Method for removing heavy metal complex and recovering heavy metal by electrically activating thiourea dioxide

Abstract

The invention discloses a method for removing a heavy metal complex and recovering heavy metals by electrically activating thiourea dioxide, which comprises the following steps: adding simulated wastewater containing the heavy metal complex and anhydrous sodium sulfate into a beaker, and placing on a magnetic stirrer to obtain a solution A; adding a reducing agent to obtain a solution B; immersing the cathode and the anode into the solution B; turning on a direct-current stabilized power supply connected with the cathode and the anode to supply power to the electrode plate; the heavy metal complex is degraded, and after complex breaking, free heavy metal is subjected to electro-adsorption, electro-deposition or electro-reduction on the cathode; and the heavy metal on the cathode is subjected to acid pickling recovery. According to the method for removing the heavy metal complex and recovering the heavy metal by using the electrically activated thiourea dioxide, the heavy metal complex in the electroplating wastewater is removed and the heavy metal is recovered by using the electrically activated reducing agent, so that the problem that the heavy metal complex and the heavy metal cannot be synchronously removed can be solved; the heavy metal complex breaking efficiency is improved, the operation cost is reduced, and wide-range application is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical water purification, and in particular relates to a method for removing heavy metal complexes and recovering heavy metals by electro-activating thiourea dioxide. Background Art

[0002] There are a lot of heavy metals in electroplating wastewater. When treating electroplating wastewater, a lot of organic substances such as chelating agents, brighteners, stabilizers, etc. are added. The heavy metals in the water are combined with these organic substances and exist stably in the form of complexes. Unlike conventional heavy metal ions, heavy metal complexes are difficult to remove efficiently through traditional methods such as chemical precipitation, adsorption, and membrane separation. In addition, electroplating wastewater also contains heavy metals with recycling value such as copper, nickel, and chromium. Therefore, it is particularly important to study a technical method that integrates the degradation of heavy metal complexes and the recovery of heavy metals.

[0003] At present, advanced oxidation processes (AOPs) are widely used in the treatment of heavy metal complexes. However, they have some disadvantages: secondary pollution will occur, some heavy metals may be released during the oxidation process, forming free and highly toxic forms, causing environmental pollution; side reactions will occur, and decomplexation will be accompanied by decarboxylation reactions, which will reduce efficiency, and may also produce toxic chlorinated organic matter, acidic or corrosive gases and other byproducts, which are harmful to the environment or human health. Advanced reduction processes (ARPs) react with heavy metal complexes by generating free radicals or active substances with strong reducing properties, directly attacking the metal center site and releasing heavy metal ions, and ARPs are less used in the treatment of heavy metal complexes. Therefore, using advanced reduction technology to break the complexed heavy metals and release heavy metal ions is the premise and basis for achieving deep purification of wastewater containing heavy metal complexes, and combined with electrochemical technology to achieve efficient removal of heavy metal complexes.

[0004] Electrochemical technology has great potential in the field of heavy metal complexes and heavy metal recovery. In electrochemical reactions, heavy metal complexes can be reduced at the cathode, including direct electroreduction and indirect electroreduction. In the former, heavy metals directly obtain electrons from the cathode surface, and in the latter, they obtain electrons with the help of reducing agents and active free radicals generated in situ. Then the heavy metal ions released after the decomplexation of the heavy metal complex are directly recovered at the cathode through electroreduction or electroadsorption. At present, electrochemical technology has limited effect on the complete removal of heavy metal complexes, and it is difficult to achieve complete degradation of heavy metal complexes. On the basis of electrochemical technology, electrochemical technology is combined with advanced reduction technology to degrade heavy metal complexes, and electrochemical technology is used to activate reducing agents to produce reducing substances with stronger reducing ability. In the prior art, electrochemical activation of the reducing agent sulfite is proposed to remove different pollutants, maximizing SO3 •− / HSO3 •− and SO4 •−Degradation of different pollutants. Proposed E-HSO3 − The system is more suitable for reduction because HSO3 •− The electro-oxidation rate and oxygen oxidation rate are lower than SO3 •− ; E-SO3 2− The system is more suitable for oxidation because of the higher conversion rate of oxygen-sulfur radicals, and the optimal parameters for the reduction and oxidation of pollutants are determined, but it does not mention the removal of heavy metal complex pollutants. In addition, a method of reducing As(III) and As(V) to As(0) by alkaline-activated and thermally activated thiourea dioxide (TDO) is proposed in the prior art. This study provides a promising method for recovering valuable As(0) from alkaline arsenic-containing wastewater. And this method shows potential in treating arsenic removal in actual copper smelting and antimony smelting wastewater, and can reduce the arsenic concentration to below the industrial wastewater discharge standard.

