A method for preparing a polysilicate aluminum-iron-PAM composite flocculant by taking red mud as a raw material

Abstract

The application aims to provide a method for preparing a poly-silicon aluminum iron-PAM amine composite flocculant from red mud, and belongs to the technical field of flocculant preparation.The red mud is subjected to acid leaching to obtain a mixed leaching solution of iron and aluminum, the mixture after acid leaching is subjected to centrifugal separation to obtain filter residue, and the filter residue is subjected to alkali leaching to obtain a silicon leaching solution, so that the red mud is fully utilized.The flocculant prepared by the method has excellent performance in treating fluorine-containing wastewater.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flocculants, and particularly relates to a method for preparing a polyaluminum ferric silicate-PAM composite flocculant by taking red mud as raw material. BACKGROUND

[0002] With the increasing requirements of society on sewage treatment, the treatment of complex water bodies has become a challenge. In this context, inorganic polymer flocculants have emerged and received extensive attention.

[0003] The preparation of a red mud-based polymeric aluminum ferric sulfate flocculant (paper: Ma Qiaoshan. Preparation and application research of red mud-based polymeric aluminum ferric sulfate flocculant. Shandong Chemical Industry) discloses that a proper amount of red mud is placed in a muffle furnace, calcined at a high temperature of 600℃ for 3h, ground, sieved and dried; 15g of red mud is weighed in a round-bottom flask, 90mL of 6mol / L sulfuric acid (solid-liquid ratio of 1:6) is added; 80℃ water bath stirring for 2h, after acid leaching, the leaching solution is obtained; a certain amount of filtrate is measured in a three-necked flask, an excess of H2O2 is added, and NaOH is added dropwise under stirring to adjust the pH value of the reaction solution at a certain temperature; after the NaOH solution is dropped, it is stirred for a period of time; after stirring, it is aged at a certain temperature for a certain time, and a red-brown polymeric aluminum ferric sulfate flocculant is obtained.

[0004] The preparation of a red mud-based polyaluminum ferric chloride flocculant (paper: Cheng Yong. Preparation and application research of red mud-based polyaluminum ferric chloride flocculant and magnetic NaP1 zeolite. Chongqing University) discloses that the red mud is first subjected to acid leaching, and the leaching conditions are as follows: liquid-solid ratio of 7:1, HCl concentration of 5mol / L, leaching time of 120min and leaching temperature of 70℃. Then, the leaching solution is centrifuged at 4000rpm for 10min, and the centrifugal supernatant is poured into a 100mL beaker. Then, FeCl3•6HO or AlCl3•6HO is added to the beaker under vigorous stirring to adjust the aluminum-iron molar ratio, and 3mol / L NaOH is added dropwise after dissolution to adjust the pH of the solution. Subsequently, the solution is aged at different temperatures for 3h, and is left to stand for 12h. Finally, the standing supernatant is poured into an oven at 105℃ and dried for 12h, and the polyaluminum ferric chloride flocculant is obtained by grinding.

[0005] A method for preparing a high-efficiency composite flocculant from red mud (patent publication number: CN112093870A) discloses:

[0006] (1) red mud and hydrochloric acid are added to a reaction kettle, and then acid leaching is carried out in the reaction kettle at 60-100℃, and then pressure filtration is carried out by using a filter press to obtain filtrate and filter cake;

[0007] (2) Put the filter cake obtained in step (1) back into the reaction kettle, add sodium hydroxide solution, stir at 80-140°C, mix for a certain time, then filter with a filter press to obtain a sodium silicate solution and a residue;

[0008] (3) Put the sodium silicate solution obtained in step (2) into the reaction kettle again, add hydrochloric acid to adjust the pH value to 1-4, then stand for 1-6h, and then adjust the pH value to 1-3 to prepare a polysilicic acid solution;

[0009] (4) Take samples of Al, Mg, Fe, Si, etc. in the solution obtained in step (1) of step (3), then add the filtrate obtained in step (1) to the solution in step (3), and add appropriate amounts of Al, Mg, Fe as needed to form a certain ratio of Al, Mg, Fe, and Si;

[0010] (5) In step (4), add sodium hydroxide solution to adjust the pH value to 3-4, and alkalinize with an alkalinizing agent, with an alkalinization degree of 0.8-1.2, to obtain a high-efficiency composite flocculant.

[0011] A method for preparing a polymeric aluminum ferric silicate flocculant from gasification slag and its application (Patent Publication No. CN115571890A) discloses:

[0012] (1) Calcination and activation: After the gasification slag is crushed and passed through a 100-mesh sieve, the gasification slag is placed in a corundum crucible, then Na2CO3 is added as a solubilizing agent and mixed uniformly, and then placed in a muffle furnace for calcination;

[0013] (2) Acid leaching: The calcined gasification slag is stirred with a 5 mol / L hydrochloric acid solution at 95°C for 1.4h, and the solid-liquid separation is performed while hot to obtain an acid leaching solution and an acid leaching residue. The residue is washed with 30mL of hot water for 3 times, and the washing liquid is mixed with the acid leaching liquid to obtain an iron-aluminum solution. The acid leaching residue is dried at 105°C for 4-8h and reserved;

[0014] (3) Alkali leaching: The acid leaching residue is ground to no obvious particle feeling, and the acid leaching residue is heated and stirred with 5mol / L NaOH at 75°C for 0.5h, and then filtered while hot to obtain a mother liquor. The filter residue is washed with 30mL of hot water for 3 times to obtain a washing liquid, and then the mother liquor and the washing liquid are made up to 50mL, and mixed with 26.5mL of 20% H2SO4 solution. Under the magnetic stirring at a speed of 600-800r / min, it is kept for 5h to obtain a polysilicic acid solution;

[0015] (4) Copolymerization: under stirring conditions, the iron-aluminum solution is added to the polysilicic acid solution at a flow rate of 1 mL / s, and a 5 mol / L NaOH solution is added dropwise to the above solution to neutralize to a predetermined pH value, and then the solution is aged at room temperature and normal pressure for 48 h to obtain the polysilicic acid aluminum iron flocculant.

