Preparation method of high-purity superfine high-whiteness calcium carbonate

Abstract

The invention discloses a preparation method of high-purity superfine high-whiteness calcium carbonate, which belongs to the field of calcium carbonate preparation, and comprises the following steps: pretreating multiple raw materials such as dolomite, steel slag and the like, adding a composite sintering aid, calcining at 700-900 DEG C, and recovering and purifying carbon dioxide; carrying out ultrasonic-assisted leaching on the calcined product, reacting with magnesium chloride, and separating to obtain a high-purity calcium chloride solution; carrying out deep impurity removal on the impurity-containing magnesium hydroxide by using a composite chelating agent, introducing carbon dioxide to obtain a magnesium ion leaching solution, and regulating and crystallizing by using a biological template to obtain magnesium carbonate trihydrate; reacting with a calcium chloride solution under the action of a reducing agent, treating a product with a composite surface modifier, and spray-drying to obtain a product; according to the method, a composite chelating agent (EDTA disodium + nano-hydroxyapatite) + reduction synergistic purification (sodium sulfite + ascorbic acid) system is adopted, colored impurity ions such as Fe < 3 + > and Mn < 2 + > are removed in a targeted mode, the problem that traditional magnesium hydroxide is not thoroughly adsorbed is solved, and the whiteness of the product is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of calcium carbonate preparation, in particular to a method for preparing high-purity, ultrafine and high-whiteness calcium carbonate. Background Art

[0002] Calcium carbonate, an important inorganic non-metallic material, is widely used in plastics, coatings, papermaking, pharmaceuticals, and other fields. Its purity, particle size, and whiteness are key indicators that determine its performance. As high-end applications continue to demand higher performance from calcium carbonate products, traditional preparation processes are gradually exposing numerous flaws.

[0003] Prior art, such as publication number CN115353139B, discloses a method for preparing high-purity calcium carbonate. Using magnesium-containing carbonate minerals as raw materials, high-purity calcium chloride is leached out, and high-purity magnesium carbonate trihydrate crystals are synthesized using the magnesium element in the magnesium-containing carbonate minerals. Then, a high-purity calcium carbonate product is synthesized using an element replacement reaction. The method for preparing high-purity calcium carbonate can remove impurities from the reaction system under mild test conditions, thereby shortening the process route for preparing high-purity calcium carbonate, reducing production costs, and simplifying production equipment. The technology of the present invention can not only reduce the purity requirements for calcium carbonate ore, but also increase the economic benefits of the enterprise, benefit the environment, and have broad development prospects.

[0004] This patent can obtain a calcium carbonate product with a purity of 99.9%-99.99% through steps such as calcination of magnesium-containing carbonate and replacement with magnesium chloride, and achieve nano-level particle size through spray drying. However, the following problems still exist:

[0005] Insufficient whiteness: Fe is not removed in a targeted manner 3+ 、Mn 2+ Colored impurity ions such as iodine and chromium are difficult to be completely removed by relying solely on magnesium hydroxide adsorption, resulting in a product whiteness of usually ≤95%, which cannot meet the high whiteness requirements of high-end fields;

[0006] High energy consumption: The calcination temperature is as high as 800-1200℃, which consumes a lot of energy and does not conform to the concept of low-carbon production;

[0007] Poor dispersibility: Nanopowders obtained by spray drying are prone to agglomeration due to their high surface energy, resulting in insufficient stability of ultrafine properties and affecting product application effects;

[0008] Low reaction efficiency: Impurity ions are not completely removed during the stirring reaction process, and the reaction time of some steps is relatively long, which restricts the efficiency of industrial production.

[0009] Therefore, a method for preparing calcium carbonate that can simultaneously achieve high purity, ultrafine particle size, high whiteness, low energy consumption and high efficiency is needed. Summary of the Invention

[0010] In view of the shortcomings of the prior art, the present invention provides a method for preparing high-purity ultrafine high-whiteness calcium carbonate, which solves the problems raised in the above background technology.

