Method and system for removing acid dyes from water

Abstract

The present invention relates to sewage treatment, specifically to a method and system for removing acid dyes from water. The Fe(III)-dye complex flocs formed by ferric ions and acid dyes are solid substances, which can be conveniently separated from water, thereby removing the acid dyes in water. Under the condition that the pH is greater than or equal to 7, the separated Fe(III)-dye complex flocs are decomplexed to obtain a concentrated acid dye solution and form Fe(OH)3 flocs; the Fe(OH)3 flocs are solid substances, which can be conveniently separated from the acid dye solution, thereby recovering ferric ions. After the Fe(OH)3 flocs are mixed with an acid solution, they become a ferric salt solution, which can be recycled for removing acid dyes from water.

Description

Technical Field

[0001] The present invention relates to sewage treatment, and specifically to a method and a system for removing acid dyes from water. Background Art

[0002] Acid dyes, also known as anionic dyes, refer to dyes that contain acidic groups (such as sulfonic acid groups, carboxyl groups, and ortho-phenolic hydroxyl azo groups) in their molecules; the main molecular parent structures are azo and anthraquinone structures, and a small number are arylmethane structures.

[0003] Acid dyes are generally toxic, and the gradual accumulation of these toxic organic substances will cause the death of some organisms in water. At the same time, acid dyes and their intermediates contain amine substances, and these amine substances have teratogenicity, carcinogenicity, and non-biodegradability, and will cause serious harm even at relatively low concentrations.

[0004] There has been a technical solution for removing acid dyes from water by using iron salt flocculants, but a large amount of sludge will be generated during the flocculation sedimentation process, and these sludges are not easy to be harmlessly treated; moreover, the consumption of iron salt flocculants is large and the cost is high. Summary of the Invention

[0005] Based on this, the present invention provides a method and a system for removing acid dyes from water, which solves at least one problem in the prior art.

[0006] In a first aspect, the present invention provides a method for removing acid dyes from water, which includes the following steps:

[0007] Mix a ferric salt or its solution with water containing acid dyes to form Fe(Ⅲ)-dye complex flocs with ferric ions and acid dyes;

[0008] Separate the Fe(Ⅲ)-dye complex flocs, adjust the pH of the Fe(Ⅲ)-dye complex flocs to be greater than or equal to 7 to cause the Fe(Ⅲ)-dye complex flocs to decomplex and form Fe(OH)3 flocs;

[0009] Separate the Fe(OH)3 flocs, mix the Fe(OH)3 flocs with an acid solution to form a ferric salt solution.

[0010] The Fe(Ⅲ)-dye complex flocs formed by ferric ions and acid dyes are solid substances, which can be conveniently separated from water, thereby removing acid dyes from water. Under the condition that the pH is greater than or equal to 7, the separated Fe(Ⅲ)-dye complex flocs decomplex to obtain a concentrated acid dye solution and form Fe(OH)3 flocs; the Fe(OH)3 flocs are solid substances, which can be conveniently separated from the acid dye solution, thereby recovering ferric ions. After the Fe(OH)3 flocs are mixed with an acid solution, they become a ferric salt solution, which can be recycled for removing acid dyes from water.

[0011] In a second aspect, the present invention provides a system for removing acid dyes from water, which includes:

[0012] A coagulation tank for containing ferric salts or their solutions and water containing acid dyes, so that ferric ions form Fe(Ⅲ)-dye complex flocs with acid dyes;

[0013] A sedimentation tank for separating out Fe(Ⅲ)-dye complex flocs by sedimentation;

[0014] A decoordination tank for containing Fe(Ⅲ)-dye complex flocs and an alkali solution to adjust the pH of the Fe(Ⅲ)-dye complex flocs to be greater than or equal to 7, so that the Fe(Ⅲ)-dye complex flocs are decoordinated and Fe(OH)3 flocs are formed;

[0015] An acidification tank for containing Fe(OH)3 flocs and an acid solution to form a ferric salt solution.

