A method for preparing magnesium aluminum hydrotalcite from sludge

Abstract

The present invention provides a method for preparing magnesium-aluminum hydrotalcite from sludge. The preparation method comprises the following steps: Step 1: drying the sludge, ball-milling it, sieving it, and mixing it with a magnesium salt to form a mixture; pouring the mixture into an acid solution, stirring it, and letting it stand; collecting the supernatant to obtain a metal salt solution; and Step 2: mixing the metal salt solution and a mixed alkaline solution in deionized water, stirring to obtain a complex; transferring the complex to a reactor for crystallization; washing, filtering, separating, and drying to obtain the magnesium-aluminum hydrotalcite. The present invention can effectively utilize the magnesium-aluminum hydrotalcite prepared from the sludge. The product can be used as an adsorbent to treat heavy metal ion wastewater, has strong adsorption properties, and high yield, thereby achieving waste treatment with waste.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste resource utilization, and particularly relates to a method for preparing magnesium-aluminum hydrotalcite from sludge. Background Art

[0002] Domestic sludge is a solid waste formed by sedimentation and concentration in municipal sewage treatment plants. As sewage treatment requirements become increasingly stringent, sludge production is rapidly increasing. Sludge is highly complex, containing toxic and hazardous substances such as heavy metals and pathogenic microorganisms. Improper treatment can pose a range of risks to the environment, flora, and fauna. Therefore, eliminating harmful heavy metal ions from water pollution is essential to improve the ecological environment and human health. Highly selective adsorption materials are crucial for the removal of heavy metal ions from water by adsorption, and functional adsorption materials are a key component of this approach.

[0003] Hydrotalcite, due to its excellent thermal stability, interlamellar anion exchangeability, controllable layer composition, and unique memory effect, can be used as an adsorbent for heavy metal ions, offering broad application prospects in wastewater treatment. Domestic sludge contains large amounts of metal elements such as magnesium, aluminum, and iron, which can be extracted through acid dissolution and co-precipitated to produce hydrotalcite. However, existing techniques for preparing magnesium-aluminum hydrotalcite use pure raw materials, resulting in high costs and low cost-performance.

[0004] Therefore, it is necessary to provide an improved technical solution to the above-mentioned deficiencies in the prior art. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing magnesium-aluminum hydrotalcite from sludge, so as to solve the problems of high cost and low cost performance of the current production of magnesium-aluminum hydrotalcite.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing magnesium-aluminum hydrotalcite from sludge, characterized in that the preparation method comprises the following steps:

[0008] Step 1: After drying the sludge, ball milling and sieving it, mixing it with magnesium salt to form a mixture, pouring the mixture into an acid solution, stirring it, and letting it stand, and taking the supernatant to obtain a metal salt solution;

[0009] Step 2: Mix the metal salt solution and the mixed alkali solution in deionized water and stir to obtain a complex; transfer the complex to a reactor for crystallization; wash, filter, separate, and dry to obtain magnesium aluminum hydrotalcite.

[0010] In the method for preparing magnesium-aluminum hydrotalcite from sludge as described above, preferably, the mixed alkaline solution is a mixture of alkaline solution and carbonate solution;

[0011] The concentrations of the alkali solution and the carbonate solution are both 1-3 mol / L;

[0012] The molar ratio of the base to the carbonate is (1-4):1.

[0013] In the method for preparing magnesium-aluminum hydrotalcite from sludge as described above, preferably, the base in step 1 is NaOH or KOH;

[0014] The carbonate is an alkali metal carbonate or bicarbonate.

[0015] In the method for preparing magnesium-aluminum hydrotalcite from sludge as described above, preferably, the magnesium salt is one of magnesium chloride, magnesium nitrate and magnesium sulfate.

[0016] In the method for preparing magnesium-aluminum hydrotalcite from sludge as described above, preferably, the mass ratio of the magnesium salt to the sludge is magnesium salt:sludge=(1-3):1.

[0017] In the method for preparing magnesium-aluminum hydrotalcite from sludge as described above, preferably, the concentration of the acid solution is 3-6 mol / L.

[0018] In the method for preparing magnesium-aluminum hydrotalcite from sludge as described above, preferably, in step 2, the temperature of the deionized water is 60-80°C.

