Light calcium carbonate and molecular sieve prepared by synergistically utilizing magnesium smelting byproducts and preparation method of light calcium carbonate and molecular sieve

Abstract

The invention provides light calcium carbonate and a molecular sieve prepared by synergistically utilizing magnesium smelting byproducts and a preparation method thereof. Carbon dioxide in magnesium smelting flue gas is captured by utilizing ammonia water, and ammonium bicarbonate is obtained through concentration, crystallization and filtration; magnesium slag is leached through an ammonium chloride solution, and leaching liquid and leaching slag are obtained through solid-liquid separation; preparing calcium carbonate from ammonium bicarbonate and the leachate; and removing impurities from the leaching residues, adding a molecular sieve seed crystal, and carrying out a hydrothermal reaction to obtain the molecular sieve. The method has the advantages that the carbon sequestration efficiency is high, the carbonization rate of calcium ions is higher, and the calcium carbonate preparation speed is higher. By adopting the method disclosed by the invention, CO2 emission of magnesium smelting enterprises can be greatly reduced, nearly all components of the magnesium slag are utilized, and calcium carbonate and molecular sieves with high application additional values can be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste resource utilization, and particularly relates to a light calcium carbonate and molecular sieve prepared by co-utilizing by-products of magnesium smelting and a preparation method thereof. Background Art

[0002] At present, most magnesium smelting enterprises in China adopt the Pidgeon process to smelt magnesium. Under vacuum conditions, crude magnesium is reduced, and finally metallic magnesium ingots are obtained through refining and surface treatment. The remaining solid residue is magnesium slag, with an annual output of up to 3 million tons. Due to the extremely low hydration activity of magnesium slag and the volume expansion phenomenon that occurs when magnesium slag reacts with water, a large amount of magnesium slag accumulates; at the same time, during the magnesium smelting process, a large amount of CO2 is emitted from the raw materials and fuels in the calcined dolomite section, resulting in a high concentration of CO2 in the flue gas. Under the background of "dual carbon", the treatment of magnesium slag and carbon dioxide emission reduction bring huge pressure to metal magnesium smelting enterprises.

[0003] The main mineral component of magnesium slag is γ-Ca2SiO4, and the proportion of CaO in it is usually above 50%. It is a potential raw material for preparing light calcium carbonate. Light calcium carbonate, also known as precipitated calcium carbonate, can be used as a filler in industries such as rubber, plastics, papermaking, coatings, and inks, and is also widely used in organic synthesis, metallurgy, glass, and asbestos production. However, due to the low solubility of CO2 in water, the reaction efficiency of the existing "direct" method (using the leaching solution of magnesium slag as the calcium source to react with CO2 in the flue gas) for preparing light calcium carbonate is low. In addition, a large amount of leaching residue will be generated after leaching calcium ions from magnesium slag, which will cause new solid waste treatment problems.

[0004] In summary, it is of great significance to design and realize the utilization of by-products of magnesium smelting, thereby achieving carbon emission reduction and nearly complete component comprehensive utilization of magnesium slag. Summary of the Invention

[0005] Aiming at the defects and deficiencies existing in the prior art, the purpose of the present invention is to provide a light calcium carbonate and molecular sieve prepared by co-utilizing by-products of magnesium smelting and a preparation method thereof, so as to improve the CO2 fixation efficiency and the preparation efficiency of magnesium slag-based light calcium carbonate, and achieve carbon emission reduction and nearly complete component comprehensive utilization of magnesium slag.

