Method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-crystal nucleus induction causticization granulation

Abstract

The invention discloses a method for preparing high-quality light calcium carbonate based on green liquid separation and impurity removal-crystal nucleus induction causticization granulation, and relates to the technical field of pulping and papermaking waste liquid treatment. According to the method, pulping black liquor is used as a raw material, calcium silicate is separated through fractional precipitation, granular calcium carbonate crystals are generated through crystal nucleus induction causticization reaction, and high-quality light calcium carbonate is prepared through multi-stage purification. The content of calcium carbonate prepared by the method can reach 98-99.5% of the purity of industrial calcium carbonate, the purity of calcium silicate byproducts is greater than or equal to 90%, the calcium silicate byproducts can be directly used for roadbed materials or cement retarders, the recovery rate of sodium hydroxide in the black liquor is greater than or equal to 92%, and resource utilization is realized.

Description

Technical Field

[0001] This invention relates to the field of pulp and paper waste liquor treatment technology, and in particular to a method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-crystal nucleation-induced causticization granulation. Background Technology

[0002] Calcium carbonate, as an inorganic material, is widely used in all aspects of the pulp and paper industry due to its excellent performance and high cost-effectiveness. It runs through the entire process of pulping, papermaking, and coating, and is a core material for improving paper quality and reducing production costs.

[0003] Precipitated calcium carbonate (PCC) is produced by calcining, digesting, and carbonizing natural minerals or other calcium-rich raw materials. During processing, the crystal morphology of calcium carbonate can be controlled, resulting in calcium carbonate products with higher purity, uniform crystal form, and controllable particle size. Therefore, PCC is widely used in papermaking and the production of high-grade coated paper due to its advantages in whiteness and particle size.

[0004] Traditional PCC production primarily uses natural minerals such as limestone and calcite as raw materials, which are non-renewable resources and face the risk of policy control. Furthermore, limestone mining requires open-pit operations, damaging surface vegetation and geological structures, and the calcination process (CaCO3→CaO) is energy-intensive and generates large carbon emissions, which is inconsistent with environmental protection trends.

[0005] In the pulping stage of pulp and paper making, raw materials need to be cooked at high temperatures along with chemicals. The resulting pulp, after washing, forms wastewater called "diluted black liquor." In traditional alkali recovery processes, the treatment of dilute black liquor involves evaporation and concentration, combustion recovery, causticization regeneration, and lime kiln calcination. After the combustion recovery process, the organic matter in the "black liquor" has been completely burned off. The residue, after being dissolved in water, forms "green liquor," which is rich in inorganic components such as sodium carbonate and sodium silicate. The causticization regeneration process involves adding an excess of lime to the green liquor, forming "green mud (calcium silicate)" and "white liquor." After further precipitation and separation, the calcium carbonate in the "white liquor" is converted into lime for reuse after being calcined in a lime kiln.

[0006] The main components of "white liquor" are sodium hydroxide and calcium carbonate precipitate. In the traditional causticizing process, the reaction temperature is 65~80℃. At this temperature, calcium carbonate particles are prone to agglomeration and disordered crystal form. The mixture of white mud (calcium carbonate) and green mud results in low purity of calcium carbonate, which cannot meet the requirements of high-quality PCC.

[0007] Compared to straw pulp, wood pulp has a lower silicate content and fewer impurities in green mud (calcium silicate). This invention addresses how to separate "green mud" during the causticization process and induce calcium carbonate to form calcite crystals, thereby improving the quality of calcium carbonate in white mud and providing a good foundation for subsequent high-value utilization. Summary of the Invention

