Composite flocculant based on nano calcium oxide and preparation method thereof

Abstract

The invention discloses a composite flocculant based on nano calcium oxide and a preparation method thereof, and relates to the technical field of sewage treatment, the composite flocculant comprises the following raw materials by weight: 10-20 parts of modified nano calcium oxide, 40-50 parts of polyaluminum chloride, 25-35 parts of modified lignin, 150-160 parts of deionized water, and 20-30 parts of absolute ethyl alcohol. According to the composite flocculant, the modified nano calcium oxide, the modified lignin and other raw materials are used in a combined mode, the modified nano calcium oxide plays a role through slow release and can be magnetically adsorbed and recycled, secondary pollution is avoided, the composite flocculant is endowed with high environmental protection performance, the molecular weight, hydrophilicity and charge density of the modified lignin are improved, and the composite flocculant has the advantages of being environmentally friendly and free of pollution. The modified lignin and the modified nano calcium oxide can react and be cross-linked, and the composite flocculant is endowed with a relatively strong flocculation effect in cooperation with the use of the polyaluminum chloride, so that the purification of complex sewage is facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sewage treatment, and in particular to a composite flocculant based on nano calcium oxide and a preparation method thereof. BACKGROUND

[0002] In the field of wastewater treatment, calcium oxide has the functions of flocculation, oxidation and disinfection, and can simultaneously remove heavy metals (such as Cr (VI)) and organic pollutants. In the field of desulfurization, calcium oxide has high adsorption capacity for sulfur dioxide. Compared with ordinary calcium oxide, nano calcium oxide has a larger specific surface area, can quickly dissolve in water to generate basic calcium hydroxide, increase the pH value of the water body, promote the destabilization of colloidal particles and form hydroxide flocs, and is suitable for acid wastewater treatment. However, in wastewater with high complexity such as high salinity (such as sulfate), it is easy to form insoluble calcium salts (such as calcium sulfate), resulting in loose flocs and poor settling properties. Moreover, if nano calcium oxide enters the water body after adsorbing heavy metals, it will form a "pollution carrier" (such as nano-CaO-Pb complex poison) in the water body, causing secondary pollution and limiting its use in complex wastewater treatment.

[0003] Lignin, as a renewable polymer compound with abundant reserves in nature, has great application potential in the field of wastewater treatment due to its unique structural characteristics and environmental friendliness. However, the heterogeneity and stubborn structure of lignin make it difficult to be used directly as an efficient flocculant. The hydrophobicity of lignin limits its application in non-alkaline or non-organic solvent systems. In addition, existing lignin-based flocculants generally have low charge density, insufficient molecular weight, and poor hydrophilicity, which further restricts their actual performance.

[0004] Therefore, it is necessary to develop a suitable modification method to improve the agglomeration of nano calcium oxide and reduce its residue in wastewater treatment, and further improve the charge density, molecular weight and hydrophilicity of lignin-based flocculants, so as to obtain an environmentally friendly composite flocculant composed of nano calcium oxide, lignin and the like with better performance. SUMMARY

[0005] To solve the above technical problems, the present application provides a composite flocculant based on nano calcium oxide and a preparation method thereof.

