A defluorination agent and a defluorination method for wastewater treatment

Abstract

This invention discloses a defluoridating agent for wastewater treatment, comprising the following components by weight: 70-80 parts of polymeric coagulant, 10-20 parts of calcium aluminum hydrotalcite, 10-20 parts of modified bentonite-fly ash composite material, 2-5 parts of disodium ethylenediaminetetraacetate, and 200-400 parts of water; wherein the modified bentonite-fly ash composite material is obtained by calcination and acidification treatment of a mixture of bentonite and fly ash. The raw materials required by this invention are inexpensive and readily available, and produce no secondary pollution. In practical applications, no additional PAM is required, yet it still exhibits good settling performance and demonstrates excellent and efficient defluoridation effects for fluoride-containing wastewater in the range of 20-100 mg / L.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to a defluorinating agent and a defluorinating method for wastewater treatment. Background Technology

[0002] Fluorides are widely used in production and daily life. They possess extremely strong oxidizing properties and, due to their high reactivity, can react with almost any other substance, thus attracting widespread attention. Fluoride-containing wastewater mainly originates from industrial production, such as the mining and synthesis of fluoride minerals, aluminum electrolytic refining, electroplating, photovoltaics, coke production, and thermal power generation. It has detrimental effects on soil, plants, human health, and other organisms.

[0003] Currently, practically applicable defluoridation technologies include adsorption, electrocoagulation, reverse osmosis, ion exchange, chemical precipitation, and coagulation sedimentation. Among these, ion exchange is expensive and requires strict control over raw water quality; electrocoagulation and reverse osmosis are complex processes with high power consumption; and adsorption has low adsorption capacity and small treatment capacity, making industrialization difficult. Polyaluminum chloride (PAC) is commonly used as a defluoridation coagulant. However, in practical engineering applications, it suffers from drawbacks such as limited composition and function, high dosage, high operating costs, and difficulty in sludge treatment and disposal. Furthermore, almost all commercially available defluoridators currently require the addition of polyacrylamide (PAM) as a coagulant aid to achieve good sedimentation, significantly increasing operating costs and production complexity.

[0004] In the actual defluorination process in factories, it is necessary to comprehensively consider the defluorination efficiency and economy based on different environments and defluorination requirements. Therefore, a more optimized and efficient defluorination technology is still needed for deep defluorination. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a highly efficient defluoridator that synergistically employs multiple defluoridation mechanisms, is applicable to a wide concentration range, exhibits excellent settling performance, requires no additional PAM coagulation aid, and is suitable for various industrial wastewaters.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A defluoridating agent for wastewater treatment comprises the following components in parts by weight:

[0008] 70-80 parts of polymeric coagulant,

[0009] 10-20 parts of calcium aluminum hydrotalcite

[0010] 10-20 parts of modified bentonite-fly ash composite material,

[0011] 2-5 parts of disodium ethylenediaminetetraacetate.

[0012] 200-400 parts water;

[0013] The modified bentonite-fly ash composite material is obtained by calcining and acidifying a mixture of bentonite and fly ash.

[0014] Preferably, the polymeric coagulant is selected from one or more of polyaluminum chloride, polyaluminum sulfate, polyferric chloride, polyaluminum ferric sulfate, polyferric chloride, and polyferric sulfate.

[0015] Preferably, the polymeric coagulant is a mixture of polyaluminum chloride, polyaluminum sulfate, polyferric chloride, and polyaluminum ferric sulfate.

[0016] Preferably, the defluorinating agent comprises the following components in parts by weight:

[0017] 30 parts polyaluminum chloride, 20 parts polyaluminum sulfate, 15 parts polyferric chloride, 10 parts polyaluminum ferric sulfate, 12 parts calcium aluminum hydrotalcite, 10 parts modified bentonite-fly ash composite material, 3 parts disodium ethylenediaminetetraacetate, and 300 parts water.

[0018] Preferably, the modified bentonite-fly ash composite material is prepared by the following method:

[0019] Bentonite and fly ash are mixed evenly and then calcined at 600-650℃ for more than 2 hours. After the product is cooled, hydrochloric acid is added and the mixture is stirred and reacted for 1-2 hours to obtain the final product.