[0016] A polysilicic acid aluminum iron flocculant and a preparation method (Patent Publication No. CN109809540A) are disclosed:

[0017] (1) One or more of coal gangue, fly ash, and red mud are ground by a ball mill to 100 mesh or more as mixed raw materials, wherein the ratio of Si / Al / Fe in the mixed raw materials is 5-30 / 20-50 / 10-40;

[0018] (2) The mixed raw materials in step (1) are mixed uniformly with an activator to prepare a raw material, wherein the activator is ammonium sulfate or ammonium chloride or a mixture of the two, and the mass ratio of the activator to the mixed raw materials is (5-10):1;

[0019] (3) The raw material in step (2) is calcined at 500-750°C for 1-3 h under a reaction pressure of 0.25-0.3 MPa to obtain a clinker;

[0020] (4) The clinker in step (3) is transferred to water of the same mass for water quenching to obtain a coarse product with a particle size of 10-100 μm. After wet grinding, the coarse product is added to 3 times the volume of water, and the mixture is stirred at 90°C for 2 h, and then solid-liquid separation is performed to obtain a filtrate A and a filter residue B;

[0021] (5) Calcium aluminate is added to the filtrate A, and an inorganic acid is added at the same time. The mixture is stirred and reacted at 60-80°C for 4 h, and then is allowed to stand for 2 h after the reaction is completed to obtain a solution C;

[0022] (6) The filter residue B is crushed and transferred to a corrosion-resistant high-pressure reaction kettle containing a sodium hydroxide solution. After being heated to 130°C, the mixture is stirred and reacted for 4 h. After being cooled to room temperature, solid-liquid separation is performed to obtain a solution D;

[0023] (7) The solution C is slowly added to the solution D at a mass ratio of (1-1.5):1. The stirring speed is not less than 150 revolutions / minute, and the reaction temperature is 40°C. After the addition of the solution C, the pH value is adjusted to 3.5-4 by adding an inorganic acid. After standing for 6-12 h, a polysilicic acid aluminum iron flocculant is obtained.

[0024] A process for preparing a polysilicic acid aluminum iron flocculant and co-producing white carbon black from red mud (Patent Publication No. CN116161757A) is disclosed:

[0025] (1) Material pretreatment: the red mud is ground and sieved to less than 100 mesh, and then is dried to obtain pretreated material for standby use;

[0026] (2) Calcination activation: the pretreated material is placed in an atmosphere furnace and calcined and activated under an air atmosphere to obtain calcined clinker;

[0027] (3) Low-temperature acid leaching: the calcined clinker is uniformly mixed with an acidic solution in proportion, and is subjected to acid leaching and dissolution at room temperature

[0028] , and solid-liquid separation to obtain acid leaching solution 1 and titanium-rich residue;

[0029] (4) Precipitation desilication: a surfactant is added to the acid leaching solution 1 at room temperature to precipitate and desilicate, and solid-liquid separation to obtain acid leaching solution 2 and white carbon black product;

[0030] (5) Alkalization polymerization: an alkalizing agent is added to the acid leaching solution 2, and a polyaluminum ferric silicate flocculant product is prepared through polymerization reaction.

[0031] A method for producing a polyaluminum calcium ferric silicate sulfate flocculant using industrial waste sulfuric acid and red mud (patent publication number: CN105502424B) discloses:

[0032] (1) The waste sulfuric acid and the red mud are mixed in a mass ratio of 0.33-2.00, mechanically stirred for 3-10 minutes to make them uniformly mixed, and then left to stand for 30-120 minutes. Water is added to make the water content in the mixture 43.7-55.8% by weight, and the mixture is mechanically stirred for 30-90 minutes. The waste gas generated in the above process is vented after being absorbed and purified by a lye;

[0033] (2) The second step: The mixture prepared in the first step is filtered to obtain filtrate A and filter cake A. Adjusting agent A is added to the filtrate A to adjust the pH value to 2.0-3.5, and then filtered to obtain filtrate B and filter cake B;

[0034] When the mass fraction of silicon dioxide in the filtrate B is less than or equal to 2.8% and the molar ratio of aluminum+calcium+iron to silicon is greater than or equal to 1.2, the filtrate B is aged at 18-30℃ for 2-24 hours to obtain a polyaluminum calcium ferric silicate sulfate solution. When the mass fraction of silicon dioxide in the filtrate B is greater than 2.8%, water is added for dilution. When the molar ratio of aluminum+calcium+iron to silicon in the filtrate B is less than 1.2, adjusting agent B is added for adjustment.

