Determination of the concentration of complexed chromium with different charge properties in tannery wastewater

Abstract

The present invention belongs to the technical field of tanning wastewater treatment, and discloses a method for determining the concentration of complexed chromium with different charge properties in tanning wastewater. The present invention addresses the problems of complex testing in the prior art and inaccurate determination of organic complexes of different molecular sizes containing chromium in tanning wastewater. The present invention uses a compounded anionic precipitant and a compounded cationic precipitant to precipitate anionic chromium complexes and cationic chromium complexes, respectively, and measures the chromium in the precipitates to obtain the concentrations of anionic chromium complexes and cationic chromium complexes in the wastewater, respectively. The neutral chromium complex concentration is then obtained by subtracting the total concentration of anionic chromium complexes and cationic chromium complexes from the total chromium concentration. The method has high accuracy, the molecular weight of the chromium complex has little effect on the detection method, and the operation is simple.

Description

Technical Field

[0001] The invention relates to the technical field of tanning wastewater treatment, and in particular to a method for determining the concentration of complexed chromium with different charge properties in tanning wastewater. Background Art

[0002] The charge of a chromium complex depends primarily on the type and number of ligands, and is the algebraic sum of the charge of the central chromium ion and the charge of the ligands. Positively charged chromium complexes are generally referred to as cationic chromium complexes, those with zero charge are neutral, and those with negative charge are anionic. Currently, the determination of the charge properties of chromium complexes primarily focuses on those in chrome tanning liquor, which is primarily obtained by complexing chromium with small molecule organic reagents (such as oxalic acid, formic acid, and citric acid). Ion exchange column chromatography, thin-layer ion exchange paper chromatography, paper electrophoresis, and gel filtration chromatography are commonly used to determine the charge properties of complexed chromium. However, during the measurement process, it was discovered that the above methods were ineffective in determining chromium complexes of varying charge properties in chrome tanning liquor, with significant errors. This is primarily because chromium complexes are not completely stable in solution; complexes of varying charge properties exist in a dynamic equilibrium. Changes in conditions, such as the addition of acid or alkali, temperature, the presence of neutral salts, and the presence of masking agents, can affect the differences in charge properties of chromium complexes. Therefore, ion exchange column chromatography is currently the most widely used of the above methods. Because gel filtration does not involve a chemical reaction, this method is generally considered to be more reliable for determining chromium complexes in chrome tanning liquor.

[0003] However, in addition to chromium-small molecule masking agent (such as acetic acid, formic acid, citric acid, etc.) complexes, the chromium complexes in tanning wastewater mainly include chromium-macromolecular organic complexes combined with tanning chemicals. When chromium-macromolecular organic complexes are determined by ion exchange column chromatography, most of the chromium-macromolecular organic complexes are incompletely eluted after gel filtration, resulting in large deviations in the determination results.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] In order to solve the problems in the background technology, the present invention provides a method for determining the concentration of complexed chromium with different charge properties in tanning wastewater. The determination method has high accuracy, the molecular weight of the chromium complex has little effect on the detection method, and the operation is simple.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The method for determining the concentration of complexed chromium with different charge properties in tanning wastewater includes:

[0008] Determination of anionic group concentration, cationic group concentration and total chromium concentration in tannery wastewater;

[0009] adding an anion precipitant to the tanning wastewater according to the anion group concentration, mixing uniformly, centrifuging, and taking the supernatant to determine a first total chromium concentration;

[0010] Adding a cationic precipitant to the tanning wastewater according to the concentration of the cationic group, mixing evenly, centrifuging, and taking the supernatant to determine the second total chromium concentration;

[0011] Calculate the charge properties of complexed chromium in tannery wastewater according to the first total chromium concentration, the second total chromium concentration and the total chromium concentration;

[0012] Wherein, the anion precipitant is a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride, the mass proportion of polydimethyldiallyl ammonium chloride in the anion precipitant is 10-40%, and the weight average molecular weight of polydimethyldiallyl ammonium chloride is 10000-100000 Mw;

[0013] The cationic precipitant is a mixture of sodium dibutylnaphthalene sulfonate and potassium poly (2-acrylamide-2-methylpropane sulfonate), the mass proportion of potassium poly (2-acrylamide-2-methylpropane sulfonate) in the cationic precipitant is 10-40%, and the weight average molecular weight of potassium poly (2-acrylamide-2-methylpropane sulfonate) is 10,000-100,000 Mw.

[0014] Preferably, the molar ratio of the anionic group to the anionic precipitant is 1:(2-5);

[0015] The molar ratio of the cationic group to the cationic precipitant is 1:(2-5).

[0016] Preferably, the first total chromium concentration is the sum of the concentrations of the cationic chromium complex and the neutral chromium complex;

[0017] The second total chromium concentration is the sum of the concentrations of the anionic chromium complex and the neutral chromium complex.

