Adsorption coagulation treatment method of perchlorate wastewater

Abstract

The invention relates to an adsorption coagulation treatment method for perchlorate wastewater. The method comprises the following steps: reducing the turbidity of the wastewater by using activated carbon as a pretreating agent; capturing perchlorate radicals through a hydrolysate by adopting polyaluminum chloride as a coagulant; then potassium permanganate and manganese chloride tetrahydrate are subjected to an oxidation-reduction reaction to generate nascent state manganese dioxide in situ; the nascent state manganese dioxide and the polyaluminum chloride hydrolysate form a composite floc through a bonding effect, and perchlorate is removed through an adsorption-coagulation synergistic effect. According to the treatment method disclosed by the invention, on the basis of the volume of the wastewater, the dosage of each component is as follows: 0.1-0.5 g / L of activated carbon, 30-45 mg / L of polyaluminum chloride, 20-80 mg / L of potassium permanganate and 40-160 mg / L of manganese chloride tetrahydrate. The invention relates to an adsorption and coagulation treatment method for perchlorate wastewater, which is used for treating perchlorate wastewater generated in industries such as military industry, spaceflight and firework production.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a highly efficient treatment method for perchlorate wastewater, and in particular an integrated treatment technology that combines activated carbon pretreatment, polyaluminum chloride coagulation, and in-situ generation of nascent manganese dioxide adsorption. Background Technology

[0002] To effectively remove perchlorate (ClO4) from water - The industry has developed and applied various technologies, mainly including ion exchange, biological reduction, and adsorption. Ion exchange uses specific anion exchange resins (such as Purolite A530E) for removal, which has some effect, but suffers from problems such as difficult resin regeneration, high operating costs (approximately 380 RMB / ton), and its selective adsorption capacity significantly decreases in wastewater containing high concentrations of competitive anions (such as SO4²⁻ and NO3⁻). Biological reduction relies on specific bacterial species (such as Dechloromonas) to remove ClO4. - The reduction to Cl⁻ is a method with a long reaction cycle (usually 24 to 48 hours), highly sensitive to water quality conditions such as dissolved oxygen and pH, and its efficiency drops by 50%-70% when coexisting with NO⁻. Microbial activity is also sharply reduced in low-temperature environments below 10℃, and toxic intermediate products may be generated during the process, limiting its widespread application. Adsorption technology utilizes materials such as activated carbon, but traditional activated carbon is ineffective against ClO₄. - Its adsorption capacity is extremely low (only about 0.2 mg / g), while specialized adsorbents such as modified chitosan face the dilemma of high cost and difficulty in large-scale application.

[0003] Perchlorate wastewater discharged from industries such as military, aerospace, and fireworks production is characterized by significant perchlorate concentrations (e.g., up to 31 mg / L) and is often accompanied by high turbidity (e.g., 509 NTU) and a certain amount of competing anions (e.g., nitrate). Simultaneously, this type of wastewater often contains inorganic ions such as calcium and magnesium, as well as high concentrations of organic matter, resulting in a complex water composition and significant treatment challenges. These characteristics lead to traditional methods such as ion exchange and biological reduction facing problems in practical applications, including low efficiency, high cost, and susceptibility to water quality interference. Summary of the Invention

[0004] In view of the defects or deficiencies of the prior art, the present invention provides an adsorption coagulation treatment method for perchlorate wastewater.

[0005] Therefore, the adsorption-coagulation treatment method for perchlorate wastewater provided by the present invention includes the following steps: Step 1: Add activated carbon to the perchlorate wastewater and stir to obtain a wastewater + activated carbon system. Step 2: Add polyaluminum chloride to the wastewater + activated carbon system, stir and mix to obtain a wastewater + activated carbon + polyaluminum chloride coagulation system; Step 3: Add potassium permanganate and manganese chloride tetrahydrate to the wastewater + activated carbon + polyaluminum chloride coagulation system, stir and mix, filter the solids, and the filtrate is the treated wastewater.

[0006] Preferably, the amount of activated carbon in step one is 0.1-0.5 g / L.

[0007] Preferably, the stirring rate in step one is 100-500 rpm and the time is 10-30 min.

[0008] Preferably, the amount of polyaluminum chloride added in step two is 30-45 mg / L.

[0009] Preferably, the stirring rate in step two is 300-500 rpm and the time is 1-3 min.