[0035] A method for preparing a phosphorite-red mud-inulin composite flocculant and a method for treating sewage (patent publication number: CN106241997A) discloses:

[0036] (1) High-temperature activation of phosphorite: The phosphorite is crushed into fine powder passing through a 100-150 mesh sieve; the sieved phosphorite fine powder is taken into a crucible and subjected to high-temperature activation at a temperature of 600-800℃ for 4-6h;

[0037] (2) The treatment of red mud: dry the red mud in a drying oven to a water content of less than 5%, then crush and grind it into red mud powder passing through a 100-150 mesh sieve; take the red mud powder and an acid solution with a H concentration of 6-10 mol / L, mix them in a container according to a solid-liquid ratio of 5-7:1, then place them in a constant-temperature water bath pot at a temperature of 80-90°C for heating reaction, take them out after 2-3 h of reaction and filter them while hot, and the obtained filtrate is an aluminum-iron leaching solution;

[0038] (3) Preparation of the composite flocculant: mix the aluminum-iron leaching solution, the high-temperature activated phosphorite and the inulin according to a weight ratio of 7-11:7-11:3-5 to react, and the phosphorite-red mud-inulin composite flocculant is obtained.

[0039] A method for preparing a multi-component flocculant and co-producing a composite white carbon black by using red mud (Patent Publication No. CN103922448A) discloses:

[0040] (1) Acid leaching of red mud: mix red mud and an acid solution according to a weight ratio of 1:1-10, stir at 30-100°C for 1-6 h, and filter to obtain an acid leaching solution and an acid leaching residue, the molar concentration of H in the acid solution is 0.5-4 mol / L, and the mass percentage of aluminum-iron metal ions in the acid leaching solution, converted into oxides, is: Al2O3, 2-10%; Fe2O3, 2-10%; and the balance is H2O and other unavoidable impurity ions; +

[0041] (2) Preparation of a polymeric aluminum-iron inorganic flocculant: mix the acid leaching solution with a polycondensation agent, stir at 30-100°C for 1-12 h, stop stirring, and age for 6-24 h to obtain a polymeric aluminum-iron inorganic flocculant, the mass percentage of aluminum-iron metal ions in the polymeric aluminum-iron flocculant, converted into oxides, is: Al2O3, 2-10%; Fe2O3, 2-10%; and the balance is H2O and other unavoidable impurity ions;

[0042] (3) Preparation of a red mud-based multi-component flocculant: mix the polymeric aluminum-iron inorganic flocculant with mineral materials and high molecular materials, stir at 10-80°C for 0.5-2 h to obtain a multi-component flocculant, the components of the multi-component flocculant are: mineral materials, 3-10%; high molecular materials, 1-10%; Al2O3, 2-10%; Fe2O3, 2-10%; and the balance is H2O and other unavoidable impurity ions. The high molecular materials are starch, polydimethyl diallyl ammonium chloride, polyacrylamide, or carboxymethyl cellulose sodium;

[0043] (4) Preparation of composite white carbon black: dry the acid leaching residue obtained in the first step at 150-600°C for 2-12 h, and the obtained solid is the composite white carbon black.​

[0044] A polymeric silico-aluminate inorganic flocculant and its preparation method and application (Patent publication number: CN112174279A) TiO2 nanoparticles load flocculation combination is disclosed:

[0045] (1) The mixed powder of fly ash and potassium carbonate with a mass ratio of 1:0.1~1 is high-temperature treated at 700~900℃ to obtain an alkali fusion product;

[0046] (2) The alkali fusion product obtained in step 1 is fully reacted with hydrochloric acid at 80~110℃ to obtain an acid paste;

[0047] (3) The acid paste obtained in step 2 is cooled to room temperature, and then butyl titanate is added dropwise to obtain a hydrolysis mixture;

[0048] (4) Potassium hydroxide is added to the hydrolysis mixture obtained in step 3, and the mixture is settled and matured at room temperature to obtain a matured liquid;

[0049] (5) The matured liquid obtained in step 4 is filtered to obtain a product, which is high-temperature activated at 150~500℃ to obtain a polymeric silico-aluminate inorganic flocculant.

[0050] An industrial solid waste-based composite flocculant and its preparation method and application (Patent publication number: CN115893803A) are disclosed:

[0051] (1) Industrial solid waste quicklime, phosphorite, red mud, and bentonite are mixed according to the proportion;

[0052] (2) The organic flocculant solution and the inorganic flocculant solution prepared by dissolving in pure water are added to the obtained industrial solid waste according to the proportion, and then mixed to obtain an industrial solid waste-based composite flocculant.

[0053] A coal mine wastewater treatment method and system (Patent publication number: CN114524558B) are disclosed:

[0054] The preparation method of the composite flocculant is as follows: 240 parts by weight of polyaluminum chloride and 50~100 parts by weight of activated carbon are mixed and dispersed in water, and then an aqueous solution of polyacrylamide and an aqueous solution of polyacrylate are added to the obtained dispersion: the solid content of the dispersion is 40~60wt%;

[0055] The concentration of polyacrylamide in the aqueous solution of polyacrylamide is 3~10wt%, and the addition amount of polyacrylamide is 0.5~1.5 parts by weight;

[0056] The concentration of polyacrylate in the aqueous solution of polyacrylate is 3~10wt%, and the addition amount of polyacrylate is 0.5~1.5 parts by weight;

[0057] In the composite flocculant, the mass concentration of polyacrylamide is 0.5-3%.