[0018] Preferably, the calculation formula for calculating the charge properties of complexed chromium in the tanning wastewater according to the first total chromium concentration, the second total chromium concentration and the total chromium concentration is:

[0019] Neutral chromium complex concentration = total chromium concentration - anionic chromium complex concentration - cationic chromium complex concentration

[0020] The proportion of anionic chromium complexes = anionic chromium complex concentration / total chromium concentration × 100%

[0021] The proportion of cationic chromium complexes = cationic chromium complex concentration / total chromium concentration × 100%

[0022] The proportion of neutral chromium complexes = medium chromium complex concentration / total chromium concentration × 100%.

[0023] Preferably, the method further comprises the step of determining the COD concentration in the tannery wastewater before determining the anionic group concentration, the cationic group concentration and the total chromium concentration in the tannery wastewater.

[0024] Preferably, if the COD concentration in the tanning wastewater is determined to be higher than 1000 mg / L, the tanning wastewater needs to be diluted to a COD less than or equal to 1000 mg / L before proceeding to subsequent steps.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The complexed chromium in the tanning wastewater of the present invention mainly consists of a chromium-medium-macromolecule organic matter complex and a chromium-small molecule organic matter complex, forming a mixed complex system. The present application adopts a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride as an anion precipitant, and a mixture of sodium dibutylnaphthalene sulfonate and poly-2-acrylamide-2-methylpropane sulfonate potassium as a cationic precipitant. By controlling the dosage and molecular weight of each precipitant, the accuracy of the determination of the concentration of complexed chromium with different charge properties is improved. The molecular weight of the chromium complex has little effect on the detection method, and the operation is simple. DETAILED DESCRIPTION

[0027] To better understand the technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with the embodiments. The embodiments of the present invention include but are not limited to the following examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. The test methods in the following examples, unless otherwise specified, are all conventional methods.

[0028] Prior art discloses the use of cationic polyurethane resin as an anionic precipitant and NekalBx as a cationic precipitant to measure the charge of complexed chromium in tanning wastewater from the dyeing and finishing process. This method directly precipitates anionic and cationic chromium complexes in the tanning wastewater and then measures the charge. The applicant also attempted this method during the development of the present application, but found that it did not completely react with the chromium complex to form a precipitate, resulting in significant deviations in the final measurement. Therefore, the applicant has proposed a method for measuring the concentration of complexed chromium with different charge properties in tanning wastewater.

[0029] The present invention provides a method for determining the concentration of complexed chromium with different charge properties in tanning wastewater, comprising:

[0030] Determination of anionic group concentration, cationic group concentration and total chromium concentration in tannery wastewater;

[0031] adding an anion precipitant to the tanning wastewater according to the anion group concentration, mixing uniformly, centrifuging, and taking the supernatant to determine a first total chromium concentration;

[0032] Adding a cationic precipitant to the tanning wastewater according to the concentration of the cationic group, mixing evenly, centrifuging, and taking the supernatant to determine the second total chromium concentration;

[0033] Calculate the charge properties of complexed chromium in tannery wastewater according to the first total chromium concentration, the second total chromium concentration and the total chromium concentration;

[0034] Wherein, the anion precipitant is a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride, the mass proportion of polydimethyldiallyl ammonium chloride in the anion precipitant is 10-40%, and the weight average molecular weight of polydimethyldiallyl ammonium chloride is 10000-100000 Mw;

[0035] The cationic precipitant is a mixture of sodium dibutylnaphthalene sulfonate and potassium poly (2-acrylamide-2-methylpropane sulfonate), the mass proportion of potassium poly (2-acrylamide-2-methylpropane sulfonate) in the cationic precipitant is 10-40%, and the weight average molecular weight of potassium poly (2-acrylamide-2-methylpropane sulfonate) is 10,000-100,000 Mw.

[0036] The embodiments of the present application are directed to the problems of complex testing in the prior art and inaccurate determination of chromium-organic complexes of different molecular sizes in tanning wastewater. By compounding a cationic precipitant and an anionic precipitant and strictly controlling the amount and molecular weight of the precipitant, it is possible to completely produce a precipitate after the precipitant reacts with the chromium complex, thereby improving the accuracy of the determination. Through continuous research and exploration by the applicant, it was found that this is because the prior art measures the wastewater from the tanning dyeing and finishing section, and the chromium complexes in the wastewater from the tanning dyeing and finishing section are almost all chromium-macromolecule organic complexes. However, in addition to the chromium-macromolecule organic complex, there are also chromium-small molecule organic complexes in the tanning wastewater. The hydrophilicity of the chromium-small molecule organic complex is stronger, and after reacting with the polyurethane resin and NekalBx used in the prior art, no precipitate can be formed, resulting in deviations in the test. Therefore, after discovering that directly using the precipitant in the prior art cannot completely precipitate with the chromium complex, the present application has found the reason and, on this basis, provides the technical solution of the embodiments of the present application.