[0016] Due to the adoption of the above technical solutions, the embodiments of the present invention have at least the following beneficial effects:

[0017] (1) Acid dye wastewater can be directly removed by complexing with ferric ions without prior neutralization pretreatment. The operation is simple, the removal efficiency can exceed 90%, and the residual COD in the water body can be lower than 0.5 mg / L;

[0018] (2) It is applicable to dyes containing two or more anionic functional groups, where the anionic functional groups include ortho-phenolic hydroxyl azo, sulfonic acid group, carboxyl group, etc.;

[0019] (3) Ferric ions can be recycled, with low cost;

[0020] (4) The concentrated dyes can be recycled. Description of the Drawings

[0021] Figure 1 It is a process flow diagram for removing acid dyes from water in an embodiment of the present invention. Among them, 1 represents a coagulation tank, 2 represents a sedimentation tank, 3 represents a decoordination tank, 4 represents an acidification tank, 5 represents the inlet of the coagulation tank, 6 represents the outlet of the sedimentation tank, 7 represents the pipeline for transporting Fe(Ⅲ)-dye complex flocs, 8 represents the pipeline for transporting iron mud, 9 represents the pipeline for circulating ferric solution, 10 represents the pipeline for transporting the mixed liquid, and 11 represents the pipeline for discharging the concentrated acid dye solution.

[0022] Figure 2 It is the standard curve of the absorbance and concentration of Acid Orange 7 (AO7) in an embodiment of the present invention.

[0023] Figure 3This is the standard curve of the absorbance and concentration of acid fuchsin in the embodiments of the present invention.

[0024] Figure 4 This is the standard curve of the absorbance and concentration of sunset yellow in the embodiments of the present invention.

[0025] Figure 5 This is the ultraviolet-visible absorption spectrum of the supernatant after the complexation of ferric ions and AO7 under different pH conditions in the embodiments of the present invention.

[0026] Figure 6 This is the absorbance graph of the supernatant after the complexation of ferric ions and AO7 under different pH conditions at a wavelength of 484 nm in the embodiments of the present invention.

[0027] Figure 7 This is the removal efficiency graph of AO7 in the supernatant after the complexation of ferric ions and AO7 under different pH conditions in the embodiments of the present invention.

[0028] Figure 8 This is the ultraviolet-visible absorption spectrum of the supernatant after the complexation of ferric ions and AO7 under different Fe / AO7 molar ratios in the embodiments of the present invention.

[0029] Figure 9 This is the absorbance graph of the supernatant after the complexation of ferric ions and AO7 under different Fe / AO7 molar ratios at a wavelength of 484 nm in the embodiments of the present invention.

[0030] Figure 10 This is the removal efficiency graph of AO7 in the supernatant after the complexation of ferric ions and AO7 under different Fe / AO7 molar ratios in the embodiments of the present invention.

[0031] Figure 11 This is the absorbance graph of the supernatant after the complexation of ferric ions and AO7 under different Fe / AO7 molar ratios and different pH conditions at a wavelength of 484 nm in the embodiments of the present invention.

[0032] Figure 12 This is the ultraviolet-visible absorption spectrum of the supernatant after the complexation of ferric ions and AO7 under different light conditions in the embodiments of the present invention.

[0033] Figure 13 This is the absorbance and COD graph of the supernatant after the complexation of ferric ions and AO7 under different light conditions at a wavelength of 484 nm in the embodiments of the present invention.

[0034] Figure 14 This is the ultraviolet-visible absorption spectrum of the liquid after the dissociation of the Fe(Ⅲ)-AO7 complex flocs under different pH conditions in the embodiments of the present invention.

[0035] Figure 15Absorbance diagram of the liquid after the dissociation of the Fe(Ⅲ)-AO7 complex flocs at a wavelength of 484 nm under different pH conditions in the embodiments of the present invention.

[0036] Figure 16 Percentage diagram of the removal rate of AO7 by ferric ions and the percentage of the dissociation of Fe(Ⅲ)-AO7 complex flocs to release AO7 under different pH conditions in the embodiments of the present invention.

[0037] Figure 17 Efficiency diagram of the removal of AO7 by the 6-cycle complexation / dissociation of ferric ions in the embodiments of the present invention.

[0038] Figure 18 Ultraviolet-visible absorption spectrum of the supernatant after the complexation of ferric ions and acid fuchsin under different pH conditions in the embodiments of the present invention.

[0039] Figure 19 Removal rate diagram of acid fuchsin after the complexation of ferric ions and acid fuchsin under different pH conditions in the embodiments of the present invention.

[0040] Figure 20 Ultraviolet-visible absorption spectrum of the supernatant after the complexation of ferric ions and sunset yellow under different pH conditions in the embodiments of the present invention.

