A method for treating arsenic-containing waste acid

Abstract

The present invention discloses a method for treating arsenic-containing waste acid, comprising the following steps: (1) subjecting the arsenic-containing waste acid to electrodialysis using a conventional electrodialysis device to obtain an arsenic-rich solution and an acid-rich solution; and (2) subjecting the acid-rich solution to electrodialysis using a bipolar membrane electrodialysis device to obtain an acid solution and a metal salt solution, thereby achieving separation of the acid, the metal element, and the arsenic. The method for treating arsenic-containing waste acid of the present invention has the characteristics of simple process operation, good separation effect, high separation efficiency, high effective resource utilization, and the ability to achieve the opening of the inorganic salt in the acid. Without the addition of exogenous agents, the method achieves the effective separation of arsenic, valuable metals, and the waste acid in the waste acid, and achieves the effective opening of the arsenic and the metal cations that are prone to scaling in the waste acid, thereby laying a solid foundation for the concentration and reuse of the waste acid.

Description

Technical Field

[0001] The present invention relates to the field of metallurgical environmental protection, and in particular to a method for treating arsenic-containing waste acid. Background Art

[0002] The nonferrous smelting process produces a large amount of sulfur dioxide flue gas containing heavy metals such as arsenic. The flue gas absorption process also produces a large amount of acidic wastewater. Arsenic is the highest concentration among the pollutants, along with heavy metal ions such as lead, cadmium, zinc, and copper, as well as anions such as fluorine and chlorine. Nonferrous smelting waste acid has complex composition, high arsenic concentration, large concentration fluctuations, and high acidity, which also poses challenges in its treatment. To implement the concept of "green development," meet the requirements for the recovery of valuable metals and acids, recycle resources, and reduce environmental pollution caused by wastewater discharge, there is an urgent need to develop an environmentally friendly and efficient process for separating arsenic and recovering valuable metals and acids.

[0003] At present, the main domestic methods for treating high-arsenic waste acid include neutralization, sulfidation, adsorption, precipitation, and membrane methods. However, all of these methods have various problems and the treatment effects are less than ideal. Among them, although the neutralization method has a simple treatment process, it produces a large amount of arsenic-alkali hazardous waste residue, which carries significant risks and high costs in storage and disposal, and results in a large amount of valuable metals and acid resources being wasted in the wastewater. Compared with the neutralization method, the sulfidation method reduces the amount of slag. However, during the sulfidation process, valuable metals such as copper and zinc are precipitated simultaneously with arsenic, which cannot achieve effective recovery of valuable metals. Moreover, during the concentration and reuse process of the recovered acid, inorganic salts accumulate continuously, leading to equipment scaling and ultimately the collapse of the acid reuse system. Membrane treatment has been a recent research hotspot and has shown good results in the separation and treatment of wastewater. Patent 202021364220.X (A device for resource utilization of brine in the non-ferrous metal smelting industry) discloses a method for resource utilization of brine using a defluorinating agent, a decalcifying agent, electrodialysis, a dechlorinating agent, and a bipolar membrane acid-base production process. It belongs to the direction of resource utilization of brine and has little relevance to the resource utilization of high-arsenic waste acid generated in the smelting industry; Patent 201510995648 (A method for purification and recycling of high-arsenic contaminated acid wastewater) discloses a "membrane distillation-reduction crystallization-sulfide precipitation-ion exchange" technology for treating arsenic-containing contaminated acid. Although it can achieve the removal of fluorine, chlorine, and heavy metals in the waste acid and the reuse of the acid, arsenic and valuable metals are co-precipitated, and the valuable metals cannot be effectively recovered, resulting in waste of resources, and the inorganic salts present in the acid cannot be opened, resulting in the accumulation of inorganic salts. Summary of the Invention

[0004] The present invention provides a method for treating arsenic-containing waste acid, which is used to solve the technical problems of low recovery efficiency and easy accumulation of inorganic salts and scaling in equipment in existing treatment methods.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A method for treating arsenic-containing waste acid comprises the following steps:

[0007] (1) performing electrodialysis treatment on the arsenic-containing waste acid using a common electrodialysis device to obtain an arsenic-rich solution and an acid-rich solution;

[0008] (2) The acid-rich solution is subjected to electrodialysis treatment using a bipolar membrane electrodialysis device to obtain an acid solution and a metal salt solution, thereby achieving separation of acid, metal elements and arsenic.

