Method for electrochemically assisted treatment of fluorine-chlorine-containing wastewater

Abstract

The invention discloses a method for electrochemically assisted treatment of fluorine-chlorine-containing wastewater. The method comprises the steps of fluorine-chlorine ion precipitation reaction, precipitate dehydration, primary electrolysis, secondary electrolysis, tertiary electrolysis and electrolyte treatment. The problems that copper and chlorine resources cannot be recycled and the treatment cost is too high in a Cu (I) precipitation dechlorination method are solved; by means of the method, the cost of the Cu (I) precipitation dechlorination method can be reduced by 90% or above, an additional product CaF2 is formed, the effect of synchronously removing fluorine and chlorine is achieved, and treatment and resource utilization of the waste water containing fluorine and chlorine are remarkably promoted; and moreover, full resource recycling of Cu, Cl and CaF and recycling of ammonia water and a KCl solution are achieved through multi-section electrolysis, closed circulation is formed, the operation cost is remarkably reduced, and resource waste is avoided.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, specifically relating to an electrochemical-assisted method for treating fluoride- and chlorine-containing wastewater. Background Technology

[0002] In the production processes of industries such as chemicals, pesticides, printing and dyeing, papermaking, electronics, and metallurgy, large amounts of wastewater containing high concentrations of fluoride and chlorine are generated. Fluoride and chlorine ions can corrode equipment, inhibit microbial activity, and even react with organic matter to form carcinogenic chlorofluorocarbons (CFCs).

[0003] Chemical precipitation is one of the main methods for treating fluoride- and chlorine-containing wastewater. Current technologies involve adding Ag(I), Cu(I), or Bi(III) to react with fluoride, chlorine, and sulfur dioxide (F). - Cl - The precipitation process produces AgCl, CuCl, BiOCl, AgF, and CuF2 precipitates. Since Ag and Bi are significantly more expensive than Cu, the Cu(I) precipitation method has greater application potential. However, due to the still high price of Cu, CuF2 and CuCl cannot be recycled after precipitation, making the treatment cost of the Cu(I) precipitation method unacceptable to enterprises. Therefore, it is essential to develop an electrochemically assisted method for treating fluoride- and chlorine-containing wastewater that can solve the above problems. Summary of the Invention

[0004] To address the challenges of recycling CuF2 and CuCl and reduce the cost of removing fluoride and chlorine using the Cu(I) precipitation method, this invention aims to provide an electrochemically assisted method for treating fluoride- and chlorine-containing wastewater. This method is highly efficient, low-cost, and enables the recycling of copper, chlorine, and fluorine resources.

[0005] The objective of this invention is achieved by including the following steps: (1) Adjust the pH value of the fluoride-containing chlorine wastewater, add Cu2O, a reagent that can generate Cu(I) in situ or copper powder, and react with the fluoride-chlorine ion precipitation reaction. (2) Collect the precipitated sludge (mainly composed of CuF2 and CuCl) from step (1), and dewater the precipitated sludge by centrifugation or filter press to reduce the sludge moisture content; (3) Electrolyze the copper-containing wastewater after step (1) to recover elemental copper at the cathode, thereby realizing the resource recovery of copper and ensuring that the effluent meets the discharge standards. (4) After adding the sludge obtained in step (2) to the KCl solution and stirring to dissolve it, the solution is electrolyzed a second time. Chlorine gas is generated at the anode and elemental copper is obtained at the cathode, realizing the resource recovery of chlorine and copper. The remaining liquid replaces the KCl solution for recycling and is used to dissolve the CuCl sludge obtained in step (2). (5) The sludge from step (4) is separated to obtain CuF2 sludge. After adding ammonia solution and stirring to dissolve, the solution is electrolyzed three times. Elemental copper is obtained at the cathode, thus realizing the resource recovery of copper. (6) In step (5), lime milk is added to the remaining electrolyte to carry out a precipitation reaction to obtain CaF2 product. The remaining ammonia water is returned to step (5) for recycling.

[0006] The materials used for the anode and cathode include, but are not limited to, common metallic and carbon materials in the field.

[0007] Preferably, step (1) adjusts the pH of the fluoride-containing chlorine wastewater to ≤4.0.

