CN101386424A - Preparation method and application of modified magnesium aluminum hydrotalcite - Google Patents

Abstract

The invention discloses a preparation method and application of modified magnesium aluminum hydrotalcite. During the preparation, a mixed salt solution and a mixed alkali solution containing Mg ²⁺ and Al ³⁺ were prepared respectively, and the two were mixed, aged and crystallized after the reaction was complete, filtered, washed, and dried to obtain magnesium aluminum hydrotalcite; The magnesium aluminum hydrotalcite and the binder are added to the magnesium salt aqueous solution to adjust the pH value of the resulting slurry, centrifuged after reaction, dried, extruded, then dried and roasted, and cooled to room temperature. The product of the present invention does not block the bed body during adsorption and ion exchange, and is easy to separate after the reaction. It is suitable for treating phosphorus and nitrogen anions in aqueous solution, sewage treatment plant water, seawater, and aquaculture wastewater. The treatment effect is good, and the discharge standard can be reached. After desorption and regeneration after use, the adsorption effect is stronger, which is conducive to the realization of industrial application.

Description

Preparation method and application of modified magnesium aluminum hydrotalcite

technical field

The invention relates to a preparation method and application of modified magnesium aluminum hydrotalcite.

Background technique

The hydrotalcite that exists in nature is a hydroxycarbonate of magnesium and aluminum, also known as magnesium aluminum hydrotalcite, and its theoretical molecular formula is Mg ₆ Al ₂ (OH) ₁₆ (CO ₃ )·4H ₂ O. Magnesium aluminum hydrotalcite is an anionic layered compound with unique anion exchangeability, cation compatibility and large specific surface area, and plays an important role in adsorption, ion exchange and catalysis. However, the current research and application of magnesium aluminum hydrotalcite is mainly limited to the powder form. There are problems such as solid suspended solids are easy to block the bed, difficult to separate after reaction, and regeneration cannot be achieved. limit. Therefore, in order to realize the practical application of magnesium aluminum hydrotalcite in adsorption and ion exchange, magnesium aluminum hydrotalcite must be effectively modified and formed to have a certain mechanical strength.

With the rapid development of industrial and agricultural production, a large amount of domestic sewage, industrial wastewater and agricultural chemical fertilizers flow into rivers and lakes, which increases the phosphorus and nitrogen content in the corresponding water bodies. Excessive phosphorus and nitrogen will not only lead to eutrophication of water bodies, but also pollute groundwater sources. Thereby causing serious harm to human health. However, according to the latest reports from the British journal Freshwater Biology and the American journal PNAS, phosphorus is the decisive factor leading to eutrophication, and it is mainly active phosphorus that plays a role. At present, more than 80% of my country's urban sewage treatment plants are mainly based on flocculation, sedimentation and biological methods, which have poor treatment effects on inorganic pollutants such as phosphorus and nitrogen. To meet the water quality discharge standards, they must go through tertiary treatment. Therefore, effective control and reduction of phosphorus and nitrogen concentrations in wastewater and advanced treatment of slightly polluted water bodies have become new topics in modern sewage treatment, and the research and development of efficient and low-consumption sewage treatment methods has important practical significance.

Contents of the invention

The object of the present invention is to provide a preparation method and application of a modified magnesium aluminum hydrotalcite, which can make up for the above-mentioned shortcomings of the prior art.

A method for preparing modified magnesium-aluminum hydrotalcite, which is characterized in that the steps are as follows: separately prepare a mixed salt solution containing Mg ²⁺ and Al ³⁺ and a mixed alkali solution, mix the two, and perform aging after the reaction is complete and crystallization, filtering, washing, and drying to obtain magnesium aluminum hydrotalcite; adding the magnesium aluminum hydrotalcite and binder into the magnesium salt solution, so that the sum of the mass of the three solids in grams and the volume of the liquid in milliliters The ratio is 1:5~15, adjust the pH value of the resulting slurry to 9~12, react for 15~180min, centrifuge, dry, extrude, dry at 100~110°C, and then dry at 350~ Baking at 700°C for 1 to 4 hours, then cooling to room temperature.

The application of the above modified magnesium aluminum hydrotalcite in the removal of phosphorus and nitrogen anions in aqueous solution, sewage treatment plant water, seawater or aquaculture wastewater.

