Composite flocculant for tailings treatment and preparation method thereof

Abstract

The application discloses a composite flocculant for tailing treatment and a preparation method thereof, and belongs to the technical field of tailing water treatment. The composite flocculant is a 4-6 arm star-shaped hybrid polyacrylamide with a double bond modified nano aluminum hydroxide as a rigid branched core, and has grafted quaternary ammonium salt cation groups, sulfonic acid groups, hydrophobic ester groups and dithio carbamate chelating groups on the molecular chain; the preparation method comprises nano core double bond modification, in-situ free radical copolymerization to construct a star-shaped skeleton and post-modification grafting of chelating groups. The application solves the problems of high viscosity, molecular chain entanglement and high single consumption of a medicament of a traditional linear flocculant through a star-shaped topological structure, and realizes multiple targets of dense flocculation, low torque operation of a thickener, deep dewatering, micro-fine particle capture and heavy metal chelation through the cooperation of a rigid core and multiple functional groups. The process is green and controllable, easy to be industrialized and enlarged, and is suitable for the efficient disposal requirements of high-muddy and high-viscosity fine-grained tailings.

Description

Technical Field

[0001] This invention relates to the field of tailings water treatment technology, and in particular to a composite flocculant for tailings treatment and its preparation method. Background Technology

[0002] As mineral resources become increasingly depleted, tailings produced during mineral processing are characterized by a high proportion of fine particles, a high degree of mudification, and strong viscosity. These tailings particles have a high negative charge density, high specific surface area, high bound water content, and a large amount of residual flotation reagents, posing a great challenge to tailings thickening, dewatering, and harmless disposal.

[0003] Existing mainstream linear polyacrylamide (PAM) flocculants have several key drawbacks: First, the linear molecular chains are prone to entanglement, resulting in extremely high solution viscosity for the same molecular weight, poor solubility and dispersibility, and high reagent consumption. Second, the resulting flocs are loose and have weak shear resistance, making them easily broken within the thickener, leading to high operating torque and a high risk of rake-related safety accidents. Third, the internal drainage channels of the flocs are prone to collapse under pressure, and the moisture content of the mud cake generally exceeds 45%, making subsequent storage and disposal difficult. Fourth, they have poor resistance to interference from flotation reagents, lack heavy metal chelation function, and cannot simultaneously achieve fine particle capture and effluent purification, making it difficult to meet the current environmental protection requirements for efficient tailings disposal.

[0004] Most existing improved star-shaped polyacrylamide flocculants use small organic molecules as branching centers and lack rigid supporting structures, so the floc density and compressibility are not substantially improved. Some hybrid flocculants that introduce inorganic nanoparticles have problems such as mismatch between functional group design and the needs of high mud tailings treatment, uncontrollable branching structure, and poor synergistic effect of multi-functional groups. They cannot simultaneously achieve multiple goals such as low reagent consumption, low thickener torque, low cake moisture content, low effluent SS and efficient removal of heavy metals. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a composite flocculant for tailings treatment and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention first proposes a composite flocculant for tailings treatment. The composite flocculant is a 4-6 arm star-shaped hybrid polyacrylamide with double bond modified nano aluminum hydroxide as a rigid branched core. The molecular chain of the star-shaped hybrid polyacrylamide is grafted with quaternary ammonium salt cationic groups, sulfonic acid groups, hydrophobic ester groups and dithiocarbamate chelating groups.

[0007] Preferably, in the composite flocculant, the functional groups corresponding to each functional monomer are 10%-12% quaternary ammonium salt cationic groups, 8%-10% sulfonic acid groups, 5%-8% hydrophobic ester groups, and the balance is amide groups provided by acrylamide monomers; the grafting amount of the dithiocarbamate chelating groups is 10%-15% of the total molar amount of acrylamide units.

[0008] Preferably, the double-bond modified nano-aluminum hydroxide is nano-aluminum hydroxide modified with silane coupling agent KH-570, with a particle size of 20-50 nm and a specific surface area ≥150 m². 2 / g; the amount of double bond modified nano aluminum hydroxide added is 2%-4% of the total monomer mass.