[0010] Preferably, the amount of potassium permanganate added in step three is 20-80 mg / L, and the amount of manganese chloride tetrahydrate is 40-160 mg / L.

[0011] Preferably, potassium permanganate and manganese chloride tetrahydrate are added during the stirring process in step three.

[0012] Preferably, the stirring method in step three is to stir at 40-500 rpm for 45-60 minutes.

[0013] In a further embodiment, the method of the present invention also includes recovering the solids filtered in step three, and then adding the solids to the perchlorate wastewater for recycling after washing and drying.

[0014] The treatment system in this invention includes activated carbon, polyaluminum chloride coagulant, potassium permanganate, and manganese chloride tetrahydrate; the manganese chloride tetrahydrate and potassium permanganate react in situ to generate nascent manganese dioxide through a redox reaction; the nascent manganese dioxide and the hydrolysis products of polyaluminum chloride form composite flocs through bonding; the composite flocs exchange ligands with perchlorate ions through adsorption sites on their surface, and achieve efficient removal through coagulation and sedimentation.

[0015] Specifically, the advantages of this invention are: (1) the removal efficiency of perchlorate is greater than 95%, and the treatment effect is stable and reliable; (2) the treatment cost is significantly reduced, and no special equipment or resin regeneration is required; (3) it has a wide applicable pH range, and the pH of the effluent can be automatically adjusted to near neutral; (4) the composite flocs have excellent settling performance, and the settling time is shorter than that of traditional methods; (5) the generated solid residue can be reused, and the removal rate remains above 85% after three cycles; (6) it has strong anti-interference ability, and the removal rate of perchlorate is still above 80% in the presence of competing NO3⁻ ions. This invention is particularly suitable for the treatment of perchlorate wastewater discharged by industries such as military, aerospace and fireworks production. Attached Figure Description

[0016] Figure 1 This describes the effect of different usage times on perchlorate removal in Example 5 of this invention.

[0017] Figure 2 These are the SEM images and EDS analysis structures of the solids collected after filtration in Example 3 of this invention; the top left image is the SEM image of the collected solids, and the subsequent images are the EDS images of O, Al, and Mn atoms at the corresponding positions, as well as the mass ratio of O, Mn, and Cl atoms at that position.

[0018] Figure 3 This is the XRD pattern of the solid powder prepared in Example 2 of this invention.

[0019] Figure 4 These are SEM images of flocculants or solids prepared in different steps in Example 2 of this invention; (a) is the solid powder after PAC coagulation after step (2), and (b) is the solid powder after step (3) is completed, i.e., the formation of nascent manganese dioxide. Detailed Implementation

[0020] The following embodiments are provided to better understand the present invention, but are not intended to limit the invention. All materials used in the following embodiments are commercially available products.

[0021] To address the challenges of high perchlorate ion stability, low removal efficiency, high cost, and susceptibility to water quality interference associated with traditional methods, the industry commonly employs coagulants to compress the electric double layer or adsorbents for physical adsorption. However, these measures have limited mechanisms of action; polyaluminum chloride (PAC) achieves less than 10% direct removal of perchlorate, while manganese dioxide, though promising, is prone to aggregation and presents difficulties in solid-liquid separation. Extensive research into perchlorate removal mechanisms has revealed that efficient removal requires simultaneously achieving two key steps: "charge neutralization disrupting stability" and "surface complexation for fixation." Individual reagent additions struggle to synergistically accomplish these two steps in both time and space.

[0022] This invention innovatively proposes a concept: designing a continuous reaction process of "first coagulation to construct the carrier, then adsorption to achieve fixation", and realizing a triple synergistic mechanism of "charge neutralization-redox-surface complexation" through the formation of "PAC-new ecological manganese dioxide" composite flocs.

[0023] This invention employs an integrated adsorption-coagulation treatment process. The treatment system comprises polyaluminum chloride (PAC), potassium permanganate (KMnO4), and manganese chloride tetrahydrate (MnCl2·4H2O). First, a small amount of activated carbon is added to the wastewater as a nucleus and coagulant aid to improve water conditions. Then, a PAC solution is preferentially added, and rapid stirring causes it to hydrolyze quickly, forming a large number of positively charged Al(OH)3 flocs. These flocs initially capture and bind perchlorate ions in the water through charge neutralization. Following this, potassium permanganate and manganese chloride tetrahydrate are added. Under stirring, they undergo a redox reaction, generating nascent manganese dioxide with a high specific surface area and abundant surface hydroxyl groups in situ inside and on the surface of the PAC flocs. This nascent manganese dioxide immediately reacts with the initially captured ClO4. - Ligand exchange reaction occurs (≡Mn-OH + ClO4) - → ≡Mn-ClO4+ OH⁻), achieving final fixation, while simultaneously binding with PAC flocs through Al-O-Mn bonds to form larger and denser composite flocs, ultimately achieving efficient removal through sedimentation.

