Preparation method of polyaluminum chloride flocculant

Abstract

The invention discloses a preparation method of a polyaluminum chloride flocculating agent, and relates to the technical field of water purifying agents. Comprising the following steps: 1, adding attapulgite into a sodium sulfide solution, and carrying out hydrothermal reaction to obtain modified attapulgite; compounding the modified attapulgite, sodium alginate and sodium metaaluminate to obtain a stabilizer; 2, sequentially adding aluminum hydroxide, hydrochloric acid and purified water into the enamel reaction kettle, and carrying out primary reaction; discharging the reacted solution into an adjusting kettle, adding calcium aluminate powder and a stabilizer, carrying out secondary reaction, and carrying out filter pressing to obtain PACV liquid; 3, cationic starch is added into the PACV liquid, heating and stirring are conducted, spray drying is conducted, and the polyaluminum chloride flocculant is obtained. According to the scheme, a compound stabilizer containing modified attapulgite and sodium alginate is introduced, so that the salinity of the polyaluminum chloride is effectively improved, and the flocculation performance of the polyaluminum chloride is enhanced; and cationic starch is further introduced as a coagulation aid subsequently, so that the bridging performance is promoted, and the water purification effect is enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of water purifiers, in particular to a method for preparing a polyaluminium chloride flocculant. Background Art

[0002] In recent years, the acceleration of industrialization has made the problem of industrial wastewater discharge increasingly prominent; the increasing amount of wastewater discharge has led to the deterioration of rivers, groundwater and other environments; therefore, the purification of industrial wastewater or polluted river water is of great significance to the protection of the ecological environment. At present, flocculation is the most convenient and rapid way to purify polluted water resources; and flocculants are key chemicals; among them, polyaluminum chloride (PAC) is an efficient and economical flocculant, which plays an important role in water treatment.

[0003] In the prior art, polyaluminium chloride has the following main disadvantages: first, the degree of polymerization of polyaluminium chloride obtained by the prior preparation process is insufficient, and the basicity is low (generally 40-50), which makes the flocculation bridging ability weak, the flocculation effect is poor, and the deturbidity effect is limited; second, the single prepared polyaluminium chloride is used as a flocculant, and it only produces flocculation through the negative charge of OH-, and its adsorption and flocculation ability for some ionic pollutants is limited, resulting in limited removal rate of chemical oxygen demand (COD) in sewage when it purifies sewage, and the water purification effect needs to be further improved.

[0004] In summary, it is of great significance to solve the above problems and prepare a polyaluminium chloride flocculant with excellent water purification effect. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a polyaluminium chloride flocculant to solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for preparing a polyaluminium chloride flocculant comprises the following steps: Step 1: adding attapulgite to a sodium sulfide solution, hydrothermally reacting at 180-200° C. for 20-24 hours, cooling, washing, and freeze-drying to obtain modified attapulgite; compounding the modified attapulgite, sodium alginate, and sodium aluminate to obtain a stabilizer; Step 2: Add aluminum hydroxide, hydrochloric acid and purified water to an enamel reactor in sequence for a primary reaction; discharge the reacted solution into a regulating kettle, add calcium aluminate powder and a stabilizer, perform a secondary reaction, and filter press to obtain PACV liquid; Step 3: Add cationic starch to the PACV liquid, heat and stir, and spray dry to obtain a polyaluminium chloride flocculant.

[0007] More optimally, the primary reaction includes one of a high temperature and high pressure reaction and a normal pressure reaction; the process parameters of the high temperature and high pressure reaction are: temperature of 135~140°C, pressure of 3~5 kg; the process parameters of the normal pressure reaction are: temperature of 95~105°C; the process parameters of the secondary reaction are: normal pressure, temperature of 70~100°C.

[0008] More optimally, the raw materials of the polyaluminum chloride flocculant include the following components: by weight, 10 to 15 parts of aluminum hydroxide, 15 to 20 parts of hydrochloric acid, 15 to 20 parts of purified water, 6 to 10 parts of calcium aluminate powder, 0.02 to 0.03 parts of stabilizer, and 0.03 to 0.045 parts of cationic starch.