[0041] Figure 21 Removal rate diagram of acid fuchsin after the complexation of ferric ions and sunset yellow under different pH conditions in the embodiments of the present invention.

[0042] Figure 22 Ultraviolet-visible absorption spectrum of the supernatant and a physical photo of the supernatant after the complexation of ferric ions and methyl orange under different pH conditions in the embodiments of the present invention.

[0043] Figure 23 Ultraviolet-visible absorption spectrum of the supernatant and a physical photo of the supernatant after the complexation of ferric ions and rhodamine B under different pH conditions in the embodiments of the present invention. Detailed implementation manners

[0044] The concept of the present invention and the resulting technical effects will be clearly and completely described below to fully elaborate the purpose, solution and effects of the present invention.

[0045] Ferric ions (Fe 3+ ) can complex with acid dyes having polyanionic functional groups (two or more anions, including sulfonic acid groups, carboxyl groups and o-phenol hydroxyl azo groups, etc.) to form Fe(Ⅲ)-dye complex flocs. After sedimentation and solid-liquid separation, adjusting the pH of the Fe(Ⅲ)-dye complex flocs to neutral or alkaline can cause their dissociation and release the dyes; at this time, Fe 3+ and OH- Combined to form Fe(OH)3 flocs. After sedimentation and solid-liquid separation, the Fe(OH)3 flocs are acidified with an acid to release Fe 3+ , which can be recycled for the complexation of acid dyes. According to this principle, the present invention provides a method and a system for removing acid dyes from water.

[0046] In a first aspect, the present invention provides a method for removing acid dyes from water, which comprises the following steps:

[0047] Mix a ferric salt or its solution with water containing an acid dye so that ferric ions form Fe(Ⅲ)-dye complex flocs with the acid dye;

[0048] Separate the Fe(Ⅲ)-dye complex flocs, adjust the pH of the Fe(Ⅲ)-dye complex flocs to be greater than or equal to 7 to cause the Fe(Ⅲ)-dye complex flocs to decomplex and form Fe(OH)3 flocs;

[0049] Separate the Fe(OH)3 flocs, and mix the Fe(OH)3 flocs with an acid solution to form a ferric salt solution.

[0050] In some alternative embodiments, the ferric salt or its solution is at least one of ferric chloride, ferric nitrate, ferric sulfate, aqueous ferric chloride solution, aqueous ferric nitrate solution, and aqueous ferric sulfate solution. Preferably, the ferric salt or its solution is ferric chloride or aqueous ferric chloride solution.

[0051] In some alternative embodiments, the acid dye is a dye containing 2 or more anionic functional groups. Preferably, the anionic functional group is a sulfonic group, a carboxyl group, or an o-phenolic hydroxyl azo group. More preferably, the acid dye is at least one of acid orange 7, acid fuchsin, and sunset yellow.

[0052] In some alternative embodiments, the molar ratio of ferric ions to the acid dye is 4:1 - 14:1. Preferably, the molar ratio of ferric ions to the acid dye is 10:1.

[0053] In some alternative embodiments, after mixing the ferric salt or its solution with water containing an acid dye, adjust the pH to 2.0 - 5.0. Preferably, after mixing the ferric salt or its solution with water containing an acid dye, adjust the pH to 3.3.

[0054] In some alternative embodiments, mix the ferric salt or its solution with water containing an acid dye under light-shielded conditions.

[0055] In some alternative embodiments, adjust the pH of the Fe(Ⅲ)-dye complex flocs to be greater than or equal to 7 with an alkali solution. Preferably, adjust the pH of the Fe(Ⅲ)-dye complex flocs to 9 with an alkali solution under light-shielded conditions.

[0056] In some alternative embodiments, the alkaline solution is an aqueous sodium hydroxide solution.

[0057] In some alternative embodiments, the acidic solution is at least one of an aqueous hydrochloric acid solution, an aqueous nitric acid solution, and an aqueous sulfuric acid solution.

