Adsorption, flocculation and sedimentation of Ca in water bodies 2+ Composite flocculants and their application in removing high concentrations of Ca from wastewater 2+ Method

Abstract

The application discloses a composite flocculant for adsorption and flocculation and settlement of Ca 2+ in water bodies and a method for removing high-concentration Ca 2+ in wastewater, and belongs to the technical field of wastewater treatment. The composite flocculant comprises sodium carbonate, magnetic seeds and organic acid modified starch. The magnetic seeds and the organic acid modified starch in the composite flocculant can promote the formation of magnetic flocs and accelerate the settling rate under the stirring action. The organic acid modified starch can form a stable chelate structure with Ca 2+ through internal hydroxyl and acid root coordination complexation, and finally remove Ca 2+ . The organic acid modified starch can also flocculate and adsorb calcium carbonate and magnetic seeds at the same time, which is beneficial to the recycling and reuse of the magnetic seeds while settling the calcium carbonate. The modified starch flocculant and the magnetic flocculation technology provided by the application can better remove impurities in wastewater. Especially for excessive calcium ions, the removal rate can be improved, the flocculation cost can be reduced, and the technology is suitable for popularization in industrial wastewater treatment.

Description

Technical Field

[0001] This invention belongs to the technical field of wastewater treatment, and particularly relates to the adsorption, flocculation and sedimentation of Ca in water bodies. 2+ Composite flocculants and their application in removing high concentrations of Ca from wastewater 2+ The method. Background Technology

[0002] Water resources are a vital resource for human survival. Although my country has abundant total water resources, their spatial and temporal distribution is uneven, and water quality is complex, making development and utilization challenging. This is especially true in the mineral mining and processing sectors, where the removal of impurities and the recycling of water resources are crucial. Currently, industrial wastewater contains significant amounts of silt, heavy metal ions, organic matter, and other ions. Direct discharge without treatment will reduce the efficiency of subsequent industrial processes, lead to substantial water waste, and cause environmental pollution.

[0003] Currently, magnetic flocculation technology is commonly used to address impurities in industrial wastewater containing excessive suspended particulate matter, colloids, and macromolecular organic matter. This involves magnetic inoculation and the addition of coagulants to achieve the separation and sedimentation of impurities. For example, Chinese patent CN 107381749 A discloses a magnetic flocculant, its preparation method, and its application. This method utilizes the tight bonding between magnetic materials and flocculants, covalently embedding Fe3O4 magnetic nanoparticles into a covalently bonded composite flocculant structure to obtain a magnetic flocculant. The separation of impurities is enhanced by the use of an external magnetic field. However, the preparation cost of this type of flocculant for sedimentation is relatively high. It requires covalent bonding with a coupling agent and the magnetic field to remove some suspended particulate matter and organic pollutants. For other impurities, especially heavy metals like Ca, the process is less effective. 2+ The removal effect is not ideal. Excessive calcium ions in water are detrimental to subsequent industrial processes. Current research on methods for removing excess calcium ions from water focuses on precipitation, with common precipitants including Na₂CO₃, NaOH, and Ca(OH)₂. However, the Na₂CO₃ precipitation method for removing calcium ions has a slow settling rate and low efficiency. Furthermore, CaCO₃ precipitates are fine-grained, easily suspended in the water, and difficult to settle. Excessive impurities in the water negatively impact subsequent processes.

[0004] Therefore, how to prepare a novel flocculant at low cost to flocculate and settle heavy metal ions (Ca) in wastewater is crucial. 2+ Improving the removal rate of impurities and the recycling rate of wastewater is of great research significance. Summary of the Invention

[0005] The technical problem to be solved by this invention is: to provide a method for adsorbing, flocculating, and settling Ca in water. 2+Composite flocculants and their application in removing high concentrations of Ca from wastewater 2+ The method is to solve the problems mentioned in the background art or to achieve better technical results.

[0006] To solve the aforementioned technical problems, the inventors, through practice and summarization, derived the technical solution of this invention. This invention discloses the adsorption, flocculation, and sedimentation of Ca in water bodies. 2+ The composite flocculant includes sodium carbonate and organic acid-modified starch;

[0007] The organic acid-modified starch is selected from either phosphate-modified starch or acetate starch.

[0008] The mass ratio of sodium carbonate to organic acid-modified starch is 8-25:1-5.

[0009] Furthermore, the organic acid-modified starch is a phosphate-modified starch, and the raw materials for the phosphate-modified starch include sodium dihydrogen phosphate dihydrate, anhydrous disodium hydrogen phosphate, and glutinous rice starch; the mass ratio of sodium carbonate to organic acid-modified starch is 35:6.

