A composite flocculant suitable for alkali-reduction wastewater treatment

Abstract

The application provides a composite flocculant suitable for alkali reduction wastewater treatment and a preparation method thereof, and relates to the technical field of wastewater treatment; the method comprises the following steps: mixing magnesite tailings and sintered red mud according to a mass ratio of 1:3 and grinding to 200 meshes, and performing ladder calcination under the protection of nitrogen to obtain a magnesite-red mud mixture; a sodium silicate solution is adjusted to a pH of 3.5 by sulfuric acid, and after stirring to form a sol, titanium tetrachloride is added to perform temperature curing to obtain a prepolymer; hydrochloric acid is added to the magnesite-red mud mixture to perform reaction, and then calcium aluminate powder, the prepolymer and konjac glucomannan phosphate are added in sequence to perform stirring reaction; calcium hydroxide suspension liquid is added to adjust the alkalinity of the system to 75-80%, and after static curing, the composite flocculant is obtained; through the multi-metal cooperation of aluminum, iron, magnesium, titanium and calcium, a four-dimensional flocculation mechanism of "electric neutralization-precipitation-net capture-bridging" is realized, and the problem of easy gelation instability of traditional polysilicate aluminum salt is solved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a composite flocculant suitable for alkali reduction wastewater treatment. Background Technology

[0002] Alkali reduction wastewater is a highly challenging wastewater generated during the deep processing of polyester textiles, characterized by its distinct features and difficulty in treatment. This wastewater originates from the sodium hydroxide reduction treatment process for polyester fabrics and contains a large amount of sodium terephthalate hydrolyzed from the fiber surface, resulting in a highly alkaline state (pH reaching 12-14). Its chemical oxygen demand (COD) is typically as high as 8000-20000 mg / L, and it also contains high concentrations of recalcitrant organic matter.

[0003] The main pollutant in wastewater, terephthalic acid, exists stably in a negatively charged colloidal form under alkaline conditions, forming a highly stable dispersion system. Traditional flocculants face multiple challenges when treating this type of wastewater: aluminum salts easily form ineffective aluminate ions (Al(OH)) in strongly alkaline environments. 4- Iron salts can form hydroxide colloids under alkaline conditions, but they have low removal efficiency for aromatic pollutants; organic polymer flocculants have problems such as high cost and residual toxicity. Summary of the Invention

[0004] The purpose of this invention is to provide a composite flocculant suitable for alkali reduction wastewater treatment, so as to at least partially solve the above-mentioned problems.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a composite flocculant suitable for alkali reduction wastewater treatment, comprising the following steps:

[0006] Magnesite tailings and sintered red mud were mixed at a mass ratio of 1:3 and ground to 200 mesh. The mixture was then subjected to step-roasting under nitrogen protection to obtain a magnesite-red mud mixture.

[0007] The pH of the sodium silicate solution was adjusted to 3.5 with sulfuric acid, and after stirring to form a sol, titanium tetrachloride was added and the mixture was heated and matured to obtain the prepolymer.

[0008] Hydrochloric acid was added to the magnesium ore-red mud mixture for reaction, and then calcium aluminate powder, prepolymer and konjac glucomannan phosphate were added in sequence and stirred for reaction.

[0009] Add calcium hydroxide suspension to adjust the alkalinity of the system to 75-80%, and obtain the composite flocculant after static aging.

[0010] Furthermore, the red mud is sintered red mud, the mass percentage of iron oxide in the red mud is 20-30%, and the mass percentage of magnesium carbonate in the magnesite tailings is 85-90%.

[0011] Furthermore, the stepped roasting includes the following steps:

[0012] Heat to 550℃ at a rate of 10℃ / min and hold for 1 hour;

[0013] The temperature was increased to 750℃ at a rate of 5℃ / min and held for 2 hours to obtain a mixture of modified red mud and activated magnesium ore products.

