A method for preparing a composite flocculant using aluminum ash slag

Abstract

The present invention discloses a method for preparing a composite flocculant using aluminum ash residue. The method includes four steps: treatment of fly ash, treatment of aluminum ash residue, preparation of a polymeric flocculant, and preparation of a composite flocculant. Based on the idea of making full use of by-products, the present invention selects fly ash and aluminum ash residue as the main raw materials to prepare a polyaluminum silicate chloride flocculant, avoiding potential equipment corrosion caused by the use of iron-based flocculants. To further enhance the flocculation effect of the flocculant, modified chitosan is also used for further compounding. The obtained composite flocculant has good flocculation effect, can simultaneously flocculate and remove high-concentration and low-concentration heavy metal ions, and complete flocculation within several minutes, with high treatment efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of flocculant preparation, and particularly relates to a method for preparing a composite flocculant by using aluminum ash slag. Background Art

[0002] With the continuous research on flocculants, the types of flocculants are becoming more and more abundant, and they can be mainly divided into organic flocculants, inorganic flocculants, microbial flocculants and composite flocculants. Organic flocculants can be divided into anionic type, cationic type and amphoteric type. They have the advantages of less dosage, fast flocculation sedimentation speed and the flocculation effect not being affected by the quality of wastewater. However, their production cost is relatively high, and hydrolysis will bring out toxic charged groups; Inorganic flocculants can be divided into two categories: aluminum ion series, iron ion series, hydrochloric acid root series or sulfuric acid root series. They are widely used flocculants, accounting for about 80% of the water treatment flocculants in China. They have the advantages of wide sources and low prices, but there are also deficiencies such as large dosage, large amount of sludge generated and high water content; Biological flocculants have good flocculation effect, no secondary pollution and are easily degraded, but the low yield and high investment greatly limit their application; Composite flocculants are formed by chemically reacting two or more single-component flocculants to form a copolymer complex with a large molecular weight, which overcomes the deficiencies of single flocculants, and the flocculants synergize with each other to achieve the best flocculation effect; The research and use of composite flocculants are increasing, such as polyaluminum ferrophosphate, calcium silicate composite polyferric chloride, polyaluminum ferric silicate, etc.

[0003] In the preparation process of flocculants, the sources of elements such as aluminum and iron show a diversified trend. For example, in the prior art, the patent document CN104310547A provides a method for preparing a flocculant by using aluminum smelting ash slag, but the prepared flocculant is single and the flocculation effect is insufficient; The patent document CN110950412B provides a method for preparing a flocculant by using aluminum ash and tuff; The patent document CN110028092B provides a method for preparing calcium aluminate by using carbide slag and aluminum ash. In fact, in the process of aluminum production and processing, aluminum slag, aluminum ash, etc. will be generated; Relevant research shows that 30 - 40 kg of aluminum ash or aluminum slag will be generated for each ton of aluminum processed and applied; And in the process of recycling waste aluminum, the generation amount of aluminum ash or aluminum slag is even larger, reaching 150 - 250 kg per ton of waste aluminum. If a large amount of aluminum ash or aluminum slag cannot be fully utilized, it will cause problems such as occupying land and polluting the environment; While its reasonable utilization can not only generate economic benefits, but also produce environmental protection benefits, which can be described as killing two birds with one stone. Fly ash is a waste of pulverized coal combustion, with a large production volume. If not reasonably utilized, it will also occupy land and cause serious environmental pollution. Around the preparation of flocculants, how to effectively utilize fly ash and aluminum ash slag is a topic worthy of continuous development and research, and has important economic and environmental protection values. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for preparing a composite flocculant using aluminum ash slag. The raw materials are common, and the prepared composite flocculant has good flocculation effect, and has both economic and environmental protection values.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A method for preparing a composite flocculant using aluminum ash slag, comprising the following steps:

[0007] (1) Treatment of fly ash: The fly ash raw material is air-dried and sieved through 50-150 meshes, and then added to a sodium hydroxide solution with a concentration of 3.5-4.5 mol / L, and stirred and reacted at 135-145 °C for 0.5-5 h; after the reaction, the leaching solution is obtained; after vacuum filtration of the leaching solution, an alkali leaching solution and alkali leaching residue are obtained;

[0008] (2) Treatment of aluminum ash slag: The aluminum ash slag raw material is air-dried and sieved through 50-150 meshes, and the sieved aluminum ash slag and all the alkali leaching residues obtained in step (1) are respectively added to a hydrochloric acid solution with a concentration of 3.8-5 mol / L, and stirred and reacted at 85-95 °C for 1-5 h; after the reaction, rapid filtration is carried out to obtain an acid leaching solution;