[0010] Furthermore, it also includes magnetic seeds, which are selected from one of hematite powder, magnetic mineral powder and Fe3O4 powder; the mass ratio of the magnetic seeds, sodium carbonate and organic acid modified starch is 0.02-0.03:8-25:1-5.

[0011] Furthermore, the magnetic seeds have a particle size of 20–30 μm.

[0012] Furthermore, the Ca in any of the above-mentioned adsorption, flocculation, and sedimentation water bodies 2+ Composite flocculants remove high concentrations of Ca from water. 2+ The method is as follows: Add high concentrations of Ca 2+ Adding a composite flocculant to wastewater allows the sodium carbonate in the composite flocculant to react with Ca... 2+ The formation of fine-grained calcium carbonate, which is difficult to settle, involves the magnetic seeds in the composite flocculant reacting with the organic acid-modified starch under stirring. The acid radicals in the organic acid-modified starch combine with the calcium carbonate, while the hydroxyl groups combine with the magnetic seeds, synergistically promoting the formation of magnetic flocs centered on the magnetic seeds and accelerating the settling rate. Furthermore, the organic acid-modified starch, through internal hydroxyl groups and acid radicals, coordinates and complexes with the calcium carbonate... 2+ A stable chelate structure is formed, ultimately removing Ca. 2+ .

[0013] Furthermore, the Ca in the adsorbed, flocculated, and settled water... 2+ Composite flocculants remove high concentrations of Ca from water. 2+ The method and steps are as follows:

[0014] (1) To high concentrations of Ca 2+ Add magnetic seeds to the wastewater at a dosage of 2-3 g / L and stir thoroughly at a speed of 500-600 rpm for 5 minutes.

[0015] (2) Add sodium carbonate to the wastewater in step (1) where magnetic seeds were added and stir thoroughly for 5 minutes to make the sodium carbonate in the mixed waste liquid 800-2500 mg / L;

[0016] (3) Add organic acid-modified starch to the waste liquid after step (2) at a dosage of 100-500 mg / L, stir thoroughly and let it settle, and then extract the supernatant.

[0017] Furthermore, in step (3), the settling time is 1 to 6 minutes.

[0018] Furthermore, in step (3), the settling time is 2 minutes.

[0019] Furthermore, the Ca in any of the above-mentioned adsorption, flocculation, and sedimentation water bodies 2+ Composite flocculants remove high concentrations of Ca from water. 2+ The method involves the use of organic acid-modified starch in composite flocculants to adsorb and flocculate heavy metal ions through coordination chelation; through a bridging flocculation mechanism, the long-chain structure of organic acid-modified starch can simultaneously adsorb multiple kaolin particles to form a bridging structure; and by adding an appropriate amount of organic acid-modified starch, a three-dimensional network structure can be formed to capture suspended particulate matter, ultimately causing impurities to settle.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. Compared with using flocculants alone to settle fine calcium carbonate precipitates, the present invention uses magnetic seeds to form dense magnetic flocs through magnetic flocculation, which accelerates the sedimentation of fine calcium carbonate precipitates that are not easy to settle.

[0022] 2. The phosphate-modified starch flocculant used in this invention has the effects of precipitating calcium carbonate and flocculating and adsorbing magnetic seeds. Furthermore, the phosphate-modified starch and magnetic seeds can work synergistically to further promote the formation of magnetic flocs, making the magnetic flocs denser and the settling speed faster.

[0023] 3. This invention addresses the shortcomings of current wastewater high-concentration calcium ion removal processes, which suffer from high costs, poor removal efficiency, and excessively long removal cycles. By employing modified starch flocculants in conjunction with magnetic powder flocculation technology, the settling time can be effectively shortened and settling efficiency improved. Furthermore, the resulting precipitate, after washing, can be recycled to recover magnetic seeds for reuse, thus reducing costs. The recovery method involves soaking the magnetic flocs in an HCl solution to remove surface calcium carbonate precipitate and phosphate-modified starch residue. The magnetic seeds are then washed with deionized water until neutral, and dried in an oven at a constant temperature for reuse. The recovery rate of the magnetic seeds reaches 95% after the first recovery, 92% after the second, and remains at 80% even after the fifth recovery.