[0011] Technical solution: To solve the above technical problems, according to one aspect of the present invention, more specifically, a method for preparing high-purity ultrafine high-whiteness calcium carbonate comprises the following steps:

[0012] S1. Diversified pretreatment of raw materials:

[0013] Dolomite tailings are subjected to magnetic separation to remove iron (to remove free Fe2O3), and steel slag is leached with hydrochloric acid (to remove silicon-based impurities such as SiO2). A composite sintering aid is added to lower the calcination temperature (the composite sintering aid is a compound system of zinc borate and alumina, with a mass ratio of 1:(0.8-1.2), which can effectively lower the calcination temperature by 100-300°C), reducing energy consumption while avoiding high-temperature activation of impurities. The collected CO2 is purified by molecular sieve to provide a high-purity carbon source for subsequent reactions.

[0014] S2, ultrasonic assisted leaching:

[0015] Ultrasonic vibration (20-30kHz) enhances the mixing of calcined products and water, promoting the full hydration of CaO and MgO; composite ultrasonic adjuvant (sodium lauryl sulfate + Tween-80) reduces the solid-liquid interfacial tension, increases the reaction rate of magnesium chloride and Ca(OH)2 by 20-30%, and shortens the reaction time by 10-20 minutes.

[0016] S3, composite deep impurity removal:

[0017] Disodium EDTA chelated Fe 3+ 、Mn 2+ Nanohydroxyapatite specifically adsorbs Cu through surface hydroxyl groups. 2+ (adsorption capacity 50-80 mg / g), solving the problem of insufficient selectivity of traditional single chelating agents; controlling the reaction pH to 8.5-9.0 to ensure sufficient leaching of magnesium ions while avoiding co-precipitation of impurities.

[0018] S4. Biological template-controlled crystallization:

[0019] Add 0.01-0.05% of a composite crystal form control agent to the magnesium ion leachate, crystallize at 25-40° C. for 1-2.5 hours, and filter to obtain high-purity magnesium carbonate trihydrate crystals;

[0020] Amino groups on chitosan molecular chains and Mg 2+Coordination guides the growth of magnesium carbonate trihydrate in one dimension, the crystal aspect ratio is increased to 5-8, and the coefficient of variation of particle size distribution is reduced from 15% to 8%, providing a high-purity magnesium source for subsequent replacement reaction (the composite crystal form controller is composed of sodium citrate and chitosan in a mass ratio of 5:1, in which the deacetylation degree of chitosan is ≥90%, which can guide the directional growth of magnesium carbonate trihydrate crystals and reduce the coefficient of variation of particle size distribution).

[0021] S5, reduction and coordinated purification:

[0022] Sodium sulfite is mixed with ascorbic acid to remove the residual Fe 3+ Reduced to easily removable Fe 2+ , while inhibiting Mn 2+ Oxidized to MnO2 (colored), wherein high-purity calcium chloride solution and magnesium carbonate trihydrate crystals are mixed in the ratio of n(MgCO3・3H2O):n(Ca 2+ )=1:1.02-1.08, add 0.1-0.3% of the mass fraction of the reducing agent, which is sodium sulfite and ascorbic acid in a mass ratio of 2:1, and the residual Fe 3+ Reduction to Fe 2+ , while inhibiting Mn 2+ Oxidation to colored MnO2; Optimization of reaction ratio (n(MgCO3・3H2O):n(Ca 2+ )=1:1.02-1.08), which increases the calcium carbonate conversion rate to over 99%.

[0023] S6. Functional modification and closed-loop circulation:

[0024] A composite surface modifier (KH-550 / TC-114) forms a hydrophobic layer on the powder surface (the composite surface modifier is composed of silane coupling agent KH-550 and titanate coupling agent TC-114 in a mass ratio of 3:1, containing 5% nano-zinc oxide (based on the total mass of the modifier), which can form a hydrophobic layer and impart antibacterial properties to the product). Combined with nano-zinc oxide, it imparts antibacterial properties (antibacterial rate against Escherichia coli ≥90%). Nanofiltration membranes separate and intercept small molecular impurities, increasing the water recycling rate to 70%. The purity of magnesium chloride hexahydrate reaches 99.5% and can be directly reused.