[0005] At present, there are several problems in treating heavy metal complexes, which are difficult-to-degrade pollutants in electroplating wastewater: First, it is impossible to completely remove heavy metal complexes. For example, adsorption and ion exchange only concentrate or transform heavy metal complexes. Second, it is impossible to directly remove heavy metal complexes and heavy metals at the same time. It is necessary to use secondary precipitation and other technologies to remove heavy metals. For example, the solution after Fenton advanced oxidation treatment is acidic, and a large amount of alkaline substances need to be added to precipitate and remove heavy metal ions. Third, similar electrochemical technologies still have the problems of low reduction efficiency, high operating costs, and difficulty in expanding applications. Fourth, advanced reduction technologies currently mainly process and recover metal ions, and have not studied heavy metal complexes.

[0006] Therefore, there is a need in the art to develop a method for removing heavy metal complexes and recovering heavy metals by electro-activating thiourea dioxide, which can effectively solve the above problems. Summary of the invention

[0007] The purpose of the present invention is to provide a method for removing heavy metal complexes and recovering heavy metals by electro-activating thiourea dioxide. The method utilizes an electro-activated reducing agent to remove heavy metal complexes in electroplating wastewater and recover heavy metals, which can solve the problem that heavy metal complexes and heavy metals cannot be removed simultaneously, and improve the efficiency of heavy metal complex decomposition and reduce operating costs, thereby achieving a wide range of applications.

[0008] To achieve the above object, the present invention provides a method for removing heavy metal complexes and recovering heavy metals by electro-activating thiourea dioxide, comprising the following steps: Step S1, adding a mixed solution of simulated wastewater containing heavy metal complexes and anhydrous sodium sulfate into a beaker, placing the mixture on a magnetic stirrer, and mixing the mixture at a speed of 700-900 r / min to obtain a solution A; Step S2, adding a reducing agent to solution A and stirring evenly to obtain solution B; Step S3, immersing the cathode and the anode into solution B; turning on the DC regulated power supply connected to the cathode and the anode to supply power to the electrode plate; Step S4: the reaction starts, the heavy metal complex is degraded in the beaker, and the free heavy metal after the complex is broken is electro-adsorbed, electro-deposited or electro-reduced on the cathode; Step S5: After the reaction is completed, the heavy metals on the cathode are recovered by acid washing.

[0009] Preferably, in step S1, the molar concentration of anhydrous sodium sulfate is 45-55 mmol / L; Simulated wastewater containing heavy metal complexes includes electroplating wastewater such as copper, nickel, and chromium.

[0010] Preferably, in step S2, the reducing agent is thiourea dioxide; wherein the minimum molar concentration ratio of thiourea dioxide to the heavy metal complex added is 2:1.

[0011] Preferably, in step S3, the cathode is carbon felt and the anode is a dimensionally stable anode.

[0012] Preferably, in step S5, the cathode is soaked in one of nitric acid, hydrochloric acid and sulfuric acid to recover the metal on the cathode by acid washing.

[0013] The present invention adopts the above-mentioned method of electro-activated thiourea dioxide to remove heavy metal complexes and recover heavy metals, and the beneficial effects are as follows: (1) Compared with the prior art, the present invention proposes a method for removing heavy metal complexes by electrochemically activating the reducing agent thiourea dioxide. The electrochemical activation of thiourea dioxide produces reducing active substances, which achieves efficient decomplexation of heavy metal complexes and simultaneously recovers heavy metals at the cathode; further reduces the energy consumption required for electrochemistry and improves the reaction rate; this method has not been mentioned in the prior art, reflecting the innovation and practical value of the present invention; (2) The present invention uses an electro-activated reducing agent to target and break heavy metal complexes, wherein the reducing substance H • Different from • OH and other oxidizing substances target the destruction of heavy metal complexes; and use the cathode to simultaneously recover heavy metals to achieve simultaneous removal of heavy metal complexes and heavy metals; it uses the method with the lowest energy consumption and the lowest amount of chemical reagents to treat wastewater containing heavy metal complexes, reducing the cost of electrochemical technology for treating wastewater containing heavy metal complexes; (3) The method of the present invention can treat different types of electroplating wastewater such as copper, nickel, chromium, etc., thereby demonstrating the practicality of the method.