[0006] To solve the above technical problems, the present invention is realized by adopting the following technical solutions: A light calcium carbonate and molecular sieve prepared by co-utilizing by-products of magnesium smelting and a preparation method thereof. Ammonia water is used to capture carbon dioxide in magnesium smelting flue gas, and ammonium bicarbonate is obtained through concentration, crystallization, and filtration; magnesium slag is leached with ammonium chloride solution, and the leaching solution and leaching residue are obtained through solid-liquid separation; calcium carbonate is prepared by using ammonium bicarbonate and the leaching solution; the leaching residue is purified and then molecular sieve seeds are added, and a molecular sieve is prepared through hydrothermal reaction; It includes the following steps: Step 1: Cool the magnesium smelting flue gas to 20 - 35°C with ice water and remove the particulate matter in the magnesium smelting flue gas to obtain the cooled flue gas; Step 2: Pass the cooled flue gas into ammonia water to obtain a saturated ammonium bicarbonate solution; Step 3: Concentrate and crystallize the obtained saturated ammonium bicarbonate solution, and perform suction filtration to obtain ammonium bicarbonate solid; Step 4: Mix the magnesium slag in a formula amount with ammonium chloride solution, and perform leaching and suction filtration to obtain a leaching solution and leaching residue; Step 5: Add ammonium bicarbonate in a formula amount to the leaching solution, and obtain calcium carbonate through stirring, suction filtration, washing, and drying; Step 6: Wash the leaching residue obtained in Step 4 with hydrochloric acid, filter, wash with deionized water, and dry to obtain a leaching residue with impurities removed; Step 7: Add the leaching residue with impurities removed, deionized water, sodium hydroxide, and molecular sieve seeds in a formula amount to a hydrothermal reaction kettle, add an aluminum source to adjust the silicon-aluminum ratio of the system, and perform a hydrothermal reaction under constant temperature conditions to obtain a reaction product; Step 8: Filter, wash, and dry the reaction product obtained in Step 7 to obtain a molecular sieve; in the said Step 4, the concentration of the ammonium chloride solution is 25% - 35%; the ammonium chloride solution and the magnesium slag have a solid-liquid ratio of 40 - 100 g / L; the leaching temperature is 10 - 80°C, and the leaching time is 20 - 180 min; In the said Step 5, the solid-liquid ratio of ammonium bicarbonate to the leaching solution is 25 - 40 g / L; In the said Step 7, the solid-liquid ratio of water to sodium hydroxide is 14 - 60 g / L, the dosage of the molecular sieve seeds is 3% - 8% of the mass of the leaching residue with impurities removed, the water-slag ratio is 10:1, and the silicon-aluminum molar ratio is 10 - 50; the hydrothermal temperature is 130 - 180°C, and the hydrothermal time is 12 - 48 h.

[0007] The present invention further includes the following technical features: Specifically, the aluminum source includes aluminum chloride, aluminum hydroxide, and metakaolin.

[0008] Furthermore, the molecular sieve seeds include ZSM-5 type molecular sieve seeds, Y type molecular sieve seeds, and ZSM-35 type molecular sieve seeds.

[0009] The present invention also protects the light calcium carbonate and molecular sieve prepared by the above method.

[0010] Compared with the prior art, the present invention has the following beneficial technical effects: (1) The preparation method provided by the present invention rapidly fixes CO2 in flue gas through the gas-liquid neutralization reaction between ammonia water and flue gas, and then obtains ammonium bicarbonate, with a higher carbon fixation efficiency; using the soluble ammonium bicarbonate obtained from carbon fixation as a carbon source, the liquid-liquid metathesis reaction between it and calcium ions in the leaching solution "indirectly" prepares light calcium carbonate, with a higher carbonization rate of calcium ions and a faster calcium carbonate preparation speed; using the leaching residue as a silicon source to prepare molecular sieves with high added value. The method of the present invention can greatly reduce the CO2 emissions of magnesium smelting enterprises, utilize magnesium slag with almost all components, and obtain calcium carbonate and molecular sieves with high application added value.

[0011] (2) The method of the present invention has the advantages of simple process and low cost, and is of great significance for extending the circular economy industrial chain of metallic magnesium. Description of the Drawings

[0012] Figure 1 It is the XRD pattern of the light calcium carbonate prepared in Example 1.

[0013] Figure 2 It is the XRD pattern of the light calcium carbonate prepared in Example 2.

[0014] Figure 3 It is the XRD pattern of the light calcium carbonate prepared in Example 3.

[0015] Figure 4 It is the scanning electron microscope photograph of the molecular sieve prepared in Example 3.