[0024] 4. The modified starch flocculation and magnetic flocculation technology provided by this invention can effectively remove heavy metal ions, particulate matter and organic matter from wastewater; especially for excessive calcium ions, it can not only improve the removal rate, but also reduce flocculation costs, making it suitable for widespread application in industrial wastewater treatment. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the magnetic flocculation process of the present invention with a flocculation settling time of 5 min;

[0026] Figure 2 This is a schematic diagram of the magnetic flocculation process of the present invention with a flocculation settling time of 2 minutes;

[0027] Figure 3 The following is a static sedimentation diagram of some of the flocculants in this invention. a, b, and c are phosphate starch, wheat starch, and PAM, respectively. Detailed Implementation

[0028] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0029] Unless otherwise specified, the raw materials or reagents used in the following examples and comparative examples are commercially available products or products prepared using conventional techniques.

[0030] The magnetic seed types used in this invention are as follows: A1 (hematite powder, purity >99.8%, Shanghai Aladdin Reagent Co., Ltd.), A2 (magnetite powder, purity >98%, Anhui Lilou Iron Mine Area), and A3 (Fe3O4 powder, purity >90%, Shenzhen Youci Technology Co., Ltd.).

[0031] The glutinous rice starch was purchased from Henan Zhongrun Grain Food Research Institute Co., Ltd., with a particle size of 150-200 mesh.

[0032] The preparation method of the phosphate-modified starch flocculant used in this invention comprises the following steps:

[0033] (1) Weigh 2-3g of sodium dihydrogen phosphate dihydrate and 4-5g of anhydrous disodium hydrogen phosphate, dissolve them in 200mL of deionized water at 35-40℃, and then add HCl solution to adjust the pH value to 6 to obtain a mixture.

[0034] (2) Weigh 100g-110g of glutinous rice starch and dissolve it in the mixture obtained in step (1). Use a magnetic stirrer to stir continuously at a speed of 60-80rpm for 25min. Filter the mixture using a Buchner funnel. After crushing the filter cake, dry it in an oven at 50℃ for 14-18h. Then place the dried filter powder in an oil bath at 150℃ and react it at high temperature for 3h. Afterward, take out the filter powder and cool it to 25℃ for later use.

[0035] (3) Take 500 mL of 50% methanol solution and mix it evenly with the filter powder obtained in step (2). Filter it through a Buchner funnel. Take the filter cake after vacuum filtration through the Buchner funnel and mix it evenly with anhydrous ethanol. Wash it repeatedly with deionized water several times. Filter it through a Buchner funnel and dry it at a constant temperature in an oven at 40°C. After grinding and passing it through a 100-mesh sieve, the phosphate-modified starch flocculant is obtained.

[0036] The method for preparing the acetate-modified starch flocculant used in this invention is as follows: 0.3g of acetate starch (purchased from Shanghai Xintai Industrial Co., Ltd.) is dissolved in 100mL of deionized water at 60-70℃ to prepare a 3g / L acetate starch solution.

[0037] Both corn starch and wheat starch were purchased from Shanghai Yuanye Technology Co., Ltd.

[0038] The polyacrylamide (PAM) flocculant was purchased from Shanghai Yuanye Technology Co., Ltd. PAM is cationic with a molecular weight of 3 million.

[0039] The waste liquid of this invention is a self-made simulated water sample, wherein the simulated water sample contains heavy metal ions including Cu. 2+ Zn 2+ Pb 2+ The concentrations were 50 mg / L, 50 mg / L, and 50 mg / L, respectively; the calcium ion concentration in the simulated water sample was 300–350 mg / L; and the suspended particulate matter in the simulated water sample was kaolin with a concentration of 10 g / L.

[0040] Example 1

[0041] Adsorption, flocculation and sedimentation of Ca in water bodies 2+ The composite flocculant includes sodium carbonate and phosphate-modified starch; the dosage of phosphate-modified starch is 100 mg / L.

[0042] The above-mentioned adsorption, flocculation and sedimentation of Ca in water bodies 2+ The method for removing impurities from water using composite flocculants comprises the following steps:

[0043] (1) Weigh 0.1g of phosphate-modified starch and dissolve it in 100mL of deionized water at 60-70℃ to prepare a 1g / L phosphate-modified starch solution.

[0044] (2) Place 80 mL of wastewater in a 250 mL beaker, add 10 mL of sodium carbonate solution with a concentration of 1750 mg / L and stir thoroughly for 5 min. Then add 10 mL of phosphate-modified starch solution from step (1), stir thoroughly for 5 min, then stop stirring and let it settle for 5 min.

[0045] (3) After sedimentation, the supernatant is drawn into a clean beaker. The transmittance of the supernatant is measured first, and then the removal rate of heavy metal ions is calculated. Then, hydrochloric acid solution is added until all the unsettled calcium carbonate precipitate is dissolved. The solution is titrated using the EDTA standardization method to calculate the removal rate of heavy metal ions.

