A method for treating textile printing and dyeing wastewater by using rare earth modified Ti-based dry gel coagulant

Abstract

This invention relates to a method for treating textile dyeing and printing wastewater using a rare earth-modified Ti-based dry gel coagulant, comprising the following steps: (1) Preparation of the rare earth-modified Ti-based dry gel coagulant: adding rare earth metal salts to a mixture of ethanol and acetylacetone, dissolving completely, and then adding titanium tetrachloride dropwise; subsequently adding a mixture of ethanol and distilled water dropwise, stirring evenly, and drying to obtain the coagulant; (2) adding the rare earth-modified Ti-based dry gel coagulant to the textile dyeing and printing wastewater, stirring, and then allowing it to stand. The treatment method of this invention has the advantages of simple operation, slow pH change in effluent, and high coagulation efficiency, and exhibits good coagulation performance for textile dyeing and printing wastewater with high turbidity and high organic matter content. Experiments show that the combination of titanium salt and rare earth metal salt fully utilizes the advantages of both metal coagulants, making the coagulation process applicable to a wider range of water quality conditions, and the synthesized composite coagulant has good stability and coagulation effect.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically a method for treating textile dyeing and printing wastewater using rare earth modified Ti-based dry gel coagulants. Background Technology

[0002] The textile printing and dyeing industry is a major contributor to industrial wastewater discharge. This wastewater primarily contains contaminants, grease, and salts from textile fibers, as well as various sizing agents, dyes, surfactants, auxiliaries, acids, and alkalis added during processing. Textile wastewater mainly consists of wastewater generated during raw material cooking, rinsing, bleaching, and sizing processes, containing natural impurities, fats, and organic matter such as starch. Printing and dyeing wastewater is generated from multiple processes including washing, dyeing, printing, and sizing. It contains large amounts of organic matter such as dyes, starch, cellulose, lignin, and detergents, as well as inorganic matter such as alkalis, sulfides, and various salts, making it highly polluting.

[0003] Textile dyeing and printing wastewater is characterized by high organic matter concentration, complex composition, deep and variable color, large pH variations, and significant fluctuations in both quantity and quality, making it a difficult-to-treat industrial wastewater. With the development of chemical fiber fabrics, the rise of imitation silk, and the increasing demands for finishing processes, large quantities of recalcitrant organic matter such as PVA sizing agents, rayon hydrolysates, new dyes, and auxiliaries are entering textile dyeing and printing wastewater, posing a serious challenge to traditional wastewater treatment processes. COD concentrations have also increased from hundreds of milligrams per liter to thousands of milligrams per liter.

[0004] Currently, the main method for treating wastewater using coagulation involves adding inorganic metal salt coagulants. These coagulants undergo a series of hydrolysis reactions to form hydrolysis products with various charges and polymerization properties. These hydrolysis products enhance binding capacity and improve coagulation efficiency. However, this method still suffers from drawbacks such as high dosage, large sludge production, low efficiency in removing small-molecule organic matter, and low effluent pH. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is how to simplify the treatment process for wastewater with high turbidity and high organic content, while simultaneously improving coagulation efficiency and causing a slow change in effluent pH. Therefore, this invention provides a method for treating textile dyeing and printing wastewater using a rare-earth modified Ti-based dry gel coagulant.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] This invention provides a method for treating textile dyeing and printing wastewater using a rare earth-modified Ti-based dry gel coagulant, comprising the following steps:

[0008] (1) Preparation of rare earth modified Ti-based dry gel coagulant:

[0009] Rare earth metal salts are added to a mixture of ethanol A and acetylacetone and completely dissolved. Then titanium tetrachloride is added dropwise. Subsequently, a mixture of ethanol B and distilled water is added dropwise. After stirring evenly, the mixture is dried to obtain the final product.

[0010] (2) Add rare earth modified Ti-based dry gel coagulant to textile printing and dyeing wastewater, stir and let stand.

[0011] Preferably, in step (1), the molar ratio of rare earth element Re in the rare earth metal salt to titanium element Ti in titanium tetrachloride is: Re / Ti=(0.01-0.05):1; the molar ratio of acetylacetone (AcAc) to titanium element Ti in titanium tetrachloride is: AcAc / Ti=1:4; the molar ratio of distilled water H2O to titanium element Ti in titanium tetrachloride is: H2O / Ti=4:1;

[0012] More preferably, the molar ratio of rare earth element Re in the rare earth metal salt to titanium element Ti in titanium tetrachloride is: Re / Ti=0.04:1;

[0013] In this invention, the preferred Re / Ti ratio is (0.01-0.05):1. If the Re / Ti ratio is too low, the proportion of mononuclear and intermediate polymers increases while the proportion of colloidal hydrolysates decreases, resulting in poor coagulation efficiency. If the Re / Ti ratio is too high, excess Re will form Re-AcAc complexes through complexation, thus limiting the polymerization of Re / Ti-based hydrolysates. This invention plays a crucial role in the coagulation mechanism by controlling the Re / Ti ratio, thereby influencing the degree of hydrolysis of Re and Ti.