[0016] Figure 5 It is the XRD pattern of the light calcium carbonate prepared in Comparative Example 1.

[0017] The technical solutions of the present invention will be further described below in conjunction with the examples. Detailed Embodiments

[0018] The present invention provides a light calcium carbonate and molecular sieve prepared from by-products of magnesium smelting and a preparation method thereof. Aiming at the problem of low efficiency of preparing light calcium carbonate from existing magnesium slag, the method proposes to prepare light calcium carbonate by an "indirect" method, which specifically includes: first, preparing ammonium bicarbonate by the gas-liquid neutralization reaction between ammonia water and CO2 in magnesium smelting flue gas, that is, rapidly fixing carbon dioxide in magnesium smelting flue gas by the neutralization reaction between alkaline ammonia water and acidic CO2, and obtaining ammonium bicarbonate through concentration, crystallization and filtration; adopting the wet leaching method to dissolve calcium elements in magnesium slag into water, obtaining a leaching solution and leaching residue through solid-liquid separation, and then using ammonium bicarbonate as a carbon source and the magnesium slag leaching solution as a calcium source to generate light calcium carbonate through a liquid-liquid metathesis reaction; further, using the magnesium slag leaching residue as a silicon source, after removing impurities, preparing a molecular sieve with high added value through the seeded hydrothermal method, which can achieve carbon emission reduction and nearly full-component comprehensive utilization of magnesium slag. In the prior art, there have been no reports on "indirectly" preparing light calcium carbonate using ammonium bicarbonate prepared by capturing CO2 in magnesium smelting flue gas with ammonia water as a carbon source and the magnesium slag leaching solution as a calcium source, and preparing a molecular sieve using the magnesium slag leaching residue.

[0019] The essence of the whole reaction is that NH3 acts as a base and preferentially and rapidly combines with acidic CO2 to form NH4HCO3, and then uses Ca 2+ to combine with HCO3 - to form a poorly soluble CaCO3 precipitate. This process is driven by the extremely low solubility product of calcium carbonate, which can greatly improve the carbon sequestration efficiency, the calcium ion carbonation rate, and the efficiency of preparing light calcium carbonate from magnesium slag; further, based on the main component of magnesium slag being γ-Ca2SiO4, the leaching residue is used as a silicon source, after removing impurities, molecular sieve seeds are added, and a molecular sieve is prepared through a hydrothermal reaction.

[0020] Preferably, it includes the following steps: Step 1: Cooling the magnesium smelting flue gas to 20-35 °C with ice water and removing particulate matter in the magnesium smelting flue gas to obtain cooled flue gas; Step 2: Passing the cooled flue gas into ammonia water to obtain a saturated ammonium bicarbonate solution; Among them, the reaction that occurs is: NH3·H2O + CO2 → NH4HCO3.

[0021] Step 3: Concentrating and crystallizing the obtained saturated ammonium bicarbonate solution, and performing suction filtration to obtain solid ammonium bicarbonate; Step 4: Mixing the formulated amount of magnesium slag with the leaching agent ammonium chloride solution, and performing leaching and suction filtration treatments to obtain a leaching solution and a leaching residue. Among them, the leaching solution is a calcium-rich leaching solution, and the leaching residue is a silicon-rich leaching residue; Preferably, the concentration of the ammonium chloride solution is 25% - 35%; the solid-liquid ratio of the ammonium chloride solution to the magnesium slag is 40-100 g / L; the leaching temperature is 10-80 °C, and the leaching time is 20-180 min.

[0022] Step 5, adding a formula amount of ammonium bicarbonate to the leaching solution, stirring, filtering, washing, and drying to obtain light calcium carbonate; Among them, the reaction of ammonium bicarbonate added to the leaching solution is: .