[0014] Furthermore, the preparation of the prepolymer includes the following steps:

[0015] Industrial sodium silicate with a film number of 3.2 was prepared into a 4% aqueous solution, and the pH was adjusted to 3.5 with sulfuric acid and stirred at room temperature for 30 min to form polysilicic acid sol.

[0016] Titanium tetrachloride was added to make the molar ratio of titanium to silicon reach 0.15:1, and then the temperature was raised to 75°C for 48 hours to obtain a blue-gray transparent gel, i.e., the prepolymer.

[0017] Furthermore, the hydrochloric acid is added to the magnesium ore-red mud mixture under the following conditions: reaction at 168-172℃ and 0.8MPa for 5 hours, followed by cooling to 100℃ and then sequentially adding calcium aluminate powder, prepolymer, and konjac glucomannan phosphate ester under stirring at 80 rpm for 2 hours.

[0018] Furthermore, calcium aluminate powder is added first to regulate and initiate the alkaline polymerization reaction, adjusting the alkalinity of the system to 45%.

[0019] Then, the prepolymer is added dropwise, and the viscosity is controlled to be less than 500 mPa·s during the dropwise addition process;

[0020] Then, konjac glucomannan phosphate is added as a selective coagulant to fully crosslink the components.

[0021] Furthermore, the calcium hydroxide suspension is added in a quantitative pulse every 10 minutes to adjust the alkalinity of the system to 75-80%.

[0022] Furthermore, the static curing conditions are static curing at 60°C for 24 hours.

[0023] On the other hand, the present invention also provides a composite flocculant suitable for alkali reduction wastewater treatment. The composite flocculant prepared according to the above preparation method includes the following components in parts by weight.

[0024] 12-18 parts calcium aluminate powder, 25-35 parts modified red mud, 8-15 parts activated magnesium ore product, 15-22 parts titanium-silicon polymer and 4-6 parts konjac glucomannan phosphate ester.

[0025] The calcium aluminate powder comprises 52-60 wt% alumina and 22-30 wt% calcium oxide, and the modified red mud comprises 20-30 wt% iron oxide.

[0026] On the other hand, the present invention also provides an application of a composite flocculant suitable for alkali reduction wastewater treatment. The composite flocculant prepared according to the above preparation method is applied in the field of wastewater treatment.

[0027] During application, the dosage of composite flocculant is 0.6-1.0 g / L. Terephthalic acid is recovered after the flocculated sludge is leached with dilute sulfuric acid.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] This invention combines the magnesium-titanium-red mud system with calcium aluminate, and achieves a four-dimensional flocculation mechanism of "electroneutralization-precipitation-encapsulation-bridging" through the multi-metal synergy of aluminum, iron, magnesium, titanium and calcium. In particular, the introduction of titanium polysilicic acid, whose stable long-chain structure is not easily dissociated in a strongly alkaline environment, solves the problem of easy gelation and instability of traditional polyaluminum silicate salts. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] This invention provides a composite flocculant suitable for alkali reduction wastewater treatment, comprising the following steps: mixing magnesite tailings and sintered red mud at a mass ratio of 1:3 and grinding to 200 mesh, and then performing step-by-step roasting under nitrogen protection to obtain a magnesite-red mud mixture;

[0032] The pH of the sodium silicate solution was adjusted to 3.5 with sulfuric acid, and after stirring to form a sol, titanium tetrachloride was added and the mixture was heated and matured to obtain the prepolymer.

[0033] Hydrochloric acid was added to the magnesium ore-red mud mixture for reaction, and then calcium aluminate powder, prepolymer and konjac glucomannan phosphate were added in sequence and stirred for reaction.

[0034] Add calcium hydroxide suspension to adjust the alkalinity of the system to 75-80%, and obtain the composite flocculant after static aging.

[0035] It should be noted that: for the characteristics of terephthalic acid, the specific precipitation effect of calcium ions is used to achieve targeted removal; for colored pollutants, the iron and titanium components in red mud provide a dual decolorization pathway of oxidation and adsorption. Red mud and magnesite tailings are used as raw materials for waste recycling, which reduces costs and complies with the principles of green chemical industry.

