A method for treating chromium-containing wastewater and its application in preparing electromagnetic shielding leather

Abstract

This invention discloses a method for treating chromium-containing wastewater and its application in the preparation of electromagnetic shielding leather. The method utilizes a Fenton-like reaction with nano-zero-valent iron as a catalyst to destroy the difficult-to-remove chromium complex structure in the chromium-containing wastewater. Simultaneously, magnesium ions are added to prepare a magnesium-chromium-iron ternary hydrotalcite nanomaterial with tanning properties. This material is used as a tanning agent in the leather tanning process, imparting electromagnetic shielding properties to the finished leather. Furthermore, the electromagnetic shielding leather prepared by this invention meets the performance requirements of leather, exhibiting good physical and mechanical properties, good resistance to hot air aging and ultraviolet light aging, and high folding resistance. As a wearable electromagnetic shielding leather, it provides 18 dB electromagnetic shielding performance in the 8–12 GHz electromagnetic wave range while retaining the softness of leather. This invention provides a pathway for the treatment of chromium-containing wastewater and the preparation of electromagnetic shielding leather.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and relates to a method for treating chromium-containing wastewater and its application in the preparation of electromagnetic shielding leather. Background Technology

[0002] Chromium in chromium-containing wastewater mainly comes from industries such as electroplating, leather making, chemicals, pigments, metallurgy, and refractory materials. Trivalent chromium in chromium-containing wastewater poses relatively little harm to human health and the environment, but its large presence in wastewater can still cause environmental pollution and resource waste.

[0003] With the development of electronic information technology, the use of numerous new electronic and electrical devices has inevitably led to electromagnetic radiation pollution. Studies have shown that prolonged exposure to radiation from electronic devices can cause sub-health symptoms such as neurasthenia, dizziness, and forgetfulness. In response, various materials with electromagnetic shielding properties have emerged.

[0004] Electromagnetic shielding is a technology that eliminates electromagnetic interference by cutting off the propagation path of electromagnetic waves. Existing technologies for preparing electromagnetically shielded leather typically involve coating the leather surface with a conductive coating. Patent CN105219895A discloses a type of leather with electromagnetic shielding properties and its preparation method. After spraying a film-forming agent onto the leather surface, nano-metal powders (silver, copper, silver-coated copper, iron(III) oxide, nickel, and zinc) are dispersed in a non-reactive neutral solvent to obtain a dispersion. This dispersion is then sprayed onto the leather surface, dried, and followed by another layer of film-forming agent. After drying, natural leather with electromagnetic shielding properties is obtained.

[0005] However, existing technologies for preparing natural leather with electromagnetic shielding properties suffer from limitations in terms of flexibility. Excessive bending can damage the electromagnetic shielding coating, restricting its application in smart wearable materials. Furthermore, current technologies do not integrate the treatment of chromium-containing wastewater with the preparation of electromagnetic shielding materials. Therefore, providing a method for treating chromium-containing wastewater while simultaneously developing electromagnetic shielding leather with good flexibility is of great significance. Summary of the Invention

[0006] To address the issue of limited flexibility in existing electromagnetic shielding leather, this invention provides a method for treating chromium-containing wastewater and its application in the preparation of electromagnetic shielding leather. It utilizes nano-zero-valent iron as a catalyst for a Fenton-like reaction in the chromium-containing wastewater. A co-precipitation method is employed to control the molar ratio of iron to chromium ions, resulting in the preparation of ternary hydrotalcite nanomaterials. These nanomaterials are then used as tanning agents in a tanning process to form multi-point cross-links with leather collagen fibers, thereby obtaining electromagnetic shielding leather. This invention provides a pathway for the treatment of chromium-containing wastewater and the preparation of electromagnetic shielding leather.

[0007] To achieve the technical objective of this invention, on one hand, this invention provides a method for treating chromium-containing wastewater, comprising adding magnesium ions and nano-zero-valent iron to the chromium-containing wastewater to obtain a mixed salt solution, adding sodium carbonate solution to the mixed salt solution, adjusting the pH to 10.0-13.0, heating in a water bath to 60-90°C, crystallizing for 4-12 hours, filtering the crystals, and the filtrate being the treated wastewater.

[0008] Furthermore, in the method for treating chromium-containing wastewater provided by this invention, the chromium-containing wastewater is one of chromium tanning wastewater or chromium-containing retanning and dyeing wastewater. The Mg content in the mixed salt solution is calculated as a molar ratio. 2+ :Fe 0 :Cr 3+ The ratio of sodium carbonate to magnesium ions is 2:1:0.8 to 2, and the ratio of sodium carbonate to magnesium ions is 1:1 to 2.