[0046] Example 2

[0047] Adsorption, flocculation and sedimentation of Ca in water bodies 2+ The composite flocculant includes sodium carbonate and phosphate-modified starch; the dosage of phosphate-modified starch is 400 mg / L.

[0048] The above-mentioned adsorption, flocculation and sedimentation of Ca in water bodies 2+ The method for removing impurities from water using a composite flocculant is the same as in Example 1, except that the concentration of the phosphate-modified starch solution in step (1) is changed to 4 g / L.

[0049] Example 3

[0050] Adsorption, flocculation and sedimentation of Ca in water bodies 2+ The composite flocculant includes sodium carbonate and phosphate-modified starch; the dosage of phosphate-modified starch is 300 mg / L.

[0051] The above-mentioned adsorption, flocculation and sedimentation of Ca in water bodies 2+ The method for removing impurities from water using a composite flocculant is the same as in Example 1, except that the concentration of the phosphate-modified starch solution in step (1) is changed to 3 g / L.

[0052] Example 4

[0053] Adsorption, flocculation and sedimentation of Ca in water bodies 2+ The composite flocculant includes sodium carbonate and acetate-modified starch; the dosage of phosphate-modified starch is 300 mg / L.

[0054] The above-mentioned adsorption, flocculation and sedimentation of Ca in water bodies 2+ The method for removing impurities from water using composite flocculants comprises the following steps:

[0055] (1) Weigh 0.3g of starch acetate and dissolve it in 100mL of deionized water at 60-70℃ to prepare a starch acetate solution of 3g / L.

[0056] (2) Place 80 mL of wastewater in a 250 mL beaker, add 10 mL of sodium carbonate solution with a concentration of 1750 mg / L and stir thoroughly for 5 min. Then add 10 mL of acetate-modified starch solution from step (1), stir thoroughly for 5 min, then stop stirring and let it settle for 5 min.

[0057] (3) After sedimentation, the supernatant is drawn into a clean beaker. The transmittance of the supernatant is measured first. Then, hydrochloric acid solution is added until all the unsettled calcium carbonate precipitate is dissolved. The solution is titrated using the EDTA titration method to calculate the removal rate of heavy metal ions.

[0058] Comparative Example 1

[0059] Adsorption, flocculation and sedimentation of Ca in water bodies 2+ The flocculant includes sodium carbonate and corn starch; the amount of corn starch used is 300 mg / L.

[0060] The above-mentioned adsorption, flocculation and sedimentation of Ca in water bodies 2+ The method for removing impurities from water using flocculants involves the following steps:

[0061] (1) Weigh 0.3g of corn starch and dissolve it in 100mL of deionized water at 60-70℃ to prepare a 3g / L corn starch solution;

[0062] (2) Place 80 mL of wastewater in a 250 mL beaker, add 10 mL of sodium carbonate solution with a concentration of 1750 mg / L and stir thoroughly for 5 min. Then add 10 mL of corn starch solution from step (1), stir thoroughly for 5 min, then stop stirring and let it settle for 5 min.

[0063] (3) After sedimentation, the supernatant is drawn into a clean beaker. The transmittance of the supernatant is measured first. Then, hydrochloric acid solution is added until all the unsettled calcium carbonate precipitate is dissolved. The solution is titrated using the EDTA titration method to calculate the removal rate of heavy metal ions.

[0064] Comparative Example 2

[0065] Adsorption, flocculation and sedimentation of Ca in water bodies 2+ The flocculant includes sodium carbonate and wheat starch; the amount of wheat starch used is 300 mg / L.

[0066] The above-mentioned adsorption, flocculation and sedimentation of Ca in water bodies 2+ The method for removing impurities from water using flocculants involves the following steps:

[0067] (1) Weigh 0.3g of wheat starch and dissolve it in 100mL of deionized water at 60-70℃ to prepare a 3g / L wheat starch solution;

[0068] (2) Place 80 mL of wastewater in a 250 mL beaker, add 10 mL of sodium carbonate solution with a concentration of 1750 mg / L and stir thoroughly for 5 min. Then add 10 mL of wheat starch solution from step (1), stir thoroughly for 5 min, then stop stirring and let it settle for 5 min.

[0069] (3) After sedimentation, the supernatant is drawn into a clean beaker. The transmittance of the supernatant is measured first. Then, hydrochloric acid solution is added until all the unsettled calcium carbonate precipitate is dissolved. The solution is titrated using the EDTA titration method to calculate the removal rate of heavy metal ions.

