Treatment method of perchlorate wastewater

Abstract

The invention relates to a perchlorate wastewater treatment method, which comprises: (1) under a stirring condition, adjusting the pH value of clarified perchlorate wastewater to an acidic state, adding a metal reducing agent, carrying out a reduction reaction, adjusting the pH value of the wastewater to a weak alkaline state by using a sodium carbonate solution, and filtering to obtain a reduced liquid; and (2) carrying out column-loading targeted deep adsorption on the reduced solution obtained in the step (1) by using anion exchange resin to obtain a solution subjected to adsorption deep treatment. The method disclosed by the invention is efficient, rapid, stable, short in flow, low in cost, safe and reliable in wastewater treatment process, simple to operate, environment-friendly, free of secondary pollution, capable of realizing up-to-standard discharge and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to a wastewater treatment method, specifically a method for treating perchlorate wastewater. Background Technology

[0002] Perchlorate is mainly used as a solid oxidant in rockets, flames, and missiles, and is also one of the raw materials in the fireworks and firecrackers production industry. However, it is an inorganic pollutant in the natural environment. The molecular structure of perchlorate ions results in its high chemical stability, and its oxidizing power in water is weaker than in its solid state (Inorganic Chemistry, Volume 2). Due to the high stability and high solubility of perchlorate, and its high concentration in wastewater, most reducing agents are also difficult to react with it. Therefore, it is difficult to effectively remove perchlorate from water using conventional methods.

[0003] Some fireworks and firecracker manufacturers discharge perchlorate-containing wastewater directly without treatment, causing surface water pollution. Perchlorate, once ingested, can interfere with the thyroid gland's absorption and utilization of iodine, leading to endocrine disorders and threatening human health, as well as harming humans and animals. Currently, relevant laws and regulations require that the concentration of perchlorate in discharged wastewater be <0.7 mg / L. Therefore, there is an urgent need to find a method for efficiently treating perchlorate wastewater.

[0004] Currently, the main methods for removing perchlorate from wastewater include chemical reduction, biological reduction, anion exchange, and reverse osmosis.

[0005] CN116903195A discloses a deep purification system and method for perchlorate in wastewater from the fireworks industry. The method involves in-situ preparation of nano-iron to reduce perchlorate ions in a fixed-bed adsorption column filled with a perchlorate-selective resin adsorbent. Unreduced perchlorate ions are then adsorbed by anion exchange resin. However, this method suffers from drawbacks such as a long process, complex operation, and difficulty in large-scale wastewater treatment.

[0006] CN118545874A discloses a method for purifying perchlorate wastewater, which involves adding ferrous salt, hydrazine hydrate, and aluminum powder as reducing agents to high-concentration perchlorate wastewater, stirring the mixture, filtering it, and then adsorbing it with an ion exchange resin to obtain the treated liquid. However, its disadvantages are that ferrous salt has poor reducing properties and produces iron slag, while hydrazine hydrate requires heating at a reduction temperature of 40–95°C, and aluminum powder poses safety hazards during transportation and use.

[0007] Therefore, there is an urgent need to find a treatment method for perchlorate wastewater that is efficient, fast, stable, has a short process, low cost, is safe and reliable in wastewater treatment, is simple to operate, environmentally friendly, has no secondary pollution, can achieve standard discharge, and is suitable for industrial production. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for treating perchlorate wastewater that is efficient, fast, stable, has a short process, low cost, is safe and reliable in wastewater treatment, is simple to operate, environmentally friendly, has no secondary pollution, can achieve standard discharge, and is suitable for industrial production.

[0009] The technical solution adopted by this invention to solve its technical problem is as follows: A method for treating perchlorate wastewater, comprising the following steps: (1) Under stirring conditions, the pH of the clarified perchlorate wastewater was adjusted to acidic, a metal reducing agent was added, a reduction reaction was carried out, and then the pH of the wastewater was adjusted to weakly alkaline with sodium carbonate solution. After filtration, the reduced liquid was obtained. (2) The reduced liquid obtained in step (1) is subjected to targeted deep adsorption on an anion exchange resin to obtain the liquid after adsorption depth treatment.