[0019] In the method for preparing magnesium-aluminum hydrotalcite from sludge as described above, preferably, the temperature of the reactor is 80-150°C.

[0020] In the method for preparing magnesium-aluminum hydrotalcite from sludge as described above, preferably, the crystallization time in the reactor is 12-48 hours.

[0021] The invention discloses magnesium-aluminum hydrotalcite prepared from sludge. The magnesium-aluminum hydrotalcite is prepared by adopting a preparation method of magnesium-aluminum hydrotalcite from sludge.

[0022] Beneficial effects:

[0023] The present invention provides a method for preparing magnesium-aluminum hydrotalcite by using sludge as raw material, which realizes high-quality utilization of sludge and has strong social and economic benefits.

[0024] The magnesium aluminum hydrotalcite in the present invention is prepared by mixing ball-milled sludge and magnesium salt to prepare a metal salt solution, and then reacting the metal salt solution with alkali solution. The preparation process is simple, easy to operate, and suitable for industrial production.

[0025] The magnesium aluminum hydrotalcite prepared by the present invention can be used as an adsorbent to treat heavy metal ion wastewater, has strong adsorption capacity for heavy metal ions in the wastewater, and has a high yield of the prepared product, thereby achieving waste treatment with waste, and is conducive to industrial batch use. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings and the accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. Among them:

[0027] Figure 1 1 is the XRD pattern of magnesium aluminum hydrotalcite prepared in different embodiments of the present invention;

[0028] Figure 2 This is a SEM image of the magnesium-aluminum hydrotalcite prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0030] The present invention will be described in detail below with reference to the embodiments. It should be noted that the embodiments and features of the embodiments of the present invention can be combined with each other without conflict.

[0031] The present invention provides a method for preparing magnesium-aluminum hydrotalcite using sludge as a raw material. The method comprises mixing a magnesium salt with the sludge, then treating the mixture with an acid solution. The resulting metal salt solution, which contains magnesium ions and aluminum ions necessary for synthesizing the magnesium-aluminum hydrotalcite, is then mixed with a mixed alkaline solution containing carbonate ions and subjected to crystallization treatment to obtain the magnesium-aluminum hydrotalcite. The sludge contains a large amount of aluminum ions and a small amount of magnesium ions required for preparing the magnesium-aluminum hydrotalcite. Mixing the magnesium salt with the sludge and then treating the mixture with an acid solution can improve the uniformity of the dissolution of the magnesium and aluminum ions, thereby ensuring a more complete reaction with the mixed alkaline solution.

[0032] The present invention provides a method for preparing hydrotalcite using sludge as raw material, comprising the following steps:

[0033] Step 1: After drying the sludge, ball milling and sieving it, mixing it with magnesium salt to form a mixture, pouring the mixture into an acid solution, stirring it, and letting it stand, and taking the supernatant to obtain a metal salt solution;

[0034] In a specific embodiment of the present invention, the sludge is dried in a constant temperature drying oven at 100-105°C (e.g., 101°C, 102°C, 103°C, 104°C) for 20-24 hours (e.g., 21 hours, 22 hours, 23 hours, 24 hours), and then ground in a planetary ball mill at 200 rpm for 8 hours. The ground sludge is passed through a 0.074 mm sieve. The purpose of ball milling and sieving is to make the sludge particle size finer and more uniform, and the particle size of the prepared magnesium-aluminum hydrotalcite is also more uniform.

[0035] In a specific embodiment of the present invention, the magnesium salt is one of magnesium chloride, magnesium nitrate and magnesium sulfate.

[0036] In a specific embodiment of the present invention, the mass ratio of magnesium salt to sludge is magnesium salt:sludge = (1-3):1 (e.g., 1:1, 1.5:1, 2:1, 2.5:1). The mass ratio of magnesium salt to sludge can be understood as the mass ratio of magnesium salt to treated sludge.

[0037] In a specific embodiment of the present invention, the concentration of the acid solution is 3-6 mol / L (such as 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L).

[0038] The acid solution is a strong acid solution, such as hydrochloric acid solution, sulfuric acid solution or nitric acid solution. The concentration and volume of the acid solution determine the amount of metal ions dissolved in the sludge. When the concentration of the acid solution is 3-6 mol / L, more metal ions in the sludge can be dissolved.