[0009] More optimally, in the raw materials of the stabilizer, the mass ratio of modified attapulgite, sodium alginate and sodium aluminate is (4.8~7.2):(0.2~0.8):(15~22).

[0010] More optimally, in the raw material of the modified attapulgite, the concentration of the sodium sulfide solution is 0.2-0.3 mol / L; the solid-liquid ratio of the attapulgite to the sodium sulfide solution is 0.1 g:100 mL.

[0011] More optimally, the preparation method of the cationic starch is: S1-1: Add bis(6-aminohexyl)amine to purified water, add sodium hydroxide aqueous solution and epichlorohydrin dropwise under ice bath; raise the temperature to 45-50°C, stir for 2-3 hours, cool, wash and dry to obtain cationic polyamine; S1-2: Add rice starch and sodium hydroxide to purified water in sequence, stir at 40-50°C for 1-2 hours; add trimethylammonium glycidyl chloride and allyl glycidyl ether, react for 2-3 hours; add cationic polyamine, heat to 65-70°C, react for 3-5 hours, cool, neutralize with acid to pH=7±0.2, wash, and freeze-dry to obtain a primary product of cationic starch; S1-3: Add the cationic starch primary product, mercaptosilane coupling agent and azobisisobutyronitrile to dimethyl sulfoxide in sequence, irradiate with ultraviolet light for 1 to 2 hours, wash and freeze-dry to obtain cationic starch.

[0012] More optimally, the raw materials of the cationic polyamine include the following components: the molar ratio of bis(6-aminohexyl)amine to epichlorohydrin is 12:11 by weight; the concentration of the sodium hydroxide aqueous solution is 5-10wt%; the mass of sodium hydroxide in the sodium hydroxide aqueous solution accounts for 4-5wt% of the bis(6-aminohexyl)amine.

[0013] More optimally, the raw materials of the cationic starch primary product include the following components: by weight, 5 parts of rice starch, 0.8~1 parts of sodium hydroxide, 2~2.5 parts of trimethylammonium chloride glycidyl, 0.3~0.6 parts of allyl glycidyl ether, and 1~1.5 parts of cationic polyamine; in the raw materials of the cationic starch, the mass ratio of the cationic starch primary product to the mercaptosilane coupling agent is 10:0.2~0.3.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) In order to increase the degree of polymerization of polyaluminium chloride, the scheme uses common sodium aluminate as the main stabilizer, and mixes modified attapulgite and sodium alginate in a specific ratio; thereby effectively increasing the degree of polymerization of polyaluminium chloride and effectively increasing its basicity to more than 85%. Among them, the modified attapulgite is prepared by adding attapulgite to sodium sulfide solution for hydrothermal reaction. In this process, sodium sulfide promotes the dissociation and recombination of Si-O-Si bonds in attapulgite, produces silanol groups, and dopes S 2- 、SO4 2- anion; and the introduction of the anion can promote the polymerization of aluminum hydroxide and effectively increase its basicity. And there is a certain interaction between the contained Si and Al-OH, which promotes the stability of polymerization. At the same time, in order to ensure the stability of polymerization, sodium alginate is further compounded, which is a high-viscosity polyanion electrolyte, which contains carboxyl groups and interacts with the polymer, and can ensure the stability of high-basicity polyaluminum chloride through bridging and complexation. It should be noted that the introduction amount of modified attapulgite should not be too high. On the contrary, too high will affect the polymerization morphology and polymerization stability of polyaluminum chloride, which is not conducive to the degree of polymerization and the flocculation effect.

[0015] (2) In order to improve the flocculation property of polyaluminium chloride and enhance the water purification effect, the prepared polyaluminium chloride flocculant is not a single polyaluminium chloride. In the scheme, modified attapulgite is first introduced in the polymerization stage; and finally cationic starch is introduced to compound with it to obtain a polyaluminium chloride flocculant with high performance.