[0010] The inventive concept of this invention is as follows: In order to improve the efficiency of perchlorate removal and accelerate the reaction rate, a magnesium alloy with stronger reducing properties than aluminum and iron is used as a reducing agent. Under the premise of ensuring operational safety and no environmental pollution, the concentration of perchlorate in the wastewater can be reduced to about 1 mg / L, thereby reducing the number of perchlorate ions adsorbed by the anion exchange resin column, thus reducing the number of times the anion exchange resin is regenerated and greatly improving the working efficiency.

[0011] Preferably, in step (1), the stirring temperature is 10-30℃ and the stirring speed is 300-400r / min.

[0012] Preferably, in step (1), the perchlorate wastewater has a perchlorate concentration of 30–200 mg / L (more preferably 50–150 mg / L) and a pH value of 5–7. The perchlorate wastewater treated by the method of the present invention originates from a fireworks company.

[0013] Preferably, in step (1), the pH of the clarified perchlorate wastewater is adjusted to 2-4 using dilute hydrochloric acid. Under acidic conditions, the oxide film on the metal surface dissolves at the beginning of the reaction, but no oxide film is generated during the reaction. The main reaction is a redox reaction, where the metal is oxidized to generate metal ions, and the perchlorate ions are reduced to generate chloride ions.

[0014] Preferably, the dilute hydrochloric acid is a hydrochloric acid solution with a concentration of 0.08 to 0.12 mol / L.

[0015] Preferably, in step (1), the amount of the metal reducing agent is ≥20 times (more preferably 40 to 140 times) the mass of the perchlorate ion. The amount of the metal reducing agent is in large excess, and any unreacted metal reducing agent can be collected and reused. When in use, the metal reducing agent is hung on the barrel wall or placed at the bottom of the barrel in the form of a thin metal sheet.

[0016] Preferably, in step (1), the metal reducing agent is in the form of a thin sheet with a thickness of 0.2–3.0 mm (more preferably 0.3–2.0 mm). More preferably, the length and width dimensions of the thin sheet metal reducing agent are (20–40) mm × (10–30) mm.

[0017] Preferably, in step (1), the metal reducing agent includes one or more of the following: magnesium-aluminum alloy, magnesium-iron alloy, aluminum-magnesium alloy, aluminum-iron alloy, or thin aluminum plate. The aluminum-magnesium alloy and aluminum-iron alloy can be derived from waste lightweight beverage cans. The main metals in the magnesium-aluminum alloy and aluminum-magnesium alloy are different, namely magnesium and aluminum, respectively. To prevent the metal reducing agent from reacting too quickly in water, and for safety during transportation and storage, magnesium alloy or aluminum alloy is preferred.

[0018] Preferably, in step (1), the magnesium-aluminum alloy or magnesium-iron alloy has a magnesium mass fraction of 80-99%. More preferably, the magnesium-aluminum alloy has a magnesium mass fraction of 80-90% and an aluminum mass fraction of 20-10%; the magnesium-iron alloy has a magnesium mass fraction of 97-99% and an iron mass fraction of 3-1%.

[0019] Preferably, in step (1), the aluminum-magnesium alloy or aluminum-iron alloy has an aluminum mass fraction of 80-99%. More preferably, the aluminum-magnesium alloy has an aluminum mass fraction of 86-96% and a magnesium mass fraction of 14-4%; the aluminum-iron alloy has an aluminum mass fraction of 97-99% and an iron mass fraction of 3-1%.

