Clean preparation method of layered double hydroxides

Abstract

The invention provides a clean preparation method of layered double hydroxides (LDHs). According to the invention, a metal hydroxide, metal soluble salt and metal basic carbonate are used as reactionraw materials, and the layered double hydroxides which are high in purity and well-defined in structure are directly synthesized in one step. Since only the metal hydroxide, the metal soluble salt andthe metal basic carbonate are used as the raw materials in a reaction process, and alkali materials such as NaOH or Na2CO3 which are commonly used in a conventional technology are not used, the alkalinity of reaction products is greatly reduced, washing with a large amount of water is avoided, a lot of water resources are saved and the environment is protected; at the same time, because the metalsoluble salt is used as the reaction raw material, compared with clean preparation methods by only using poorly soluble metal hydroxides or oxides as the reaction raw material, the method provided bythe invention is reduced in reaction temperature, shortened in reaction time, mild in reaction conditions, low in production cost and energy consumption, low in requirements on a reaction device, less in equipment investment and simple in process flow, has basically no environmental pollution, and is an environmentally-friendly process.

Description

Technical field: [0001] The invention relates to a clean preparation method of layered composite metal hydroxide, which belongs to the field of preparation of inorganic non-metallic functional materials. technical background: [0002] Layered double hydroxides (LDHs) is an anionic layered material, also known as hydrotalcite, which has the form of M 2+ 1-x m 3+ x (OH) 2 (A n- ) x / n mH 2 The general chemical composition formula of O, where M 2+ and M 3+ are divalent and trivalent metal cations, respectively, A n- is the interlayer anion, x is M 3+ / (M 2+ +M 3+ ) molar ratio, m is the quantity of crystal water. The type and composition ratio of the main layer of hydrotalcite, the type and quantity of interlayer objects, and the two-dimensional channel structure can be adjusted in a wide range according to the needs, so as to obtain materials with special structures and functions. The unique two-dimensional layered structure and compositional variability of LDHs, ...

AI Technical Summary

Problems solved by technology

The traditional production method has the following disadvantages: (1) A large amount of inorganic sodium salt is produced by co-precipitation of mixed salt solution and mixed alkali solution to generate LDHs, and about 2 tons of sodium salt is produced by producing 1 ton of LDHs, and the output of sodium salt is relatively large , and the use value is not high, and the concentration consumes a lot of energy. Generally, it is directly discharged, causing pollution to the environment; (2) due to the excessive use of strong alkali in the reaction raw materials, in order to obtain pure LDHs products, it is necessary to repeatedly wash the precipitated products. The product requires a large amount of water for washing to remove the sodium ions and hydroxide ions adhering to the surface of the crystal particles. It takes about 150 tons of pure water to produce 1 ton of LDHs, which causes a serious waste of water resources; (3) a large amount of salt The mother liquor needs to be treated to meet the emission standards, which requires serious energy consumption and high production costs

Literature Xiang Yu Xu, Dian Qing Li, Jia Qing Song, Yan JunLin, Zhi Lv, Min Wei, Xue Duan, PARTICUOLOGY, 2010,8(3):198-201 reported that Mg(OH) 2 and Al(OH) 3 As raw material, add (NH 4 ) 2 CO 3 As an alkali source, MgAl-LDHs were prepared at 200 °C, and a large amount of NH was present in the reaction product 3 By-products, the cost of recovery and reuse is high, and the recovery efficiency is low. At the same time, the reaction product is relatively alkaline, which requires a large amount of water to be washed repeatedly. In addition, the reaction temperature is high, the requirements for the reaction device are high, and the production cost increases.

Literature Li Bing Liao, Ning Zhao, Zhi Guo Xia, Mater.Res.Bull., 2012,47(11):3897-3901 proposed to use Mg(OH) 2 , Al(OH) 3 and MgCO 3 As the reaction raw material, add NaHCO 3 or NaOH as the alkali source, reacted at 180°C for 36h to prepare the target product MgAl-CO 3 -LDHs, there is a by-product sodium salt in the reaction product, and a large amount of water is required to wash the Na attached to the LDHs multiple times + and OH - ions, and because the reaction raw materials are all insoluble substances, the reaction temperature is high, the reaction time is long, the reaction conditions are high, and the production cost is high

Chinese invention patent (CN 105753022A) uses calcium oxide or calcium magnesium oxide as the alkali source, and prepares MgAl-CO by a two-step method with soluble magnesium salt, soluble aluminum salt and urea 3 -LDHs, with many by-products, including calcium salts, magnesium salts and nitrogen-containing compounds, high energy consumption for recovery and cleaning, and complicated preparation steps, which is not conducive to large-scale production

Chinese invention patent (CN1994888B) with Mg(OH) 2 , Al(OH) 3 and CO 2 As raw material, stirred and reacted at 100°C for 4 days to obtain MgAl-CO 3 -LDHs, this reaction requires continuous CO 2 Provide CO 3 2- And to ensure the pressure required for the reaction, it is necessary to consume a large amount of CO 2 , many restrictive conditions, high requirements for reaction equipment, not suitable for large-scale industrial production

Chinese invention patent (CN 102701241B) uses insoluble reactant Mg(OH) 2 , Al(OH) 3 The target product of MgAl-LDHs is prepared by reacting with basic magnesium carbonate at 180°C. The reaction temperature is high, the reaction time is long, and the reaction conditions are relatively high. The energy consumption and production cost of this reaction are high, and it is not suitable for large-scale industry. Promote production, and the particle size of the reaction product depends on the particle size of the reaction raw material in the slurry, so it is impossible to effectively control the particle size of LDHs

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