at a constant speed to obtain reaction solution; wherein the sodium silicate solution is obtained by leaching and desiliconizing fly ash with alkali liquor, and the calcium in the calcium nitrate and the silicon in the sodium silicate solution in the step (1) are CaO: SiO₂The calculated molar ratio is 0.9;

(4) reacting the reaction liquid at 100 ℃ for 10 hours, centrifugally separating the prepared calcium silicate and the reaction slurry by using a centrifugal machine, washing the filtered calcium silicate for three times by using clear water, and freeze-drying the washed calcium silicate at-40 ℃ under the condition that the vacuum degree is 0.015kPa to obtain the calcium silicate with controllable particle size.

Example 6

This example provides a method of preparing calcium silicate, comprising the steps of:

(1) taking 0.04L of sodium hydroxide solution containing silicate radicals as auxiliary liquid, and uniformly mixing the auxiliary liquid with lime milk under the stirring condition of 600r/min to obtain mixed liquid, wherein the alkali concentration in the sodium hydroxide solution containing silicate radicals is Na₂O is 30g/L, and the concentration of silicate is SiO₂The amount is 0.01g/L, and the addition amount of lime in the lime milk is 200g per liter;

(2) heating the mixed solution to 60 ℃;

(3) adding 0.04L of alkali in Na concentration at 60 deg.C for 3h₂O is 20g/L, and the concentration of silicate is SiO₂Dripping 15g/L sodium silicate solution into the mixed solution at a constant speed to obtain reaction solution; wherein the sodium silicate solution is obtained by leaching and desiliconizing waste catalytic cracking (FCC) catalyst with alkali liquor, and the calcium in the lime milk and the silicon in the sodium silicate solution in the step (1) are CaO SiO₂The calculated molar ratio is 1.1;

(4) reacting the reaction liquid at 60 ℃ for 1h, centrifugally separating the prepared calcium silicate and the reaction slurry by using a centrifugal machine, washing the filtered calcium silicate for three times by using clear water, and carrying out forced air drying on the washed calcium silicate at 70 ℃ to obtain the calcium silicate with controllable particle size.

Second, comparative example

Comparative example 1

This comparative example provides a method of preparing calcium silicate, the method comprising the steps of:

(1) uniformly mixing 0.1L of sodium silicate solution and lime under the stirring condition of 400r/min to obtain mixed solution, wherein the alkali concentration in the sodium silicate solution is Na₂The O content is 96g/L, and the silicate concentration is SiO₂Calculated as 37.8g/L, the calcium in the lime and the silicon in the sodium silicate solution are calculated according to the ratio of CaO to SiO₂The calculated molar ratio is 1.2;

(2) heating the mixed solution to 96 ℃;

(3) reacting the mixed solution at 96 ℃ for 2h, filtering the prepared calcium silicate and the reaction slurry by using a vacuum suction filter, washing the filtered calcium silicate for three times by using clean water, and carrying out forced air drying on the washed calcium silicate at 100 ℃ to obtain the calcium silicate.

Comparative example 2

The comparative example provides a preparation method of calcium silicate, except that the method is modified from the step (3) of example 4 in that the sodium silicate solution is dropped into the mixed solution at a constant speed for 0.6h to the step of pouring the sodium silicate solution into the mixed solution at one time to directly mix the sodium silicate solution and the mixed solution, the other steps and process parameters are the same as those of example 4, and the step (3) is specifically:

(3) at 98 deg.C, 0.2L of alkali is added in Na₂The O content is 96g/L, and the silicate concentration is SiO₂Pouring the 37g/L sodium silicate solution into the mixed solution at one time to directly mix the sodium silicate solution and the mixed solution to obtain a reaction solution; wherein the sodium silicate solution is obtained by leaching and desiliconizing fly ash with alkali liquor, and the calcium in the lime milk and the silicon in the sodium silicate solution in the step (1) are CaO: SiO₂The molar ratio was 1.2.