[0016] Among them, after the attapulgite is modified, the negative charge on the surface increases, which promotes ion adsorption and produces flocculation in coordination with polyaluminium chloride through adsorption bridging and other effects; and it can increase the density of flocs, reduce the volume of flocs, promote flocculation sedimentation, and reduce turbidity; but due to its limited introduction amount, cationic starch is further introduced to promote flocculation. Cationic starch contains a strong positive charge and can effectively flocculate negatively charged inorganic or organic substances, such as titanium dioxide, calcium carbonate and other organic or inorganic substances; and its molecular weight is relatively long, which can adsorb multiple tiny flocs, and cooperate with the modified attapulgite net to capture a large number of tiny flocs around the convolution to form larger flocs, effectively increasing the sedimentation speed and efficiency; at the same time, its overcharge neutralization, adsorption bridging and other effects can effectively improve the removal rate of COD in polluted water.

[0017] Among them, compared with common cationic starch, in this application, a large molecular weight cationic polyamine is prepared by reacting bis(6-aminohexyl)amine and epichlorohydrin, and it is grafted with starch together with trimethyl ammonium chloride of small molecular segments, and the grafting of the two is limited by the amount and order of raw material introduction, so as to maximize its flocculation. Among them, the cationic polyamine with a large molecular weight has more positive charge, which can produce more electrostatic adsorption, promote flocculation, and improve the removal rate of COD; however, the introduction of too many macromolecular segments will make the molecular weight too large, reducing its solubility and dispersibility in water; and the grafting of too many cationic polyamines with a large molecular weight will affect the contact and combination with particulate matter in polluted water, reducing the flocculation effect; there is also a situation in which some organic matter that is not completely neutralized is wrapped during the flocculation process, affecting the contact with the flocculant, thereby reducing the removal efficiency of COD; therefore, the use of trimethyl ammonium chloride of small molecular weight for co-grafting, on the basis of not reducing the dispersibility of the flocculant, synergistically provides stronger electrical neutralization ability and adsorption bridging effect, and improves the water purification effect.

[0018] In addition, in the scheme, allyl glycidyl ether is grafted onto starch at the same time, and a silane coupling agent is grafted using a click reaction, thereby enhancing the interaction between cationic starch and polyaluminum chloride, utilizing silicon-containing chain segments to effectively inhibit the hydrolysis of polyaluminum chloride, and synergistically enhancing the COD removal rate of the polyaluminum chloride flocculant together with attapulgite. DETAILED DESCRIPTION

[0019] 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 them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] It should be noted that the following parts are parts by mass, and the concentration of hydrochloric acid in the following examples is 30%; the item number of the attapulgite is YK2910, purchased from Hubei Yongkuo; the rice starch has a purity of 98%, purchased from Hubei Hengjingrui; and the remaining raw materials are commercially available.

[0021] Unless otherwise specified, in the implementation mode, the preparation process of the modified attapulgite and cationic starch is as follows: (1) Preparation of modified attapulgite: adding attapulgite to a 0.2 mol / L sodium sulfide solution with a solid-liquid ratio of 0.1:100 mL; subjecting the mixture to a hydrothermal reaction at 200° C. for 24 hours, cooling, washing, and freeze-drying to obtain modified attapulgite; (2) Preparation of cationic starch: S1-1: Weigh bis(6-aminohexyl)amine and epichlorohydrin in a molar ratio of 12:11, and weigh sodium hydroxide accounting for 5 wt% of the mass of bis(6-aminohexyl)amine; add bis(6-aminohexyl)amine into purified water to obtain a 15 wt% mixed solution, and add 5 wt% sodium hydroxide aqueous solution and epichlorohydrin dropwise in sequence under an ice bath; heat to 50°C, stir for 2 hours, cool, wash, and dry to obtain a cationic polyamine; S1-2: Add 5 parts of rice starch and 1 part of sodium hydroxide to purified water, stir at 50°C for 2 hours; add 2.3 parts of trimethylammonium glycidyl chloride and 0.5 parts of allyl glycidyl ether, stir and react for 2 hours; add 1.2 parts of cationic polyamine, heat to 70°C and react for 3 hours, cool, neutralize with acid to neutral, wash, and freeze-dry to obtain a cationic starch primary product; S1-3: The cationic starch primary product and mercaptosilane coupling agent KH-580 in a mass ratio of 10:0.25 are added to dimethyl sulfoxide in sequence, azobisisobutyronitrile is added as an initiator (the introduced amount accounts for 0.2wt% of the cationic starch primary product), ultraviolet light is applied for 2 hours, washed, and freeze-dried to obtain cationic starch.