[0025] S7, online monitoring and intelligent control:

[0026] The laser particle size analyzer monitors the particle size in real time (accuracy ±1nm), the whiteness meter detects the whiteness online (accuracy ±0.1%), and the PLC system automatically adjusts the spray drying temperature and modifier dosage. The product batch stability RSD is ≤1%.

[0027] The beneficial effects of the method for preparing high-purity, ultrafine, high-whiteness calcium carbonate of the present invention are:

[0028] (1) The present invention adopts the "composite chelating agent (disodium EDTA + nano-hydroxyapatite) + reduction synergistic purification (sodium sulfite + ascorbic acid)" system to remove Fe 3+ 、Mn 2+ It can remove colored impurity ions, solve the problem of incomplete adsorption of traditional magnesium hydroxide, and improve the whiteness of the product.

[0029] (2) The present invention forms a hydrophobic layer on the powder surface by using a composite surface modifier (a compound of silane coupling agent KH-550 and titanate coupling agent TC-114). Combined with the spray drying process, it effectively inhibits the agglomeration of nanopowders caused by excessively high surface energy, thereby ensuring the stability of ultrafine properties (particle size ≤ 30 nm).

[0030] (3) The present invention uses ultrasonic assisted leaching in combination with a composite auxiliary agent to accelerate the reaction rate of magnesium chloride and Ca(OH)2 and shorten the reaction time;

[0031] The composite deep impurity removal process (chelation + adsorption) improves the efficiency of impurity ion removal, avoids the problem of insufficient selectivity of traditional single impurity removers, and reduces the time-consuming reaction steps.

[0032] The introduction of composite sintering aids (zinc borate and alumina) significantly reduces energy consumption;

[0033] Nanofiltration membrane separation is used to achieve water circulation and reuse of magnesium chloride hexahydrate, forming a closed-loop cycle and reducing pollution and raw material consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0035] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application can be combined with each other.

[0037] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Example 1:

[0039] refer to Figure 1 A method for preparing high-purity, ultrafine, high-whiteness calcium carbonate (dolomite raw material) comprises the following steps:

[0040] S1: Dolomite (CaO 28%, MgO 19%) was crushed to 4 mm, 2% composite sintering aid (zinc borate:alumina = 1:1) was added, calcined at 800 °C for 4 h, and CO2 was purified by 13X molecular sieve (purity 99.6%).

[0041] S2: The calcined product was mixed with water at a ratio of 1:20, 1% composite ultrasonic auxiliary agent (sodium lauryl sulfate: Tween-80 = 3:1) was added, and ultrasonic stirring was performed at 25kHz for 40min. 2+ ):n(Ca 2+ )=1:1.08, add magnesium chloride, react at 500r / min for 30min, and filter;

[0042] S3: Magnesium hydroxide and water were slurried at a ratio of 1:40, 0.3 mol / L composite chelating agent (disodium EDTA: nano-HAP = 10:1) was added, stirred at 45°C for 20 min, transferred to an autoclave (65% by volume), and purified CO2 was introduced at 0.5 MPa and 20°C to react until the pH reached 8.8, and filtered.

[0043] S4: Add 0.03% composite crystal form control agent (sodium citrate: chitosan = 5:1) to the leachate, crystallize at 30℃ for 2h, and filter;

[0044] S5: Mix calcium chloride solution and magnesium carbonate trihydrate at a ratio of 1:1.05, add 0.2% composite reducing agent (sodium sulfite: ascorbic acid = 2:1), react at 600 r / min for 2 h, and wash until there is no Cl - ;

[0045] S6: Filter cake and water were mixed in a ratio of 1:30, 1.0% composite surface modifier (KH-550:TC-114 = 3:1, containing 5% nano zinc oxide) was added, and spray dried (300°C inlet air, 100°C exhaust air);

[0046] S7: Online monitoring of particle size and whiteness, PLC adjustment parameters, final product: purity 99.995%, particle size 45nm, whiteness 98.5%, antibacterial rate against Escherichia coli 92%.