[0058] A polyaluminum chloride-chitosan composite flocculant and its preparation method and application (Patent Publication No.: CN107500393A) discloses:

[0059] (1) Grind and sieve the aluminum ash, mix it with water, ultrasonically treat it at 40~70℃ for 10~20min, separate the solid and liquid, and dry it to obtain the pretreated aluminum ash;

[0060] (2) Mix the aluminum ash obtained in step (1) with water to obtain an aluminum ash suspension; add concentrated hydrochloric acid to the aluminum ash suspension; stir and react to mature the mixture to obtain polyaluminum chloride;

[0061] (3) Dissolve chitosan in acetic acid solution to obtain chitosan / acetic acid solution;

[0062] (4) Add the chitosan / acetic acid solution obtained in step (3) dropwise to the sodium polyphosphate solution, and then adjust the pH of the reaction system to 4~5; stir the reaction at 200~500r / min for 10~20min, and then stir the reaction at 50~100r / min for 30~60min to obtain a mixture;

[0063] (5) Add the polyaluminum chloride obtained in step (3) to the mixture obtained in step (4), stir and react at 80~100℃ for 1~3h to obtain polyaluminum chloride-chitosan composite flocculant.

[0064] These flocculants are primarily based on traditional flocculants such as aluminum and iron salts. Aluminum salt flocculants pose potential health risks; long-term ingestion or exposure to aluminum-containing environments can lead to aluminum accumulation in the body, which may have chronic effects on multiple systems. Iron salt flocculants may corrode water treatment equipment, affecting its lifespan and maintenance costs. Furthermore, large dosages may cause discoloration in the treated water, potentially impacting its sensory quality.

[0065] Moreover, most studies focus on extracting iron and aluminum from red mud and preparing flocculants, while there are few studies on the reuse of waste residue after iron and aluminum extraction. Summary of the Invention

[0066] To address the aforementioned problems, this invention provides a method for preparing polyaluminum silicate iron-PAM composite flocculant using red mud as raw material. By introducing aluminum and iron ions during the polymerization of silica, a polyaluminum silicate iron flocculant with excellent flocculation performance can be obtained. This not only retains the advantages of the original product and avoids to some extent the disadvantages of aluminum salt and iron salt flocculants, but also significantly improves its stability.

[0067] The application obtains an iron-aluminum mixed leaching solution by acid leaching of the red mud raw material, and obtains a silicon leaching solution by alkali leaching of the residue after centrifugal separation of the mixture after acid leaching, thereby realizing more sufficient utilization of the red mud.

[0068] The application adopts the following technical scheme:

[0069] A method for preparing a polysilicate aluminum iron-PAM composite flocculant by taking red mud as a raw material, comprising the following steps:

[0070] First step, thermal activation: after the original red mud is naturally air-dried for two weeks, it is ground through a 100-mesh sieve, and the sieved red mud powder is placed in a muffle furnace for calcination;

[0071] Second step, acid leaching: after the calcined red mud is mixed with a hydrochloric acid solution under water bath stirring, centrifugal filtration is performed to obtain an acid leaching solution and an acid leaching residue; wherein the acid leaching solution is a mixed solution containing iron and aluminum, and the acid leaching residue is dried for later use;

[0072] Third step, alkali leaching: after the dried acid leaching residue is mixed with a sodium hydroxide solution under heating and stirring, centrifugal filtration is performed to obtain an alkali leaching solution and an alkali leaching residue; wherein the alkali leaching solution is a solution containing silicon;

[0073] Fourth step, preparation of a polysilicate solution: the concentration of silicon in the alkali leaching solution is adjusted, and the adjusted solution is added dropwise into a stirred hydrochloric acid solution, the pH is adjusted, and a polysilicate solution is obtained after activation;

[0074] Fifth step, copolymerization: under stirring, an iron-aluminum mixed solution with different proportions is added to the polysilicate solution, NaOH solution is added to the above solution to adjust the degree of alkalization, and the polysilicate aluminum iron flocculant PSAF is obtained after aging under normal temperature and pressure;

[0075] Sixth step, preparation of PSAF-PAM composite flocculant: polysilicate aluminum iron flocculant and acrylamide are taken in a three-necked flask, which is placed in a constant-temperature water bath kettle, K2S2O8 solution is added to the reactor, and the mixed solution is continuously stirred while being purged with ultra-pure nitrogen to remove dissolved oxygen and carbon dioxide, FeSO4 solution is added to the solution after 15 minutes, and the PSAF-PAM composite flocculant is prepared after four hours of reaction under a nitrogen atmosphere.

[0076] Further, the red mud powder in the first step is 5g, the muffle furnace calcination temperature is 800℃, and the calcination time is 3h.

[0077] Further, in the second step, the concentration of the hydrochloric acid solution is 7mol / L, the water bath temperature is 70℃, the stirring time is 180min, and the ratio of the hydrochloric acid solution to the red mud is 7mL:1g; the drying temperature of the acid leaching residue is 110℃, and the drying time is 12h.

[0078] Further, in the third step, the mass concentration of the sodium hydroxide solution is 15%, the heating temperature is 80℃, and the stirring time is 90 min; the ratio of the sodium hydroxide solution to the acid leaching residue is 7 mL:1 g.

[0079] Further, in the fourth step, the concentration of silicon in the adjusted alkaline leaching solution is 0.3 mol / L; the hydrochloric acid is 1 volume of hydrochloric acid + 1 volume of water; the pH is adjusted to 3; and the activation time is 2 h.