[0008] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art, and thus proposes a method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-crystal nucleus-induced causticization granulation.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal followed by nucleation-induced causticization granulation includes the following steps: Step 1: Preprocessing (2) Dissolve the black liquor residue in water to obtain green liquor; Step 2: Separation of calcium silicate by fractional precipitation (2) Detect and analyze the concentration of Na2SiO3 in the green solution; (3) Pump the green liquid into the reactor and stir it at a certain temperature, and add calcium hydroxide at 1.0-1.1 times the measured concentration of Na2SiO3 to react; (4) After the reaction is completed, the green liquid and slag are transferred to the sedimentation tank and separated by vacuum filter paper filtration or plate and frame filter press to obtain supernatant and calcium silicate precipitate. Step 3: Nucleus-induced causticization reaction (5) Detect and analyze CO3 in the supernatant 2- concentration; (6) Pump the supernatant into the crystallization reactor, and pre-add calcite-form CaCO3 seed crystals to the crystallization reactor; and use the measured CO3 2- Add calcium hydroxide at 1.0-1.1 times its concentration to react; (7) Control the temperature of the crystallization reactor within a certain range, and use a circulating pump for hydraulic stirring. After a certain reaction time, measure the particle size of CaCO3 crystals in the crystallization reactor and stop the reaction when it reaches 0.1 mm. Step 4: Multi-stage cleaning and purification (8) Transfer the CaCO3 crystals into a countercurrent washing tower and wash them with deionized water at least twice in a countercurrent manner, separating them with a centrifuge each time. (9) Add dilute hydrochloric acid to the washed CaCO3 crystals and stir at room temperature to dissolve the metal oxide into a soluble salt. After precipitation and separation, wash the crystals with deionized water. (10) Add CaCO3 crystals to H2O2 solution and stir to remove organic pigment residues. Then, vacuum dry the CaCO3 crystals to obtain the finished product.

[0010] Preferably, in step (1), the water-to-solid ratio of black liquor residue to clean water is 1:1.3 to 1.5, and the temperature of the clean water is 60 to 80°C.

[0011] Preferably, in step (3), the reaction temperature is controlled at 50-60℃, the stirring rate is 60-80r / min, and the reaction time is 15-20min.

[0012] Preferably, in step (4), the vacuum filter paper has a filtration accuracy of 25-100 μm, and the plate and frame filter press uses a filter cloth of 200-350 mesh.

[0013] Preferably, in step (6), the CaCO3 seed crystals in the reactor have a particle size of 80 to 150 mesh.

[0014] Preferably, in step (7), the reaction temperature is 50-60℃, the upward flow rate of the crystallization reactor is controlled at 30-80m / h, and the reaction time is 5-10min.

[0015] Preferably, in step (8), the temperature of the deionized water is 40-55℃, the centrifuge speed is 4000-4500r / min, until the conductivity of the filtrate is ≤30μS / cm.

[0016] Preferably, in step (9), the concentration of dilute hydrochloric acid is 0.01-0.1 mol / L, the stirring rate is 60-80 r / min, the stirring time is 5-10 min, and the pH of the deionized water washing is 6.5-7.0.

[0017] Preferably, in step (10), the H2O2 solution concentration is 30%, the amount prepared is 0.05 to 0.2% of the CaCO3 crystals, the mixture is stirred at 50 to 55°C for 30 to 40 minutes, the vacuum drying temperature is 90 to 95°C, the vacuum degree is -0.08 to -0.09 MPa, and the drying time is 2 to 3 hours.

[0018] Preferably, in step (7), the crystallization reactor includes a mixing zone, a reaction zone, and a separation zone; the supernatant and seed crystals are mixed in the mixing zone, and the residence time in the mixing zone is 10-20% of the total residence time, and not less than 1 min; the water flows upward in the reaction zone, and the residence time in the reaction zone is 50-70% of the total residence time, and not less than 3 min, and the upward flow velocity in the reaction zone is 50-80 m / h; the residence time in the separation zone is 20-30% of the total residence time, and the upward flow velocity of the water in the separation zone is <40 m / h.

[0019] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: This invention detects the sodium silicate concentration in the green liquor containing the black liquor residue, adds calcium hydroxide in the prescribed amount to precipitate the green mud, and further improves the separation effect of the green mud by adding vacuum filtration or plate and frame filtration, thereby improving the removal effect of silicon in the green liquor and making the silicate content in the mixed liquor less than 0.5 mg / L.

[0020] This invention utilizes nucleus-induced crystal technology to directly generate granular calcium carbonate crystals during the causticization stage. This allows for directional growth of the crystal nuclei, resulting in CaCO3 crystals with a uniform particle size of 0.1 mm and regular crystal shapes, all being cubic or spindle-shaped. This eliminates the need for lime kilns and carbonation regeneration processes, shortening the process flow, reducing energy consumption, and avoiding impurity migration caused by high temperatures. Combined with further purification, the heavy metal content is reduced, resulting in fewer impurities and high whiteness of the prepared calcium carbonate, producing high-quality calcium carbonate.

