Re-dyeing process of waste decolorized liquid of colored cellulose fabric

Abstract

This invention relates to the field of textile decolorization and dyeing technology, specifically a process for re-dyeing cellulose fabrics using waste decolorization wastewater from waste colored cellulose fabrics. The process includes: first, decolorizing the waste colored cellulose fabrics to obtain decolorization wastewater; then, adjusting the pH value of the decolorized wastewater; evaporating and concentrating the decolorization wastewater, and determining the chromophore content in the concentrated decolorization wastewater using spectrophotometry to obtain concentrated decolorization wastewater; adding soft water to the concentrated decolorization wastewater to prepare a dyeing mother liquor of a predetermined concentration; subjecting the cellulose fabric to be dyed to cationic modification treatment, and then dyeing it using the dyeing mother liquor; finally, performing alkaline washing and color fixing treatment. This process recycles and utilizes the decolorization wastewater from the pulping process of colored cotton or regenerated cellulose fabrics, using its chromophores to re-dye the cellulose fabrics. This method recycles wastewater, representing a greater recycling of resources during the recycling and regeneration of waste textiles, effectively reducing wastewater discharge, lowering costs, saving energy, and protecting the environment, thus possessing significant economic benefits and social value.

Description

Technical Field

[0001] This invention relates to the field of textile decolorization and dyeing technology, and in particular to a process for re-dyeing cellulose fabrics with waste decolorization waste liquid from waste colored cellulose fabrics. Background Technology

[0002] With the continuous improvement of people's living standards, the amount of discarded clothing is increasing. Globally, over 50 million tons of textile waste are produced annually, making the issue of recycling waste textiles increasingly prominent. Recycling waste textiles can save resources and protect the environment; however, currently, my country's waste textile recycling and industrial reuse systems are not effectively integrated, resulting in a large amount of waste textiles not being utilized as resources.

[0003] Cotton is the most widely used natural textile fiber globally, with an annual production of 24 million tons. However, 15% of cotton is unusable in fashion manufacturing, and nearly 60% of clothing sold is discarded as waste within a year. A small portion of this waste cotton textile is recycled into recycled cotton filling or woven into lower-grade textiles; the majority is ultimately incinerated or landfilled, polluting the atmosphere and water resources. Utilizing waste cellulose fabrics, such as cotton or viscose fibers, to produce pulp and then manufacturing new fibers and fabrics represents a high-value and economically viable approach to recycling waste textiles. New fibers, such as recycled viscose or lyocell fibers, offer superior performance, possessing better softness and moisture absorption and breathability than cotton.

[0004] When waste colored cellulose fabrics, such as cotton or viscose fiber fabrics, are used to make pulp, the fabrics need to be decolorized. For fabrics dyed with reactive dyes, the reactive dyes and fabric fibers are bonded by covalent bonds, requiring decolorization using an alkali-reduction system solution. After decolorization, the reactive dyes themselves lose their active groups and can no longer form strong covalent bonds with the fibers. Furthermore, because some dyes are degraded during decolorization, they are even more difficult to adsorb onto the fabric and cannot be directly used for dyeing. The waste liquid after decolorization contains a large number of chromophores. Some of these chromophores are hydrolyzed reactive dyes, while others are decomposed reactive dyes. Since the chromophores themselves are negatively charged, and the fibers of cellulose fabrics are also negatively charged in aqueous solutions, conventional dyeing processes result in very light colors and poor colorfastness in cellulose fabrics. In other words, the chromophores in the decolorization liquid of waste colored cellulose fabrics cannot be used as dyes for cellulose fabrics and can only be used for wastewater treatment. However, the chromophores in the decolorization waste liquid have a high chroma, and direct wastewater treatment would increase wastewater treatment costs and waste chromophore resources.

[0005] To date, the decolorizing wastewater generated during the pulping process of waste colored cellulose fabrics, such as waste cotton or viscose fiber fabrics, is mostly treated directly as sewage. There are no related patents or reports on the recycling and utilization of decolorizing wastewater. If the chromophores in the pulping and decolorizing wastewater can be fully utilized to achieve resource recycling and reuse of the decolorizing wastewater, it can effectively reduce sewage discharge, reduce the burden of sewage treatment, save water and energy, and at the same time, it can further recycle resources during the recycling and regeneration of waste textiles, with significant economic benefits and social value in terms of energy saving, environmental protection, and ecology.