[0009] Preferably, the quaternary ammonium salt cationic group is derived from methacryloyloxyethyltrimethylammonium chloride, the sulfonic acid group is derived from 2-acrylamido-2-methylpropanesulfonic acid, and the hydrophobic ester group is derived from butyl methacrylate.

[0010] Preferably, the composite flocculant has an absolute molecular weight of 8-10 million and a branching degree of 0.45-0.55, corresponding to a 4-6 arm star topology.

[0011] This invention also proposes a method for preparing the aforementioned composite flocculant for tailings treatment, comprising the following steps: S1. Nanocore modification: Nano aluminum hydroxide is dispersed in anhydrous ethanol and ultrasonically dispersed to obtain a uniform suspension. The pH is adjusted to 4.0-5.0, the temperature is raised to 60℃, silane coupling agent KH-570 is added dropwise, and the reaction is carried out under reflux for 4-6 hours. After centrifugation, washing, and vacuum drying, modified nano aluminum hydroxide with polymerizable double bonds grafted on the surface is obtained. The silane coupling agent KH-570 (γ-methacryloyloxypropyltrimethoxysilane) undergoes hydrolysis under weakly acidic conditions to generate silanol. The silanol then undergoes dehydration condensation with the hydroxyl groups (Al-OH) on the surface of nano-aluminum hydroxide, forming covalent Al-O-Si bonds. Through chemical bonding, polymerizable vinyl double bonds are introduced onto the surface of hydrophilic inorganic nanoparticles, transforming the originally inert inorganic core into a macromonomer capable of participating in free radical polymerization, thus providing branching sites for subsequent in-situ polymerization.

[0012] S2. In-situ copolymerization: Modified nano-aluminum hydroxide is dispersed in the aqueous phase under nitrogen protection and mixed with acrylamide, cationic monomer, sulfonic acid monomer and hydrophobic ester monomer. The pH of the system is adjusted to 6.0-7.0. In-situ free radical copolymerization is initiated by redox initiation system at 35-40℃ for 6-8h to obtain 4-6 arm star-shaped hybrid polyacrylamide precursor. Under the action of a redox initiator, acrylamide (AM) and three functional monomers (cationic DMC, sulfonic acid AMPS, and hydrophobic BMA) in the system undergo free radical copolymerization with the double bonds on the surface of modified nano-aluminum hydroxide. The monomers in the solution not only polymerize with each other, but also preferentially react with the active double bonds on the surface of the nanocore, causing polymer chains to grow outward from the surface of the nanocore, forming a star-shaped hybrid structure with the nanocore as the center and the polymer chains as the arms.

[0013] By controlling the content of nanonuclei and the amount of initiator, and limiting the number of arms (4-6 arms), linear or cross-linking side reactions were avoided. AMPS provides rigid sulfonic acid groups (enhancing chain extension), DMC provides cationic charge, and BMA provides hydrophobic segments, thus completing the main chain construction and functionalization in one step.

[0014] S3. Chelating group modification: The star-shaped hybrid polyacrylamide precursor is diluted with deionized water to a solid content of 10%, the pH is adjusted to 10.0-11.0, the temperature is raised to 40-45℃, formaldehyde and diethylenetriamine are added and reacted at the temperature for 3-4 hours to complete amination; the temperature is lowered to 25-30℃, carbon disulfide is added dropwise, and the reaction is maintained at the temperature for 4-6 hours. After precipitation, washing, drying and pulverizing, the composite flocculant product is obtained.

[0015] The amide group (-CONH2) on the precursor undergoes a Mannich reaction with formaldehyde and diethylenetriamine under alkaline conditions, introducing a polyamine side chain. The introduced amine group (-NH2, -NH-) then undergoes nucleophilic addition with carbon disulfide (CS2) under alkaline conditions to generate dithiocarbamate (DTC).

[0016] Because DTC groups have a strong chelating ability for heavy metal ions, but DTC-containing monomers are difficult to directly participate in copolymerization (due to easy chain transfer or complexation initiators), a strategy of first polymerizing and then performing polymer grafting modification is adopted. The generated DTC groups contain S and N atoms, which can form stable five-membered ring chelates with heavy metal ions in tailings, achieving chemical capture of heavy metals.