[0009] (3) Preparation of polymeric flocculant: Heat all the acid leaching solutions obtained in step (2) to 50-65 °C, and then slowly add aluminum hydroxide sol, and stir and react for 0.5-2 h; after the reaction, add a mixed solution of yttrium nitrate and lanthanum nitrate, and stir and react again for 0.5-2 h; after the reaction, a mixture 1 is obtained; then, under stirring conditions, slowly drop all the alkali leaching solutions obtained in step (1) into the mixture 1; after the addition of the alkali leaching solution is completed, continue to stir for 5-30 min, adjust the pH value to 3-4, and stand and ripen at room temperature for 0.5-5 h to obtain a mixture 2;

[0010] (4) Preparation of composite flocculant: Mix the mixture 2 obtained in step (3) with modified chitosan, add sodium acetate, and after ripening treatment, the composite flocculant is obtained.

[0011] Preferably, in the aluminum ash slag raw material, calculated on the basis of 100% by mass fraction, the content of aluminum oxide is 68.37%, and the content of silicon dioxide is 12.66%; in the fly ash raw material, calculated on the basis of 100% by mass fraction, the content of aluminum oxide is 25.05%, and the content of silicon dioxide is 60.84%.

[0012] Preferably, in step (1), the mass ratio of the sodium hydroxide solution to the fly ash raw material is 6-15 mL: 1 g.

[0013] Preferably, the mass ratio of the fly ash raw material in step (1) to the aluminum ash slag raw material in step (2) is 100:30 - 80, and the mass ratio of the aluminum ash slag raw material to the hydrochloric acid solution is 1:6 - 15.

[0014] Preferably, in step (3), the molar ratio of yttrium nitrate to lanthanum nitrate is 1:1, and the total concentration of the mixed solution of yttrium nitrate and lanthanum nitrate is 0.5 - 1.5 mol / L, the concentration of aluminum hydroxide colloid is 1.5 - 2.5 mol / L, and the pH value is 6.2 - 6.8;

[0015] The mass dosage ratio of the yttrium nitrate solution, aluminum hydroxide sol to the acid leaching solution is 0.5:4 - 10:5 - 12.

[0016] Preferably, in step (4), the aging time is 8 - 36 h, and the aging temperature is 25 - 50 °C.

[0017] Preferably, in step (4), the mass ratio of mixture 2, modified chitosan, and sodium acetate is 100:1 - 2:2 - 5.

[0018] Preferably, in step (4), the preparation of the modified chitosan includes the following steps:

[0019] S1. Add chitosan and citric acid to ethanol respectively, and then carry out a stirring reaction; after the reaction is completed, centrifuge the obtained reaction product first, and then carry out washing and drying treatments to obtain pre-modified chitosan;

[0020] S2. Carry out low-temperature plasma treatment on the pre-modified chitosan obtained in step S1, and after the treatment is completed, obtain modified chitosan.

[0021] Preferably, in step S1, the dosage ratio of chitosan, citric acid, and ethanol is 1 mol:1 - 1.5 mol:10 - 25 mL; the stirring reaction temperature is room temperature, and the stirring reaction time is 0.5 - 2 h.

[0022] Preferably, in step S2, the discharge power is 45 - 60 W, and the discharge time is 0.5 - 8 min.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] Centering on the idea of making full use of by-products, the present invention selects fly ash and aluminum ash slag as the main raw materials to prepare a polyaluminum silicate chloride flocculant, avoiding potential equipment corrosion caused by the use of iron flocculants; in order to further enhance the flocculation effect of the flocculant, modified chitosan is also used for further compounding. The obtained composite flocculant has a good flocculation effect, can simultaneously flocculate and remove high-concentration and low-concentration heavy metal ions, and completes flocculation within a few minutes, with high treatment efficiency.