[0006] The purpose of this invention is to solve the problem of wastewater treatment from the decolorization process of pulping waste colored cellulose fabrics, such as cotton or viscose fiber fabrics. It provides a process for re-dyeing cellulose fabrics using the decolorization wastewater from waste colored cellulose fabrics. This method achieves the recycling and reuse of the decolorization wastewater during fabric sizing, reducing the burden of wastewater treatment and enabling greater recycling of resources from waste textiles. Furthermore, this process is low-cost, energy-saving, and environmentally friendly.

[0007] Specifically, the present invention adopts the following technical solution:

[0008] A process for re-dyeing cellulose fabrics using waste decolorizing liquid from discarded colored cellulose fabrics, the re-dyeing process comprising the following steps:

[0009] (1) First, the waste colored cellulose fabric is crushed and then decolorized in an alkali-reduction system solution to obtain decolorized waste liquid.

[0010] (2) Then, adjust the pH of the decolorized waste liquid to 6-7 with acid;

[0011] (3) The decolorized waste liquid after pH adjustment is evaporated and concentrated, and the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry. After the chromophore content reaches the required level, the concentrated decolorized waste liquid is obtained.

[0012] (4) Add soft water to the concentrated decolorizing waste liquid and prepare the concentrated decolorizing waste liquid into a dyeing mother liquor of a predetermined concentration;

[0013] (5) The cellulose fabric to be dyed is first subjected to cationic modification treatment;

[0014] (6) Dye the cellulose fabric to be dyed after the cationic modification treatment in step (5) using the dyeing mother liquor obtained in step (4);

[0015] (7) Remove excess dye from dyed cellulosic fabrics by alkaline washing;

[0016] (8) Fix the fabric after removing the floating color.

[0017] As a preferred embodiment, in step (1), the alkali-reduction system solution is: sodium hydroxide is used as the alkali, and sodium dithionite and / or sodium sulfite is used as the reducing agent; in the decolorization treatment: the bath ratio is 1:40~50, the treatment temperature is 75~80℃, the treatment time is 50~60min, the concentration of alkali is 35g / L, and the concentration of reducing agent is 5g / L.

[0018] As a preferred option, in step (2), the acid used is one or more of hydrochloric acid, acetic acid, citric acid, etc.

[0019] As a preferred option, in step (3), the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry. Specifically, the concentrated decolorized waste liquid is first diluted 50 times, and then the absorbance is greater than or equal to 0.6 Abs in the range of maximum absorption wavelength of 400~780nm. The chromophore content is then determined.

[0020] As a preferred option, in step (4), the concentration of the concentrated decolorizing waste liquid in the dyeing mother liquor is 1%~10%.

[0021] As a preferred embodiment, in step (5), the cationic modification treatment specifically involves two processes. The first process is as follows: the cellulose fabric to be dyed is placed in a mixed solution of polyethyleneimine and acetic acid as the cationic modification treatment solution, and the temperature is raised to 50-60℃ at a heating rate of 0.5℃ / min according to a bath ratio of 1:20~40 and kept at 50-60℃ for 20-40min. After completion, it is washed with clean water and the temperature is raised to 50-60℃ at a heating rate of 2℃ / min and kept at 50-60℃ for 20-40min. The concentration of polyethyleneimine is 2g / L and the concentration of acetic acid is 1g / L.

[0022] As a preferred option, the second specific process for cationic modification treatment is as follows: The cellulosic fabric to be dyed is placed in a mixed solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride and sodium hydroxide as the cationic modification treatment solution. The temperature is increased to 60-70℃ at a heating rate of 2℃ / min according to a bath ratio of 1:20-40 and held for 20-40 minutes. Then, it is acid-washed with a bath ratio of 1:20-40 and the temperature is increased to 60-70℃ at a heating rate of 2℃ / min and held for 20-40 minutes. The concentration of 3-chloro-2-hydroxypropyltrimethylammonium chloride is 50 g / L and the concentration of sodium hydroxide is 15 g / L.