[0017] Preferably, in S1, the mass ratio of nano-aluminum hydroxide to KH-570 is 100:10-15.

[0018] Preferably, in step S2, the redox initiation system is an ammonium persulfate-sodium bisulfite system, and the amount of initiator added is 0.2%-0.3% of the total monomer mass.

[0019] Preferably, in S3, the molar ratio of formaldehyde, diethylenetriamine, and carbon disulfide is 1:1.2:1.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. A 4-6 arm star structure is constructed using modified nano-aluminum hydroxide as a rigid branched core. The molecular chains extend radially, eliminating the problem of entanglement and collapse of wireless molecules. The solution viscosity is reduced by more than 35% at the same molecular weight, and the adsorption sites are fully exposed. The reagent consumption can be controlled within 0.4 kg / t dry ore, which is far lower than the industry standard. The rigid nano-core provides permanent internal support for the flocs, avoiding shearing, breakage and compression deformation of the flocs, thus structurally solving the industry problem of loose flocs.

[0021] 2. Quaternary ammonium salt cationic groups rapidly compress the double electric layer of clay particles, achieving destabilization of highly muddy tailings; sulfonic acid groups enhance the rigidity of molecular chain segments, synergistically improving floc density with rigid cores, making flocs easy to roll, and thickener operating torque ≤26%; hydrophobic ester groups eliminate interference from residual flotation reagents through hydrophobic association, while forming hydrophobic micro-regions inside the flocs, strongly displacing bound water, reducing the moisture content of the mud cake to below 35%; dithiocarbamate groups efficiently chelate heavy metals, synergistically capturing fine particles with cationic groups, resulting in effluent SS ≤300mg / L and heavy metal removal rate ≥95%, achieving the full-process goals of tailings thickening, dewatering, and water purification with a single addition.

[0022] 3. The three-step aqueous phase process of "nanocore modification - in-situ copolymerization - post-modification grafting" is adopted, which avoids the use of large amounts of toxic organic solvents and is green and environmentally friendly. By adjusting the nanocore grafting density, monomer ratio and reaction conditions, the number of polymer arms, branching degree and functional group grafting rate can be precisely controlled, and the product performance is stable. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] Example 1: A composite flocculant for tailings treatment, consisting of a 4-6 arm star-shaped hybrid polyacrylamide with double bond modified nano-aluminum hydroxide as a rigid branched core, and molecularly linked with quaternary ammonium salt cationic groups, sulfonic acid groups, hydrophobic ester groups and dithiocarbamate chelating groups. Based on the total molar amount of monomers, the product contains 11% quaternary ammonium cation groups, 9% sulfonic acid groups, 6% hydrophobic ester groups, and the remainder is acrylamide amide groups; the amount of dithiocarbamate chelating groups grafted is 12% of the total molar amount of acrylamide units; the modified nano aluminum hydroxide particles have a diameter of 30 nm and are added at 3% of the total monomer mass; the product has an absolute molecular weight of 9 million and a branching degree of 0.5.

[0025] The preparation method steps are as follows: S1. Nanonucleus modification: 100g of dried nano-aluminum hydroxide was dispersed in 500g of anhydrous ethanol and ultrasonically dispersed for 30min to obtain a uniform suspension. The pH was adjusted to 4.5 with glacial acetic acid, the temperature was raised to 60℃, and 12g of KH-570 was slowly added dropwise over 30min. The mixture was kept warm and refluxed for 5h. After the reaction was completed, the mixture was centrifuged at 4000rpm for 15min, washed 3 times with anhydrous ethanol, vacuum dried at 60℃ for 12h, and pulverized through a 200-mesh sieve to obtain modified nano-aluminum hydroxide.