[0014] Preferably, the volume ratio of ethanol A to ethanol B is 2:1; the volume ratio of ethanol B to distilled water is 5:1.

[0015] Preferably, the rare earth metal salt is a rare earth metal nitrate, a rare earth metal hydrochloride, or a rare earth metal carbonate.

[0016] More preferably, the rare earth metal salt is a rare earth metal nitrate;

[0017] The different coordination abilities of nitrate, carbonate, and chloride ions lead to varying hydrolysis characteristics, resulting in differences in the properties of the synthesized materials. This is due to the different coordination abilities of Cl... - and CO3 2- For Ti 4+ Its coordination ability is greater than that of NO3 - Much weaker. Once dissolved in water, Ti 4+ The ions quickly coordinate with the H₂O molecule and rapidly hydrolyze to form a mononuclear hydroxyl complex. One of the coordinated H₂O molecules is first reacted with NO₃⁻. - Substitution, then with hydrolyzed Ti 4+-H2O complexes form bidentate complexes, and then undergo a dehydration process to form NO3-containing complexes. - Ti-O-Ti clusters. Containing NO3. - The further transformation of the clusters involves two processes: denitrification and dehydration, ultimately forming polymeric Ti-O-Ti clusters.

[0018] Preferably, the rare earth element in the rare earth metal salt is La, Ce, Nd, Y, Sm, Gd, Pr, Eu, or Ho;

[0019] More preferably, the rare earth element in the rare earth metal salt is Ho;

[0020] Among them, since the atomic radius of rare earth elements gradually decreases with the increase of atomic number, and holmium has the smallest atomic radius, Ti is more likely to be incorporated into the framework of Ho hydrolysate to form Ho-O-Ti bonds. In addition, the floc properties indicate that Ho-Ti gel promotes the formation of flocs with larger particle size and denser structure compared to other Ti-Re gels.

[0021] Preferably, the stirring time is 90 min; the drying temperature is 50℃, and drying continues until a dry gel of constant weight is obtained.

[0022] Preferably, in step (2), the textile dyeing wastewater is first stirred at a speed of 200-300 rpm for 30-40 seconds, then rare earth modified Ti-based dry gel coagulant is added to the textile dyeing wastewater, stirred at a speed of 200-300 rpm for 1-2 minutes, then stirred at a speed of 40 rpm for 15-20 minutes, and then left to stand for 20-30 minutes.

[0023] More preferably, in step (2), the textile dyeing wastewater is first stirred at 200 rpm for 30 seconds, then rare earth modified Ti-based dry gel coagulant is added to the textile dyeing wastewater, stirred at 200 rpm for 1 minute, stirred at 40 rpm for 15 minutes, and then left to stand for 20 minutes.

[0024] Preferably, the turbidity of the textile dyeing wastewater is ≥35 NTU, the pH is 8-12, and the UV absorbance is... 254 ≥2.5;

[0025] Preferably, the textile dyeing wastewater is textile wastewater or dyeing wastewater;

[0026] Preferably, when the textile dyeing wastewater is textile wastewater, the mass percentage content of organic matter in the textile wastewater before treatment is ≥80%; the organic matter in the textile wastewater before treatment includes: fulvic acid, humic acid and other organic matter;

[0027] Preferably, when the textile dyeing wastewater is dyeing wastewater, the organic matter in the dyeing wastewater before treatment includes dyes, organic solvents, and other organic matter:

[0028] Preferably, the mass ratio of rare earth modified Ti-based dry gel coagulant to the volume ratio of textile printing and dyeing wastewater is (0.25-1.05) g: 1 L;

[0029] Preferably, the textile dyeing wastewater is textile wastewater; the mass ratio of rare earth modified Ti-based dry gel coagulant to the volume ratio of textile wastewater is (0.8-1.05) g: 1 L;

[0030] More preferably, the mass ratio of rare earth modified Ti-based dry gel coagulant to the volume ratio of textile wastewater is 0.95 g: 1 L;

[0031] The preferred dosage of this invention is (0.8-1.05) g: 1 L. If the dosage is too low, insufficient coagulant may prevent the effective condensation of suspended solids and colloids, resulting in poor sedimentation and insignificant reduction in wastewater turbidity, leading to substandard effluent quality. If the dosage is too high, excessive coagulant may result in too much residual coagulant entering the wastewater, affecting the efficiency of subsequent treatment processes and potentially causing secondary water pollution and increased treatment costs.

