Method for treating high-chlorine industrial wastewater and recycling chlorine

Abstract

The invention discloses a high-chlorine industrial wastewater treatment and chlorine recovery method, which comprises the following steps: sequentially adding copper sulfate and a carbon-sulfur reducing agent into to-be-treated high-chlorine wastewater according to a ratio, adjusting the pH value, generating chlorine-containing residues, precipitating and separating out the chlorine-containing residues from a water body, and carrying out decoloration treatment on dechlorinated tail water by adopting an electrolytic bath, copper sponge deposited at the cathode is subjected to impurity removal treatment and then is merged into a copper salt circulating system; chlorine-containing residues are subjected to dissolution and quality-divided treatment, an obtained solution phase is concentrated / crystallized, KCl is recycled, an obtained copper-containing precipitate and the sponge copper are combined and collected, the mixture is dissolved by means of dilute sulfuric acid in the oxidizing atmosphere, and the whole mixture returns to a wastewater dechlorination treatment system. CuSO4 is reduced to generate Cu < + > ions to precipitate and remove chloride ions in the wastewater, the obtained KCl product is used at a high value, and the cuprous precipitate is subjected to conversion treatment and is completely reused in the dechlorination process, so that the wastewater treatment cost is remarkably reduced, and the method has the obvious advantages of high dechlorination efficiency, no generation of solid wastes and the like, and is suitable for industrial production. And the method has wide adaptability to industrial circulating water containing 2.5-8.5 g / L of chlorine, membrane-process strong brine and the like.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment and resource recovery technology, specifically relating to a method for industrial wastewater treatment and chlorine recovery. Background Technology

[0002] Chlorine-containing industrial wastewater widely originates from industries such as chemical production, printing and dyeing and textiles, metallurgy, pesticide production, petroleum refining, metal processing, and surface treatment. Taking the steel industry as an example, the chloride ion content in industrial circulating water often exceeds 2500 mg / L, while the chloride ion content in limestone-gypsum desulfurization wastewater can reach as high as 8500-26000 mg / L. Chloride ions are toxic and corrosive, posing significant harm to human health, plant growth, industrial equipment, and building steel reinforcement. Therefore, identifying the sources of chlorine-containing industrial wastewater and employing appropriate technologies for effective treatment is a crucial aspect of industrial pollution control and water environment protection.