[0026] S2. In-situ copolymerization: Add 8500g of deionized water to a 10L reactor, purge with nitrogen for 10 min to remove oxygen, add 45g of modified nano-aluminum hydroxide, and ultrasonically disperse for 20 min; add 1020g of acrylamide, 165g of 80% methacryloyloxyethyltrimethylammonium chloride, 135g of 2-acrylamido-2-methylpropanesulfonic acid, and 90g of butyl methacrylate sequentially, and stir until completely dissolved. Adjust the pH to 6.5 with sodium hydroxide; purge with nitrogen for 30 min, raise the temperature to 38℃, and simultaneously add 22.5g of 10% ammonium persulfate aqueous solution and 15g of 10% sodium bisulfite aqueous solution within 20 min. After the addition is complete, maintain the temperature at 38℃ for 7 h, stirring at low speed and under nitrogen protection throughout, to obtain a star-shaped hybrid polyacrylamide precursor.

[0027] S3. Chelating group modification: 1000g of 10% solids-containing precursor aqueous solution was added to the reaction vessel, the pH was adjusted to 10.5 with sodium hydroxide, the temperature was raised to 42℃, and 30g of 37% formaldehyde and 36g of diethylenetriamine were added dropwise in sequence. After the addition was completed, the reaction was kept at the temperature for 3.5h. The temperature was lowered to 28℃, and 30g of carbon disulfide was slowly added dropwise over 40min. After the addition was completed, the reaction was kept at the temperature for 5h. The product was precipitated with anhydrous ethanol, washed 3 times, vacuum dried at 60℃ for 12h, and pulverized through an 80-mesh sieve to obtain the finished product.

[0028] Example 2: The composite flocculant for tailings treatment in this example, based on the total molar amount of monomers, contains 10% quaternary ammonium salt cationic groups, 8% sulfonic acid groups, 5% hydrophobic ester groups, and the remainder is acrylamide amide groups; the amount of dithiocarbamate chelating groups grafted is 10% of the total molar amount of acrylamide units. The modified nano-aluminum hydroxide has a particle size of 20nm and is added at 2% of the total monomer mass; the product has an absolute molecular weight of 8 million, a branching degree of 0.45, and corresponds to a 4-arm star structure.

[0029] The preparation method steps are as follows: S1. Nanonucleus modification: The mass ratio of nano-aluminum hydroxide to KH-570 is 100:10, and the reaction is carried out under reflux for 4 hours. The other parameters are the same as in Example 1.

[0030] S2, In-situ copolymerization: The monomer ratio is adjusted according to the functional group ratio, the initiator addition is 0.2% of the total monomer mass, the reaction temperature is 35℃, the reaction time is 8h, and the other parameters are the same as in Example 1.

[0031] S3, Chelating group modification: formaldehyde, diethylenetriamine, carbon disulfide molar ratio 1:1.2:1, amination reaction temperature 40℃, reaction time 4h; carbon disulfide drop addition temperature 25℃, reaction time 6h, other parameters are the same as in Example 1.

[0032] Example 3: The composite flocculant for tailings treatment in this example, based on the total molar amount of monomers, contains 12% quaternary ammonium salt cationic groups, 10% sulfonic acid groups, 8% hydrophobic ester groups, and the balance is acrylamide amide groups; the amount of dithiocarbamate chelating groups grafted is 15% of the total molar amount of acrylamide units. The modified nano-aluminum hydroxide has a particle size of 50 nm and is added at 4% of the total monomer mass; the product has an absolute molecular weight of 10 million, a branching degree of 0.55, and corresponds to a 6-arm star structure.

[0033] The preparation method steps are as follows: S1. Nanonucleus modification: The mass ratio of nano-aluminum hydroxide to KH-570 is 100:15, and the reaction is carried out under reflux for 6 hours. The other parameters are the same as in Example 1.

[0034] S2, In-situ copolymerization: The monomer ratio is adjusted according to the functional group ratio, the initiator addition is 0.3% of the total monomer mass, the reaction temperature is 40℃, the reaction time is 6h, and the other parameters are the same as in Example 1.

[0035] S3, Chelating group modification: formaldehyde, diethylenetriamine, carbon disulfide molar ratio 1:1.2:1, amination reaction temperature 45℃, reaction time 3h; carbon disulfide drop addition temperature 30℃, reaction time 4h, other parameters are the same as in Example 1.

[0036] The following comparison model was also set: Comparative Example 1: Commercially available conventional linear cationic polyacrylamide, molecular weight 12 million, cationicity 11%.