[0025] Specifically: In the present invention, fly ash is first subjected to alkali leaching treatment to obtain alkali leached residue and a silicon-containing alkali leached solution; subsequently, the aluminum ash residue and the alkali leached residue are mixed and then subjected to acid leaching treatment to obtain an acid leached solution containing aluminum ions; during the treatment of the acid leached solution, rare earth ions yttrium and lanthanum are first used for treatment. By doing so, yttrium and lanthanum ion complexes and various hydroxy complexes such as aluminum and / or silicon are generated, making the prepared polymer have better positive charge property and specific surface area, and strengthening the flocculation effect; it should be particularly noted that compared with using a single lanthanum substance for modification, the combined modification of lanthanum nitrate and yttrium nitrate and the use in combination with modified chitosan have better effects; and during the preparation of the polymeric flocculant, through exploration, it is found that the flocculation effect of the composite flocculant obtained by adding a mixed solution of yttrium nitrate and lanthanum nitrate after treatment with aluminum hydroxide sol is better; in addition, modified chitosan is added to the polyaluminum silicate chloride flocculant, which can further improve the positive charge property of the flocculant system and further strengthen the flocculation ability; however, chitosan itself has the deficiencies of poor water solubility and poor processability. In the present invention, chitosan is first modified with citric acid to preliminarily improve the water solubility of chitosan; subsequently, chitosan is subjected to low-temperature plasma treatment, aiming to further improve the water solubility and reactivity of chitosan. The inherent amino, hydroxyl and other active groups in chitosan can complex with aluminum ions in polyaluminum silicate chloride to form a large bridging structure. The overall formed composite flocculant has better electrostatic and physical adsorption effects, achieving a better flocculation effect; the modification of chitosan and the optimization of the overall process can make the prepared composite flocculant have a good flocculation effect and a shorter flocculation time.

[0026] In summary, in the present invention, common fly ash and aluminum ash residue are used as synthetic raw materials, improving the resource utilization efficiency; at the same time, by optimizing the acid leaching and alkali leaching process conditions and the two-step modification method of chitosan, the prepared composite flocculant has a good flocculation effect, a relatively simple process flow, controllable cost, and has good application prospects. Specific Embodiments

[0027] The embodiments of the present invention are described in detail below. All the embodiments are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0028] In each embodiment of the present invention, the aluminum ash residue is sourced from an aluminum products factory, and the main components are as follows:

[0029] Table 1 Composition of Aluminum Ash Residue

[0030] Composition <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> MgO CaO <![CDATA[SiO2]]> Loss on Ignition Others Content / % 68.37 2.08 4.53 1.98 12.66 3.05 Balance

[0031] In each embodiment of the present invention, the fly ash is sourced from a power plant, and the main components are as follows:

[0032] Table 2 Composition of Fly Ash

[0033] Composition <![CDATA[Al2O3]]> <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> MgO CaO <![CDATA[K2O]]> <![CDATA[Na2O]]> Others Content / % 25.05 60.84 3.18 0.87 0.66 2.38 0.35 Balance

[0034] In each embodiment of the present invention, chitosan is purchased from Jinan Haidebei Marine Bioengineering Co., Ltd., with a deacetylation degree of about 86% and a viscosity of about 800 mPa·s at 20°C.

[0035] In the present invention, the other unstated parts are all conventional means mastered by those skilled in the art; the materials without specified sources are all commercially available.

[0036] Example 1

[0037] A method for preparing a composite flocculant using aluminum ash slag includes the following steps:

[0038] (1) Treatment of fly ash: The fly ash raw material is air-dried and sieved through 80 meshes; subsequently, according to the dosage of the mass ratio of sodium hydroxide to fly ash raw material of 10 mL:1 g, the sieved fly ash is added to a 4 mol / L sodium hydroxide solution, and stirred and reacted at 140°C for 1 h; after the reaction ends, a leaching solution is obtained; after vacuum filtration of the leaching solution, an alkali leaching solution and alkali leaching residue are obtained;

[0039] (2) Treatment of aluminum ash slag: According to the dosage of the mass ratio of fly ash raw material to aluminum ash slag raw material of 100:60, the aluminum ash slag raw material is air-dried and sieved through 80 meshes, and the sieved aluminum ash slag and all the alkali leaching residues obtained in step (1) are respectively added to a 4.2 mol / L hydrochloric acid solution, and stirred and reacted at 90°C for 1.5 h; after the reaction ends, rapid filtration is carried out to obtain an acid leaching solution;

[0040] (3) Preparation of polymeric flocculant: Heat all the acid leaching solutions obtained in step (2) to 60°C, and then slowly add a 2.2 mol / L aluminum hydroxide sol (pH value is 6.5), and stir and react for 0.5 h; after the reaction ends, add a mixed solution of yttrium nitrate and lanthanum nitrate with a total concentration of 1.2 mol / L (the molar ratio of yttrium nitrate to lanthanum nitrate is 1:1), and stir and react again for 0.5 h; after the reaction ends, a mixture 1 is obtained; then, under stirring conditions, slowly drop all the alkali leaching solutions obtained in step (1) into the mixture 1; after the addition of the alkali leaching solution is completed, continue to stir for 10 min, adjust the pH value to 3.5, and stand and cure at room temperature for 2 h to obtain a mixture 2;

[0041] (4) Preparation of composite flocculant: Mix the mixture 2 obtained in step (3) with modified chitosan, add sodium acetate, and cure at 35°C for 16 h to obtain the composite flocculant.