[0058] In a second aspect, the present invention provides a system for removing acid dyes from water, as Figure 1 shown, which includes:

[0059] A coagulation tank 1 for containing a ferric salt or its solution and water containing acid dyes, so that ferric ions form Fe(Ⅲ)-dye complex flocs with the acid dyes;

[0060] A sedimentation tank 2 for separating out the Fe(Ⅲ)-dye complex flocs by sedimentation;

[0061] A decomplexation tank 3 for containing the Fe(Ⅲ)-dye complex flocs and an alkaline solution to adjust the pH of the Fe(Ⅲ)-dye complex flocs to be greater than or equal to 7, so that the Fe(Ⅲ)-dye complex flocs are decomplexed and form Fe(OH)3 flocs;

[0062] An acidification tank 4 for containing the Fe(OH)3 flocs and an acid solution to form a ferric salt solution.

[0063] In some alternative embodiments, the coagulation tank 1 is connected to the sedimentation tank 2 through a mixed liquid conveying pipeline 10, the bottom of the sedimentation tank 2 is connected to the decomplexation tank 3 through an Fe(Ⅲ)-dye complex floc conveying pipeline 7, the decomplexation tank 3 is connected to the acidification tank 4 through an iron sludge conveying pipeline 8, and the acidification tank 4 is connected to the coagulation tank 1 through a ferric solution circulation pipeline 9.

[0064] Some typical embodiments are introduced below.

[0065] In the following embodiments, the information of the acid dyes is shown in Table 1.

[0066] Table 1 Information of Acid Dyes

[0067]

[0068] In the following embodiments, the ultraviolet-visible spectrophotometry and the chemical oxygen demand (COD) method are combined to measure the concentration of the dyes.

[0069] Ultraviolet-visible spectrophotometry:

[0070] Taking Acid Orange 7 (AO7) as an example, a series of AO7 solutions with different concentrations were prepared. A certain volume of the solution was pipetted into a 2 mm quartz cuvette and scanned and tested using a UV-Vis spectrometer in the wavelength range of 200 - 800 nm. At the maximum absorption wavelength of 484 nm, the absorbance value was taken to plot the absorbance-concentration curve (A-C curve), as shown in Figure 2 . Similarly, for Sunset Yellow (SY) at the maximum absorption wavelength of 482 nm and Acid Fuchsin (AF) at the maximum absorption wavelength of 545 nm, the absorbance values were taken to plot the A-C curves, as shown in Figure 3 and Figure 4 . Figures 2 - 4 It is shown that the absorbance at the maximum wavelength of the dye is proportional to the concentration. Therefore, the complexation removal rate (CRR) of the dye can be calculated by the following formula:

[0071] CRR = [C0 - C t / C0 × 100% = [A0 - A t / A0 × 100%

[0072] where C0 and A0 are the concentration of the dye solution and the initial absorbance at the maximum absorption wavelength respectively, while C t and A t are the concentration of the dye in the supernatant of the complexation reaction and the absorbance at the maximum absorption wavelength respectively.

[0073] The corresponding decomplexation release rate of the dye (DRR) can be calculated by the following formula: DRR = C t / C0 × 100% = A t / A0 × 100%.

[0074] Chemical Oxygen Demand (COD) method:

[0075] Using potassium dichromate (K2Cr2O7) as the oxidant, at a temperature of 150 - 180 °C, the organic matter in the water sample is oxidized to CO2 and H2O, while K2Cr2O7 itself is reduced to Cr 3+ ; after the reaction, the increase in the absorbance of Cr 3+ is measured by a spectrophotometer to determine the COD value of the water sample.

[0076] Example 1

[0077] The ferric chloride solution was mixed with the Acid Orange 7 (AO7) solution, and only the pH of the mixed solution was changed to study the effect of pH on the formation of Fe(III)-dye complex flocs. Specifically, under light-shielded conditions, 23.98 mg / L of ferric chloride solution was added to 5 portions of 15 mg / L AO7 solution respectively. The molar ratio of ferric ion to AO7 (Fe / AO7 ratio) was fixed at 10, and the pH of the solution was adjusted to 2.0, 2.8, 3.3, 4.0, and 5.0 respectively. First, it was stirred rapidly for 3 minutes, then stirred slowly for 20 minutes. After standing for 3 hours, the supernatant was taken to measure the ultraviolet-visible absorption spectrum and COD concentration.