[0021] This invention purifies the generated calcium carbonate by countercurrent washing, combined with dilute hydrochloric acid cleaning, and then bleaching with H2O2 through a multi-stage process, removing more than 99% of sodium salts, more than 95% of metallic impurities, and organic pigments. This successfully solves the bottleneck of low purity in existing calcium carbonate production technology, and the generated calcium silicate byproduct has a purity of more than 90%, with a sodium hydroxide recovery rate of more than 92%, thus successfully realizing resource utilization. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of a method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal followed by nucleus-induced causticization granulation according to the present invention.

[0023] Figure 2 This is a laboratory test image of a method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-crystal nucleus-induced causticization granulation according to the present invention.

[0024] Figure 3 This is an electron microscope image of calcium carbonate prepared by the method of this invention.

[0025] Figure 4 This is a morphological and compositional analysis diagram of calcium carbonate prepared by the method of this invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] A method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal followed by nucleation-induced causticization granulation, such as... Figure 1 The process flow diagram shown includes the following steps: Step 1: Preprocessing (3) Dissolve the black liquor residue in water to obtain green liquor; Step 2: Separation of calcium silicate by fractional precipitation (2) Detect and analyze the concentration of Na2SiO3 in the green solution; (3) Pump the green liquid into the reactor and stir it at a certain temperature, and add calcium hydroxide at 1.0-1.1 times the measured concentration of Na2SiO3 to react; (4) After the reaction is completed, the green liquid and slag are transferred to the sedimentation tank and separated by vacuum filter paper filtration or plate and frame filter press to obtain supernatant and calcium silicate precipitate. Step 3: Nucleus-induced causticization reaction (5) Detect and analyze CO3 in the supernatant 2- concentration; (6) Pump the supernatant into the crystallization reactor, and pre-add calcite-form CaCO3 seed crystals to the crystallization reactor; and use the measured CO3 2- Add calcium hydroxide at 1.0-1.1 times its concentration to react; (7) Control the temperature of the crystallization reactor within a certain range, and use a circulating pump for hydraulic stirring. After a certain reaction time, measure the particle size of CaCO3 crystals in the crystallization reactor and stop the reaction when it reaches 0.1 mm. Step 4: Multi-stage cleaning and purification (8) Transfer the CaCO3 crystals into a countercurrent washing tower and wash them with deionized water at least twice in a countercurrent manner, separating them with a centrifuge each time. (9) Add dilute hydrochloric acid to the washed CaCO3 crystals and stir at room temperature to dissolve the metal oxide into a soluble salt. After precipitation and separation, wash the crystals with deionized water. (10) Add CaCO3 crystals to H2O2 solution and stir to remove organic pigment residues. Then, vacuum dry the CaCO3 crystals to obtain the finished product.

[0028] In one embodiment, in step (1), the water-to-solid ratio of black liquor residue to clean water is 1:1.3 to 1.5, and the temperature of the clean water is 60 to 80°C.

[0029] In one embodiment, in step (3), the reaction temperature is controlled at 50-60°C, the stirring rate is 60-80 r / min, and the reaction time is 15-20 min.

[0030] In one embodiment, in step (4), the vacuum filter paper has a filtration accuracy of 25-100 μm, and the plate and frame filter uses a 200-350 mesh filter cloth.

[0031] In one embodiment, in step (6), the CaCO3 seed crystals in the reactor have a particle size of 80 to 150 mesh.

[0032] In one embodiment, in step (7), the reaction temperature is 50-60°C, the upward flow rate of the crystallization reactor is controlled at 30-80 m / h, and the reaction time is 5-10 min.

[0033] In one embodiment, in step (8), the temperature of the deionized water is 40-55°C, the centrifuge speed is 4000-4500 r / min, until the conductivity of the filtrate is ≤30 μS / cm.

[0034] In one embodiment, in step (9), the concentration of dilute hydrochloric acid is 0.01-0.1 mol / L, the stirring rate is 60-80 r / min, the stirring time is 5-10 min, and the pH of the deionized water washing is 6.5-7.0.