[0020] The chemical reaction principle of this invention is as follows: the standard electrode potential E° of magnesium is -2.37V, that of aluminum is -1.66V, and that of iron is -0.44V. Therefore, among iron, aluminum, and magnesium, magnesium has the lowest standard electrode potential and the strongest reducing ability. This invention uses high-content magnesium alloys, aluminum alloys, or aluminum as reducing agents for perchlorate, achieving good reduction results. The chemical reaction equation for the perchlorate wastewater treatment process is as follows: ClO4 - + 4Mg + 8H + = 4Mg 2+ + Cl - + 4H2O (1); 3ClO4 -+ 8Al + 24H + = 8Al 3+ + 3Cl - + 12H2O(2; Mg 2+ + CO3 2- = MgCO3↓(3; Al 3+ + 3OH - = Al(OH)3↓(4).

[0021] Preferably, in step (1), the reduction reaction takes 2 to 3 hours. This reaction time is more conducive to the complete reaction of the above reaction equations (1) and (2).

[0022] Preferably, in step (1), the pH of the wastewater is adjusted to 7.5–8.5 using sodium carbonate solution. The purpose of adjusting the pH is to remove magnesium and aluminum ions according to the above reaction equations (3) and (4) to form magnesium carbonate or aluminum hydroxide precipitates. The filter residue produced by filtration is sent for external disposal.

[0023] Preferably, in step (1), the mass concentration of the sodium carbonate solution is 2-4%.

[0024] Preferably, in step (2), the diameter-to-height ratio of the resin column used for targeted deep adsorption is 1:3 to 6 (more preferably 1:4 to 5).

[0025] Preferably, in step (2), the flow rate of the column-targeted deep adsorption is 20–30 BV / h. The purpose of column-targeted deep adsorption is to deeply remove trace amounts of perchlorate ions remaining in the reduced solution. The adsorption reaction equation is: RN (CH)3Cl + ClO4 - = (RN(CH)3)ClO4 + Cl - (Underlined indicates resin). At the specified column flow rate, the resin adsorption capacity is increased; if the column flow rate is too high, the adsorption capacity is too low.

[0026] Preferably, in step (2), the anion exchange resin includes a macroporous strong-base styrene-based anion exchange resin, Amberlite IRA-400, or AB-17, etc. More preferably, the macroporous strong-base styrene-based anion exchange resin is of type D296. Amberlite IRA-400 is made in the USA, and AB-17 is made in Russia.

[0027] Preferably, after the targeted deep adsorption, the elution and regeneration method of the anion exchange resin is as follows: first, the anion exchange resin after the targeted deep adsorption in step (2) is eluted and regenerated with an elution solution to obtain an elution and regeneration solution, and then the anion exchange resin is washed with water until neutral to obtain a water washing solution.

[0028] Preferably, the eluent is an alkaline salt solution with a mass concentration of 8-12% NaCl + 0.1-0.3% NaOH.

[0029] Preferably, the total volume of the eluent is 4 to 5 times the resin volume, and the elution regeneration flow rate is 4 to 6 BV / h. Elution regeneration displaces perchlorate ions from the anion exchange resin. If the total volume of the eluent is too small, the elution effect will be poor, and the re-adsorption effect of the anion exchange resin will deteriorate. At the specified elution regeneration flow rate, the elution regeneration effect is better.

[0030] Preferably, the neutral pH value is 6 to 8.

[0031] The elution and regeneration solution is recycled to the perchlorate metal reduction process in step (1) for further processing; the water washing solution can be recycled.

[0032] In the method of this invention, the perchlorate concentration in the perchlorate wastewater, the reduced solution, and the solution after adsorption deep treatment is detected by ion chromatography.