[0080] Further, in the fifth step, the different proportions of iron-aluminum mixed solution are 0.5 mol / L of ferric chloride solution and 0.5 mol / L of aluminum sulfate solution adjusted to the acid leaching solution of the second step;

[0081] The molar ratio of aluminum to iron is 1-7:1, and the molar ratio of (aluminum + iron) to silicon is 0.5-3:1.

[0082] The concentration of the NaOH solution is 0.3 mol / L, the adjusted alkalinity is 0.25-0.75, and the aging time is 24 h.

[0083] Preferably, the molar ratio of aluminum to iron is 5:1, the molar ratio of (aluminum + iron) to silicon is 1:1, and the adjusted alkalinity is 0.5.

[0084] Further, in the sixth step, the ratio of the polysilicate aluminum iron flocculant and acrylamide is 50 mL:0.5 g; the temperature of the water bath is 25±2℃; the mass concentration of the K2S2O8 solution is 1%, the addition amount is 1 mL; the mass concentration of the FeSO4 solution is 1%, the molar ratio of S2O8 2- to Fe 2+ is 5:4.

[0085] The beneficial effects of the present application are as follows:

[0086] PSAF has excellent performance in treating fluorine-containing wastewater due to its unique polysilicate modification structure. PSAF has high removal rate of F - and is less affected by coexisting ions. Compared with commercially available polyaluminum chloride and polymeric ferric sulfate, the polysilicate aluminum iron flocculant has better flocculation effect, showing good application prospect and potential industrial value, and has good application prospect. Future research can further optimize the preparation process and use conditions of PSAF to achieve more efficient and more economical wastewater treatment. BRIEF DESCRIPTION OF DRAWINGS

[0087] Figure 1 The flow chart of the preparation method of the present application. DETAILED DESCRIPTION

[0088] The present application is further described in conjunction with specific embodiments.

[0089] Example 1

[0090] Thermal activation: The raw red mud was air-dried for two weeks and ground to pass through a 100 mesh sieve. 5 g of the red mud powder was calcined at 800°C for 3 h in a muffle furnace;

[0091] Acid leaching: The calcined red mud was stirred with 7 mol / L hydrochloric acid solution at 70°C for 180 min with a liquid-to-solid ratio of 7 mL:1 g. The acid leaching solution and residue were obtained by centrifugal filtration. The acid leaching solution was a mixed solution containing iron and aluminum, and the acid leaching residue was dried at 110°C for 12 h;

[0092] Alkaline leaching: The dried acid leaching residue was stirred with 15% NaOH solution at 80°C for 90 min with a liquid-to-solid ratio of 7 mL:1 g. The alkaline leaching solution and residue were obtained by centrifugal filtration. The alkaline leaching solution was a silicon-containing solution;

[0093] The concentration of silicon in the alkaline leaching solution was adjusted to 0.3 mol / L. The calibrated silicon solution was added dropwise to 5 mL of stirring hydrochloric acid (1+1 (V / V)) to adjust the pH to about 3. After activation for two hours, a polysilicic acid solution was obtained. Under stirring conditions, aluminum-iron mixed solution was added to the polysilicic acid solution under the conditions of aluminum-iron molar ratio of 1:1, 3:1, 5:1, 7:1, and (aluminum+iron) / silicon molar ratio of 1:1. 0.3 mol / L NaOH solution was added to the above solution to adjust the alkalinity to 0.5. After aging for 24 h at room temperature and normal pressure, a polysilicic acid aluminum-iron flocculant (PSAF) was obtained.

[0094] 1 L of simulated fluorine-containing wastewater (initial turbidity: 100 NTU; F - concentration: 10 mg / L) was added with 0.66 mmol / L of self-made PSAF. The mixture was stirred on a programmed coagulation experiment stirrer at a speed of 250 r / min for 2 min, then at a speed of 90 r / min for 10 min, and then allowed to stand for 20 min. The supernatant was taken to measure the turbidity and F - concentration. Under the optimal conditions, the turbidity and F - removal rates were 82.3% and 65.7%, 85.5% and 66.8%, 97.6% and 80.8%, and 96.7% and 76.8%, respectively.

[0095] Example 2

[0096] Thermal activation: The raw red mud was air-dried for two weeks and ground to pass through a 100 mesh sieve. 5 g of the red mud powder was calcined at 800°C for 3 h in a muffle furnace;

[0097] Acid leaching: the roasted red mud was stirred with 7 mol / L HCl solution at 70℃ for 180 min, the liquid-solid ratio was 7 mL:1 g, and the acid leaching liquid and residue were obtained by centrifugal filtration. The acid leaching liquid was a mixed solution containing iron and aluminum, and the acid leaching residue was dried at 110℃ for 12 h for standby;

[0098] Alkaline leaching: the dried acid leaching residue was heated and stirred with 15% NaOH solution at 80℃ for 90 min, the liquid-solid ratio was 7 mL:1 g, and the alkaline leaching liquid and residue were obtained by centrifugal filtration. The alkaline leaching liquid was a silicon-containing solution;

[0099] The concentration of silicon in the alkaline leaching liquid was adjusted to 0.3 mol / L, and the calibrated silicon solution was added dropwise into 5 mL stirring hydrochloric acid (1+1(V / V)) to adjust the pH to about 3. After activation for two hours, a polysilicic acid solution was obtained. Under stirring conditions, aluminum-iron mixed solution was added to the polysilicic acid solution under the conditions of aluminum-iron molar ratio of 5:1, (aluminum+iron) / silicon molar ratio of 0.5:1, 1:1, and 3:1. 0.3 mol / L NaOH solution was added to the above solution to adjust the alkalinity to 0.5. After aging for 24 h at normal temperature and pressure, a polysilicic acid aluminum-iron flocculant (PSAF) was obtained.