[0003] Currently, the main dechlorination methods used domestically and internationally include membrane separation, ion exchange, electrochemical treatment, evaporation concentration, and chemical precipitation. For industrial wastewater with high chlorine content and large volume, existing research largely employs chemical precipitation for dechlorination. This involves adding chemical reagents to combine with chloride ions in the wastewater, reacting to form slightly soluble, sparingly soluble, or insoluble precipitates that are then removed from the aqueous phase. Commonly used precipitation methods include argentometric precipitation, bismuth oxide precipitation, cuprous chloride precipitation, and ultra-high lime-aluminum precipitation. Argentometric precipitation has relatively high dechlorination efficiency, but the difficulty in recovering silver ions leads to extremely high water treatment costs, making it difficult to scale up industrial applications. Bismuth oxide precipitation dechlorination has only been reported in a few laboratory settings and has not been practically applied to industrial production. The ultra-high lime-aluminum precipitation method involves adding calcium oxide and sodium aluminate to chlorine-containing wastewater to form calcium-aluminum chloride precipitates, thus achieving dechlorination. This method is simple to operate and has abundant raw materials, but it also suffers from a series of problems such as high raw material consumption, large amounts of precipitates generated, low reagent utilization, and high water treatment operating costs. When removing chloride ions from water using the cuprous chloride method, a reducing agent is used to remove Cu ions from the water. 2+ Reduced to Cu + Cu + With Cl - The reaction produces a precipitate, which is then removed from the water. For hydrometallurgical industrial wastewater, some studies have used copper or zinc powder to reduce Cu. 2+ And the formation of Cu +The precipitation dechlorination effect is about 60%-70% (Wang Hai, et al. Comparative analysis of the application of precipitation method for removing chloride ions in wastewater. Anhui Chemical Industry, 2021, 47(3): 40-43). There is an existing patent ZL201210231025.3 that provides a method for removing impurities from zinc sulfate solution by circulating cuprous salt. Copper sulfate is dissolved in a chlorinated zinc sulfate solution. After continuously adding metallic zinc powder, the generated dechlorination solution is sent to the purification electrolytic zinc extraction. The generated dechlorination residue is leached with NaCl salt to produce cuprous solution and sponge copper. The obtained cuprous solution is added with 50% NaOH alkaline solution to produce synthetic residue and cuprous salt. The cuprous salt is returned to the dechlorination process for recycling. This technical method is based on the product characteristics of the zinc smelting industry and uses metallic zinc powder to reduce Cu 2+ Cu + This process precipitates cuprous chloride, achieving dechlorination of zinc sulfate solutions containing 1.0-20.0 g / L of chlorine. However, for non-smelting enterprises, reducing Cu with copper or zinc powder is not feasible. 2+ When using precipitation to remove high concentrations of chloride ions from wastewater, the large consumption and high cost of reducing agents make the cuprous chloride method for water dechlorination difficult to apply in engineering due to its poor economic viability. In the dechlorination process described in patent ZL201210231025.3, when zinc powder is used to reduce copper sulfate, elemental Cu and Cu2+ are simultaneously generated. + Therefore, sponge copper precipitates out after NaCl salt leaching of the dechlorination residue. Although all cuprous salts in the process system are returned to the dechlorination process, the copper:chlorine mass ratio is significantly reduced. This necessitates the external addition of a large amount of copper sulfate to maintain the desired dechlorination effect, inevitably leading to significantly higher wastewater treatment costs. Furthermore, after adding NaOH alkaline solution to the cuprous solution, the precipitated solids are mainly Cu₂O and CuOH. Due to the disproportionation reaction of the cuprous salts themselves and contact with oxygen in the air during operation, Cu and Cu(OH)₂ may also be present in the solids. When this portion of the cuprous salt solids is directly returned to the dechlorination unit, the elemental copper cannot react with zinc powder under acidic conditions to form Cu. + This means that directly returning cuprous salts to the dechlorination unit is not conducive to wastewater sedimentation and dechlorination.

[0004] Overall, cuprous chloride precipitation for chlorination has many advantages, including fast reaction rate, high selectivity, strong compatibility with hydrometallurgical processes, and no subsequent solid waste disposal issues. However, it also has drawbacks such as the instability of cuprous ions, high requirements for reduction conditions, the risk of copper ion residue in the effluent, and precipitation back-dissolution. Developing and implementing efficient and relatively low-cost methods for treating high-salinity wastewater and recovering chlorine, tailored to the specific characteristics of the wastewater, is a core issue that urgently needs to be addressed in industrial wastewater treatment and pollution control. Summary of the Invention

[0005] This invention provides a method for treating and recovering chlorine from high-chlorine industrial wastewater, utilizing a carbon-sulfur composite reducing agent to reduce copper sulfate to Cu under acidic conditions. + The copper ions then react with chloride ions in the water to precipitate. The dechlorination effluent is decolorized in an electrochemical cell, and sponge copper is recovered. The chloride-containing slag undergoes a complexation reaction and fractional treatment to obtain a leachate and copper-containing precipitate. KCl is recovered from the leachate for high-value utilization. The copper-containing precipitate and sponge copper are collected together and then mixed with dilute sulfuric acid and an oxidant. The resulting copper-containing solution is returned in full to the wastewater dechlorination treatment system. This invention efficiently removes chloride ions from industrial wastewater based on cuprous salt precipitation, eliminating the need for zinc or copper powder as reducing agents. The copper sulfate content replenished during continuous operation is less than 6%, effectively reducing water treatment operating costs.

