Wastewater dechlorination method based on reduction-precipitation principle

Abstract

The invention relates to a wastewater dechlorination method based on a reduction-precipitation principle, belongs to the technical field of water treatment, and solves the problems of extremely high required acidity, high agent dosage, low efficiency and high residual copper ion concentration in wastewater dechlorination by an existing cuprous method. The method comprises the following step: mixing the chlorine-containing wastewater with sulfite and a copper ion-containing compound for reaction. According to the method, a traditional copper elementary substance reducing agent is replaced by a sulfite reducing agent, and the sulfite and the copper ion-containing compound are added into the chlorine-containing wastewater at the same time, so that the chloride ions are efficiently removed, the use amount of the copper ions and the concentration of the residual copper ions are reduced, the cost of the reducing agent is reduced, and meanwhile, the chloride ion removal efficiency is improved; and the required sulfuric acid concentration is low.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, in particular to a wastewater dechlorination method based on the reduction-precipitation principle. Background Art

[0002] Chloride ions are a common pollutant in industrial wastewater. Their concentrations and sources are mainly as follows: (1) Chlor-alkali industry: produced during the production of chlorine, sodium hydroxide and hydrogen (10,000-100,000 mg / L); (2) Production of organic chlorine compounds: such as the production of vinyl chloride and methyl chloride (1,000-50,000 mg / L); (3) Metal processing: use of chlorine-containing compounds (such as hydrochloric acid) for metal cleaning and etching (500-10,000 mg / L); (4) Ore processing: use of chlorine-containing compounds in certain ore processing processes (1,000-20,000 mg / L); (5) Oil and gas production: formation water contains chloride ions, which are discharged with wastewater during the production process (5000-200000 mg / L); (6) Oil refining process: crude oil contains chlorine compounds, which are produced during the refining process (100-5000 mg / L); (7) Bleaching and dyeing: use of chlorine-containing bleach and dyes (100-20000 mg / L); (8) Pickling and preservation: use of sodium chloride for food pickling and preservation (100-5000 mg / L); (9) Pharmaceutical industry: chlorine-containing compounds (100-10000 mg / L) are used in the production of certain drugs.

[0003] Discharge of high-concentration chlorine-containing industrial wastewater without treatment will cause the following hazards. (1) Equipment and pipeline corrosion: Chloride ions are highly corrosive to metals (such as stainless steel and carbon steel), leading to equipment damage and increased maintenance costs; (2) Water pollution: Chlorine-containing wastewater discharged into water bodies causes water quality deterioration and affects aquatic ecosystems; (3) Soil pollution: Chlorine-containing wastewater seeps into the soil, affecting soil structure and plant growth; (4) Drinking water pollution: Chlorine-containing wastewater discharged into water sources may cause the chloride ion concentration in drinking water to exceed the standard, which is harmful to health if consumed for a long time; (5) Toxic effects: High concentrations of chloride ions are toxic to aquatic organisms and affect the balance of aquatic ecosystems. Therefore, it is necessary to strictly limit the chloride ion concentration in industrial wastewater.

[0004] Chloride ions in wastewater are extremely stable and non-biodegradable, and can only be removed by chemical methods. The removal principles mainly include: (1) replacement by other anions; (2) removal together with other cations. Currently, the most commonly used methods for treating chlorine-containing wastewater include precipitation, evaporation concentration, membrane treatment, adsorption, electrolysis, solvent extraction, and ion exchange. Among them, precipitation has strong adaptability to chloride ion concentration and is simple to operate. It is the most commonly used dechlorination method in industry.

[0005] There are many types of precipitation methods, the most common of which are the silver method, the cuprous method, and the ultra-high lime-alumina method. Among them, the use of silver ions as a precipitant is economically unfeasible; the ultra-high lime-alumina method requires precise pH control and results in the production of large amounts of sludge.

[0006] Cuprous ions are unstable in aqueous solution and can be rapidly disproportionated (as shown in formula (1)). However, in the presence of chloride ions, the disproportionation reaction will proceed in the opposite direction, that is, copper ions react with copper element to form cuprous ions, which then react with chloride ions to form cuprous chloride precipitates (as shown in formula (2)). This is the Cu-based 2+ 、Cu 0 and Cl - Chlorine removal technology for neutralization reaction. This method is low-cost, highly stable, and technically mature, but it still has problems such as the extremely high acidity required, high dosage of reagents, low efficiency, and high residual copper ion concentration.