[0037] Comparative Example 2: A four-armed star-shaped cationic polyacrylamide without a rigid core, with a molecular weight of 9 million, a cationicity of 11%, and other functional groups consistent with Example 1.

[0038] Comparative Example 3: A composite flocculant without sulfonic acid groups, with the same structure, proportions and preparation method as in Example 1.

[0039] Comparative Example 4: A composite flocculant without hydrophobic ester groups, with the same structure, proportions and preparation method as in Example 1.

[0040] Comparative Example 5: A composite flocculant without dithiocarbamate chelating groups, with the same structure, proportions, and preparation method as in Example 1.

[0041] The test subject was a highly muddy, highly viscous fine-grained tailings from an iron ore mine. Basic parameters: -200 mesh 92%, -400 mesh 75%, clay mineral content 32%, residual flotation reagent content 85 g / t, pulp concentration 30%, initial Pb... 2+ Content 12.6 mg / L.

[0042] Test method: Add reagent at a rate of 0.35 kg / t dry ore, and determine settling velocity, effluent suspended solids (SS), thickener simulated torque, cake moisture content, and Pb. 2+ The removal rate and test results are shown in the table below: Table 1. Performance test results for each group: Data Analysis: The test results of Examples 1-3 and Comparative Examples 1-5 show that the star-shaped hybrid polyacrylamide designed in this invention, with double-bond modified nano-aluminum hydroxide as a rigid core, exhibits significant comprehensive performance advantages in treating highly muddy fine-grained tailings. In all three examples, with a reagent consumption of only 0.35 kg / t, the initial settling velocity reached over 16.2 m / h, the suspended solids in the effluent were below 300 mg / L, the thickener torque was controlled within a low range of 24%-26%, and the cake moisture content was below 35%. Simultaneously, Pb... 2+ With a removal rate exceeding 95%, it fully meets the stringent requirements for tailings treatment.

[0043] Comparative Example 1, using conventional linear cationic polyacrylamide, exhibited a settling velocity of only 8.6 m / h, an effluent SS concentration as high as 605 mg / L, a torque increase to 52%, and a cake moisture content of 46.5%, with many indicators severely exceeding standards. This is mainly due to the easy breakage of linear molecular chains under shearing action, resulting in loose and porous flocs, leading to low flocculation efficiency and difficulty in dewatering. In contrast, the star-shaped hybrid structure used in the example provides stable branching points through a rigid nano-aluminum hydroxide core, with the molecular chains extending radially. This significantly reduces the solution viscosity (approximately 200 mPa·s in the example, compared to 386 mPa·s in Comparative Example 1), ensuring rapid dispersion of the reagent in the slurry while forming highly dense and shear-resistant flocs, thereby simultaneously improving settling velocity and dewatering effect.

[0044] Comparative Example 2, a star-shaped polyacrylamide without a rigid core, showed that while the star-shaped topology improved the solution viscosity (287 mPa·s) and settling velocity (11.3 m / h) to some extent, the lack of inorganic core support resulted in insufficient floc density, and the torque (41%) and cake moisture content (41.2%) were still significantly higher than in the Example. This indicates that nano-aluminum hydroxide not only acts as a branching point to control molecular topology, but its rigid nature also directly enhances the floc's resistance to compression, maintaining structural stability during thickener shearing and filter press dewatering. This is crucial for achieving a torque ≤26% and a moisture content ≤35%.

[0045] Comparative Examples 3, 4, and 5 lacked sulfonic acid groups, hydrophobic ester groups, and dithiocarbamate groups, respectively. Comparative Example 3, lacking sulfonic acid groups, saw its effluent SS increase to 378 mg / L, torque rise to 38%, and cake moisture content reach 39.6%. This was attributed to the reduced strong hydration and chain rigidity of the sulfonic acid groups, making the flocs more prone to deformation under shear. Comparative Example 4, lacking hydrophobic ester groups, saw its cake moisture content recover to 42.8%, and torque reach 39%, confirming that hydrophobic groups effectively reduce the hydrophilicity of the floc surface and promote water release during the pressure filtration process. Comparative Example 5, lacking DTC chelating groups, showed Pb... 2+ The removal rate dropped sharply to 23.5%, but other physical indicators were close to those of the example, indicating that the introduction of DTC mainly contributed to the chemical capture of heavy metals, and had no negative impact on the flocculation and sedimentation process itself, thus achieving the functional integration of physical flocculation and chemical stabilization.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite flocculant for tailings treatment, characterized in that, The composite flocculant is a 4-6 arm star-shaped hybrid polyacrylamide with double bond-modified nano-aluminum hydroxide as a rigid branched core. The molecular chain of the star-shaped hybrid polyacrylamide is grafted with quaternary ammonium salt cationic groups, sulfonic acid groups, hydrophobic ester groups and dithiocarbamate chelating groups.