[0042] Among them, in step (2), the mass ratio of the aluminum ash slag raw material to the hydrochloric acid solution is 1:12.

[0043] Among them, in step (3), the mass ratio of the yttrium nitrate solution, the aluminum hydroxide sol, and the acid leaching solution is 0.5:5:7.

[0044] Among them, in step (4), the mass ratio of mixture 2, modified chitosan, and sodium acetate is 100:1.5:2.5.

[0045] Among them, in step (4), the preparation of the modified chitosan includes the following steps:

[0046] S1. Add chitosan and citric acid to ethanol respectively, and then stir and react at room temperature for 1.5 h; after the reaction is completed, centrifuge the obtained reaction product first, and then perform washing and drying treatments to obtain pre-modified chitosan; among them, the dosage ratio of chitosan, citric acid, and ethanol is 1 mol:1.2 mol:15 mL;

[0047] S2. Perform low-temperature plasma treatment on the pre-modified chitosan obtained in step S1 (the discharge power is 50 W and the discharge time is 4 min), and after the treatment is completed, obtain the modified chitosan.

[0048] Example 2

[0049] A method for preparing a composite flocculant using aluminum ash slag, including the following steps:

[0050] (1) Treatment of fly ash: Air-dry the fly ash raw material and then sieve it through 80 mesh; then, according to the mass ratio of sodium hydroxide to the fly ash raw material of 10 mL:1.1 g, add the sieved fly ash to a 4 mol / L sodium hydroxide solution, and stir and react at 140 °C for 1 h; after the reaction is completed, obtain a leaching solution; after vacuum filtration of the leaching solution, obtain an alkali leaching solution and an alkali leaching residue;

[0051] (2) Treatment of aluminum ash slag: According to the mass ratio of the fly ash raw material and the aluminum ash slag raw material of 100:58, air-dry the aluminum ash slag raw material and then sieve it through 80 mesh, and add the sieved aluminum ash slag and all the alkali leaching residues obtained in step (1) to a 4.2 mol / L hydrochloric acid solution respectively, and stir and react at 95 °C for 1 h; after the reaction is completed, quickly filter to obtain an acid leaching solution;

[0052] (3) Preparation of the polymeric flocculant: Heat all the acid leaching solution obtained in step (2) to 60 °C, and then slowly add 2.2 mol / L aluminum hydroxide sol (pH value is 6.5), and stir and react for 0.5 h; after the reaction ends, add a mixed solution of yttrium nitrate and lanthanum nitrate with a total concentration of 1.1 mol / L (the molar ratio of yttrium nitrate to lanthanum nitrate is 1:1), and stir and react again for 1 h; after the reaction ends, obtain mixture 1; then, under stirring conditions, slowly drop all the alkali leaching solution obtained in step (1) into the mixture 1; after the dropping of the alkali leaching solution is completed, continue to stir for 10 min, adjust the pH value to 3.6, and stand and age at room temperature for 3 h to obtain mixture 2;

[0053] (4) Preparation of the composite flocculant: Mix the mixture 2 obtained in step (3) with modified chitosan, add sodium acetate, and carry out aging treatment at 35 °C for 24 h to obtain the composite flocculant.

[0054] Among them, in step (2), the mass ratio of the aluminum ash slag raw material to the hydrochloric acid solution is 1:13.

[0055] Among them, in step (3), the mass dosage ratio of the yttrium nitrate solution, aluminum hydroxide sol and acid leaching solution is 0.5:4.8:6.5.

[0056] Among them, in step (4), the mass ratio of mixture 2, modified chitosan and sodium acetate is 100:1.3:2.2.

[0057] Among them, in step (4), the preparation of the modified chitosan includes the following steps:

[0058] S1. Add chitosan and citric acid into ethanol respectively, and then stir and react at room temperature for 2 h; after the reaction ends, first centrifuge the obtained reaction product, and then carry out washing and drying treatments to obtain pre-modified chitosan; among them, the dosage ratio of chitosan, citric acid and ethanol is 1 mol:1.3 mol:20 mL;

[0059] S2. Carry out low-temperature plasma treatment on the pre-modified chitosan obtained in step S1 (discharge power is 50 W, discharge time is 4 min), and after the treatment is completed, obtain the modified chitosan.