[0033] The beneficial effects of the method of the present invention are as follows: (1) The present invention proposes for the first time to use magnesium alloy thin plates or waste lightweight beverage cans as metal reducing agents when treating perchlorate wastewater from the fireworks and firecrackers industry, so as to achieve efficient, rapid and stable removal of perchlorate. The perchlorate concentration in the treated liquid is <0.5mg / L, which meets the requirements of Hunan Province's "Industrial Wastewater Perchlorate Pollutant Discharge Standard" (DB43 / 3001-2024) that the perchlorate concentration is <0.6mg / L, and the perchlorate removal rate is >99.5%. The present invention is simple to operate, environmentally friendly, and has no secondary pollution. The treated effluent meets the standards and can be used for workshop cleaning. (2) The method of the present invention uses magnesium alloy plates or waste lightweight beverage cans as metal reducing agents, which not only utilizes the strong reducing properties of magnesium or aluminum, but also eliminates the safety hazards caused by metal powder, which is conducive to safe production; at the same time, since the concentration of perchlorate in wastewater can be reduced to about 1 mg / L through oxidation-reduction reaction, the amount of perchlorate ions adsorbed by the anion exchange resin column is reduced, thereby reducing the number of times the anion exchange resin is regenerated and greatly improving the work efficiency. (3) The method of the present invention is suitable for the treatment of complex wastewater systems containing perchlorate. It has a small footprint, short process, low cost, simple equipment, and the raw material can be waste aluminum cans, turning waste into treasure. The entire wastewater treatment process meets the requirements of energy conservation and emission reduction. The perchlorate wastewater treatment system is easy to industrialize. Detailed Implementation

[0034] The present invention will be further described below with reference to the embodiments.

[0035] The perchlorate wastewater treated in the embodiments and comparative examples of this invention originated from a fireworks company, with a perchlorate concentration of 98.5 mg / L and a pH of 7. The D296 macroporous strong base styrene-based anion exchange resin used in the embodiments of this invention was purchased from Shanghai Nankai Resin Co., Ltd. Unless otherwise specified, the raw materials or chemical reagents used in the embodiments and comparative examples of this invention were obtained through conventional commercial channels.

[0036] In the embodiments and comparative examples of this invention, the perchlorate concentration in the perchlorate wastewater, the reduced solution, and the solution after adsorption deep treatment was detected by ion chromatography.

[0037] Example 1 (1) At 10℃ and a stirring speed of 300r / min, 1500L of clarified perchlorate wastewater was adjusted to pH 2.0 with 0.1mol / L hydrochloric acid solution, and 20kg of magnesium-aluminum alloy sheets (magnesium mass fraction of 85%, aluminum mass fraction of 15%, 30mm×20mm×1mm) were added. After the reduction reaction was carried out for 2h, the pH was adjusted to 7.5 with 3% sodium carbonate solution. After filtration, 1500L of reduced solution (perchlorate concentration of 0.95mg / L) was obtained. The unreacted magnesium-aluminum alloy sheets were taken out and kept for the next use. (2) The 1500L reduced solution obtained in step (1) was subjected to targeted deep adsorption on a column (the size of the resin column is φ40cm×160cm) using a D296 type macroporous strong base styrene-based anion exchange resin at a flow rate of 20BV / h to obtain the adsorption depth treated solution.

[0038] Sampling analysis showed that the concentration of perchlorate in the adsorption depth-treated liquid obtained in step (2) was <0.5 mg / L, which meets the requirements of Hunan Province's "Industrial Wastewater Perchlorate Pollutant Discharge Standard" (DB43 / 3001-2024) that the perchlorate concentration is <0.6 mg / L, and the perchlorate removal rate is >99.5%.

[0039] The elution and regeneration method of the anion exchange resin after targeted deep adsorption is as follows: First, use an alkaline salt solution with a mass concentration of 10% NaCl + 0.2% NaOH as the eluent, with a total volume of 4 times the resin volume, and an elution and regeneration flow rate of 5 BV / h. After elution and regeneration of the ion exchange resin after targeted deep adsorption in step (2), the eluted and regenerated solution is obtained. Then, the anion exchange resin is washed with water until the pH value is 7, and the washed solution is obtained. The eluted and regenerated solution is recycled to the perchlorate metal reduction process in step (1) for treatment; the washed solution can be recycled.

