Chitosan-zinc-rare earth ternary functional composite polymeric ferric sulfate and a preparation method thereof

Abstract

The present application relates to the field of water treatment flocculants, and specifically discloses a chitosan-zinc-rare earth ternary functional composite polymeric ferric sulfate and a preparation method thereof, the preparation method comprising: mixing iron-containing raw materials with acid to form an acid-containing reaction solution; adding chitosan, zinc-containing compounds and rare earth-containing compounds to the reaction solution, controlling the chitosan addition amount to be 0.5% to 5% of the mass of the iron-containing raw materials, the Zn / Fe molar ratio to be 0.03 to 0.12, and the rare earth / Fe molar ratio to be 0.005 to 0.05, and allowing the chitosan to coordinate and combine with iron ions in a catalytic oxidation polymerization process to form a ternary functional composite intermediate; and drying to obtain a solid product. The present application embeds chitosan, zinc and rare earth into the molecular structure of polymeric ferric sulfate through synchronous chemical bonding, realizes molecular-level synergistic effect of the three components, significantly improves the flocculation performance, accelerates the flocculation settling, and can utilize titanium white waste acid resources to produce.

Description

Technical Field

[0001] This invention belongs to the field of water treatment flocculants, specifically a chitosan-zinc-rare earth ternary functional composite polymeric ferric sulfate and its preparation method. Background Technology

[0002] Polyferric sulfate (PFLS) is an inorganic polymeric flocculant with multiple functions, including turbidity removal, decolorization, and removal of organic matter, and is widely used in water treatment. Traditional PFLS primarily works by hydrolyzing and polymerizing iron ions to form polynuclear hydroxyl complexes; its flocculation performance is closely related to its polymerization morphology, basicity, and other structural parameters. To improve the overall performance of PFLS, researchers both domestically and internationally have attempted functional modifications. For example, introducing chitosan to enhance the adsorption capacity for heavy metals and organic pollutants using its abundant amino and hydroxyl groups; introducing zinc ions to strengthen charge neutralization and bridging flocculation effects; or introducing rare earth ions to regulate the polymerization morphology of iron species to improve floc strength and sedimentation performance. These modification methods have improved the application effects of PFLS to some extent.

[0003] However, existing modification technologies typically introduce only single or binary functional components into polyferric sulfate, mostly through physical mixing or simple compounding. These components lack chemical bonding, making it difficult to form an integrated structure at the molecular level. This simple physical mixing results in functional components such as chitosan, zinc, and rare earth elements existing independently, unable to work synergistically, leading to limited improvement in flocculation performance and poor product stability. How to embed multiple functional components into the molecular structure of polyferric sulfate through chemical bonding to achieve synergistic effects is a pressing technical problem to be solved in this field. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a chitosan-zinc-rare earth ternary functional composite polyferric sulfate and its preparation method, thereby solving the problem that in the prior art, the functional components of polyferric sulfate are single or binary and are mostly physically mixed, making it difficult to achieve chemical bonding and synergistic effects among the three components of chitosan, zinc, and rare earth.

[0005] This invention provides a method for preparing chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate, comprising the following steps:

[0006] Step (a): Mix the iron-containing raw material with acid to form an iron-containing... The acidic reaction solution;

[0007] Step (b): Chitosan, a zinc-containing compound, and a rare earth-containing compound are added to the acidic reaction solution, such that the amount of chitosan added is 0.5% to 5% of the mass of the iron-containing raw material, the Zn / Fe molar ratio is 0.03 to 0.12, and the rare earth / Fe molar ratio is 0.005 to 0.05; during the catalytic oxidative polymerization reaction, the active functional groups on the chitosan molecular chain coordinate with iron ions to form a chitosan-zinc-rare earth ternary functional composite polymeric ferric sulfate intermediate;

[0008] Step (c): The ternary functionalized composite ferric sulfate intermediate obtained in step (b) is dried to obtain solid chitosan-zinc-rare earth ternary functionalized composite ferric sulfate.