[0060] Example 3

[0061] A method for preparing a composite flocculant using aluminum ash slag, including the following steps:

[0062] (1) Treatment of fly ash: Air-dry the fly ash raw material and sieve it through a 80-mesh sieve; subsequently, add the sieved fly ash into a 4 mol / L sodium hydroxide solution according to the dosage of the mass ratio of sodium hydroxide to fly ash raw material of 10 mL: 0.9 g, and stir and react at 140 °C for 1.5 h; after the reaction ends, obtain a leaching solution; after vacuum filtration of the leaching solution, obtain an alkali leaching solution and alkali leaching residue;

[0063] (2) Treatment of aluminum ash residue: According to the dosage of the mass ratio of fly ash raw material to aluminum ash residue raw material of 100:62, air-dry the aluminum ash residue raw material and sieve it through a 80-mesh sieve, and add the sieved aluminum ash residue and all the alkali leaching residues obtained in step (1) into a 4.2 mol / L hydrochloric acid solution respectively, and stir and react at 90 °C for 2 h; after the reaction ends, quickly filter to obtain an acid leaching solution;

[0064] (3) Preparation of polymeric flocculant: Heat all the acid leaching solutions obtained in step (2) to 60 °C, and then slowly add a 2.2 mol / L aluminum hydroxide sol (pH value is 6.5), and stir and react for 0.5 h; after the reaction ends, add a mixed solution of yttrium nitrate and lanthanum nitrate with a total concentration of 1.15 mol / L (the molar ratio of yttrium nitrate to lanthanum nitrate is 1:1), and stir and react again for 1 h; after the reaction ends, obtain mixture 1; then, under stirring conditions, slowly dropwise add all the alkali leaching solutions obtained in step (1) into the mixture 1; after the dropping of the alkali leaching solution is completed, continue to stir for 10 min, adjust the pH value to 3.5, and stand and ripen at room temperature for 2.5 h to obtain mixture 2;

[0065] (4) Preparation of composite flocculant: Mix the mixture 2 obtained in step (3) with modified chitosan and add sodium acetate, and carry out ripening treatment at 35 °C for 12 h to obtain the composite flocculant.

[0066] Among them, in step (2), the mass ratio of the aluminum ash residue raw material to the hydrochloric acid solution is 1:11.

[0067] Among them, in step (3), the mass dosage ratio of the yttrium nitrate solution, aluminum hydroxide sol and acid leaching solution is 0.5:5.2:7.5.

[0068] Among them, in step (4), the mass ratio of mixture 2, modified chitosan and sodium acetate is 100:1.7:2.7.

[0069] Among them, in step (4), the preparation of the modified chitosan includes the following steps:

[0070] S1. Add chitosan and citric acid into ethanol respectively, and then stir and react at room temperature for 2 h. After the reaction, centrifuge the obtained reaction product first, and then wash and dry it to obtain pre-modified chitosan. Among them, the dosage ratio of chitosan, citric acid and ethanol is 1 mol: 1.1 mol: 18 mL.

[0071] S2. Perform low-temperature plasma treatment on the pre-modified chitosan obtained in step S1 (discharge power is 50 W, discharge time is 4 min). After the treatment is completed, modified chitosan is obtained.

[0072] Comparative Example 1

[0073] A method for preparing a composite flocculant using aluminum ash slag includes the following steps:

[0074] (1) Treatment of fly ash: Air-dry the fly ash raw material and then sieve it through 80 meshes. Subsequently, add the sieved fly ash into a 4 mol / L sodium hydroxide solution according to the mass ratio of sodium hydroxide to fly ash raw material of 10 mL: 1 g, and stir and react at 140 °C for 1 h. After the reaction, obtain a leaching solution. After vacuum filtration of the leaching solution, obtain an alkali leaching solution and alkali leaching residue.

[0075] (2) Treatment of aluminum ash slag: According to the mass ratio of fly ash raw material to aluminum ash slag raw material of 100:60, air-dry the aluminum ash slag raw material and then sieve it through 80 meshes. Add the sieved aluminum ash slag and all the alkali leaching residues obtained in step (1) into a 4.2 mol / L hydrochloric acid solution respectively, and stir and react at 90 °C for 1.5 h. After the reaction, quickly filter to obtain an acid leaching solution.

[0076] (3) Preparation of polymeric flocculant: Heat all the acid leaching solutions obtained in step (2) to 60 °C, and then slowly add 2.2 mol / L aluminum hydroxide sol (pH value is 6.5), and stir and react for 0.5 h. After the reaction, add a mixed solution of yttrium nitrate and lanthanum nitrate with a total concentration of 1.2 mol / L (the molar ratio of yttrium nitrate to lanthanum nitrate is 1:1), and stir and react again for 0.5 h. After the reaction, obtain mixture 1. Then, under stirring conditions, slowly drop all the alkali leaching solutions obtained in step (1) into mixture 1. After the addition of the alkali leaching solution is completed, continue to stir for 10 min, adjust the pH value to 3.5, and stand and ripen at room temperature for 2 h to obtain mixture 2.