[0006] The specific implementation steps of this invention are as follows: (1) Copper sulfate and carbon-sulfur reducing agent were added to the high-chlorine industrial wastewater to be treated in batches to adjust the pH value to acidic. Under acidic and continuous stirring conditions, oxidation-reduction and precipitation reactions occurred in the water treatment reaction tank, chlorine-containing slag was precipitated, and solid-liquid separation was performed to obtain filter residue and dechlorinated tailwater. (2) Electrochemical decolorization treatment is carried out on the dechlorination tailwater, and the sponge copper deposited on the cathode plate is recovered and returned to the copper salt recycling system after being purified by dilute sulfuric acid. (3) Add saturated potassium chloride solution to the chlorine-containing slag to dissolve the slag phase, then add alkaline substances for fractional treatment to obtain chlorine-containing fractional liquid and copper-containing precipitate; adjust the pH of the chlorine-containing fractional liquid to near neutral with dilute hydrochloric acid, then concentrate and crystallize to recover KCl; (4) The copper-containing precipitate and the sponge copper after impurity removal in step (2) are combined and collected to obtain copper-containing solid phase. Sulfur solution and oxidant are added to dissolve the solid phase, and CuSO4 solution is prepared and returned to the dechlorination process in step (1) for recycling.

[0007] Preferably, in step (1) Cu 2+ Cl - The mass ratio is 2.0∶1-2.6∶1, Cu 2+ The mass ratio of the carbon-sulfur reducing agent to the reaction tank is 1:0.95-1:1.05, and the water temperature in the reaction tank is 35-55℃.

[0008] Preferably, the carbon-sulfur reducing agent in step (1) is composed of sodium sulfite, sodium thiosulfate, glucose and acetonitrile, wherein the mass fraction of sodium sulfite is 74%-84%, the mass fraction of sodium thiosulfate is 1.0%-1.5%, the mass fraction of glucose is 15%-25%, and the mass fraction of acetonitrile is 0.03%-0.10%.

[0009] Preferably, in step (1), the pH value is adjusted to 2.5-5.0, and the precipitation time of the chlorine-containing slag is 70-100 min.

[0010] Preferably, during the electrochemical treatment of the dechlorinated tailwater in step (2), the current density is 20-40 mA / cm². 2 The electrode spacing is 2-3 cm, and the electrolysis time is 80-120 min.

[0011] Preferably, the mass ratio of chlorine-containing slag to potassium chloride saturated solution in step (3) is 1:7.5-1:9.0.

[0012] Preferably, the alkaline substance in step (3) is a mixture of potassium oxide and potassium hydroxide, wherein the mass fraction of potassium oxide is 15%-30% and the mass fraction of potassium hydroxide is 70%-85%.

[0013] Preferably, in step (3), the pH is adjusted to 13.2-14.0 when adding alkaline substances for fractionation treatment, and the pH of the chlorine-containing fractionation solution is adjusted to 7.0-7.3 before concentration and crystallization.

[0014] Preferably, in step (4), the amount of sulfuric acid solution added is 100-150 mL per 100 g of copper-containing solid, and the concentration of the sulfuric acid solution is 2-5 mol / L.

[0015] Preferably, in step (4), the oxidant is a 30% hydrogen peroxide solution, and the amount added is 50-70 mL of hydrogen peroxide solution per 100 g of copper-containing solid phase, and the oxidation treatment time is 15-30 min.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses a carbon-sulfur composite reducing agent composed of sodium sulfite, sodium thiosulfate, glucose, and acetonitrile to control the reduction conditions, which not only effectively inhibits Cu + The disproportionation reaction also avoids the formation of elemental copper when zinc powder reduces copper sulfate. At the same time, it eliminates the need to use expensive zinc powder or copper powder as reducing agents, effectively ensuring the dechlorination effect of cuprous salt precipitation while significantly reducing the procurement cost of reducing agents.