[0009] Preferably, the chitosan is selected from at least one of chitosan, carboxymethyl chitosan, and quaternized chitosan; the zinc-containing compound is selected from... Or at least one of ZnO; the rare earth compound is selected from at least one of cerium-containing compounds or lanthanum-containing compounds.

[0010] Preferably, the catalytic oxidative polymerization reaction is carried out under pressure, with a reaction pressure of 0.3 to 1.2 MPa, a reaction temperature of 50 to 90°C, oxygen or oxygen-enriched air as an oxidant, and a reaction time of 2 to 5 hours.

[0011] Preferably, the chitosan in step (b) is pre-dissolved in an acetic acid solution with a pH of 2 to 4 to form a chitosan acetic acid solution before being added to the acidic reaction solution.

[0012] Preferably, after the catalytic oxidative polymerization reaction is completed, the reaction solution is rapidly cooled to below 30°C at a rate of 5–15°C / min.

[0013] Preferably, the drying process is spray drying, rotary kiln drying, or a combination of spray drying and rotary kiln drying; the drying process is carried out under an inert gas atmosphere.

[0014] Preferably, the iron-containing raw material is a mixture of waste sulfuric acid generated during the titanium dioxide production process and at least one iron-containing solid waste selected from ferrous sulfate heptahydrate, ferrous sulfate monohydrate, ferrous sulfide, and acid leaching residue; the mass concentration of the waste sulfuric acid is 15% to 25%.

[0015] This invention also provides a chitosan-zinc-rare earth ternary functional composite polyferric sulfate prepared according to the above method, wherein its molecular structure simultaneously contains chitosan, zinc, and rare earth elements, wherein the mass fraction of chitosan is 0.5%–5%, the Zn / Fe molar ratio is 0.03–0.12, and the rare earth / Fe molar ratio is 0.005–0.05; the polyferric sulfate contains dimeric iron (… Ferric iron (Fe3+) accounts for 15%–30% of the total iron content. It accounts for 10% to 25% of the total iron content and has a basicity of 8% to 16%.

[0016] Preferably, the rare earth element is cerium or lanthanum.

[0017] Preferably, the polyferric sulfate is a solid powder obtained by spray drying or rotary kiln drying.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] By simultaneously introducing chitosan, zinc-containing compounds, and rare earth-containing compounds into the catalytic oxidation polymerization reaction system, the active functional groups on the chitosan molecular chain are coordinated with iron ions, while zinc ions and rare earth ions are chemically bonded into the polyferric sulfate molecular structure, thus forming a chitosan-zinc-rare earth ternary functional composite polyferric sulfate.

[0020] This method utilizes the high molecular structure and abundant functional groups of chitosan, the charge neutralization ability of zinc ions, and the fine control of the polymerization morphology of iron species by rare earth elements to achieve integrated synergy of the three components at the molecular level. This overcomes the defects of poor compatibility and insufficient synergistic effect between components in physical mixing or binary composites in existing technologies. The molecular structure of the prepared product contains chitosan, zinc, and rare earth elements simultaneously, and the distribution ratio of dimeric and trimeric iron and the basicity are controlled within an appropriate range, giving the product excellent flocculation performance and structural stability.

[0021] This preparation method employs a one-pot in-situ polymerization process, which is simple, convenient, and can utilize titanium dioxide waste acid and iron-containing solid waste as raw materials, thus achieving resource utilization. Compared with ordinary polyferric sulfate or binary composite products, the ternary functional composite product of this invention shows significant improvements in removing organic pollutants, reducing color, accelerating floc settling, and reducing residual iron content in effluent. It has excellent overall flocculation performance and is particularly suitable for the deep treatment of complex wastewater from printing and dyeing, papermaking, and chemical industries. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the preparation method of chitosan-zinc-rare earth ternary functional composite polymeric ferric sulfate according to the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1: A method for preparing a chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate, such as... Figure 1 As shown, it includes the following steps:

[0025] Step (a): Preparation of iron-containing raw materials and acidic reaction solution

[0026] Take 1000L of waste sulfuric acid generated during the titanium dioxide production process. Its mass concentration is 18% and its density is approximately 1.12g / mL. Add ferrous sulfate heptahydrate (… 350 kg of a solution (98% purity) was stirred and dissolved, then filtered to remove insoluble residue, yielding a solution containing... The reaction solution was acidic; the total amount of iron in the reaction solution was determined to be approximately 1100 mol (calculated as Fe), and the pH was approximately 1.3.

[0027] Step (b): Preparation of chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate intermediate

[0028] Weigh 8.75 kg of chitosan (90% degree of deacetylation, 150,000 Da molecular weight), which is 2.5% of the mass of 350 kg of ferrous sulfate heptahydrate containing iron. Dissolve the chitosan in 150 L of acetic acid solution with pH=2.5 (adjust the pH with glacial acetic acid) and stir for 2 hours until completely dissolved to obtain chitosan acetic acid solution.

[0029] Take another (Molecular weight 287.5) 23.5 kg, dissolved and diluted with deionized water to 500 L; take (Molecular weight 568) 5.5 kg, dissolved and diluted with deionized water to 50 L.

[0030] The above chitosan acetic acid solution, solution and The solution was added sequentially to the acidic reaction solution prepared in step (a) and stirred until homogeneous. In the resulting mixture, the Zn / Fe molar ratio was (23.5 / 287.5) / 1100≈0.0743, and the rare earth / Fe molar ratio was (5.5 / 568×2) / 1100≈0.0176.

[0031] The mixture was transferred to a high-pressure reactor, sealed, and oxygen was introduced until the internal pressure reached 0.6 MPa. The temperature was raised to 70°C, and the reaction was carried out for 3 hours at a stirring speed of 200 rpm. During the reaction, the amino groups on the chitosan molecular chains ( The chitosan-zinc-rare earth ternary functionalized composite polymeric ferric sulfate intermediate liquid was obtained by coordinating the chitosan and hydroxyl groups (-OH) with iron ions. After the reaction was completed, the temperature was rapidly reduced to 25℃ at a rate of 10℃ / min to obtain the chitosan-zinc-rare earth ternary functionalized composite polymeric ferric sulfate intermediate liquid.

[0032] Step (c): Drying treatment

[0033] The above intermediate liquid was spray-dried under a nitrogen atmosphere. The spray drying conditions were: inlet air temperature 200℃, outlet air temperature 95℃, atomizer speed 15000rpm, and feed rate 20L / h. The dried powder was collected to obtain a solid chitosan-zinc-rare earth ternary functional composite polyferric sulfate product, about 480kg, with a moisture content of ≤5%.

[0034] Performance characterization of the product obtained in this embodiment: Total iron content: 18.5% (mass fraction); Content: 0.3%; Basicity: 12.5%; Chitosan mass fraction: 2.3% (Kjeldahl method); Zn / Fe molar ratio: 0.072 (atomic absorption spectrometry); Ce / Fe molar ratio: 0.0172 (inductively coupled plasma atomic emission spectrometry); Dimeric iron ( ) Percentage of total iron: 22% (electrospray ionization mass spectrometry); ferric iron ( (This accounts for 18% of the total iron ore production.)

[0035] Example 2: A method for preparing a chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate, comprising the following steps:

[0036] Step (a): Preparation of iron-containing raw materials and acidic reaction solution

[0037] Take 900L of waste sulfuric acid generated during the titanium dioxide production process. Its mass concentration is 22% and its density is approximately 1.15g / mL. Add ferrous sulfate monohydrate (… 280 kg of iron (99% purity) was stirred and dissolved, then filtered; the total amount of iron in the reaction solution was approximately 1200 mol (calculated as Fe).