[0036] In a further embodiment of this example, the red mud is sintered red mud, the mass percentage of iron oxide in the red mud is 20-30%, and the mass percentage of magnesium carbonate in the magnesite tailings is 85-90%.

[0037] In a further embodiment of this example, the stepped calcination includes the following steps:

[0038] The temperature was increased to 550℃ at a rate of 10℃ / min and held for 1 hour to decompose magnesite into active magnesium oxide.

[0039] The temperature was increased to 750℃ at a rate of 5℃ / min and held for 2 hours to convert α-Fe2O3 in the red mud into γ-Fe2O3 and form a microporous structure, resulting in a mixture of modified red mud and magnesium ore activation products.

[0040] In a further embodiment of this example, the preparation of the prepolymer includes the following steps:

[0041] Industrial sodium silicate with a film number of 3.2 was prepared into a 4% aqueous solution, and the pH was adjusted to 3.5 with sulfuric acid and stirred at room temperature for 30 min to form polysilicic acid sol.

[0042] Titanium tetrachloride was added to make the molar ratio of titanium to silicon reach 0.15:1, and then the temperature was raised to 75°C for 48 hours to obtain a blue-gray transparent gel, i.e., the prepolymer.

[0043] In a further embodiment of this example, the hydrochloric acid added to the magnesium ore-red mud mixture is reacted at 168-172℃ and 0.8MPa for 5 hours, so that the acid solubility rates of magnesium oxide, iron oxide and iron oxide reach 95%, 88% and 90% respectively, forming a composite chloride solution rich in aluminum ions, iron ions and magnesium ions. Then, after cooling to 100℃, calcium aluminate powder, prepolymer and konjac glucomannan phosphate are added sequentially and reacted under stirring at 80 rpm at a reaction temperature of 95-100℃ for 2 hours.

[0044] In a further embodiment of this example, calcium aluminate powder is first added to adjust the initiation of the alkaline polymerization reaction, and the alkalinity of the system is adjusted to 45%.

[0045] Then, the prepolymer is added dropwise, and the viscosity is controlled to be less than 500 mPa·s during the dropwise addition process;

[0046] Then, konjac glucomannan phosphate is added as a selective coagulant to fully crosslink the components.

[0047] In a further embodiment of this example, the calcium hydroxide suspension is added in a quantitative pulse every 10 minutes to adjust the alkalinity of the system to 75-80%.

[0048] In a further embodiment of this example, the static curing conditions are static curing at 60°C for 24 hours, and the curing process promotes [Al3O4(OH)]... 24 (H2O) 12 ] 7+ and [Fe2(OH)2] 4+ High-valence polymers and titanium-silicon chains form a stable hybrid structure, preventing "aging" and precipitation in liquid products.

[0049] On the other hand, embodiments of the present invention also provide a composite flocculant suitable for alkali reduction wastewater treatment. The composite flocculant prepared according to the above preparation method includes the following components in parts by weight.

[0050] 12-18 parts calcium aluminate powder, 25-35 parts modified red mud, 8-15 parts activated magnesium ore product, 15-22 parts titanium-silicon polymer and 4-6 parts konjac glucomannan phosphate ester.

[0051] The calcium aluminate powder comprises 52-60 wt% alumina and 22-30 wt% calcium oxide, and the modified red mud comprises 20-30 wt% iron oxide.

[0052] It should be noted that calcium aluminate powder serves as the basic aluminum and calcium source for the system, providing highly reactive aluminum and calcium ions. Calcium ions effectively neutralize the negative charge of terephthalic acid colloids and form insoluble calcium terephthalate precipitate through ionic bonding.

[0053] Sintering red mud provides iron-based decolorizing components and a porous carrier structure. During acidic activation, the iron in the red mud is converted into polyferric chloride, which forms highly charged Fe(OH) in alkaline wastewater. 4- It enhances charge neutralization capacity; its porous structure provides adsorption sites.