[0024] The perchlorate wastewater treated in the following examples was generated during the on-site extraction of HTPB propellant via hydraulic cavitation. The filter residue was removed by filtration, and the composition of the original wastewater filtrate was analyzed as shown in Table 1 below. The results showed that the wastewater contained 31 mg / L of perchlorate ions.

[0025] Table 1

[0026] Example 1: (1) Add 0.1 g / L activated carbon to perchlorate wastewater and stir magnetically at 100 rpm for 10 min. The turbidity of the wastewater will decrease significantly and precipitate will be produced. (2) Add 30 mg / L polyaluminum chloride to the wastewater solution after step (1) and stir magnetically at 300 rpm for 1 min; Al(OH)3 flocs are generated in the wastewater. (3) Add 20 mg / L potassium permanganate and 40 mg / L manganese chloride tetrahydrate to the wastewater obtained after step 2, stir at 40 rpm for 45 min, filter the solids, and the filtrate is the treated wastewater.

[0027] Example 2: (1) Add 0.1 g / L activated carbon to the perchlorate wastewater and stir magnetically at 500 rpm for 30 min; (2) Add 45 mg / L polyaluminum chloride to the wastewater solution and stir magnetically at 500 rpm for 3 min; (3) Add 80 mg / L potassium permanganate and 160 mg / L manganese chloride tetrahydrate to the wastewater solution, stir at 500 rpm for 60 min, filter the solids, and the filtrate is the treated wastewater.

[0028] Example 3: (1) Add 0.3 g / L activated carbon to the perchlorate wastewater and stir magnetically at 250 rpm for 15 min; (2) Add 40 mg / L polyaluminum chloride to the wastewater solution and stir magnetically at 400 rpm for 2 min; (3) Add 60 mg / L potassium permanganate and 100 mg / L manganese chloride tetrahydrate to the wastewater solution, stir at 270 rpm for 50 min, filter the solids, and the filtrate is the treated wastewater.

[0029] Example 4: (1) Add 31 mg / L of sodium nitrate to the perchlorate wastewater and stir thoroughly to form mixed salt wastewater; (2) Add 0.1 g / L activated carbon to the mixed salt wastewater and stir magnetically at 500 rpm for 30 min; (3) Add 45 mg / L polyaluminum chloride to the wastewater solution and stir magnetically at 500 rpm for 3 min; (4) Add 80 mg / L potassium permanganate and 160 mg / L manganese chloride tetrahydrate to the wastewater solution, stir at 500 rpm for 60 min, filter the solids, and the filtrate is the treated wastewater.

[0030] Example 5: (1) Add 0.1 g / L activated carbon to the perchlorate wastewater and stir magnetically at 100 rpm for 30 min; (2) Add 36 mg / L polyaluminum chloride to the wastewater solution and stir magnetically at 300 rpm for 1 min; (3) Add 40 mg / L potassium permanganate and 140 mg / L manganese chloride tetrahydrate to the wastewater solution, stir at 300 rpm for 45 min, filter the solids, and the filtrate is the treated wastewater; (4) Wash the filtered solid with water and dry it at 50°C; (5) Use all the solid powder dried in step (4) to treat the wastewater, and stir magnetically at 300 rpm for 40 min; (6) Repeat (4) and (5) three times.

[0031] Comparative Example 1: The difference between this comparative example and Example 2 is that step (2) is omitted, while the rest of the process remains the same.

[0032] Comparative Example 2: The difference between this comparative example and Example 2 is that the order of steps (3) and (2) is reversed, while the rest of the operations are the same as in Example 2.

[0033] Comparative Example 3: The difference between this comparative example and Example 2 is that step (3) is not performed, while the rest of the operations are the same as in Example 2.