[0100] Take 1 L of simulated fluorine-containing wastewater (initial turbidity: 100 NTU; F- concentration: 10 mg / L), add 0.66 mmol / L of self-made PSAF, and place it on a program-controlled coagulation experiment stirrer. Stir at 250 r / min for 2 min, then stir at 90 r / min for 10 min, and then stand for 20 min. Take the supernatant to measure the turbidity and F - concentration. Under the optimal conditions, the turbidity and F - removal rates were 41.7% and 18.3%, 97.6% and 80.8%, and 90.3% and 58.4%, respectively.

[0101] Example 3

[0102] Thermal activation: the raw red mud was naturally air-dried for two weeks and ground through a 100-mesh sieve for standby. Take 5 g of red mud powder and roast in a muffle furnace at 800℃ for 3 h;

[0103] Acid leaching: the roasted red mud was stirred with 7 mol / L HCl solution at 70℃ for 180 min, the liquid-solid ratio was 7 mL:1 g, and the acid leaching liquid and residue were obtained by centrifugal filtration. The acid leaching liquid was a mixed solution containing iron and aluminum, and the acid leaching residue was dried at 110℃ for 12 h for standby;

[0104] Alkaline leaching: the acid leaching residue after drying above was heated and stirred with 15% NaOH solution at 80℃ for 90 min, the liquid-solid ratio was 7 mL: 1 g, and the alkaline leaching liquid and residue were obtained by centrifugal filtration, the alkaline leaching liquid was a silicon-containing solution;

[0105] The concentration of silicon in the alkaline leaching liquid was adjusted to 0.3 mol / L, the calibrated silicon solution was added dropwise into 5 mL stirring hydrochloric acid (1+1 (V / V)), the pH was adjusted to about 3, and the polysilicic acid solution was obtained after activation for two hours; under stirring, the aluminum-iron mixed solution was added to the polysilicic acid solution under the conditions that the aluminum-iron molar ratio was 5:1 and the (aluminum+iron) / silicon molar ratio was 1:1, 0.3 mol / L NaOH solution was added to the above solution, the alkalization degree was adjusted to 0.25, 0.5 and 0.75, and the polysilicic acid aluminum-iron flocculant (PSAF) was obtained after aging for 24 h at normal temperature and pressure;

[0106] Take 1 L of simulated fluorine-containing wastewater (initial turbidity: 100 NTU; F - concentration: 10 mg / L), add 0.66 mmol / L of self-made PSAF, place it on a program-controlled coagulation experiment stirrer, stir at a speed of 250 r / min for 2 min, then stir at a speed of 90 r / min for 10 min, and then stand for 20 min, take the supernatant to measure the turbidity and F - concentration, and the turbidity and F - removal rates were 97.2% and 46.1%, 97.6% and 80.8%, and 93.0% and 44.8%, respectively.

[0107] Example 4

[0108] Thermal activation: the raw red mud was naturally air-dried for two weeks, and then ground through a 100-mesh sieve for use. 5 g of red mud powder was calcined in a muffle furnace at 800℃ for 3 h;

[0109] Acid leaching: the calcined red mud was stirred with 7 mol / L hydrochloric acid solution in a 70℃ water bath for 180 min, the liquid-solid ratio was 7 mL: 1 g, and the acid leaching liquid and residue were obtained by centrifugal filtration, the acid leaching liquid was a mixed solution containing iron and aluminum; the acid leaching residue was dried at 110℃ for 12 h for standby;

[0110] Alkaline leaching: the acid leaching residue after drying above was heated and stirred with 15% NaOH solution at 80℃ for 90 min, the liquid-solid ratio was 7 mL: 1 g, and the alkaline leaching liquid and residue were obtained by centrifugal filtration, the alkaline leaching liquid was a silicon-containing solution;

[0111] The concentration of silicon in the alkali leaching solution is adjusted to 0.3 mol / L, the calibrated silicon solution is added dropwise into 5 mL stirring hydrochloric acid (1+1 (V / V)), the pH is adjusted to about 3, and the polysilicic acid solution is obtained after activation for two hours; under stirring, the aluminum-iron mixed solution is added into the polysilicic acid solution under the conditions that the molar ratio of aluminum to iron is 5:1 and the molar ratio of (aluminum+iron) to silicon is 1:1, the 0.3 mol / L NaOH solution is added into the above solution, the alkalization degree is adjusted to 0.5, and the polysilicic acid aluminum-iron flocculant (PSAF) is obtained after aging for 24 h under normal temperature and pressure;

[0112] 50 mL of the polysilicic acid aluminum-iron flocculant and 0.5 g of acrylamide (AM) are taken in a three-necked flask, which is placed in a constant-temperature water bath to be heated, the temperature is kept at 25±2 ℃, 1 mL of 1% K2S2O8 solution is added into the reactor, and the mixed solution is continuously stirred and purged with ultra-pure nitrogen to remove dissolved oxygen and carbon dioxide. After 15 min, 1% FeSO4 (n(S2O8 2- ) : n(Fe 2+ )=5:4) solution is added into the solution, the PSAF-PAM composite flocculant is prepared after reaction for four hours under nitrogen atmosphere;

[0113] 1 L of simulated fluorine-containing wastewater (initial turbidity: 100 NTU; F - concentration: 10 mg / L) is taken, 0.66 mmol / L of the self-made PSAF-PAM composite flocculant is added, and the mixture is placed on a program-controlled coagulation experiment stirrer, stirred at a speed of 250 r / min for 2 min, then stirred at a speed of 90 r / min for 10 min, and then left to stand for 20 min, the supernatant is taken to measure the turbidity and F - concentration, and under the optimal conditions, the turbidity and F - removal rates are 97.6% and 66.0%, respectively.