[0017] (2) The decolorization of the dechlorination tailwater is carried out by electrochemical means, and sponge copper is recovered. It is combined with the cuprous precipitate obtained after separate treatment and collected. The precipitate is dissolved in sulfuric acid in an oxidizing atmosphere, and the resulting CuSO4 solution is 100% returned to the wastewater dechlorination treatment system. During continuous operation, the replenishment of fresh copper sulfate is less than 6%, which significantly reduces the water treatment operating cost while achieving efficient dechlorination.

[0018] (3) The wastewater dechlorination process of this invention does not produce new solid substances that need to be further processed. The recovered KCl solids are used as first-grade potassium fertilizer to achieve high-value utilization. Attached Figure Description

[0019] Figure 1 This is a process flow diagram for the treatment and chlorine recovery of high-chlorine industrial wastewater according to the present invention. Detailed Implementation

[0020] The following specific implementation examples further illustrate the present invention, providing detailed implementation methods and operating procedures, but the scope of protection of the present invention is not limited to the content described.

[0021] Example 1 The membrane method for treating concentrated brine in the industrial circulating water system of an iron and steel enterprise using this invention resulted in iron and copper ion concentrations of 16.7 and 7.9 mg / L, respectively, and Cl... - SO4 2- NO3 - NH4 + -N concentrations were 4560, 3880, 850, and 93 mg / L, respectively, with a pH of 7.33. 2 L of membrane-processed concentrated brine was fed into the first-stage dechlorination reactor, maintaining the water temperature at 40℃, and proceeding according to Cu... 2+ Cl - Mass ratio 2.5:1 and Cu 2+ The dosage of industrial-grade anhydrous copper sulfate was determined to be 37.5 g with a carbon-sulfur reducing agent mass ratio of 1:1.0, and the dosage of carbon-sulfur composite reducing agent was 14.8 g. The carbon-sulfur composite reducing agent contained sodium sulfite, sodium thiosulfate, glucose, and acetonitrile at mass fractions of 83.6%, 1.25%, 15.1%, and 0.05%, respectively. Copper sulfate and carbon-sulfur reducing agent were added sequentially to the wastewater in the primary reactor every 15 minutes, with thorough stirring. The copper sulfate and carbon-sulfur composite reducing agent were added in three separate additions. The pH of the water was adjusted to 4.7. From the time of reagent addition to the subsequent solid-liquid separation operation, the precipitation time of chlorine-containing slag in the primary reactor was controlled to be 80 minutes. The dechlorination tailwater was introduced into an electrochemical device with a titanium plate as the cathode and graphite as the anode for decolorization treatment at a current density of 25 mA / cm². 2Two sets of series electrolytic cells were used for 100 min of treatment with a 2 cm electrode spacing. The effluent after decolorization was adjusted to pH 6.2 with quicklime and reused in the slag flushing system of the steel plant. Metals were stripped from the cathode plates of the electrolytic cells and leached with dilute sulfuric acid for 20 min to remove the small amount of elemental iron that had precipitated. The resulting sponge copper was incorporated into the copper salt recycling system. The precipitate from the primary reactor was transferred to the secondary reactor, washed twice with pure water and the washing liquid was skimmed off. A saturated potassium chloride solution was added according to the dry weight of the precipitate at a mass ratio of 1:7.5. The mixture was stirred thoroughly for 15 min to allow the precipitated cuprous chloride to re-complex and re-enter the liquid phase. Subsequently, a mixed alkaline solid substance containing 25% K2O and 75% KOH was added to adjust the pH of the complexed solution in the reactor to 13.5. After separation and treatment for 15 min, the solution was allowed to settle. The supernatant was introduced into the tertiary reactor, and the pH of the solution was adjusted to 7.1 with dilute hydrochloric acid. The solution was then introduced into an evaporation / concentration device to obtain KCl crystals. The precipitate obtained from the fractional treatment is retained in the secondary reactor, washed twice with pure water and the washing liquid is skimmed off. The sponge copper obtained from the tailwater decolorization process is then combined with the precipitate obtained from the fractional treatment. 120 mL of 4 mol / L sulfuric acid solution and 60 mL of 30% hydrogen peroxide solution are added for every 100 g of copper-containing solids. The mixture is then acid-dissolved in an oxidizing atmosphere for 25 min. The resulting copper sulfate solution is returned in its entirety to the subsequent wastewater dechlorination treatment.