[0038] Step (b): Preparation of chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate intermediate

[0039] Weigh 14 kg of carboxymethyl chitosan (degree of substitution 0.8), which is 5.0% of the mass of 280 kg of ferrous sulfate monohydrate containing iron. Dissolve the carboxymethyl chitosan in 250 L of acetic acid solution with pH=3.0 and stir until completely dissolved.

[0040] Separately, 11.7 kg of ZnO (molecular weight 81.4) was dissolved in a small amount of dilute sulfuric acid and converted into... Solution; take 26.0 kg of (molecular weight 433) was dissolved in deionized water. The above solution was added to the acidic reaction solution prepared in step (a) and stirred until homogeneous. In the resulting mixture, the Zn / Fe molar ratio was (11.7 / 81.4) / 1200≈0.12 and the rare earth / Fe molar ratio was (26.0 / 433) / 1200≈0.05.

[0041] The mixture was transferred to a high-pressure reactor, sealed, and oxygen was introduced until the pressure inside the reactor reached 0.3 MPa. The temperature was raised to 50°C and the reaction was carried out for 5 hours. After the reaction was completed, the temperature was rapidly reduced to below 30°C at a rate of 5°C / min to obtain the intermediate liquid.

[0042] Step (c): Drying treatment

[0043] The above intermediate liquid was dried in a rotary kiln under a nitrogen atmosphere; drying conditions: kiln head temperature 180℃, kiln tail temperature 90℃, residence time 30min, to obtain a solid product.

[0044] The performance characteristics of the product obtained in this embodiment are as follows: basicity: 8.5%; chitosan mass fraction: 4.8%; Zn / Fe molar ratio: 0.118; La / Fe molar ratio: 0.048; dimeric iron (… ) accounts for 15% of the total iron content; trimeric iron ( (This accounts for 10% of the total iron content.)

[0045] Example 3: A method for preparing a chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate, comprising the following steps:

[0046] Step (a): Preparation of iron-containing raw materials and acidic reaction solution

[0047] Take 800L of waste sulfuric acid generated during the titanium dioxide production process, with a mass concentration of 15%; add 200kg of ferrous sulfate (containing about 30% iron) to it, stir to dissolve, and filter; the total amount of iron in the reaction solution is about 900mol (calculated as Fe).

[0048] Step (b): Preparation of chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate intermediate

[0049] Weigh 1.98 kg of quaternized chitosan (quaternization degree 70%, molecular weight 100,000 Da), which is 0.99% of the mass of 200 kg of iron-containing raw material ferrous sulfide (at this dosage, the chitosan content in the product can reach more than 0.5%). Dissolve the quaternized chitosan in 50 L of acetic acid solution with pH=2.0 and stir to dissolve.

[0050] Take another 7.8 kg, dissolved in deionized water; take (Molecular weight 172.1) 0.80 kg, dissolved in a small amount of concentrated sulfuric acid at 60°C, is converted to After further dilution, the solution was added to the acidic reaction solution and stirred until homogeneous. In the resulting mixture, the Zn / Fe molar ratio was (7.8 / 287.5) / 900≈0.0302, and the rare earth / Fe molar ratio was (0.80 / 172.1) / 900≈0.0052.

[0051] The mixture was transferred to a high-pressure reactor, sealed, and oxygen-enriched air (50% oxygen by volume) was introduced until the pressure inside the reactor reached 1.2 MPa. The temperature was raised to 90°C and the reaction was carried out for 2 hours. After the reaction was completed, the temperature was rapidly reduced to 20°C at a rate of 15°C / min to obtain the intermediate liquid.

[0052] Step (c): Drying treatment

[0053] The above intermediate liquid was spray-dried under a nitrogen atmosphere, under the same conditions as in Example 1, to obtain a solid product.