[0078] As Figure 5 shown, the ultraviolet spectrum of the 15 mg / L pure AO7 solution has two relatively obvious characteristic peaks. The peak at 230 nm belongs to the benzene ring structure in AO7, the absorption peak at 306 nm represents the naphthalene ring structure of AO7, and the peak at 484 nm indicates the hydrazone structure of AO7. The chromogenic groups in AO7 are mainly azo bonds (-N=N-) and unsaturated -S=O-. AO7 will undergo keto-enol tautomerism in the solution to produce hydrazone structure and exist in the form of a mixture of azo-hydrazone. The shoulder peak at 430 nm is the azo structure of AO7. As Figure 5 can be seen from 3+ , when Fe 3+ was added to the 15 mg / L AO7 solution and the pH was adjusted in the range of 2.0 - 5.0, both the peak position and peak intensity of the ultraviolet-visible absorption spectrum of the supernatant changed significantly.

[0079] As Figure 6 and Table 2 show, the absorbance (A 484 ) of the supernatant at a wavelength of 484 nm first decreased and then increased. The A 484 was the lowest at pH 3.3, and the color of the supernatant was close to colorless (see the inset in Figure 6 ). According to the calculation of A 484 , the removal rate of AO7 exceeded 90% ( Figure 7 ). At pH 3.3, the COD test result of the supernatant showed only 2.34, indicating that AO7 in the supernatant was directly removed. When the pH increased and decreased, the solution color gradually deepened, and the removal rate of AO7 also gradually decreased. The main reason for the complexation and removal of AO7 by Fe 3+ is that AO7 contains 2 anionic functional groups (1 sulfonic acid group and 1 o-hydroxyazo group), which can complex with Fe 3+ to form sedimentable flocs under the condition of pH about 3.3, so as to be removed from the water.

[0080] Table 2 Fe 3+Detection results of the supernatant after complexation sedimentation of AO7 at different pH values

[0081]

[0082] Example 2

[0083] Mix the ferric chloride solution with the AO7 solution, and only change the molar ratio of ferric ions to AO7 to study the effect of the Fe / AO7 molar ratio on the formation of Fe(Ⅲ)-dye complex flocs. Specifically, under light-shielded conditions, add 2.40, 4.80, 9.59, 14.39, 19.18, 23.98, 28.77, and 33.57 mg / L of ferric chloride solution to 8 portions of 200 mL of AO7 solution with a concentration of 15 mg / L respectively, so that the Fe / AO7 molar ratios are 1, 2, 4, 6, 8, 10, 12, and 14 respectively, and fix the pH at 3.3; first stir rapidly for 3 minutes, then stir slowly for 20 minutes, let it stand for 3 hours, take the supernatant, and measure the ultraviolet-visible absorption spectrum and COD concentration.

[0084] The results are as Figures 8 - 10 shown in Table 3, the Fe / AO7 molar ratio has an important influence on the removal of AO7. At pH 3.3, the larger the Fe / AO7 molar ratio, the lower the A 484 value of the supernatant, and the better the removal effect of AO7 in the water body. When the Fe / AO7 molar ratio exceeds 8:1, the removal rate of AO7 tends to be stable and the removal rate is about 90%. Within a certain dosage range, the dye removal rate increases with the increase of the Fe / AO7 molar ratio. As the dosage continues to increase, the removal effect remains basically unchanged after reaching the optimal effect. As can be seen from the inset in Figure 9 , after adding Fe 3+ , the color of the supernatant solution is significantly lighter than that of the original AO7 solution.

[0085] Table 3 Detection results of the supernatant after complexation sedimentation of AO7 at different Fe / AO7 molar ratios 3+ Detection results of the supernatant after complexation sedimentation of AO7 at different Fe / AO7 molar ratios

[0086]

[0087] Example 3

[0088] Under light-shielded conditions, add ferric chloride solution to 20 portions of 15 mg / L AO7 solution respectively, and adjust the Fe / AO7 molar ratios of 4 groups (5 portions in each group) of the mixed solutions to 4, 6, 7, and 8 respectively, and adjust the pH values of each group of mixed solutions to 3.2, 3.3, 3.5, 3.6, and 3.8 respectively; first stir rapidly for 3 minutes, then stir slowly for 20 minutes, after standing for 3 hours, take the supernatant and measure the ultraviolet-visible absorption spectrum.

[0089] As Figure 11 shown, when the Fe / AO7 molar ratio is above 5 and the pH is below 3.4, the absorbance of the supernatant is significantly lower, which is beneficial to the removal of AO7.

