A method for recovering metallic silver from printing films and fixing solutions

Abstract

The present invention discloses a method for recovering metallic silver from printed films and fixing solutions. The method comprises the following steps: crushing the waste films used for film printing and mixing them with waste fixing solutions, adding a pH regulator until the pH value of the solution is less than 4.0; adding hydrogen peroxide to the above solution, stirring for a period of time, adding MXene material, fully stirring, centrifuging the above solution at high speed, pouring off the supernatant, and obtaining a precipitate enriched with metallic silver. In the present invention, the MXene material has excellent adsorption affinity and reducibility for silver ions, converts the silver ions in the waste printed films and waste fixing solutions into metallic silver, and realizes the recycling of metallic silver. The use of MXene material can simply, conveniently and quickly recover metallic silver from waste printed films and fixing solutions.

Description

Technical Field

[0001] The present invention belongs to the field of recycling of waste resources, and particularly relates to a method for recovering metallic silver from printing films and fixing solutions. Background Art

[0002] Silver is a precious metal. Due to the limited reserves and output of its mineral resources, it is expensive. According to statistics, the consumption of silver in the world is mainly used for the production of photographic materials. During the use of the photographic materials, after imaging through developing, fixing, etc., the silver attached to the film exists as elemental silver in the emulsion layer, generally containing 0.5% - 1.2% silver, and most of the remaining silver enters the fixing solution and exists in the form of silver dithiosulfate complex ions with a mass concentration of 2 - 10 g / L. Therefore, if waste fixing solutions and waste printing films are not treated, they will not only pollute the environment but also cause waste of secondary resources.

[0003] Currently, the main recovery methods for metallic silver in waste fixing solutions are chemical precipitation method and electrolysis method. The electrolysis method has high efficiency and large processing capacity, and can directly produce silver powder, which is suitable for large-scale photo-processing factories or workshops for centralized treatment of waste fixing solutions. However, it has high power consumption and extremely high requirements for the purity of the electrodes. The advantages of the chemical precipitation method are simple and convenient, fast reaction speed, low cost, and the poor solution after treatment has low silver content and high total recovery rate. The main methods for recovering silver from waste films are incineration method, chemical treatment method, and biological treatment method. Although the incineration method is simple and has a large processing capacity, silver is easily carried away by soot during incineration, resulting in low recovery rate. At the same time, the valuable film base is also burned, wasting resources. The biological treatment method has harsh process and difficult operation. Compared with other methods, the chemical treatment method can treat waste fixing solutions and waste films simultaneously, is simple and convenient, has a fast reaction speed, simple operation, and is conducive to the recovery of metallic silver.

[0004] Selecting appropriate chemical reagents is the key factor for recovering metallic silver from waste printing films and waste fixing solutions. Therefore, when recovering metallic silver from waste films and waste fixing solutions, it is necessary to select appropriate reducing materials, which are required to have excellent adsorption affinity and reducibility for silver ions. Two-dimensional transition metal material MXene has unique self-adsorption and reduction capabilities for metal ions and is often used in the research and development of conductive materials and sensors. Summary of the Invention

[0005] In order to further improve the treatment efficiency and recovery rate of silver recovery from waste fixing solutions, the present invention provides a method for recovering metallic silver from film printing fixing solutions. The purpose of the present invention is to provide a method for simply and quickly recovering metallic silver from waste fixing solutions for treating waste fixing solutions and waste films generated during the use of photographic materials.

[0006] The object of the present invention is achieved as follows. In the method for recovering metallic silver from a film printing fixing solution, waste films used in film printing are crushed and mixed with waste fixing solution, a pH regulator is added until the pH value of the solution is less than 4.0, and then a hydrogen peroxide solution is added to the solution, followed by stirring and reacting for a certain period of time. To the solution obtained above, an MXene material is added, after stirring and reacting for a period of time, the above solution is centrifuged at high speed, and the supernatant is poured off to obtain a precipitate enriched with metallic silver.

[0007] Further, the pH regulator is one or more of nitric acid, hydrofluoric acid, perchloric acid, citric acid, oxalic acid, and acetic acid.

[0008] Further, the mass ratio of the hydrogen peroxide solution to the solution obtained in step (1) is 1% - 5%, the concentration of the hydrogen peroxide solution is 30%, and the stirring and reaction time is 10 - 120 min.

[0009] Further, the MXene is a layered material of metal carbide or nitride prepared by etching the intermediate layer atoms in MAX ceramics, specifically obtained by etching the intermediate layer atoms of MAX ceramics with a hydrofluoric acid solution. MAX is a ceramic material with the molecular formula Mn + 1 AXn, where n = 1, 2, 3. Among them, M is mainly early transition metal elements, including but not limited to Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta; A is group III and IV main group elements, including but not limited to Al, P, S, Ge, As, Cd, In, Sn, Tl, and Pb; X is C and / or N elements. Preferably, M is Ti or Nb, and A is Al.

[0010] Further, the amount of MXene added is 10 - 100 mg / L, and the stirring and reaction time is 10 - 120 min.

[0011] The beneficial effect of the present invention is that the present invention recovers metallic silver from waste film printing and waste fixing solution by using the excellent adsorption affinity and reducibility of the MXene material for silver ions. MXene has a unique self-adsorption and reduction ability for metal ions, and can simply, conveniently, and quickly achieve the recovery of metallic silver. It has excellent performance in recovering metallic silver from waste film printing and waste fixing solution. Specific Embodiments

[0012] The following examples are used to further illustrate the present invention, but the present invention is not limited in any way. Any transformation or substitution based on the teachings of the present invention belongs to the protection scope of the present invention.