[0023] Preferably, the solid-liquid ratio of ammonium bicarbonate to the leaching solution is 25-40 g / L; in addition, the remaining residual liquid is mainly composed of ammonium chloride, which can be recycled as a leaching solution; Step 6, washing the leached residue obtained in step 4 with hydrochloric acid, filtering, washing with deionized water and drying in sequence to obtain impurity-removed leached residue; Step 7, adding the formulated amount of impurity-removed leaching residue, deionized water, sodium hydroxide and molecular sieve seed crystals into a hydrothermal reactor, adding an aluminum source to adjust the silicon-aluminum ratio of the system, and performing a hydrothermal reaction under a constant temperature condition to obtain a reaction product; Preferably, the solid-liquid ratio of water to sodium hydroxide is 14-60 g / L, the amount of molecular sieve seeds is 3%-8% of the mass of the impurity-removing leaching slag, the water-slag ratio is 10:1, and the silicon-aluminum molar ratio is 10-50.

[0024] Preferably, the aluminum source includes aluminum chloride, aluminum hydroxide and metakaolin.

[0025] Preferably, the hydrothermal temperature is 130-180° C. and the hydrothermal time is 12-48 hours.

[0026] Preferably, the molecular sieve seeds include ZSM-5 molecular sieve seeds, Y-type molecular sieve seeds and ZSM-35 molecular sieve seeds.

[0027] Step 8: Filter, wash and dry the reaction product obtained in step 7 in sequence to obtain a molecular sieve.

[0028] In the present invention, magnesium smelting flue gas refers to the flue gas containing high concentration of CO2 generated in the dolomite calcining section.

[0029] Unless otherwise specified, the raw materials used in the present invention are all commercially available, including: Magnesium slag is produced by Shaanxi Tianyu Magnesium Industry Group Co., Ltd. and is set aside after drying.

[0030] The main chemical components of magnesium slag are: CaO (61.1%), SiO2 (30.6%), Fe2O3 (4.1%), MgO (2.4%), and Al2O3 (0.5%).

[0031] Ammonia water, concentration 30%, was purchased from Aladdin Chemical Reagent.

[0032] Ammonium chloride, analytical reagent, purchased from Tianjin Damao Chemical Reagent Factory.

[0033] Solid sodium hydroxide, analytical reagent, Sinopharm Chemical Reagent Co., Ltd.

[0034] ZSM-5 molecular sieve seeds, purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.

[0035] Following the above technical solution, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and any equivalent transformation based on the technical solution of this application falls within the protection scope of the present invention.

[0036] Example 1 Following the above technical solution, this embodiment discloses a preparation method of synergistically utilizing light calcium carbonate and molecular sieve prepared from magnesium smelting by-products, including the following steps: Step 1: Pass the magnesium smelting flue gas into a cooling tower filled with ice water for cooling and impurity removal to obtain cooled flue gas after cooling and impurity removal of the flue gas. Step 2: Pass the cooled flue gas into an absorption tower filled with ammonia water, and collect saturated ammonium bicarbonate solution at the bottom of the absorption tower. Step 3: Add the obtained saturated ammonium bicarbonate solution into a concentration crystallizer for concentration crystallization, and filter to obtain solid ammonium bicarbonate. Step 4: Mix 10 g of magnesium slag with 100 mL of ammonium chloride solution with a concentration of 35%, add it to a leaching stirrer, and leach for 2 h at a temperature of 60 °C and a stirring speed of 200 r / min. After the reaction, filter to obtain leaching solution and leaching residue. Step 5: Add 3 g of ammonium bicarbonate to the leaching solution. A large amount of white precipitate appears after stirring for 2 s. Filter, wash with deionized water, and dry at 105 °C for 6 h to obtain light calcium carbonate; the X-ray diffraction pattern of the obtained calcium carbonate is as Figure 1 shown. It can be seen from the figure that the obtained light calcium carbonate is a single calcite phase calcium carbonate, and there are no impurity peaks in the X-ray diffraction pattern of the sample, indicating that the light calcium carbonate prepared by this method has high purity.