[0047] This example uses conventional dolomite (containing 28% CaO and 19% MgO) as raw material to demonstrate the applicability of this preparation method for traditional magnesium-containing carbonate minerals. Through standardized processes (such as calcination at 800°C and 25kHz ultrasonic-assisted leaching), a calcium carbonate product with a purity of 99.995%, a particle size of 45nm, a whiteness of 98.5%, and an antibacterial rate of 92% was successfully prepared. This demonstrates that this method can consistently achieve the core goals of "high purity, ultrafineness, high whiteness," and functional properties (antibacterial properties) using conventional mineral raw materials, providing a viable solution for the high-value utilization of traditional mineral resources.

[0048] Example 2:

[0049] refer to Figure 1 A method for preparing high-purity, ultrafine, high-whiteness calcium carbonate (steel slag raw material) comprises the following steps:

[0050] S1: Steel slag (CaO 35%) was desiliconized by 10% hydrochloric acid leaching, crushed to 3 mm, added with 1.5% composite sintering aid (zinc borate: alumina = 1:0.8), calcined at 750℃ for 3.5h, and purified to 99.5% CO2;

[0051] S2: The calcined product was mixed with water at a ratio of 1:15, 0.8% composite ultrasonic auxiliary agent was added, and ultrasonic stirring was performed at 20kHz for 35min. 2+ ):n(Ca 2+ )=1:1.05, add magnesium chloride, react at 400r / min for 25min, and filter;

[0052] S3: Magnesium hydroxide and water were slurried at a ratio of 1:35, 0.2 mol / L composite chelating agent was added, stirred at 40°C for 18 min, transferred to a high-pressure reactor (60% by volume), and CO2 was introduced at 0.4 MPa and 18°C ​​to react until the pH reached 8.6, and filtered;

[0053] S4: Add 0.02% composite crystal form control agent to the leachate, crystallize at 28℃ for 1.5h, and filter;

[0054] S5: Mix calcium chloride solution and magnesium carbonate trihydrate at a ratio of 1:1.03, add 0.15% composite reducing agent, react at 500 r / min for 1.5 hours, and wash until there is no Cl - ;

[0055] S6: Filter cake and water are mixed in a ratio of 1:25, 0.8% composite surface modifier is added, and spray drying is performed (280°C inlet air, 95°C exhaust air);

[0056] S7: After online regulation, the product has the following characteristics: purity 99.992%, particle size 48nm, whiteness 98.2%, and antibacterial rate against Escherichia coli 90%.

[0057] This example uses industrial solid waste steel slag (containing 35% CaO) as raw material, highlighting the application value of this method in the field of solid waste resource utilization. Through targeted pretreatment (10% hydrochloric acid leaching to remove silicon-based impurities) combined with optimized processes (calcination at 750°C, carbonization reaction at 0.4 MPa), the steel slag is converted into a calcium carbonate product with a purity of 99.992%, a particle size of 48 nm, and a whiteness of 98.2%. The product also exhibits a 90% antibacterial rate. This method demonstrates that industrial waste (steel slag) can be converted into high-value-added products, achieving the dual environmental benefits of "solid waste reduction" and "resource recycling," while also diversifying the source of raw materials.

[0058] Example 3:

[0059] refer to Figure 1 A method for preparing high-purity, ultrafine, high-whiteness calcium carbonate (dolomite tailings raw material) comprises the following steps:

[0060] S1: Dolomite tailings (CaO22%) were subjected to magnetic separation (1500Gs) to remove iron, crushed to 3mm, added with 2% composite sintering aid, calcined at 800℃ for 4h, and purified with CO2 to 99.6%;

[0061] S2-S6: same parameters as in Example 1;

[0062] Product performance: purity 99.996%, particle size 28nm, whiteness 99.2%, antibacterial rate against Escherichia coli 93%.