[0007] 2Cu + → Cu + Cu 2+ Formula (1),

[0008] Cu+Cu 2+ +2Cl - →2CuCl↓Formula (2). Summary of the Invention

[0009] In view of the above analysis, the embodiments of the present invention aim to provide a wastewater dechlorination method based on the reduction-precipitation principle to solve the problems of extremely high acidity required, high dosage of reagents, low efficiency and high residual copper ion concentration in the existing cuprous method for wastewater dechlorination.

[0010] The invention provides a wastewater dechlorination method based on the reduction-precipitation principle. The method comprises: mixing chlorine-containing wastewater with sulfite and a copper ion-containing compound for reaction.

[0011] Preferably, the amount of sulfite used is such that the molar ratio of sulfite to chloride ion in the chlorine-containing wastewater is 0.5-3:1.

[0012] Preferably, the amount of the copper ion-containing compound used is such that the molar ratio of copper ions to chloride ions in the chlorine-containing wastewater is 1-6:1.

[0013] Preferably, the sulfite is at least one of sodium sulfite, sodium bisulfite, potassium sulfite, potassium bisulfite and ammonium sulfite.

[0014] Preferably, the copper ion-containing compound is copper sulfate.

[0015] Preferably, in the chlorine-containing wastewater, the concentration of sulfuric acid is 0-20 g / L, and the concentration of chloride ions is 0.5-100 g / L.

[0016] Preferably, the temperature of the mixing reaction is 0-80° C., and the time is 10-60 min.

[0017] Preferably, the method further comprises: performing solid-liquid separation on the solid-liquid mixture after the mixed reaction to obtain a solid and a filtrate, and drying the solid to obtain cuprous chloride.

[0018] Preferably, the drying temperature is 30-90° C. and the drying time is 2-18 hours.

[0019] Preferably, the method further comprises removing copper ions in the filtrate.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. Low dosage of reagent: Compared with the traditional cuprous method for dechlorination, the molar amount of copper ions required is 8 times the molar amount of chloride ions. The method of the present invention reduces it to less than 6 times (preferably 4 times), reducing secondary pollution and facilitating the subsequent removal of residual copper ions.

[0022] 2. Low reagent cost: The reducing agent is replaced by the traditional expensive copper element with the low-priced sodium sulfite, which greatly reduces the cost.

[0023] 3. Improved chloride ion removal efficiency: The chloride ion removal efficiency of the traditional cuprous method is less than 80%. Under the same initial chloride ion concentration, the chloride ion removal efficiency of the present invention can be as high as 96% or more.

[0024] 4. Low sulfuric acid concentration required: The traditional cuprous precipitation method is only applicable to wastewater with a sulfuric acid concentration higher than 50 g / L. In the method of the present invention, under the premise of a sulfuric acid concentration of 0-20 g / L, the chloride ion removal efficiency is higher than 90%.

[0025] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the subsequent description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the contents particularly pointed out in the description. DETAILED DESCRIPTION

[0026] The preferred embodiments of the present invention are described in detail below. The embodiments of the present invention are used to illustrate the principles of the present invention and are not used to limit the scope of the present invention.

[0027] The inventors discovered that the existing cuprous method for wastewater dechlorination has the problems of extremely high required acidity, high dosage of reagents, low efficiency, and high residual copper ion concentration, which are caused by the poor reduction effect of copper element on copper ions. Therefore, the present invention introduces a new copper ion reducing agent to solve the above problems.

[0028] The invention provides a wastewater dechlorination method based on the reduction-precipitation principle. The method comprises: mixing chlorine-containing wastewater with sulfite and a copper ion-containing compound for reaction.

[0029] Compared with the prior art, the present invention replaces the traditional copper element reducing agent with a sulfite reducing agent, and achieves efficient removal of chloride ions by simultaneously adding sulfite and a copper ion-containing compound to chlorine-containing wastewater, thereby reducing the amount of copper ions used and the residual copper ion concentration, reducing the reducing agent cost, and at the same time, improving the chloride ion removal efficiency. In addition, the required sulfuric acid concentration is low.