[0039] Step 2: Mix the metal salt solution and the mixed alkali solution in deionized water and stir to obtain a complex; transfer the complex to a reactor for crystallization; wash, filter, separate, and dry to obtain magnesium aluminum hydrotalcite.

[0040] In a specific embodiment of the present invention, the mixed alkaline solution is a mixture of an alkaline solution and a carbonate solution;

[0041] The concentrations of the alkali solution and the carbonate solution are both 1-3 mol / L (e.g., 1.5 mol / L, 2 mol / L, 2.5 mol / L); the molar ratio of the alkali to the carbonate is (1-4):1 (e.g., 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1). The resulting mixed alkali solution not only provides an alkaline environment for preparing the magnesium-aluminum hydrotalcite, but also provides the carbonate ions required for the formation of the magnesium-aluminum hydrotalcite. The higher the concentration of the metal salt solution, the more alkali and carbonate solutions need to be added.

[0042] In a specific embodiment of the present invention, the base is NaOH or KOH.

[0043] In a specific embodiment of the present invention, the carbonate is an alkali metal carbonate or bicarbonate, such as sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate.

[0044] In a specific embodiment of the present invention, after the metal salt solution and the excess mixed alkali solution are mixed, the pH of the mixed solution after the mixed alkali solution and the metal salt solution are dissolved in deionized water is ensured to be between 10 and 12. In this application, the magnesium-aluminum hydrotalcite is prepared using a co-precipitation method, which can be understood as dissolving the magnesium ions and aluminum ions in a metal salt solution, adding the solution to an excess mixed alkali solution, and providing a sufficient amount of hydroxide ions in the mixed alkali solution to carry out a precipitation reaction. Maintaining continuous salt solution precipitation allows for a more complete reaction and a higher yield of the resulting magnesium-aluminum hydrotalcite.

[0045] In a specific embodiment of the present invention, the temperature of the deionized water is 60-80° C. (eg, 65° C., 70° C., 75° C.).

[0046] In a specific embodiment of the present invention, the reactor temperature is 80-150°C (e.g., 90°C, 100°C, 110°C, 120°C, 130°C, or 140°C). Higher crystallization temperatures yield higher and more uniform crystallinity in the resulting octahedral magnesium-aluminum hydrotalcite. However, lower temperatures hinder the crystallization of free magnesium and aluminum ions to form magnesium-aluminum hydrotalcite, reducing yield and the adsorption of heavy metal ions.

[0047] In a specific embodiment of the present invention, the crystallization time is 12-48 hours (e.g., 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours).

[0048] Example 1

[0049] This embodiment provides a method for preparing magnesium-aluminum hydrotalcite from sludge, comprising the following steps:

[0050] 1) The sludge was dried in a constant temperature drying oven at 105°C for 24 hours. The dried sludge was ground in a planetary ball mill at 200 rpm for 8 hours. The ground sludge was passed through a 0.074 mm sieve to obtain the treated sludge for use;

[0051] Magnesium chloride and treated sludge are mixed in a mass ratio of 1:1, and 3 mol / L hydrochloric acid solution is added. After stirring, the mixture is allowed to settle and stand, and the supernatant is taken to obtain a metal salt solution containing magnesium and aluminum;

[0052] 2) preparing 2 mol / L solutions of NaOH and Na2CO3 powder solids, respectively, and mixing them in a molar ratio of 3:1 to obtain a mixed alkali solution. The mixed alkali solution and the metal salt solution were mixed in a mass ratio of 1:1 in deionized water at 60°C and rapidly stirred until the pH of the mixed solution was 11, thereby obtaining a mixture;

[0053] 3) The obtained mixture was transferred to a reactor and crystallized at 80° C. for 24 h, washed, filtered, and separated to obtain a precipitate, which was then dried to obtain magnesium-aluminum hydrotalcite.

[0054] The XRD pattern analysis of the magnesium aluminum hydrotalcite obtained in the above steps is as follows: Figure 1 As shown in the SEM image of magnesium aluminum hydrotalcite Figure 2 As shown. Figure 2 It can be seen from the SEM image that the magnesium-aluminum hydrotalcite synthesized by the method of the present invention has a uniform and regular microscopic morphology in the form of hexagonal flakes.