[0020] Preferably, the preparation method further includes washing, filtering, and drying steps of the reaction product.

[0021] The present invention also provides a method for defluoridation in wastewater treatment, comprising the following steps:

[0022] The above-mentioned defluorinating agent is added to the fluoride-containing wastewater and mixed evenly, and the pH is controlled at 6.0-7.0 by adding alkali.

[0023] Preferably, the alkali is a liquid alkali with a mass fraction of 32%.

[0024] Preferably, the fluoride ion content in the fluoride-containing wastewater is 20–100 mg / L.

[0025] Preferably, the dosage of the defluorinating agent is 2.5 to 3.5 mL / L.

[0026] The beneficial effects of this invention are as follows:

[0027] Hydrotalcite-like minerals (TLMs) are anionic layered compounds with a unique structure consisting of interlayers of divalent and trivalent cations and anions. The diverse ratios and types of anions and cations result in a multivariate chemical composition. Compared to other adsorbents, TTLs possess advantages such as strong anion exchange capacity and a well-developed pore structure. Furthermore, the "memory effect" of TTLs allows for material regeneration, making them excellent adsorbents for fluoride ions in water. When combined with aluminum salt coagulants, the coagulants penetrate the interlayers and pores of the TTLs, providing a framework for the attachment of inorganic metal ions and increasing the contact area with fluoride ions, thus achieving highly efficient fluoride removal.

[0028] The components of the defluorinating agent of the present invention are hydrolyzed to produce mononuclear hydroxy complexes and polynuclear hydroxy polymers, which form strong chemical bonds with fluoride ions in wastewater as polydentate ligands.

[0029] Metal cations and oxygen atoms, or metal ions, combine with hydroxyl groups to form M-OH and MOM bonds, F - It undergoes ligand exchange with -OH to form an MFM complex.

[0030] Calcium aluminum hydrotalcite (Ca / Al-LDHs) for F - The adsorption mainly involves -OH and NO3. - With F - Ion exchange occurs, and simultaneously, the metal cations on the surface of the hydrotalcite-like mineral react with F. - A certain degree of integration occurred.

[0031] The raw materials required for this invention are inexpensive, readily available, and produce no secondary pollution.

[0032] The defluorinating agent prepared by this invention does not require additional PAM addition in practical applications and still has good sedimentation performance, and can settle completely in about 5 minutes.

[0033] The defluoridating agent prepared by this invention has a wide range of applications and has a good and efficient defluoridation effect on fluoride-containing wastewater in the range of 20-100 mg / L. Attached Figure Description

[0034] Figure 1 This is a comparison diagram of the sedimentation effects of the defluorinating agent of the present invention and a commercially available defluorinating agent in Example 6. Among them, (a) is the sedimentation diagram of the defluorinating agent prepared in Example 1 of the present invention, and (b) is the sedimentation diagram of commercially available defluorinating agent a. Detailed Implementation

[0035] Example 1

[0036] The defluorinating agent in this embodiment is composed of the following components by weight: 30 parts polyaluminum chloride, 20 parts polyaluminum sulfate, 15 parts polyferric chloride, 10 parts polyaluminum ferric sulfate, 12 parts Ca / Al type hydrotalcite, 10 parts modified bentonite-fly ash composite material, and 3 parts disodium ethylenediaminetetraacetate. The above-mentioned components are uniformly mixed and dissolved in water to form a homogeneous solution with a weight fraction of 25%, thus obtaining the defluorinating agent for fluoride-containing wastewater of this invention.

[0037] Example 2

[0038] The defluorinating agent in this embodiment is composed of the following components by weight: 20 parts polyaluminum chloride, 30 parts polyaluminum sulfate, 13 parts polyferric chloride, 11 parts polyaluminum ferric sulfate, 13 parts Ca / Al type hydrotalcite, 10 parts modified bentonite-fly ash composite material, and 3 parts disodium ethylenediaminetetraacetate. The above-mentioned components are uniformly mixed and dissolved in water to form a homogeneous solution with a weight fraction of 25%, thus obtaining the defluorinating agent for fluoride-containing wastewater of this invention.