[0023] As a preferred option, the dyeing process in step (5) is as follows: the liquor ratio is 1:20~40, the temperature is raised to 75~85℃ at a heating rate of 2℃ / min, and the temperature is maintained for 40~60min.

[0024] As a preferred option, the alkaline washing process in step (6) is as follows: the bath ratio is 1:20~40, the temperature is raised to 50~60℃ at a heating rate of 2℃ / min, and the temperature is held for 20~40min. The concentration of the acid-releasing agent is 0.5 g / L.

[0025] As a preferred option, the color-fixing treatment in step (7) is specifically as follows: with a bath ratio of 1:20~40, the temperature is raised to 50~60℃ at full speed and kept warm for 30~50 minutes.

[0026] As a preferred option, the cellulose fabric is a cotton or regenerated cellulose fiber fabric (viscose, modal, lyocell).

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] This invention decolorizes waste colored cellulose fabrics, then recovers the chromophores from the decolorization wastewater, and uses these chromophores to re-dye the cellulose fabrics that require dyeing. Fabrics treated with this re-dyeing process exhibit high color fastness and color stability. This method of dyeing fabrics using recovered chromophores effectively reduces wastewater discharge during the pulping of colored cotton or regenerated cellulose fabrics, lowers the burden on wastewater treatment, saves water and energy, and also promotes greater recycling of waste textile resources. It has significant economic and social benefits, including energy conservation, environmental protection, and ecological benefits.

[0029] In this invention, the cellulose fabric to be dyed is cationically modified, which increases the directness of the cellulose fibers to the chromophores in the decolorizing waste liquid, facilitating the adsorption of sufficient chromophores. The adsorbed chromophores are bonded to the cellulose fabric via ionic bonds, resulting in high color fastness. Simultaneously, excess floating dye is washed away in a high-temperature alkaline bath, further improving color fastness and light stability. Copper sulfate is used for color fixing, improving light fastness and wash fastness to meet clothing standards.

[0030] This invention effectively recovers and utilizes chromophore resources in decolorization wastewater, reduces wastewater discharge, and has low process costs, greatly reducing the use of salt and alkali, thus meeting the needs of green and sustainable production. Detailed Implementation

[0031] Representative embodiments will now be further refined. It should be understood that the following description is not intended to limit the embodiments to a single preferred embodiment. Rather, it is intended to cover alternatives, modifications, and equivalents that may be included within the substance and scope of the embodiments defined by the appended claims.

[0032] This invention provides a solution for the secondary utilization of waste colored cellulose fabrics. The details are as follows.

[0033] A process for re-dyeing cellulose fabrics using waste decolorizing liquid from discarded colored cellulose fabrics, the re-dyeing process comprising the following steps:

[0034] (1) First, the waste colored cellulose fabric is crushed and then decolorized in an alkali-reduction system solution to obtain decolorized waste liquid; the alkali-reduction system solution is: sodium hydroxide is used as alkali, and sodium dithionite and / or sodium sulfite are used as reducing agents; in the decolorization process: the bath ratio is 1:40~50, the treatment temperature is 75~80℃, the treatment time is 50~60min, the concentration of alkali is 35g / L, and the concentration of reducing agent is 5g / L;

[0035] (2) Then, the pH of the decolorized waste liquid is adjusted to 6-7 using acid; the decolorized waste liquid after pH adjustment is evaporated and concentrated, and the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry. After the chromophore content reaches the required level, the concentrated decolorized waste liquid is obtained; the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry as follows: first, the concentrated decolorized waste liquid is diluted 50 times, and then the absorbance is greater than or equal to 0.6 Abs in the range of maximum absorption wavelength of 400nm~780nm to determine the chromophore content;

[0036] (3) Add soft water to the concentrated decolorizing waste liquid to prepare a dyeing mother liquor of a predetermined concentration; the concentration of the concentrated decolorizing waste liquid in the dyeing mother liquor is 1%~10%;