[0070] Comparative Example 3

[0071] Adsorption, flocculation and sedimentation of Ca in water bodies 2+ The flocculants include sodium carbonate and polyacrylamide (PAM); the dosage of polyacrylamide (PAM) is 300 mg / L.

[0072] The above-mentioned adsorption, flocculation and sedimentation of Ca in water bodies 2+ The method for removing impurities from water using flocculants employs polyacrylamide (PAM) as the flocculant, and the steps are as follows:

[0073] (1) Weigh 0.3g of PAM and dissolve it in 100mL of deionized water at 20-30℃ to prepare a 3g / L PAM solution;

[0074] (2) Place 80 mL of wastewater in a 250 mL beaker, add 10 mL of sodium carbonate solution with a concentration of 1750 mg / L and stir thoroughly for 5 min. Then add 10 mL of PAM solution from step (1), stir thoroughly for 5 min, then stop stirring and let it settle for 5 min.

[0075] (3) After sedimentation, the supernatant is drawn into a clean beaker. The transmittance of the supernatant is measured first. Then, hydrochloric acid solution is added until all the unsettled calcium carbonate precipitate is dissolved. The solution is titrated using the EDTA titration method to calculate the removal rate of heavy metal ions.

[0076] The results of removing impurities from water using adsorption-flocculation-sedimentation technology in Examples 1-4 and Comparative Examples 1-3 are shown in Table 1 below. Figure 3 As shown.

[0077] Table 1. Comparison of the results of impurity removal from water based on adsorption flocculation sedimentation technology in Examples 1-4 and Comparative Examples 1-3.

[0078]

[0079]

[0080] As shown in Table 1, considering the treatment results of the three waste liquids, the treatment results of Examples 2 and 3 are better. The amount of phosphate-modified starch used in Example 2 is 400 mg / L, while the amount of phosphate-modified starch used in Example 3 is 300 mg / L. Considering the cost, Example 3 is the best.

[0081] This invention differs from methods that combine modified starch gelatinization with polyacrylamide flocculant as a flocculating component to degrade impurities. Instead, it adds sodium carbonate solution to make Ca... 2+ It reacts with sodium carbonate solution to form calcium carbonate precipitate, but the calcium carbonate precipitate is of a fine particle size and is difficult to settle. Adding phosphate-modified starch causes the fine calcium carbonate precipitate to aggregate into flocs, accelerating sedimentation. Furthermore, the phosphate-modified starch flocculant can also, through coordination complexation, bind with Ca through the coordination ability of hydroxyl groups and phosphate groups. 2+ A stable chelate structure is formed, ultimately effectively removing Ca. 2+ Treatment of Cu 2+ Zn 2+ Pb 2+ The principle of heavy metal removal is that flocculants adsorb and flocculate heavy metal ions through coordination chelation. Furthermore, the long-chain structure of the flocculant molecules can also adsorb heavy metal ions; that is, heavy metal ions are first adsorbed through adsorption bridging, and then removed through a net-like capture and sweeping mechanism. The principle of treating kaolin suspension is based on a bridging flocculation mechanism, where the long-chain structure of the flocculant molecules simultaneously adsorbs multiple kaolin particles, forming a bridged structure. Net-like capture and sweeping is another important mechanism; when an appropriate amount of flocculant is added, a three-dimensional network structure can be formed to capture suspended kaolin particles.

[0082] Example 5

[0083] The adsorption, flocculation and sedimentation of Ca in water bodies disclosed in Example 3 were used. 2+ A method for removing impurities from water using a composite flocculant was described. 80 mL of wastewater with a calcium ion concentration of 330 mg / L was placed in a 250 mL beaker and stirred thoroughly at 500–600 rpm for 5 minutes. Then, 10 mL of sodium carbonate solutions of varying concentrations (800–2500 mg / L) were added and stirred thoroughly for 5 minutes. Stirring was then stopped, and the mixture was allowed to settle for 5 minutes. The supernatant was then transferred to a clean beaker and titrated using the EDTA standardization method. The calcium ion removal rate was calculated as follows:

[0084] As shown in Table 2.

[0085]

[0086]

[0087] Table 2 shows that when the sodium carbonate solution dosage is 1750 mg / L, the Ca in the wastewater... 2+ It reacts with sodium carbonate solution to form calcium carbonate precipitate, Ca 2+ The removal rate has reached 99.12%, and almost all of it has formed a precipitate. Therefore, the optimal amount of sodium carbonate solution selected in this invention is 1750 mg / L.

