Treatment method of silver-containing wastewater

Abstract

The invention discloses a silver-containing wastewater treatment method which comprises the following steps: S1, adding alkali liquor into silver-containing wastewater to obtain primary mixed liquor; s2, adding activated carbon and chlorine salt into the primary mixed solution, and mixing and reacting to obtain a secondary mixed solution; and S3, filtering the secondary mixed solution, and separating filter residues to obtain a treated clear solution. The method comprises the following steps: adding alkali liquor into the silver-containing wastewater, enabling a part of silver ions (Ag < + >) to react with hydroxyl ions (OH <->) to form insoluble silver oxide (Ag2O), and creating an alkaline condition for the next operation, so that the silver ions are precipitated, and enabling chloride ions (Cl <->) to react with the silver ions (Ag < + >) to form silver chloride (AgCl) precipitate; meanwhile, under the alkaline condition, the activated carbon can adsorb silver ions and silver particles, the adsorption capacity of the activated carbon is improved under the alkaline condition, silver can be effectively removed from the waste liquid, and the purification effect of silver in the silver-containing wastewater is improved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for treating silver-containing wastewater. Background Art

[0002] Silver is a typical pollution factor. With the widespread application of silver in the chemical industry, the increasing amount of silver-containing wastewater has become a major hidden danger threatening the ecological environment. Given the high value of silver as a precious metal, purifying and recovering trace silver elements in these wastewaters is not only a major contribution to environmental protection, but also a key measure to improve corporate economic benefits and achieve sustainable development. Therefore, efficient purification and recovery of silver elements in silver-containing wastewater has become an urgent and important research topic faced by both environmental protection and corporate development.

[0003] At present, conventional treatment methods for silver-containing wastewater include alkali precipitation, chlorine precipitation, sulfur precipitation and evaporative precipitation, etc. The above methods have problems such as high cost, difficulty in post-treatment silver recovery and poor purification effect due to silver ion back dissolution. The silver content in wastewater after treatment by traditional purification methods is generally 2-9PPm.

[0004] Therefore, how to effectively improve the purification effect of silver in silver-containing wastewater remains a technical problem that needs to be solved urgently. Summary of the invention

[0005] The present invention aims to solve the above technical problems existing in the prior art. To this end, the present invention proposes a method for treating silver-containing wastewater, which improves the purification effect of silver in the silver-containing wastewater.

[0006] According to one aspect of the present invention, a method for treating silver-containing wastewater is provided, comprising:

[0007] S1. Adding alkali solution to the silver-containing wastewater to obtain a mixed solution;

[0008] S2. Adding activated carbon and chloride salt to the primary mixed solution to obtain a secondary mixed solution;

[0009] S3. Filter the secondary mixed liquid, separate the filter residue and obtain the treated clear liquid.

[0010] The reaction principle of the present invention is:

[0011] By adding alkali solution to the silver-containing wastewater, a portion of the silver ions (Ag + ) and hydroxide ions (OH - ) to form insoluble silver oxide (Ag 2 O), while creating alkaline conditions for the next step, thereby precipitating silver ions and using chloride ions (Cl - ) and silver ions (Ag +) reaction to form silver chloride (AgCl) precipitate; at the same time, under alkaline conditions, activated carbon can adsorb silver ions and silver particles. The adsorption capacity of activated carbon is improved under alkaline conditions, which can effectively remove silver from the waste liquid.

[0012] According to the first aspect of the present invention, there are at least the following beneficial effects:

[0013] Ag + It is a soft acid, and a high concentration of strong alkali can make Ag + It precipitates in the form of silver oxide (brown). In alkaline solution, when the pH value is greater than 7, silver ions will precipitate in the form of Ag. 2 O. In acidic solution, silver ions precipitate as silver chloride; in neutral solution, silver ions precipitate as silver hydroxide. The reaction principle is: 2OH - +2Ag + =Ag 2 O↓+H2O;Cl - +Ag+=AgCl↓, activated carbon is mostly made from plant materials by carbonization, and like plant materials, contains a large number of phenolic hydroxyl, carboxyl, (-NH 2 ) and (=NH), Ag + Can be used with (-NH 2 Silver reacts with the amino and imino groups on the surface of activated carbon to form a stable complex with activated carbon-NH 2 Ag + and activated carbon = NHAg + At the same time, the adsorption capacity of activated carbon is mainly due to its pore structure, including micropores, mesopores and macropores. These pore structures provide a large surface area, allowing the activated carbon to adsorb silver oxide particulate matter. When the gas or liquid passes through the activated carbon, the particulate matter can be attached to the surface of the activated carbon by physical adsorption or chemical adsorption, and thus be effectively removed.

[0014] In some embodiments of the present invention, the alkali solution comprises NaOH, KOH and Ca(OH) 2 One or more of .

[0015] In some embodiments of the present invention, the pH value of the primary mixed solution is 9-12.

[0016] In some embodiments of the present invention, the chloride salt includes NaCl, KCl and CaCl 2 One or more of .

[0017] In some embodiments of the present invention, the molar ratio of the chloride ion content contained in the chloride salt to the silver ion content in the silver-containing wastewater is greater than 1:1.

[0018] In some embodiments of the present invention, the activated carbon includes one or more of fruit shell activated carbon, coal-based activated carbon and wood-based activated carbon.

[0019] In some embodiments of the present invention, the mass-to-liquid ratio of the activated carbon to the silver-containing wastewater is 0.1-5 g / L.

[0020] In some embodiments of the present invention, the activated carbon is modified activated carbon; and the preparation method of the modified activated carbon comprises mixing the activated carbon with an alkali solution.

[0021] In some embodiments of the present invention, the pH value of the solution after the activated carbon and the alkali solution are mixed is 10-14.

[0022] Under alkaline conditions, the ability of activated carbon to adsorb silver particles is improved. The surface of activated carbon has a variety of functional groups (such as carboxyl, phenolic hydroxyl, etc.). These functional groups may undergo charge changes under alkaline conditions to form negative charges, thereby enhancing its adsorption capacity for positively charged silver ions. Especially in an alkaline environment, the adsorption capacity of activated carbon is usually enhanced, and the adsorption of silver ions by activated carbon is more effective at this time.

[0023] In some embodiments of the present invention, activated carbon and chloride salt are added to the primary mixed liquid in sequence to obtain a secondary mixed liquid.

[0024] Activated carbon can be added before adding chloride salt or after silver precipitation with chloride salt. It is preferred to add activated carbon before adding chloride salt. 1. When activated carbon is added first, it will immediately begin to adsorb free silver ions. Activated carbon has rich surface pore structure and functional groups (such as carboxyl, phenolic hydroxyl, etc.). These functional groups can undergo physical or chemical adsorption with silver ions. The electrostatic attraction and coordination between silver ions and the negative charge on the surface of activated carbon allow silver ions to be rapidly adsorbed. Before chloride salt (such as NaCl) is added, the silver ions in the wastewater are free and can directly undergo adsorption reaction with the surface of activated carbon. After adding chloride salt, silver ions (Ag + ) and chloride ion (Cl -) reacts to form an insoluble silver chloride precipitate (AgCl), which causes some silver ions to transform into solid precipitates. Although precipitation is helpful for the removal of silver, if chloride salts are added first, the activated carbon will mainly adsorb the precipitated silver particles, and the efficiency of adsorbing silver ions will be low. Therefore, adding activated carbon first can maximize the adsorption of free silver ions and ensure that the silver ion concentration drops even lower. Therefore, adding activated carbon first helps to adsorb silver ions to the greatest extent, especially when the silver ions are in a free state. By utilizing the functional groups and pore structure on the surface of activated carbon, the silver ions are adsorbed before the silver ions react with chloride ions to form a precipitate, thereby avoiding the loss of silver ions after the precipitate is formed. At the same time, activated carbon can also adsorb the silver particles formed after precipitation, further removing silver from the wastewater, thereby lowering the silver ion content. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0026] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0027] Unless otherwise specified, "room temperature" in the present invention means 25°C±5°C.