[0037] Based on these inventive discoveries, the applicant believes it is necessary to select polydimethyldiallyl ammonium chloride and poly(2-acrylamide-2-methylpropanesulfonate), which have larger molecular weights and certain hydrophobic chains, as precipitants for chromium-small molecule organic complexes. Considering that tanning wastewater is a complex mixed system, this application uses a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride as an anionic precipitant, and a mixture of sodium dibutylnaphthalene sulfonate and poly(2-acrylamide-2-methylpropanesulfonate) as a cationic precipitant, strictly controlling the respective dosages and molecular weights. Furthermore, wastewater from the tanning and dyeing process (primarily chromium-medium and macromolecular organic complexes) accounts for approximately 30% of the total wastewater. Chrome tanning process wastewater (primarily chromium-small molecule organic complexes) is currently primarily recycled directly by the factory, with only a small portion discharged into the integrated wastewater system for treatment. Therefore, tanning wastewater is primarily composed of chromium-medium and macromolecular organic complexes and a small amount of chromium-small molecule organic complexes. The method has high accuracy, the molecular weight of the chromium complex has little effect on the detection method, and the operation is simple.

[0038] It should be noted that, since the tanning wastewater is mainly composed of chromium-medium macromolecular organic complex and a small amount of chromium-small molecule organic complex, chromium-small molecule organic complex accounts for a small proportion in the tanning wastewater, it has been found through a large number of experiments that by controlling the mass proportion of polydimethyldiallyl ammonium chloride in anionic precipitant to 10-40%, and controlling the mass proportion of poly-2-acrylamide-2-methylpropanesulfonic acid potassium in cationic precipitant to 10-40%, it is more effective to achieve that the complex in the wastewater is precipitated. In addition, since the present application is to react with chromium complex of different charge properties to form a precipitate, it has been found through a large number of experiments that limiting the weight-average molecular weight of polydimethyldiallyl ammonium chloride and poly-2-acrylamide-2-methylpropanesulfonic acid potassium to 10000-100000 Mw is more effective to achieve that the complex in the wastewater is precipitated, and molecular weight is too small to form a precipitate, and molecular weight is too large to easily form a net capture and sweeping effect, resulting in a large test error.

[0039] After treatment with a cationic precipitant, the cationic chromium complex is primarily present in the insolubles as a precipitate, and the Cr in the supernatant is primarily the sum of the anionic chromium complex and the neutral chromium complex. Therefore, the first total chromium concentration is the sum of the concentrations of the cationic chromium complex and the neutral chromium complex. Conversely, after treatment with an anionic precipitant, the anionic chromium complex is primarily present in the insolubles as a precipitate, and the Cr in the supernatant is primarily the sum of the concentrations of the anionic chromium complex and the neutral chromium complex. Therefore, the second total chromium concentration is the sum of the concentrations of the anionic chromium complex and the neutral chromium complex. The total chromium concentration is the total Cr content in the wastewater.

[0040] There are no specific limitations on the amount of the anionic group to the anionic precipitant, or the amount of the cationic group to the cationic precipitant, as long as both the cationic and anionic groups are completely precipitated. These amounts can be adjusted as needed by those skilled in the art. In a preferred embodiment, the molar ratio of the anionic group to the anionic precipitant is 1:(2-5), and the molar ratio of the cationic group to the cationic precipitant is 1:(2-5).

[0041] Furthermore, during the implementation of this application, the applicant discovered that high COD wastewater has excessively high organic matter concentrations. This can cause the added precipitant to be swept into the precipitate through the netting process, entraining some neutral and cationic chromium complexes, leading to inaccurate testing. Therefore, for tanning wastewater with high COD concentrations, it is necessary to dilute the tanning wastewater before adding the precipitant for treatment. In some preferred embodiments, for wastewater with a COD greater than 1000 mg / L, it is necessary to dilute the wastewater before proceeding to subsequent steps.

[0042] The following describes in detail the determination method and effect of the concentration of complexed chromium with different charge properties in tanning wastewater through a number of specific examples.

[0043] Example 1

[0044] Determination of the concentration of complexed chromium with different charge properties in tanning wastewater:

[0045] A: Take tanning wastewater and measure the total chromium concentration to be 45.9 mg / L. Then measure the COD concentration in the wastewater to be 4730 mg / L. The wastewater needs to be diluted to a COD of 946 mg / L before measuring the concentration of chromium complexes with different charges.

[0046] B: The concentration of anionic groups in the tanning wastewater was determined by colloid titration to be 29.37 mmol / L and the concentration of cationic groups was 0.48 mmol / L.

[0047] C: Take 100 mL of the diluted tanning wastewater in step A, add an anionic precipitant, a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride (wherein the mass proportion of polydimethyldiallyl ammonium chloride is 10%, and the weight-average molecular weight of polydimethyldiallyl ammonium chloride is 10,000 MW), wherein the molar ratio of the anionic group concentration to the anionic precipitant is 1:2, mix well, centrifuge, and take the precipitate to determine the total chromium concentration, which is the anionic chromium complex concentration of 43.8 mg / L. At the same time, take the supernatant to determine the first total chromium concentration, which is the sum of the cationic chromium complex and the neutral chromium complex, which is 2.1 mg / L.