[0032] Preferably, the textile dyeing wastewater is dyeing wastewater; the mass ratio of rare earth modified Ti-based dry gel coagulant to the volume ratio of dyeing wastewater is (0.25-0.45) g: 1 L.

[0033] More preferably, the mass ratio of rare earth modified Ti-based dry gel coagulant to the volume ratio of dyeing and printing wastewater is 0.35 g: 1 L.

[0034] In this invention, the preferred dosage is (0.25-0.45) g: 1 L. If the dosage is too low, the dye and suspended solids in the wastewater may not be effectively removed due to insufficient coagulant, resulting in unsatisfactory turbidity and dye pollutant removal in the dyeing wastewater. If the dosage is too high, the excess coagulant may lead to an increase in residual coagulant substances, which will affect subsequent water treatment steps (such as sedimentation and filtration of suspended particles).

[0035] Preferably, when the textile dyeing and printing wastewater is textile wastewater, the turbidity of the treated textile wastewater is ≤0.56 NTU, the pH is 6-6.3, and the UV absorbance is [not specified]. 254 ≤0.05; the mass percentage content of organic matter in the treated textile wastewater is ≤0.52%;

[0036] Preferably, when the textile dyeing wastewater is dyeing wastewater, the turbidity of the treated wastewater is ≤15 NTU, the pH is 6.2-6.5, and the UV absorbance is [not specified]. 254 ≤0.32.

[0037] The technical solution of the present invention achieves the following beneficial technical effects:

[0038] The titanium salt coagulant prepared in this invention is a macromolecular structure formed by the condensation of titanium hydrolysates complexed with acetylacetone. Because rare earth metals possess abundant energy levels and a unique 4f outer electron shell structure, they more readily combine with organic or inorganic functional groups through coordination bonds to form compounds with multiple valence states and coordination numbers, making them more advantageous as reinforcing agents for coagulants. This invention selects rare earth metal nitrates as modifying elements and combines them with acetylacetone and titanium salts. By controlling the molar ratio of rare earth Ho to titanium, a Re-Ti gel coagulant is finally prepared. The hydrolysates of the obtained gel coagulant are all in an amorphous form resulting from the incomplete hydrolysis and polymerization of titanium. Simultaneously, by controlling the dosage of the gel coagulant in textile dyeing wastewater, and the stirring speed and time before and after adding the gel coagulant, the treatment method of this invention is made more suitable for treating textile dyeing wastewater.

[0039] The treatment method of this invention has advantages such as simple operation, slow pH change in effluent, and high coagulation efficiency, exhibiting excellent coagulation performance for textile dyeing and printing wastewater with high turbidity and high organic matter content. Experiments show that the preparation of composite coagulants by modifying Ti-based dry gels with rare earth metals, compared with single titanium-based coagulants, fully leverages the advantages of both metal coagulants and compensates for the shortcomings of single metal-based coagulants, thus maximizing their respective strengths and compensating for their weaknesses. This makes the coagulation process applicable to a wider range of water quality conditions, such as textile dyeing and printing wastewater with high turbidity and high organic matter content. The development of titanium-containing composite coagulants using the sol-gel method retains the dual advantages of both the composite process and the sol-gel method, and the synthesized composite coagulant exhibits good stability and coagulation effect. Attached Figure Description

[0040] Figure 1 The images show the XRD patterns of Ti-Ho dry gel coagulants with different Ho / Ti molar ratios in Example 4 of the present invention and the Ti gel (titanium tetrachloride) in Comparative Example 1. Detailed Implementation

[0041] Example 1

[0042] This embodiment provides a method for treating textile dyeing and printing wastewater using a rare earth-modified Ti-based dry gel coagulant, including the following steps:

[0043] (1) Preparation of rare earth modified Ti-based dry gel coagulant:

[0044] Ti-Re dry gels were prepared using acetylacetone (AcAc) as a hydrolysis inhibitor via a sol-gel method. The specific process is as follows:

[0045] 0.0011 mol of rare earth metal salt (holmium nitrate) was added to a mixture of ethanol A (20 mL) and acetylacetone. After complete dissolution, 0.028 mol of titanium tetrachloride was added dropwise. Subsequently, a mixture of ethanol B (10 mL) and distilled water was added dropwise. After stirring for 90 min, a homogeneous sol was obtained. The sol was dried in a vacuum drying oven at 50 °C until it became a dry gel of constant weight. The gel was then dried and stored.