[0035] In one embodiment, in step (10), the H2O2 solution concentration is 30%, the amount prepared is 0.05 to 0.2% of the CaCO3 crystals, the mixture is stirred at 50 to 55°C for 30 to 40 minutes, the vacuum drying temperature is 90 to 95°C, the vacuum degree is -0.08 to -0.09 MPa, and the drying time is 2 to 3 hours.

[0036] Example 1 This embodiment can be used to reproduce the technical route of this invention patent on a laboratory scale, such as... Figure 2 Connection diagram.

[0037] I. Experimental Materials and Equipment ①Ingredients: The pulping black liquor evaporation residue, calcium hydroxide (analytical grade, purity ≥95%), dilute hydrochloric acid (analytical grade, concentration 37%), 30% hydrogen peroxide solution (analytical grade), and deionized water.

[0038] ② Experimental apparatus: 5L glass beaker, constant temperature water bath, stirrer (speed range 0-500 rad / min), centrifuge (maximum speed 5000 rad / min), vacuum drying oven (temperature control range 50-200℃, vacuum degree range -0.1MPa), conductivity meter, pH meter, particle size analyzer, electronic balance (accuracy 0.001g), vacuum filter device (equipped with 25μm vacuum filter paper), 150 mesh standard sieve.

[0039] II. Experimental Procedure ①Preparation of green solution: Weigh 1000g of black liquor evaporation residue, add 1300g of deionized water at 70℃ according to a water-to-solid ratio of 1:1.3, and stir at 60rad / min for 30min to dissolve and obtain green liquor for later use.

[0040] ② Separation of calcium silicate by fractional precipitation: The concentration of Na₂SiO₃ in the green solution was determined by chemical titration. The prepared green solution was pumped into a 5L glass reactor, and a constant temperature water bath was turned on to control the reaction temperature at 55℃. The stirrer speed was adjusted to 70 rad / min. Calculated at 1.05 times the molar concentration of Na₂SiO₃, 0.84 mol (i.e., 63.4 g) of calcium hydroxide was added, and the reaction was allowed to proceed for 18 min. After the reaction, the mixture was transferred to a vacuum filtration device and filtered using a 45 μm vacuum filter membrane. The supernatant (green solution after silicon removal) and calcium silicate precipitate were collected. The filtered supernatant could be returned to the original reaction vessel.

[0041] ③ Nucleus-induced causticization reaction to prepare granular calcium carbonate crystals: Calcite crystals, screened at 150 mesh, were selected as the crystal nuclei and added to the filtered reactor at a dosage of 10 g / 5 L. The alkalinity of the carbonate in the supernatant was measured. The desiliconized supernatant was continuously pumped into the crystallization reactor. Sodium hydroxide was added, calculated to be 1.05 times the carbonate alkalinity. The circulating pump was started for hydraulic stirring, and the reactor upflow velocity was controlled at 60 m / h, with a reaction residence time of 8 min. The particle size of the crystals in the reactor was periodically measured. When the calcium carbonate particle size reached 0.1 mm, the crystals were discharged and new seed crystals were added.

[0042] ④ Multi-stage cleaning and purification The CaCO3 crystals were transferred to a countercurrent washing tower and washed three times countercurrently with deionized water (40–55°C). After each wash, the crystals were separated by centrifugation (4000–4500 rad / min) until the conductivity of the filtrate was ≤30 μS / cm (ensuring sodium salt residue ≤0.01%). Dilute hydrochloric acid with a molar concentration of 0.01–0.1 mol / L was added to the washed CaCO3 crystals, and the mixture was stirred at 60–80 rad / min at room temperature for 5–10 min to dissolve iron, magnesium, and other metal oxides (such as Fe2O3 and MgO) into soluble salts. After precipitation and separation, the crystals were washed with deionized water until the pH reached 6.5–7.0. The sodium- and weight-removed CaCO3 crystals were then added to a solution containing 0.05–0.2% sodium- and weight-removed ... A 30% H2O2 solution was stirred at 50-55℃ for 30 minutes to remove residual organic pigments and improve whiteness. The purified calcium carbonate was then vacuum dried at 90-95℃ (vacuum degree -0.08 to -0.09MPa) for 2-3 hours to obtain a high-quality CaCO3 product.

[0043] The green liquor precipitate was tested using the fractional precipitation method described above, and the data are shown in Table 1.