[0034] The wastewater treatment effects of the above embodiments and comparative examples were evaluated: (1) Perchlorate removal rate: The concentration of perchlorate ions in the water sample before and after treatment was determined by ion chromatography (HJ 1044-2019) and the removal rate was calculated. The specific method was to take the supernatant, filter it through a 0.45 μm aqueous filter membrane and then inject it for analysis. The results are shown in Table 2.

[0035] (2) Reuse performance: The solid powder from Example 5, after multiple cycles of use, was evaluated for performance. The recovered solid powder was used to treat new perchlorate wastewater according to the method described in Example 5, and was reused 3 times. The removal rate of perchlorate was measured each time. The results are shown in […]. Figure 1 .

[0036] (3) Elemental composition and bonding mechanism of composite flocs: The surface micro-area analysis of the solid obtained by filtration in step (3) of Example 3 was performed using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The distribution and content of Al, Mn, O and Cl elements in the flocs were determined. The results are shown in the figure. Figure 2 Meanwhile, XRD analysis was performed on the solid powder prepared in Example 2, and the results are shown in [Figure 1]. Figure 3 .

[0037] (4) Morphology and structural evolution of flocs: The micromorphology, size and spatial structure of the flocs generated in step (2) and the solids obtained by filtration in step (3) of Example 2 were observed using scanning electron microscopy (SEM). The formation process from the initial flocs to the final composite flocs was analyzed. The results are shown in the figure. Figure 4 .

[0038] The perchlorate removal rate and pH value results of the embodiments and comparative examples of the present invention are shown in Table 2 below: Table 2

[0039] Implementation effect analysis: (1) According to the results shown in Table 2, it can be seen from the perchlorate removal rates of Examples 1, 2, 3 and 4 that the present invention has the advantage of high efficiency in removal. Under the preferred conditions, the removal rate of perchlorate exceeds 85%. Compared with Example 2 and Comparative Example 1 (without PAC) and Comparative Example 3 (without the addition of nascent manganese dioxide formed by KMnO4 and MnCl2·4H2O), with the same dosage of potassium permanganate and manganese chloride tetrahydrate or the same dosage of polyaluminum chloride, the present invention improves the removal rate by 57.3% and 67.61% respectively by forming composite flocs, and also improves the pH value of the treated solution.

[0040] Comparing the removal effects of Example 2 and Comparative Example 2 (with a change in the order of addition), it can be seen that the specific addition order of "PAC coagulation followed by nascent manganese dioxide adsorption" designed in this invention has significant technical advantages. Using the same reagent components, Comparative Example 2, which only changed the addition order, achieved a removal rate of only 76.33%, while Example 2, with the complete process, achieved a removal rate of 97.82%, demonstrating the crucial influence of the addition order on the synergistic effect.

[0041] Comparing the removal effects of Examples 1, 2, and 3, it can be seen that optimizing the ratio of each component has a significant impact on the treatment effect. Example 2 achieved the best removal effect under the conditions of 36 mg / L polyaluminum chloride, 40 mg / L potassium permanganate, and 140 mg / L manganese chloride tetrahydrate. Too much or too little reagent will affect the formation efficiency and stability of the composite flocs.

[0042] Comparing the removal effects of Example 2 and Example 4, it can be seen that the solution of the present invention has strong anti-interference ability, even in the presence of NO3. - The removal rate of perchlorate ions remained at 83.21% even in the presence of competing ions.

[0043] From the pH changes of the treated wastewater, all Examples 1-4 that fully implemented the process of this invention showed stable effluent pH values ​​between 5.83 and 6.91, close to neutral; while Comparative Examples 1-3, which lacked the key step, showed acidic effluent pH values ​​(5.29–5.65). This difference directly confirms the core reaction mechanism of this invention—the ligand exchange reaction between nascent manganese dioxide and perchlorate ions releases OH⁻ ions, thereby automatically adjusting the effluent pH to near neutral.

[0044] (2) Comparison Figure 2 The EDS analysis results show that characteristic signals of Al, Mn, O, and Cl elements were simultaneously detected in the solids generated after wastewater treatment according to this invention, and the elements were evenly distributed, confirming the existence of Al-O-Mn bonding and the successful immobilization of ClO4⁻ on the composite flocs; from Figure 3 The XRD patterns further verified the crystal structure characteristics of the composite flocs. Through the formation of the "PAC-nascent manganese dioxide" composite flocs, a triple synergistic mechanism of "charge neutralization-redox-surface complexation" is achieved.