[0054] Magnesium carbonate in magnesite tailings is roasted to obtain active magnesium oxide, which forms nano-sheet magnesium hydroxide precipitate in an alkaline environment, playing a net-like and sweeping role. Magnesium colloid has a stronger positive charge than aluminum and iron colloids, and still maintains high flocculation ability under high pH conditions.

[0055] Titanium polysilicic acid prepolymer forms an ultra-high molecular weight chain structure. Its abundant silanol groups (-Si-OH) on the surface can form hydrogen bonds with organic pollutants. The long chain structure realizes the dual function of "bridging and trapping", which significantly improves the size and density of flocs.

[0056] Konjac glucomannan phosphate, as an anionic natural modified polysaccharide, contains high-density phosphate groups and can be used as a selective coagulant aid. Its molecular chain combines with metal ions through coordination bonds to form an "organic-inorganic hybrid network" that strengthens the floc structure. At the same time, its phosphate groups can also specifically adsorb positively charged disperse dye residues.

[0057] On the other hand, the present invention also provides an application of a composite flocculant suitable for alkali reduction wastewater treatment. The composite flocculant prepared according to the above preparation method is applied in the field of wastewater treatment.

[0058] During application, the dosage of composite flocculant is 0.6-1.0 g / L. Terephthalic acid is recovered after the flocculated sludge is leached with dilute sulfuric acid.

[0059] In a strongly alkaline wastewater environment, the various metal ions released by this composite flocculant undergo directional hydrolysis and coordination, including calcium ions (Ca2+). + ) and terephthalic acid anion (TA2) - A specific precipitation reaction occurs:

[0060] Ca 2+ +TA 2- →CaTA.

[0061] The precipitate has extremely low solubility and can capture more than 80% of TA (terephthalic acid) in wastewater in solid form. Calcium ions play a "molecular anchoring" role in this process, which specifically addresses the core pollutants in alkali reduction wastewater.

[0062] [Al3O4(OH) 24 (H2O) 12 ] 7+ and [Fe2(OH)2] 4+ High-valence polymers adsorb onto the surface of negatively charged colloidal microparticles, rapidly compressing the electric double layer.

[0063] Example 1

[0064] Magnesite tailings and sintered red mud were mixed at a mass ratio of 1:3 and ground to 200 mesh. Under nitrogen flow rate of 0.5 L / min protection, the temperature was first raised to 550℃ at 10℃ / min and maintained for 1 h, and then raised to 750℃ at 5℃ / min and maintained for 2 h to obtain a mixture of modified red mud and magnesite activation product.

[0065] Sodium silicate with a membrane number of 3.2 was prepared into a 4% sodium silicate aqueous solution, and the pH was adjusted to 3.5 by sulfuric acid. The solution was stirred at room temperature for 30 minutes to form a polysilicic acid sol, i.e., a prepolymer.

[0066] Titanium tetrachloride was added to make the molar ratio of titanium to silicon reach 0.15:1, and then the temperature was raised to 75°C for 48 hours to obtain a blue-gray transparent gel.

[0067] 2.5 L of 30% hydrochloric acid was added to 1 kg of magnesium ore-red mud mixture and reacted at 170 °C and 0.8 MPa for 5 h. Calcium aluminate powder was added first to adjust and initiate the alkaline polymerization reaction, and the alkalinity of the system was adjusted to 45%.

[0068] Then add 400g of prepolymer dropwise, controlling the viscosity to be less than 500mPa·s during the dropwise addition process;

[0069] Add another 100g of konjac glucomannan phosphate, and maintain the temperature at 95-100℃ and stir at a low speed of 80rpm for 2 hours.

[0070] The alkalinity of the system was adjusted to 75% by adding 5g of calcium hydroxide suspension in pulses every 10 minutes. The mixture was then transferred to a curing tank and statically cured at 60°C for 24 hours to obtain a composite flocculant.