[0039] Example 3

[0040] The defluorinating agent in this embodiment is composed of the following components by weight: 28 parts polyaluminum chloride, 20 parts polyaluminum sulfate, 13 parts polyferric chloride, 9 parts polyaluminum ferric sulfate, 20 parts Ca / Al type hydrotalcite, 7 parts modified bentonite-fly ash composite material, and 3 parts disodium ethylenediaminetetraacetate. The above-mentioned components are uniformly mixed and dissolved in water to form a homogeneous solution with a weight fraction of 25%, thus obtaining the defluorinating agent for fluoride-containing wastewater of this invention.

[0041] Example 4

[0042] The defluorinating agent in this embodiment is composed of the following components by weight: 28 parts polyaluminum chloride, 18 parts polyaluminum sulfate, 13 parts polyferric chloride, 9 parts polyaluminum ferric sulfate, 10 parts Ca / Al type hydrotalcite, 20 parts modified bentonite-fly ash composite material, and 2 parts disodium ethylenediaminetetraacetate. The components in the above formula are uniformly mixed and dissolved in water to form a homogeneous solution with a weight fraction of 25%, thus obtaining the defluorinating agent for fluoride-containing wastewater of this invention.

[0043] Comparative Example 1 (without Ca / Al type hydrotalcite)

[0044] The defluorinating agent in this embodiment is composed of the following components by weight: 32 parts polyaluminum chloride, 22 parts polyaluminum sulfate, 16 parts polyferric chloride, 13 parts polyaluminum ferric sulfate, 12 parts modified bentonite-fly ash composite material, and 5 parts disodium ethylenediaminetetraacetate. The components in the above formula are uniformly mixed and dissolved in water to form a homogeneous solution with a weight fraction of 25%, thus obtaining the defluorinating agent for fluoride-containing wastewater of this invention.

[0045] Comparative Example 2 (Unmodified bentonite-fly ash composite material)

[0046] The defluorinating agent in this embodiment is composed of the following components by weight: 35 parts polyaluminum chloride, 23 parts polyaluminum sulfate, 14 parts polyferric chloride, 12 parts polyaluminum ferric sulfate, 11 parts Ca / Al type hydrotalcite, and 5 parts disodium ethylenediaminetetraacetate. The components in the above formula are uniformly mixed and dissolved in water to form a homogeneous solution with a weight fraction of 25%, thus obtaining the defluorinating agent for fluoride-containing wastewater of this invention.

[0047] Example 5

[0048] Take 1L of fluoride-containing wastewater from the secondary sedimentation tanks of different sewage treatment plants, and add the defluoridating agents prepared in Examples 1-4 and Comparative Examples 1 and 2 respectively. Stir for 5 minutes, and add 32% liquid alkali to control the reaction pH between 6.0 and 7.0. After the reaction, no additional PAM is needed. After sedimentation for 10 minutes, take the supernatant and test the fluoride ion concentration.

[0049] A comparative experiment on defluoridation agents was conducted using the effluent from the secondary sedimentation tank of Wastewater Treatment Plant A. Specifically, in this experiment, the dosage of defluoridation agent was 2.5 ml / L, with the target effluent fluoride concentration being reduced to below 1.5 mg / L. The comparison results are shown in Table 1.

[0050] Table 1 Comparison of fluoride removal effects of various samples at a dosage of 2.5 ml / L

[0051] Example 1 20 1.23 93.8 Example 2 20 1.56 91.7 Example 3 20 1.83 90.8 Example 4 20 1.69 91.5 Comparative Example 1 20 2.47 87.6 Comparative Example 2 20 2.11 89.5

[0052] A comparative experiment on defluoridation agents was conducted using the effluent from the secondary sedimentation tank of Wastewater Treatment Plant B. Specifically, in this experiment, the dosage of defluoridation agent was 3.5 ml / L, with the target effluent fluoride concentration being reduced to below 10 mg / L. The comparison results are shown in Table 2.