[0088] Example 6

[0089] The phosphate-modified starch flocculant from Example 3 and the flocculants from Comparative Examples 1-3 were used to remove high concentrations of calcium ions (calcium ion concentration of 300-350 mg / L) from water through flocculation and sedimentation. The operation process is as follows: Figure 1 As shown;

[0090] The specific magnetic flocculation sedimentation method is as follows:

[0091] 80 mL of water sample with a calcium ion concentration of 330 mg / L was placed in a 250 mL beaker. Fe3O4 powder with a particle size of 20 μm to 50 μm was added at a fixed dosage of 3 g / L, and stirred thoroughly at 500 to 600 rpm for 5 min. Then, 10 mL of sodium carbonate solution with a concentration of 1750 mg / L was added and stirred thoroughly for 5 min. One of the flocculants in Example 3 and Comparative Examples 1 to 3 was added and stirred thoroughly for 5 min. Then, stirring was stopped and the mixture was allowed to settle for 5 min. After that, the supernatant was drawn into a clean beaker, and hydrochloric acid solution was added until all the unsettled calcium carbonate precipitate was dissolved. The solution was titrated using the EDTA standardization method, and the calcium ion removal rate was calculated as shown in Table 3.

[0092] Table 3 Comparison of calcium ion removal rates in wastewater by different flocculants

[0093]

[0094] As shown in Table 3, after adding magnetic seeds, the composite flocculant in Example 3 effectively treated high concentrations of Ca. 2+ The flocculation and sedimentation effect of the wastewater is significantly better than that of the flocculants in Comparative Examples 1 to 3. This is because the phosphate-modified starch selected in this invention can have excellent flocculation and adsorption effects on both calcium carbonate precipitation and magnetic seeds. Furthermore, the synergistic use of phosphate-modified starch and magnetic seeds can further promote the formation of magnetic flocs. The denser the magnetic flocs, the faster the sedimentation rate.

[0095] Analysis of Table 3 further reveals that, after the addition of magnetic seeds, the phosphate-modified starch flocculant prepared in Example 3 of this invention exhibits better performance against high concentrations of Ca. 2+ The flocculation and sedimentation effect of wastewater showed a trend of first increasing and then decreasing as the flocculant dosage increased from 0 to 500 mg / L; when the flocculant dosage was 300 mg / L, the flocculation and sedimentation Ca... 2+ The optimal effect is achieved because the phosphate-modified starch flocculant, through charge neutralization and adsorption bridging, aggregates the difficult-to-settle fine calcium carbonate particles into magnetic flocs. When flocculation has not reached equilibrium, the more flocculant added, the more flocs are formed, and the magnetic flocculation effect increases with the increase of flocculant dosage. When flocculation reaches equilibrium, excessive flocculant will cause restabilization, increasing the repulsive force between suspended calcium carbonate particles, which will inhibit magnetic flocculation and lead to a decrease in removal rate.

[0096] Comparative Example 4

[0097] No flocculant was used to remove high concentrations of calcium ions from the water. During the magnetic flocculation process, all parameters and steps were the same as in Example 6, except that no flocculant was added. That is, this comparative example only used sodium carbonate solution to react with calcium ions in the water to generate fine-particle calcium carbonate precipitate. The experimental results are shown in Table 4 below.

[0098] Table 4 Results of blank control experiment on calcium ion removal by sodium carbonate

[0099] 1 73.86 2 74.25 3 74.32 4 73.89 5 74.93

[0100] A comparison of Table 4 and Example 6 shows that, under the same magnetic flocculation conditions, the flocculants (wheat starch, corn starch, and PAM) showed poor removal rates for high concentrations of calcium ions in water. However, when the flocculant was replaced with the phosphate-modified starch flocculant of this invention, which simultaneously adsorbs calcium carbonate precipitates and magnetic seeds, the removal rate of high concentrations of calcium ions in water was significantly improved. The phosphate-modified starch flocculant achieved its highest removal rate at a dosage of 300 mg / L. This indicates that the flocculant involved in this invention can efficiently remove high concentrations of calcium ions from water, and it achieves excellent removal effects even at low dosages, greatly reducing the cost of flocculants.

[0101] Example 7

[0102] This embodiment studies the effect of different magnetic seed species on the precipitation of fine calcium carbonate particles under the optimal flocculant dosage (300 mg / L). The flocculant dosage is 300 mg / L, and the magnetic flocculation process is the same as in Example 6. The experimental results are shown in Table 5.