[0048] D: Take 100 mL of the diluted tanning wastewater from step A and add a cationic precipitant, a mixture of sodium dibutylnaphthalene sulfonate and potassium poly(2-acrylamide-2-methylpropanesulfonate) (wherein the mass proportion of potassium poly(2-acrylamide-2-methylpropanesulfonate) is between 10% and the weight-average molecular weight of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 10,000 MW). The two precipitants respectively capture cationic chromium-organic complexes of different molecular weights, wherein the molar ratio of the cationic group to the cationic precipitant is 1:2. After uniform mixing, centrifugation is performed, and the precipitate is collected for determination of the total chromium concentration, which is 0.3 mg / L for the cationic chromium complex. Simultaneously, the supernatant is collected for determination of a second total chromium concentration, which is the sum of the anionic chromium complex and the neutral chromium complex, and is 45.6 mg / L. The neutral chromium complex concentration is calculated to be 1.8 mg / L.

[0049] Example 2

[0050] Determination of the concentration of complexed chromium with different charge properties in tanning wastewater:

[0051] A: Take tanning wastewater and measure the total chromium concentration to be 45.9 mg / L. Then measure the COD concentration in the wastewater to be 4730 mg / L. The wastewater needs to be diluted to a COD of 946 mg / L before measuring the concentration of chromium complexes with different charges.

[0052] B: The concentration of anionic groups in the tanning wastewater was determined by colloid titration to be 29.37 mmol / L and the concentration of cationic groups was 0.48 mmol / L.

[0053] C: Take 100 mL of the diluted tanning wastewater in step A, add an anionic precipitant, a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride (wherein the mass proportion of polydimethyldiallyl ammonium chloride is 40%, and the weight-average molecular weight of polydimethyldiallyl ammonium chloride is 100,000 MW), wherein the molar ratio of the anionic group concentration to the anionic precipitant is 1:5, mix well, centrifuge, and take the precipitate to determine the total chromium concentration, which is the anionic chromium complex concentration of 43.8 mg / L. At the same time, take the supernatant to determine the first total chromium concentration, which is the sum of the cationic chromium complex and the neutral chromium complex, which is 2.1 mg / L.

[0054] D: Take 100 mL of the diluted tanning wastewater from step A and add a cationic precipitant, a mixture of sodium dibutylnaphthalene sulfonate and potassium poly(2-acrylamide-2-methylpropanesulfonate), (wherein the mass proportion of potassium poly(2-acrylamide-2-methylpropanesulfonate) is between 40% and the weight-average molecular weight of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 100,000 MW. The two precipitants capture cationic chromium-organic complexes of different molecular weights, respectively. The molar ratio of the cation to the cationic precipitant is 1:5. After uniform mixing, centrifugation is performed and the precipitate is collected for determination of the total chromium concentration. The concentration is 0.4 mg / L for the cationic chromium complex. Simultaneously, the supernatant is collected for determination of a second total chromium concentration. The second total chromium concentration is the sum of the anionic chromium complex and the neutral chromium complex, which is 45.5 mg / L. The neutral chromium complex concentration is calculated to be 1.7 mg / L.

[0055] Example 3

[0056] Determination of the concentration of complexed chromium with different charge properties in tanning wastewater:

[0057] A: Take tanning wastewater and measure the total chromium concentration to be 45.9 mg / L. Then measure the COD concentration in the wastewater to be 4730 mg / L. The wastewater needs to be diluted to a COD of 946 mg / L before measuring the concentration of chromium complexes with different charges.

[0058] B: The concentration of anionic groups and cationic groups in tanning wastewater was determined by colloid titration.

[0059] C: Take 100 mL of the diluted tanning wastewater in step A, add an anionic precipitant, a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride (wherein the mass proportion of polydimethyldiallyl ammonium chloride is 20%, and the weight-average molecular weight of polydimethyldiallyl ammonium chloride is 50,000 MW), wherein the molar ratio of the anionic group concentration to the anionic precipitant is 1:3, mix well, centrifuge, and take the precipitate to determine the total chromium concentration, which is the anionic chromium complex concentration of 43.7 mg / L. At the same time, take the supernatant to determine the first total chromium concentration, which is the sum of the cationic chromium complex and the neutral chromium complex, which is 2.2 mg / L.

[0060] D: Take 100 mL of the diluted tanning wastewater from step A and add a cationic precipitant, a mixture of sodium dibutylnaphthalene sulfonate and potassium poly(2-acrylamide-2-methylpropanesulfonate) (wherein the mass proportion of potassium poly(2-acrylamide-2-methylpropanesulfonate) is between 30% and the weight-average molecular weight of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 60,000 MW). The two precipitants respectively capture cationic chromium-organic complexes of different molecular weights, wherein the molar ratio of the cation to the cationic precipitant is 1:4. After uniform mixing, centrifugation is performed, and the precipitate is collected for determination of the total chromium concentration, which is 0.4 mg / L for the cationic chromium complex. Simultaneously, the supernatant is collected for determination of a second total chromium concentration, which is the sum of the anionic chromium complex and the neutral chromium complex, and is 45.5 mg / L. The neutral chromium complex concentration is calculated to be 1.8 mg / L.