[0054] Performance characterization of the product obtained in this embodiment: basicity: 15.8%; chitosan mass fraction: 0.52%; Zn / Fe molar ratio: 0.031; Ce / Fe molar ratio: 0.0051; dimeric iron (… ) accounts for 30% of the total iron content; trimeric iron ( (This accounts for 25% of the total iron content.)

[0055] Example 4: A method for preparing a chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate, comprising the following steps:

[0056] Step (a): Preparation of iron-containing raw materials and acidic reaction solution

[0057] Same as in Example 1, the total amount of iron is 1100 mol.

[0058] Step (b): Preparation of chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate intermediate

[0059] Weigh 5.25 kg of chitosan (same as in Example 1), which is 1.5% of the iron-containing raw material mass; dissolve it in an acetic acid solution with pH=3.5; separately take... 19.0 kg (Zn / Fe = 0.06), take (Molecular weight 694) 7.63 kg (rare earth / Fe = 0.01); each solution was added to the acidic reaction solution in sequence; reaction conditions: pressure 0.8 MPa, temperature 80℃, time 4 hours, oxygen as oxidant; cooling rate 8℃ / min.

[0060] Step (c): Drying treatment: spray drying (nitrogen atmosphere).

[0061] The performance characteristics of the product obtained in this embodiment are as follows: basicity: 10.2%; chitosan mass fraction: 1.4%; Zn / Fe molar ratio: 0.058; La / Fe molar ratio: 0.0096; diferric: 20%; triferric: 16%.

[0062] Example 5: A method for preparing a chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate, comprising the following steps:

[0063] Step (a): Preparation of iron-containing raw materials and acidic reaction solution

[0064] Take waste sulfuric acid from titanium dioxide and ferrous sulfate heptahydrate, with a total iron content of 1000 mol.

[0065] Step (b): Preparation of chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate intermediate

[0066] Weigh 2.1 kg of carboxymethyl chitosan (degree of substitution 0.8), which is 0.6% of the iron-containing raw material mass (based on 350 kg); dissolve it in an acetic acid solution with pH=2.5; separately take 3.26 kg of ZnO (Zn / Fe=0.04), and take... 2.27 kg (rare earth / Fe = 0.008); reaction conditions: pressure 0.5 MPa, temperature 65℃, time 3.5 hours, oxygen; cooling rate 12℃ / min.

[0067] Step (c): Drying treatment: rotary kiln drying (nitrogen atmosphere).

[0068] The performance characteristics of the product obtained in this embodiment are as follows: basicity: 13.0%; chitosan mass fraction: 0.51%; Zn / Fe molar ratio: 0.039; Ce / Fe molar ratio: 0.0078; diferric: 23%; triferric: 19%.

[0069] Example 6: A method for preparing a chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate, comprising the following steps:

[0070] Step (a): Preparation of iron-containing raw materials and acidic reaction solution

[0071] Total iron 1000 mol.

[0072] Step (b): Preparation of chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate intermediate

[0073] Weigh 7.0 kg of chitosan (containing 2.0% of the iron content of the raw material) and dissolve it in an acetic acid solution with pH=3.0; separately take... 14.4kg (Zn / Fe=0.05), take 2.38 kg (rare earth / Fe = 0.0055); reaction conditions: pressure 0.7 MPa, temperature 75℃, time 3 hours, oxygen; cooling rate 10℃ / min.

[0074] Step (c): Drying treatment: spray drying (nitrogen atmosphere).

[0075] The performance characteristics of the product obtained in this embodiment are as follows: basicity: 11.0%; chitosan mass fraction: 1.9%; Zn / Fe molar ratio: 0.049; La / Fe molar ratio: 0.0053; diferric: 24%; triferric: 18%.

[0076] Example 7: A method for preparing a chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate, comprising the following steps:

[0077] Step (a): Preparation of iron-containing raw materials and acidic reaction solution

[0078] Total iron 900 mol.