[0008] Preferably, the reagent that can generate Cu(I) in situ in step (1) is a mixture of Cu(II) oxide or Cu(II) metal salt and reducing agent.

[0009] Preferably, step (3) electrolysis is direct current or alternating current electrolysis, with a current density of 100~500 A / m. 2 Step (4) electrolysis is performed using direct current or alternating current, with a current density of 100~500 A / m. 2 Step (5) involves electrolysis using direct current or alternating current, with a current density of 100~500 A / m. 2 .

[0010] Preferably, the concentration of the KCl solution used for the first time in step (4) is ≥10g / L.

[0011] Preferably, the ammonia concentration in step (6) is 10%~30%, and the ammonia concentration mentioned in this article is a mass fraction.

[0012] Preferably, the mass fraction of lime slurry in step (6) is 5% to 30%.

[0013] Preferably, the elemental copper obtained in steps (3), (4), and (5) is used to prepare the Cu(I) oxide, reagents that can generate Cu(I) in situ, or copper powder required in step (1).

[0014] The beneficial effects of this invention are as follows: This invention solves the problem of high processing costs and unrecoverable copper and chlorine resources in the Cu(I) precipitation dechlorination method by electrochemically assisting the electrolysis of a CuCl-containing KCl solution; this invention achieves copper recovery by electrochemically assisting the electrolysis of ammonia solution containing CuF2, and then recovers CaF2 product by adding lime slurry; this invention can reduce the cost of the Cu(I) precipitation dechlorination method by more than 90%, and form the by-product CaF2, achieving the effect of simultaneous removal of fluoride and chlorine, significantly promoting the treatment and resource utilization of fluoride and chlorine-containing wastewater; moreover, this invention achieves full resource recovery of Cu, Cl2, and CaF2 through multi-stage electrolysis, and the ammonia and KCl solution are recycled to form a closed loop, significantly reducing operating costs and avoiding resource waste. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0016] The present invention will be further described below with reference to the embodiments and accompanying drawings, but this does not limit the present invention in any way. Any changes or substitutions made based on the teachings of the present invention shall fall within the protection scope of the present invention.

[0017] Example 1 Wastewater treatment for flue gas scrubbing at a copper smelter (pH=2.5, F⁻=1.2 g / L, Cl⁻=0.8 g / L, Cu²⁺=0.5 g / L); see attached. Figure 1 As shown, the method for electrochemically assisted treatment of fluoride- and chlorine-containing wastewater according to this embodiment is implemented, including the following steps: (1) Adjust the pH of the fluoride-containing chlorine wastewater to 4.0 with NaOH solution, add Cu2O, with a molar ratio of Cu⁺:(F⁻+Cl⁻)=1.2:1, and react with fluoride-chlorine ions to precipitate. The reaction temperature is 25℃, the stirring speed is 200 rpm, and the time is 30 min. N2 is introduced for protection to prevent Cu(Ⅰ) oxidation and the generation of sludge (CuF2, CuCl). (2) Collect the sludge from step (1), and centrifuge the sludge to dewater it until the moisture content is 40%; (3) Using titanium as the cathode and graphite as the anode, with a current density of 100 A / m², the copper-containing wastewater treated in step (1) is electrolyzed once. The cathode recovers elemental copper (copper purity 95%, recovery rate 95%, current efficiency 93%). The effluent Cu²⁺ < 1.0 mg / L, F⁻ < ​​3.0 mg / L, Cl⁻ < 1.0 mg / L (meets GB 25467-2010 standard) and is discharged. (4) The sludge treated in step (2) is added to a 200 g / L KCl solution (the solid-liquid ratio of sludge to KCl solution is 1 kg: 5 L). After stirring and dissolving, the solution is subjected to secondary electrolysis. Titanium is used as the cathode and DSA (RuO2-IrO2) is used as the anode. The current density is 500 A / m². Chlorine gas is generated at the anode, and elemental copper is obtained at the cathode (the purity of elemental copper is 96%, the recovery rate is 97%, and the current efficiency is 90%). The remaining liquid replaces the KCl solution for recycling and is used to dissolve the CuCl sludge obtained in step (2). (5) The sludge from step (4) is separated to obtain CuF2 sludge. 20% ammonia water (the solid-liquid ratio of sludge to ammonia water is 1kg:4L) is added and stirred to dissolve. The solution is then electrolyzed three times. Stainless steel is used as the cathode and platinum-plated titanium is used as the anode. The current density is 300 A / m². Elemental copper is obtained from the cathode (the purity of elemental copper is 96%, the recovery rate is 95%, and the current efficiency is 93%). (6) Add 5% lime milk to the remaining electrolyte in step (5) to carry out precipitation reaction to obtain CaF2 (purity 93%). The remaining ammonia water is returned to step (5) for recycling, with an ammonia water recycling rate of 95%. Steps (3), (4), and (5) yield elemental copper for the preparation of Cu2O required in step (1).