[0071] Alkali reduction wastewater with a COD of 14000 mg / L and a pH of 13.2 was treated with 0.6 g / L of the composite flocculant prepared above. After treatment, the COD removal rate reached 96.5%, the color removal rate was 95.2%, the TA recovery rate was 85.5%, the effluent COD dropped to 490 mg / L, the pH naturally dropped to 8.5, and the TA-Ca content in the flocculated sludge was 62%. After leaching with 5% H2SO4 dilute acid, terephthalic acid with a purity of 98.2% was recovered, and the TA recovery amount per ton of wastewater was 14.5 kg.

[0072] Example 2

[0073] Magnesite tailings and sintered red mud were mixed at a mass ratio of 1:3 and ground to 200 mesh. Under nitrogen flow rate of 0.5 L / min protection, the temperature was first raised to 550℃ at 10℃ / min and maintained for 1 h, and then raised to 750℃ at 5℃ / min and maintained for 2 h to obtain a mixture of modified red mud and magnesite activation product.

[0074] Sodium silicate with a membrane number of 3.2 was prepared into a 4% sodium silicate aqueous solution, and the pH was adjusted to 3.5 by sulfuric acid. The solution was stirred at room temperature for 30 minutes to form a polysilicic acid sol, i.e., a prepolymer.

[0075] Titanium tetrachloride was added to make the molar ratio of titanium to silicon reach 0.15:1, and then the temperature was raised to 75°C for 48 hours to obtain a blue-gray transparent gel.

[0076] 2.5 L of 30% hydrochloric acid was added to 1 kg of magnesium ore-red mud mixture and reacted at 170 °C and 0.8 MPa for 5 h. Calcium aluminate powder was added first to adjust and initiate the alkaline polymerization reaction, and the alkalinity of the system was adjusted to 45%.

[0077] Then, 440g of prepolymer was added dropwise, with the viscosity controlled to be less than 500mPa·s during the addition process.

[0078] Add 110g of konjac glucomannan phosphate, and maintain the temperature at 95-100℃ and stir at 80rpm for 2 hours.

[0079] The alkalinity of the system was adjusted to 78% by adding 5g of calcium hydroxide suspension in pulses every 10 minutes. The mixture was then transferred to a curing tank and statically cured at 60°C for 24 hours to obtain a composite flocculant.

[0080] Alkali reduction wastewater with a COD of 14000 mg / L and a pH of 13.2 was treated with 0.6 g / L of the composite flocculant prepared above. After treatment, the COD removal rate reached 96.8%, the color removal rate was 96.1%, the TA recovery rate was 86.8%, the effluent COD dropped to 448 mg / L, the pH naturally dropped to 8.8, and the TA-Ca content in the flocculated sludge was 63%. After leaching with 5% H2SO4 dilute acid, terephthalic acid with a purity of 98.5% was recovered, and the TA recovery amount per ton of wastewater was 15.2 kg.

[0081] Example 3

[0082] Magnesite tailings and sintered red mud were mixed at a mass ratio of 1:3 and ground to 200 mesh. Under nitrogen flow rate of 0.5 L / min protection, the temperature was first raised to 550℃ at 10℃ / min and maintained for 1 h, and then raised to 750℃ at 5℃ / min and maintained for 2 h to obtain a mixture of modified red mud and magnesite activation product.

[0083] Sodium silicate with a membrane number of 3.2 was prepared into a 4% sodium silicate aqueous solution, and the pH was adjusted to 3.5 by sulfuric acid. The solution was stirred at room temperature for 30 minutes to form a polysilicic acid sol, i.e., a prepolymer.

[0084] Titanium tetrachloride was added to make the molar ratio of titanium to silicon reach 0.15:1, and then the temperature was raised to 75°C for 48 hours to obtain a blue-gray transparent gel.

[0085] 2.5 L of 30% hydrochloric acid was added to 1 kg of magnesium ore-red mud mixture and reacted at 170 °C and 0.8 MPa for 5 h. Calcium aluminate powder was added first to adjust and initiate the alkaline polymerization reaction, and the alkalinity of the system was adjusted to 45%.

