Method for synchronously removing, separating and purifying precious metal silver and harmful metal in wastewater

Abstract

The invention relates to the technical field of water treatment and precious metal separation and purification, and particularly discloses a method for synchronously removing, separating and purifying precious metal silver and harmful metal in wastewater. The method comprises the following steps: (1) adding an adsorbent containing amidoxime groups on the surface into wastewater, and carrying out adsorption treatment; (2) adding the adsorbent after adsorption into a primary desorption solution of non-oxidizing acid, and carrying out primary desorption to remove hetero-ions except silver; and (3) the adsorbent obtained after primary desorption is added into a secondary desorption solution of oxidizing acid, secondary desorption is conducted, and a high-purity silver solution is obtained. The method is based on the principle that amidoxime groups can spontaneously reduce silver ions into acid-resistant silver nanoparticles, and other metal ions form acidolysis complexes. The method is simple and convenient, an external electric field or a reducing agent is not needed, water purification and high-purity recovery of silver are achieved, and remarkable economic and environmental benefits are achieved.

Description

Technical Field

[0001] This invention belongs to the field of water treatment and precious metal separation and purification technology, specifically relating to a method and application for the simultaneous removal and separation and purification of precious metal silver and harmful metals in wastewater. Background Technology

[0002] Silver, as an important precious metal, is widely used in electronics, medicine, and energy. The discharge of silver-containing wastewater not only poses risks to the environment and health but also represents a waste of precious metal resources. Therefore, recovering silver from wastewater is of great significance.

[0003] Currently, common technologies for silver recovery include chemical precipitation, membrane separation, electrolysis, and adsorption. Adsorption is particularly noteworthy due to its operational flexibility and high efficiency at low concentrations. However, real wastewater often contains competing heavy metal ions such as iron, copper, and lead, and traditional adsorbents lack sufficient selectivity for silver, resulting in poor recovery efficiency. Existing technologies often improve selectivity by introducing sulfur-containing functional groups for modification, but the modification process often involves organic solvents or strong acids, and sulfur-containing groups readily coordinate with other heavy metals, leading to the coexistence of silver and impurity ions in the desorbate, requiring subsequent purification. Furthermore, while electrolysis can enrich silver, it suffers from cumbersome preparation processes and high energy consumption.

[0004] Amine oxime materials have been extensively studied due to their universality in adsorbing various metal ions; however, current research has not yet solved the problem of coexistence of silver with other metals in the desorption solution. Therefore, how to simultaneously achieve water treatment and silver purification based on existing adsorption processes is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the simultaneous removal and separation purification of precious metal silver and harmful metals in wastewater.

[0006] The specific technical solution of this invention is as follows: A method for the simultaneous removal, separation, and purification of precious metal silver and harmful metals in wastewater, comprising the following steps: (1) Add an adsorbent containing a amine oxime group on its surface to the wastewater for adsorption treatment; (2) Add the adsorbent after adsorption to the primary desorption solution of a non-oxidizing acid to perform the first desorption and remove impurity ions other than silver; (3) Add the adsorbent after the first desorption to the secondary desorption solution of the oxidizing acid for a second desorption to obtain a high-purity silver solution.

[0007] The mechanism of this invention is inferred as follows: Based on the difference in the interaction mechanism between the amylopime group and different metal ions, the chemical change from silver ions to elemental silver has a relatively positive redox potential (+0.80V). Therefore, compared with common metal ions, the reduction of silver ions is more easily achieved through the electron transfer process from ligands to metal ions. In addition, silver ions in the aqueous phase actually exist as silver dihydrate complex ions, and their coordination number is lower than that of most metal ions. Therefore, through ligand exchange between the amylopime group and bound water, its solvation layer can be stripped to a great extent. Furthermore, due to the large number of lone pairs of electrons in the amylopime group, the amylopime-silver complex has electron-rich ligands and electron-deficient silver centers, thus exhibiting a low band gap and chemical activity. At this time, the HOMO electrons located in the amylopime group can jump to the LUMO orbital of silver ions without the introduction of light, electric field or reducing reagents, spontaneously reducing silver ions to silver nanoparticles and depositing them on the surface of the adsorbent.