[0018] Example 2 The treatment of fluoride- and chlorine-containing wastewater generated during the synthesis of a certain pesticide has the following water quality parameters: pH = 1.5~2.0, F⁻ = 3.2 g / L, Cl⁻ = 2.8 g / L (mainly from raw materials HF and HCl), Cu²⁺ = 0.2 g / L (from catalyst residue). This embodiment implements the electrochemical-assisted treatment method for fluoride- and chlorine-containing wastewater. This embodiment is based on Example 1, but differs from Example 1 in the following ways: Step (1) Add Cu2O, with a molar ratio of Cu⁺:(F⁻+Cl⁻)=1.3:1, stirring speed 150 rpm, reaction time 45 min; Step (2) The sludge is subjected to plate and frame filter press filtration until the moisture content is 35%; Step (3) The cathode is a titanium-based platinum-plated electrode with a current density of 150 A / m²; the purity of the recovered elemental copper is 96%, the recovery rate is 95%, and the current efficiency is 93%; the effluent Cu²⁺ < 0.6 mg / L, F⁻ < ​​5 mg / L, and Cl⁻ < 3 mg / L; Step (4) uses a 10 g / L KCl solution with a solid-liquid ratio of 1 kg: 6 L and a current density of 100 A / m²; the recovered copper has a purity of 96%, a recovery rate of 97%, and a current efficiency of 96%. Step (5) uses 30% ammonia water, with a solid-liquid ratio of 1kg:5L, a current density of 250 A / m², and the purity of the recovered copper is 97%, the recovery rate is 95%, and the current efficiency is 97%. Step (6) uses 30% lime milk to obtain CaF2 with a purity of 90%; the ammonia water recycling rate is 95%.

[0019] Example 3 A chemical production plant is generating fluoride- and chlorine-containing wastewater (fluoride ion concentration 1 g / L, chloride ion concentration 2 g / L, initial pH 2.0, containing a small amount of heavy metal ions). This embodiment describes the electrochemical-assisted treatment method for fluoride- and chlorine-containing wastewater. This embodiment is based on Embodiment 1, but differs from Embodiment 1 in the following ways: Step (1) Add Cu2O, with a molar ratio of Cu⁺:(F⁻+Cl⁻)=1.5:1, and a reaction time of 45 min; Step (2) The sludge is subjected to plate and frame filter press filtration until the moisture content is 55%; Step (3) The cathode is a titanium-based platinum-plated electrode with a current density of 150 A / m²; the purity of the recovered elemental copper is 96%, the recovery rate is 95%, and the current efficiency is 96%; the effluent Cu²⁺ < 0.5 mg / L, F⁻ < ​​5 mg / L, Cl⁻ < 4 mg / L; Step (4) uses a 112 g / L KCl solution with a solid-liquid ratio of 1 kg:12 L and a current density of 100 A / m²; the recovered elemental copper has a purity of 97%, a recovery rate of 95%, and a current efficiency of 92%. Step (5) uses 15% ammonia water, with a solid-liquid ratio of 1kg:10L, a current density of 100 A / m², and the purity of the recovered copper is 95%, the recovery rate is 95%, and the current efficiency is 94%. Step (6) uses 10% lime milk by mass to obtain CaF2 with a purity of 92%.