[0053] Table 2 Comparison of fluoride removal effects of various samples at a dosage of 3.5 ml / L

[0054]

[0055]

[0056] A comparative experiment on defluoridation agents was conducted using the effluent from the secondary sedimentation tank of Wastewater Treatment Plant C. Specifically, in this experiment, the dosage of defluoridation agent was 0.5 ml / L, with the target effluent fluoride concentration being reduced to below 1.5 mg / L. The comparison results are shown in Table 3.

[0057] Table 3 Comparison of fluoride removal effects of various samples at a dosage of 0.5 ml / L

[0058] Example 1 2.69 1.25 53.53 Example 2 2.69 1.31 51.30 Example 3 2.69 1.46 45.72 Example 4 2.69 1.39 48.33 Comparative Example 1 2.69 1.93 28.25 Comparative Example 2 2.69 1.86 30.86

[0059] Example 6

[0060] The defluorinating agent prepared in Example 1 was compared with commercially available defluorinating agent a under the condition of achieving the same defluorination effect. The dosage of the agent, the dosage of liquid alkali, the sludge production, and the sludge settling performance were compared. Settling performance was as follows: Figure 1 Other comparison results are shown in Table 4:

[0061] Table 4 Comparison of the effects of the defluoridating agent of this invention with commercially available products.

[0062] Fluoride ion concentration before treatment (mg / L) 20 20 Defluoridator dosage (ml / L) 2.5 3.5 32% liquid caustic soda dosage (ml / L) 0.5 1.83 reaction time min 5 10 Fluoride ion concentration after treatment (mg / L) 1.24 1.25 Removal rate % 93.8 93.75 Oven-dried sludge yield (mg / L) 408 897 sludge settling time (min) 10 20

Claims

1. A method for defluoridation in wastewater treatment, characterized in that, Includes the following steps: The defluorinating agent is added to the fluoride-containing wastewater and mixed evenly. The pH is controlled at 6.0-7.0 by adding alkali, without the need for additional PAM. The components of the defluorinating agent hydrolyze to produce mononuclear hydroxy complexes and polynuclear hydroxy polymers, which form strong chemical bonds with fluoride ions in the wastewater using polydentate ligands. The defluorinating agent is composed of the following components in parts by weight: 70-80 parts of polymeric coagulant, 10-20 parts of calcium aluminum hydrotalcite 10-20 parts of modified bentonite-fly ash composite material, 2-5 parts of disodium ethylenediaminetetraacetate. 200-400 parts water; The modified bentonite-fly ash composite material is obtained by calcining and acidifying a mixture of bentonite and fly ash. The polymeric coagulant penetrates through the interlayers and channels of the calcium aluminum hydrotalcite.

2. The defluorination method according to claim 1, characterized in that, The polymeric coagulant is selected from one or more of polyaluminum chloride, polyaluminum sulfate, polyaluminum ferric sulfate, polyferric chloride, and polyferric sulfate.

3. The defluorination method according to any one of claims 1-2, characterized in that, The defluorinating agent is composed of the following components in parts by weight: 30 parts polyaluminum chloride, 20 parts polyaluminum sulfate, 15 parts polyferric chloride, 10 parts polyaluminum ferric sulfate, 12 parts calcium aluminum hydrotalcite, 10 parts modified bentonite-fly ash composite material, 3 parts disodium ethylenediaminetetraacetate, and 300 parts water.

4. The defluorination method according to claim 1, characterized in that, The modified bentonite-fly ash composite material is prepared by the following method: Bentonite and fly ash are mixed evenly and then calcined at 600-650℃ for more than 2 hours. After the product is cooled, hydrochloric acid is added and the mixture is stirred and reacted for 1-2 hours to obtain the final product.

5. The defluorination method according to claim 1, characterized in that, The alkali is a liquid alkali with a mass fraction of 32%.

6. The defluorination method according to claim 1, characterized in that, The fluoride-containing wastewater has a fluoride ion content of 20~100 mg / L.

7. The defluorination method according to claim 1, characterized in that, The dosage of the defluorinating agent is 2.5~3.5 mL / L.

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