[0008] Based on the chemical inertness of elemental silver in non-oxidizing acids, this invention employs a two-step desorption strategy: using non-oxidizing acids as the primary desorption solution to remove impurity ions, and using oxidizing acids as the secondary desorption solution to recover silver, thereby achieving simultaneous wastewater treatment and separation and purification of precious metal silver.

[0009] In some embodiments, the adsorbent in step (1) is a polyacrylonitrile fiber with a surface modified with a amine oxime group.

[0010] In some embodiments, the wastewater in step (1) contains one or more of silver ions, iron ions, copper ions and lead ions.

[0011] In some embodiments, the wastewater in step (1) has a pH of 2-7. This pH range is designed to avoid co-reduction by other metal ions without inhibiting silver reduction, while simultaneously deprotonating the amine oxime group (–NH2 / =NO). - The electron density increases, improving the silver adsorption capacity while balancing high silver adsorption with low interference from impurities.

[0012] In some embodiments, in step (1), the amount of modification of the adsorbent containing the amylopyrime group on the surface is 19%-30%. This high modification amount significantly increases the lone pair electron density on the adsorbent surface, forming a strongly polarized complex of "electron-rich ligand-electron-deficient silver ion". This structure reduces the band gap (ΔE) of the complex to 0.8-1.2 eV (indirectly verified by XRD and XPS characterization), which is much lower than the 2.0 eV of the prior art. Electrons can spontaneously jump from the HOMO orbital of the amylopyrime group to the LUMO orbital of the silver ion without external energy drive, thus completing the reduction.

[0013] In some embodiments, in step (1), the adsorption treatment time is 20-30 h at a temperature of 15-40℃. At this temperature, the LMCT activation energy is satisfied, and silver is completely reduced. Within this adsorption time range, adsorption equilibrium is reached. If the adsorption time is too long, the adsorbed particles will agglomerate, the surface energy will increase, and the silver loss during desorption will be too large.

[0014] In some embodiments, the primary desorption solution in step (2) is any one of hydrochloric acid, sulfuric acid, or phosphoric acid, with a concentration of 0.1-2 mol / L. Within this range, impurity ions form coordinated anions, resulting in complete desorption. If the concentration is below 0.1 mol / L, Fe... 3+ / Cu 2+ Incomplete desorption leads to the co-dissolution of impurities during secondary desorption. If the concentration exceeds 2 mol / L, slight oxidation of the silver nanoparticle surface can increase silver loss during secondary desorption.

[0015] In some embodiments, in step (2), the solid-liquid ratio of the adsorbent to the primary desorption solution is 1g:200-2000mL.

[0016] In some embodiments, the desorption time in step (2) is 2-10 hours.

[0017] In some embodiments, the secondary desorption solution in step (3) is nitric acid with a concentration of 0.5-2 mol / L. Within this range, Ag is oxidized. 0 For Ag + It forms an AgNO3 complex ion, and the oxidation is complete.

[0018] In some embodiments, in step (3), the solid-liquid ratio of the adsorbent to the secondary desorption liquid is 1g:200-2000mL.

[0019] In some embodiments, the desorption time in step (3) is 2-10 hours.

[0020] The beneficial effects of this invention are as follows: 1. Existing research on amylopyramidized materials mainly focuses on their universal adsorption performance for heavy metal ions (such as copper, lead, and nickel), which are typically immobilized through the formation of amorphous surface complexes. While research has been conducted on silver ions, the coexistence of silver with other metals in the desorption solution remains a problem due to the lack of discovery or utilization of the aforementioned spontaneous reduction mechanism. This means that existing amylopyramidized materials may only utilize their coordination adsorption properties, without leveraging their unique reduction-purification coupling characteristics. However, the method of this invention uses amylopyramidized materials as adsorbents, utilizing their aforementioned spontaneous reduction mechanism to transform solvated hydrated silver ions in the aqueous phase into crystalline elemental nanoparticles without the need for an additional electric field or reducing reagent. This reduces reagent usage and energy consumption, and lowers environmental pollution.

[0021] 2. The two-step desorption strategy adopted in this invention is based on the chemical inertness of elemental silver in non-oxidizing acids. In the first desorption process, impurity ions are almost completely removed, while the elemental silver nanoparticles that have been reduced and fixed on the surface of the adsorbent exhibit extremely low leaching, which creates conditions for obtaining a high-purity silver solution with a purity greater than 99%.