[0103] Table 5. Effects of different magnetic seed species on calcium ion removal rate

[0104] A1 86.33 A2 90.71 A3 98.74

[0105] As shown in Table 5, the type of magnetic seed affects the calcium ion removal rate. When Fe3O4 powder is selected as the magnetic seed, the calcium ion removal rate is the highest. Therefore, Fe3O4 powder can be selected as the best type of magnetic seed for this experiment. In actual industrial applications, the selection can be adjusted appropriately according to cost.

[0106] Example 8

[0107] This embodiment differs from Embodiment 6 in that different amounts of magnetic seeds were used to test the effect of removing calcium ions from the waste liquid. The flocculant dosage was the optimal dosage (300 mg / L) in Embodiment 6, and the magnetic flocculation process was the same as in Embodiment 6. The experimental results are shown in Table 6. The magnetic seeds used in the experiment were Fe3O4 powder from Embodiment 7, with dosages of 0 g / L, 1 g / L, 2 g / L, 3 g / L, and 4 g / L. The test results are shown in Table 6 below.

[0108] Table 6. Effect of different magnetic seed dosages on calcium ion removal rate

[0109] 0 93.85 1 97.49 2 98.33 3 98.74 4 98.46

[0110] The results in Table 6 show that the dosage of magnetic seeds has a significant impact on the calcium ion removal rate. A dosage range of 2–3 g / L is optimal, effectively removing 98% of calcium ions. However, excessively low magnetic seed dosage reduces the calcium ion removal rate, and when the dosage exceeds 3 g / L, the removal rate also decreases to some extent. In summary, the phosphate-modified starch flocculant achieves the best calcium ion removal efficiency at a magnetic seed dosage of 3 g / L. Therefore, 3 g / L can be selected as the optimal magnetic seed dosage for this experiment. In actual industrial applications, this dosage can be adjusted appropriately based on cost.

[0111] Example 9

[0112] Compared with Example 8, the only difference is that the magnetic flocculation sedimentation time is changed, while other parameters and magnetic flocculation steps remain unchanged. The test results are shown in Table 7 below.

[0113] The magnetic seeds used in this embodiment are Fe3O4 powder, with a dosage of 3 g / L; the sedimentation times involved in the experiment were selected as follows: 1 min, 2 min, 3 min, 4 min, 5 min, and 6 min.

[0114] Table 7 Comparison of calcium ion removal rates with different settling times

[0115] 1 93.26 2 97.86 3 97.86 4 97.86 5 98.74 6 98.74

[0116] As shown in Table 7, settling time affects the calcium ion removal rate. Considering the industrial process time, a settling time of 2 minutes effectively removes 97% of calcium ions. While longer settling times can increase the removal rate, they also increase costs due to longer cycles, and the removal rate is not significantly higher than that at 2 minutes. Therefore, a settling time of 2 minutes can be selected as the optimal settling time for magnetic flocculation to remove calcium ions. Figure 2 As shown.

[0117] Example 10

[0118] Compared with Example 6, the only difference is that the magnetic seed particle size is changed, while other parameters and magnetic flocculation steps remain unchanged. The test results are shown in Table 8 below.

[0119] The magnetic seed particle sizes used in this embodiment are S0 (<5μm), S1 (5~10μm), S2 (10~20μm), S3 (20~30μm), M1 (30~40μm), and M2 (40~50μm).

[0120] Table 8 Comparison of the effects of magnetic seeds of different particle sizes on calcium ion removal rate

[0121]

[0122]

[0123] Table 8 shows that the magnetic seed particle size affects the calcium ion removal rate. Within a certain range, the smaller the magnetic seed particle size, the higher the calcium ion removal rate; however, excessively small magnetic seed particle size can actually reduce the calcium ion removal rate. Small magnetic seed particle size requires high-precision grinding equipment, and grinding with fine magnetic seeds increases the wear rate of the grinding equipment, thus increasing the annual maintenance cost. Grinding fine magnetic seeds also leads to increased grinding time, which in turn increases the electricity cost of the grinding equipment. Considering these industrial cost considerations, a magnetic seed particle size of 20–30 μm was selected.