[0009] The design concept of the above technical solution lies in the use of an "electrodialysis-bipolar membrane electrodialysis" process to treat high-arsenic waste acid. This provides a new solution and approach to the problems of difficult recovery and utilization of valuable metal resources in high-arsenic waste acid and the accumulation of inorganic salts in the acid. Electrodialysis technology is used to separate arsenic. Due to the valence characteristics of trivalent arsenic, it is difficult for it to pass through anion and cation exchange membranes and is therefore trapped in the dilute chamber of the electrodialysis process, thereby separating the arsenic and providing a basis for further step-by-step recovery of acid and valuable metals. Bipolar membrane electrodialysis can effectively separate acid and valuable metals, respectively recovering acid solution in the acid chamber and salt solution containing valuable metal ions such as copper and zinc in the salt chamber, achieving the goal of efficiently recovering valuable metals and acid from the waste acid. At the same time, the general technical route of existing waste acid treatment and reuse technology is "precipitation for heavy metal removal - evaporation for defluorination and chlorination - acid concentration - reuse". Its inorganic salts enter the recovered acid. During the evaporation and concentration process, the inorganic salts in the recovered acid continue to accumulate as the acid concentration increases, causing equipment scaling and ultimately the collapse of the acid concentration system. The present invention can well solve this problem, separating more than 95% of metal ions such as Mg, Ca, Fe, Mn, Cd, and Pb from more than 90% of ions such as Na and K in waste acid, thereby opening a circuit for metal ions such as Ca and Mg that are prone to forming scale in the recycled acid, and providing a good foundation for concentrated reuse of the acid.

[0010] As a further preferred embodiment of the above technical solution, the metal salt solution in step (2) is recycled for electrolysis after precipitation and acid dissolution, thereby achieving effective recovery of valuable metal resources such as copper and zinc.

[0011] As a further preferred embodiment of the above technical solution, the acid solution is concentrated and then reused to realize the resource utilization of the acid.

[0012] As a further preferred embodiment of the above technical solution, the conventional electrodialysis device includes a plurality of electrodialysis units connected in series; the electrodialysis unit includes an anion exchange membrane, a cation exchange membrane, and an anion exchange membrane assembled in sequence; the bipolar membrane electrodialysis device includes a plurality of bipolar membrane electrodialysis units connected in series; the bipolar membrane electrodialysis unit includes a bipolar membrane, an anion exchange membrane, a cation exchange membrane, an anion exchange membrane, and a bipolar membrane assembled in sequence. Compared with conventional electrodialysis membrane stacks, the membrane stack configuration of the electrodialysis device of the present invention has bipolar membranes added at both ends. The bipolar membranes can effectively block the valuable metals and other ions in the compartments at both ends from entering the anode and cathode chambers, thereby effectively improving the recovery rate of valuable metals while avoiding polar liquid contamination.

[0013] As a further preferred embodiment of the above technical solution, bipolar membranes are provided at both the cathode and anode ends of the electrodialysis unit. Using bipolar membranes instead of the anionic and cationic membranes at the anode and cathode of the electrodialysis device can prevent anions and cations in the waste acid from entering the cathode solution, thereby avoiding electrode corrosion and loss of valuable metal ions. In a further preferred embodiment of the above technical solution, the anion exchange membrane is one or a combination of an amine amino exchange membrane and an aromatic amino exchange membrane; and the cation exchange membrane is one or a combination of a sulfonic acid exchange membrane, a carboxylic acid exchange membrane, and a phosphate exchange membrane.

[0014] As a further preferred embodiment of the above technical solution, in the electrodialysis unit, the total effective area of ​​the anion exchange membrane and the cation exchange membrane is 550 cm 2 .

[0015] As a further preferred embodiment of the above technical solution, in the electrodialysis unit, adjacent ion exchange membranes are separated by partitions.