[0037] (4) The cellulose fabric to be dyed is first subjected to cationic modification treatment. The cationic modification treatment is carried out in one of two ways. One way is to put the cellulose fabric to be dyed into a mixed solution of polyethyleneimine and acetic acid as the cationic modification treatment solution, and heat it to 50-60℃ at a heating rate of 0.5℃ / min according to a bath ratio of 1:20~40 and keep it at 50-60℃ for 20-40min. After completion, wash with clean water and heat it to 50-60℃ at a heating rate of 2℃ / min and keep it at 50-60℃ for 20-40min. The concentration of polyethyleneimine is 2g / L and the concentration of acetic acid is 1g / L. Another method involves immersing the cellulosic fabric to be dyed in a mixed solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride and sodium hydroxide as a cationic modification treatment solution. The solution is heated to 60-70°C at a rate of 2°C / min with a bath ratio of 1:20-40, and held for 20-40 minutes. Then, acid washing is performed with a bath ratio of 1:20-40, heated to 50-60°C at a rate of 2°C / min, and held for 20-40 minutes. The concentration of 3-chloro-2-hydroxypropyltrimethylammonium chloride is 50 g / L, and the concentration of sodium hydroxide is 15 g / L.

[0038] (5) The cellulose fabric to be dyed after the cationic modification treatment in step (4) is dyed with the dyeing mother liquor obtained in step (3); the dyeing process is as follows: the liquor ratio is 1:20~40, the temperature is raised to 75~85℃ at a heating rate of 2℃ / min, and the temperature is held for 40~60min.

[0039] (6) Remove the floating color by alkaline washing of the dyed cellulose fabric; the alkaline washing process is as follows: the bath ratio is 1:20~40, the temperature is raised to 50~60℃ at a heating rate of 2℃ / min, and the temperature is held for 20~40min. The concentration of the acid-releasing agent is 0.5 g / L.

[0040] (7) The fabric after removing the floating color is subjected to color fixing treatment; the color fixing treatment is as follows: with a bath ratio of 1:20, the temperature is raised to 60℃ at full speed and kept warm for 30 minutes.

[0041] Example 1: A process for re-dyeing cellulose fabrics using waste decolorizing liquid from discarded colored cellulose fabrics, comprising the following steps:

[0042] (1) First, the waste colored cellulose fabric is crushed and then decolorized using an alkali-reduction system solution to obtain decolorized waste liquid. The alkali-reduction system solution is: sodium hydroxide with a concentration of 35 g / L is used as the alkali, and sodium dithionite with a concentration of 5 g / L is used as the reducing agent. In the decolorization process, the bath ratio is 1:50, the treatment temperature is 75℃, and the treatment time is 50 min.

[0043] (2) Then, the pH of the decolorized waste liquid is adjusted to 6.5 with acid; the decolorized waste liquid after pH adjustment is evaporated and concentrated, and the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry. After the chromophore content reaches the required content, the concentrated decolorized waste liquid is obtained; the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry as follows: first, the concentrated decolorized waste liquid is diluted 50 times, and then the absorbance is greater than or equal to 0.6 Abs in the range of maximum absorption wavelength of 400nm~780nm to determine the chromophore content;

[0044] (3) Add soft water to the concentrated decolorizing waste liquid to prepare a dyeing mother liquor of a predetermined concentration; the concentration of the concentrated decolorizing waste liquid in the dyeing mother liquor is 10%;

[0045] (4) The cellulose fabric to be dyed is first subjected to cationic modification treatment. The cationic modification treatment is as follows: the cellulose fabric to be dyed is placed in a mixed solution of polyethyleneimine-1800 and acetic acid as the cationic modification treatment solution, and the temperature is raised to 60℃ for 20min at a heating rate of 0.5℃ / min according to the bath ratio of 1:20. After completion, it is washed with water and heated to 60℃ at a heating rate of 2℃ / min and kept for 20min. The concentration of polyethyleneimine-1800 is 2g / L and the concentration of acetic acid is 1g / L.

[0046] (5) The lyocell fiber fabric to be dyed after the cationic modification treatment in step (4) is dyed with the dyeing mother liquor obtained in step (3); the dyeing process is as follows: the liquor ratio is 1:20, the temperature is raised to 85℃ at a heating rate of 2℃ / min, and the temperature is held for 40min.