[0028] Unless otherwise specified, "about" in the present invention means that the allowable error is within ±2%.

[0029] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0030] A first aspect of the present invention provides a method for treating silver-containing wastewater, comprising:

[0031] S1. Adding alkali solution to the silver-containing wastewater to obtain a mixed solution;

[0032] S2. Adding activated carbon and chloride salt to the primary mixed solution to obtain a secondary mixed solution;

[0033] S3. Filter the secondary mixed liquid, separate the filter residue and obtain the treated clear liquid.

[0034] The reaction principle of the present invention is:

[0035] By adding alkali solution to the silver-containing wastewater, a portion of the silver ions (Ag + ) and hydroxide ions (OH - ) to form insoluble silver oxide (Ag 2 O), and at the same time create alkaline conditions for the next step, thereby precipitating silver ions, using chloride ions (Cl-) and silver ions (Ag + ) reaction to form silver chloride (AgCl) precipitate; at the same time, under alkaline conditions, activated carbon can adsorb silver ions and silver particles. The adsorption capacity of activated carbon is improved under alkaline conditions, which can effectively remove silver from the waste liquid.

[0036] According to the first aspect of the present invention, there are at least the following beneficial effects:

[0037] Ag + It is a soft acid, and a high concentration of strong alkali can make Ag + It precipitates in the form of silver oxide (brown). In alkaline solution, when the pH value is greater than 7, silver ions will precipitate in the form of Ag. 2 O. In acidic solution, silver ions precipitate as silver chloride; in neutral solution, silver ions precipitate as silver hydroxide. The reaction principle is: 2OH - +2Ag + =Ag 2 O↓+H2O;Cl - +Ag+=AgCl↓, activated carbon is mostly made from plant materials by carbonization, and like plant materials, contains a large number of phenolic hydroxyl, carboxyl, (-NH 2 ) and (=NH), Ag + Can be used with (-NH 2 Silver reacts with the amino and imino groups on the surface of activated carbon to form a stable complex with activated carbon-NH 2 Ag + and activated carbon = NHAg + At the same time, the adsorption capacity of activated carbon is mainly due to its pore structure, including micropores, mesopores and macropores. These pore structures provide a large surface area, allowing the activated carbon to adsorb silver oxide particulate matter. When the gas or liquid passes through the activated carbon, the particulate matter can be attached to the surface of the activated carbon by physical adsorption or chemical adsorption, and thus be effectively removed.

[0038] In some embodiments of the present invention, the alkali solution comprises NaOH, KOH and Ca(OH) 2 One or more of .

[0039] In some embodiments of the present invention, the pH value of the primary mixed solution is 9-12.

[0040] In some embodiments of the present invention, the chloride salt includes NaCl, KCl and CaCl 2 One or more of .

[0041] In some embodiments of the present invention, the molar ratio of the chloride ion content contained in the chloride salt to the silver ion content in the silver-containing wastewater is greater than 1:1.

[0042] In some embodiments of the present invention, the activated carbon includes one or more of fruit shell activated carbon, coal-based activated carbon and wood-based activated carbon.

[0043] In some embodiments of the present invention, the mass-to-liquid ratio of the activated carbon to the silver-containing wastewater is 0.1-5 g / L.

[0044] In some embodiments of the present invention, the activated carbon is modified activated carbon; and the preparation method of the modified activated carbon comprises mixing the activated carbon with an alkali solution.

[0045] In some embodiments of the present invention, the pH value of the solution after the activated carbon and the alkali solution are mixed is 10-14.

[0046] Under alkaline conditions, the ability of activated carbon to adsorb silver particles is improved. The surface of activated carbon has a variety of functional groups (such as carboxyl, phenolic hydroxyl, etc.). These functional groups may undergo charge changes under alkaline conditions to form negative charges, thereby enhancing its adsorption capacity for positively charged silver ions. Especially in an alkaline environment, the adsorption capacity of activated carbon is usually enhanced, and the adsorption of silver ions by activated carbon is more effective at this time.