[0086] Then add 400g of prepolymer dropwise, controlling the viscosity to be less than 500mPa·s during the dropwise addition process;

[0087] Add 104g of konjac glucomannan phosphate, and maintain the temperature at 95-100℃ and stir at a low speed of 80rpm for 2 hours.

[0088] The alkalinity of the system was adjusted to 80% by adding 5g of calcium hydroxide suspension in pulses every 10 minutes. The mixture was then transferred to a curing tank and statically cured at 60°C for 24 hours to obtain a composite flocculant.

[0089] Alkali reduction wastewater with a COD of 14000 mg / L and a pH of 13.2 was treated with 0.65 g / L of the composite flocculant prepared above. After treatment, the COD removal rate reached 97.1%, the color removal rate was 97.3%, the TA recovery rate was 88.1%, the effluent COD dropped to 406 mg / L, the pH naturally dropped to 8.6, and the TA-Ca content in the flocculated sludge was 63%. After leaching with 5% H2SO4 dilute acid, terephthalic acid with a purity of 98.8% was recovered, and the TA recovery amount per ton of wastewater was 16.1 kg.

[0090] Example 4

[0091] Magnesite tailings and sintered red mud were mixed at a mass ratio of 1:3 and ground to 200 mesh. Under nitrogen flow rate of 0.5 L / min protection, the temperature was first raised to 550℃ at 10℃ / min and maintained for 1 h, and then raised to 750℃ at 5℃ / min and maintained for 2 h to obtain a mixture of modified red mud and magnesite activation product.

[0092] Sodium silicate with a membrane number of 3.2 was prepared into a 4% sodium silicate aqueous solution, and the pH was adjusted to 3.5 by sulfuric acid. The solution was stirred at room temperature for 30 minutes to form a polysilicic acid sol, i.e., a prepolymer.

[0093] Titanium tetrachloride was added to make the molar ratio of titanium to silicon reach 0.15:1, and then the temperature was raised to 75°C for 48 hours to obtain a blue-gray transparent gel.

[0094] 2.5 L of 30% hydrochloric acid was added to 1 kg of magnesium ore-red mud mixture and reacted at 170 °C and 0.8 MPa for 5 h. Calcium aluminate powder was added first to adjust and initiate the alkaline polymerization reaction, and the alkalinity of the system was adjusted to 45%.

[0095] Then add 410g of prepolymer dropwise, controlling the viscosity to be less than 500mPa·s during the dropwise addition process;

[0096] Add 96g of konjac glucomannan phosphate ester, and maintain the temperature at 95-100℃ and stir at a low speed of 80rpm for 2 hours.

[0097] The alkalinity of the system was adjusted to 76% by adding 5g of calcium hydroxide suspension in pulses every 10 minutes. The mixture was then transferred to a curing tank and statically cured at 60°C for 24 hours to obtain the composite flocculant.

[0098] Alkali reduction wastewater with a COD of 14000 mg / L and a pH of 13.2 was treated with 0.6 g / L of the composite flocculant prepared above. After treatment, the COD removal rate reached 96.2%, the color removal rate was 95.8%, the TA recovery rate was 87.2%, the effluent COD dropped to 532 mg / L, the pH naturally dropped to 8.7, and the TA-Ca content in the flocculated sludge was 63%. After leaching with 5% H2SO4 dilute acid, terephthalic acid with a purity of 98.5% was recovered, and the TA recovery amount per ton of wastewater was 15.2 kg.

[0099] Comparative Example 1

[0100] Magnesite tailings and sintered red mud were mixed at a mass ratio of 1:3 and ground to 200 mesh. Under nitrogen flow rate of 0.5 L / min protection, the temperature was first raised to 550℃ at 10℃ / min and maintained for 1 h, and then raised to 750℃ at 5℃ / min and maintained for 2 h to obtain a mixture of modified red mud and magnesite activation product.