[0037] Step 6: Wash the leaching residue obtained in Step 4 successively with 4 mol / L hydrochloric acid to remove impurities therein, then filter, wash with deionized water until the filtrate is neutral, and dry at 105 °C for 6 h to obtain impurity-removed leaching residue. Step 7: Add 5 g of impurity-removed leaching residue, 50 mL of deionized water, 1.4 g of sodium hydroxide, and 2.5 g of ZSM-5 molecular sieve seeds into a hydrothermal reaction kettle, add 0.4 g of aluminum chloride to adjust the silicon-aluminum ratio of the system, and place it in an incubator at 160 °C for hydrothermal reaction for 24 h to obtain a reaction product. Step 8: Filter, wash, and dry the reaction product obtained in Step 7 to obtain molecular sieve.

[0038] Example 2 Following the above technical solution, this example discloses a preparation method for synergistically utilizing light calcium carbonate and molecular sieve prepared from by-products of magnesium smelting. The steps and raw material components of the method disclosed in this example are the same as those in Example 1, except that: in Step 4, 10 g of magnesium slag is mixed with 200 mL of ammonium chloride solution with a concentration of 30%; in Step 5, 5 g of ammonium bicarbonate is added to the leaching solution; in Step 7, the addition amount of sodium hydroxide is 2 g; 0.56 g of aluminum chloride is added to adjust the silicon-aluminum ratio of the system; and it is placed in a constant temperature oven at 140 °C for hydrothermal reaction for 12 h.

[0039] This example finally prepared light calcium carbonate and molecular sieve, and the X-ray diffraction pattern of the obtained calcium carbonate is as Figure 2 shown. It can be seen from the figure that the prepared light calcium carbonate is single-phase calcite calcium carbonate, and there are no impurity peaks in the X-ray diffraction pattern of the sample, indicating that the light calcium carbonate prepared by this method has high purity.

[0040] Example 3 Following the above technical solution, this example discloses a preparation method for synergistically utilizing light calcium carbonate and molecular sieve prepared from by-products of magnesium smelting. The steps and raw material components of the method disclosed in this example are the same as those in Example 2, except that: in Step 7, the addition amount of sodium hydroxide is 2 g; 0.7 g of aluminum chloride is added to adjust the silicon-aluminum ratio of the system; and it is placed in a constant temperature oven at 160 °C for hydrothermal reaction for 12 h.

[0041] This example finally prepared light calcium carbonate and molecular sieve, and the X-ray diffraction pattern of the obtained calcium carbonate is as Figure 3 shown. It can be seen from the figure that the prepared molecular sieve is ZSM-5 type molecular sieve; the scanning electron microscope photo of the molecular sieve is as Figure 4 shown. It can be seen from the figure that the prepared molecular sieve sample has a hexagonal plate-like morphology with a size of about 500 - 800 nm, which is a typical morphology of ZSM-5 molecular sieve, and this is also consistent with its XRD results.

[0042] Comparative Example 1 This comparative example uses high-purity CO2 as simulated flue gas and prepares light calcium carbonate by directly introducing the flue gas into the magnesium slag leaching solution, including the following steps: Step 1: Mix 10 g of magnesium slag with 200 mL of ammonium chloride solution with a concentration of 30%, add it to a leaching stirrer, and leach for 2 h at a temperature of 60 °C and a stirring speed of 200 r / min. After the reaction ends, filter by suction to obtain the leaching solution and leaching residue; Step 2: Use 1 mol / L NaOH solution to adjust the pH of the leaching solution to 9 - 10; Step 3: Directly introduce the simulated flue gas into the magnesium slag leaching solution, and continuously stir it with a magnetic stirrer at 200 r / min. After about 15 minutes, white precipitates begin to appear. Continue stirring until the pH of the solution drops to 7 to stop the reaction. Then, perform suction filtration, wash it with deionized water, and dry it at 105 °C for 6 hours to obtain light calcium carbonate. The X-ray diffraction pattern of the obtained calcium carbonate is as shown in Figure 5 shown. It can be seen from Figure 5 that the calcium carbonate prepared by directly reacting the magnesium slag leaching solution with CO2 is a mixed-phase calcium carbonate of vaterite phase and calcite phase.