[0090] Example 4

[0091] The ultraviolet-visible absorption spectra of the AO7 solution and the mixed solution of AO7 and ferric chloride were measured under dark, natural light, and ultraviolet light irradiation conditions respectively to study the effect of light conditions on the removal of AO7. Specifically, six reactors were prepared in parallel, and 200 mL of a 1 mM AO7 solution was added. 1 mM ferric chloride solution (Fe / AO7 molar ratio was 10, pH was 3.3) was added to the 2nd, 4th, and 6th reactors respectively, and no ferric chloride solution was added to the other reactors (pH was 3.3); the 1st and 2nd reactors were in the dark; the 3rd and 4th reactors were irradiated with natural light; the 5th and 6th reactors were irradiated with an ultraviolet lamp (Xenon, ultraviolet); first, stir rapidly for 3 minutes, then stir slowly for 20 minutes, let stand for 3 hours, take the supernatant, measure the ultraviolet-visible absorption spectrum, and measure the COD content of the supernatant.

[0092] As Figure 12 and Figure 13 shown in Table 4, compared with the dark condition, when no Fe 3+ was added, the A 484 of AO7 under natural light and ultraviolet irradiation both decreased, from 2.402 under dark condition to 2.144 and 1.859 respectively, indicating that light has a certain degree of degradation on AO7, and ultraviolet light has a greater degree of degradation on AO7 than visible light. After adding Fe 3+ to the solution, the A 3+ of the ultraviolet-visible absorption spectrum of the supernatant after the complexation of AO7 and Fe 484 both decreased sharply.

[0093] Under the irradiation of the ultraviolet lamp, not only the supernatant decolorized, but also the settled flocs gradually decolorized, indicating that the Fe(Ⅲ)-AO7 complex flocs can undergo photocatalytic degradation reactions, and such reactions may cause changes in the structure of the complex, resulting in color changes. Under dark or natural light irradiation, due to the relatively small influence of photocatalytic degradation reactions, the color of the Fe(Ⅲ)-AO7 complex flocs may be relatively stable. This shows that the Fe(Ⅲ)-AO7 complex flocs have photocatalytic activity both in solution and in aggregates, and the color of the Fe(Ⅲ)-AO7 complex flocs does not change under dark and natural light conditions.

[0094] COD reflects the degree of pollution of water by substances. The larger the COD, the higher the concentration of organic matter in the water. As shown in Table 4, under dark conditions, without adding Fe 3+ the COD of the supernatant was about 50 mg / L; when Fe 3+ was added to the AO7 solution, the COD of the supernatant decreased to 0.4 mg / L and 3.8 mg / L, indicating that the content of organic matter in the supernatant was low at this time; that is, under dark conditions, AO7 and Fe 3+ formed flocs and entered the sludge phase. However, under natural light or ultraviolet light irradiation conditions, the COD concentration of the supernatant increased after adding Fe 3+ ; in particular, under ultraviolet light irradiation, the COD of the supernatant was relatively high, reaching 30.9 mg / L after adding Fe 3+ . At this time, photocatalytic degradation occurred, causing AO7 to decompose into small-molecule organic matter and exist in the water body, and it could not be removed by complexation coagulation with Fe 3+ . The above results show that when using Fe 3+ complexation coagulation to remove AO7, it should be carried out under dark conditions as much as possible to avoid photocatalytic decomposition of AO7 to generate small-molecule organic matter that cannot be removed by complexation coagulation.

[0095] Table 4 Detection results of the supernatant after complexation sedimentation of Fe 3+ with AO7 under different light conditions

[0096]

[0097] Example 5

[0098] Mix the AO7 solution with an initial concentration of 50 mg / L and the ferric chloride solution so that the Fe / AO7 molar ratio is 10, adjust the pH to 3.3 to form Fe(Ⅲ)-AO7 complex flocs; then separate the Fe(Ⅲ)-AO7 complex flocs by sedimentation, and add 0.1 mol / L NaOH solution to make the pH 2.0, 2.8, 3.3, 5.0, 6.0, 7.0, 8.0 and 9.0 respectively, so that the Fe(Ⅲ)-AO7 complex flocs are decomplexed. Take the decomplexed solution, measure its ultraviolet-visible absorption spectrum, and measure the COD content of its supernatant.