[0044] Table 1 The calcium removal experiment was conducted using the method described above, and the data are shown in Tables 2 and 3.

[0045] Table 2 Table 3 The method for preparing granular calcium carbonate crystals by nucleus-induced causticization reaction described above was used to granulate the clear liquid. Experiments were conducted in 2025, and the data are shown in Tables 4-7.

[0046] Table 4 Table 5 Table 6 Table 7 ⑤ Crystal characterization and purity testing: The results of the crystal particle morphology and composition analysis of the CaCO3 product prepared above using a scanning electron microscope are as follows: Figure 3 , Figure 4 As shown, the calcium carbonate particles prepared by the above method were tested and found to have a calcium carbonate content greater than 99.5% and a whiteness greater than 98%.

[0047] Example 2 I. Materials and Equipment Raw materials: Similar to those in Example 1.

[0048] Equipment: 500L stainless steel reactor (with jacketed temperature control and mechanical stirring device), 500L crystallization reactor (customized, including mixing zone, reaction zone, and separation zone, equipped with online particle size monitor), plate and frame filter press (equipped with 200-mesh filter cloth), countercurrent scrubbing tower (diameter 500mm, height 3m), horizontal screw centrifuge (processing capacity 5m³ / h), vacuum drying kiln (temperature control range 80-120℃, vacuum degree -0.08~-0.09MPa), online conductivity monitor, online pH monitor.

[0049] II. Steps ① Separation of calcium silicate: Green liquor was directly extracted from the supernatant in the filtrate dissolution tank of a certain project and transferred to a stainless steel reactor. The Na2SiO3 concentration in the green liquor was measured, and liquid alkali was added at 1.1 times the molar concentration of Na2SiO3. During the reaction, the stirring speed was adjusted to 75 rad / min, and the reaction was carried out for 16 min. After the reaction was completed, the mixture was sent to a plate and frame filter press (equipped with 300-mesh filter cloth) for pressure filtration and separation. The supernatant (green liquor after silica removal) and calcium silicate precipitate were collected.

[0050] ② Preparation of granular calcium carbonate crystals by nucleus-induced causticization reaction: 150-mesh calcium carbonate seed crystals were added at 10% of the reactor volume. The supernatant after silicon removal was continuously pumped into the crystallization reactor. The basicity concentration of carbonate in the supernatant was measured. Sodium hydroxide was added according to 1.1 times the molar concentration of basicity of carbonate. The upward flow rate in the reaction zone was controlled at 70 m / h by a circulating pump, and the reaction residence time was 7 min.

[0051] When the sampled crystal size reaches 0.1 mm, the operation is suspended, the crystals are discharged, and 2 kg of new seed crystals are added to the reactor before operation can continue.

[0052] ③ Multi-stage cleaning and purification: Soluble salt washing: The discharged crystals are sent to a countercurrent washing tower and washed three times countercurrently with industrial deionized water. After each washing, the crystals are separated by a horizontal screw centrifuge. The conductivity of the filtrate is monitored online. The final conductivity of the filtrate is less than 25 μS / cm, which meets the requirements for sodium salt residue.

[0053] Heavy metal hydrochloric acid washing: Add dilute hydrochloric acid with a molar concentration of 0.1 mol / L to the washed crystals, stir at a speed of 25 rad / min, wash with industrial deionized water until the online pH is >6.0, and then separate the precipitate.

[0054] Oxidative bleaching: Prepare a 0.10% solution of 30% industrial-grade H2O2 based on the weight of the crystalline solid. Soak and wash the treated crystals in this solution to remove organic pigments.

[0055] Drying: The bleached calcium carbonate is sent into a vacuum drying kiln and dried for 4-6 hours to obtain a batch of high-quality calcium carbonate products.

[0056] ④ Crystal purity test: The calcium carbonate particles prepared by the above method have a calcium carbonate content greater than 98% and a whiteness greater than 95%.

[0057] This embodiment can be used to reproduce the technical route of this invention patent on a small scale.