Comparative example 3

This comparative example provides a process for the preparation of calcium silicate, except that in example 4 0.06L of the silicate-containing sodium hydroxide solution was replaced with 0.06L of sodium hydroxide solution containing no silicate, wherein the alkali concentration of the sodium hydroxide solution was Na₂O is 115g/L, which is consistent with example 4, and the rest steps and process parametersThe method is the same as the embodiment 4, and the step (1) is specifically as follows:

(1) uniformly mixing 0.06L of sodium hydroxide solution as auxiliary liquid with lime milk under the stirring condition of 500r/min to obtain a mixed solution, wherein the alkali concentration in the sodium hydroxide solution is Na₂O is measured to be 115g/L, and the addition amount of lime in the lime milk is 100g per liter.

Comparative example 4

This comparative example provides a method for the preparation of calcium silicate, except that the silicate-containing sodium hydroxide solution of example 4 was replaced with a sodium silicate solution (prepared directly from sodium silicate nonahydrate solution) without the addition of additional alkali, wherein the silicate concentration in the sodium silicate solution was SiO₂Calculated as 0.07g/L, which is consistent with the embodiment 4, the other steps and the process parameters are the same as the embodiment 4, and the step (1) is specifically as follows:

(1) 0.06L of sodium silicate solution is taken as auxiliary liquid to be uniformly mixed with lime milk under the stirring condition of 500r/min to obtain mixed liquid, wherein the silicate concentration in the sodium silicate solution is SiO₂The amount is 0.07g/L, and the addition amount of lime in the lime milk is 100g per liter.

Third, test methods and results

The particle size test method comprises the following steps: the calcium silicate prepared in examples 1 to 6 and comparative examples 1 to 4 was measured using a malvern Mastersizer-2000 laser particle sizer, the measurement method being carried out with reference to the Mastersizer-2000 user manual. In the measurement, water was used as a dispersion medium, and the average of 5 measurements was taken as the final result of the sample.

The results of the particle size tests of examples 1 to 6 and comparative examples 1 to 4 are shown in Table 1.

TABLE 1

From table 1, the following points can be seen:

(1) it can be seen from the comprehensive examples 1 to 6 that the calcium silicate prepared by the preparation method provided by the invention has uniform particle size distribution, the distribution Span is less than or equal to 1.58, the average particle size D50 can be controlled within the range of 10.36 to 12.76 μm, the particle size of the calcium silicate can be controlled, the content of calcium silicate particles larger than or equal to 45 μm in the calcium silicate prepared by the examples 1 to 6 is less than or equal to 0.18 wt%, the requirement that the content of 325 mesh (45 μm) screen residue in papermaking filler is less than or equal to 0.2% can be better met, and the calcium silicate prepared by the preparation method can be better applied to the papermaking field, the plastic field or the rubber field, when the calcium silicate is used as the papermaking filler, the wood usage can be reduced, and the particle size is small, the abrasion of particles to a net and wet end equipment of a high-speed paper machine can be;

(2) it can be seen from the comprehensive results of examples 1-6 and comparative example 1 that, in examples 1-6 of the present invention, by slowly adding sodium silicate solution dropwise into the reaction system at the reaction temperature, compared with the method of comparative example 1 in which the reaction system is directly mixed and then the temperature is raised for reaction, the particle size distribution Span of the calcium silicate particles prepared in examples 1-6 is no more than 1.58, the average particle size D50 is 10.36-12.76 μm, the maximum particle size is only 30.2-64.25 μm, while the calcium silicate particles prepared in comparative example 1 had an average particle diameter D50 of 24.98 μm, a maximum particle diameter of 206.93 μm, a distribution Span of 19.47, a non-uniform particle size distribution, therefore, the preparation method has the advantages that the preparation of the calcium silicate with controllable particle size can be realized by adopting a reaction control mode of slowly dropwise adding without additionally adding a particle size control agent or sieving the product slurry, and the preparation method has higher economic value;