[0022] 3. This invention can simultaneously purify water and precious metals, and has significant economic benefits for optimizing process routes in related fields.

[0023] 4. This invention is still based on a single adsorption method and does not introduce other water treatment or precious metal purification methods such as chemical precipitation, electrolysis and membrane separation. It can be directly adapted to existing adsorption process equipment.

[0024] 5. The present invention is simple and easy to implement, energy-saving and environmentally friendly, and low in cost. It is applicable to large-scale industrial production and application, and has significant economic and social value. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is the specific structure of the amine oxime group described in this invention.

[0027] Figure 2 This is a process flow diagram of the method for simultaneously removing harmful metals and separating and purifying precious silver from complex wastewater according to the present invention.

[0028] Figure 3The images shown are SEM images of the amylated polyacrylonitrile fibers before and after adsorption in Example 1.

[0029] Figure 4 The fine 3d spectrum of Ag after adsorption of silver ions in Example 1 of the present invention is shown.

[0030] Figure 5 The images show the XRD patterns of the amylated polyacrylonitrile fibers before and after adsorption in Example 1. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0032] The present invention will be further described below with reference to specific embodiments.

[0033] Example 1 This embodiment illustrates the basic adsorption performance of the amylopyridine-oxime-modified polyacrylonitrile fiber for silver ions described in this invention, and includes the following steps: (1) Dissolve 5g of hydroxylamine hydrochloride in 100mL of deionized water and adjust its pH to 7 with alkali. Immerse commercially available polyacrylonitrile fiber in the solution and heat it to 70℃ for reaction. The reaction time is 4h. After the reaction is completed, take out the fiber, wash it with water and dry it to obtain a amine-oxime-modified polyacrylonitrile fiber. The amount of amine-oxime group modification is 28% by the weight gain method.

[0034] (2) Weigh 0.02g of amine oxime-modified polyacrylonitrile fiber and add it to 50mL of simulated wastewater with a silver ion concentration of 20mg / L and pH=6.5. Adsorb at 25℃ for 24h.

[0035] (3) Take out the adsorbed amylopyridine polyacrylonitrile fiber, wash it with water, add it to 20 mL of 0.5 mol / L nitric acid, and desorb for 5 h.

[0036] Example 2 This embodiment illustrates the basic adsorption performance of the amylopyridine-oxime-modified polyacrylonitrile fiber for silver ions described in this invention, and includes the following steps: (1) Dissolve 3g of hydroxylamine hydrochloride in 100mL of deionized water and adjust its pH to 7 with alkali. Immerse commercially available polyacrylonitrile fiber in the solution and heat it to 75℃ for reaction. The reaction time is 4h. After the reaction is completed, take out the fiber, wash it with water and dry it to obtain a methylamine oxime-modified polyacrylonitrile fiber. The amount of methylamine oxime modification is 19.8% by the weight gain method.

[0037] (2) Weigh 0.02g of amine oxime-modified polyacrylonitrile fiber and add it to 50mL of simulated wastewater with a silver ion concentration of 20mg / L and pH=6.5. Adsorb at 25℃ for 24h.

[0038] (3) Take out the adsorbed amylopyridine polyacrylonitrile fiber, wash it with water, add it to 20 mL of 0.5 mol / L nitric acid, and desorb for 5 h.

[0039] Example 3 A method for the simultaneous removal, separation, and purification of precious metal silver and harmful metals from wastewater, comprising the following steps: (1) Weigh 0.02g of 28% modified amylated polyacrylonitrile fiber and add it to 50mL of simulated wastewater with a silver concentration of 100mg / L, an iron ion concentration of 100mg / L, and a pH of 2.0. Adsorb at 25℃ for 24h.

[0040] (2) Take out the adsorbed amylopyridine polyacrylonitrile fiber, wash it with water, add it to 20 mL of 0.5 mol / L hydrochloric acid, and desorb for 5 h.

[0041] (3) Take out the amylated polyacrylonitrile fiber after hydrochloric acid desorption, wash it with water, add it to 20 mL of 0.5 mol / L nitric acid, and desorb for 5 h.

[0042] Example 4 Simulated wastewater conditions: silver ions 100 mg / L, copper ions 100 mg / L, pH 3.0. The remaining steps are the same as in Example 3.