[0009] On the other hand, the present invention provides a tanning agent, which is obtained by drying crystals after treating chromium-containing wastewater as described above. The preparation of the tanning agent also includes washing the crystals obtained after treating the chromium-containing wastewater with deionized water until the pH of the washing solution is neutral, and drying them at 40-60°C for 6-8 hours to obtain the tanning agent. The tanning agent is specifically a magnesium chromium iron ternary hydrotalcite (MgCrFe-LDH) nanomaterial.

[0010] On the other hand, the present invention seeks protection for the application of the above-mentioned method for treating chromium-containing wastewater in the preparation of tanning agents.

[0011] On the other hand, the present invention provides an electromagnetic shielding leather, which uses tanned leather as raw material. The tanned leather is placed in a drum, and water, salt, and formic acid are added. The pH in the drum is controlled at 2.5, and the drum is rotated for 30 minutes for acid immersion treatment. Then, tanning agent is added, and the drum is rotated for 120 minutes. Baking soda is added to adjust the pH to 3.5, and the drum is rotated for 30 minutes. After that, the drum is stopped and left overnight to obtain electromagnetic shielding leather.

[0012] Furthermore, in the electromagnetic shielding leather provided by this invention, the amount of water added is 200% of the leather tannin, the amount of salt added is 7% of the leather tannin, and the amount of formic acid added is 1% of the leather tannin. The concentration of formic acid is 1%, and the leather is selected from sheepskin and cowhide. The amount of tanning agent added, by mass percentage, is 5% to 10% of the leather tannin; preferably, the amount of tanning agent added, by mass percentage, is 9% of the leather tannin.

[0013] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0014] This invention utilizes a Fenton-like reaction with nano-zero-valent iron as a catalyst to disrupt the difficult-to-remove chromium complex structure in chromium-containing wastewater, thus fully treating the wastewater and reducing factory wastewater treatment costs. Simultaneously, the treated chromium-containing wastewater is used to prepare a ternary hydrotalcite nano-tanning agent with tanning properties, effectively utilizing chromium resources and reducing waste.

[0015] This invention utilizes chromium-containing wastewater to prepare a magnesium-chromium-iron ternary hydrotalcite nano-tanning agent. This not only increases the shrinkage temperature of the finished leather to ≥90℃, but also enhances its tensile strength and tear strength. Furthermore, the magnesium-chromium-iron ternary hydrotalcite nano-tanning agent imparts electromagnetic shielding properties to the leather during tanning, effectively meeting the leather market's demand for functional and intelligent chrome-tanned leather. The tanned leather achieves an electromagnetic shielding effect of 18dB against 8–12GHz electromagnetic waves, satisfying both market demands and the concept of intelligent leather production. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention.

[0017] Figure 1 The graph shows the electromagnetic shielding performance of electromagnetically shielded leathers with different amounts of MgCrFe-LDH tanning agent at 8.2 GHz.

[0018] Figure 2 This is a diagram illustrating the electromagnetic shielding performance of electromagnetic shielding leather. Detailed Implementation

[0019] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially.

[0020] Example 1

[0021] This embodiment provides a method for preparing hydrotalcite nano-tanning agents and obtaining electromagnetically shielded leather using chromium-containing wastewater, specifically including the following steps:

[0022] S1: Take 100 mL of filtered chromium tanning waste liquid (Cr2O3 is 0.1 mol / L), add 5.13 g magnesium nitrate hexahydrate and 0.56 g nano zero-valent iron (purchased from Nangong Xindun Alloy Welding Material Spraying Co., Ltd.), stir at 50℃ for 15 min to prepare a mixed salt solution.

[0023] S2: Weigh 2.12g of sodium carbonate and dissolve it in 100mL of deionized water to obtain an alkaline solution.

[0024] S3: Add the mixed salt solution to the alkaline solution at a dropping rate of 30s / drop, while stirring at high speed during the process.

[0025] S4: After the addition is complete, adjust the pH of the solution to 10.0 with 1 mol / L NaOH solution, heat in a water bath to 80℃, and crystallize for 6 hours.