[0101] Sodium silicate with a membrane number of 3.2 was prepared into a 4% sodium silicate aqueous solution, and the pH was adjusted to 3.5 by sulfuric acid. The solution was stirred at room temperature for 30 minutes to form a polysilicic acid sol, i.e., a prepolymer.

[0102] Titanium tetrachloride was added to make the molar ratio of titanium to silicon reach 0.15:1, and then the temperature was raised to 75°C for 48 hours to obtain a blue-gray transparent gel.

[0103] 2.5L of 30% hydrochloric acid was added to 1Kg of magnesium ore-red mud mixture and reacted at 170℃ and 0.8MPa for 5h. 50g of calcium aluminate powder was added first to adjust and initiate the alkali polymerization reaction.

[0104] Then add 400g of prepolymer dropwise, controlling the viscosity to be less than 500mPa·s during the dropwise addition process;

[0105] Add 96g of konjac glucomannan phosphate ester, and maintain the temperature at 95-100℃ and stir at a low speed of 80rpm for 2 hours.

[0106] The alkalinity of the system was adjusted by adding 5g of calcium hydroxide suspension in a pulse manner every 10 minutes. Due to the insufficient amount of calcium aluminate powder, the alkalinity of the system was difficult to increase to a suitable range during the alkalinization polymerization stage. The final alkalinity only reached 40%. The system was then transferred to a curing tank and statically cured at 60°C for 24 hours to obtain the composite flocculant.

[0107] Alkali reduction wastewater with COD of 14000 mg / L and pH of 13.2 was treated with 0.8 g / L of the composite flocculant prepared above. The COD removal rate was 65.3%, the color removal rate was 70.4%, the TA recovery rate was 50%, the effluent COD was reduced to 4858 mg / L, and the pH naturally dropped to 10.5. The insufficient aluminum and calcium sources provided by the calcium aluminate powder led to a weakening of the exclusive precipitation effect of calcium ions on TA, a small amount of polynuclear hydroxy complexes formed by aluminum ions, and insufficient charge neutralization capacity, resulting in a significant reduction in the overall flocculation effect.

[0108] Comparative Example 2

[0109] Magnesite tailings and sintered red mud were mixed at a mass ratio of 1:3 and ground to 200 mesh. Under nitrogen flow rate of 0.5 L / min protection, the temperature was first raised to 550℃ at 10℃ / min and maintained for 1 h, and then raised to 750℃ at 5℃ / min and maintained for 2 h to obtain a mixture of modified red mud and magnesite activation product.

[0110] Sodium silicate with a membrane number of 3.2 was prepared into a 4% sodium silicate aqueous solution, and the pH was adjusted to 3.5 by sulfuric acid. The solution was stirred at room temperature for 30 minutes to form a polysilicic acid sol, i.e., a prepolymer.

[0111] Titanium tetrachloride was added to make the molar ratio of titanium to silicon reach 0.15:1, and then the temperature was raised to 75°C for 48 hours to obtain a blue-gray transparent gel.

[0112] 2.5 L of 30% hydrochloric acid was added to 1 kg of magnesium ore-red mud mixture and reacted at 170 °C and 0.8 MPa for 5 h. Calcium aluminate powder was added first to adjust and initiate the alkaline polymerization reaction, and the alkalinity of the system was adjusted to 45%.

[0113] Add 100g of konjac glucomannan phosphate and maintain the temperature at 95-100℃ while stirring at 80rpm for 2 hours.

[0114] The alkalinity of the system was adjusted to 75% by adding 5g of calcium hydroxide suspension in pulses every 10 minutes. The mixture was then transferred to a curing tank and statically cured at 60°C for 24 hours to obtain a composite flocculant.

[0115] Alkali reduction wastewater with COD of 14000 mg / L and pH of 13.2 was treated with 0.8 g / L of the composite flocculant prepared above. The COD removal rate was 78%, the color removal rate was 80%, the TA recovery rate was 65%, the effluent COD dropped to 3080 mg / L, and the pH naturally dropped to 9.5. However, due to the lack of titanium polysilicic acid prepolymer, the flocculant lacked the bridging and trapping effect of long-chain structure, making it difficult for the flocs to grow and become dense effectively. This significantly reduced the ability to remove dissolved organic matter, resulting in poor overall treatment effect.