[0022] Embodiment 1: A method for preparing a polyaluminium chloride flocculant, comprising the following steps: Step 1: uniformly mix the modified attapulgite, sodium alginate and sodium aluminate in a mass ratio of 6.5:0.5:21 to obtain a stabilizer; Step 2: 12.5 parts of aluminum hydroxide, 16 parts of hydrochloric acid, and 17 parts of purified water are sequentially added to an enameled reactor, and reacted at a temperature of 140° C. under a pressure of 4 kg for 3 hours; the reacted solution is discharged into a regulating kettle, 8 parts of calcium aluminate powder and 0.028 parts of a stabilizer are added, and reacted at 80° C. under normal pressure for 3 hours, and filtered to obtain PACV liquid; Step 3: Add 0.04 parts of cationic starch to the PACV liquid, heat and stir at 70°C for 1 hour, and spray dry to obtain a polyaluminum chloride flocculant.

[0023] Embodiment 2: A method for preparing a polyaluminium chloride flocculant, comprising the following steps: Step 1: uniformly mix the modified attapulgite, sodium alginate and sodium aluminate in a mass ratio of 4.8:0.2:15 to obtain a stabilizer; Step 2: 10 parts of aluminum hydroxide, 15 parts of hydrochloric acid, and 15 parts of purified water are sequentially added to an enameled reactor, and reacted at a temperature of 140° C. under a pressure of 4 kg for 3 hours; the reacted solution is discharged into a regulating kettle, 6 parts of calcium aluminate powder and 0.02 parts of a stabilizer are added, and reacted at 80° C. under normal pressure for 3 hours, and filtered to obtain PACV liquid; Step 3: Add 0.03 parts of cationic starch to the PACV liquid, heat and stir at 70°C for 1 hour, and spray dry to obtain a polyaluminum chloride flocculant.

[0024] Embodiment 3: A method for preparing a polyaluminium chloride flocculant, comprising the following steps: Step 1: uniformly mix the modified attapulgite, sodium alginate and sodium aluminate in a mass ratio of 7.2:0.8:22 to obtain a stabilizer; Step 2: 15 parts of aluminum hydroxide, 20 parts of hydrochloric acid, and 20 parts of purified water are sequentially added to an enameled reactor, and reacted at a temperature of 140° C. under a pressure of 4 kg for 3 hours; the reacted solution is discharged into a regulating kettle, 10 parts of calcium aluminate powder and 0.03 parts of a stabilizer are added, and reacted at 80° C. under normal pressure for 3 hours, and filtered to obtain PACV liquid; Step 3: Add 0.045 parts of cationic starch to the PACV liquid, heat and stir at 70°C for 1 hour, and spray dry to obtain a polyaluminum chloride flocculant.

[0025] Comparative Example 1: Based on Example 1, a non-modified conventional attapulgite was used; the specific process is as follows: Step 1: Evenly mix attapulgite (purchased directly), sodium alginate, and sodium aluminate in a mass ratio of 6.5:0.5:21 to obtain a stabilizer; Step 2: 12.5 parts of aluminum hydroxide, 16 parts of hydrochloric acid, and 17 parts of purified water are sequentially added to an enameled reactor, and reacted at a temperature of 140° C. under a pressure of 4 kg for 3 hours; the reacted solution is discharged into a regulating kettle, 8 parts of calcium aluminate powder and 0.028 parts of a stabilizer are added, and reacted at 80° C. under normal pressure for 3 hours, and filtered to obtain PACV liquid; Step 3: Add 0.04 parts of cationic starch to the PACV liquid, heat and stir at 70°C for 1 hour, and spray dry to obtain a polyaluminum chloride flocculant.