[0077] (4) Preparation of composite flocculant: Mix the mixture 2 obtained in step (3) with modified chitosan, add sodium acetate, and carry out ripening treatment at 35 °C for 16 h to obtain the composite flocculant.

[0078] Among them, in step (2), the mass ratio of the aluminum ash slag raw material to the hydrochloric acid solution is 1:12.

[0079] Among them, in step (3), the mass ratio of the yttrium nitrate solution, aluminum hydroxide sol, and acid leaching solution is 0.5:5:7.

[0080] Among them, in step (4), the mass ratio of mixture 2, modified chitosan, and sodium acetate is 100:1.5:2.5.

[0081] Among them, in step (4), the preparation of the modified chitosan includes the following steps:

[0082] S1. Add chitosan and citric acid to ethanol respectively, and then stir and react at room temperature for 1.5 h; after the reaction is completed, centrifuge the obtained reaction product first, and then wash and dry it to obtain modified chitosan; among them, the dosage ratio of chitosan, citric acid, and ethanol is 1 mol:1.2 mol:15 mL.

[0083] The difference between this comparative example and Example 1 is that the modified chitosan is not subjected to low-temperature plasma treatment.

[0084] Comparative Example 2

[0085] A method for preparing a composite flocculant using aluminum ash slag includes the following steps:

[0086] (1) Treatment of fly ash: Air-dry the fly ash raw material and sieve it through 80 meshes; then, according to the mass ratio of sodium hydroxide to fly ash raw material of 10 mL:1 g, add the sieved fly ash to a 4 mol / L sodium hydroxide solution, and stir and react at 140 °C for 1 h; after the reaction is completed, obtain a leaching solution; after vacuum filtration of the leaching solution, obtain an alkali leaching solution and an alkali leaching residue;

[0087] (2) Treatment of aluminum ash slag: According to the mass ratio of fly ash raw material and aluminum ash slag raw material of 100:60, air-dry the aluminum ash slag raw material and sieve it through 80 meshes, and add the sieved aluminum ash slag and all the alkali leaching residues obtained in step (1) to a 4.2 mol / L hydrochloric acid solution respectively, and stir and react at 90 °C for 1.5 h; after the reaction is completed, quickly filter to obtain an acid leaching solution;

[0088] (3) Preparation of the polymeric flocculant: Heat all the acid leaching solutions obtained in step (2) to 60 °C, then slowly add a 2.2 mol / L aluminum hydroxide sol (pH value is 6.5), and stir and react for 0.5 h; after the reaction is completed, add a mixed solution of yttrium nitrate and lanthanum nitrate with a total concentration of 1.2 mol / L (the molar ratio of yttrium nitrate and lanthanum nitrate is 1:1), and stir and react again for 0.5 h; after the reaction is completed, obtain mixture 1; then, under stirring conditions, slowly drop all the alkali leaching solutions obtained in step (1) into mixture 1; after the addition of the alkali leaching solution is completed, continue to stir for 10 min, adjust the pH value to 3.5, and let it stand and age at room temperature for 2 h to obtain mixture 2;

[0089] (4) Preparation of the composite flocculant: Mix the mixture 2 obtained in step (3) with modified chitosan, add sodium acetate, and cure at 35 °C for 16 h to obtain the composite flocculant.

[0090] Among them, in step (2), the mass ratio of the aluminum ash residue raw material to the hydrochloric acid solution is 1:12.

[0091] Among them, in step (3), the mass ratio of the yttrium nitrate solution, the aluminum hydroxide sol, and the acid leaching solution is 0.5:5:7.

[0092] Among them, in step (4), the mass ratio of the mixture 2, modified chitosan, and sodium acetate is 100:1.5:2.5.

[0093] Among them, in step (4), the preparation of the modified chitosan includes the following steps:

[0094] S2. Perform low-temperature plasma treatment on chitosan (discharge power is 50 W, discharge time is 4 min). After the treatment is completed, the modified chitosan is obtained.

[0095] The difference between this comparative example and Example 1 is that the modified chitosan is not treated with citric acid.