[0006] The object of the present application can be achieved by the following technical solutions: A composite flocculant based on nano calcium oxide, comprising the following raw materials by weight: modified nano calcium oxide 10-20 parts, polyaluminum chloride 40-50 parts, modified lignin 25-35 parts, deionized water 150-160 parts, and anhydrous ethanol 20-30 parts. The preparation method of the composite flocculant based on nano calcium oxide comprises the following steps: The modified nano calcium oxide, polyaluminum chloride, modified lignin, deionized water and anhydrous ethanol are mixed and ultrasonically dispersed for 1-1.5 h, the pH is controlled to be 6.5-7, and the reaction is stirred at 45-55℃ for 2-2.5 h. After centrifugation, pressure filtration and drying, the product is crushed, passed through a 100-200 mesh sieve, and a nano calcium oxide-based composite flocculant is obtained; The modified nano calcium oxide is prepared by the following steps: Step M1: After the biochar and the oxidizing agent are mixed and ultrasonically dispersed, the product m1 is obtained by washing with water until neutral and drying after temperature stirring reaction; the nano calcium oxide, the fatty acid and the ethanol are mixed, ultrasonically dispersed, centrifuged, washed and dried to obtain the product m2; Step M2: The product m2 and ethyl acetate are mixed and ultrasonically dispersed, then the peroxo acid is added, and the product m3 is obtained by stirring at room temperature; the product m1 and anhydrous ethanol are mixed and ultrasonically dispersed, protective gas is introduced, then 4-dimethylaminopyridine and the product m3 are added after temperature rising, and the product m4 is obtained by stirring reaction; Step M3: The nano ferric oxide and ethanol are mixed and ultrasonically dispersed, then the hydrolysis solution is added, the reflux is started, the product m5 is obtained by temperature rising reflux stirring reaction, centrifugation and washing, and vacuum drying; the product m4, the product m5, ethyl acetate and DMF are mixed and ultrasonically dispersed, then triethylamine is added, and the product m6 is obtained by heating reflux stirring; the product m6, epichlorohydrin and DMSO are mixed and ultrasonically dispersed, then the alkali solution and tetraethylammonium bromide are added, and the modified nano calcium oxide is obtained by temperature rising stirring reaction; The preparation of the modified nano calcium oxide includes the following specific steps: Step M1: The biochar and the oxidizing agent are mixed and ultrasonically dispersed for 30-35 min, the temperature is raised to 75-80℃, and the product m1 is obtained by stirring reaction for 1.5-1.7 h, washing with water until neutral and drying; the nano calcium oxide, the fatty acid and the ethanol are mixed, ultrasonically dispersed at a power of 20-40 kHz for 1-1.2 h, centrifuged, washed and dried to obtain the product m2; Further, the biochar and the oxidizing agent are used in a ratio of 1-1.2 g:60-80 mL; the biochar is wheat straw biochar or rice straw biochar; the oxidizing agent is a 0.3-0.5 mol / L potassium permanganate solution; the nano calcium oxide, the fatty acid and the ethanol are used in a ratio of 1-1.5 g:0.2-0.5 g:50-60 mL; the fatty acid is oleic acid; and the volume fraction of the ethanol is 95%; During the step M1 reaction process, the biochar is oxidized by the oxidizing agent to obtain the product m1, i.e. the surface carboxylated biochar; the fatty acid is used to modify the surface of the nano calcium oxide to obtain the nano calcium oxide containing double bonds, i.e. the product m2; Step M2: product m2, ethyl acetate were mixed and ultrasonically dispersed for 35-40 min, peracid was added, and the reaction was stirred at room temperature for 2.5-3 h to obtain product m3; product m1, anhydrous ethanol were mixed and ultrasonically dispersed, protective gas was introduced, and the temperature was increased to 50-55℃, 4-dimethylaminopyridine and product m3 were added, and the reaction was stirred for 9-9.5 h to obtain product m4; Further, the amount ratio of product m2, ethyl acetate, peracid was 3-3.5 g: 150-160 mL: 0.55-0.65 g; the peracid was meta-chloroperbenzoic acid; the amount ratio of product m1, anhydrous ethanol, 4-dimethylaminopyridine, product m3 was 4-5 g: 180-190 mL; 0.8-1.0 g: 1.8-2 g; During the reaction of step M2, the double bond on the surface of product m2 was converted to an epoxy group under the action of peracid to obtain product m3; the carboxyl group of product m1 reacted with the epoxy group of product m3 to obtain a product grafted with nano calcium oxide and biochar containing a hydroxyl group, i.e., product m4; Step M3: nano magnetite, ethanol were mixed and ultrasonically dispersed for 40-45 min, hydrolyzate was added, and the reflux was started, the temperature was increased to 65-75℃, and the reaction was stirred under reflux for 5-5.5 h, and then centrifuged, washed and vacuum dried at 60-65℃ to obtain product m5; product m4, product m5, ethyl acetate, DMF were mixed and ultrasonically dispersed for 25-35 min, triethylamine was added, and the reaction was stirred under reflux at 80-90℃ for 6-6.5 h to obtain product m6; product m6, epichlorohydrin, DMSO were mixed and ultrasonically dispersed for 50-55 min, alkali solution and tetraethylammonium bromide were added, the temperature was increased to 50-60℃, and the reaction was stirred for 7-7.5 h to obtain modified nano calcium oxide; Further, the amount ratio of nano magnetite, ethanol, hydrolyzate was 5-6 g: 100-110 mL: 13-15 mL; the hydrolyzate was obtained by mixing 3-glycidyloxypropyl triethoxysilane, ethanol and deionized water in a ratio of 14.5-15 g: 23-25 mL: 5-7 mL, and then stirring at a temperature of 40-50℃ and a pH of 4.5-5 for 1-1.5 h; the volume fraction of ethanol was 95%; the amount ratio of product m4, product m5, ethyl acetate, DMF, triethylamine was 6-7 g: 2.5-3 g: 100-110 mL: 160-170 mL: 30-35 mL; the amount ratio of product m6, epichlorohydrin, DMSO, alkali solution, tetraethylammonium bromide was 10-12 g: 6-6.5 g: 280-290 mL: 8-10 mL: 0.8-1.2 g; the alkali solution was a 40-45% potassium hydroxide solution by mass fraction; In the reaction process of step M3, the surface of the nano-magnetic iron oxide is modified by hydrolysis of 3-glycidyloxypropyltriethoxysilane to obtain nano-magnetic iron oxide containing epoxy groups, i.e., product m5; the hydroxyl group of product m4 reacts with the epoxy group of product m5 to obtain a product of nano-magnetic iron oxide, nano-calcium oxide and biochar grafting, i.e., product m6; the hydroxyl group of product m6 is opened and then closed to form an epoxy group after ring-opening of epichlorohydrin to obtain modified nano-calcium oxide; The modified lignin is prepared by the following steps: Step N1, mix lignin, anhydrous DMSO, potassium carbonate solution, and pass in protective gas. Stir for 1-1.2 h, add halogenated styrene and hydroquinone, and heat to 55-65°C. Stir for 16-17 h, cool with an ice water bath, and then process to obtain product n1. In a protective gas atmosphere, mix product n1 and 1,4-dioxane, stir for 30-40 min, add sodium bicarbonate solution and tetra-n-butylammonium bromide, and stir to cool to 0-5°C. Add solution a dropwise, heat to 25-30°C, and stir to react for 8.5-9 h to obtain product n2; Step N2, mix tertiary phosphine and anhydrous THF, and add solution b dropwise while stirring. Start refluxing, heat to reflux and stir to react, cool to room temperature, filter, wash with diethyl ether, and vacuum dry to obtain product n3. Mix product n3 and DMF, pass in protective gas, heat to add pyridine and product n2, and stir to react to obtain product n4; Step N3, mix potassium aminobenzoate, epichlorohydrin, tetrabutylammonium chloride, and DMF, heat to reflux and stir to react, cool to room temperature, add sodium hydroxide solution, and stir to obtain product n5. Mix product n5, product n4, DMAC, and acetonitrile, stir to add N,N-dimethylbutylamine, heat to reflux and stir to obtain product n6. Mix product n6, DMSO, and methanol, stir to add safety powder, heat to stir and react to obtain modified lignin; The modified lignin is prepared by the following steps: Step N1, mix lignin, anhydrous DMSO, potassium carbonate solution, and pass in protective gas. Stir for 1-1.2 h, add halogenated styrene and hydroquinone, and heat to 55-65°C. Stir for 16-17 h, cool with an ice water bath, and then process to obtain product n1. In a protective gas atmosphere, mix product n1 and 1,4-dioxane, stir for 30-40 min, add sodium bicarbonate solution and tetra-n-butylammonium bromide, and stir to cool to 0-5°C. Add solution a dropwise, heat to 25-30°C, and stir to react for 8.5-9 h to obtain product n2; Further, the lignin, anhydrous DMSO, potassium carbonate solution, halogenated styrene, hydroquinone are in a ratio of 10-11 g: 80-100 mL: 28-32 mL: 20-22 g: 0.08-0.12 g; the mass fraction of the potassium carbonate solution is 50-55%; the halogenated styrene is 4-chloromethylstyrene; the product n1, 1,4-dioxane, sodium bicarbonate solution, tetra-n-butylammonium bromide, solution a are in a ratio of 15-17 g: 80-90 mL: 7-9 mL: 1.8-2 g: 24-26 mL; the mass fraction of the sodium bicarbonate solution is 40-45%; solution a is a mixture of m-chloroperoxybenzoic acid and 1,4-dioxane in a ratio of 8.8-9.2 g: 18-20 mL, which is stirred at 40-45°C and then cooled to obtain; In the reaction of step N1, the phenolic hydroxyl group of the lignin reacts with the halogenated styrene to remove hydrogen halide, and a terminal alkenyl group is introduced into the lignin to obtain the product n1; the terminal alkenyl group of the product n1 is oxidized to an epoxy group to obtain the product n2; In step N2, the tertiary phosphine and anhydrous THF are mixed, solution b is added dropwise under stirring, and the mixture is heated to 90-95°C under reflux, stirred under reflux for 12-13 h, cooled to room temperature, filtered under suction, washed with diethyl ether, and dried under vacuum at 40-45°C to obtain the product n3; the product n3 and DMF are mixed, protective gas is introduced, the temperature is raised to 50-55°C, pyridine and the product n2 are added, and the mixture is stirred for 9-9.5 h to obtain the product n4; Further, the tertiary phosphine, anhydrous THF, and solution b are in a ratio of 10.5-11 g: 25-30 mL: 30-35 mL; the tertiary phosphine is tributylphosphine; solution b is obtained by mixing halogenated aliphatic acid and anhydrous THF in a ratio of 9-9.5 g: 20-25 mL and stirring at 45-50°C for 25-30 min; the halogenated aliphatic acid is 4-bromobutyric acid; the product n3, DMF, pyridine, and the product n2 are in a ratio of 21-22 g: 45-50 mL: 0.8-1.2 g: 18-19 g; In the reaction of step N2, the tertiary phosphine reacts with the halogenated aliphatic acid to generate the product n3 containing a quaternary phosphonium salt and a carboxyl group; the carboxyl group of the product n3 reacts with the epoxy group of the product n2 to obtain the lignin containing a secondary alcohol hydroxyl group and a quaternary phosphonium salt, i.e., the product n4; Step N3, mix amino benzoic acid potassium, epichlorohydrin, tetrabutylammonium chloride, DMF, warm to 100-105 DEG C, reflux stirring reaction 4-4.5h, cool to room temperature, add sodium hydroxide solution, stir for 6-6.5h, to obtain product n5;Product n5, product n4, DMAC, acetonitrile are mixed and stirred for 40-45min, N,N-dimethylbutylamine is added, and stirring is carried out at 90-95 DEG C under reflux for 7.5-8h to obtain product n6;Product n6, DMSO, methanol are mixed and stirred for 40-50min, and safety powder is added, and the temperature is warmed to 50-60 DEG C, and stirring is carried out for 5-6h to obtain modified lignin; Further, the amount ratio of amino benzoic acid potassium, epichlorohydrin, tetrabutylammonium chloride, DMF and sodium hydroxide solution is 11.5-12g:10-10.5g:0.8-1g:55-60mL:15-20mL;Amino benzoic acid potassium is potassium 2-amino-5-nitrobenzoate;The mass fraction of sodium hydroxide solution is 50-55%;The amount ratio of product n5, product n4, DMAC, acetonitrile and N,N-dimethylbutylamine is 22.5-23.5g:40.5-41.5g:110-120mL:45-55mL:2.5-3.5g;The amount ratio of product n6, DMSO, methanol and safety powder is 35-40g:150-160mL:20-25mL:10-15g; In the process of step N3 reaction, the amino group of amino benzoic acid potassium is ring-opened and closed to obtain product n5 containing epoxy group and nitro group;The epoxy group of product n5 is ring-opened with the secondary alcohol hydroxyl group of product n4 to obtain product n6 containing hydroxyl group;The nitro group in product n6 is reduced to amino group to obtain modified lignin; The application discloses a composite flocculant based on nano calcium oxide and a preparation method thereof.