[0016] As a further preferred embodiment of the above technical solution, in step (2), the acid-rich solution is treated by bipolar membrane electrodialysis under constant current conditions, and the density of the constant current is 1.0 to 2.0 mA / cm 2 The current density defined in this preferred embodiment can take into account both current efficiency and production energy consumption.

[0017] As a further preferred embodiment of the above technical solution, in step (1), the arsenic-containing waste acid is treated using multi-stage electrodialysis. In this preferred embodiment, the high-arsenic-containing waste acid is treated using two or more stages of electrodialysis in series, which can remove more than 99% of the high-concentration arsenic, improve the arsenic recovery efficiency, and reduce the impurity ions in the subsequent acid solution.

[0018] As a further preferred embodiment of the above technical solution, before subjecting the arsenic-containing waste acid to electrodialysis treatment in step (1), the step further includes filtering the arsenic-containing waste acid through a filter membrane.

[0019] As a further preferred embodiment of the above technical solution, the pore size of the filter membrane is 0.2-0.8 μm; the material of the filter membrane is an organic porous material, and the organic porous material includes one or more of PP, PE, PVDF and PTFE.

[0020] As a further preferred embodiment of the above technical solution, in the arsenic-containing waste acid, the copper ion concentration is 0-5.0 g / L, the zinc ion concentration is 0-5.0 g / L, the acid concentration is 0.1-1.0 mol / L, and the arsenic concentration is 0-15 g / L.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] The treatment method of arsenic-containing waste acid of the present invention has the characteristics of simple process operation, good separation effect, high separation efficiency, high effective resource utilization, and the ability to open the circuit of inorganic salts in the acid. Without the addition of exogenous agents, the effective separation of arsenic, valuable metals (including metal cations) and waste acid in the waste acid is achieved, and the effective opening of arsenic and metal cations that are prone to scaling in the waste acid is achieved, laying a solid foundation for the concentration and reuse of the waste acid. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a process flow chart of the method for treating arsenic-containing waste acid in Example 1;

[0024] Figure 2 Schematic diagram of the structure and operating principle of the electrodialysis unit in Example 1;

[0025] Figure 3 Schematic diagram of the structure and operating principle of the electrodialysis unit in Example 2;

[0026] Figure 4 Schematic diagram of the structure and operating principle of the bipolar membrane electrodialysis unit in Example 1. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to specific embodiments.

[0028] Example 1:

[0029] The process flow chart of the treatment method of arsenic-containing waste acid in this embodiment is as follows: Figure 1 As shown, the above treatment method treats arsenic-containing waste acid with a copper ion content of 518 mg / L, a zinc ion content of 260 mg / L, an acid concentration of 0.34 mol / L, and an arsenic concentration of 510 mg / L, comprising the following steps:

[0030] (1) Filtering the arsenic-containing waste acid by vacuum filtration to obtain a filtrate; wherein the pore size of the filter membrane used is 0.45 μm; the filter membrane material is an organic porous material, and the material is PP;

[0031] (2) The filtrate in step (1) is subjected to a two-stage electrodialysis series treatment to recover an arsenic-rich solution from the dilute chamber and an acid-rich solution from the concentrated chamber; the electrodialysis equipment used in this step has a membrane stack configuration consisting of a plurality of electrodialysis units connected in series, and the structure and operating principle of each electrodialysis unit are as follows: Figure 2 As shown in the figure, the assembly order from cathode to anode is anion exchange membrane, cation exchange membrane, and anion exchange membrane, and adjacent membranes are separated by a separator. The cathode of the electrodialysis is connected to the negative pole of the DC power supply, and the anode is connected to the positive pole of the DC power supply. The dilution chamber of the electrodialysis is connected to the desalination tank, referred to as the S chamber; the concentration chamber of the electrodialysis is connected to the concentration tank, referred to as the B chamber. During the electrodialysis process, the current density is adjusted to 1.5 mA / cm 2 The experimental time is 120 minutes. After testing, the separation rate of arsenic in the dilute chamber is 92%, the recovery rate of copper ions in the concentrated chamber is 74%, the recovery rate of zinc ions is 70%, and the recovery rate of acid is 80%.