[0043] Example 5 Simulated wastewater conditions: silver ions 100 mg / L, lead ions 500 mg / L, pH 6.5. The remaining steps are the same as in Example 3.

[0044] Example 6 Simulated wastewater conditions: silver ions 100 mg / L, manganese ions 500 mg / L, pH 6.5. The remaining steps are the same as in Example 3.

[0045] Example 7 Weigh 0.02 g of 19.8% modified amylated polyacrylonitrile fiber and add it to 50 mL of simulated wastewater (silver ions 100 mg / L, nickel ions 500 mg / L, pH 6.5). Adsorption is carried out at 25 °C for 24 h. The first desorption uses 0.5 mol / L sulfuric acid, and the second desorption uses 0.5 mol / L nitric acid.

[0046] Comparative Example 1 The difference between this comparative example and Example 1 is that the adsorbent is unmodified commercially available polyacrylonitrile fiber.

[0047] Comparative Example 2 The difference between this comparative example and Example 3 is that the adsorbent is hydrolyzed polyacrylonitrile fiber (by immersing commercially available polyacrylonitrile fiber in a 2% sodium hydroxide solution and boiling it until the fiber color turns completely orange-red, then cooling it, taking it out, washing it with water and drying it, the hydrolyzed polyacrylonitrile fiber contains carboxyl groups).

[0048] Comparative Example 3 The difference between this comparative example and Example 3 is that the adsorbent is polyacrylonitrile fiber with a 4.7% amylopyridine modification amount (by immersing commercially available polyacrylonitrile fiber in a 2% hydroxylamine hydrochloride solution and heating it to 60°C for 2 hours, after which the fiber is removed, washed with water and dried to obtain a 5.7% amylopyridine modified polyacrylonitrile fiber).

[0049] Comparative Example 4 The difference between this comparative example and Example 3 is that the desorption solution was replaced with 0.5 mol / L disodium ethylenediaminetetraacetate.

[0050] Comparative Example 5 The difference between this comparative example and Example 3 is that stepwise desorption is not performed; instead, 0.5 mol / L nitric acid is used directly for desorption.

[0051] The concentration of metal ions in the solutions at different stages of the implementation of Examples 1-6 and Comparative Examples 1-4 was determined by ultraviolet-visible spectrophotometry. The adsorption amount, desorption rate and the mass fraction of silver in the final desorption solution were calculated by the following formulas. The results are shown in Table 1.

[0052]

[0053] In the formula, Q e —Adsorption capacity (mg / g); C e —Initial metal ion concentration (mg / L); C0 — the concentration of metal ions at adsorption equilibrium (mg / L). V — Solution volume (L); m — Adsorbent dosage (g).

[0054]

[0055] In the formula, R e —Desorption rate (%); C R —Concentration of metal ions in the desorption solution (mg / L); V R — Desorption volume (L).

[0056] In the formula, W Ag —Silver purity (%); m Ag —Silver content in the desorption solution (g); m M —Non-silver metal content in the desorption solution (g).

[0057] Table 1. Results of adsorption capacity, desorption rate, and silver mass fraction determination for Examples 1-5 and Comparative Examples 1-4

[0058] As can be seen from Table 1, under different competing ion conditions, the first desorption process of the present invention can remove impurity metals with a low silver desorption rate, thereby creating conditions for obtaining a high-purity silver solution through secondary desorption. The final silver content of the metal species is greater than 99%.

[0059] As can be seen from the results of Example 1 and Comparative Example 1, the amylopyridine adsorbent of the present invention has basic adsorption performance for silver ions due to the affinity between the amylopyridine group and silver ions. The silver adsorption capacity of the amylopyridine adsorbent is 42.96 mg / g, which is significantly higher than that of the unamyridine adsorbent.

[0060] As can be seen from the results of Example 3 and Comparative Example 2, compared with the amylated oxime adsorbent described in this invention, the hydrolyzed carboxylated adsorbent has significantly poor selectivity for silver and lacks effective reducing ability to effectively fix silver in a single desorption process, resulting in a silver purity of only 85.29% in the final product.

[0061] The results of Examples 3, 7 and Comparative Example 3 show that although the purity of silver in the final product obtained by using an adsorbent with a 4.7% amylopectin modification can reach a high level, the silver ions are difficult to completely reduce due to the low functional group density in the adsorbent. Most of them still exist in the form of complex ions, which makes it impossible to effectively fix silver in one desorption process.