[0007] The modified nano calcium oxide used in the application is obtained by grafting and loading of nano calcium oxide modified by fatty acid, nano ferroferric oxide modified by silane and carboxylated biochar;After the long-chain acid modification and grafting and loading of the nano calcium oxide on the biochar, the agglomeration of the nano calcium oxide is greatly improved, and the nano calcium oxide can play a role by slow release, and the use of the nano ferroferric oxide enables the modified nano calcium oxide to be magnetically adsorbed and recovered, thereby avoiding secondary pollution caused by residues, and after the ferroferric oxide is grafted and loaded on the biochar, the physical barrier can also weaken the adverse effect of the solution acidity and alkalinity on the magnetism of the ferroferric oxide.

[0008] The modified lignin used in the application is obtained by reaction of tertiary phosphine, halogenated fatty acid, lignin, halogenated styrene, potassium aminobenzoate, etc., and the molecular weight of the lignin-based flocculant is improved; the tertiary phosphine, halogenated fatty acid and potassium aminobenzoate are combined to graft quaternary phosphonium salt cations and carboxylate anions on the lignin, so that the hydrophilicity and charge density of the modified lignin are greatly improved, electrostatic attraction occurs between the modified lignin and the colloidal particles or pollutants with opposite charges in the sewage, the charges on the surface of the colloidal particles are neutralized and the particles are destabilized and aggregated and settled, the quaternary phosphonium salt also has strong broad-spectrum antibacterial property, which can reduce the consumption of medicaments in the subsequent disinfection step of sewage treatment; the use of potassium aminobenzoate also introduces amino groups and alcohol hydroxyl groups into the modified lignin, which can form a dense crosslinked network with the epoxy groups in the modified nano calcium oxide, enhance the net capture, adsorption and bridging effect of the composite flocculant on the surrounding small particles and colloidal substances, and cooperate with the use of polyaluminum chloride to give the composite flocculant strong flocculation performance, which is beneficial to the purification of complex sewage. DETAILED DESCRIPTION

[0009] The technical solutions in the embodiments of the application will be described below in a clear and complete manner. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application. EMBODIMENT