[0063] This example uses dolomite tailings (containing 22% CaO), a solid waste from mines, as raw material, highlighting the method's ability to efficiently utilize low-grade tailings and optimize their performance. Through targeted pretreatment, including magnetic separation for iron removal (1500 Gs), combined with core processes consistent with Example 1, the final product achieves 99.996% purity, a particle size reduced to 28 nm, an increased whiteness to 99.2%, and a 93% antibacterial rate, surpassing all other performance indicators of the previous two examples. This demonstrates the method's ability to improve the quality and efficiency of low-value solid wastes such as mine tailings. Not only does it achieve tailings resource utilization, but it also overcomes the bottlenecks of whiteness and particle size through precise impurity removal and regulation, demonstrating the method's advantages in increasing the added value of solid waste utilization.

[0064] Through multi-dimensional optimization, the present invention significantly improves the whiteness of the product while maintaining high purity and ultrafine properties, while reducing energy consumption and improving efficiency, making it suitable for industrial production.

[0065] Working principle:

[0066] Diversification of raw materials and recycling of solid waste: Using dolomite tailings and steel slag as raw materials, we remove impurities through pre-treatment to reduce costs and achieve solid waste reduction;

[0067] Composite impurity removal system: using "chelating agent + nano-adsorbent" to synergistically remove Fe 3+ 、Mn 2+ Etc., combined with reducing agents to inhibit ion oxidation and discoloration, breaking through the whiteness bottleneck, reduction and synergistic purification uses sodium sulfite and ascorbic acid compound reducing agents to specifically inhibit the oxidation of colored ions;

[0068] Bio-templated crystallization: natural polymers are used to guide the directional growth of crystals, reduce the coefficient of variation of particle size distribution, and ensure the uniformity of ultrafine particles. The composite crystal form controller (sodium citrate-chitosan) guides crystal growth through amino coordination to ensure the uniformity of ultrafine particles.

[0069] Functional modification and closed-loop process: A composite surface modifier is introduced to impart antibacterial properties, and water circulation is achieved through a nanofiltration membrane, reducing energy consumption and pollution. The composite surface modifier (KH-550 / TC-114) is combined with nano-zinc oxide to impart antibacterial properties to the product in a ratio of 3:1.

[0070] Intelligent control: Online monitoring of particle size and whiteness, real-time adjustment of reaction parameters, and improved batch stability.