The modified magnesium-aluminum hydrotalcite of the present invention is an adsorbent with high efficiency and low consumption, which does not block the bed body during adsorption and ion exchange, and is easy to separate and regenerate after the reaction; it can solve the current treatment effect of phosphorus and nitrogen in water bodies It is suitable for treating phosphorus and nitrogen anions in aqueous solution, sewage treatment plant water, seawater, and aquaculture wastewater to meet the discharge standards, and the adsorption effect is stronger after desorption and regeneration, laying the foundation for industrial application.

Detailed ways

Example 1

Preparation method of modified magnesium aluminum hydrotalcite

3000 mol of MgSO ₄ and 500 mol of Al ₂ (SO ₄ ) ₃ were formulated into a mixed brine solution (a total of 4.0 m ³ ), and 5,000 mol of NaOH and 10,000 mol of Na ₂ CO ₃ were formulated into a mixed alkaline aqueous solution (a total of 4.0 m m ³ ), put the two aqueous solutions into the fully mixed jet reactor through the pipeline, and react under the condition of controlling the pH value of 8-9 to obtain a milky white slurry, which is directly added to the aging tank and kept After the reaction is complete, seal the aging tank, heat it to 130°C, and keep the temperature at (130±5)°C, crystallize for 24 hours, then add the crystallized material to a plate and frame filter press, and wash it with tap water No sulfate radicals are detected in the filtrate, and the pH value of the filtrate is 7. Finally, the washed material is spray-dried, and the inlet and outlet temperatures of the spray-drying tower are kept at 300°C and 120°C respectively to obtain unmodified The magnesium aluminum hydrotalcite of permanent formation; This magnesium aluminum hydrotalcite and binder sodium silicate are added in Mg(Ac) _2In the aqueous solution, make the mass ratio of three kinds of solids be 47.5:2.5:50, the mass ratio of three kinds of solids The ratio of the number of grams of the mixture to the number of milliliters of the liquid volume is 1:10. Use NH ₃ ·H ₂ O to adjust the pH value of the above slurry to 10. After reacting for 1 hour, centrifuge and dry until it can be kneaded into agglomerates. A cylindrical adsorbent with a diameter of 2mm was made by a catalyst molding machine, dried at 110°C, then calcined at 350°C for 3 hours, and cooled to room temperature to obtain a modified magnesium aluminum hydrotalcite, which was stored for later use.

The Mg/Al molar ratio in the above MgSO ₄ and Al ₂ (SO ₄ ) ₃ is 2-3:1; the magnesium salt in the magnesium salt aqueous solution can be MgCl ₂ , Mg(NO ₃ ) ₂ , MgSO ₄ , Mg(Ac) ₂ , MgC ₂ O ₄ , MgCO ₃ , one or more of basic magnesium carbonate; the binder is silica sol and/or sodium silicate; the magnesium aluminum hydrotalcite The mass ratio range of the three solids, binder and magnesium salt is 5-99:0-10:1-95.

Example 2

Removal of PO ₄ ^3- , P ₃ O ₁₀ ^5- , NO ₃ ^- , NO ₂ ^-

The unmodified and modified magnesium-aluminum hydrotalcites prepared in Example 1 were loaded into the adsorption column with diameter-to-height ratio of 1.1:10, respectively, and PO 4 3- , PO ₄ ^3- , P ₃ O ₁₀ ^5- , NO ₃ ^- , NO ₂ ^- , their respective initial concentrations calculated as phosphorus or nitrogen, are all 50mg/L, and the flow rate of the aqueous solution through the adsorption column is controlled to be 5mL/min. According to the first-level standard of national comprehensive sewage discharge standard, the first-level standard of national drinking water source water quality and the groundwater quality standard, the concentration of phosphorus in the aqueous solution after adsorption is 0.5mg/L, the concentration of nitrate nitrogen is 10mg/L, and the concentration of nitrite is 10mg/L. The concentration of nitrogen is 1.0 mg/L as the allowable discharge concentration of phosphorus or nitrogen, that is, the breakthrough point concentration, and the breakthrough adsorption amount is shown in Table 1. Control the flow through the adsorption column to 5mL/min, and use 0.1mol/L NaOH and 3mol/L NaOH to remove PO ₄ ^3- , P ₃ O ₁₀ ^5- and NO ₂ ^- Desorb NaCl mixed solution (desorb with 0.2mol/L NaOH after removing NO ₃ ^- ) until the concentration of phosphorus or nitrogen in the effluent is basically unchanged, and then regenerate with 300mL aqueous solution containing 75g MgCl ₂ , it can be reused and penetrated The adsorption amount is shown in Table 1.