[0014] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a comparative diagram of the removal effects of different oxidants and reducing agents on copper in an embodiment of the method for removing heavy metal complexes and recovering heavy metals using electro-activated thiourea dioxide; Figure 2 This is a comparative diagram of the effects of different processes on the destruction of Cu(II)-EDTA complexes and the recovery of Cu in the method for removing heavy metal complexes and recovering heavy metals using electro-activated thiourea dioxide in the present invention; Figure 3 This is a diagram showing the removal effect of different heavy metal complexes in Example 3 of the method for removing heavy metal complexes and recovering heavy metals using electro-activated thiourea dioxide; Figure 4 This is a diagram showing the removal effect of copper on Example 2 of the method for removing heavy metal complexes and recovering heavy metals using electro-activated thiourea dioxide. DETAILED DESCRIPTION

[0016] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0017] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0018] Embodiment 1 The method for removing heavy metal complexes and recovering heavy metals by electro-activating thiourea dioxide comprises the following steps: Step S1, add 200 mL of a mixed solution of simulated wastewater containing disodium copper ethylenediaminetetraacetate (Cu(II)-EDTA) with a molar concentration of 0.1 mmol / L and anhydrous sodium sulfate with a molar concentration of 50 mmol / L into a beaker, place on a magnetic stirrer, and mix evenly at a speed of 800 r / min to obtain solution A.

[0019] Step S2: adding thiourea dioxide (TDO) with a molar concentration of 0.2 mmol / L to solution A, and stirring the mixture evenly to obtain solution B.

[0020] Step S3, immersing the carbon felt and the dimensionally stable anode as the cathode and the anode respectively into the solution B. Turning on the DC regulated power supply connected to the cathode and the anode to supply power to the electrode plate.

[0021] Step S4: The reaction starts, the heavy metal complex is degraded in the beaker, and the free heavy metal after the complex is broken is electro-adsorbed, electro-deposited or electro-reduced on the cathode.

[0022] Step S5: After the reaction is completed, the heavy metals on the cathode are recovered by acid washing.

[0023] The method of Example 1 is compared with other process methods for the decomposition of Cu-EDTA and the recovery of Cu. Figure 2 As shown in the figure, the copper recovery efficiency in the argon-electro-activated thiourea dioxide process is the highest, followed by the electro-activated thiourea dioxide process, and the electrochemical process is second, and the copper recovery efficiency of thiourea dioxide is the lowest. Therefore, the composite process of electrochemical activated thiourea dioxide has the best treatment effect on Cu-EDTA.

[0024] Embodiment 2 The method for removing heavy metal complexes and recovering heavy metals by electro-activating thiourea dioxide comprises the following steps: Step S1, add 200 mL of a mixed solution of simulated wastewater containing disodium copper ethylenediaminetetraacetate (Cu(II)-EDTA) and anhydrous sodium sulfate with a molar concentration of 50 mmol / L into a beaker, place it on a magnetic stirrer, and mix it evenly at a speed of 800 r / min to obtain solution A.

[0025] Step S2, adding thiourea dioxide to solution A, wherein the molar concentration ratio of TDO to Cu(II)-EDTA is 3:1, and stirring evenly to obtain solution B.

[0026] Step S3, immersing the carbon felt and the dimensionally stable anode as the cathode and the anode respectively into the solution B. Turning on the DC regulated power supply connected to the cathode and the anode to supply power to the electrode plate.

[0027] Step S4: The reaction starts, the heavy metal complex is degraded in the beaker, and the free heavy metal after the complex is broken is electro-adsorbed, electro-deposited or electro-reduced on the cathode.

[0028] Step S5: After the reaction is completed, the heavy metals on the cathode are recovered by acid washing.

[0029] like Figure 4 As shown, when the molar concentration ratio of TDO to Cu(II)-EDTA is 3:1, copper obtains a better recovery efficiency.

[0030] Embodiment 3 The method for removing heavy metal complexes and recovering heavy metals by electro-activating thiourea dioxide comprises the following steps: Step S1, respectively placing a mixed solution of simulated wastewater containing Cu(II)-EDTA, lead disodium ethylenediaminetetraacetate (Pb(II)-EDTA), manganese disodium ethylenediaminetetraacetate (Mn(II)-EDTA), zinc disodium ethylenediaminetetraacetate (Zn(II)-EDTA), nickel disodium ethylenediaminetetraacetate (Ni(II)-EDTA) and Cr(III)-EDTA with a molar concentration of 0.1 mmol / L and anhydrous sodium sulfate with a molar concentration of 50 mmol / L in a beaker, placing it on a magnetic stirrer, and mixing them evenly at a speed of 800 r / min to obtain a solution A.

[0031] Preparation of Cr(III)-EDTA: Use chromium sulfate and disodium ethylenediaminetetraacetate (EDTA) in a 1:1 molar concentration ratio of chromium (Cr) to EDTA, stir for 2 hours to allow for complexation before use.

[0032] Step S2, adding thiourea dioxide with a molar concentration of 1.0 mmol / L to solution A, and stirring evenly to obtain solution B.

[0033] Step S3, immersing the carbon felt and the dimensionally stable anode as the cathode and the anode respectively into the solution B. Turning on the DC regulated power supply connected to the cathode and the anode to supply power to the electrode plate.