[0099] As Figures 14 - 16 shown, under the condition of pH less than 7, the percentage of decomplexation and release of AO7 (DRR) from the Fe(Ⅲ)-AO7 complex flocs is very small, less than 20%, and the decomplexation effect is poor; under the condition of pH greater than or equal to 7, the decomplexation effect of the Fe(Ⅲ)-AO7 complex flocs is good. At pH 8.0, the DRR exceeds 90%, indicating that Fe 3+ complexation decomplexation can remove and recover AO7 in the water body.

[0100] Example 6

[0101] Mix the AO7 solution with an initial concentration of 50 mg / L with the ferric chloride solution so that the Fe / AO7 molar ratio is 10, adjust the pH to 3.3 to form Fe(Ⅲ)-AO7 complex flocs; then separate the Fe(Ⅲ)-AO7 complex flocs by sedimentation, add 0.1 mol / L NaOH solution to make the pH 8.0, so that the Fe(Ⅲ)-AO7 complex flocs are decomplexed to obtain Fe(OH)3 flocs and a concentrated AO7 solution; separate the Fe(OH)3 flocs by sedimentation, add HCl solution with a concentration of 0.1 mol / L to form FeCl3 solution, and mix this FeCl3 solution with a new portion of AO7 solution with an initial concentration of 50 mg / L, and cycle the complexation / decomplexation 6 times. As Figure 17 shown, after cycling the complexation / decomplexation 6 times, the removal rate of AO7 in the AO7 solution by the FeCl3 solution remains at about 75%.

[0102] Example 7

[0103] This example is basically the same as Example 1, except that: 50 mg / L of AO7 is replaced by acid fuchsin (AF).

[0104] As Figure 18 and 19 shown, when Fe 3+ is added to the AF solution, at pH 3.0, Fe 3+ complexes with AF and forms AF-Fe 3 + flocs that settle to the bottom. The supernatant changes from red to nearly colorless, and the absorbance at the maximum absorption wavelength of 545 nm decreases sharply, indicating that the concentration of AF in the supernatant decreases sharply. As the pH gradually increases to more than 7.0, the color of the supernatant gradually deepens from colorless to red, and the absorbance also gradually increases, indicating that AF is gradually released back into the solution and the concentration gradually increases. The main reason is that AF contains 3 sulfonic acid groups and can complex with Fe 3+ to form sedimentable flocs AF-Fe 3+ at about pH 3.0; while when the pH exceeds 7.0, the AF-Fe 3+ flocs can be decomplexed and released. The results show that AF can be removed by Fe 3+ complexation coagulation method and decomplexed and recycled for recovery.

[0105] Example 8

[0106] This example is basically the same as Example 1, except that: AO7 is replaced by sunset yellow (SY).

[0107] AsFigures 20 - 21 As shown, Fe was added to the SY solution 3+ , and at pH 3.0, Fe 3+ complexed with SY to form SY-Fe 3+ flocs that settled to the bottom. The supernatant changed from yellow to nearly colorless, and the absorbance at the maximum absorption wavelength of 482 nm decreased sharply, indicating that the concentration of SY in the supernatant decreased sharply. As the pH gradually increased beyond 6.0, the color of the supernatant gradually darkened from colorless to yellow, and the absorbance also gradually increased, indicating that SY was gradually released back into the solution and its concentration gradually increased. The main reason is that SY contains 1 ortho-phenolic hydroxyl azo group and 2 sulfonic acid groups, which can complex with Fe 3+ to form sedimentable SY-Fe 3+ flocs; while at pH above 7.0, the SY-Fe 3+ flocs can decomplex and release SY. The results show that SY can be removed by Fe 3+ complexation coagulation and decomplexed and recycled. It should be noted that since the structure of SY is similar to AO7 and both contain ortho-phenolic hydroxyl azo groups, it is necessary to avoid light as much as possible during the Fe 3+ complexation removal process.

[0108] Comparative Example 1

[0109] A methyl orange (MO) solution with an initial concentration of 50 mg / L was mixed with a ferric chloride solution to make the Fe / methyl orange molar ratio 10. 0.1 mol / L NaOH solution was added respectively to make the pH 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0. The complexed solution was taken and its ultraviolet-visible absorption spectrum was measured.