[0040] Example 2 (1) At 20℃ and a stirring speed of 350r / min, 1200L of clarified perchlorate wastewater was adjusted to pH 3.0 with 0.1mol / L hydrochloric acid solution, and then 12kg of magnesium-iron alloy sheet (magnesium mass fraction of 98%, iron mass fraction of 2%, 30mm×20mm×0.5mm) was added. After the reduction reaction was carried out for 2.5h, the pH was adjusted to 8.0 with 3% sodium carbonate solution. After filtration, 1200L of reduced solution (perchlorate concentration of 0.93 mg / L) was obtained. The unreacted magnesium-iron alloy sheet was taken out and kept for the next use. (2) The 1200L reduced solution obtained in step (1) was subjected to targeted deep adsorption on a column (the size of the resin column is φ40cm×200cm) using a D296 type macroporous strong base styrene-based anion exchange resin at a flow rate of 22BV / h to obtain the adsorption depth treated solution.

[0041] According to the sampling analysis, the concentration of perchlorate in the adsorption depth treatment liquid obtained in step (2) is <0.4mg / L, which meets the requirements of Hunan Province's "Industrial Wastewater Perchlorate Pollutant Discharge Standard" (DB43 / 3001-2024) that the perchlorate concentration is <0.6mg / L, and the perchlorate removal rate is >99.6%.

[0042] The elution and regeneration method of the anion exchange resin after deep adsorption is the same as in Example 1.

[0043] Example 3 (1) At 30℃ and a stirring speed of 400r / min, 1800L of clarified perchlorate wastewater was adjusted to pH 4.0 with 0.1mol / L hydrochloric acid solution, and then 12kg of waste lightweight aluminum cans (aluminum mass fraction of 95-96%, magnesium mass fraction of 4-5%, 30mm×20mm×0.32mm) were added and the reduction reaction was carried out for 3h. Then, the pH was adjusted to 8.5 with 3% sodium carbonate solution and filtered to obtain 1800L of reduced liquid (perchlorate concentration of 0.97 mg / L). The unreacted waste lightweight aluminum cans were taken out and kept for the next use. (2) The 1800L reduced liquid obtained in step (1) was subjected to targeted deep adsorption on a column (the size of the resin column is φ40cm×200cm) with the D296 macroporous strong base styrene-based anion exchange resin obtained after regeneration in Example 1 at a flow rate of 24BV / h, to obtain the liquid after adsorption depth treatment.

[0044] According to the sampling analysis, the concentration of perchlorate in the adsorption depth treatment liquid obtained in step (2) is <0.5mg / L, which meets the requirements of Hunan Province's "Industrial Wastewater Perchlorate Pollutant Discharge Standard" (DB43 / 3001-2024) that the perchlorate concentration is <0.6mg / L, and the removal rate of perchlorate is >99.5%.

[0045] The elution and regeneration method of the anion exchange resin after deep adsorption is the same as in Example 1.

[0046] Comparative Example 1 The only difference between this comparative example and Example 1 is that in step (1), 20 kg of magnesium-aluminum alloy sheets (magnesium mass fraction of 85%, aluminum mass fraction of 15%, 30 mm × 20 mm × 1 mm) are replaced with 20 kg of metallic iron powder with a particle size of 1-2 mm; step (2) is deleted. The rest is the same as in Example 1.

[0047] Sampling analysis showed that the concentration of perchlorate in the reduced solution obtained in step (1) was 21.7 mg / L, which far exceeded the requirement of <0.6 mg / L for perchlorate concentration in the "Discharge Standard of Industrial Wastewater Perchlorate Pollutants" (DB43 / 3001-2024) of Hunan Province. The removal rate of perchlorate was only 78.0%.

[0048] Comparative Example 2 The only difference between this comparative example and Example 1 is that in step (1), 20 kg of magnesium-aluminum alloy sheets (magnesium mass fraction of 85%, aluminum mass fraction of 15%, 30 mm × 20 mm × 1 mm) are replaced with 20 kg of metallic aluminum powder with a particle size of 2-3 mm; step (2) is deleted. The rest is the same as in Example 1.