[0010] A modified nano calcium oxide, the preparation thereof comprises the following steps: Step M1: mixing biochar (supplier: Zhengzhou Jinbang Environmental Protection Technology Co., Ltd., 80 mesh) and an oxidizing agent, ultrasonic dispersion for 30 min, heating to 75 DEG C, stirring reaction for 1.5 h, washing with water to neutral after reaction, drying to obtain product m1; mixing nano calcium oxide (supplier: Nangong City Juxin New Material Technology Co., Ltd.), oleic acid and ethanol, ultrasonic dispersion for 1 h under the power of 25 kHz, centrifugation, washing and drying to obtain product m2; the amount ratio of biochar to oxidizing agent is 1g:60mL; the biochar is wheat straw biochar; the oxidizing agent is 0.3mol / L potassium permanganate solution; the amount ratio of nano calcium oxide, oleic acid and ethanol is 1g:0.2g:50mL; the volume fraction of ethanol is 95%; Step M2: product m2, ethyl acetate were mixed and ultrasonically dispersed for 35 min, m-chloroperbenzoic acid was added, and the reaction was stirred at room temperature for 2.5 h to obtain product m3; product m1, anhydrous ethanol were mixed and ultrasonically dispersed for 35 min, nitrogen was introduced, and the temperature was raised to 50°C, 4-dimethylaminopyridine, product m3 were added, and the reaction was stirred for 9 h to obtain product m4; the amount ratio of product m2, ethyl acetate, m-chloroperbenzoic acid was 3 g: 150 mL: 0.55 g; the amount ratio of product m1, anhydrous ethanol, 4-dimethylaminopyridine, product m3 was 4 g: 180 mL: 0.8 g: 1.8 g; Step M3: nanometer-sized ferriferrous oxide (supplier: Hangzhou Jili Biological Material Co., Ltd., specification 100 nm), ethanol were mixed and ultrasonically dispersed for 40 min, hydrolysis solution was added, reflux was started, the temperature was raised to 65°C, and the reaction was stirred under reflux for 5 h; after centrifugal washing, product m5 was obtained by vacuum drying at 60°C; product m4, product m5, ethyl acetate, DMF were mixed and ultrasonically dispersed for 25 min, triethylamine was added, and the reaction was stirred under reflux at 80°C for 6 h to obtain product m6; product m6, epichlorohydrin, DMSO were mixed and ultrasonically dispersed for 50 min, lye, tetraethylammonium bromide were added, the temperature was raised to 50°C, and the reaction was stirred for 7 h to obtain modified nanometer-sized calcium oxide; the amount ratio of nanometer-sized ferriferrous oxide, ethanol, hydrolysis solution was 5 g: 100 mL: 13 mL; the hydrolysis solution was obtained by mixing 3-glycidyloxypropyltriethoxysilane, ethanol, deionized water in a proportion of 14.5 g: 23 mL: 5 mL, and then stirring at a temperature of 40°C and a pH of 4.6 for 1 h; the volume fraction of ethanol was 95%; the amount ratio of product m4, product m5, ethyl acetate, DMF, triethylamine was 6 g: 2.5 g: 100 mL: 160 mL: 30 mL; the amount ratio of product m6, epichlorohydrin, DMSO, lye, tetraethylammonium bromide was 10 g: 6 g: 280 mL: 8 mL: 0.8 g; the lye was a 40% mass fraction potassium hydroxide solution. Embodiment

[0011] A modified nanometer-sized calcium oxide, the preparation of which comprises the following steps: Step M1: Biochar (supplier: Zhengzhou Jinbang Environmental Protection Technology Co., Ltd., 90 mesh) and oxidant were mixed and ultrasonically dispersed for 33 min, heated to 78℃, and stirred for 1.6 h. After the reaction, the mixture was washed with water until neutral and dried to obtain product m1. Nano-calcium oxide (supplier: Nangong Jiuxin New Material Technology Co., Ltd.), oleic acid, and ethanol were mixed and ultrasonically dispersed at 30 kHz power for 1.1 h. After centrifugation, washing, and drying, product m2 was obtained. The ratio of biochar to oxidant was 1.1 g: 70 mL. The biochar was rice straw biochar. The oxidant was 0.4 mol / L potassium permanganate solution. The ratio of nano-calcium oxide, oleic acid, and ethanol was 1.3 g: 0.35 g: 55 mL. The volume fraction of ethanol was 95%. Step M2: Mix product m2 and ethyl acetate and ultrasonically disperse for 38 min, add m-chloroperoxybenzoic acid, and stir at room temperature for 2.8 h to obtain product m3; mix product m1 and anhydrous ethanol and ultrasonically disperse for 38 min, purge with nitrogen, heat to 53℃, add 4-dimethylaminopyridine and product m3, and stir for 9.3 h to obtain product m4; the molar ratio of product m2, ethyl acetate, and m-chloroperoxybenzoic acid is 3.3 g: 155 mL: 0.60 g; the molar ratio of product m1, anhydrous ethanol, 4-dimethylaminopyridine, and product m3 is 4.5 g: 185 mL; 0.9 g: 1.9 g; Step M3: Nano-iron oxide (supplier: Hangzhou Jiuli Biomaterials Co., Ltd., specification 150nm) and ethanol were mixed and ultrasonically dispersed for 43 min. Hydrolysate was added, reflux was started, the temperature was raised to 70℃, and the mixture was stirred under reflux for 5.3 h. After centrifugation and washing, the mixture was vacuum dried at 63℃ to obtain product m5. Product m4, product m5, ethyl acetate, and DMF were mixed and ultrasonically dispersed for 30 min. Triethylamine was added, and the mixture was stirred under reflux at 85℃ for 6.3 h to obtain product m6. Product m6, epichlorohydrin, and DMSO were mixed and ultrasonically dispersed for 53 min. Alkali solution and tetraethylammonium bromide were added, and the mixture was heated to 55℃ and stirred for 7.3 h to obtain modified nano-calcium oxide. Nano-iron oxide, ethanol, and water The hydrolysate was prepared by mixing 3-glycidyl etheroxypropyltriethoxysilane, ethanol, and deionized water in a ratio of 14.8 g: 24 mL: 6 mL and stirring at 45 °C and pH 4.7 for 1.3 h; the volume fraction of ethanol was 95%; the ratio of product m4, product m5, ethyl acetate, DMF, and triethylamine was 6.5 g: 2.8 g: 105 mL: 165 mL: 33 mL; the ratio of product m6, epichlorohydrin, DMSO, alkali solution, and tetraethylammonium bromide was 11 g: 6.3 g: 285 mL: 9 mL: 1.0 g; the alkali solution was a 43% potassium hydroxide solution. Example