[0047] In some embodiments of the present invention, activated carbon and chloride salt are added to the primary mixed liquid in sequence to obtain a secondary mixed liquid.

[0048] Activated carbon can be added before adding chloride salt or after silver precipitation with chloride salt. It is preferred to add activated carbon before adding chloride salt. 1. When activated carbon is added first, it will immediately begin to adsorb free silver ions. Activated carbon has rich surface pore structure and functional groups (such as carboxyl, phenolic hydroxyl, etc.). These functional groups can undergo physical or chemical adsorption with silver ions. The electrostatic attraction and coordination between silver ions and the negative charge on the surface of activated carbon allow silver ions to be rapidly adsorbed. Before chloride salt (such as NaCl) is added, the silver ions in the wastewater are free and can directly undergo adsorption reaction with the surface of activated carbon. After adding chloride salt, silver ions (Ag + ) and chloride ion (Cl - ) reacts to form an insoluble silver chloride precipitate (AgCl), which causes some silver ions to transform into solid precipitates. Although precipitation is helpful for the removal of silver, if chloride salts are added first, the activated carbon will mainly adsorb the precipitated silver particles, and the efficiency of adsorbing silver ions will be low. Therefore, adding activated carbon first can maximize the adsorption of free silver ions and ensure that the silver ion concentration drops even lower. Therefore, adding activated carbon first helps to adsorb silver ions to the greatest extent, especially when the silver ions are in a free state. By utilizing the functional groups and pore structure on the surface of activated carbon, the silver ions are adsorbed before the silver ions react with chloride ions to form a precipitate, thereby avoiding the loss of silver ions after the precipitate is formed. At the same time, activated carbon can also adsorb the silver particles formed after precipitation, further removing silver from the wastewater, thereby lowering the silver ion content.

[0049] Example 1

[0050] This embodiment provides a method for treating silver-containing wastewater, specifically:

[0051] A1. Under normal temperature conditions, take 100mL of silver-containing wastewater (silver ion concentration 8.59mg / L), add NaOH to the silver-containing wastewater, adjust the wastewater pH to 9 to obtain a mixed solution, and the silver ions are Ag 2 O precipitation, the reaction chemical formula is: 2OH - +2Ag + =2AgOH, the generated AgOH is extremely unstable and decomposes to produce Ag 2 O, the reaction chemical formula is: 2AgOH=Ag 2 O+H 2 O;

[0052] A2. Add excess NaCl to the mixed solution, the molar ratio of NaCl to silver ions in the silver-containing wastewater is 1.5:1, and further precipitate to form AgCl precipitate, the reaction chemical formula is: Ag + +Cl - =AgCl↓;

[0053] A3. Add 0.05g of activated carbon, that is, 0.5g / L of activated carbon (fruit shell activated carbon) for 100mL of silver-containing wastewater, stir thoroughly, adsorb silver ions and silver precipitates, and filter the treated waste liquid to separate the clear liquid and the silver-containing filter residue.

[0054] It should be noted that the "excessive" in Example A2. adding an excess of NaCl to the mixed solution means that the molar ratio of chloride ions in the NaCl added to the mixed solution to silver ions in the silver-containing wastewater is at least greater than 1:1. In actual industrial applications, the ratio can be 1.2:1, 1.8:1, 2:1, 3:1, etc., and is not limited to the ratio of 1.5:1 used in this example. The same applies to other chloride salts.

[0055] Example 2

[0056] This embodiment provides a method for treating silver-containing wastewater, which is different from Example 1 in that NaOH is added to adjust the pH of the wastewater to 10, and the other conditions are the same.

[0057] Example 3

[0058] This embodiment provides a method for treating silver-containing wastewater, which is different from Example 1 in that NaOH is added to adjust the pH of the wastewater to 12, and the other conditions are the same.