[0026] Comparative Example 2: Based on Example 1, a modified attapulgite with an excessively high content was introduced; the specific process is as follows: Step 1: uniformly mix the modified attapulgite, sodium alginate and sodium aluminate in a mass ratio of 10.5:0.5:17 to obtain a stabilizer; Step 2: 12.5 parts of aluminum hydroxide, 16 parts of hydrochloric acid, and 17 parts of purified water are sequentially added to an enameled reactor, and reacted at a temperature of 140° C. under a pressure of 4 kg for 3 hours; the reacted solution is discharged into a regulating kettle, 8 parts of calcium aluminate powder and 0.028 parts of a stabilizer are added, and reacted at 80° C. under normal pressure for 3 hours, and filtered to obtain PACV liquid; Step 3: Add 0.04 parts of cationic starch to the PACV liquid, heat and stir at 70°C for 1 hour, and spray dry to obtain a polyaluminum chloride flocculant.

[0027] Comparative Example 3: Based on Example 1, cationic starch is not introduced; the specific process is as follows: Step 1: uniformly mix the modified attapulgite, sodium alginate and sodium aluminate in a mass ratio of 6.5:0.5:21 to obtain a stabilizer; Step 2: 12.5 parts of aluminum hydroxide, 16 parts of hydrochloric acid, and 17 parts of purified water are sequentially added to an enameled reactor, and reacted at a temperature of 140° C. under a pressure of 4 kg for 3 hours; the reacted solution is discharged into a regulating kettle, 8 parts of calcium aluminate powder and 0.028 parts of a stabilizer are added, and reacted at 80° C. under normal pressure for 3 hours, and filtered to obtain PACV liquid; Step 3: spray-dry the PACV liquid to obtain a polyaluminium chloride flocculant.

[0028] Comparative Example 4: Based on Example 1, in the preparation process of cationic starch, cationic polyamine was used for grafting, and small molecule glycidyl trimethyl ammonium chloride was not grafted; the specific process is as follows: Pre-preparation: S1-1: Weigh bis(6-aminohexyl)amine and epichlorohydrin in a molar ratio of 12:11, and weigh sodium hydroxide accounting for 5 wt% of the mass of bis(6-aminohexyl)amine; add bis(6-aminohexyl)amine into purified water to obtain a 15 wt% mixed solution, and sequentially add a 5 wt% sodium hydroxide aqueous solution and epichlorohydrin dropwise under an ice bath; heat to 50° C., stir for 2 hours, cool, wash, and dry to obtain a cationic polyamine; S1-2: Add 5 parts of rice starch and 1 part of sodium hydroxide to purified water, stir at 50°C for 2 hours; add 0.5 parts of allyl glycidyl ether, stir and react for 1 hour; add 3.5 parts of cationic polyamine, heat to 70°C and react for 3 hours, cool, neutralize with acid to neutral, wash, and freeze-dry to obtain a cationic starch primary product; S1-3: adding a cationic starch primary product and a mercaptosilane coupling agent in a mass ratio of 10:0.25 to dimethyl sulfoxide in sequence, adding azobisisobutyronitrile as an initiator (the amount introduced accounts for 0.2wt% of the cationic starch primary product), irradiating with ultraviolet light for 2 hours, washing, and freeze-drying to obtain cationic starch; Step 1: uniformly mix the modified attapulgite, sodium alginate and sodium aluminate in a mass ratio of 6.5:0.5:21 to obtain a stabilizer; Step 2: 12.5 parts of aluminum hydroxide, 16 parts of hydrochloric acid, and 17 parts of purified water are sequentially added to an enameled reactor, and reacted at a temperature of 140° C. under a pressure of 4 kg for 3 hours; the reacted solution is discharged into a regulating kettle, 8 parts of calcium aluminate powder and 0.028 parts of a stabilizer are added, and reacted at 80° C. under normal pressure for 3 hours, and filtered to obtain PACV liquid; Step 3: Add 0.04 parts of cationic starch to the PACV liquid, heat and stir at 70°C for 1 hour, and spray dry to obtain a polyaluminum chloride flocculant.