[0012] A modified nano-calcium oxide, the preparation of which includes the following steps: Step M1: Biochar (supplier: Zhengzhou Jinbang Environmental Protection Technology Co., Ltd., 100 mesh) and oxidant were mixed and ultrasonically dispersed for 35 min, heated to 80℃, and stirred for 1.7 h. After the reaction, the mixture was washed with water until neutral and dried to obtain product m1. Nano-calcium oxide (supplier: Nangong Jiuxin New Material Technology Co., Ltd.), oleic acid, and ethanol were mixed and ultrasonically dispersed at 40 kHz power for 1.2 h. After centrifugation, washing, and drying, product m2 was obtained. The ratio of biochar to oxidant was 1.2 g: 80 mL. The biochar was wheat straw biochar. The oxidant was 0.5 mol / L potassium permanganate solution. The ratio of nano-calcium oxide, oleic acid, and ethanol was 1.5 g: 0.5 g: 60 mL. The volume fraction of ethanol was 95%. Step M2: Mix product m2 and ethyl acetate and ultrasonically disperse for 40 min, add m-chloroperoxybenzoic acid, and stir at room temperature for 3 h to obtain product m3; mix product m1 and anhydrous ethanol and ultrasonically disperse for 40 min, purge with nitrogen, heat to 55℃, add 4-dimethylaminopyridine and product m3, and stir for 9.5 h to obtain product m4; the molar ratio of product m2, ethyl acetate, and m-chloroperoxybenzoic acid is 3.5 g: 160 mL: 0.65 g; the molar ratio of product m1, anhydrous ethanol, 4-dimethylaminopyridine, and product m3 is 5 g: 190 mL; 1.0 g: 2 g; Step M3: Nano-iron oxide (supplier: Hangzhou Jiuli Biomaterials Co., Ltd., specification 200nm) and ethanol were mixed and ultrasonically dispersed for 45 min. Hydrolysate was added, reflux was started, and the temperature was raised to 75℃. The mixture was stirred under reflux for 5.5 h. After centrifugation and washing, the mixture was vacuum dried at 65℃ to obtain product m5. Product m4, product m5, ethyl acetate, and DMF were mixed and ultrasonically dispersed for 35 min. Triethylamine was added, and the mixture was stirred under reflux at 90℃ for 6.5 h to obtain product m6. Product m6, epichlorohydrin, and DMSO were mixed and ultrasonically dispersed for 55 min. Alkali solution and tetraethylammonium bromide were added, and the mixture was heated to 60℃ and stirred for 7.5 h to obtain modified nano-calcium oxide. Nano-iron oxide, The ratio of ethanol to hydrolysate was 6g:110mL:15mL; the hydrolysate was obtained by mixing 3-glycidyl etheroxypropyltriethoxysilane, ethanol, and deionized water in a ratio of 15g:25mL:7mL, and then stirring at 50℃ and pH 5 for 1.5h; the volume fraction of ethanol was 95%; the ratio of product m4, product m5, ethyl acetate, DMF, and triethylamine was 7g:3g:110mL:170mL:35mL; the ratio of product m6, epichlorohydrin, DMSO, alkali solution, and tetraethylammonium bromide was 12g:6.5g:290mL:10mL:1.2g; the alkali solution was a 45% potassium hydroxide solution. Example

[0013] A modified lignin, the preparation of which includes the following steps: Step N1: Mix lignin (supplier: Hubei Langbowan Biomedical Co., Ltd., specification 1kg), anhydrous DMSO, and potassium carbonate solution, purge with nitrogen, stir for 1 hour, add 4-chloromethylstyrene and hydroquinone, heat to 55℃, stir for 16 hours, cool with an ice-water bath, and post-process to obtain product n1; Under a nitrogen atmosphere, mix product n1 and 1,4-dioxane and stir for 30 minutes, add sodium bicarbonate solution and tetra-n-butylammonium bromide, stir and cool to 0℃, add solution a dropwise, heat to 25℃, stir for 8.5 hours to obtain product n2; lignin, The ratio of anhydrous DMSO, potassium carbonate solution, 4-chloromethylstyrene, and hydroquinone was 10g:80mL:28mL:20g:0.08g; the mass fraction of potassium carbonate solution was 50%. The ratio of product n1, 1,4-dioxane, sodium bicarbonate solution, tetrabutylammonium bromide, and solution a was 15g:80mL:7mL:1.8g:24mL; the mass fraction of sodium bicarbonate solution was 40%. Solution a was obtained by mixing m-chloroperoxybenzoic acid and 1,4-dioxane at a ratio of 8.8g:18mL, stirring and mixing at 40℃, and then cooling. Step N2: Tributylphosphine and anhydrous THF are mixed, and solution b is added dropwise with stirring. Reflux is started, and the mixture is heated to 90°C and stirred under reflux for 12 hours. After cooling to room temperature, the mixture is filtered, washed with ether, and dried under vacuum at 40°C to obtain product n3. Product n3 and DMF are mixed, nitrogen gas is introduced, and the temperature is raised to 50°C. Pyridine and product n2 are added, and the mixture is stirred for 9 hours to obtain product n4. The ratio of tributylphosphine, anhydrous THF, and solution b is 10.5 g: 25 mL: 30 mL. Solution b is obtained by mixing 4-bromobutyric acid and anhydrous THF in a ratio of 9 g: 20 mL and stirring at 45°C for 25 minutes. The ratio of product n3, DMF, pyridine, and product n2 is 21 g: 45 mL: 0.8 g: 18 g. Step N3: Potassium 2-amino-5-nitrobenzoate, epichlorohydrin, tetrabutylammonium chloride, and DMF are mixed, heated to 100°C, and stirred under reflux for 4 hours. After cooling to room temperature, sodium hydroxide solution is added, and the mixture is stirred for 6 hours to obtain product n5. Product n5, product n4, DMAC, and acetonitrile are mixed and stirred for 40 minutes. N,N-dimethylbutylamine is added, and the mixture is stirred under reflux at 90°C for 7.5 hours to obtain product n6. Product n6, DMSO, and methanol are mixed and stirred for 40 minutes. Sodium hydrosulfite is added, and the mixture is heated to 50°C and stirred for 5 hours to obtain... Modified lignin; the ratio of potassium 2-amino-5-nitrobenzoate, epichlorohydrin, tetrabutylammonium chloride, DMF, and sodium hydroxide solution was 11.5g:10g:0.8g:55mL:15mL; the mass fraction of sodium hydroxide solution was 50%; the ratio of product n5, product n4, DMAC, acetonitrile, and N,N-dimethylbutylamine was 22.5g:40.5g:110mL:45mL:2.5g; the ratio of product n6, DMSO, methanol, and sodium hydrosulfite was 35g:150mL:20mL:10g. Example