Table 1 The breakthrough adsorption capacity of unmodified and modified magnesium aluminum hydrotalcites on PO ₄ ^3- , P ₃ O ₁₀ ^5- , NO ₃ ^- , NO ₂ ^- in aqueous solution (mg/g)

Taking PO ₄ ^3- as an example, the first breakthrough adsorption capacity of modified magnesium aluminum hydrotalcite to PO ₄ ^3- is 13.49 mg/g, which is 13.49 mg/g for PO ₄ ^3- by unmodified magnesium aluminum hydrotalcite. The breakthrough adsorption capacity is more than 6 times of that of PO 4 3-, and after desorption and regeneration twice, the breakthrough adsorption capacity for PO ₄ ^3- is 17.03 and 13.23 mg/g. It can be seen that the modified magnesium aluminum hydrotalcite can effectively remove PO ₄ ^3- in aqueous solution, and can be reused after desorption and regeneration, and the removal effect is enhanced.

Example 3

The modified magnesium aluminum hydrotalcite simultaneously removes PO ₄ ^3- , ^P ₃ O ₁₀ ^5- , NO ₃ ^- , NO ₂ in the aqueous solution. The modified magnesium aluminum hydrotalcite prepared in Example 1 was The diameter-to-height ratio is 1.1:15 and loaded into the adsorption column to simultaneously remove PO ₄ ^3- , P ₃ O ₁₀ ^5- , NO ₃ ^- , NO ₂ ^- in the aqueous solution, and their respective initial concentrations are calculated by phosphorus or nitrogen. , are both 25mg/L, and the flow rate of the aqueous solution through the adsorption column is controlled to be 5mL/min. The breakthrough concentration of each ion is as described in Example 2. The breakthrough times of PO ₄ ^3- , P ₃ O ₁₀ ^5- , and NO ₂ ^- are 95, 75, and 75 minutes, while NO ₃ ^- has not been detected within 300 minutes. penetrate. It can be seen that the modified magnesium aluminum hydrotalcite can simultaneously remove PO ₄ ^3- , P ₃ O ₁₀ ^5- , NO ₃ ^- , and NO ₂ ^- in aqueous solution. Due to the strong competitive adsorption between various ions, P ₃ O ₁₀ ^5- and NO ₂ ^- first penetrate the adsorption column at 75 minutes, but still have strong adsorption capacity for PO ₄ ^3- and NO ₃ ^- , in order to make full use of the adsorption column, several adsorption columns can be used in series to improve the efficiency of the adsorption column.

Example 4

Simultaneous removal of PO ₄ ^3- , NO ₃ ^-

The modified magnesium-aluminum hydrotalcite prepared in Example 1 is loaded into the adsorption column with a diameter-to-height ratio of 1.1:10, and simultaneously removes PO ₄ ^3- and NO ₃ in the wastewater after the secondary treatment of the sewage treatment plant ^- , their initial concentrations are 4.61 and 2.97mg/L in terms of phosphorus or nitrogen, respectively, and the flow rate of wastewater passing through the adsorption column after secondary treatment in the sewage treatment plant is controlled at 5mL/min. The penetration point concentration of each ion is as described in Example 2, and PO ₄ ^3- and NO ₃ ^- have not penetrated within 540 minutes; the flow through the adsorption column is controlled to 5mL/min, and the modified and shaped Magnesium aluminum hydrotalcite is desorbed with a mixed solution of 0.1mol/L NaOH and 3mol/L NaCl until the concentration of phosphorus or nitrogen in the effluent is basically unchanged, and then regenerated with 300mL aqueous solution containing 75g MgCl ₂ , the reaction to PO ₄ ^3- The breakthrough time was 450 minutes, while NO ₃ ^- did not break through in 540 minutes. It shows that the modified magnesium aluminum hydrotalcite has a strong ability to remove PO ₄ ^3- and NO ₃ ^- in the wastewater after the secondary treatment of the sewage treatment plant, and can be reused after desorption and regeneration.