[0062] The results of Examples 3 and 7 and Comparative Example 4 show that, compared to the non-oxidizing acid described in this invention as a primary desorption solvent, the complexing agent lacks effective desorption. After desorption, most of the impurity metals remain on the adsorbent, resulting in a silver purity of only 18.01% in the final product. As can be seen from the results of Example 3 and Comparative Example 5, compared with the two-step desorption process described in this invention, directly using the effective desorption solution for silver results in silver and impurity metals being desorbed into the solution together, resulting in the purity of silver in the final product being only 71.27%.

[0063] Figure 3 The XRD patterns of Example 1 of the present invention before and after silver ion adsorption are shown. Figure 3 It can be seen that the amylopyridine adsorbent described in this invention can reduce silver ions from +1 to 0 valence while adsorbing them. The valence state of silver gives it inertness in non-oxidizing acids, creating conditions for the removal of impurity metals.

[0064] Figure 4 This paper presents a fine 3d spectra of Ag after silver ion adsorption in Example 1 of the present invention. Figure 4 It can be seen that the double peaks of the Ag 3d orbital are sharp and symmetrical, and its binding energy is in a low oxidation state, indicating that the adsorbed silver ions are converted to 0 valence and the consistency of valence state.

[0065] Figure 5 The image shows SEM images of Example 1 of the present invention before and after silver ion adsorption. Figure 4 As can be seen, the amylopyridine adsorbent of the present invention essentially transforms silver ions into silver nanoparticles during the reduction of silver ions to elemental form and loads them onto the surface of the adsorbent, thereby ensuring low silver loss during the removal of impurities.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for the simultaneous removal and separation purification of precious metal silver and harmful metals from wastewater, characterized in that, Includes the following steps: (1) Add an adsorbent containing a amine oxime group on its surface to the wastewater for adsorption treatment; (2) Add the adsorbent after adsorption to the primary desorption solution of a non-oxidizing acid to perform the first desorption and remove impurity ions other than silver; (3) Add the adsorbent after the first desorption to the secondary desorption solution of the oxidizing acid for a second desorption to obtain a high-purity silver solution.

2. The method for simultaneous removal and separation purification of precious metal silver and harmful metals in wastewater according to claim 1, characterized in that, The adsorbent in step (1) is polyacrylonitrile fiber with a surface modified with a amine oxime group.

3. The method for simultaneous removal and separation purification of precious metal silver and harmful metals in wastewater according to claim 1 or 2, characterized in that, The wastewater in step (1) contains one or more of the following: silver ions, iron ions, copper ions, and lead ions.

4. The method for simultaneous removal and separation purification of precious metal silver and harmful metals in wastewater according to claim 3, characterized in that, The wastewater in step (1) has a pH of 2-7.

5. The method for simultaneous removal and separation purification of precious metal silver and harmful metals in wastewater according to claim 1, characterized in that, In step (1), the amount of modification of the adsorbent containing the amygdoxime group on the surface is 19%-30%.

6. The method for simultaneous removal and separation purification of precious metal silver and harmful metals in wastewater according to claim 5, characterized in that, In step (1), the adsorption treatment time is 20-30h under the condition of 15-40℃.

7. The method for simultaneous removal and separation purification of precious metal silver and harmful metals in wastewater according to claim 1, characterized in that, The primary desorption solution in step (2) is any one of hydrochloric acid, sulfuric acid, or phosphoric acid, with a concentration of 0.1-2 mol / L; the solid-liquid ratio of the adsorbent to the primary desorption solution is 1 g: 200-2000 mL.

8. The method for simultaneous removal and separation purification of precious metal silver and harmful metals in wastewater according to claim 7, characterized in that, The desorption time in step (2) is 2-10 hours.

9. The method for simultaneous removal and separation purification of precious metal silver and harmful metals in wastewater according to claim 1, characterized in that, The secondary desorption solution in step (3) is nitric acid with a concentration of 0.5-2 mol / L; the solid-liquid ratio of the adsorbent to the secondary desorption solution is 1 g: 200-2000 mL.

10. The method for simultaneous removal and separation purification of precious metal silver and harmful metals in wastewater according to claim 9, characterized in that, The desorption time in step (3) is 2-10 hours.

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