[0030] Illustratively, the sulfite is used in an amount such that the molar ratio of sulfite to chloride ions in the chlorinated wastewater is 0.5-3:1, for example, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, or 3:1. Sodium sulfite is a reducing agent that converts copper ions into cuprous ions. A too low molar ratio of sulfite to chloride ions in the chlorinated wastewater results in poor copper ion reduction, a small amount of cuprous ions generated, and poor chlorine removal. A too high molar ratio causes excess sulfite to react with cuprous ions to form a cuprous sulfite precipitate, resulting in a waste of reagent.

[0031] Illustratively, the copper ion-containing compound is used in an amount such that the molar ratio of copper ions to chloride ions in the chlorine-containing wastewater is 1-6:1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, or 6:1.

[0032] Illustratively, the sulfite is at least one of sodium sulfite, sodium bisulfite, potassium sulfite, potassium bisulfite and ammonium sulfite.

[0033] Exemplarily, the copper ion-containing compound is copper sulfate, more preferably copper sulfate pentahydrate. Compared with anhydrous copper sulfate, copper sulfate pentahydrate is cheaper and more readily available.

[0034] Illustratively, sulfite and the copper ion-containing compound are added to the chlorine-containing wastewater simultaneously, or sulfite is added first and then the copper ion-containing compound, or the copper ion-containing compound is added first and then the sulfite.

[0035] Illustratively, the concentration of sulfuric acid in the chlorine-containing wastewater is 0-20 g / L, for example, 0 g / L, 2.5 g / L, 5 g / L, 7.5 g / L, 10 g / L, 12.5 g / L, 15 g / L, 17.5 g / L, and 20 g / L.

[0036] Illustratively, in the chlorine-containing wastewater, the concentration of chloride ions is 0.5-100 g / L, for example, 0.5 g / L, 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, and 100 g / L.

[0037] Illustratively, the amount of the chlorine-containing wastewater is 100-1000 mL.

[0038] Illustratively, the temperature of the mixing reaction is 0-80°C, for example, 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C; and the time is 10-60 min, for example, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min.

[0039] Exemplarily, the temperature of the mixing reaction is achieved by heating in a water bath.

[0040] Illustratively, the mixing reaction is carried out under stirring.

[0041] Illustratively, the stirring may be one of magnetic stirring, mechanical stirring and rotational mixing.

[0042] Illustratively, the method further includes: performing solid-liquid separation on the solid-liquid mixture after the mixed reaction to obtain a solid and a filtrate, and drying the solid to obtain cuprous chloride.

[0043] Exemplarily, the solid-liquid separation method is atmospheric pressure filtration or vacuum filtration.

[0044] Illustratively, the drying temperature is 30-90°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C; and the drying time is 2-18h, for example, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h.

[0045] Exemplarily, the method further comprises removing copper ions from the filtrate.

[0046] Specifically, the method for removing copper ions from the filtrate includes: adding sulfide to the filtrate, stirring, and performing a copper ion precipitation reaction; then introducing air or high-purity nitrogen into the filtrate to remove residual hydrogen sulfide; solid-liquid separation to obtain a purified liquid and copper sulfide solid, and drying the copper sulfide solid.

[0047] Illustratively, the sulfide is hydrogen sulfide and / or sodium sulfide.

[0048] Illustratively, the amount of the sulfide is 1-3 times the stoichiometric ratio, for example, 1 time, 1.5 times, 2 times, 2.5 times, or 3 times.

[0049] Illustratively, the temperature of the copper ion precipitation reaction is 0-80°C, for example, 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C; and the time is 2-10 min, for example, 2 min, 4 min, 6 min, 8 min, 10 min.

[0050] Illustratively, the flow rate of air or high-purity nitrogen is 0.005-0.03 L / min, for example, 0.005 L / min, 0.01 L / min, 0.015 L / min, 0.02 L / min, 0.025 L / min, 0.03 L / min.

[0051] Exemplarily, the time for passing air or high-purity nitrogen is 5-20 minutes, such as 5 minutes, 10 minutes, 15 minutes, or 20 minutes.

[0052] Exemplarily, the solid-liquid separation method is atmospheric pressure filtration or vacuum filtration.

[0053] Illustratively, the drying temperature is 30-90°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C; and the drying time is 2-18h, for example, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h.

[0054] The wastewater dechlorination method based on the reduction-precipitation principle of the present invention is further illustrated below by means of specific examples.