(3) it can be seen from the combination of example 4 and comparative example 2 that, in example 4 of the present invention, the "sodium silicate solution is dropped into the mixed solution at a constant speed for 0.6 h", compared with comparative example 2, the "sodium silicate solution is poured into the mixed solution at one time, in the mode of directly mixing the sodium silicate solution with the mixed solution ", the calcium silicate particles prepared in example 4 had an average particle diameter D50 of 10.92 μm, a distribution Span as low as 0.95, a calcium silicate particle content of 45 μm or more of 0, while the calcium silicate particles prepared in comparative example 2 had an average particle diameter D50 of 21.6 μm, a distribution Span of 2.45, and a calcium silicate particle content of 45 μm or more as high as 15.7 wt%, which was difficult to satisfy the requirements of a papermaking filler, therefore, the invention can achieve the purpose of controlling the particle size of calcium silicate by slowly dripping the sodium silicate solution into the mixed solution at the reaction temperature and controlling the proportion of silicon and calcium in the reaction process;

(4) it can be seen from the combination of example 4 and comparative example 3 that, in example 4 of the present invention, the sodium hydroxide solution containing silicate groups is used as the auxiliary solution, and compared with comparative example 3, which only uses the sodium hydroxide solution as the auxiliary solution, the Span of the particle size distribution of the calcium silicate particles prepared in example 4 is as low as 0.95, and the content of the calcium silicate particles with a particle size of 45 μm or more is 0, while the calcium silicate particles prepared in comparative example 3 had an average particle diameter D50 of only 5.58 μm, but the particle size is easy to agglomerate and uneven in particle size distribution, the distribution Span reaches 2.98, the maximum particle size is 79.43 mu m, and the content of calcium silicate particles larger than or equal to 45 mu m is as high as 1.71 wt%, the requirement of papermaking filler is difficult to meet, therefore, silicate is added into the sodium hydroxide solution, reaction seed nuclei can be provided for reaction, and the particle size distribution and morphology of the calcium silicate product are further controlled, so that calcium silicate particles with small particle size and low distribution span are prepared;

(5) it can be seen from the combination of example 4 and comparative example 4 that, in example 4 of the present invention, a sodium hydroxide solution containing silicate groups is used as an auxiliary solution, and a sodium silicate solution without an additional alkali is used as an auxiliary solution compared with comparative example 3, the particle size distribution Span of calcium silicate particles prepared in example 4 is as low as 0.95, the content of calcium silicate particles with particle size of 45 μm or more is 0, and the average particle size D50 of calcium silicate particles prepared in comparative example 4 is as high as 17.2 μm and the particle size distribution is not uniform, the distribution Span is as high as 1.64, and the content of calcium silicate particles with particle size of 45 μm or more is as high as 3.04 wt%.

In conclusion, according to the preparation method of calcium silicate provided by the invention, after alkali liquor containing silicate radicals is used as auxiliary liquor and mixed with a calcium source to prepare mixed liquor, sodium silicate solution is slowly dripped into the mixed liquor at a reaction temperature, the particle size, distribution Span and morphology of calcium silicate can be better controlled in a reaction control mode, the distribution Span of the prepared calcium silicate is less than or equal to 1.58, the average particle size D50 can be controlled within 10.36-12.76 mu m, the content of calcium silicate particles larger than or equal to 45 mu m is less than or equal to 0.18 wt%, and the requirement that the content of 325-mesh (45 mu m) screen residue in papermaking filler is less than or equal to 0.2% can be better met; the calcium silicate prepared by the method is applied to the paper making filler, and the abrasion of particles to a forming net and wet-end equipment of a high-speed paper machine can be well reduced due to the small particle size of the product, so that the problem in the existing calcium silicate filler industrialization process is well solved, and the calcium silicate filler has high industrial application value.

The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.