[0079] Step (b): Preparation of chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate intermediate

[0080] Weigh 17.5 kg of chitosan (containing 5.0% of the iron content of the raw material) and dissolve it in an acetic acid solution with pH=2.5; separately take... 25.9 kg (Zn / Fe = 0.10), take 7.67 kg (rare earth / Fe = 0.03); reaction conditions: pressure 0.9 MPa, temperature 85℃, time 2.5 hours, oxygen; cooling rate 7℃ / min.

[0081] Step (c): Drying treatment: rotary kiln drying (nitrogen atmosphere).

[0082] The performance characteristics of the product obtained in this embodiment are as follows: basicity: 9.5%; chitosan mass fraction: 4.9%; Zn / Fe molar ratio: 0.098; Ce / Fe molar ratio: 0.029; diferric iron: 17%; triferric iron: 12%.

[0083] Experimental Example: Comparative Experiment on the Flocculation Performance of Chitosan-Zinc-Rare Earth Ternary Functional Composite Polyferric Sulfate

[0084] I. Experimental Objective

[0085] By comparing the flocculation performance of the product of Example 1 of this invention with comparative products with different missing components and deviations in proportion in the treatment of dyeing and printing wastewater, the synergistic effect of chitosan, zinc and rare earth components in the molecular structure of polyferric sulfate is verified, demonstrating the excellent effect of the technical solution of this invention.

[0086] II. Experimental Samples

[0087] The chitosan-zinc-rare earth ternary functionalized polyferric sulfate prepared in Example 1 was used as the reference group (sample A); the following comparative sample was also prepared:

[0088] Sample A (reference group) Prepared according to Example 1, with chitosan addition of 2.5%, Zn / Fe = 0.074, Ce / Fe = 0.0176. none Sample B Same as Example 1, but without the addition of chitosan. Chitosan-free Sample C Same as Example 1, but without adding Zinc-free Sample D Same as Example 1, but without adding Rare earth-free Sample E Same as Example 1, but without the addition of zinc and rare earth elements. Chitosan alone + PFS Sample F Same as Example 1, but Zn / Fe = 0.15, Ce / Fe = 0.08. The proportions of zinc and rare earth elements both exceeded the acceptable range. Sample G Same as Example 1, but with a chitosan addition amount of 6%. Excess chitosan Sample H (commercially available ordinary polyferric sulfate) Commercially available product (industrial grade, basicity 12%, total iron content 19%) Unmodified

[0089] III. Experimental Scheme

[0090] 3.1: Water used in the experiment

[0091] Water quality samples were taken from the wastewater equalization tank of a dyeing and printing factory. The water quality indicators are as follows:

[0092] CODcr (mg / L) 850±50 Color intensity (multiple) 500±30 pH 8.5±0.3 SS (mg / L) 280±20 Total iron (mg / L) 0.5

[0093] 3.2: Experimental Methods

[0094] The beaker flocculation test method was adopted (refer to GB / T 16881-2008 "Beaker Test Method for Coagulation and Sedimentation of Water").

[0095] Operating steps:

[0096] Take 1L of water sample and place it in a beaker of a six-piece stirrer.

[0097] Each sample was prepared into a 10 g / L solution (based on the product) using deionized water.

[0098] The above flocculant solution was added to the water sample at a dosage of 2.0 mL / L (i.e., the product dosage was 20 mg / L).

[0099] Stir quickly (300 rpm, 1 min), stir slowly (60 rpm, 15 min), and let stand for 30 min to settle.

[0100] Take a sample of the supernatant 2 cm below the liquid surface and measure CODcr, color, turbidity, and residual total iron.

[0101] Measurement method:

[0102] CODcr: Potassium dichromate method (HJ 828-2017);

[0103] Colorimetric analysis: Dilution factor method (GB / T 11903-89);

[0104] Turbidity: Turbidity meter method (GB / T 13200-91);

[0105] Total residual iron: o-phenanthroline spectrophotometric method (HJ / T 345-2007);

[0106] Three parallel samples were made for each group of experiments, and the average value of the results was taken.