[0045] Figure 4 The morphological and structural changes of flocs in Example 2 at different treatment stages were compared using scanning electron microscopy (SEM). Figure 4 (a) is the flocs formed after adding only polyaluminum chloride (PAC) and coagulating. It is a loose, irregular and rough flocculent agglomerate with a loose structure and large pores, indicating that the flocs formed by simple PAC coagulation have a limited degree of aggregation. Figure 4 (b) The final composite flocs formed after the continued addition of potassium permanganate and manganese chloride tetrahydrate and their reaction exhibit a significant morphological transformation into aggregates with a denser structure, larger particle size, and more uniform surface. Fine particles are visible tightly adhering to the floc surface and internal pores, indicating that the nascent manganese dioxide generated in situ and the PAC hydrolysis products form a stable composite structure with a larger specific surface area through Al-O-Mn bonding. This morphological evolution directly confirms the process design concept of "first coagulation to construct the carrier, then adsorption to achieve fixation." The formation of composite flocs not only enhances structural stability but also provides more active sites for ligand exchange and fixation of perchlorate ions, thereby significantly improving sedimentation performance and removal efficiency.

[0046] The above results indicate that the positively charged Al(OH)3 flocs produced by PAC hydrolysis can preferentially capture and initially bind ClO4 through charge neutralization. - The newly formed manganese dioxide that subsequently forms in situ has abundant ≡Mn-OH groups on its surface, which can interact with the initially bound ClO4. - Ligand exchange occurs, forming a stable ≡Mn-ClO4 surface complex. The key lies in the reaction sequence and timing: if potassium permanganate is added first, its strong oxidizing properties will destroy the positive charge of PAC, weakening its charge neutralization ability; if PAC and potassium permanganate are added simultaneously, they will interfere with each other, forming an amorphous precipitate and reducing the effective reaction surface area.

[0047] (3) Comparison Figure 1 The recycling results demonstrate that the solid residue generated by this invention has excellent reuse performance. After three cycles, the removal rate of perchlorate remains above 85%, realizing the circular economy concept of "treating waste with waste" and significantly reducing operating costs.

[0048] The above description provides examples of the preferred embodiments of the present invention. Parts not detailed herein are common knowledge to those skilled in the art. The scope of protection of the present invention is determined by the claims. Any equivalent modifications based on the technical teachings of the present invention are also within the scope of protection of the present invention.

Claims

1. A method for adsorptive coagulation treatment of perchlorate wastewater, characterized by, The method comprises the following steps: Step one, adding activated carbon into perchlorate wastewater, stirring and mixing to obtain a wastewater + activated carbon system; Step two, adding polyaluminum chloride into the wastewater + activated carbon system, stirring and mixing to obtain a wastewater + activated carbon + polyaluminum chloride coagulation system; Step three, adding potassium permanganate and manganese chloride tetrahydrate into the wastewater + activated carbon + polyaluminum chloride coagulation system, stirring and mixing, filtering the solid, and the filtrate is the treated wastewater.

2. The method of claim 1, wherein the method is characterized by, The amount of activated carbon in step one is 0.1-0.5 g / L.

3. The method of claim 1, wherein the method is characterized by, The stirring rate in step one is 100-500 rpm, and the stirring time is 10-30 min.

4. The method of claim 1, wherein the method is characterized by, The adding amount of polyaluminum chloride in step two is 30-45 mg / L.

5. The method of claim 1, wherein the method is characterized by, The stirring rate in step two is 300-500 rpm, and the stirring time is 1-3 min.

6. The method of claim 1, wherein the adsorptive coagulation treatment of perchlorate wastewater is characterized by, The adding amount of potassium permanganate in step three is 20-80 mg / L, and the adding amount of manganese chloride tetrahydrate is 40-160 mg / L.

7. The method of claim 1, wherein the method is characterized by, The potassium permanganate and manganese chloride tetrahydrate are added during the stirring in step three.

8. The method of claim 1 or 7, wherein the method is characterized by, The stirring mode in step three is 40-500 rpm, and the stirring time is 45-60 min.

9. The method of claim 1 or 7, wherein the method is characterized by, The method further comprises recovering the solid filtered in step three, washing and drying the solid, and adding the solid into the perchlorate wastewater for recycling treatment.

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