[0058] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal followed by nucleation-induced causticization granulation, characterized in that, Includes the following steps: Step 1: Preprocessing (1) Dissolve the black liquor residue in water to obtain green liquor; Step 2: Separation of calcium silicate by fractional precipitation (2) Detect and analyze the concentration of Na2SiO3 in the green solution; (3) Pump the green liquid into the reactor and stir it at a certain temperature, and add calcium hydroxide at 1.0-1.1 times the measured concentration of Na2SiO3 to react; (4) After the reaction is completed, the green liquid and slag are transferred to the sedimentation tank and separated by vacuum filter paper filtration or plate and frame filter press to obtain supernatant and calcium silicate precipitate. Step 3: Nucleus-induced causticization reaction (5) Detect and analyze CO3 in the supernatant 2- concentration; (6) Pump the supernatant into the crystallization reactor, and pre-add calcite-form CaCO3 seed crystals to the crystallization reactor; and use the measured CO3 2- Add calcium hydroxide at 1.0-1.1 times its concentration to react; (7) Control the temperature of the crystallization reactor within a certain range, and use a circulating pump for hydraulic stirring. After a certain reaction time, measure the particle size of CaCO3 crystals in the crystallization reactor and stop the reaction when it reaches 0.1 mm. Step 4: Multi-stage cleaning and purification (8) Transfer the CaCO3 crystals into a countercurrent washing tower and wash them with deionized water at least twice in a countercurrent manner, separating them with a centrifuge each time. (9) Add dilute hydrochloric acid to the washed CaCO3 crystals and stir at room temperature to dissolve the metal oxide into a soluble salt. After precipitation and separation, wash the crystals with deionized water. (10) Add CaCO3 crystals to H2O2 solution and stir to remove organic pigment residues. Then, vacuum dry the CaCO3 crystals to obtain the finished product.

2. The method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-nucleation induced causticizing granulation according to claim 1, characterized in that, In step (1), the water-to-solid ratio of black liquor residue to clear water is 1:1.3 to 1.5, and the temperature of the clear water is 60 to 80°C.

3. The method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-nucleation induced causticizing granulation according to claim 1, characterized in that, In step (3), the reaction temperature is controlled at 50-60℃, the stirring rate is 60-80r / min, and the reaction time is 15-20min.

4. The method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-nucleation induced causticizing granulation according to claim 1, characterized in that, In step (4), the filtration accuracy of the vacuum filter paper is 25-100 μm, and the plate and frame filter press uses a filter cloth of 200-350 mesh.

5. The method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-nucleation induced causticizing granulation according to claim 1, characterized in that, In step (6), the CaCO3 seed crystals in the reactor have a particle size of 80 to 150 mesh.

6. The method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-nucleation-induced causticization granulation according to claim 1, characterized in that, In step (7), the reaction temperature is 50-60℃, the upward flow rate of the crystallization reactor is controlled at 30-80m / h, and the reaction time is 5-10min.

7. The method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-nucleation induced causticizing granulation according to claim 1, characterized in that, In step (8), the temperature of the deionized water is 40-55℃, the centrifuge speed is 4000-4500r / min, until the conductivity of the filtrate is ≤30μS / cm.

8. The method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-nucleation induced causticizing granulation according to claim 1, characterized in that, In step (9), the concentration of dilute hydrochloric acid is 0.01-0.1 mol / L, the stirring rate is 60-80 r / min, the stirring time is 5-10 min, and the pH of the deionized water washing is 6.5-7.

0.

9. The method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-nucleation induced causticizing granulation according to claim 1, characterized in that, In step (10), the H2O2 solution concentration is 30%, the amount prepared is 0.05 to 0.2% of the CaCO3 crystals, the mixture is stirred at 50 to 55°C for 30 to 40 minutes, the vacuum drying temperature is 90 to 95°C, the vacuum degree is -0.08 to -0.09 MPa, and the drying time is 2 to 3 hours.

10. The method for preparing high-quality light calcium carbonate based on green liquor separation and impurity removal-nucleation induced causticizing granulation according to claim 6, characterized in that, In step (7), the crystallization reactor includes a mixing zone, a reaction zone, and a separation zone; the supernatant and seed crystals are mixed in the mixing zone, and the residence time in the mixing zone is 10-20% of the total residence time, and not less than 1 min; the water flows upward in the reaction zone, and the residence time in the reaction zone is 50-70% of the total residence time, and not less than 3 min, and the upward flow velocity in the reaction zone is 50-80 m / h; the residence time in the separation zone is 20-30% of the total residence time, and the upward flow velocity of the water in the separation zone is <40 m / h.

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