[0055] Example 1

[0056] This embodiment provides a method for dechlorinating wastewater based on the reduction-precipitation principle. The wastewater is coking wastewater (after biochemical treatment, the main composition is shown in Table 1). The method comprises the following steps: first, adding 16 g of copper sulfate pentahydrate (the molar ratio of copper ion to chloride ion is 4.03:1) and 3 g of sodium sulfite (the molar ratio of sulfite ion to chloride ion is 1.50:1) to 500 mL of the biochemically treated coking wastewater at one time; heating the mixture in a 60°C water bath with magnetic stirring (300 r / min) for 30 min; and measuring the residual chloride ion concentration using the ion electrode standard addition method to obtain a chloride ion removal rate of 95.9%. The solid-liquid mixture was vacuum filtered to obtain a solid product and a filtrate. The solid product was dried at 50°C for 12 hours to obtain a cuprous chloride solid product. 4.0 g of sodium sulfide (1.05 times the stoichiometric ratio) was added to the filtrate. After magnetic stirring (300 rpm) at 25°C for 10 minutes, air was introduced at a flow rate of 0.01 L / min for a total of 10 minutes. The solid-liquid mixture was vacuum filtered to obtain a solid byproduct and a purified liquid. The solid byproduct was dried at 50°C for 12 hours to obtain a copper sulfide byproduct. The residual copper ion concentration in the purified liquid was determined by ICP-MS to be 0.11 mg / L.

[0057] Example 2

[0058] This embodiment provides a method for dechlorinating wastewater based on the reduction-precipitation principle. The wastewater is desulfurization wastewater from a coal-fired power plant (the main composition is shown in Table 1). The method comprises the following steps: first, adding 4.1 g of copper sulfate pentahydrate (the molar ratio of copper ion to chloride ion is 4.01:1) to 200 mL of the desulfurization wastewater; after the copper sulfate pentahydrate is completely dissolved, adding 0.77 g of sodium sulfite (the molar ratio of sulfite ion to chloride ion is 1.49:1); heating the mixture in a 60° C. water bath with magnetic stirring (300 rpm) for 20 min; and measuring the residual chloride ion concentration using the ion electrode standard addition method. The result is 34.6 mg / L, and the chloride ion removal rate is 95.2%. The solid-liquid mixture was vacuum filtered to obtain a solid product and a filtrate; the solid product was dried at 50° C. for 12 hours to obtain a cuprous chloride solid product; hydrogen sulfide and air were sequentially introduced into the filtrate at a gas flow rate of 0.01 L / min for 10 minutes each, and the solid-liquid mixture was vacuum filtered to obtain a solid by-product and a purified liquid; the solid by-product was dried at 50° C. for 12 hours to obtain a copper sulfide by-product, and the residual copper ion concentration in the purified liquid was determined by ICP-MS to be 0.07 mg / L.

[0059] Example 3

[0060] This embodiment provides a method for dechlorinating wastewater based on the reduction-precipitation principle. The wastewater is vegetable pickling wastewater (after biochemical treatment, the main composition is shown in Table 1). The method comprises: first, adding 132 g of copper sulfate pentahydrate (the molar ratio of copper ion to chloride ion is 4.00:1) to 1 L of the biochemically treated vegetable pickling wastewater. After the copper sulfate pentahydrate is completely dissolved, 25 g of sodium sulfite (the molar ratio of sulfite ion to chloride ion is 1.50:1) is added. After heating in a 60°C water bath with magnetic stirring (500 rpm) for 90 minutes, the residual chloride ion concentration is determined by ion chromatography to be 97.1 mg / L, and the chloride ion removal efficiency is 97.9%. The solid-liquid mixture is then vacuum filtered. A solid product and a filtrate were obtained; the solid product was dried at 50° C. for 12 h to obtain a cuprous chloride solid product; hydrogen sulfide and air were sequentially introduced into the filtrate at a gas flow rate of 0.01 L / min for 40 min each, and the solid-liquid mixture was vacuum filtered to obtain a solid by-product and a purified liquid; the solid by-product was dried at 50° C. for 12 h to obtain a copper sulfide by-product, and the residual copper ion concentration in the purified liquid was determined by ICP-MS to be 0.15 mg / L.

[0061] Table 1

[0062]

[0063]

[0064] Comparative Example 1

[0065] This comparative example provides a method for dechlorinating wastewater similar to that of Example 1, except that the amount of sodium sulfite used is such that the molar ratio of sulfite to chloride ion in the chlorine-containing wastewater is 0.3:1.