[0047] (6) The dyed cellulose fabrics are alkali washed to remove the floating color; the alkali washing process is as follows: the bath ratio is 1:20, the temperature is raised to 60℃ at a heating rate of 2℃ / min, and the temperature is kept for 20min. The concentration of the acid release agent is 0.5 g / L; the acid release agent is the commercially available pH slip agent CY product from Hangzhou Duon Co., Ltd.

[0048] (7) The fabric after removing the floating color is subjected to color fixing treatment; the color fixing treatment is as follows: with a bath ratio of 1:20, the temperature is raised to 60℃ at full speed and kept warm for 30 minutes.

[0049] Example 2: A process for re-dyeing cellulose fabrics using waste decolorizing liquid from discarded colored cellulose fabrics, comprising the following steps:

[0050] (1) First, the waste colored cellulose fabric is crushed and then decolorized using an alkali-reduction system solution to obtain decolorized waste liquid. The alkali-reduction system solution is: sodium hydroxide with a concentration of 35 g / L is used as the alkali, and sodium dithionite with a concentration of 5 g / L is used as the reducing agent. In the decolorization process, the bath ratio is 1:50, the treatment temperature is 75℃, and the treatment time is 50 min.

[0051] (2) Then, the pH of the decolorized waste liquid is adjusted to 6.5 with acid; the decolorized waste liquid after pH adjustment is evaporated and concentrated, and the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry. After the chromophore content reaches the required content, the concentrated decolorized waste liquid is obtained; the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry as follows: first, the concentrated decolorized waste liquid is diluted 50 times, and then the absorbance is greater than or equal to 0.6 Abs in the range of maximum absorption wavelength of 400nm~780nm to determine the chromophore content;

[0052] (3) Add soft water to the concentrated decolorizing waste liquid to prepare a dyeing mother liquor of a predetermined concentration; the concentration of the concentrated decolorizing waste liquid in the dyeing mother liquor is 10%;

[0053] (4) The cellulose fabric to be dyed is first subjected to cationic modification treatment; cationic modification treatment: the cellulose fabric to be dyed is placed in a mixed solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride with a concentration of 50 g / L and sodium hydroxide with a concentration of 15 g / L as the cationic modification treatment solution. The temperature is raised to 70°C at a heating rate of 2°C / min according to the bath ratio of 1:20 and kept at 2°C / min for 20 min. Then, it is acid washed with acetic acid 1.5 g / L at a bath ratio of 1:20 and the temperature is raised to 60°C at a heating rate of 2°C / min and kept at 60°C for 20 min.

[0054] (5) The lyocell fiber fabric to be dyed after the cationic modification treatment in step (4) is dyed with the dyeing mother liquor obtained in step (3); the dyeing process is as follows: the liquor ratio is 1:20, the temperature is raised to 85℃ at a heating rate of 2℃ / min, and the temperature is held for 40min.

[0055] (6) The dyed cellulose fabrics are alkali washed to remove the floating color; the alkali washing process is as follows: the bath ratio is 1:20, the temperature is raised to 60℃ at a heating rate of 2℃ / min, and the temperature is kept for 20min. The concentration of the acid release agent is 0.5 g / L; the acid release agent is the commercially available pH slip agent CY product from Hangzhou Duon Co., Ltd.

[0056] (7) The fabric after removing the floating color is subjected to color fixing treatment; the color fixing treatment is as follows: with a bath ratio of 1:20, the temperature is raised to 60℃ at full speed and kept warm for 30 minutes.

[0057] Example 3: A process for re-dyeing cellulose fabrics using waste decolorizing liquid from discarded colored cellulose fabrics, comprising the following steps:

[0058] (1) First, the waste colored cellulose fabric is crushed and then decolorized using an alkali-reduction system solution to obtain decolorized waste liquid. The alkali-reduction system solution is: sodium hydroxide with a concentration of 35 g / L is used as the alkali, and sodium dithionite with a concentration of 3 g / L and sodium sulfite with a concentration of 1 g / L are used as the reducing agents. In the decolorization process, the bath ratio is 1:50, the treatment temperature is 75℃, and the treatment time is 50 min.