[0020] Example 4 The wastewater from polycrystalline silicon cutting and grinding has a fluoride ion concentration of 450 mg / L, a chloride ion concentration of 600 mg / L, an initial pH of 2.5, and contains trace amounts of silicon powder and lead ions (Pb²⁺ < 5 mg / L). This embodiment describes the electrochemical-assisted treatment method for fluoride- and chloride-containing wastewater. This embodiment is based on Embodiment 1, but differs from Embodiment 1 in the following ways: Step (1) Add CuSO4·5H2O at a total molar ratio of Cu to chloride fluoride ions of 1.3:1, and immediately add sodium sulfite (Na2SO3) solution, controlling the molar ratio of Na2SO3 to CuSO4 to be 1.1:1 to ensure that Cu(II) is fully reduced to Cu(I), stirring speed 200 rpm, reaction time 40 min; Step (2) The sludge is subjected to plate and frame filter press filtration until the moisture content is 58%; Step (3) The cathode is a titanium-based platinum-plated electrode with a current density of 110 A / m²; the purity of the recovered elemental copper is 97%, the recovery rate is 98%, and the current efficiency is 98%; the effluent Cu²⁺ < 0.6 mg / L, F⁻ < ​​5.5 mg / L, and Cl⁻ < 5.0 mg / L; Step (4) uses a 100 g / L KCl solution with a solid-liquid ratio of 1 kg:10 L and a current density of 250 A / m²; the recovered copper has a purity of 97%, a recovery rate of 98%, and a current efficiency of 97%. Step (5) uses 10% ammonia water, with a solid-liquid ratio of 1kg:9L, a current density of 300 A / m², and the purity of the recovered elemental copper is 96%, the recovery rate is 98%, and the current efficiency is 98%. Step (6) uses 15% lime milk by mass to obtain CaF2 with a purity of 85%; Steps (3), (4), and (5) yield elemental copper for the preparation of CuSO4·5H2O required in step (1).

[0021] Example 5 A steel pickling wastewater has a fluoride ion concentration of 150 mg / L, a chloride ion concentration as high as 5 g / L, a pH < 1.0, and contains a small amount of Fe²⁺. The electrochemical-assisted treatment method for fluoride- and chloride-containing wastewater in this embodiment is implemented. This embodiment is based on Example 1, but differs from Example 1 in the following ways: Adjust the pH of a steel pickling wastewater to 1.0; Step (1) Add an excess of 20% (mass fraction) of 200-mesh copper powder (calculated according to theoretical calculation of Cu). 0 With a 2:1 molar ratio of copper to F⁻, the copper powder partially dissolves in the acidic chlorine-containing system, undergoing a chemical shift reaction (Cu⁻). 0 + Cu²⁺ ⇌ 2Cu⁺) and the reverse reaction of disproportionation, to establish Cu(I) equilibrium concentration in solution, stirring speed 150 rpm, reaction time 60 min; Step (2) Dewater the sludge to a moisture content of 52%; unreacted copper powder can be recycled; Step (3) DSA is used as the anode and copper starting plate is used as the cathode. The current density is 180 A / m². The purity of the recovered elemental copper is 99%, the recovery rate is 97%, and the current efficiency is 96%. The effluent Cu²⁺ is <1.0 mg / L, F⁻ is <6.0 mg / L, and Cl⁻ is <7.0 mg / L. The chloride ion concentration is extremely high at the beginning, so the absolute removal amount is large, but the residual concentration is still relatively high. It can be met by subsequent conventional treatment. Step (4) uses a 220 g / L KCl solution with a solid-liquid ratio of 1 kg:10 L and a current density of 100 A / m²; the recovered copper has a purity of 98%, a recovery rate of 97%, and a current efficiency of 95%. Step (5) uses 15% ammonia water, with a solid-liquid ratio of 1kg:10L, a current density of 200 A / m², and the recovered copper has a purity of 98%, a recovery rate of 95%, and a current efficiency of 96%. Step (6) uses 20% lime milk by mass to obtain CaF2 with a purity of 92%.