[0061] Example 4

[0062] Determination of the concentration of complexed chromium with different charge properties in tanning wastewater:

[0063] A: Take tanning wastewater and measure the total chromium concentration to be 45.9 mg / L. Then measure the COD concentration in the wastewater to be 4730 mg / L. The wastewater needs to be diluted to a COD of 946 mg / L before measuring the concentration of chromium complexes with different charges.

[0064] B: The concentration of anionic groups in the tanning wastewater was determined by colloid titration to be 29.37 mmol / L and the concentration of cationic groups was 0.48 mmol / L.

[0065] C: Take 100 mL of the diluted tanning wastewater in step A, add an anionic precipitant, a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride (wherein the mass proportion of polydimethyldiallyl ammonium chloride is 30%, and the weight-average molecular weight of polydimethyldiallyl ammonium chloride is 30,000 MW), wherein the molar ratio of the anionic group concentration to the anionic precipitant is 1:4, mix well, centrifuge, and take the precipitate to determine the total chromium concentration, which is the anionic chromium complex concentration of 43.8 mg / L. At the same time, take the supernatant to determine the first total chromium concentration, which is the sum of the cationic chromium complex and the neutral chromium complex, which is 2.1 mg / L.

[0066] D: Take 100 mL of the diluted tanning wastewater from step A and add a cationic precipitant, a mixture of sodium dibutylnaphthalene sulfonate and potassium poly(2-acrylamide-2-methylpropanesulfonate), (wherein the mass proportion of potassium poly(2-acrylamide-2-methylpropanesulfonate) is between 20% and the weight-average molecular weight of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 50,000 MW. The two precipitants capture cationic chromium-organic complexes of different molecular weights, respectively. The molar ratio of the cation to the cationic precipitant is 1:3. After uniform mixing, centrifugation is performed and the precipitate is collected for determination of the total chromium concentration. The concentration is 0.5 mg / L for the cationic chromium complex. Simultaneously, the supernatant is collected for determination of a second total chromium concentration. The second total chromium concentration is the sum of the anionic chromium complex and the neutral chromium complex, which is 45.4 mg / L. The neutral chromium complex concentration is calculated to be 1.6 mg / L.

[0067] Example 5

[0068] Determination of charge properties of complexed chromium in tannery wastewater:

[0069] A: Take the tanning wastewater and measure the total chromium concentration to be 6.7 mg / L. Then measure the COD concentration in the wastewater to find that it is 485 mg / L.

[0070] B: The concentration of anionic groups in the tanning wastewater was determined by colloid titration to be 7.51 mmol / L and the concentration of cationic groups was 0.13 mmol / L.

[0071] C: Take 100 mL of the tanning wastewater from step A, add an anionic precipitant, a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride (wherein the mass proportion of polydimethyldiallyl ammonium chloride is 30%, and the weight-average molecular weight of polydimethyldiallyl ammonium chloride is 30,000 MW), wherein the molar ratio of the anionic group concentration to the anionic precipitant is 1:4, mix well, centrifuge, and take the precipitate to determine the total chromium concentration, which is the anionic chromium complex concentration of 7.38 mg / L. At the same time, take the supernatant to determine the first total chromium concentration, which is the sum of the cationic chromium complex and the neutral chromium complex, which is 0.13 mg / L.

[0072] D: Take 100 mL of the tanning wastewater from step A, add a cationic precipitant, a mixture of sodium dibutylnaphthalene sulfonate and potassium poly(2-acrylamide-2-methylpropanesulfonate), (wherein the mass proportion of potassium poly(2-acrylamide-2-methylpropanesulfonate) is between 20% and the weight-average molecular weight of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 50,000 MW, and the two precipitants capture cationic chromium-organic complexes of different molecular weights, respectively, wherein the molar ratio of the cation to the cationic precipitant is 1:3. After uniform mixing, centrifugation is performed, and the precipitate is collected for determination of the total chromium concentration, which is 0.04 mg / L for the cationic chromium complex. Simultaneously, the supernatant is collected for determination of a second total chromium concentration, which is the sum of the anionic chromium complex and the neutral chromium complex, and is 7.34 mg / L.

[0073] Comparative Example 1

[0074] Comparative Example 1 refers to the method of Example 4, except that the tanning wastewater is directly measured without dilution.

[0075] A: Take tanning wastewater and measure the total chromium concentration to be 45.9 mg / L. Then measure the COD concentration in the wastewater to be 4730 mg / L. Measure directly without dilution.

[0076] B: The concentration of anionic groups in the tanning wastewater was determined by colloid titration to be 29.37 mmol / L and the concentration of cationic groups was 0.48 mmol / L.