[0055] The magnesium aluminum hydrotalcite sample prepared in this example was ground into powder, 0.1 g of the powder was weighed and poured into the prepared 200 mg / L lead ion solution, mixed and stirred for 10 h and then allowed to stand. The supernatant was filtered with a 0.45 μm microporous membrane, and the lead ion concentration after adsorption was measured by atomic absorption spectrophotometer. The adsorption of magnesium aluminum hydrotalcite to Pb was calculated. 2+ The adsorption capacity is 106.61 mg / g.

[0056] The yield of magnesium-aluminum hydrotalcite prepared in this example was 25.8%. The yield in this example was calculated as the ratio of the dried mass of the precipitate prepared in step 3) to the raw material in step 1) (the sum of the mass of the dried sludge and magnesium salt). The calculation method used in the following examples and comparative examples is the same.

[0057] The treated sludge in this example is replaced by aluminum salt (aluminum sulfate) of the same mass, and the yield of the prepared magnesium-aluminum hydrotalcite is 63.8%. Due to the large amount of impurities in the sludge, the yield will be reduced.

[0058] Example 2

[0059] This embodiment provides a method for preparing magnesium-aluminum hydrotalcite from sludge, comprising the following steps:

[0060] 1) The sludge was dried in a constant temperature drying oven at 105°C for 24 hours. The dried sludge was ground in a planetary ball mill at 200 rpm for 8 hours. The ground sludge was passed through a 0.074 mm sieve to obtain the treated sludge for use;

[0061] The mass ratio of magnesium oxide to sludge is 3:1. Magnesium oxide is added to the sludge, and a 5 mol / L hydrochloric acid solution is added. After stirring, the precipitate is allowed to stand, and the supernatant is taken to obtain a metal salt solution containing magnesium and aluminum;

[0062] 2) KOH and K2CO3 were separately prepared into 2 mol / L solutions and then mixed in a molar ratio of 1:1 to obtain a mixed alkaline solution. The mixed alkaline solution and the metal salt solution were mixed in a mass ratio of 1:1 in deionized water at 80° C. and rapidly stirred. The pH of the mixed solution was controlled to 10 to obtain a mixture;

[0063] 3) The obtained mixture was transferred to a reactor and crystallized at 100° C. for 48 hours, washed, filtered, and separated to obtain a precipitate, which was then dried to obtain magnesium-aluminum hydrotalcite.

[0064] The XRD pattern analysis of the magnesium aluminum hydrotalcite obtained in the above steps is as follows: Figure 1 As shown in the figure, the prepared magnesium aluminum hydrotalcite sample was ground into powder, 0.1g of the powder was weighed and poured into the prepared 200mg / L lead ion solution, mixed and stirred for 10h and then allowed to stand. The supernatant was filtered with a 0.45um microporous filter membrane, and the lead ion concentration after adsorption was measured by atomic absorption spectrophotometer. The adsorption of magnesium aluminum hydrotalcite to Pb was calculated. 2+ The adsorption capacity is 96.32 mg / g.

[0065] The yield of the magnesium-aluminum hydrotalcite prepared in this example is 24.6%.

[0066] Example 3

[0067] This embodiment provides a method for preparing magnesium-aluminum hydrotalcite from sludge, comprising the following steps:

[0068] 1) The sludge was dried in a constant temperature drying oven at 105°C for 24 hours. The dried sludge was ground in a planetary ball mill at 200 rpm for 8 hours. The ground sludge was passed through a 0.074 mm sieve to obtain the treated sludge for use;

[0069] Magnesium nitrate and sludge are added to the sludge at a mass ratio of 2:1, and 4 mol / L hydrochloric acid solution is added to obtain a metal salt solution containing magnesium and aluminum;

[0070] 2) preparing 2 mol / L solutions of NaOH and K2CO3, respectively, and mixing them in a molar ratio of 1:1 to obtain an alkaline solution. The alkaline solution and the metal salt solution were mixed in a mass ratio of 1:1 in deionized water at 70°C and rapidly stirred. The pH of the mixed solution was controlled to 10 to obtain a mixture.