[0096] Comparative Example 3

[0097] A method for preparing a composite flocculant using aluminum ash residue, comprising the following steps:

[0098] (1) Treatment of fly ash: Air-dry the fly ash raw material and then sieve it through 80 meshes; subsequently, add the sieved fly ash to a 4 mol / L sodium hydroxide solution according to the mass ratio of 10 mL:1 g of sodium hydroxide to the fly ash raw material, and stir and react at 140 °C for 1 h; after the reaction ends, obtain a leaching solution; after vacuum filtration of the leaching solution, obtain an alkali leaching solution and an alkali leaching residue;

[0099] (2) Treatment of aluminum ash residue: Air-dry the aluminum ash residue raw material and sieve it through 80 meshes according to the mass ratio of 100:60 of the fly ash raw material and the aluminum ash residue raw material. Add the sieved aluminum ash residue and all the alkali leaching residues obtained in step (1) to a 4.2 mol / L hydrochloric acid solution, and stir and react at 90 °C for 1.5 h; after the reaction ends, quickly filter to obtain an acid leaching solution;

[0100] (3) Preparation of the polymeric flocculant: Heat all the acid leaching solution obtained in step (2) to 60 °C, and then slowly add 2.2 mol / L aluminum hydroxide sol (pH value is 6.5), and stir and react for 0.5 h; after the reaction is completed, add 1.2 mol / L lanthanum nitrate solution, and stir and react again for 0.5 h; after the reaction is completed, obtain mixture 1; then, under stirring conditions, slowly drop all the alkali leaching solution obtained in step (1) into the mixture 1; after the dropping of the alkali leaching solution is completed, continue to stir for 10 min, adjust the pH value to 3.5, and let it stand and age at room temperature for 2 h to obtain mixture 2;

[0101] (4) Preparation of the composite flocculant: Mix the mixture 2 obtained in step (3) with modified chitosan, add sodium acetate, and cure and treat at 35 °C for 16 h to obtain the composite flocculant.

[0102] Among them, in step (2), the mass ratio of the aluminum ash slag raw material to the hydrochloric acid solution is 1:12.

[0103] Among them, in step (3), the mass dosage ratio of the lanthanum nitrate solution, aluminum hydroxide sol and acid leaching solution is 1:5:7.

[0104] Among them, in step (4), the mass ratio of mixture 2, modified chitosan and sodium acetate is 100:1.5:2.5.

[0105] Among them, in step (4), the preparation of the modified chitosan includes the following steps:

[0106] S1. Add chitosan and citric acid to ethanol respectively, and then stir and react at room temperature for 1.5 h; after the reaction is completed, centrifuge the obtained reaction product first, and then wash and dry it to obtain pre-modified chitosan; among them, the dosage ratio of chitosan, citric acid and ethanol is 1 mol:1.2 mol:15 mL;

[0107] S2. Perform low-temperature plasma treatment on the pre-modified chitosan obtained in step S1 (discharge power is 50 W, discharge time is 4 min), and after the treatment is completed, obtain the modified chitosan.

[0108] The difference between this comparative example and Example 1 is that it is treated with lanthanum nitrate solution instead of a mixed solution of yttrium nitrate and lanthanum nitrate.

[0109] Perform performance tests on the composite flocculants prepared in Examples 1 to 3 and Comparative Examples 1 to 3, and the test results are shown in Tables 3 and 4. Among them, the test method is as follows:

[0110] Turbidity test: Prepare an artificial kaolin turbid solution with a turbidity of 100 NTU, take 500 mL, add each flocculant according to a dosage of 0.1 g / L, stir at 300 rpm for 1 min, stir at 150 rpm for 2 min, stir at 70 rpm for 2 min, then let it stand for 5 min, measure its turbidity, and calculate the turbidity removal rate.

[0111] Metal adsorption test: Prepare heavy metal-containing wastewater containing Cr 6+ (concentrations of 1000 mg / L and 10 mg / L) and containing Pb 2+ (concentration of 10 mg / L) respectively. Take 100 mL of the above wastewater, add each flocculant according to a dosage of 0.1 g / L, stir rapidly at 200 rpm for 1 min, stir at 50 rpm for 3 min, then let it stand for 4 min. Use atomic absorption spectrophotometry to detect the content of metal ions respectively, and calculate the removal rate.

[0112] Table 3 Turbidity test results

[0113] Turbidity Removal Rate / % Example 1 99.6 Example 2 99.1 Example 3 99.3 Comparative Example 1 96.2 Comparative Example 2 97.8 Comparative Example 3 94.9

[0114] Table 4 Heavy metal flocculation test results

[0115]

[0116] As can be seen from Table 3 and Table 4, the turbidity removal rate and heavy metal ion removal rate of the composite flocculants prepared in each embodiment of the present invention are both relatively high. It can not only have good removal effects on both high-concentration and low-concentration metal ions, but also has a short flocculation treatment time and high treatment efficiency.