Example 5

Modified magnesium aluminum hydrotalcite to remove PO ₄ ^3-

The modified magnesium-aluminum hydrotalcite prepared in Example 1 was loaded into an adsorption column with a diameter-to-height ratio of 1.1:10 to remove PO ₄ from the seawater of Wheat Island, Sunny Day and Olympic Sailing Competition coastline respectively. ^3- , the initial concentration in the seawater of the three sections is 1.818, 1.10, and 0.526 μmol/L in terms of phosphorus, and the flow rate of seawater passing through the adsorption column is controlled to be 5mL/min. According to the first-class standard of seawater quality, the concentration of phosphorus after adsorption is 0.48 μmol/L as the breakthrough point concentration of PO ₄ ^3- in seawater, and the breakthrough adsorption amount of PO ₄ ^3- at Wheat Island is 0.29 μg/g, The PO ₄ ^3- in the seawater of the sunny day and the coastline of the Olympic Sailing Competition has not penetrated within 5 hours. It shows that the modified magnesium aluminum hydrotalcite has a strong ability to remove low concentration PO ₄ ^3- in seawater in different parts of Qingdao.

Example 6

Removal of PO ₄ ^3- from aquaculture wastewater by modified magnesium aluminum hydrotalcite

The modified magnesium aluminum hydrotalcite obtained in Example 1 was loaded into an adsorption column with an aspect ratio of 1.1:10 to remove PO ₄ ^3- in the aquaculture wastewater, with an initial concentration of 25 mg/L. The flow rate of the aquaculture wastewater through the adsorption column was controlled to be 5mL/min, and the concentration of phosphorus in the aquaculture wastewater after adsorption was 0.5mg/L as the breakthrough point concentration, and the breakthrough adsorption amount was 17.35mg/g. It shows that the modified magnesium aluminum hydrotalcite has a strong ability to remove PO ₄ ^3- in aquaculture wastewater.

The flow range of the liquid passing through the adsorption column in the above-mentioned Examples 2-6 is 3-7mL/min, and the diameter-to-height ratio is 1.1:5-15. Control the flow rate through the adsorption column to 5mL/min, and desorb the modified magnesium-aluminum hydrotalcite after adsorption with a mixed solution of 0-0.5mol/L NaOH and 0-5mol/L NaCl to the concentration of phosphorus or nitrogen in the effluent. Basically unchanged, and then regenerated with 300mL aqueous solution containing 50-150g MgCl ₂ , it can be used repeatedly, and the effect is strengthened after regeneration.

Claims (5)

1. the preparation method of the magnesium aluminum-hydrotalcite of a modification forming is characterized in that step is as follows: prepare respectively and contain Mg ²⁺, Al ³⁺The mixed-salt aqueous solution and the mixed base aqueous solution, with the two mixing, question response wears out and crystallization after fully, after filtration, washing, drying obtain magnesium aluminum-hydrotalcite; This magnesium aluminum-hydrotalcite and binding agent are joined in the magnesium salt solution, the gram number that makes three kinds of solid quality sums is 1:5～15 with the ratio of the volume milliliter number of liquid, the pH value of regulating the gained soup compound is 9～12, reaction 15～180min, centrifugation, oven dry, extrusion moulding, 100～110 ℃ of oven dry down,, be cooled to room temperature then 350～700 ℃ of following roastings 1～4 hour.

2. the magnesium aluminum-hydrotalcite of the described modification forming of claim 1 application in the phosphorus nitrogen negatively charged ion in removing the aqueous solution, sewage work's water, seawater or breeding wastewater.

3. the preparation method of the magnesium aluminum-hydrotalcite of modification forming as claimed in claim 1 is characterized in that the magnesium salts in the described magnesium salt solution is MgCl ₂, Mg (Ac) ₂, Mg (NO ₃) ₂, MgSO ₄In one or more.

4. the preparation method of the magnesium aluminum-hydrotalcite of modification forming as claimed in claim 1 is characterized in that described binding agent is silicon sol and/or water glass.

5. the preparation method of the magnesium aluminum-hydrotalcite of modification forming as claimed in claim 1 is characterized in that described magnesium aluminum-hydrotalcite, binding agent and three kinds of solid quality of magnesium salts are 5～99:0～10:1～95 than scope.