[0059] Example 4

[0060] This embodiment provides a method for treating silver-containing wastewater, specifically:

[0061] A1. Under normal temperature conditions, take 100mL of silver-containing wastewater (silver ion concentration 8.59mg / L), add NaOH to the silver-containing wastewater, and adjust the wastewater pH = 10 to obtain a mixed solution;

[0062] A2. Add 0.05 g of activated carbon to the mixture, i.e., 100 mL of silver-containing wastewater corresponds to 0.5 g / L of activated carbon;

[0063] A3. Add excess NaCl, stir thoroughly, and further precipitate to form AgCl precipitate. After adsorbing silver ions and silver precipitate, filter and separate the treated waste liquid to separate the clear liquid and the silver-containing filter residue.

[0064] Example 5

[0065] This embodiment provides a method for treating silver-containing wastewater, specifically:

[0066] A1. Under normal temperature conditions, take 100mL of silver-containing wastewater (silver ion concentration 8.59mg / L), add NaOH to the silver-containing wastewater, and adjust the wastewater pH = 10 to obtain a mixed solution;

[0067] A2. Add 0.05 g of modified activated carbon to the mixed solution, i.e., 100 mL of silver-containing wastewater corresponds to a ratio of 0.5 g / L of modified activated carbon;

[0068] A2. Add an excess of NaCl, stir thoroughly, and further precipitate to form AgCl precipitate, adsorb silver ions and silver precipitate, and then filter and separate the treated waste liquid to separate the clear liquid and the silver-containing residue;

[0069] The preparation method of the modified activated carbon is as follows: 0.05 g of activated carbon is modified using alkaline solution, specifically, activated carbon is added to a NaOH solution, the pH of the solution is maintained at 10, the activated carbon is stirred and soaked in the alkaline solution for more than 10 minutes, and the modified activated carbon is obtained by filtering.

[0070] Embodiment 6:

[0071] This embodiment provides a method for treating silver-containing wastewater, which is different from Example 5 in that the activated carbon modification treatment is to add activated carbon to a NaOH solution and maintain the pH of the solution at 14.

[0072] Embodiment 7:

[0073] This embodiment provides a method for treating silver-containing wastewater, which is different from Example 2 in that the amount of activated carbon used is 0.01 g (ratio to wastewater 0.1 g / L).

[0074] Embodiment 8:

[0075] This embodiment provides a method for treating silver-containing wastewater, which is different from Example 2 in that the amount of activated carbon used is 0.08 g (ratio to wastewater 0.8 g / L).

[0076] Comparative Example 1:

[0077] This comparative example provides a method for treating silver-containing wastewater, which is different from Example 1 in that hydrochloric acid is used to adjust the pH of the wastewater to 2.

[0078] Comparative Example 2:

[0079] This comparative example provides a method for treating silver-containing wastewater, which is different from Example 1 in that NaOH is added to adjust the pH value of the wastewater to 13.

[0080] Comparative Example 3:

[0081] This comparative example provides a method for treating silver-containing wastewater, which is different from Example 5 in that the activated carbon modification treatment is to add activated carbon to a hydrochloric acid solution and maintain the pH of the solution at 4.

[0082] Comparative Example 4:

[0083] This comparative example provides a method for treating silver-containing wastewater, which is different from Example 1 in that no activated carbon is added during the entire treatment process.

[0084] Test Case

[0085] The Agilent 5800 ICP-OES device was used to detect silver ions in the wastewater after treatment in each embodiment and comparative example using ICP spectroscopy, and the following data were obtained. The results are shown in Table 1.

[0086] Table 1. Wastewater for silver ion detection

[0087]

[0088]

[0089] It can be seen from the above table that in Example 1, activated carbon and chloride salt were used under alkaline conditions of pH = 9, and the silver content of the wastewater after treatment was low, and the treatment effect was good;

[0090] From Examples 2 and 3, it can be seen that the treatment effect is better when activated carbon and chloride salt are used under conditions of increased alkalinity compared to Example 1.