[0071] 3) The obtained mixture was transferred to a reactor and crystallized at 150° C. for 12 h, washed, filtered, and separated to obtain a precipitate, which was then dried to obtain magnesium-aluminum hydrotalcite.

[0072] The XRD pattern analysis of the magnesium aluminum hydrotalcite obtained in the above steps is as follows: Figure 1 As shown in the figure, the prepared magnesium aluminum hydrotalcite sample was ground into powder, 0.1g of the powder was weighed and poured into the prepared 200mg / L lead ion solution, mixed and stirred for 10h and then allowed to stand. The supernatant was filtered with a 0.45um microporous filter membrane, and the lead ion concentration after adsorption was measured by atomic absorption spectrophotometer. The adsorption of magnesium aluminum hydrotalcite to Pb was calculated. 2+ The adsorption capacity is 101.2 mg / g.

[0073] The yield of the magnesium-aluminum hydrotalcite prepared in this example is 23.9%.

[0074] Example 4

[0075] This embodiment provides a method for preparing magnesium-aluminum hydrotalcite from sludge, comprising the following steps:

[0076] 1) The sludge was dried in a constant temperature drying oven at 100°C for 24 hours. The dried sludge was ground in a planetary ball mill at 200 rpm for 8 hours. The ground sludge was passed through a 0.074 mm sieve to obtain the treated sludge for later use.

[0077] Magnesium sulfate and sludge are added to the sludge at a mass ratio of 2:1, and 3 mol / L sulfuric acid solution is added. After stirring, the precipitate is allowed to stand, and the supernatant is taken to obtain a metal salt solution containing magnesium and aluminum;

[0078] 2) KOH and Na2CO3 were separately prepared into 3 mol / L solutions and then mixed in a molar ratio of 2:1 to obtain a mixed alkaline solution. The mixed alkaline solution and the metal salt solution were mixed in a mass ratio of 1:1 in deionized water at 60°C and rapidly stirred. The pH of the mixed solution was controlled to 10 to obtain a mixture;

[0079] 3) The obtained mixture was transferred to a reactor and crystallized at 120° C. for 24 h, washed, filtered, and separated to obtain a precipitate, which was then dried to obtain magnesium-aluminum hydrotalcite.

[0080] The XRD pattern analysis of the magnesium aluminum hydrotalcite obtained in the above steps is as follows: Figure 1 As shown in the figure, the prepared magnesium aluminum hydrotalcite sample was ground into powder, 0.1g of the powder was weighed and poured into the prepared 200mg / L lead ion solution, mixed and stirred for 10h and then allowed to stand. The supernatant was filtered with a 0.45um microporous filter membrane, and the lead ion concentration after adsorption was measured by atomic absorption spectrophotometer. The adsorption of magnesium aluminum hydrotalcite to Pb was calculated. 2+ The adsorption capacity is 86.5 mg / g.

[0081] The yield of the magnesium-aluminum hydrotalcite prepared in this example is 25.6%.

[0082] Example 5

[0083] This embodiment provides a method for preparing magnesium-aluminum hydrotalcite from sludge, comprising the following steps:

[0084] 1) The sludge was dried in a constant temperature drying oven at 105°C for 24 hours. The dried sludge was ground in a planetary ball mill at 200 rpm for 8 hours. The ground sludge was passed through a 0.074 mm sieve to obtain the treated sludge for use;

[0085] Magnesium chloride is added to the sludge at a mass ratio of 2:1, and a 6 mol / L nitric acid solution is added. After stirring, the precipitate is allowed to stand, and the supernatant is taken to obtain a metal salt solution containing magnesium and aluminum;

[0086] 2) NaOH and KHCO3 were separately prepared into 2 mol / L solutions and then mixed in a molar ratio of 4:1 to obtain a mixed alkaline solution. The mixed alkaline solution and the metal salt solution were mixed in a mass ratio of 1:1 in deionized water at 60° C. and rapidly stirred. The pH of the mixed solution was controlled to 12 to obtain a mixture;

[0087] 3) The obtained mixture was transferred to a reactor and crystallized at 150° C. for 24 hours, washed, filtered, and separated to obtain a precipitate, which was then dried to obtain magnesium-aluminum hydrotalcite.