[0029] Comparative Example 5: Based on Example 1, during the preparation of cationic starch, silicon chains were not grafted, and the specific process was as follows: Pre-preparation: S1-1: Weigh bis(6-aminohexyl)amine and epichlorohydrin in a molar ratio of 12:11, and weigh sodium hydroxide accounting for 5 wt% of the mass of bis(6-aminohexyl)amine; add bis(6-aminohexyl)amine into purified water to obtain a 15 wt% mixed solution, and sequentially add a 5 wt% sodium hydroxide aqueous solution and epichlorohydrin dropwise under an ice bath; heat to 50° C., stir for 2 hours, cool, wash, and dry to obtain a cationic polyamine; S1-2: Add 5 parts of rice starch and 1 part of sodium hydroxide to purified water, stir at 50°C for 2 hours; add 2.3 parts of trimethylammonium glycidyl chloride, stir and react for 2 hours; add 1.2 parts of cationic polyamine, heat to 70°C and react for 3 hours, cool, neutralize with acid to neutral, wash, and freeze-dry to obtain cationic starch; Step 1: uniformly mix the modified attapulgite, sodium alginate and sodium aluminate in a mass ratio of 6.5:0.5:21 to obtain a stabilizer; Step 2: 12.5 parts of aluminum hydroxide, 16 parts of hydrochloric acid, and 17 parts of purified water are sequentially added to an enameled reactor, and reacted at a temperature of 140° C. under a pressure of 4 kg for 3 hours; the reacted solution is discharged into a regulating kettle, 8 parts of calcium aluminate powder and 0.028 parts of a stabilizer are added, and reacted at 80° C. under normal pressure for 3 hours, and filtered to obtain PACV liquid; Step 3: Add 0.04 parts of cationic starch to the PACV liquid, heat and stir at 70°C for 1 hour, and spray dry to obtain a polyaluminum chloride flocculant.

[0030] Performance test: The polyaluminium chloride flocculants prepared in the examples and comparative examples were subjected to relevant performance tests; (1) the basicity was tested in accordance with the relevant contents of GB15892-2009; (2) the polyaluminium chloride flocculants were added to the wastewater at a dosage of 0.3wt% and flocculated at a rate of 150rpm for 2 minutes, and then left to stand for 10 minutes to test the purification effect; the relevant parameters before the wastewater treatment were: turbidity of 233.14NTU and COD content of 357.35mg / L. The results are shown in the following table: Conclusion: From the data in the above table, it can be seen that the basicity of the polyaluminum chloride flocculant is effectively enhanced by introducing modified attapulgite in this application, and the water purification effect of the flocculant is effectively enhanced by introducing cationic starch containing specific chain segments. Among them, in comparative examples 1 to 2, due to the use of unmodified conventional attapulgite and the introduction of excessively high content of modified attapulgite, the polymerization stability and polymerization morphology are affected, resulting in a decrease in basicity and a decrease in water purification effect; in comparative examples 3 to 5, due to the lack of introduction of cationic starch and the change of different grafted chain segments in the cationic starch, there are differences in their electrical neutralization ability and adsorption bridging effect, which reduces the relevant performance.

[0031] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a polyaluminium chloride flocculant, characterized in that: The following steps are involved: Step 1: adding the attapulgite into a sodium sulfide solution, hydrothermally reacting at 180-200° C. for 20-24 hours, cooling, washing, and freeze-drying to obtain a modified attapulgite; The modified attapulgite, sodium alginate and sodium aluminate are compounded to obtain a stabilizer; Step 2: Add aluminum hydroxide, hydrochloric acid and purified water to an enamel reactor in sequence for a primary reaction; discharge the reacted solution into a regulating kettle, add calcium aluminate powder and a stabilizer, perform a secondary reaction, and filter press to obtain PACV liquid; Step 3: Add cationic starch to the PACV liquid, heat and stir, and spray dry to obtain a polyaluminium chloride flocculant.