[0077] C: Take 100 mL of undiluted tanning wastewater from step A, add an anionic precipitant, a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride (wherein the mass proportion of polydimethyldiallyl ammonium chloride is 30%, and the weight-average molecular weight of polydimethyldiallyl ammonium chloride is 30,000 MW), wherein the molar ratio of the anionic group concentration to the anionic precipitant is 1:4, mix well, centrifuge, and take the precipitate to determine the total chromium concentration, which is the anionic chromium complex concentration of 45.3 mg / L. At the same time, take the supernatant to determine the first total chromium concentration, which is the sum of the cationic chromium complex and the neutral chromium complex, which is 0.6 mg / L.

[0078] D: Take 100 mL of the undiluted tannery wastewater from step A and add a cationic precipitant, a mixture of sodium dibutylnaphthalene sulfonate and potassium poly(2-acrylamide-2-methylpropanesulfonate), (wherein the mass proportion of potassium poly(2-acrylamide-2-methylpropanesulfonate) is between 20% and the weight-average molecular weight of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 50,000 MW. The two precipitants capture cationic chromium-organic complexes of different molecular weights, respectively. The molar ratio of the cation to the cationic precipitant is 1:3. After uniform mixing, centrifugation is performed and the precipitate is collected for determination of the total chromium concentration. The concentration is 0.4 mg / L for the cationic chromium complex. Simultaneously, the supernatant is collected for determination of a second total chromium concentration. The second total chromium concentration is the sum of the anionic chromium complex and the neutral chromium complex, which is 45.5 mg / L. The neutral chromium complex concentration is calculated to be 0.2 mg / L.

[0079] Comparative Example 2

[0080] Comparative Example 2 refers to the method of Example 4, except that dicyandiamide formaldehyde resin and sodium dibutylnaphthalene sulfonate are used as the precipitant.

[0081] A: Take tanning wastewater and measure the total chromium concentration to be 45.9 mg / L. Then measure the COD concentration in the wastewater to be 4730 mg / L. The wastewater needs to be diluted to a COD of 946 mg / L before measuring the concentration of chromium complexes with different charges.

[0082] B: The concentration of anionic groups in the tanning wastewater was determined by colloid titration to be 29.37 mmol / L and the concentration of cationic groups was 0.48 mmol / L.

[0083] C: Take 100 mL of the diluted tanning wastewater from step A, add dicyandiamide formaldehyde resin, wherein the molar ratio of the anionic group concentration to the anionic precipitant is 1:4, mix well, centrifuge, and take the precipitate to determine the total chromium concentration. The concentration is the anionic chromium complex concentration of 35.4 mg / L. At the same time, take the supernatant to determine the first total chromium concentration. The first total chromium concentration is the sum of the cationic chromium complex and the neutral chromium complex, which is 10.5 mg / L.

[0084] D: Take 100 mL of the diluted tanning wastewater from step A, add sodium dibutylnaphthalene sulfonate in a molar ratio of cation to cationic precipitant of 1:3, mix well, and centrifuge. The precipitate is collected and the total chromium concentration is determined. This concentration is the cationic chromium complex concentration of 2.3 mg / L. Simultaneously, the supernatant is collected and a second total chromium concentration is determined. This second total chromium concentration is the sum of the anionic chromium complex and the neutral chromium complex, which is 43.6 mg / L. The neutral chromium complex concentration is calculated to be 8.2 mg / L.

[0085] Comparative Example 3

[0086] Comparative Example 3 refers to the method of Example 4, except that only the proportion and molecular weight of the anion precipitant are changed.

[0087] A: Take tanning wastewater and measure the total chromium concentration to be 45.9 mg / L. Then measure the COD concentration in the wastewater to be 4730 mg / L. The wastewater needs to be diluted to a COD of 946 mg / L before measuring the concentration of chromium complexes with different charges.

[0088] B: The concentration of anionic groups and cationic groups in tanning wastewater was determined by colloid titration.

[0089] C: Take 100 mL of the diluted tanning wastewater in step A, add an anionic precipitant, a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride (wherein the mass proportion of polydimethyldiallyl ammonium chloride is 5%, and the weight-average molecular weight of polydimethyldiallyl ammonium chloride is 5000 MW), wherein the molar ratio of the anionic group concentration to the anionic precipitant is 1:4, mix well, centrifuge, and take the precipitate to determine the total chromium concentration, which is the anionic chromium complex concentration of 38.4 mg / L. At the same time, take the supernatant to determine the first total chromium concentration, which is the sum of the cationic chromium complex and the neutral chromium complex, which is 7.5 mg / L.

[0090] D: Take 100 mL of the diluted tanning wastewater from step A and add a cationic precipitant, a mixture of sodium dibutylnaphthalene sulfonate and potassium poly(2-acrylamide-2-methylpropanesulfonate), (wherein the mass proportion of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 20% and the weight-average molecular weight of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 50000 MW. The two precipitants capture cationic chromium-organic complexes of different molecular weights, respectively. The molar ratio of the cation to the cationic precipitant is 1:3. After uniform mixing, centrifugation is performed and the precipitate is collected for determination of the total chromium concentration. The concentration is 0.1 mg / L for the cationic chromium complex. Simultaneously, the supernatant is collected for determination of a second total chromium concentration. The second total chromium concentration is the sum of the anionic chromium complex and the neutral chromium complex, which is 45.8 mg / L. The neutral chromium complex concentration is calculated to be 7.4 mg / L.