[0071] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing high-purity ultrafine high-whiteness calcium carbonate, characterized in that: The following steps are involved: S1. Raw material pretreatment: crush the magnesium carbonate to a particle size of less than 5 mm, add 1-3% by mass of a composite sintering aid, calcine at 700-900°C for 3-5 hours, and collect the calcined solid product and carbon dioxide gas; S2. Ultrasonic assisted leaching: The calcined solid product and deionized water are mixed into a slurry at a mass ratio of 1:8-30, and an ultrasonic auxiliary agent (selected from sodium lauryl sulfate and Tween-80 at a mass ratio of 3:1) with a mass fraction of 0.5-2% is added. Stir for 30-60 minutes under the action of 20-30kHz ultrasonic waves, and then press n(Mg 2+ ):n(Ca 2+ )=1:1.05-1.1 add magnesium chloride solution, react at room temperature, stirring speed 300-600r / min for 20-40min, filter to obtain high-purity calcium chloride solution and impurity-containing magnesium hydroxide solid; S3, composite deep impurity removal: the impurity-containing magnesium hydroxide solid and deionized water are mixed into a slurry according to n(Mg(OH)2):m(H2O)=1:30-60, 0.1-0.5 mol / L of a chelating agent is added, and the mixture is stirred at 40-50°C for 15-30 min, and transferred to a high-pressure reactor, and the carbon dioxide gas collected in step S1 is introduced, and the mixture is reacted at a pressure of 0.4-0.6 MPa, a temperature of 15-25°C, and a stirring speed of 300-500 r / min until the system pH is 8.5-9.0, and the magnesium ion leachate is obtained by filtration; S4. Biological template regulated crystallization: add 0.01-0.05% of a composite crystal form control agent to the magnesium ion leachate, crystallize at 25-40°C for 1-2.5 hours, and filter to obtain high-purity magnesium carbonate trihydrate crystals; S5, reduction and coordinated purification: high-purity calcium chloride solution and magnesium carbonate trihydrate crystals are mixed according to n(MgCO3・3H2O):n(Ca 2+ )=1:1.02-1.08, add 0.1-0.3% of reducing agent by mass, react at room temperature and stirring speed of 400-800r / min for 1-3h, filter and wash the filter cake with deionized water until there is no Cl - ; S6, functional modification and closed-loop circulation: the filter cake and deionized water are mixed into a slurry at a ratio of m(CaCO3):m(H2O)=1:20-40, 0.5-1.5% of a composite surface modifier is added, the mixture is stirred evenly and spray-dried, and the dry powder is collected to obtain a high-purity, ultrafine, high-whiteness calcium carbonate product; at the same time, the filtrate of step S5 is separated by a nanofiltration membrane, evaporated and crystallized to obtain magnesium chloride hexahydrate, and the retained liquid is reused for the slurry preparation in step S2; S7. Online monitoring and intelligent control: In steps S3, S5, and S6, a laser particle size analyzer and a whiteness analyzer are introduced to monitor the particle size and whiteness in real time. The reaction parameters are automatically adjusted through the PLC system to ensure the stability of product performance.

2. The method for preparing high-purity ultrafine high-whiteness calcium carbonate according to claim 1, wherein: The magnesium-containing carbonate is any one of dolomite, limestone, marble or dolomite tailings / steel slag.

3. The method for preparing high-purity ultrafine high-whiteness calcium carbonate according to claim 1, wherein: The pretreatment of dolomite tailings in the S1 raw material diversified pretreatment step includes magnetic separation to remove iron, and the steel slag needs to be pretreated by 10% hydrochloric acid leaching to remove silicon-based impurities.

4. The method for preparing high-purity ultrafine high-whiteness calcium carbonate according to claim 1, wherein: In the S3 composite deep impurity removal step, the particle size of the nano-hydroxyapatite is 50-100 nm, and the added amount is 5-10% of the total mass of the chelating agent.

5. The method for preparing high-purity ultrafine high-whiteness calcium carbonate according to claim 1, wherein: The molecular weight cut-off of the nanofiltration membrane in the S6 functional modification and closed-loop circulation step is 100-300 Da, and the operating pressure is 0.2-0.4 MPa.

6. The method for preparing high-purity ultrafine high-whiteness calcium carbonate according to claim 1, wherein: The prepared calcium carbonate product has a calcium carbonate mass content of ≥99.995%, a particle size of ≤30nm, a whiteness of ≥99%, and antibacterial properties.

7. The method for preparing high-purity ultrafine high-whiteness calcium carbonate according to claim 1, wherein: The composite sintering aid in the S2 ultrasonic-assisted leaching step is a composite system of zinc borate and aluminum oxide, with a mass ratio of 1:(0.8-1.2).

8. The method for preparing high-purity ultrafine high-whiteness calcium carbonate according to claim 1, wherein: The composite crystal form controlling agent in the S4 biological template regulated crystallization step is a compound system of sodium citrate and chitosan, the mass ratio of the two is 5:1, and the deacetylation degree of chitosan is ≥90%.

9. The method for preparing high-purity ultrafine high-whiteness calcium carbonate according to claim 1, wherein: The reducing agent in the S5 reduction-coordination purification step is a compound system of sodium sulfite and ascorbic acid, with a mass ratio of 2:1; the composite surface modifier in S6 is a compound system of KH-550 and TC-114, with a mass ratio of 3:1, and contains 5% nano zinc oxide.

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