[0026] S5: Filter the crystallized liquid from S4, wash with deionized water until the pH of the filtrate is neutral, and dry the filtered solid in a 60℃ constant temperature drying oven for 6 hours to obtain magnesium chromium iron ternary hydrotalcite, which is then ground for later use.

[0027] S6: Place 25g of goatskin in a rotating drum, add 50g of water, 1.75g ​​of salt, and 0.25g of formic acid. Add the formic acid in small amounts several times to control the pH in the drum at 2.5. Rotate for 30 minutes to perform acid soaking treatment. To reduce experimental errors caused by long-term storage of the goatskin, the goatskin is subjected to acid soaking treatment.

[0028] S7: Use magnesium-chromium-iron ternary hydrotalcite as a tanning agent. Take 2.25g and add it to the drum containing goatskin after S6 pickling treatment. After rotating for 120 minutes, add small amounts of baking soda several times to adjust the pH to 3.5. Rotate for 10 minutes after each addition of baking soda to ensure uniform mixing. After adjusting the pH, rotate for another 90 minutes and then stop the drum overnight to obtain electromagnetic shielding leather.

[0029] The chromium ion content in the chromium-containing wastewater before and after treatment in this embodiment is shown in Table 1.

[0030] Example 2

[0031] This embodiment provides a method for preparing hydrotalcite nano-tanning agents and obtaining electromagnetically shielded leather using chromium-containing wastewater, specifically including the following steps:

[0032] S1: Measure 250 mL of filtered chromium tanning waste liquid (Cr2O3 is 0.06 mol / L), add 7.69 g magnesium nitrate hexahydrate and 0.84 g nano zero-valent iron, stir at 50℃ for 15 min to prepare a mixed salt solution.

[0033] S2: Weigh 3.18g of sodium carbonate and dissolve it in 100mL of deionized water to obtain an alkaline solution.

[0034] S3: Add the mixed salt solution to the alkaline solution at a dropping rate of 30s / drop, while stirring at high speed during the process.

[0035] S4: After the addition is complete, adjust the pH of the solution to 10.0 with 1 mol / L NaOH solution, heat in a water bath to 60℃, and crystallize for 12 hours.

[0036] S5: Filter the crystallized liquid from S4, wash with deionized water until the pH of the filtrate is neutral, and dry the filtered solid in a 40℃ constant temperature drying oven for 8 hours to obtain magnesium chromium iron ternary hydrotalcite, which is then ground for later use.

[0037] S6: Place 50g of goatskin in a rotating drum, add 100g of water, 3.5g of salt, and 0.5g of formic acid. Add the formic acid in small amounts several times to control the pH in the drum at 2.5. Rotate for 30 minutes to perform acid immersion treatment. To reduce experimental errors caused by long-term storage of the goatskin, the goatskin is subjected to acid immersion treatment.

[0038] S7: Use magnesium-chromium-iron ternary hydrotalcite as a tanning agent. Take 4.5g and add it to the drum containing goatskin after S6 pickling treatment. After rotating for 120 minutes, add small amounts of baking soda several times to adjust the pH to 3.5. Rotate for 10 minutes after each addition of baking soda to ensure uniform mixing. After adjusting the pH, rotate for another 90 minutes and then stop the drum overnight to obtain electromagnetic shielding leather.

[0039] The chromium ion content in the chromium-containing wastewater before and after treatment in this embodiment is shown in Table 1.

[0040] Example 3

[0041] This embodiment provides a method for preparing hydrotalcite nano-tanning agents and obtaining electromagnetically shielded leather using chromium-containing wastewater, specifically including the following steps:

[0042] S1: Measure 160 mL of filtered chromium tanning waste liquid (Cr2O3 is 0.1 mol / L), add 20.51 g magnesium nitrate hexahydrate and 2.24 g nano zero-valent iron, stir at 50℃ for 15 min to prepare a mixed salt solution.

[0043] S2: Weigh 8.48g of sodium carbonate and dissolve it in 100mL of deionized water to obtain an alkaline solution.

[0044] S3: Add the mixed salt solution to the alkaline solution at a dropping rate of 30s / drop, while stirring at high speed during the process.

[0045] S4: After the addition is complete, adjust the pH of the solution to 10.0 with 1 mol / L NaOH solution, heat in a water bath to 70℃, and crystallize for 8 hours.

[0046] S5: Filter the crystallized liquid from S4, wash with deionized water until the pH of the filtrate is neutral, and dry the filtered solid in a 50℃ constant temperature drying oven for 7 hours to obtain magnesium chromium iron ternary hydrotalcite, which is then ground for later use.