[0114] Example 5

[0115] Thermal activation: the raw red mud is naturally air-dried for two weeks, and then ground through a 100-mesh sieve for use. 5 g of red mud powder is calcined in a muffle furnace at 800 ℃ for 3 h;

[0116] Acid leaching: the calcined red mud is stirred with a hydrochloric acid solution with a concentration of 7 mol / L under the condition of a 70 ℃ water bath for 180 min, the liquid-solid ratio is 7 mL:1 g, and after centrifugal filtration, an acid leaching solution and an acid leaching residue are obtained, the acid leaching solution is a mixed solution containing iron and aluminum; the acid leaching residue is dried at 110 ℃ for 12 h for standby use;

[0117] Alkali leaching: the above dried acid leaching residue is heated and stirred with a NaOH solution with a mass concentration of 15% under the condition of 80 ℃ for 90 min, the liquid-solid ratio is 7 mL:1 g, and after centrifugal filtration, an alkali leaching solution and an alkali leaching residue are obtained, the alkali leaching solution is a silicon-containing solution;

[0118] The concentration of silicon in the alkali leaching solution was adjusted to 0.3 mol / L, the calibrated silicon solution was added to 5 mL of stirring (1+1 (V / V) hydrochloric acid, the pH was adjusted to about 3, and the polysilicic acid solution was obtained after activation for two hours; under stirring conditions, the aluminum-iron mixed solution was added to the polysilicic acid solution under the conditions that the molar ratio of aluminum to iron was 5:1 and the molar ratio of (aluminum+iron) to silicon was 1:1, 0.3 mol / L NaOH solution was added to the above solution, the degree of alkalization was adjusted to 0.5, and the polysilicic acid aluminum-iron flocculant (PSAF) was obtained after aging for 24 h under normal temperature and pressure.

[0119] 1 L of actual fluorine-containing wastewater (initial turbidity: 1 NTU; F - concentration: 1 mg / L) was taken, 0.66 mmol / L of self-made PSAF was added, and it was placed on a programmed coagulation experiment stirrer, stirred at a speed of 200 r / min for 2 min, then stirred at a speed of 60 r / min for 10 min, and then statically precipitated for 20 min, and the supernatant was taken to measure the turbidity and F - concentration, under the optimal conditions, the turbidity and F - removal rates were 81.8% and 60.6%, respectively.

[0120] Example 6

[0121] Thermal activation: the raw red mud was naturally air-dried for two weeks, ground through a 100-mesh sieve and used. 5 g of red mud powder was calcined in a muffle furnace at 800℃ for 3 h;

[0122] Acid leaching: the calcined red mud was stirred with a hydrochloric acid solution with a concentration of 7 mol / L at 70℃ in a water bath for 180 min, the liquid-solid ratio was 7 mL:1 g, and after centrifugal filtration, an acid leaching solution and an acid leaching residue were obtained, the acid leaching solution was a mixed solution containing iron and aluminum; the acid leaching residue was dried at 110℃ for 12 h and used;

[0123] Alkali leaching: the above dried acid leaching residue was heated and stirred with a NaOH solution with a mass concentration of 15% at 80℃ for 90 min, the liquid-solid ratio was 7 mL:1 g, and after centrifugal filtration, an alkali leaching solution and an alkali leaching residue were obtained, the alkali leaching solution was a silicon-containing solution;

[0124] The concentration of silicon in the alkali leaching solution was adjusted to 0.3 mol / L, the calibrated silicon solution was added to 5 mL of stirring (1+1 (V / V) hydrochloric acid, the pH was adjusted to about 3, and the polysilicic acid solution was obtained after activation for two hours; under stirring conditions, the aluminum-iron mixed solution was added to the polysilicic acid solution under the conditions that the molar ratio of aluminum to iron was 5:1 and the molar ratio of (aluminum+iron) to silicon was 1:1, 0.3 mol / L NaOH solution was added to the above solution, the degree of alkalization was adjusted to 0.5, and the polysilicic acid aluminum-iron flocculant (PSAF) was obtained after aging for 24 h under normal temperature and pressure.

[0125] Take 1 L self-made fluorine-containing river water (initial turbidity: 1 NTU; F - concentration: 10 mg / L), add 0.66 mmol / L self-made PSAF, place in a program-controlled coagulation experiment stirrer, stir at 250 r / min for 2 min, then stir at 90 r / min for 10 min, stand for 20 min, take the supernatant to measure its turbidity and F - concentration, under the optimal conditions, turbidity and F - removal rates were 75.1% and 51.2%, respectively.