[0049] Sampling analysis showed that the concentration of perchlorate in the reduced solution obtained in step (1) was 5.47 mg / L, which far exceeded the requirement of <0.6 mg / L for perchlorate concentration in the "Discharge Standard of Industrial Wastewater Perchlorate Pollutants" (DB43 / 3001-2024) of Hunan Province. The removal rate of perchlorate was only 94.4%.

Claims

1. A method for treating perchlorate wastewater, characterized in that, Includes the following steps: (1) Under stirring conditions, the pH of the clarified perchlorate wastewater was adjusted to acidic, a metal reducing agent was added, a reduction reaction was carried out, and then the pH of the wastewater was adjusted to weakly alkaline with sodium carbonate solution. After filtration, the reduced liquid was obtained. (2) The reduced liquid obtained in step (1) is subjected to targeted deep adsorption on an anion exchange resin to obtain the liquid after adsorption depth treatment.

2. The method for treating perchlorate wastewater according to claim 1, characterized in that: In step (1), the stirring temperature is 10–30°C and the stirring speed is 300–400 r / min; the perchlorate wastewater has a perchlorate concentration of 30–200 ppm. The pH value of the clarified perchlorate wastewater is adjusted to 2-4 using dilute hydrochloric acid (mg / L, pH 5-7); the dilute hydrochloric acid is a hydrochloric acid solution with a concentration of 0.08-0.12 mol / L; the amount of the metal reducing agent is ≥20 times the mass of the perchlorate ion; the metal reducing agent is in the form of thin flakes with a thickness of 0.2-3.0 mm; the metal reducing agent includes one or more of magnesium-aluminum alloy, magnesium-iron alloy, aluminum-magnesium alloy, aluminum-iron alloy, or thin aluminum plate; in the magnesium-aluminum alloy or magnesium-iron alloy, the mass fraction of magnesium is 80-99%; in the aluminum-magnesium alloy or aluminum-iron alloy, the mass fraction of aluminum is 80-99%; the reduction reaction time is 2-3 h; the pH value of the wastewater is adjusted to 7.5-8.5 using sodium carbonate solution; the mass concentration of the sodium carbonate solution is 2-4%.

3. The method for treating perchlorate wastewater according to claim 1 or 2, characterized in that: In step (2), the diameter-to-height ratio of the resin column used for targeted deep adsorption is 1:3 to 6; the flow rate of the targeted deep adsorption is 20 to 30 BV / h; the anion exchange resin includes macroporous strong base styrene-based anion exchange resin, Amberlite IRA-400, or AB-17.

4. The method for treating perchlorate wastewater according to claim 1 or 2, characterized in that: The elution and regeneration method of the anion exchange resin after targeted deep adsorption is as follows: first, the anion exchange resin after targeted deep adsorption in step (2) is eluted and regenerated with an eluent to obtain an eluted and regenerated solution; then, the anion exchange resin is washed with water until neutral to obtain a water-washed solution; the eluent is an alkaline salt solution with a mass concentration of 8-12% NaCl + 0.1-0.3% NaOH; the total amount of the eluent is 4-5 times the volume of the resin, the elution and regeneration flow rate is 4-6 BV / h; the neutral pH value is 6-8.

5. The method for treating perchlorate wastewater according to claim 3, characterized in that: The elution and regeneration method of the anion exchange resin after targeted deep adsorption is as follows: first, the anion exchange resin after targeted deep adsorption in step (2) is eluted and regenerated with an eluent to obtain an eluted and regenerated solution; then, the anion exchange resin is washed with water until neutral to obtain a water-washed solution; the eluent is an alkaline salt solution with a mass concentration of 8-12% NaCl + 0.1-0.3% NaOH; the total amount of the eluent is 4-5 times the volume of the resin, the elution and regeneration flow rate is 4-6 BV / h; the neutral pH value is 6-8.