[0022] Example 6 A glass etching wastewater has a fluoride ion concentration of 300 mg / L, a chloride ion concentration of 400 mg / L, an initial pH of 4.0, and contains a small amount of silicate. The electrochemical-assisted treatment method for fluoride- and chloride-containing wastewater in this embodiment is implemented. This embodiment is based on Embodiment 1, but differs from Embodiment 1 in the following ways: Step (1) Add CuSO4 (0.4 g / L) and ascorbic acid (as a reducing agent, added at a molar ratio of 1:1 with CuSO4) to generate Cu(I) in situ. Stir at 120 rpm for 40 min. Step (2) Dewater the sludge to a moisture content of 60%; Step (3) Current density 120 A / m²; the purity of the recovered elemental copper is 98%, the recovery rate is 99%, and the current efficiency is 96%; the effluent Cu²⁺ < 1.0 mg / L, F⁻ < ​​3.0 mg / L, Cl⁻ < 8.0 mg / L; Step (4) uses a 100 g / L KCl solution and a current density of 150 A / m²; the recovered elemental copper has a purity of 97%, a recovery rate of 98%, and a current efficiency of 98%. Step (5) uses 10% ammonia water, with a solid-liquid ratio of 1kg:4L, a current density of 300 A / m², and the purity of the recovered copper is 95%, the recovery rate is 96%, and the current efficiency is 97%. Step (6) uses 17.5% lime milk to obtain CaF2.

Claims

1. A method for electrochemically assisted treatment of fluoride- and chlorine-containing wastewater, characterized in that... Includes the following steps: (1) Adjust the pH value of the fluoride-containing chlorine wastewater, add Cu2O, a reagent that can generate Cu(I) in situ or copper powder, and react with the fluoride-chlorine ion precipitation reaction. (2) Collect the sludge from step (1) and dewater it by centrifugation or filter press. (3) Electrolyze the copper-containing wastewater after step (1) once, and recover elemental copper from the cathode; (4) After adding the sludge obtained in step (2) to the KCl solution and stirring to dissolve it, the solution is electrolyzed a second time. Chlorine gas is generated at the anode and elemental copper is obtained at the cathode. The remaining liquid replaces the KCl solution for recycling and is used to dissolve the CuCl sludge obtained in step (2). (5) The sludge from step (4) is separated to obtain CuF2 sludge. After adding ammonia solution and stirring to dissolve, the solution is electrolyzed three times to obtain elemental copper at the cathode. (6) In step (5), lime milk is added to the remaining electrolyte to carry out a precipitation reaction to obtain CaF2 product. The remaining ammonia water is returned to step (5) for recycling.

2. The method for electrochemically assisted treatment of fluoride- and chlorine-containing wastewater according to claim 1, characterized in that... Step (1) Adjust the pH of the fluoride-containing chlorine wastewater to ≤4.

0.

3. The method for electrochemically assisted treatment of fluoride- and chlorine-containing wastewater according to claim 1, characterized in that... The reagent that can generate Cu(I) in situ in step (1) is a mixture of Cu(II) oxide or Cu(II) metal salt and reducing agent.

4. The method for electrochemically assisted treatment of fluoride- and chlorine-containing wastewater according to claim 1, characterized in that... Step (3) Electrolysis is performed using direct current or alternating current, with a current density of 100~500 A / m. 2 Step (4) electrolysis is performed using direct current or alternating current, with a current density of 100~500 A / m. 2 Step (5) involves electrolysis using direct current or alternating current, with a current density of 100~500 A / m. 2 .

5. The method for electrochemically assisted treatment of fluoride- and chlorine-containing wastewater according to claim 1, characterized in that... Step (4) The concentration of the KCl solution used for the first time is ≥10g / L.

6. The method for electrochemically assisted treatment of fluoride- and chlorine-containing wastewater according to claim 1, characterized in that... In step (6), the concentration of ammonia water is 10%~30%.

7. The method for electrochemically assisted treatment of fluoride- and chlorine-containing wastewater according to claim 1, characterized in that... In step (6), the mass fraction of lime slurry is 5%~30%.

8. The method for electrochemically assisted treatment of fluoride- and chlorine-containing wastewater according to claim 1, characterized in that... Steps (3), (4), and (5) yield elemental copper, which is used to prepare Cu(I) oxide, reagents that can generate Cu(I) in situ, or copper powder required in step (1).

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