[0116] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a composite flocculant suitable for alkali reduction wastewater treatment, characterized in that, Includes the following steps: Magnesite tailings and sintered red mud were mixed at a mass ratio of 1:3 and ground to 200 mesh. The mixture was then subjected to step-roasting under nitrogen protection to obtain a magnesite-red mud mixture. The pH of the sodium silicate solution was adjusted to 3.5 with sulfuric acid, and after stirring to form a sol, titanium tetrachloride was added and the mixture was heated and matured to obtain the prepolymer. Hydrochloric acid was added to the magnesium ore-red mud mixture for reaction, and then calcium aluminate powder, prepolymer and konjac glucomannan phosphate were added in sequence and stirred for reaction. Add calcium hydroxide suspension to adjust the alkalinity of the system to 75-80%, and obtain the composite flocculant after static aging; The red mud is sintered red mud, the mass percentage of iron oxide in the red mud is 20-30%, and the mass percentage of magnesium carbonate in the magnesite tailings is 85-90%. The stepped roasting process includes the following steps: Heat to 550℃ at a rate of 10℃ / min and hold for 1 hour; The temperature was increased to 750℃ at a rate of 5℃ / min and held for 2 hours to obtain a mixture of modified red mud and magnesium ore activation products; The preparation of the prepolymer includes the following steps: Industrial sodium silicate with a film number of 3.2 was prepared into a 4% aqueous solution, and the pH was adjusted to 3.5 with sulfuric acid and stirred at room temperature for 30 min to form polysilicic acid sol. Titanium tetrachloride was added to make the molar ratio of titanium to silicon reach 0.15:1, and then the temperature was raised to 75°C for 48 hours to obtain a blue-gray transparent gel, i.e., the prepolymer. The reaction conditions for adding hydrochloric acid to the magnesium ore-red mud mixture are as follows: reaction at 168-172℃ and 0.8MPa for 5 hours, then cooling to 100℃ and adding calcium aluminate powder, prepolymer and konjac glucomannan phosphate in sequence, and reacting under stirring at 80rpm at a reaction temperature of 95-100℃ for 2 hours. First, add calcium aluminate powder to regulate and initiate the alkaline polymerization reaction, adjusting the alkalinity of the system to 45%. Then, the prepolymer is added dropwise, and the viscosity is controlled to be less than 500 mPa·s during the dropwise addition process; Then, konjac glucomannan phosphate is added as a selective coagulant to fully crosslink the components; The calcium hydroxide suspension was added in quantitative pulses every 10 minutes to adjust the alkalinity of the system to 75-80%, and the calcium ions underwent a specific precipitation reaction with terephthalic acid to achieve targeted removal. The static curing conditions are: static curing at 60°C for 24 hours; The composite flocculant is applied to strongly alkaline wastewater with a pH of 13.2 for alkali reduction.

2. A composite flocculant suitable for alkali reduction wastewater treatment, characterized in that, The composite flocculant prepared according to the preparation method described in claim 1; The composite flocculant comprises the following components in parts by weight: 12-18 parts calcium aluminate powder, 25-35 parts modified red mud, 8-15 parts activated magnesium ore product, 15-22 parts titanium-silicon polymer and 4-6 parts konjac glucomannan phosphate ester. The calcium aluminate powder comprises 52-60 wt% alumina and 22-30 wt% calcium oxide, and the modified red mud comprises 20-30 wt% iron oxide.

3. An application of a composite flocculant suitable for alkali reduction wastewater treatment, characterized in that, The composite flocculant prepared by the method according to claim 1 is used in the field of wastewater treatment; During application, the dosage of composite flocculant is 0.6-1.0 g / L. Terephthalic acid is recovered after the flocculated sludge is leached with dilute sulfuric acid.