[0032] (3) The acid-rich solution in step (2) is treated by two-compartment bipolar membrane electrodialysis, and a metal salt solution containing valuable metal ions such as copper and zinc is recovered from the salt chamber, and an acid solution is recovered from the acid chamber; the two-compartment bipolar membrane electrodialysis membrane stack configuration is composed of a plurality of bipolar membrane electrodialysis units connected in series, and the structure and operating principle of the bipolar membrane electrodialysis unit are as follows: Figure 4 As shown in the figure, the assembly order of each bipolar membrane electrodialysis unit from cathode to anode is bipolar membrane, anion exchange membrane and bipolar membrane, and the two adjacent membranes are separated by a partition; the current density is adjusted to 1.5mA / cm during the electrodialysis process. 2 The experimental time is 90 minutes. The test shows that the acid recovery rate in the acid chamber is 99%, and the recovery rate of valuable metal ions such as copper and zinc in the salt chamber is 99%.

[0033] The high-arsenic waste acid treated in step (3) obtains an acid solution and a metal salt solution. The obtained acid concentration is 0.27 mol / L and the comprehensive recovery rate is 80%. In the metal salt solution, the comprehensive recovery rates of copper and zinc ions are 74% and 73%, respectively, and the comprehensive separation rate of arsenic is 92%.

[0034] The acid obtained in step (3) is concentrated to a purity of 96%, thereby realizing resource utilization of the acid.

[0035] The metal salt solution obtained in step (3) contains copper and zinc ion concentrations of 344.5 mg / L and 176.9 mg / L (recovery rates of 74% and 69%), respectively, and an arsenic concentration of 40 mg / L (arsenic separation rate of more than 92%). After precipitation and acid dissolution, the solution is reused for electrolysis to achieve effective recovery of valuable metal resources such as copper and zinc.

[0036] Example 2:

[0037] The method for treating arsenic-containing waste acid of this embodiment comprises the following steps:

[0038] (1) Filtering the arsenic-containing waste acid by vacuum filtration to obtain a filtrate; wherein the pore size of the filter membrane used is 0.45 μm; the filter membrane material is an organic porous material, and the material is PP;

[0039] (2) The filtrate in step (1) is subjected to a two-stage electrodialysis series treatment to recover an arsenic-rich solution from the dilute chamber and an acid-rich solution from the concentrated chamber; the electrodialysis equipment used in this step has a membrane stack configuration consisting of a plurality of electrodialysis units connected in series, and the structure and operating principle of each electrodialysis unit are as follows: Figure 3 As shown, the assembly order from cathode to anode is anion exchange membrane, cation exchange membrane, and anion exchange membrane. Two bipolar membranes replace the anionic membrane and cation membrane at the cathode and anode ends respectively, and the two adjacent membranes are separated by a partition. The cathode of the electrodialysis is connected to the negative pole of the DC power supply, and the anode is connected to the positive pole of the DC power supply. The desalination chamber of the electrodialysis is connected to the desalination tank, referred to as the S chamber; the concentration chamber of the electrodialysis is connected to the concentration tank, referred to as the B chamber. The current density is adjusted to 4mA / cm during the electrodialysis process. 2 The experimental time was 60 minutes. After testing, the separation rate of arsenic in the dilute chamber was 99.3%, the copper ion recovery rate in the concentrated chamber was 94.4%, the zinc ion recovery rate was 94.00%, and the acid recovery rate was 96.2%.

[0040] (3) The acid-rich solution in step (2) is treated by two-compartment bipolar membrane electrodialysis, and a metal salt solution containing valuable metal ions such as copper and zinc is recovered from the salt chamber, and an acid solution is recovered from the acid chamber; the two-compartment bipolar membrane electrodialysis membrane stack configuration is composed of a plurality of bipolar membrane electrodialysis units connected in series, and the assembly order of each bipolar membrane electrodialysis unit from cathode to anode is bipolar membrane, anion exchange membrane and bipolar membrane, and two adjacent membranes are separated by a partition; the current density is adjusted to 1.5 mA / cm during the electrodialysis process 2 The experimental time is 90 minutes. The test shows that the acid recovery rate in the acid chamber is 99.1%, and the recovery rate of valuable metal ions such as copper and zinc in the salt chamber is 99.0%.