2. The composite flocculant for tailings treatment according to claim 1, characterized in that, In the composite flocculant, the functional groups corresponding to each functional monomer are 10%-12% quaternary ammonium salt cationic groups, 8%-10% sulfonic acid groups, 5%-8% hydrophobic ester groups, and the balance is amide groups provided by acrylamide monomers; the grafting amount of the dithiocarbamate chelating groups is 10%-15% of the total molar amount of acrylamide units.

3. The composite flocculant for tailings treatment according to claim 1, characterized in that, The double-bond modified nano-aluminum hydroxide is nano-aluminum hydroxide modified with silane coupling agent KH-570, with a particle size of 20-50 nm and a specific surface area ≥150 m². 2 / g; the amount of double bond modified nano aluminum hydroxide added is 2%-4% of the total monomer mass.

4. The composite flocculant for tailings treatment according to claim 1, characterized in that, The quaternary ammonium salt cationic group is derived from methacryloyloxyethyltrimethylammonium chloride, the sulfonic acid group is derived from 2-acrylamide-2-methylpropanesulfonic acid, and the hydrophobic ester group is derived from butyl methacrylate.

5. The composite flocculant for tailings treatment according to claim 1, characterized in that, The composite flocculant has an absolute molecular weight of 8-10 million and a branching degree of 0.45-0.55, corresponding to a 4-6 arm star topology.

6. A method for preparing a composite flocculant for tailings treatment as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Nanocore modification: Nano aluminum hydroxide is dispersed in anhydrous ethanol and ultrasonically dispersed to obtain a uniform suspension. The pH is adjusted to 4.0-5.0, the temperature is raised to 60℃, silane coupling agent KH-570 is added dropwise, and the reaction is carried out under reflux for 4-6 hours. After centrifugation, washing, and vacuum drying, modified nano aluminum hydroxide with polymerizable double bonds grafted on the surface is obtained. S2. In-situ copolymerization: Modified nano-aluminum hydroxide is dispersed in the aqueous phase under nitrogen protection and mixed with acrylamide, cationic monomer, sulfonic acid monomer and hydrophobic ester monomer. The pH of the system is adjusted to 6.0-7.

0. In-situ free radical copolymerization is initiated by redox initiation system at 35-40℃ for 6-8h to obtain 4-6 arm star-shaped hybrid polyacrylamide precursor. S3. Chelating group modification: The star-shaped hybrid polyacrylamide precursor is diluted with deionized water to a solid content of 10%, the pH is adjusted to 10.0-11.0, the temperature is raised to 40-45℃, formaldehyde and diethylenetriamine are added and reacted at the temperature for 3-4 hours to complete amination; the temperature is lowered to 25-30℃, carbon disulfide is added dropwise, and the reaction is maintained at the temperature for 4-6 hours. After precipitation, washing, drying and pulverizing, the composite flocculant product is obtained.

7. The method for preparing the composite flocculant for tailings treatment according to claim 6, characterized in that, In S1, the mass ratio of nano-aluminum hydroxide to KH-570 is 100:10-15.

8. The method for preparing the composite flocculant for tailings treatment according to claim 6, characterized in that, In S2, the redox initiation system is an ammonium persulfate-sodium bisulfite system, and the amount of initiator added is 0.2%-0.3% of the total monomer mass.

9. The method for preparing the composite flocculant for tailings treatment according to claim 6, characterized in that, In S3, the molar ratio of formaldehyde, diethylenetriamine, and carbon disulfide is 1:1.2:1.

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