[0126] Example 7

[0127] The self-made flocculant (PSAF) was compared with the commercially available flocculants (PAC, PSF) in terms of effect. Take 3 1 L simulated fluorine-containing wastewater (initial turbidity: 100 NTU; F - concentration: 10 mg / L), add 0.66 mmol / L self-made PSAF, PAC and PSF containing equal amounts of aluminum and iron active ingredients, respectively, place in a program-controlled coagulation experiment stirrer, stir at 250 r / min for 2 min, then stir at 90 r / min for 10 min, stand for 20 min, take the supernatant to measure its turbidity and F - concentration, PSAF turbidity and F - removal rates were 97.6% and 80.8%, respectively, PAC turbidity and F - removal rates were 89.8% and 18.3%, respectively, PSF turbidity and F - removal rates were 89.9% and 4.3%, respectively, the flocculation effect of PSAF was obviously better than that of PAC and PSF.

[0128] PSAF, due to its unique polysilicic acid modification structure, has shown excellent performance in treating fluorine-containing wastewater. PSAF has high removal rate of F - and is less affected by coexisting ions. Compared with commercially available polyaluminum chloride and polymeric ferric sulfate, the flocculation effect of polysilicic aluminum iron flocculant is better, showing good application prospect and potential industrial value, and has good application prospect. Future research can further optimize the preparation process and use conditions of PSAF to achieve more efficient and more economical wastewater treatment.

Claims

1. A method for preparing polyaluminum silicate iron-PAM composite flocculant using red mud as raw material, characterized in that: Includes the following steps: Step 1, thermal activation: After the original red mud is naturally air-dried for two weeks, it is ground through a 100-mesh sieve, and the sieved red mud powder is placed in a muffle furnace for roasting. The second step is acid leaching: the roasted red mud is mixed with hydrochloric acid solution under water bath conditions, centrifuged and filtered to obtain acid leaching solution and acid leaching residue; the acid leaching solution is a mixture containing iron and aluminum, and the acid leaching residue is dried for later use. The third step is alkaline leaching: The dried acid leaching residue is heated and stirred with sodium hydroxide solution, then centrifuged and filtered to obtain alkaline leaching solution and alkaline leaching residue; wherein, the alkaline leaching solution is a silicon-containing solution; Step 4, preparation of polysilicic acid solution: Adjust the concentration of silicon in the alkaline leaching solution, then add it dropwise to hydrochloric acid under stirring, adjust the pH, and after activation, obtain polysilicic acid solution; Step 5, copolymerization: Under stirring conditions, iron-aluminum mixtures of different proportions are added to polysilicic acid solution. NaOH solution is added to the above solution to adjust the alkalinity. The mixture is aged at room temperature and pressure to obtain polyaluminum-iron polysilicate flocculant PSAF. The different proportions of iron-aluminum mixed solutions are 0.5 mol / L ferric chloride solution and 0.5 mol / L aluminum sulfate solution used to adjust the acid leaching solution in the second step; The molar ratio of aluminum to iron is 1~7:1, and the molar ratio of (aluminum + iron) to silicon is 0.5~3:

1. The NaOH solution concentration was 0.3 mol / L, and the alkalinity was adjusted to 0.25~0.75; the aging time was 24 h. Step 6, Preparation of PSAF-PAM composite flocculant: Take polyaluminum iron silicate flocculant and acrylamide into a three-necked flask, place it in a constant temperature water bath and heat it. After adding K2S2O8 solution into the reactor, stir the mixed solution continuously and purge with ultrapure nitrogen to remove dissolved oxygen and carbon dioxide. After 15 minutes, add FeSO4 solution to the solution. After reacting for four hours under a nitrogen atmosphere, PSAF-PAM composite flocculant is prepared. The ratio of polyaluminum ferric silicate flocculant to acrylamide is 50 mL: 0.5 g; the water bath temperature is 25 ± 2 °C; the mass concentration of K2S2O8 solution is 1%, and the addition amount is 1 mL; the mass concentration of FeSO4 solution is 1%, and the S2O8... 2- with Fe 2+ The molar ratio is 5:

4.

2. The method for preparing polyaluminum silicate iron-PAM composite flocculant using red mud as raw material according to claim 1, characterized in that: The red mud powder mentioned in the first step is 5g, the muffle furnace roasting temperature is 800℃, and the roasting time is 3h.

3. The method for preparing polyaluminum silicate iron-PAM composite flocculant using red mud as raw material according to claim 1, characterized in that: The concentration of the hydrochloric acid solution in the second step is 7 mol / L, the water bath temperature is 70℃, the stirring time is 180 min, and the ratio of hydrochloric acid solution to red mud is 7 mL: 1 g; the drying temperature of the acid leaching residue is 110℃, and the drying time is 12 h.

4. The method for preparing polyaluminum silicate iron-PAM composite flocculant using red mud as raw material according to claim 1, characterized in that: The sodium hydroxide solution in the third step has a mass concentration of 15%, a heating temperature of 80℃, and a stirring time of 90 min; the ratio of sodium hydroxide solution to acid leaching residue is 7 mL: 1 g.

5. The method for preparing polyaluminum silicate iron-PAM composite flocculant using red mud as raw material according to claim 1, characterized in that: In step four, the concentration of silicon in the alkaline leaching solution is adjusted to 0.3 mol / L; the hydrochloric acid solution is 1 volume of hydrochloric acid + 1 volume of water; and the pH is adjusted to 3. The activation time is 2 hours.

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