[0014] A modified lignin, the preparation of which includes the following steps: Step N1: Mix lignin (supplier: Hubei Langbowan Biomedical Co., Ltd., specification 1kg), anhydrous DMSO, and potassium carbonate solution, purge with nitrogen, stir for 1.1h, add 4-chloromethylstyrene and hydroquinone, heat to 60℃, stir for 16.5h, cool with an ice-water bath, and post-process to obtain product n1; Under a nitrogen atmosphere, mix product n1 and 1,4-dioxane and stir for 35min, add sodium bicarbonate solution and tetra-n-butylammonium bromide, stir and cool to 0℃, add solution a dropwise, heat to 28℃, stir for 8.8h to obtain product n2; lignin The ratio of anhydrous DMSO, potassium carbonate solution, 4-chloromethylstyrene, and hydroquinone was 10.5 g: 90 mL: 30 mL: 21 g: 0.10 g; the mass fraction of potassium carbonate solution was 53%; the ratio of product n1, 1,4-dioxane, sodium bicarbonate solution, tetrabutylammonium bromide, and solution a was 16 g: 85 mL: 8 mL: 1.9 g: 25 mL; the mass fraction of sodium bicarbonate solution was 43%; solution a was obtained by mixing m-chloroperoxybenzoic acid and 1,4-dioxane at a ratio of 9.0 g: 19 mL, stirring and mixing at 43 °C, and then cooling. Step N2: Tributylphosphine and anhydrous THF were mixed, and solution b was added dropwise with stirring. Reflux was started, and the mixture was heated to 93°C and stirred under reflux for 12.5 h. After cooling to room temperature, the mixture was filtered, washed with ether, and dried under vacuum at 43°C to obtain product n3. Product n3 and DMF were mixed, nitrogen gas was introduced, and the temperature was raised to 53°C. Pyridine and product n2 were added, and the mixture was stirred for 9.3 h to obtain product n4. The ratio of tributylphosphine, anhydrous THF, and solution b was 10.8 g: 28 mL: 33 mL. Solution b was obtained by mixing 4-bromobutyric acid and anhydrous THF in a ratio of 9.3 g: 23 mL and stirring at 48°C for 28 min. The ratio of product n3, DMF, pyridine, and product n2 was 21.5 g: 48 mL: 1.0 g: 18.5 g. Step N3: Potassium 2-amino-5-nitrobenzoate, epichlorohydrin, tetrabutylammonium chloride, and DMF are mixed, heated to 103°C, and stirred under reflux for 4.3 h. After cooling to room temperature, sodium hydroxide solution is added, and the mixture is stirred for 6.3 h to obtain product n5. Product n5, product n4, DMAC, and acetonitrile are mixed and stirred for 43 min. N,N-dimethylbutylamine is added, and the mixture is stirred under reflux at 93°C for 7.8 h to obtain product n6. Product n6, DMSO, and methanol are mixed and stirred for 45 min. Sodium hydrosulfite is added, and the mixture is heated to 55°C and stirred for 5.5 h. Modified lignin was obtained; the ratio of potassium 2-amino-5-nitrobenzoate, epichlorohydrin, tetrabutylammonium chloride, DMF, and sodium hydroxide solution was 11.8 g: 10.3 g: 0.9 g: 58 mL: 18 mL; the mass fraction of sodium hydroxide solution was 53%; the ratio of product n5, product n4, DMAC, acetonitrile, and N,N-dimethylbutylamine was 23.0 g: 41 g: 115 mL: 50 mL: 3.0 g; the ratio of product n6, DMSO, methanol, and sodium hydrosulfite was 38 g: 155 mL: 23 mL: 13 g. Example

[0015] A modified lignin, the preparation of which includes the following steps: Step N1: Mix lignin (supplier: Hubei Langbowan Biomedical Co., Ltd., specification 1kg), anhydrous DMSO, and potassium carbonate solution, purge with nitrogen, stir for 1.2h, add 4-chloromethylstyrene and hydroquinone, heat to 65℃, stir for 17h, cool with an ice-water bath, and post-process to obtain product n1; Under a nitrogen atmosphere, mix product n1 and 1,4-dioxane and stir for 40min, add sodium bicarbonate solution and tetra-n-butylammonium bromide, stir and cool to 0℃, add solution a dropwise, heat to 30℃, stir for 9h to obtain product n2; lignin, The ratio of anhydrous DMSO, potassium carbonate solution, 4-chloromethylstyrene, and hydroquinone was 11 g: 100 mL: 32 mL: 22 g: 0.12 g; the mass fraction of potassium carbonate solution was 55%. The ratio of product n1, 1,4-dioxane, sodium bicarbonate solution, tetrabutylammonium bromide, and solution a was 17 g: 90 mL: 9 mL: 2 g: 26 mL; the mass fraction of sodium bicarbonate solution was 45%. Solution a was obtained by mixing m-chloroperoxybenzoic acid and 1,4-dioxane at a ratio of 9.2 g: 20 mL, stirring and mixing at 45 °C, and then cooling. Step N2: Tributylphosphine and anhydrous THF were mixed, and solution b was added dropwise with stirring. Reflux was started, and the mixture was heated to 95°C and stirred under reflux for 13 hours. After cooling to room temperature, the mixture was filtered, washed with ether, and dried under vacuum at 45°C to obtain product n3. Product n3 and DMF were mixed, nitrogen gas was introduced, and the temperature was raised to 55°C. Pyridine and product n2 were added, and the mixture was stirred for 9.5 hours to obtain product n4. The ratio of tributylphosphine, anhydrous THF, and solution b was 11 g: 30 mL: 35 mL. Solution b was obtained by mixing 4-bromobutyric acid and anhydrous THF in a ratio of 9.5 g: 25 mL and stirring at 50°C for 30 minutes. The ratio of product n3, DMF, pyridine, and product n2 was 22 g: 50 mL: 1.2 g: 19 g. Step N3: Potassium 2-amino-5-nitrobenzene, epichlorohydrin, tetrabutylammonium chloride, and DMF are mixed, heated to 105°C, and stirred under reflux for 4.5 h. After cooling to room temperature, sodium hydroxide solution is added, and the mixture is stirred for 6.5 h to obtain product n5. Product n5, product n4, DMAC, and acetonitrile are mixed and stirred for 45 min. N,N-dimethylbutylamine is added, and the mixture is stirred under reflux at 95°C for 8 h to obtain product n6. Product n6, DMSO, and methanol are mixed and stirred for 50 min. Sodium hydrosulfite is added, and the mixture is heated to 60°C and stirred for 6 h. Modified lignin was obtained; the ratio of potassium 2-amino-5-nitrobenzoate, epichlorohydrin, tetrabutylammonium chloride, DMF, and sodium hydroxide solution was 12g:10.5g:1g:60mL:20mL; the mass fraction of sodium hydroxide solution was 55%; the ratio of product n5, product n4, DMAC, acetonitrile, and N,N-dimethylbutylamine was 23.5g:41.5g:120mL:55mL:3.5g; the ratio of product n6, DMSO, methanol, and sodium hydrosulfite was 40g:160mL:25mL:15g. Example