[0066] The remaining chloride ion concentration after cuprous chloride precipitation was 934.5 mg / L, and the chloride ion removal rate was 17.1%. The remaining copper ion concentration in the purified liquid was 1357.4 mg / L.

[0067] Comparative Example 2

[0068] This comparative example provides a wastewater dechlorination method similar to Example 1, except that the amount of copper sulfate pentahydrate used is such that the molar ratio of copper ions to chloride ions in the chlorine-containing wastewater is 0.8:1.

[0069] The remaining chloride ion concentration after cuprous chloride precipitation was 633.7 mg / L, and the chloride ion removal rate was 43.8%. The remaining copper ion concentration in the purified liquid was 0.08 mg / L.

[0070] Comparative Example 3

[0071] This comparative example provides a method for dechlorinating wastewater similar to Example 1, except that the amount of copper sulfate pentahydrate used is such that the molar ratio of copper ions to chloride ions in the chlorine-containing wastewater is 7:1.

[0072] The remaining chloride ion concentration after cuprous chloride precipitation was 32.9 mg / L, and the chloride ion removal rate was 97.1%; the remaining copper ion concentration in the liquid after purification was 5719 mg / L.

[0073] Comparative Example 4

[0074] This comparative example provides a wastewater dechlorination method for treating the same wastewater as Example 1, comprising the following steps: first, adding 16 g of copper sulfate pentahydrate (the molar ratio of copper ions to chloride ions is 4.03:1) and 1.52 g of pure copper powder (the molar ratio of pure copper powder to chloride ions is 1.50:1) to 500 mL of biochemically treated coking wastewater at one time; heating the mixture in a 60°C water bath with magnetic stirring (300 r / min) for 30 min; and determining the residual chloride ion concentration by an ion electrode standard addition method, which is 637.4 mg / L, and a chloride ion removal rate of 43.4%. The solid-liquid mixture was vacuum filtered to obtain a solid product and a filtrate. The solid product was dried at 50°C for 12 hours to obtain a solid product mixed with cuprous chloride and copper powder. 4.0 g of sodium sulfide (1.07 times the stoichiometric ratio) was added to the filtrate. After magnetic stirring (300 rpm) at 25°C for 10 minutes, air was introduced at a flow rate of 0.01 L / min for a total of 10 minutes. The solid-liquid mixture was vacuum filtered to obtain a solid byproduct and a purified liquid. The solid byproduct was dried at 50°C for 12 hours to obtain a copper sulfide byproduct. The residual copper ion concentration in the purified liquid was determined by ICP-MS to be 1189.3 mg / L.

[0075] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for dechlorination of wastewater based on the reduction-precipitation principle, characterized in that: The method comprises: mixing chlorine-containing wastewater with sulfite and a copper ion-containing compound for reaction.

2. The method for dechlorinating wastewater according to claim 1, wherein: The amount of sulfite used is such that the molar ratio of sulfite to chloride ion in the chlorine-containing wastewater is 0.5-3:

1.

3. The method for dechlorination of wastewater according to claim 1, wherein: The amount of the copper ion-containing compound is such that the molar ratio of copper ions to chloride ions in the chlorine-containing wastewater is 1-6:

1.

4. The method for dechlorination of wastewater according to claim 1, wherein: The sulfite is at least one of sodium sulfite, sodium bisulfite, potassium sulfite, potassium bisulfite and ammonium sulfite.

5. The method for dechlorination of wastewater according to claim 1, wherein: The copper ion-containing compound is copper sulfate.

6. The method for dechlorination of wastewater according to claim 1, wherein: In the chlorine-containing wastewater, the concentration of sulfuric acid is 0-20 g / L, and the concentration of chloride ions is 0.5-100 g / L.

7. The method for dechlorination of wastewater according to claim 1, wherein: The temperature of the mixing reaction is 0-80° C., and the time is 10-60 minutes.

8. The method for dechlorination of wastewater according to claim 1, wherein: The method further comprises: performing solid-liquid separation on the solid-liquid mixture after the mixed reaction to obtain a solid and a filtrate, and drying the solid to obtain cuprous chloride.

9. The method for dechlorination of wastewater according to claim 8, characterized in that: The drying temperature is 30-90° C. and the drying time is 2-18 hours.

10. The method for dechlorination of wastewater according to claim 8, characterized in that: The method further includes removing copper ions from the filtrate.

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