[0043] It can be seen from Examples 1 to 3 and Comparative Example 1 that: Compared with the existing "direct" method, the "indirect" method for preparing light calcium carbonate provided by the present invention has the advantages of higher carbon sequestration efficiency, higher calcium ion carbonation rate, and faster calcium carbonate preparation speed. Moreover, there are significant differences in the crystal forms of the light calcium carbonate prepared by the "indirect" method of the present invention and the existing "direct" method.

[0044] The preferred embodiments of the present disclosure have been described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0045] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any appropriate manner. To avoid unnecessary repetition, the present disclosure will not separately describe various possible combination methods.

[0046] Furthermore, any combination can be made between various different embodiments of the present disclosure as long as it does not violate the idea of the present disclosure, and it should also be regarded as the content disclosed by the present disclosure.

Claims

1. A preparation method of synergistically utilizing light calcium carbonate and molecular sieve prepared from by-products of magnesium smelting, characterized in that, Carbon dioxide in the magnesium smelting flue gas is captured by ammonia water, and ammonium bicarbonate is obtained through concentration, crystallization and filtration; magnesium slag is leached with ammonium chloride solution, and the leaching solution and leaching residue are obtained through solid-liquid separation; calcium carbonate is prepared from ammonium bicarbonate and the leaching solution; the leaching residue is purified and then molecular sieve seeds are added, and molecular sieve is prepared through hydrothermal reaction; It includes the following steps: Step 1: Cool the magnesium smelting flue gas to 20-35 °C with ice water, and remove the particulate matter in the magnesium smelting flue gas to obtain the cooled flue gas; Step 2: Pass the cooled flue gas into ammonia water to obtain a saturated ammonium bicarbonate solution; Step 3: Concentrate and crystallize the obtained saturated ammonium bicarbonate solution, and filter by suction to obtain solid ammonium bicarbonate; Step 4: Mix the magnesium slag in a formula amount with ammonium chloride solution, and perform leaching and suction filtration to obtain a leaching solution and a leaching residue; Step 5: Add ammonium bicarbonate in a formula amount to the leaching solution, and obtain calcium carbonate through stirring, suction filtration, washing and drying; Step 6: Wash the leaching residue obtained in Step 4 with hydrochloric acid, filter, wash with deionized water and dry in sequence to obtain the purified leaching residue; Step 7: Add the purified leaching residue, deionized water, sodium hydroxide and molecular sieve seeds in a formula amount to a hydrothermal reaction kettle, add an aluminum source to adjust the silicon-aluminum ratio of the system, and perform hydrothermal reaction under constant temperature conditions to obtain a reaction product; Step 8: Filter, wash and dry the reaction product obtained in Step 7 in sequence to obtain molecular sieve; in the said Step 4, the concentration of ammonium chloride solution is 25%-35%; the ammonium chloride solution and the magnesium slag The solid-liquid ratio is 40-100 g / L; the leaching temperature is 10-80 °C, and the leaching time is 20-180 min; In the said Step 5, the solid-liquid ratio of ammonium bicarbonate to the leaching solution is 25-40 g / L; In the said Step 7, the solid-liquid ratio of water to sodium hydroxide is 14-60 g / L, the dosage of molecular sieve seeds is 3%-8% of the mass of the purified leaching residue, the water-slag ratio is 10:1, and the silicon-aluminum molar ratio is 10-50; the hydrothermal temperature is 130-180 °C, and the hydrothermal time is 12-48 h.

2. The preparation method of light calcium carbonate and molecular sieve co-prepared by utilizing magnesium smelting by-products according to claim 1, wherein The said aluminum source includes aluminum chloride, aluminum hydroxide and metakaolin.

3. The preparation method of light calcium carbonate and molecular sieve co-prepared by utilizing magnesium smelting by-products according to claim 1, characterized in that, The said molecular sieve seeds include ZSM-5 type molecular sieve seeds, Y type molecular sieve seeds and ZSM-35 type molecular sieve seeds.

4. Light calcium carbonate and molecular sieve prepared by the preparation method of light calcium carbonate and molecular sieve prepared by synergistically using magnesium smelting by-products as described in any one of claims 1-3.

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