[0016] A composite flocculant based on nano-calcium oxide comprises the following raw materials in parts by weight: 10 parts modified nano-calcium oxide, 40 parts polyaluminum chloride, 25 parts modified lignin, 150 parts deionized water, and 20 parts anhydrous ethanol. The preparation method of the composite flocculant based on nano-calcium oxide includes the following steps: The modified nano-calcium oxide obtained in Example 1, polyaluminum chloride, modified lignin obtained in Example 4, deionized water, and anhydrous ethanol were mixed and ultrasonically dispersed for 1 hour, with the pH controlled at 6.6. The mixture was stirred and reacted at 45°C for 2 hours, centrifuged, filtered, vacuum dried at 70°C, pulverized, and passed through a 100-mesh sieve to obtain a composite flocculant based on nano-calcium oxide. Example

[0017] A composite flocculant based on nano-calcium oxide comprises the following raw materials in parts by weight: 15 parts modified nano-calcium oxide, 45 parts polyaluminum chloride, 30 parts modified lignin, 155 parts deionized water, and 25 parts anhydrous ethanol. The preparation method of the composite flocculant based on nano-calcium oxide includes the following steps: The modified nano-calcium oxide obtained in Example 2, polyaluminum chloride, modified lignin obtained in Example 5, deionized water, and anhydrous ethanol were mixed and ultrasonically dispersed for 1.3 h, with the pH controlled at 6.8. The mixture was stirred and reacted at 50 °C for 2.3 h, centrifuged, filtered, vacuum dried at 75 °C, pulverized, and passed through a 150-mesh sieve to obtain a composite flocculant based on nano-calcium oxide. Example

[0018] A composite flocculant based on nano-calcium oxide comprises the following raw materials in parts by weight: 20 parts modified nano-calcium oxide, 50 parts polyaluminum chloride, 35 parts modified lignin, 160 parts deionized water, and 30 parts anhydrous ethanol. The preparation method of the composite flocculant based on nano-calcium oxide includes the following steps: The modified nano-calcium oxide obtained in Example 3, polyaluminum chloride, modified lignin obtained in Example 6, deionized water, and anhydrous ethanol were mixed and ultrasonically dispersed for 1.5 h, the pH was controlled at 7, and the mixture was stirred and reacted at 55 °C for 2.5 h. After centrifugation and pressure filtration, the mixture was vacuum dried at 80 °C and then pulverized and passed through a 200-mesh sieve to obtain a composite flocculant based on nano-calcium oxide.

[0019] Comparative Example 1 Compared with Example 9, the modified nano-calcium carbonate used was replaced with product m6, and the rest was exactly the same as in Example 9, to obtain a composite flocculant.

[0020] Comparative Example 2 Compared with Example 9, the biochar used in the preparation process of modified nano-calcium carbonate was replaced with carbon nanotubes (supplier: Beijing Deco Island Gold Technology Co., Ltd., model: CNT107), and the rest was exactly the same as in Example 9, to obtain a composite flocculant.

[0021] Comparative Example 3 Compared with Example 9, the modified lignin used was replaced with product n6, and the rest was exactly the same as in Example 9, to obtain a composite flocculant.

[0022] Comparative Example 4 Compared with Example 9, the tributylphosphine used in the modified lignin preparation process was replaced with triisobutylamine, and the rest was exactly the same as in Example 9, to obtain a composite flocculant.

[0023] Comparative Example 5 Compared with Example 9, the potassium 2-amino-5-nitrobenzoate used in the modified lignin preparation process was replaced with sodium aminobenzenesulfonate, and the rest was exactly the same as in Example 9, to obtain a composite flocculant.

[0024] The composite flocculant prepared in this invention was further tested for its effectiveness, and the results are as follows.

[0025] Wastewater was collected with a turbidity of 300 NTU, a COD of 5240 mg / L, a BOD of 2735 mg / L, and a total phosphorus of 13.4 mg / L. The composite flocculants obtained in Examples 7-9 and Comparative Examples 1-5 of this invention were applied to the above wastewater treatment. The remaining amounts of turbidity, COD, BOD, and total phosphorus in the treated wastewater were measured, and the removal rate was calculated to evaluate the treatment effect of the composite flocculant on wastewater. The results are recorded in Table 1; Table 1: Test Results Example 7 Example 8 Example 9 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Turbidity removal rate (%) 96.2 95.6 96.8 92.4 91.3 92.9 93.9 92.1 COD removal rate (%) 91.1 90.5 92.2 88.1 86.7 88.9 89.6 87.8 BOD removal rate (%) 86.4 86.0 87.3 83.5 81.8 84.1 84.7 83.1 Total phosphorus removal rate (%) 69.7 69.0 71.3 67.7 65.6 67.9 68.4 67.2 According to the data in Table 1, the composite flocculant of the present invention has a good flocculation effect on wastewater and a good removal effect on turbidity, COD, BOD, and total phosphorus in wastewater. Comparing Example 9 with Comparative Example 1, it can be seen that replacing the modified nano-calcium carbonate used with product m6 weakens the cross-linking between the hydroxyl groups in product m6 and the amino and alcohol hydroxyl groups in the modified lignin, resulting in a worse flocculation effect of the composite flocculant and a worse removal effect on turbidity, COD, BOD, and total phosphorus in wastewater. Comparing Example 9 with Comparative Example 2, it can be seen that replacing the biochar in the preparation process of the modified nano-calcium carbonate used with carbon nanotubes significantly worsens the flocculation effect of the composite flocculant and a significantly worse removal effect on turbidity, COD, BOD, and total phosphorus in wastewater. Comparing Example 9 with Comparative Example 3, it can be seen that replacing the modified lignin used with product n6 weakens the cross-linking between the nitro and alcohol hydroxyl groups in product n6 and the epoxy groups in the modified nano-calcium carbonate, resulting in a poorer flocculation effect of the composite flocculant and a worse removal effect on turbidity, COD, BOD, and total phosphorus in wastewater. Comparing Example 9 with Comparative Example 4, it can be seen that replacing tributylphosphine in the modified lignin preparation process with triisobutylamine weakens the effect on increasing the charge density of the modified lignin, resulting in a worse flocculation effect of the composite flocculant. Comparing Example 9 with Comparative Example 5, it can be seen that replacing potassium 2-amino-5-nitrobenzoate in the modified lignin preparation process with sodium aminobenzenesulfonate worsens the flocculation effect of the composite flocculant.