[0022] After treatment with the above process, the chloride ion removal rate of the concentrated brine using membrane technology is 65.7%, and the Cu in the effluent is reduced. 2+ The concentration is 46 mg / L; the K2O content of the KCl solid obtained by evaporation / crystallization is 62.2%, which can be used as a first-grade fertilizer-grade potassium chloride.

[0023] Example 2 This invention is used to treat concentrated brine from the industrial circulating water system of a steel enterprise using a membrane process for secondary wastewater dechlorination. The water temperature in the primary reactor is 40 °C, and the temperature is determined by Cu. 2+ Cl - The required Cu for water dechlorination is determined by a mass ratio of 2.1:1. 2+ The theoretical consumption, after adding the copper sulfate solution obtained by acid dissolution under the oxidizing atmosphere conditions of Example 1, is calculated according to Cu... 2+ Add 1.0 g of fresh industrial-grade anhydrous copper sulfate at a theoretical consumption ratio of 3%, according to Cu 2+The reducing agent dosage was determined to be 13.2 g using a carbon-sulfur reducing agent mass ratio of 1:1.05, with sodium sulfite, sodium thiosulfate, glucose, and acetonitrile mass fractions of 78.5%, 1.3%, 20.15%, and 0.05%, respectively. A recycled copper sulfate solution (with fresh anhydrous copper sulfate pre-dissolved) and the carbon-sulfur reducing agent were added in three stages to the wastewater to be treated in the primary reactor to adjust the pH to 2.9. The precipitation time of the chlorine-containing slag was controlled to 90 min. During the electrochemical decolorization treatment of the dechlorination tailwater, the current density was 30 mA / cm². 2 Three sets of series electrolytic cells were used for 80 min under a plate spacing of 2.5 cm. The dechlorination residue precipitated from the primary reactor was complexed with a saturated potassium chloride solution at a mass ratio of 1:8.0. Subsequently, a mixed alkaline solid substance containing 20% ​​K2O and 80% KOH was added to adjust the pH of the complexation solution in the reactor to 14.0. After separation treatment, the mixture was allowed to settle, and the pH of the supernatant was adjusted to 7.0 before evaporation / concentration. The precipitates obtained from the separation treatment and the sponge copper obtained from the decolorization treatment were collected together. For every 100 g of copper-containing solid phase, 100 mL of 5 mol / L sulfuric acid solution and 55 mL of 30% hydrogen peroxide solution were added, and the mixture was acid-dissolved for 20 min to obtain a copper sulfate solution, which was returned in full to the subsequent wastewater dechlorination treatment. The operating steps and process parameters not mentioned are the same as in Example 1.

[0024] After treatment with the above process, the chloride ion removal rate of the concentrated brine using membrane technology reached 64.2%, and the Cu in the effluent was reduced. 2+ The concentration is 43 mg / L; the K2O content of the KCl solid obtained by evaporation / crystallization is 62.5%, which can be used as a first-grade fertilizer-grade potassium chloride.