[0088] The XRD pattern analysis of the magnesium aluminum hydrotalcite obtained in the above steps is as follows: Figure 1 As shown in the figure, the prepared magnesium aluminum hydrotalcite sample was ground into powder, 0.1g of the powder was weighed and poured into the prepared 200mg / L lead ion solution, mixed and stirred for 10h and then allowed to stand. The supernatant was filtered with a 0.45um microporous filter membrane, and the lead ion concentration after adsorption was measured by atomic absorption spectrophotometer. The adsorption of magnesium aluminum hydrotalcite to Pb was calculated. 2+ The adsorption capacity is 92.35 mg / g.

[0089] The yield of the magnesium-aluminum hydrotalcite prepared in this example is 24.7%.

[0090] The products in the above examples 1-5 were subjected to XRD tests respectively. Figure 1 It can be seen that the XRD diffraction peaks of the obtained product are consistent with the No. 54-1030 magnesium aluminum hydrotalcite standard spectrum Mg6Al2(OH)16CO3.4H2O published by the International Diffraction Data Center, and correspond to the (003), (006), and (012) crystal planes at 11°, 23°, and 35°, respectively. The baseline is stable, the characteristic peaks are sharp and symmetrically distributed, indicating that the synthetic crystal plane has good purity, and there are no obvious impurity peaks, indicating that the synthesized hydrotalcite is of high purity.

[0091] Comparative Example 1

[0092] This reference example provides a method for preparing magnesium-aluminum hydrotalcite from sludge. The difference between this reference example and Example 1 is that the ratio of magnesium chloride to treated sludge in step 1) is different, and the concentration of the acid solution is different. The rest is the same as Example 1 and will not be repeated here.

[0093] In this comparative example, magnesium chloride and treated sludge were mixed in a mass ratio of 1:5, and 1 mol / L hydrochloric acid solution was added. After stirring, the mixture was allowed to settle and the supernatant was taken to obtain a metal salt solution containing magnesium and aluminum.

[0094] The magnesium aluminum hydrotalcite sample prepared in this comparative example was ground into powder, 0.1 g of the powder was weighed and poured into the prepared 200 mg / L lead ion solution, mixed and stirred for 10 h and then allowed to stand. The supernatant was filtered with a 0.45 μm microporous membrane, and the lead ion concentration after adsorption was measured by atomic absorption spectrophotometer. The adsorption of magnesium aluminum hydrotalcite to Pb was calculated. 2+ The adsorption capacity is 95.8 mg / g.

[0095] The yield of the magnesium aluminum hydrotalcite prepared in this comparative example was 15.3%.

[0096] The adsorption capacity of the magnesium-aluminum hydrotalcite prepared in this comparative example for heavy metal lead ions is greatly reduced because: the structural formula of magnesium-aluminum hydrotalcite is Mg6Al2(OH) 16 CO₃·4H₂O. In this control example, the sludge contained a high concentration of sludge, low magnesium chloride, and low acid content. Because the sludge itself contained very low magnesium ions, magnesium chloride was added. However, the amount of added magnesium chloride in this control example was relatively low, resulting in a low magnesium ion content. This means that most impurity ions would occupy the positions of magnesium ions, significantly reducing the yield of magnesium-aluminum hydrotalcite.

[0097] Comparative Example 2

[0098] This example provides a method for preparing magnesium-aluminum hydrotalcite from sludge. The difference between this comparative example and Example 1 is that the molar ratio of NaOH and Na2CO3 in step 2) is different. The rest is the same as Example 1 and will not be repeated here.

[0099] Specifically:

[0100] 2) NaOH and Na2CO3 were separately prepared into 2 mol / L solutions and then mixed in a molar ratio of 1:2 to obtain an alkaline solution. The alkaline solution and the metal salt solution were mixed in a mass ratio of 1:1 in deionized water at 60°C and rapidly stirred. The pH of the mixed solution was controlled to 8 to obtain a mixture.

[0101] The magnesium aluminum hydrotalcite sample prepared in this comparative example was ground into powder, 0.1 g of the powder was weighed and poured into the prepared 200 mg / L lead ion solution, mixed and stirred for 10 h and then allowed to stand. The supernatant was filtered with a 0.45 μm microporous membrane, and the lead ion concentration after adsorption was measured by atomic absorption spectrophotometer. The adsorption of magnesium aluminum hydrotalcite to Pb was calculated. 2+ The adsorption capacity is 91.4 mg / g. The yield of the magnesium aluminum hydrotalcite prepared in this comparative example is 12.9%.