[0107] 3.3: Experimental Conditions

[0108] Temperature: 25±2℃;

[0109] Initial pH: No adjustment (raw water pH=8.5);

[0110] Standing time: 30 minutes;

[0111] IV. Experimental Results

[0112] 4.1: Comparison of flocculation effects

[0113] A 92.3 98.5 97.2 0.12 Quick (settling complete in about 3 minutes) Large and dense B 68.5 72.3 81.5 0.28 medium medium C 71.2 75.6 83.0 0.25 medium medium D 73.5 78.2 85.1 0.22 medium medium E 62.8 65.5 78.0 0.32 slow Small and loose F 75.2 80.5 86.3 0.26 Medium to slow Uneven size G 78.5 83.2 88.0 0.24 medium Partial rise H 72.0 75.0 82.5 0.30 medium medium

[0114] 4.2: Flocculation settling performance (change in settling volume over time)

[0115] A 28 15 12 B 65 42 35 C 58 38 32 D 55 36 30 E 78 55 48 F 52 34 28 G 60 40 34 H 62 45 38

[0116] V. Analysis of Experimental Results

[0117] 5.1: Analysis of the ternary synergistic effect

[0118] Compare sample A with samples B, C, D, and E:

[0119] Sample B: COD removal rate decreased from 92.3% to 68.5%, a decrease of 23.8 percentage points; color removal rate decreased from 98.5% to 72.3%, a decrease of 26.2 percentage points; indicating that the organic polymer structure and active functional groups of chitosan play a key role in adsorbing organic matter and decolorizing.

[0120] Sample C: COD removal rate decreased to 71.2%, a decrease of 21.1 percentage points; the lack of zinc ions led to a decrease in charge neutralization capacity and a slower floc formation rate.

[0121] Sample D: COD removal rate dropped to 73.5%, a decrease of 18.8 percentage points; rare earth deficiency led to loss of the ability to regulate the polymerization morphology of iron species, the ratio of diferric and triferric deviated from the optimal range, and the floc strength decreased.

[0122] Sample E: COD removal rate was only 62.8%, a decrease of 29.5 percentage points; relying solely on chitosan-PFS composite, lacking the synergistic effect of zinc and rare earth elements, it had the worst performance.

[0123] The above results indicate that when chitosan, zinc, and rare earth elements coexist, the COD removal rate is 18–29 percentage points higher than any binary composite system and 20 percentage points higher than commercially available PFS; there is a significant synergistic effect among the three elements, rather than a simple summation.

[0124] 5.2: Analysis of the Reasonableness of the Proportion Range

[0125] Sample F: COD removal rate was only 75.2%, which was 17.1 percentage points lower than that of sample A; excessive zinc and rare earth elements caused instability in the system, resulting in precipitation, which destroyed the polyferric sulfate skeleton, and the basicity and iron speciation distribution deviated from the target range.

[0126] Sample G: COD removal rate was 78.5%, which was 13.8 percentage points lower than that of Sample A. In addition, some of the flocs floated to the surface, indicating that the excess chitosan failed to bind effectively and instead affected the flocculation effect.

[0127] The above results demonstrate that the chitosan addition of 0.5% to 5%, Zn / Fe ratio of 0.03 to 0.12, and rare earth / Fe ratio of 0.005 to 0.05 specified in this invention are the optimal ranges verified by experiments. Exceeding these ranges will lead to a significant decrease in performance.

[0128] 5.3: Analysis of Floc Settling Performance

[0129] After 5 minutes of settling, the floc volume of sample A was only 28 mL / L, and after 30 minutes of settling, it dropped to 12 mL / L, which is far superior to other samples. The commercially available PFS still had 38 mL / L after 30 minutes of settling, indicating that the flocs formed by the product of this invention are larger, denser, and settle faster, which is beneficial to solid-liquid separation in practical engineering.