Claims

1. A method for treating and recovering chlorine from high-chlorine industrial wastewater, characterized in that... Includes the following steps: (1) Copper sulfate and carbon-sulfur reducing agent are gradually added to the high-chlorine industrial wastewater to be treated, and the pH value is adjusted to acidic. Under stirring conditions, oxidation-reduction and precipitation reactions occur, and chlorine-containing slag is precipitated in the water. Solid-liquid separation yields filter residue and dechlorinated tailwater. (2) The dechlorination tailwater is directly discharged or reused after electrochemical decolorization treatment. The sponge copper deposited at the cathode in the electrochemical process is incorporated into the copper salt recycling system after being treated with dilute sulfuric acid to remove impurities. (3) Add saturated potassium chloride solution to the chlorine-containing slag to dissolve the slag phase, and then continue to add alkaline substances for fractional treatment to obtain chlorine-containing fractional liquid and copper-containing precipitate; adjust the pH of the chlorine-containing fractional liquid to near neutral with dilute hydrochloric acid, and then concentrate and crystallize to recover KCl; (4) The copper-containing precipitate and the sponge copper after impurity removal in step (2) are combined and collected to obtain copper-containing solid phase. Sulfuric acid solution and oxidant are added to dissolve the copper-containing solution. All the copper-containing solution is returned to the dechlorination process in step (1) for recycling.

2. The method for treating high-chlorine industrial wastewater and recovering chlorine according to claim 1, characterized in that... In step (1) Cu 2 + Cl - The mass ratio is 2.0∶1-2.6∶1, Cu 2+ The mass ratio of the carbon-sulfur reducing agent to the carbon-sulfur reducing agent is 1:0.95-1:1.05, and the reaction system temperature is 35-55 ℃.

3. The method for treating and recovering chlorine from high-chlorine industrial wastewater according to claim 1 or 2, characterized in that... The carbon-sulfur reducing agent is sodium sulfite, sodium thiosulfate, glucose, and acetonitrile, wherein the mass fraction of sodium sulfite is 74%-84%, the mass fraction of sodium thiosulfate is 1.0%-1.5%, the mass fraction of glucose is 15%-25%, and the mass fraction of acetonitrile is 0.03%-0.10%.

4. The method for treating high-chlorine industrial wastewater and recovering chlorine according to claim 1, characterized in that... In step (1), the pH value is adjusted to 2.5-5.0, and the precipitation time of chlorine-containing slag is 70-100 min.

5. The method for treating high-chlorine industrial wastewater and recovering chlorine according to claim 1, characterized in that... In step (2), during the electrochemical decolorization treatment of the dechlorinated tailwater, the current density is 20-40 mA / cm². 2 The electrode spacing is 2-3 cm, and the electrolysis time is 80-120 min.

6. The method for treating high-chlorine industrial wastewater and recovering chlorine according to claim 1, characterized in that... In step (3), the mass ratio of chlorine-containing slag to potassium chloride saturated solution is 1:7.5-1:9.

0.

7. The method for treating high-chlorine industrial wastewater and recovering chlorine according to claim 1, characterized in that... In step (3), the alkaline substance is a mixture of potassium oxide and potassium hydroxide, wherein the mass fraction of potassium oxide is 15%-30% and the mass fraction of potassium hydroxide is 70%-85%.

8. The method for treating high-chlorine industrial wastewater and recovering chlorine according to claim 1, characterized in that... When adding alkaline substances in step (3), the pH is adjusted to 13.2-14.

0. Before concentration and crystallization, the pH of the chlorine-containing fraction is adjusted to 7.0-7.

3.

9. The method for treating high-chlorine industrial wastewater and recovering chlorine according to claim 1, characterized in that... In step (4), the amount of sulfuric acid solution added is 100-150 mL per 100 g of copper-containing solid, and the concentration of the sulfuric acid solution is 2-5 mol / L.

10. The method for treating high-chlorine industrial wastewater and recovering chlorine according to claim 1, characterized in that... In step (4), the oxidant is a 30% hydrogen peroxide solution, and the amount added is 50-70 mL of hydrogen peroxide solution per 100 g of copper-containing solid phase. The oxidation treatment time is 15-30 min.

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