[0047] S6: Place 50g of goatskin in a rotating drum, add 100g of water, 3.5g of salt, and 0.5g of formic acid. Add the formic acid in small amounts several times to control the pH in the drum at 2.5. Rotate for 30 minutes to perform acid immersion treatment. To reduce experimental errors caused by long-term storage of the goatskin, the goatskin is subjected to acid immersion treatment.

[0048] S7: Use magnesium-chromium-iron ternary hydrotalcite as a tanning agent. Take 4.5g and add it to the drum containing goatskin after S6 pickling treatment. After rotating for 120 minutes, add small amounts of baking soda several times to adjust the pH to 3.5. Rotate for 10 minutes after each addition of baking soda to ensure uniform mixing. After adjusting the pH, rotate for another 90 minutes and then stop the drum overnight to obtain electromagnetic shielding leather.

[0049] The chromium ion content in the chromium-containing wastewater before and after treatment in this embodiment is shown in Table 1.

[0050] Example 4

[0051] This embodiment provides a method for preparing hydrotalcite nano-tanning agents and obtaining electromagnetically shielded leather using chromium-containing wastewater, specifically including the following steps:

[0052] S1: Take 400 mL of the filtered retanning and dyeing chromium-containing waste liquid (Cr2O3 is 0.05 mol / L), add 20.51 g of magnesium nitrate hexahydrate and 2.24 g of nano zero-valent iron, stir at 50℃ for 15 min, and prepare a mixed salt solution.

[0053] S2: Weigh 4.24g of sodium carbonate and dissolve it in 100mL of deionized water to obtain an alkaline solution.

[0054] S3: Add the mixed salt solution to the alkaline solution at a dropping rate of 30s / drop, while stirring at high speed during the process.

[0055] S4: After the addition is complete, adjust the pH of the solution to 13.0 with 1 mol / L NaOH solution, heat in a water bath to 90℃, and crystallize for 4 hours.

[0056] S5: Filter the crystallized liquid from S4, wash with deionized water until the pH of the filtrate is neutral, and dry the filtered solid in a 60℃ constant temperature drying oven for 6 hours to obtain magnesium chromium iron ternary hydrotalcite, which is then ground for later use.

[0057] S6: Place 30g of cowhide in a rotating drum, add 60g of water, 2.1g of salt, and 0.3g of formic acid. Add the formic acid in small amounts several times to control the pH in the drum to 2.5. Rotate for 30 minutes to perform acid soaking treatment. To reduce experimental errors caused by long-term storage of the cowhide, the cowhide is subjected to acid soaking treatment.

[0058] S7: Use magnesium-chromium-iron ternary hydrotalcite as a tanning agent. Take 2.7g and add it to the drum containing cowhide after S6 acid treatment. After rotating for 120 minutes, add small amounts of baking soda several times to adjust the pH to 3.5. Rotate for 10 minutes after each addition of baking soda to ensure uniform mixing. After adjusting the pH, rotate for another 90 minutes and then stop the drum overnight to obtain electromagnetic shielding leather.

[0059] The chromium ion content in the chromium-containing wastewater before and after treatment in this embodiment is shown in Table 1.

[0060] Table 1: Chromium ion content before and after treatment of chromium-containing wastewater

[0061]

[0062]

[0063] As shown in Table 1, after treatment by the chromium-containing wastewater treatment method provided by this invention, the Cr content in the chromium-containing wastewater is reduced. 3+ The method achieves good recovery of chromium in chromium-containing wastewater. 3+ The recovery rate reaches 98% to 99%.

[0064] Example 5

[0065] This embodiment provides the performance testing of the electromagnetic shielding leather prepared in Examples 1-4, specifically including the following steps:

[0066] 1. Determination of the physical properties of electromagnetic shielding leather

[0067] The electromagnetic shielding leathers prepared in Examples 1-4 were subjected to tanning effect tests (shrinkage temperature of the raw leather after tanning) (refer to QB / T 3812.8-1999), tear resistance tests (refer to QB / T2711-2005), and aging resistance tests (refer to ASTM G154). The test results are shown in Table 1.