2. The method for preparing a polyaluminium chloride flocculant according to claim 1, characterized in that: The primary reaction includes one of a high-temperature and high-pressure reaction and a normal-pressure reaction; the process parameters of the high-temperature and high-pressure reaction are: temperature of 135-140°C, pressure of 3-5 kg; the process parameters of the normal-pressure reaction are: temperature of 95-105°C; the process parameters of the secondary reaction are: normal pressure, temperature of 70-100°C.

3. The method for preparing a polyaluminium chloride flocculant according to claim 1, characterized in that: The raw materials of the polyaluminium chloride flocculant include the following components: by weight, 10-15 parts of aluminium hydroxide, 15-20 parts of hydrochloric acid, 15-20 parts of purified water, 6-10 parts of calcium aluminate powder, 0.02-0.03 parts of a stabilizer, and 0.03-0.045 parts of cationic starch.

4. The method for preparing a polyaluminium chloride flocculant according to claim 1, characterized in that: Among the raw materials of the stabilizer, the mass ratio of modified attapulgite, sodium alginate and sodium aluminate is (4.8-7.2): (0.2-0.8): (15-22).

5. The method for preparing a polyaluminium chloride flocculant according to claim 1, characterized in that: In the raw material of the modified attapulgite, the concentration of the sodium sulfide solution is 0.2-0.3 mol / L; the solid-liquid ratio of the attapulgite to the sodium sulfide solution is 0.1 g:100 mL.

6. The method for preparing a polyaluminium chloride flocculant according to claim 1, characterized in that: The preparation method of the cationic starch is: S1-1: Add bis(6-aminohexyl)amine to purified water, add sodium hydroxide aqueous solution and epichlorohydrin dropwise under ice bath; raise the temperature to 45-50°C, stir for 2-3 hours, cool, wash and dry to obtain cationic polyamine; S1-2: Add rice starch and sodium hydroxide to purified water in sequence, stir at 40-50°C for 1-2 hours; add trimethylammonium glycidyl chloride and allyl glycidyl ether, react for 2-3 hours; add cationic polyamine, heat to 65-70°C, react for 3-5 hours, cool, neutralize with acid to pH=7±0.2, wash, and freeze-dry to obtain a primary product of cationic starch; S1-3: Add the cationic starch primary product, mercaptosilane coupling agent and azobisisobutyronitrile to dimethyl sulfoxide in sequence, irradiate with ultraviolet light for 1 to 2 hours, wash and freeze-dry to obtain cationic starch.

7. The method for preparing a polyaluminium chloride flocculant according to claim 6, characterized in that: The raw materials of the cationic polyamine include the following components: in terms of weight, the molar ratio of bis(6-aminohexyl)amine to epichlorohydrin is 12:11; the concentration of the sodium hydroxide aqueous solution is 5-10wt%; the mass of the sodium hydroxide in the sodium hydroxide aqueous solution accounts for 4-5wt% of the bis(6-aminohexyl)amine.

8. The method for preparing a polyaluminium chloride flocculant according to claim 6, characterized in that: The raw materials of the cationic starch primary product include the following components: by weight, 5 parts of rice starch, 0.8-1 parts of sodium hydroxide, 2-2.5 parts of glycidyl trimethylammonium chloride, 0.3-0.6 parts of allyl glycidyl ether, and 1-1.5 parts of cationic polyamine; in the raw materials of the cationic starch, the mass ratio of the cationic starch primary product to the mercaptosilane coupling agent is 10:0.2-0.

3.

9. The polyaluminium chloride flocculant prepared according to the method for preparing a polyaluminium chloride flocculant according to any one of claims 1 to 8.

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