[0102] The adsorption capacity of heavy metal lead ions by the magnesium-aluminum hydrotalcite prepared in this control example is greatly reduced. The reason is that: in this control example, the ratio of NaOH and Na2CO3 is 1:2, the mixed alkaline solution provides fewer hydroxide ions and more carbonate ions, and the pH of the mixed solution after mixing with deionized water is 8, which is weakly alkaline, so that the yield of the prepared product is greatly reduced, and the output of magnesium-aluminum hydrotalcite is reduced.

[0103] Comparative Example 3

[0104] The difference between this comparative example and Example 1 is that in step 3), the mixture is crystallized in a reactor at 60° C. for 24 h. The rest is the same as in Example 1 and will not be described again.

[0105] The same test method as in the example was used to test the effect of magnesium-aluminum hydrotalcite on Pb 2+ The adsorption capacity is 83.5 mg / g. The yield of the magnesium aluminum hydrotalcite prepared in this comparative example is 11.3%.

[0106] The crystallization temperature in the reactor in this comparative example is low, and the crystallization temperature of the magnesium-aluminum hydrotalcite is not suitable. Therefore, the prepared magnesium-aluminum hydrotalcite not only has a low yield, but also has a reduced adsorption capacity for lead ions in wastewater. It is speculated that this may be because the crystal structure of the magnesium-aluminum hydrotalcite has changed, which is not conducive to the adsorption of lead ions.

[0107] In summary, the present invention provides a method for preparing magnesium-aluminum hydrotalcite using sludge as raw material, which achieves high-quality utilization of sludge and has strong social and economic benefits.

[0108] The magnesium aluminum hydrotalcite in the present invention is prepared by mixing ball-milled sludge and magnesium salt to prepare a metal salt solution, and then reacting the metal salt solution with alkali solution. The preparation process is simple, easy to operate, and suitable for industrial production.

[0109] The magnesium aluminum hydrotalcite prepared by the present invention can be used as an adsorbent to treat heavy metal ion wastewater, has strong adsorption capacity for heavy metal ions in the wastewater, and has a high yield of the prepared product, thereby achieving waste treatment with waste, and is conducive to industrial batch use.

[0110] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing magnesium aluminum hydrotalcite from sludge, characterized in that: The method comprises the following steps: Step 1: After drying the sludge, ball milling and sieving it, mixing it with magnesium salt to form a mixture, pouring the mixture into a 3-6 mol / L acid solution, stirring it and letting it stand, and collecting the supernatant to obtain a metal salt solution; the mass ratio of the magnesium salt to the sludge is (1-3):1; Step 2: mixing the metal salt solution and the mixed alkali solution in deionized water, ensuring that the pH value of the mixed solution after the mixed alkali solution and the metal salt solution are dissolved in deionized water is 10-12, stirring to obtain a complex, transferring the complex to a reactor for crystallization, washing, filtering, separating, and drying to obtain magnesium aluminum hydrotalcite; In step 2, the mixed alkaline solution is a mixture of an alkaline solution and a carbonate solution; the concentrations of the alkaline solution and the carbonate solution are both 1-3 mol / L; the molar ratio of the alkali to the carbonate is (1-4):1; The temperature of the deionized water is 60-80° C.; the temperature of the reactor is 80-150° C.; and the crystallization time in the reactor is 12-48 h.

2. The method for preparing magnesium-aluminum hydrotalcite from sludge according to claim 1, characterized in that: The base in step 2 is NaOH or KOH; The carbonate is an alkali metal carbonate or bicarbonate.

3. The method for preparing magnesium-aluminum hydrotalcite from sludge according to claim 1, characterized in that: The magnesium salt is one of magnesium chloride, magnesium nitrate and magnesium sulfate.

4. A magnesium aluminum hydrotalcite prepared from sludge, characterized in that: The magnesium-aluminum hydrotalcite is prepared by the method for preparing magnesium-aluminum hydrotalcite from sludge as claimed in any one of claims 1 to 3.

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