[0110] As Figure 22 shown, after adding ferric chloride to the MO solution, only a weak color change (yellow - red - yellow) occurred under different pH conditions. The results of the ultraviolet-visible absorption spectrum showed that the absorption peak of the solution shifted, but the absorbance intensity changed little, indicating that the concentration of MO in the solution did not change significantly, that is, MO could not be removed by Fe 3+ complexation coagulation. The main reason is that MO only contains 1 anionic functional group (sulfonic acid group), and Fe 3+ cannot form sedimentable flocs with MO.

[0111] Comparative Example 2

[0112] This comparative example is basically the same as Comparative Example 1, with the only difference being that MO was replaced by rhodamine B (RhB).

[0113] As Figure 23 shown, after adding Fe to the RhB solution 3+, as the pH value changes, the color of the solution does not change significantly. The ultraviolet-visible absorption spectrum shows that at the characteristic absorption wavelength of 560 nm, the absorbance does not change significantly, indicating that the concentration of RhB in the solution does not change significantly, that is, RhB cannot be removed by the Fe 3+ complexation coagulation method. The main reason is that RhB only contains one anionic functional group (carboxyl group), and Fe 3+ cannot form sedimentable flocs with RhB.

[0114] As mentioned above, these are only the preferred embodiments of the present invention. The present invention is not limited to the above-mentioned embodiments. As long as the same or equivalent means are used to achieve the technical effects of the present invention, they should fall within the protection scope of the present invention. Within the protection scope of the present invention, various modifications and changes can be made to its technical solutions and / or implementation manners.

Claims

1. A method for removing acid dyes from water, characterized in that, It includes the following steps: Mix a ferric salt or its solution with water containing an acid dye, so that ferric ions and the acid dye form Fe(Ⅲ)-dye complex flocs; Separate the Fe(Ⅲ)-dye complex flocs, adjust the pH of the Fe(Ⅲ)-dye complex flocs to be greater than or equal to 7, so that the Fe(Ⅲ)-dye complex flocs are decomplexed and form Fe(OH)3 flocs; Separate the Fe(OH)3 flocs, mix the Fe(OH)3 flocs with an acid solution to form a ferric salt solution; Wherein, the acid dye is a dye containing 2 or more anionic functional groups, and the anionic functional groups are sulfonic acid groups, carboxyl groups or ortho-phenol hydroxyl azo groups.

2. The method according to claim 1, wherein The ferric salt or its solution is at least one of ferric chloride, ferric nitrate, ferric sulfate, aqueous ferric chloride solution, aqueous ferric nitrate solution, and aqueous ferric sulfate solution.

3. The method according to claim 1, characterized in that The acid dye is at least one of acid orange 7, acid fuchsin, and sunset yellow.

4. The method according to claim 1, characterized in that The molar ratio of ferric ions to the acid dye is 4:1 - 14:

1.

5. The method according to claim 1, characterized in that, After mixing the ferric salt or its solution with water containing an acid dye, adjust the pH to 2.0 - 5.

0.

6. The method according to claim 1, characterized in that, Mix the ferric salt or its solution with water containing an acid dye under light-shielded conditions.

7. A system for removing acid dyes from water, characterized in that, It includes: A coagulation tank for accommodating a ferric salt or its solution and water containing an acid dye, so that ferric ions and the acid dye form Fe(Ⅲ)-dye complex flocs; A sedimentation tank for separating the Fe(Ⅲ)-dye complex flocs by sedimentation; A decomplexing tank for accommodating the Fe(Ⅲ)-dye complex flocs and an alkali solution to adjust the pH of the Fe(Ⅲ)-dye complex flocs to be greater than or equal to 7, so that the Fe(Ⅲ)-dye complex flocs are decomplexed and form Fe(OH)3 flocs; An acidification tank for accommodating the Fe(OH)3 flocs and an acid solution to form a ferric salt solution; Wherein, the acid dye is a dye containing 2 or more anionic functional groups, and the anionic functional groups are sulfonic acid groups, carboxyl groups or ortho-phenol hydroxyl azo groups.

8. The system for removing acid dyes from water according to claim 7, characterized in that, The coagulation tank is connected to the sedimentation tank through a mixed liquid conveying pipeline, the bottom of the sedimentation tank is connected to the decomplexing tank through an Fe(Ⅲ)-dye complex flocs conveying pipeline, the decomplexing tank is connected to the acidification tank through an iron sludge conveying pipeline, and the acidification tank is connected to the coagulation tank through a ferric solution circulation pipeline.

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