[0059] (2) Then, the pH of the decolorized waste liquid is adjusted to 6.5 with acid; the decolorized waste liquid after pH adjustment is evaporated and concentrated, and the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry. After the chromophore content reaches the required content, the concentrated decolorized waste liquid is obtained; the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry as follows: first, the concentrated decolorized waste liquid is diluted 50 times, and then the absorbance is greater than or equal to 0.6 Abs in the range of maximum absorption wavelength of 400nm~780nm to determine the chromophore content;

[0060] (3) Add soft water to the concentrated decolorizing waste liquid to prepare a dyeing mother liquor of a predetermined concentration; the concentration of the concentrated decolorizing waste liquid in the dyeing mother liquor is 10%;

[0061] (4) The lyocell fiber fabric to be dyed is first subjected to cationic modification treatment. Cationic modification treatment: The lyocell fabric to be dyed is placed in a mixed solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride with a concentration of 50 g / L and sodium hydroxide with a concentration of 15 g / L as the cationic modification treatment solution. The temperature is raised to 70°C at a heating rate of 2°C / min according to the bath ratio of 1:20 and kept at 70°C for 20 min. Then, it is acid washed with acetic acid 1.5 g / L at a bath ratio of 1:20 and heated to 60°C at a heating rate of 2°C / min and kept at 60°C for 20 min.

[0062] (5) The cellulose fabric to be dyed after the cationic modification treatment in step (4) is dyed with the dyeing mother liquor obtained in step (3); the dyeing process is as follows: the liquor ratio is 1:20, the temperature is raised to 85℃ at a heating rate of 2℃ / min, and the temperature is held for 40min.

[0063] (6) The dyed cellulose fabrics are alkali washed to remove the floating color; the alkali washing process is as follows: the bath ratio is 1:20, the temperature is raised to 60℃ at a heating rate of 2℃ / min, and the temperature is kept for 20min. The concentration of the acid release agent is 0.5 g / L; the acid release agent is the commercially available pH slip agent CY product from Hangzhou Duon Co., Ltd.

[0064] (7) The fabric after removing the floating color is subjected to color fixing treatment; the color fixing treatment is as follows: with a bath ratio of 1:20, the temperature is raised to 60℃ at full speed and kept warm for 30 minutes.

[0065] Comparative Example 1:

[0066] The lyocell fibers of the cellulosic fabric to be dyed were dyed using conventional dye solutions.

[0067] Sexual function tests were conducted on the dyed products of Examples 1-3 and Comparative Example 1, specifically, tests were performed according to relevant national standards on perspiration fastness (acid), perspiration fastness (alkali), soaping fastness, and light fastness. The test results are shown in the table below.

[0068]

[0069] Based on the test results of the products in the above embodiments, it can be seen that the dyeing results of the products meet the relevant national dyeing standards in terms of sweat fastness (acid), sweat fastness (alkali), soaping fastness, and light fastness. Some indicators show excellent performance, and the results are comparable to those of conventional dye liquor indices.

[0070] It will be apparent to those skilled in the art that modifications, combinations, and variations can be made to the teachings described above.

Claims

1. A process for re-dyeing cellulose fabrics using waste decolorizing liquid from discarded colored cellulose fabrics, characterized in that: The re-dyeing process includes the following steps: (1) First, the waste colored cellulose fabric is crushed and then decolorized in an alkali-reduction system solution to obtain decolorized waste liquid. (2) Then, adjust the pH of the decolorized waste liquid to 6-7 with acid; (3) The decolorized waste liquid after pH adjustment is evaporated and concentrated, and the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry. After the chromophore content reaches the required level, the concentrated decolorized waste liquid is obtained. (4) Add soft water to the concentrated decolorizing waste liquid and prepare the concentrated decolorizing waste liquid into a dyeing mother liquor of a predetermined concentration; (5) The cellulose fabric to be dyed is first subjected to cationic modification treatment; (6) Dye the cellulose fabric to be dyed after the cationic modification treatment in step (5) using the dyeing mother liquor obtained in step (4); (7) Remove excess dye from dyed cellulosic fabrics by alkaline washing; (8) Perform color-fixing treatment on the fabric after removing the floating color; In step (1), the alkali-reduction system solution is as follows: sodium hydroxide is used as the alkali, and sodium dithionite and / or sodium sulfite are used as the reducing agent; in the decolorization treatment, the bath ratio is 1:40~50, the treatment temperature is 75~80℃, the treatment time is 50~60min, the concentration of alkali is 35g / L, and the concentration of reducing agent is 5g / L.