[0091] Comparative Example 4

[0092] Comparative Example 4 refers to the method of Example 4, except that only the proportion and molecular weight of the cationic precipitant are changed.

[0093] A: Take tanning wastewater and measure the total chromium concentration to be 45.9 mg / L. Then measure the COD concentration in the wastewater to be 4730 mg / L. The wastewater needs to be diluted to a COD of 946 mg / L before measuring the concentration of chromium complexes with different charges.

[0094] B: The concentration of anionic groups and cationic groups in tanning wastewater was determined by colloid titration.

[0095] C: Take 100 mL of the diluted tanning wastewater in step A, add an anionic precipitant, a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride (wherein the mass proportion of polydimethyldiallyl ammonium chloride is 30%, and the weight-average molecular weight of polydimethyldiallyl ammonium chloride is 30,000 MW), wherein the molar ratio of the anionic group concentration to the anionic precipitant is 1:4, mix well, centrifuge, and take the precipitate to determine the total chromium concentration, which is the anionic chromium complex concentration of 40.7 mg / L. At the same time, take the supernatant to determine the first total chromium concentration, which is the sum of the cationic chromium complex and the neutral chromium complex, which is 5.2 mg / L.

[0096] D: Take 100 mL of the diluted tanning wastewater from step A and add a cationic precipitant, a mixture of sodium dibutylnaphthalene sulfonate and potassium poly(2-acrylamide-2-methylpropanesulfonate) (wherein the mass proportion of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 70% and the weight-average molecular weight of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 200,000 MW). The two precipitants respectively capture cationic chromium-organic complexes of different molecular weights. The molar ratio of the cation to the cationic precipitant is 1:3. After uniform mixing, centrifugation is performed and the precipitate is collected for determination of the total chromium concentration. The concentration is 1.3 mg / L for the cationic chromium complex. Simultaneously, the supernatant is collected for determination of a second total chromium concentration. The second total chromium concentration is the sum of the anionic chromium complex and the neutral chromium complex, which is 44.6 mg / L. The calculated neutral chromium complex concentration is 3.9 mg / L.

[0097] Experimental example

[0098] In order to illustrate that the determination method provided in the embodiment of the present application is more accurate than the determination method in the prior art using cationic polyurethane resin as an anion precipitant and NekalBx as a cationic precipitant, this experimental example simulates tanning wastewater and uses different methods to determine the concentrations of anionic, intermediate and cationic chromium complexes in the simulated tanning wastewater to compare the accuracy of the determination results.

[0099] Preparation method of simulated leather wastewater: chrome tanning agent and acrylic acid retanning agent (PAA) were used to prepare n(Cr 3+ ):n(COO-)=1:20 macromolecular anionic Cr complex (Cr-PAA) solution, the total chromium concentration of the solution was 20.7 mg / L, all of which were anionic chromium complexes. At the same time, tanning agent and citric acid were used to prepare n(Cr 3+A small molecule anionic chromium complex (Cr-citric acid) solution with a ratio of 1:20 (COO-):n(COO-) was tested. The total chromium concentration in the solution was 20.3 mg / L, consisting entirely of anionic chromium complexes. Simulated tanning wastewater was prepared by mixing Cr-PAA solution and Cr-citric acid solution in a 1:1 volume ratio. The total chromium concentration in the simulated tanning wastewater was 20.5 mg / L, consisting entirely of anionic chromium complexes. The COD in the simulated tanning wastewater was measured to be 2457 mg / L.

[0100] Determination method:

[0101] The simulated tannery wastewater prepared above was tested for a total chromium concentration of 20.5 mg / L. The COD concentration was then measured at 2457 mg / L. The wastewater was diluted to a COD of 819 mg / L before measuring the concentrations of chromium complexes of varying charges. The concentration of anionic groups in the tannery wastewater was determined to be 2.75 mmol / L and the concentration of cationic groups was 0.0 mmol / L using colloidal titration.

[0102] Experimental group: 100 mL of the diluted tanning wastewater was added to an anionic precipitant, a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride (polydimethyldiallyl ammonium chloride accounted for 30% by mass and had a weight-average molecular weight of 30,000 MW), with a molar ratio of anionic group concentration to anionic precipitant of 1:4. After mixing evenly, the mixture was centrifuged and the precipitate was taken to determine the total chromium concentration, which was an anionic chromium complex concentration of 20.5 mg / L. At the same time, the supernatant was taken to determine the first total chromium concentration, which was the sum of the cationic chromium complex and the neutral chromium complex, which was 0.0 mg / L.