[0068] Table 1: Performance Test Results of Electromagnetic Shielding Leather

[0069] Shrinkage temperature of tanned raw leather (°C) Tear force (N) Tear strength (N) after aging Sour skin 40 42 30 Example 1 93 82 66 Example 2 90 80 69 Example 3 95 83 70 Example 4 90 81 68

[0070] As shown in Table 2, the shrinkage temperature of the tanned leather produced by the tanning agent (MgFeCr-LDH) provided by this invention is greater than 90℃, which is significantly higher than that of untanned sourdough. This indicates that the MgFeCr-LDH nano-tanning agent can be used as a leather tanning agent with good tanning effect. The leather tanned with the tanning agent provided by this invention has a maximum tear strength of 83N, which is superior to untanned sourdough in terms of tensile strength and tear strength, exhibiting better physical and mechanical properties. Tear strength tests after aging show that the electromagnetic shielding leather prepared by this invention has good resistance to hot air aging and ultraviolet light aging, extending the service life of the finished leather. Even after aging, it still possesses good physical and mechanical properties. The above tests demonstrate that the electromagnetic shielding leather prepared by this invention meets the performance requirements of leather and can be used as a raw material for clothing and daily necessities.

[0071] 2. Electromagnetic shielding performance test of electromagnetic shielding leather

[0072] The electromagnetic shielding performance of the electromagnetic shielding leathers prepared in Examples 1-4 was tested using a vector network analyzer. The test results are as follows: Figure 1 and Figure 2 As shown.

[0073] Depend on Figure 1 and Figure 2 It is known that untanned leather has virtually no electromagnetic shielding effect. However, after tanning with the tanning agent (MgFeCr-LDH) provided by this invention, the increased cross-linking degree of collagen fibers in the leather leads to increased electron transport efficiency and electromagnetic wave reflection, giving the finished leather electromagnetic shielding properties. Leather tanned with 9% of the tanning agent exhibits an optimal electromagnetic shielding effect of 18 dB, and the tanned leather can achieve an electromagnetic shielding effect exceeding 15 dB against electromagnetic waves of 8–12 GHz.

[0074] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for treating chromium-containing wastewater, characterized by, The method comprises adding magnesium ions and nano zero-valent iron into chromium-containing wastewater to obtain a mixed salt solution, adding an alkali solution into the mixed salt solution, adjusting pH and heating for crystallization, and filtering the crystals to obtain treated wastewater; The ratio of Mg 2+ :Fe 0 :Cr 3+ in the mixed salt solution is 2:1:0.8~2 in terms of molar ratio. The alkali reagent in the alkali solution is sodium carbonate; The ratio of the sodium carbonate to the magnesium ions is 1:1-2 in terms of molar ratio; The pH is 10.0-13.0; The temperature for heating for crystallization is 60-90 ℃, and the time for heating for crystallization is 4-12 h.

2. The method of treating chromium-containing wastewater according to claim 1, characterized in that, The chromium-containing wastewater is one of chromium tanning wastewater and chromium-containing wastewater in dyeing and retanning.

3. A tanning agent, characterized by, The method for preparing the tanning agent comprises drying the crystals.

4. The tanning agent according to claim 3, characterized in that, The tanning agent is magnesium-chromium-iron ternary hydrotalcite nanomaterials; The crystals need to be washed to neutral pH before drying; The drying temperature is 40-60 ℃, and the drying time is 6-8 h.

5. Use of the method for treating chromium-containing wastewater according to any one of claims 1-2 in the preparation of a tanning agent.

6. An electromagnetic shielding leather, characterized by The electromagnetic shielding leather is prepared by tanning a leather crust; The leather crust is put into a rotating drum, water, salt and formic acid are added, the pH in the rotating drum is controlled to be 2.5, and the leather crust is rotated for 30 min to perform acid dipping treatment; The amount of the water added is 200% of the leather crust, the amount of the salt added is 7% of the leather crust, and the amount of the formic acid added is 1% of the leather crust; The concentration of the formic acid is 1%; The leather is selected from one of sheepskin and cowhide; The tanning agent used in the tanning is the tanning agent according to any one of claims 3-4; The tanning comprises: rotating the leather crust in the rotating drum for 120 min after adding the tanning agent, then adding baking soda to adjust the pH to 3.5, rotating the leather crust in the rotating drum for 30 min, and then stopping the rotation and leaving overnight; The amount of the tanning agent added is 5%-10% of the leather crust in terms of mass percentage.

7. The electromagnetic shielding leather according to claim 6, characterized in that, The amount of the tanning agent added is 9% of the leather crust in terms of mass percentage.

8. Use of the electromagnetic shielding leather according to claim 6 in the preparation of electromagnetic shielding performance leather.

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