[0124] This invention discloses a method for removing impurities from water based on adsorption-flocculation sedimentation technology. In addition to using phosphate-modified starch as a flocculant, it adds magnetic seeds. The flocculant (phosphate-modified starch) can simultaneously flocculate fine-particle calcium carbonate precipitate and magnetic seeds. Results from Examples 1-10 demonstrate that phosphate-modified starch can effectively adsorb and aggregate fine-particle calcium carbonate precipitate and magnetic seeds, forming dense magnetic flocs with the magnetic seeds as the core, accelerating the sedimentation of fine-particle calcium carbonate precipitate. The addition of magnetic seeds allows them to combine with phosphate-modified starch through electrostatic attraction, forming a composite magnetic floc of phosphate-modified starch-magnetic seeds-calcium carbonate precipitate, enhancing the flocculation effect of phosphate-modified starch. This effectively flocculates and precipitates difficult-to-settle fine-particle calcium carbonate precipitate in water, resulting in larger, denser, and less easily broken magnetic flocs. The magnetic seeds can be recycled and reused after washing. The recycling method involves soaking the magnetic flocs in an HCl solution to remove surface calcium carbonate precipitate and phosphate-modified starch residue. Then, the magnetic seeds are washed with deionized water until neutral and dried in an oven at a constant temperature for reuse. The recovery rate of the magnetic seeds after the first recycling can reach 95%, the recovery rate after the second recycling can reach 92%, and the recovery rate after the fifth recycling can still be maintained at 80%. This achieves the goal of removing high concentrations of calcium ions from water at low cost, providing a new solution to the problem of fine-grained calcium carbonate being difficult to settle or costly.

Claims

1. Adsorption, flocculation, and sedimentation of Ca in water bodies 2+ A composite flocculant, comprising sodium carbonate, characterized in that, It also includes organic acid-modified starch and magnetic seeds; The organic acid-modified starch is selected from one of phosphate ester-modified starch and acetate starch; the raw materials for the phosphate ester-modified starch include sodium dihydrogen phosphate dihydrate, anhydrous disodium hydrogen phosphate, and glutinous rice starch. The magnetic seeds are selected from one of hematite powder, magnetic mineral powder and Fe3O4 powder; the particle size of the magnetic seeds is 20~30μm; The mass ratio of the magnetic seeds, sodium carbonate, and organic acid-modified starch is 0.02~0.03:8~25:1~5.

2. The adsorption, flocculation, and sedimentation of Ca in water as described in claim 1 2+ Composite flocculants remove high concentrations of Ca from water. 2+ The method is characterized by, To high concentration of Ca 2+ Adding a composite flocculant to wastewater allows the sodium carbonate in the composite flocculant to react with Ca... 2+ The formation of fine-grained calcium carbonate is achieved. Under stirring, the magnetic seeds in the composite flocculant and the organic acid-modified starch synergistically promote the formation of magnetic flocs and accelerate the sedimentation rate. The organic acid-modified starch, through internal hydroxyl groups and acid radicals, coordinates and complexes with Ca... 2+ A stable chelate structure is formed, ultimately removing Ca. 2+ .

3. The adsorption, flocculation, and sedimentation of Ca in water as described in claim 2 2+ Composite flocculants remove high concentrations of Ca from water. 2+ The method is characterized by, The steps are as follows: (1) To high concentration of Ca 2+ Add magnetic seeds to the wastewater at a dosage of 2~3g / L and stir thoroughly at a speed of 500~600rpm for 5min; (2) Add sodium carbonate to the wastewater in step (1) where magnetic seeds were added and stir thoroughly for 5 minutes to make the sodium carbonate in the mixed waste liquid 800~2500 mg / L; (3) Add organic acid modified starch to the waste liquid after step (2) at a dosage of 100~500mg / L, stir thoroughly and let it settle, and then extract the supernatant.

4. The adsorption, flocculation, and sedimentation of Ca in water as described in claim 3 2+ Composite flocculants remove high concentrations of Ca from water. 2+ The method is characterized by, In step (3), the settling time is 1 to 6 minutes.

5. The adsorption, flocculation, and sedimentation of Ca in water as described in claim 3 2+ Composite flocculants remove high concentrations of Ca from water. 2+ The method is characterized by, In step (3), the settling time is 2 minutes.

6. The adsorption, flocculation, and sedimentation of Ca in water bodies according to any one of claims 2 to 5 2+ Composite flocculants remove high concentrations of Ca from water. 2+ The method is characterized by, The organic acid-modified starch in the composite flocculant adsorbs and flocculates heavy metal ions through coordination chelation; through the bridging flocculation mechanism, the long chain structure of the organic acid-modified starch can simultaneously adsorb multiple kaolin particles to form a bridging structure; the dosage of the organic acid-modified starch is 100~500mg / L, which enables the organic acid-modified starch to form a three-dimensional network structure in the wastewater, capturing suspended particulate matter and ultimately causing impurities to settle.

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