[0103] 100 mL of the diluted tanning wastewater from step A was added, and a cationic precipitant, a mixture of sodium dibutylnaphthalene sulfonate and potassium poly(2-acrylamide-2-methylpropanesulfonate), (wherein the mass proportion of potassium poly(2-acrylamide-2-methylpropanesulfonate) is between 20% and the weight-average molecular weight of potassium poly(2-acrylamide-2-methylpropanesulfonate) is 50,000 MW. The two precipitants respectively capture cationic chromium-organic complexes of different molecular weights, wherein the molar ratio of the cation to the cationic precipitant is 1:3. After uniform mixing, the mixture was centrifuged, and the precipitate was taken to determine the total chromium concentration, which was 0.0 mg / L for the cationic chromium complex. At the same time, the supernatant was taken to determine the second total chromium concentration, which was the sum of the anionic chromium complex and the neutral chromium complex, which was 20.5 mg / L.

[0104] Control group: Take 100 mL of the diluted tanning wastewater in step A, add dicyandiamide formaldehyde resin, wherein the molar ratio of the anionic group concentration to the anionic precipitant is 1:4, mix well, centrifuge, and take the precipitate to determine the total chromium concentration. The concentration is the anionic chromium complex concentration of 12.4 mg / L. At the same time, take the supernatant to determine the first total chromium concentration. The first total chromium concentration is the sum of the cationic chromium complex and the neutral chromium complex, which is 8.1 mg / L.

[0105] D: Take 100 mL of the diluted tanning wastewater from step A, add sodium dibutylnaphthalene sulfonate in a molar ratio of cation to cationic precipitant of 1:3, mix well, and centrifuge. Take the precipitate to measure the total chromium concentration, which is the cationic chromium complex concentration of 0 mg / L. Simultaneously, take the supernatant to measure a second total chromium concentration, which is the sum of the anionic chromium complex and the neutral chromium complex, and is 20.5 mg / L.

[0106] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for determining the concentration of complexed chromium with different charge properties in tanning wastewater, characterized in that: Include: Determination of anionic group concentration, cationic group concentration and total chromium concentration in tannery wastewater; adding an anion precipitant to the tanning wastewater according to the anion group concentration, mixing uniformly, centrifuging, and taking the supernatant to determine a first total chromium concentration; Adding a cationic precipitant to the tanning wastewater according to the concentration of the cationic group, mixing evenly, centrifuging, and taking the supernatant to determine the second total chromium concentration; Calculate the charge properties of complexed chromium in tannery wastewater according to the first total chromium concentration, the second total chromium concentration and the total chromium concentration; Wherein, the anion precipitant is a mixture of dicyandiamide formaldehyde resin and polydimethyldiallyl ammonium chloride, the mass proportion of polydimethyldiallyl ammonium chloride in the anion precipitant is 10-40%, and the weight average molecular weight of polydimethyldiallyl ammonium chloride is 10000-100000 Mw; The cationic precipitant is a mixture of sodium dibutylnaphthalene sulfonate and potassium poly (2-acrylamide-2-methylpropane sulfonate), the mass proportion of potassium poly (2-acrylamide-2-methylpropane sulfonate) in the cationic precipitant is 10-40%, and the weight average molecular weight of potassium poly (2-acrylamide-2-methylpropane sulfonate) is 10,000-100,000 Mw.

2. The method for determining the concentration of complexed chromium with different charge properties in tanning wastewater according to claim 1, wherein: The molar ratio of the anionic group to the anionic precipitant is 1:(2-5); the molar ratio of the cationic group to the cationic precipitant is 1:(2-5).

3. The method for determining the concentration of complexed chromium with different charge properties in tanning wastewater according to claim 1, wherein: The first total chromium concentration is the sum of the concentrations of the cationic chromium complex and the neutral chromium complex; The second total chromium concentration is the sum of the concentrations of the anionic chromium complex and the neutral chromium complex.

4. The method for determining the concentration of complexed chromium with different charge properties in tanning wastewater according to claim 3, wherein: The calculation formula for calculating the charge properties of complexed chromium in tannery wastewater based on the first total chromium concentration, the second total chromium concentration and the total chromium concentration is: Neutral chromium complex concentration = total chromium concentration - anionic chromium complex concentration - cationic chromium complex concentration The proportion of anionic chromium complexes = anionic chromium complex concentration / total chromium concentration × 100% The proportion of cationic chromium complexes = cationic chromium complex concentration / total chromium concentration × 100% The proportion of neutral chromium complexes = neutral chromium complex concentration / total chromium concentration × 100%.

5. The method for determining the concentration of complexed chromium with different charge properties in tanning wastewater according to any one of claims 1 to 4, characterized in that: Before measuring the anionic group concentration, cationic group concentration and total chromium concentration in the tanning wastewater, the method further comprises the step of measuring the COD concentration in the tanning wastewater.

6. The method for determining the concentration of complexed chromium with different charge properties in tanning wastewater according to claim 5, characterized in that: If the COD concentration in the tanning wastewater is determined to be higher than 1000 mg / L, the tanning wastewater needs to be diluted to a COD less than or equal to 1000 mg / L before proceeding to the subsequent steps.