[0117] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite flocculant using aluminum ash slag, characterized in that, It includes the following steps: (1) Treatment of fly ash: The fly ash raw material is air-dried and sieved through 50 - 150 meshes, and then added to a sodium hydroxide solution with a concentration of 3.5 - 4.5 mol / L. Stir and react at 135 - 145 °C for 0.5 - 5 h. After the reaction, the leaching solution is obtained. After vacuum filtration of the leaching solution, an alkali leaching solution and alkali leaching residue are obtained; (2) Treatment of aluminum ash residue: The aluminum ash residue raw material is air-dried and sieved through 50 - 150 meshes. The sieved aluminum ash residue and all the alkali leaching residues obtained in step (1) are respectively added to a hydrochloric acid solution with a concentration of 3.8 - 5 mol / L. Stir and react at 85 - 95 °C for 1 - 5 h. After the reaction, quickly filter to obtain an acid leaching solution; (3) Preparation of polymeric flocculant: Heat all the acid leaching solutions obtained in step (2) to 50 - 65 °C, and then slowly add aluminum hydroxide sol. Stir and react for 0.5 - 2 h. After the reaction, add a mixed solution of yttrium nitrate and lanthanum nitrate, and stir and react again for 0.5 - 2 h. After the reaction, a first mixture is obtained. Then, under stirring conditions, slowly drop all the alkali leaching solutions obtained in step (1) into the first mixture. After the addition of the alkali leaching solution is completed, continue to stir for 5 - 30 min, adjust the pH value to 3 - 4, and stand and ripen at room temperature for 0.5 - 5 h to obtain a second mixture; (4) Preparation of composite flocculant: Mix the second mixture obtained in step (3) with modified chitosan, add sodium acetate, and after ripening treatment, the composite flocculant is obtained; Among them, in step (1), the volume - mass ratio of the sodium hydroxide solution to the fly ash raw material is (6 - 15) mL:1 g; Among them, the mass ratio of the fly ash raw material in step (1) to the aluminum ash residue raw material in step (2) is 100:(30 - 80), and the mass ratio of the aluminum ash residue raw material to the hydrochloric acid solution is 1:6 - 15; Among them, in step (3), the molar ratio of yttrium nitrate to lanthanum nitrate is 1:1, and the total concentration of the mixed solution of yttrium nitrate and lanthanum nitrate is 0.5 - 1.5 mol / L, the concentration of aluminum hydroxide sol is 1.5 - 2.5 mol / L, and the pH value is 6.2 - 6.8; The mass dosage ratio of yttrium nitrate solution, aluminum hydroxide sol to the acid leaching solution is 0.5:(4 - 10):(5 - 12); Among them, in step (4), the mass ratio of the second mixture, modified chitosan, and sodium acetate is 100:(1 - 2):(2 - 5).

2. The method for preparing a composite flocculant using aluminum ash residue according to claim 1, characterized in that, In the aluminum ash residue raw material, calculated by mass fraction of 100%, the content of aluminum oxide is 68.37%, and the content of silicon dioxide is 12.66%. In the fly ash raw material, calculated by mass fraction of 100%, the content of aluminum oxide is 25.05%, and the content of silicon dioxide is 60.84%.

3. A method for preparing a composite flocculant using aluminum ash slag according to claim 1, characterized in that, In step (4), the ripening time is 8 - 36 h, and the ripening temperature is 25 - 50 °C.

4. A method for preparing a composite flocculant using aluminum ash residue according to claim 1, characterized in that, In step (4), the preparation of modified chitosan includes the following steps: S1. Add chitosan and citric acid to ethanol respectively, and then stir and react. After the reaction, first centrifuge the obtained reaction product, and then wash and dry it to obtain pre - modified chitosan; S2. Perform low-temperature plasma treatment on the pre-modified chitosan obtained in step S1. After the treatment is completed, modified chitosan is obtained.

5. A method for preparing a composite flocculant using aluminum ash slag according to claim 4, characterized in that, In step S1, the dosage ratio of chitosan, citric acid, and ethanol is 1 mol : (1 - 1.5) mol : (10 - 25) mL; the stirring reaction temperature is room temperature, and the stirring reaction time is 0.5 - 2 h.

6. A method for preparing a composite flocculant using aluminum ash residue according to claim 4, characterized in that, In step S2, the discharge power is 45 - 60 W, and the discharge time is 0.5 - 8 min.

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