[0013] In the following examples, the test methods are all conventional methods unless otherwise specified; the reagents and materials can all be obtained from commercial channels unless otherwise specified.

[0014] Example 1

[0015] 50 g of waste color film containing 1.012% silver (total silver content of 0.5060 g) was crushed and mixed with 100 ml of waste fixing solution (silver content of 8.59 g / L) in a 250 mL beaker. 1 mol / L phosphoric acid solution was added to adjust the pH value to 3.5, and then 14 mL of 30% H2O2 solution was slowly added to the solution. A magnetic stirrer was used to stir evenly for 30 min. 5 mg of Ti2AlN powder was added to the above solution, and stirring continued for 30 min. The obtained solution was centrifuged at high speed, and the supernatant was poured off to obtain 1.540 g of a precipitate enriched with metallic silver, with a silver content of 1.350 g and a recovery rate of 87.66%.

[0016] Example 2

[0017] 50 g of waste color film containing 0.972% silver (total silver content of 0.4860 g) was crushed and mixed with 100 ml of waste fixing solution (silver content of 8.90 g / L) in a 250 mL beaker. 1 mol / L oxalic acid solution was added to adjust the solution pH value to 3.9, and then 35 mL of 30% H2O2 solution was slowly added to the solution. A magnetic stirrer was used to stir evenly for 45 min. 7 mg of Ti3C2 powder was added to the above solution, and stirring continued for 45 min. The obtained solution was centrifuged at high speed, and the supernatant was poured off to obtain 1.531 g of a precipitate enriched with metallic silver, with a silver content of 1.356 g and a recovery rate of 88.63%.

[0018] Example 3

[0019] 50 g of waste color film containing 0.972% silver (total silver content of 0.4860 g) was crushed and mixed with 100 ml of waste fixing solution (silver content of 8.90 g / L) in a 250 mL beaker. 1 mol / L perchloric acid solution was added to adjust the solution pH value to 3.0, and then 50 mL of 30% H2O2 solution was slowly added to the solution. A magnetic stirrer was used to stir evenly for 45 min. 8 mg of Mo2C powder was added to the above solution, and stirring continued for 50 min. The obtained solution was centrifuged at high speed, and the supernatant was poured off to obtain 1.530 g of a precipitate enriched with metallic silver, with a silver content of 1.376 g and a recovery rate of 89.93%.

[0020] Example 4

[0021] 50 g of waste color film with a silver content of 1.112% (total silver content of 0.5560 g) was crushed and mixed with 100 ml of waste fixing solution (silver content of 8.59 g / L) in a 250 mL beaker. A 1 mol / L citric acid solution was added to adjust the pH value to 3.2, and then 65 mL of 30% H2O2 solution was slowly added to the solution. The mixture was stirred evenly with a magnetic stirrer for 30 min. 9 mg of Nb2C powder was added to the above solution, and stirring continued for 60 min. The resulting solution was centrifuged at high speed, and the supernatant was poured off to obtain 1.539 g of a precipitate enriched in metallic silver, with a silver content of 1.415 g and a recovery rate of 91.94%.

[0022] Example 5

[0023] 50 g of waste color film with a silver content of 1.241% (total silver content of 0.6205 g) was crushed and mixed with 100 ml of waste fixing solution (silver content of 7.92 g / L) in a 250 mL beaker. 1 mol / L hydrofluoric acid was added to adjust the pH value of the solution to less than 4.0, and then 70 mL of 30% H2O2 solution was slowly added to the solution. The mixture was stirred evenly with a magnetic stirrer for 45 min. 10 mg of V2C powder was added to the above solution, and stirring continued for 90 min. The resulting solution was centrifuged at high speed, and the supernatant was poured off to obtain 1.502 g of a precipitate enriched in metallic silver, with a silver content of 1.4125 g and a recovery rate of 94.04%.

Claims

1. A method for recovering metallic silver from photographic film and fixing bath, characterized in that The following steps are involved: (1) Crushing waste film used in film printing and mixing it with waste fixing solution, adding pH regulator until the pH value of the solution is less than 4.0; (2) adding hydrogen peroxide solution to the solution obtained in step (1) and stirring thoroughly; the mass ratio of hydrogen peroxide solution to the solution obtained in step (1) is 1%-5%, the concentration of the hydrogen peroxide solution is 30%, and the stirring reaction time is 10-120 min; (3) Add MXene material to the solution obtained in step (2), stir and react for a period of time, then centrifuge the solution at high speed, discard the supernatant, and obtain a precipitate enriched in metallic silver.

2. The method according to claim 1, wherein: The pH regulator is one or more of nitric acid, hydrofluoric acid, perchloric acid, citric acid, oxalic acid, and acetic acid.

3. The method according to claim 1, wherein: The MXene is a metal carbide or nitride layered material obtained by etching the middle layer atoms in MAX ceramics, specifically by etching the middle layer atoms of MAX ceramics using a hydrofluoric acid solution.

4. The method according to claim 1, wherein: The amount of MXene added is 10-100 mg / L, and the stirring reaction time is 10-120 min.

5. The method according to claim 1, wherein: The metallic silver in the collected precipitate exists in the form of elemental silver.