[0091] From Example 4, it can be seen that when using activated carbon and chloride salt to purify silver-containing wastewater under alkaline conditions, adding activated carbon first is more effective than adding chloride salt first.

[0092] It can be seen from Example 5 that adding modified activated carbon has a better effect. The surface of activated carbon has a variety of functional groups (such as carboxyl, phenolic hydroxyl, etc.). These functional groups may undergo charge changes under alkaline conditions to form negative charges, thereby enhancing their adsorption capacity for positively charged silver ions. Especially in an alkaline environment, the adsorption capacity of activated carbon is usually enhanced, and the adsorption of silver ions by activated carbon is more effective.

[0093] It can be seen from Example 6 that the higher the pH of the alkaline solution used to treat the activated carbon, the better the treatment effect. After the treatment in this example, silver ions can no longer be detected in the wastewater using conventional detection methods.

[0094] It can be seen from Example 7 that as the amount of activated carbon is reduced, the treatment effect becomes worse, but adding activated carbon at a ratio of 0.1 g / L still achieves good results.

[0095] It can be seen from Example 8 that the treatment effect is improved with the increase in the amount of activated carbon. It should be noted that when applied to actual industrial treatment, the amount of activated carbon can generally be increased to 5 g / L, within which the cost of using activated carbon, the amount of alkali solution required for modification, and the cost and process complexity of subsequent filtration and separation will not be significantly increased.

[0096] It can be seen from Comparative Example 1 that the treatment effect of using activated carbon and chloride salt under acidic conditions is poor, and the silver ion concentration of the wastewater after treatment is too high to meet the requirements.

[0097] From Comparative Example 2, it can be seen that the effect of using activated carbon and chloride salt treatment decreases when pH=13.

[0098] From Comparative Example 3, it can be seen that using alkaline solution to pre-treat activated carbon can achieve better results, while using acid solution to pre-treat activated carbon has a reduced effect.

[0099] From Comparative Example 4, it can be seen that the effect of silver precipitation treatment using only NaOH and NaCl without adding activated carbon is the worst.

[0100] The above is a detailed description of the embodiments of the present invention, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for treating silver-containing wastewater, characterized in that: include: S1. Adding alkali solution to the silver-containing wastewater to obtain a mixed solution; S2. Adding activated carbon and chloride salt to the primary mixed solution to obtain a secondary mixed solution; S3. Filter the secondary mixed liquid, separate the filter residue and obtain the treated clear liquid.

2. The method for treating silver-containing wastewater according to claim 1, characterized in that: The alkali solution includes one or more of NaOH, KOH and Ca(OH)2.

3. The method for treating silver-containing wastewater according to claim 2, wherein: The pH value of the primary mixed solution is 9-12.

4. The method for treating silver-containing wastewater according to claim 1, characterized in that: The chloride salt includes one or more of NaCl, KCl and CaCl2.

5. The method for treating silver-containing wastewater according to claim 4, characterized in that: The molar ratio of the chloride ion content contained in the chloride salt to the silver ion content in the silver-containing wastewater is greater than 1:

1.

6. The method for treating silver-containing wastewater according to claim 1, characterized in that: The activated carbon includes one or more of fruit shell activated carbon, coal-based activated carbon and wood-based activated carbon.

7. The method for treating silver-containing wastewater according to claim 6, characterized in that: The mass-to-liquid ratio of the activated carbon to the silver-containing wastewater is 0.1-5 g / L.

8. The method for treating silver-containing wastewater according to any one of claims 1 to 7, characterized in that: The activated carbon is modified activated carbon; the preparation method of the modified activated carbon comprises mixing the activated carbon and alkali solution.

9. The method for treating silver-containing wastewater according to claim 8, characterized in that: The pH value of the solution after the activated carbon and the alkali solution are mixed is 10-14.

10. The method for treating silver-containing wastewater according to claim 9, characterized in that: Activated carbon and chloride salt are added to the primary mixed liquid in sequence to obtain a secondary mixed liquid.

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