[0041] The high-arsenic waste acid treated in step (3) obtains an acid solution and a metal salt solution. The obtained acid concentration is 0.30 mol / L and the comprehensive recovery rate is 95.1%. In the metal salt solution, the comprehensive recovery rates of copper and zinc ions are 93.6% and 93.1%, respectively, and the comprehensive separation rate of arsenic is 99.4%.

[0042] The acid obtained in step (3) can be concentrated to a purity of 94.5%, realizing resource utilization of the acid. Less than 5% of the metal ions such as Mg, Ca, Fe, Mn, Cd, and Pb, and less than 10% of Na and K in the waste acid enter the recovered acid, thus achieving an open circuit for the metal ions such as Ca and Mg in the waste acid that are prone to forming scale.

[0043] The metal salt solution obtained in step (3) contains copper and zinc ion concentrations of 393.4 mg / L and 215.7 mg / L, respectively (comprehensive recovery rates of 93.6% and 93.1%, respectively) and an arsenic concentration of 40 mg / L (arsenic separation rate of more than 92%). After precipitation and acid dissolution, it is reused for electrolysis to achieve effective recovery of valuable metal resources such as copper and zinc.

[0044] The above is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiment. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. A method for treating arsenic-containing waste acid, characterized in that: The following steps are involved: (1) performing electrodialysis treatment on the arsenic-containing waste acid using a common electrodialysis device to obtain an arsenic-rich solution and an acid-rich solution; (2) subjecting the acid-rich solution to electrodialysis using a bipolar membrane electrodialysis device to obtain an acid solution and a metal salt solution, thereby achieving separation of the acid, metal elements, and arsenic; The conventional electrodialysis equipment comprises a plurality of electrodialysis units connected in series; the electrodialysis unit comprises an anion exchange membrane, a cation exchange membrane and an anion exchange membrane assembled in sequence; a bipolar membrane is provided at both the cathode and the anode of the electrodialysis unit; The bipolar membrane electrodialysis equipment comprises a plurality of bipolar membrane electrodialysis units connected in series; the bipolar membrane electrodialysis unit comprises a bipolar membrane, an anion exchange membrane and a bipolar membrane assembled in sequence; During the electrodialysis process in step (1), the current density was adjusted to 4 mA / cm 2 , the experimental time is 60min.

2. The method for treating arsenic-containing waste acid according to claim 1, wherein: The anion exchange membrane is one or a combination of amine amino exchange membrane and aromatic amino exchange membrane; the cation exchange membrane is one or a combination of sulfonic acid exchange membrane, carboxylic acid exchange membrane and phosphate exchange membrane.

3. The method for treating arsenic-containing waste acid according to claim 1, wherein: In step (2), the acid-rich solution is treated by bipolar membrane electrodialysis under constant current conditions, and the density of the constant current is 1.0-2.0 mA / cm 2 .

4. The method for treating arsenic-containing waste acid according to claim 1, wherein: In step (1), multi-stage electrodialysis is used to treat the arsenic-containing waste acid.

5. The method for treating arsenic-containing waste acid according to claim 1, wherein: Before the arsenic-containing waste acid is subjected to electrodialysis treatment in step (1), the step further includes filtering the arsenic-containing waste acid through a filter membrane.

6. The method for treating arsenic-containing waste acid according to claim 5, wherein: The pore size of the filter membrane is 0.2-0.8 μm; the material of the filter membrane is an organic porous material, and the organic porous material includes one or more of PP, PE, PVDF and PTFE.

7. The method for treating arsenic-containing waste acid according to any one of claims 1 to 6, characterized in that: In the arsenic-containing waste acid, the copper ion concentration is 0-5.0 g / L, the zinc ion concentration is 0-5.0 g / L, the acid concentration is 0.1-1.0 mol / L, and the arsenic concentration is 0-15 g / L.

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