2. The re-dyeing process for cellulose fabrics using waste decolorizing wastewater from waste colored cellulose fabrics according to claim 1, characterized in that: In step (2), the acid used is one or more of hydrochloric acid, acetic acid, and citric acid.

3. The re-dyeing process for cellulose fabrics using waste decolorizing wastewater from waste colored cellulose fabrics according to claim 1, characterized in that: In step (3), the chromophore content in the concentrated decolorized waste liquid is determined by spectrophotometry. Specifically, the concentrated decolorized waste liquid is first diluted 50 times, and then the absorbance is greater than or equal to 0.6 Abs in the range of maximum absorption wavelength of 400~780nm. The chromophore content is then determined.

4. The re-dyeing process for cellulose fabrics using waste decolorizing wastewater from waste colored cellulose fabrics according to claim 1, characterized in that: In step (4), the concentration of the concentrated decolorizing waste liquid in the dyeing mother liquor is 1%~10%.

5. The re-dyeing process for cellulose fabrics using waste decolorizing wastewater from waste colored cellulose fabrics according to claim 1, characterized in that: In step (5), the cation modification treatment specifically involves two processes; The first process involves immersing the cellulose fabric to be dyed in a mixed solution of polyethyleneimine and acetic acid as a cationic modification treatment solution. The solution is heated to 50-60°C at a rate of 0.5°C / min with a bath ratio of 1:20-40, and held for 20-40 minutes. After completion, the fabric is washed with clean water, and then heated to 50-60°C with a rate of 2°C / min and held for 20-40 minutes. The concentration of polyethyleneimine is 2 g / L, and the concentration of acetic acid is 1 g / L. Process 2 is as follows: The cellulose fabric to be dyed is placed in a mixed solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride and sodium hydroxide as a cationic modification treatment solution. The temperature is increased to 60-70℃ at a heating rate of 2℃ / min according to a bath ratio of 1:20-40 and held for 20-40 minutes. Then, it is acid washed with a bath ratio of 1:20-40 and the temperature is increased to 60-70℃ at a heating rate of 2℃ / min and held for 20-40 minutes. The concentration of 3-chloro-2-hydroxypropyltrimethylammonium chloride is 50 g / L and the concentration of sodium hydroxide is 15 g / L.

6. The re-dyeing process for cellulose fabrics using waste decolorizing wastewater from waste colored cellulose fabrics according to claim 1, characterized in that: The dyeing process in step (6) is as follows: the liquor ratio is 1:20~40, the temperature is raised to 75~85℃ at a heating rate of 2℃ / min, and the temperature is maintained for 40~60min.

7. The re-dyeing process for cellulose fabrics using waste decolorizing wastewater from waste colored cellulose fabrics according to claim 1, characterized in that: The alkaline washing process in step (7) is as follows: the bath ratio is 1:20~40, the temperature is raised to 50~60℃ at a heating rate of 2℃ / min, and the temperature is held for 20~40min. The concentration of the acid-releasing agent is 0.5 g / L.

8. The re-dyeing process for cellulose fabrics using waste decolorizing wastewater from waste colored cellulose fabrics according to claim 1, characterized in that: The color-fixing treatment in step (8) is as follows: with a liquor ratio of 1:20~40, heat up to 50~60℃ at full speed and keep warm for 30~50 minutes.

9. The re-dyeing process for cellulose fabrics using waste decolorizing liquid from waste colored cellulose fabrics according to claim 1, characterized in that: Cellulose fabrics are made of cotton or regenerated cellulose fibers.

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