[0026] The above description is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A composite flocculant based on nano calcium oxide, characterized in that: The modified nano calcium oxide, the polyaluminum chloride, the modified lignin, the deionized water and the anhydrous ethanol are mixed to obtain the modified nano calcium oxide composite flocculating agent. The modified nano calcium oxide is prepared by the following steps: Step M1: the biochar and the oxidant are mixed and ultrasonically dispersed, then stirred and reacted under heating, washed with water until neutral, and dried to obtain product m1; the nano calcium oxide, the fatty acid and the ethanol are mixed, ultrasonically dispersed, centrifuged, washed and dried to obtain product m2; Step M2: the product m2 and the ethyl acetate are mixed and ultrasonically dispersed, then the peroxy acid is added, and stirred and reacted at room temperature to obtain product m3; the product m1 and the anhydrous ethanol are mixed and ultrasonically dispersed, then the protective gas is introduced, heated, and then the 4-dimethylaminopyridine and the product m3 are added, and stirred and reacted to obtain product m4; Step M3: the nano ferriferrous oxide and the ethanol are mixed and ultrasonically dispersed, then the hydrolysis solution is added, and stirred and reacted under heating and reflux, centrifuged, washed and vacuum dried to obtain product m5; the product m4, the product m5, the ethyl acetate and the DMF are mixed and ultrasonically dispersed, then the triethylamine is added, and stirred and reacted under heating and reflux to obtain product m6; the product m6, the epichlorohydrin and the DMSO are mixed and ultrasonically dispersed, then the lye and the tetraethylammonium bromide are added, and stirred and reacted under heating to obtain the modified nano calcium oxide.

2. A composite flocculant based on nano calcium oxide according to claim 1, characterized in that: In step M1, the fatty acid is oleic acid.

3. A composite flocculants based on nano calcium oxide as claimed in claim 1, wherein: In step M3, the hydrolysis solution is prepared by mixing 3-glycidyloxypropyl triethoxysilane, the ethanol and the deionized water in a ratio of 14.5-15g:23-25mL:5-7mL, and then stirring at a temperature of 40-50℃ and a pH of 4.5-5 for 1-1.5h.

4. A composite flocculants based on nano calcium oxide as claimed in claim 1, wherein: The modified lignin is prepared by the following steps: Step N1: the lignin, the anhydrous DMSO and the potassium carbonate solution are mixed, the protective gas is introduced, stirred, then the halogenated styrene and the hydroquinone are added, and stirred and reacted under heating, cooled with an ice water bath, and then post-treated to obtain product n1; in the protective gas atmosphere, the product n1 and the 1,4-dioxane are mixed and stirred, then the sodium bicarbonate solution and the tetra-n-butylammonium bromide are added, stirred, cooled, the solution a is added dropwise, and stirred and reacted under heating to obtain product n2; Step N2: the tertiary phosphine and the anhydrous THF are mixed, the solution b is added dropwise under stirring, heated and stirred under reflux, then cooled to room temperature, filtered, washed with diethyl ether, and vacuum dried to obtain product n3; the product n3 and the DMF are mixed, the protective gas is introduced, heated, then the pyridine and the product n2 are added, and stirred and reacted to obtain product n4; Step N3: the potassium aminobenzoate, the epichlorohydrin, the tetrabutylammonium chloride and the DMF are mixed, stirred and reacted under heating and reflux, cooled to room temperature, the sodium hydroxide solution is added, and stirred to obtain product n5; the product n5, the product n4, the DMAC and the acetonitrile are mixed and stirred, then the N,N-dimethylbutylamine is added, and stirred and reacted under heating and reflux to obtain product n6; the product n6, the DMSO and the methanol are mixed and stirred, then the safety powder is added, and stirred and reacted under heating to obtain the modified lignin.

5. A composite flocculants based on nano calcium oxide as claimed in claim 4, wherein: In step N1, the halogenated styrene is 4-chloromethylstyrene.

6. A composite flocculants based on nano calcium oxide as claimed in claim 4, wherein: In step N1, the solution a is prepared by mixing m-chloroperbenzoic acid and 1,4-dioxane in a ratio of 8.8-9.2 g: 18-20 mL, stirring at 40-45 ℃, and then cooling to obtain.

7. A composite flocculants based on nano calcium oxide as claimed in claim 4, wherein: In step N2, the tertiary phosphine is tributylphosphine.

8. A composite flocculants based on nano calcium oxide as claimed in claim 4, wherein: In step N2, the solution b is prepared by mixing halogenated aliphatic acid and anhydrous THF in a ratio of 9-9.5 g: 20-25 mL, stirring at 45-50 ℃ for 25-30 min to obtain; the halogenated aliphatic acid is 4-bromobutyric acid.

9. A composite flocculants based on nano calcium oxide as claimed in claim 4, wherein: In step N3, the potassium aminobenzoate is potassium 2-amino-5-nitrobenzoate.

10. A method of preparing the nanocalcium oxide based composite flocculants according to any one of claims 1 to 9, characterized by: The method comprises the following steps: The modified nano calcium oxide, polyaluminum chloride, modified lignin, deionized water, and anhydrous ethanol are mixed and ultrasonically dispersed for 1-1.5 h, the pH is controlled to be 6.5-7, and stirring reaction is carried out at 45-55 ℃ for 2-2.5 h; then, centrifugation, pressure filtration, drying, crushing, and sieving through a 100-200 mesh sieve are carried out to obtain a composite flocculant based on nano calcium oxide.