[0034] Step S4: The reaction starts, the heavy metal complex is degraded in the beaker, and the free heavy metal after the complex is broken is electro-adsorbed, electro-deposited or electro-reduced on the cathode.

[0035] Step S5: After the reaction is completed, the heavy metals on the cathode are recovered by acid washing.

[0036] like Figure 3 As shown, copper (Cu) and lead (Pb) have the fastest recovery efficiency, and zinc (Zn), manganese (Mn), nickel (Ni), and chromium (Cr(III)) also have good recovery efficiency. Therefore, the composite process of electrochemically activated thiourea dioxide has a good treatment effect on different heavy metal complexes.

[0037] Comparative Example The method for removing heavy metal complexes and recovering heavy metals by electro-activating thiourea dioxide comprises the following steps: Step S1, add 200 mL of a mixed solution of simulated wastewater containing Cu-EDTA with a molar concentration of 0.1 mmol / L and anhydrous sodium sulfate with a molar concentration of 50 mmol / L into a beaker, place it on a magnetic stirrer, and mix it evenly at a speed of 800 r / min to obtain solution A.

[0038] Step S2, adding a reducing agent (sodium sulfite) and an oxidizing agent (hydrogen peroxide, potassium persulfate, potassium persulfate, peracetic acid, sodium percarbonate) with a molar concentration of 0.2 mmol / L to solution A respectively, and stirring evenly to obtain solution B respectively.

[0039] Step S3, immersing the carbon felt and the dimensionally stable anode as the cathode and the anode respectively into the solution B. Turning on the DC regulated power supply connected to the cathode and the anode to supply power to the electrode plate.

[0040] Step S4: The reaction starts, the heavy metal complex is degraded in the beaker, and the free heavy metal after the complex is broken is electro-adsorbed, electro-deposited or electro-reduced on the cathode.

[0041] Step S5: After the reaction is completed, the heavy metals on the cathode are recovered by acid washing.

[0042] Compare the method of Example 1 with that of the comparative example. Figure 1 As shown in the figure, the copper recovery efficiency in the electro-activated thiourea dioxide process is the highest, and the copper recovery efficiency of other electro-activated reducing agents and oxidants is lower than that of the electro-activated thiourea dioxide process. Therefore, the electrochemically activated reducing agent thiourea dioxide process has the best treatment effect on Cu-EDTA.

[0043] Therefore, the present invention adopts the above-mentioned method of electro-activated thiourea dioxide to remove heavy metal complexes and recover heavy metals. The method uses an electro-activated reducing agent to remove heavy metal complexes in electroplating wastewater and recover heavy metals, which can solve the problem that heavy metal complexes and heavy metals cannot be removed simultaneously, and improve the efficiency of heavy metal complex decomposition and reduce operating costs, thereby realizing a wide range of applications.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for removing heavy metal complexes and recovering heavy metals by electro-activating thiourea dioxide, characterized in that: The following steps are involved: Step S1, adding a mixed solution of simulated wastewater containing heavy metal complexes and anhydrous sodium sulfate into a beaker, placing the mixture on a magnetic stirrer, and mixing the mixture at a speed of 700-900 r / min to obtain a solution A; Step S2, adding a reducing agent to solution A and stirring evenly to obtain solution B; Step S3, immersing the cathode and the anode into solution B; turning on the DC regulated power supply connected to the cathode and the anode to supply power to the electrode plate; Step S4: the reaction starts, the heavy metal complex is degraded in the beaker, and the free heavy metal after the complex is broken is electro-adsorbed, electro-deposited or electro-reduced on the cathode; Step S5: After the reaction is completed, the heavy metals on the cathode are recovered by acid washing.

2. The method for removing heavy metal complexes and recovering heavy metals by electro-activated thiourea dioxide according to claim 1, characterized in that: In step S1, the molar concentration of anhydrous sodium sulfate is 45-55 mmol / L; The simulated wastewater containing heavy metal complexes includes copper, nickel and chromium electroplating wastewater.

3. The method for removing heavy metal complexes and recovering heavy metals by electro-activated thiourea dioxide according to claim 2, characterized in that: In step S2, the reducing agent is thiourea dioxide; wherein the minimum molar concentration ratio of thiourea dioxide to the heavy metal complex is 2:

1.

4. The method for removing heavy metal complexes and recovering heavy metals by electro-activated thiourea dioxide according to claim 1, characterized in that: In step S3, the cathode is carbon felt, and the anode is a dimensionally stable anode.

5. The method for removing heavy metal complexes and recovering heavy metals by electro-activated thiourea dioxide according to claim 1, characterized in that: In step S5, the cathode is soaked in one of nitric acid, hydrochloric acid and sulfuric acid to recover the metal on the cathode by pickling.

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