[0130] 5.4: Analysis of residual total iron in effluent

[0131] The residual total iron in the effluent of sample A was only 0.12 mg / L, which was lower than all other samples (0.22-0.32 mg / L) and far lower than the total iron limit (2.0 mg / L) in the first-level standard of the national "Integrated Wastewater Discharge Standard" (GB 8978-1996); this indicates that the iron utilization rate of the product of this invention is high and the risk of secondary pollution is low.

[0132] The embodiments of the present invention are given for the purposes of illustration and description. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made by those skilled in the art to the above embodiments within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate, characterized in that, Includes the following steps: Step (a): Mix the iron-containing raw material with acid to form an iron-containing... The acidic reaction solution; Step (b): Chitosan, a zinc-containing compound, and a rare earth-containing compound are added to the acidic reaction solution, such that the amount of chitosan added is 0.5% to 5% of the mass of the iron-containing raw material, the Zn / Fe molar ratio is 0.03 to 0.12, and the rare earth / Fe molar ratio is 0.005 to 0.05; during the catalytic oxidative polymerization reaction, the active functional groups on the chitosan molecular chain coordinate with iron ions to form a chitosan-zinc-rare earth ternary functional composite polymeric ferric sulfate intermediate; Step (c): The ternary functionalized composite ferric sulfate intermediate obtained in step (b) is dried to obtain solid chitosan-zinc-rare earth ternary functionalized composite ferric sulfate.

2. The method according to claim 1, characterized in that, The chitosan is selected from at least one of chitosan, carboxymethyl chitosan, and quaternized chitosan; the zinc-containing compound is selected from... Or at least one of ZnO; the rare earth compound is selected from at least one of cerium-containing compounds or lanthanum-containing compounds.

3. The method according to claim 1, characterized in that, The catalytic oxidation polymerization reaction is carried out under pressure, with a reaction pressure of 0.3–1.2 MPa and a reaction temperature of 50–90°C. Oxygen or oxygen-enriched air is introduced as an oxidant, and the reaction time is 2–5 hours.

4. The method according to claim 1, characterized in that, In step (b), the chitosan is first dissolved in an acetic acid solution with a pH of 2 to 4 to form a chitosan acetic acid solution, which is then added to the acidic reaction solution.

5. The method according to claim 1, characterized in that, After the catalytic oxidation polymerization reaction is completed, the reaction solution is rapidly cooled to below 30°C at a rate of 5–15°C / min.

6. The method according to claim 1, characterized in that, The drying process is spray drying, rotary kiln drying, or a combination of spray drying and rotary kiln drying; the drying process is carried out under an inert gas atmosphere.

7. The method according to claim 1, characterized in that, The iron-containing raw material is a mixture of waste sulfuric acid generated during the titanium dioxide production process and at least one iron-containing solid waste selected from ferrous sulfate heptahydrate, ferrous sulfate monohydrate, ferrous flavonoids, and acid leaching residue; the mass concentration of the waste sulfuric acid is 15% to 25%.

8. A chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate prepared according to the method of claim 1, characterized in that, Its molecular structure contains chitosan, zinc, and rare earth elements. The mass fraction of chitosan is 0.5% to 5%, the Zn / Fe molar ratio is 0.03 to 0.12, and the rare earth / Fe molar ratio is 0.005 to 0.

05. The polyferric sulfate contains 15% to 30% diferric iron and 10% to 25% triferric iron, and has a basicity of 8% to 16%.

9. The chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate according to claim 8, characterized in that, The rare earth element is cerium or lanthanum.

10. The chitosan-zinc-rare earth ternary functionalized composite polyferric sulfate according to claim 8, characterized in that, The polyferric sulfate is a solid powder obtained by spray drying or rotary kiln drying.

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