[0046] The molar ratio of rare earth element Ho in rare earth metal salts to titanium element Ti in titanium tetrachloride is Ho / Ti = 0.04:1; the molar ratio of acetylacetone (AcAc) to titanium element Ti in titanium tetrachloride is AcAc / Ti = 1:4; the molar ratio of distilled water H2O to titanium element Ti in titanium tetrachloride is H2O / Ti = 4:1; the volume ratio of ethanol A to ethanol B is 2:1; and the mixed volume ratio of ethanol B and distilled water is 5:1.

[0047] (2) At 25℃, the textile dyeing wastewater was stirred at 200 rpm for 30 seconds, then rare earth modified Ti-based dry gel coagulant was added to the textile dyeing wastewater and stirred at 200 rpm for 1 minute, then stirred at 40 rpm for 15 minutes, and then left to stand for 20 minutes.

[0048] Wherein, when the textile dyeing wastewater is textile wastewater (e.g., cotton pulp black liquor), the mass ratio of rare earth modified Ti-based dry gel coagulant to the volume of textile wastewater is 0.95 g: 1 L; when the textile dyeing wastewater is dyeing wastewater, the mass ratio of rare earth modified Ti-based dry gel coagulant to the volume of dyeing wastewater is 0.35 g: 1 L.

[0049] In this embodiment, the wastewater samples used were: cotton pulp black liquor from Alar Zhongtai Textile Technology Co., Ltd., and dyeing wastewater from Alar Xingmeida Dyeing Co., Ltd. Textile wastewater (cotton pulp black liquor) mainly contains organic matter such as fulvic acid and humic acid, while dyeing wastewater mainly contains large amounts of dyes and organic solvents. Therefore, the absorbance (UV value) at 254 nm was measured using a UV-Vis spectrophotometer. 254 The values ​​characterize the organic matter content in wastewater. The water quality indicators of the actual wastewater (untreated wastewater) are shown in Table 1.

[0050] Table 1 Water Quality Indicators

[0051]

[0052] Example 2: Determination of the types of anions in rare earth metal salts

[0053] To investigate the coagulation performance of Ti-Nd synthesized from different neodymium sources, this study primarily compared the turbidity removal (turbidity removal rate) and organic matter removal (UV) performance of Ti-Nd dry gel coagulants synthesized from neodymium nitrate, neodymium chloride, and neodymium carbonate in treating actual wastewater. 254 The removal rate is shown in Table 2.

[0054] The preparation method of Ti-Nd dry gel coagulant synthesized with neodymium nitrate, neodymium chloride and neodymium carbonate differs from step (1) of Example 1 only in that the rare earth metal salt (holmium nitrate) is replaced with neodymium nitrate, neodymium chloride and neodymium carbonate in this example, while the other parameters are the same.

[0055] At 25°C, 300 mL of wastewater sample (cotton pulp black liquor) was placed in a beaker, and the dry gel coagulant prepared in this embodiment was added. After treatment according to step (2) of Example 1, the water sample to be tested was taken 2 cm below the surface of the liquid after stirring and standing with a syringe, and the water quality index was determined.

[0056] The water sample was filtered through a 0.45 μm microporous membrane, and the absorbance (UV value) at 254 nm was measured using a UV-Vis spectrophotometer. 254 Removal rate = (initial UV) 254 - UV treatment 254 ) / Initial UV 254 ×100%.

[0057] The turbidity value was measured directly using a turbidimeter (without filtration). The turbidity removal rate (%) = (initial turbidity - turbidity after treatment) / initial turbidity × 100%.

[0058] Table 2. Coagulation properties of Ti-Nd dry gels synthesized with different neodymium sources

[0059] Nylon <![CDATA[UV 254 Removal rate / % Turbidity removal rate / % <![CDATA[Nd(NO3)3]]> 95.0 85.0 <![CDATA[NdCl3]]> 75.0 80.0 <![CDATA[Nd(CO3)3]]> 83.2 87.2

[0060] The turbidity and organic matter removal rate of Ti-Nd synthesized from neodymium nitrate are higher than those synthesized from neodymium chloride and neodymium carbonate. At the same dosage, neodymium nitrate Ti-Nd exhibits turbidity removal efficiency of 11.8% and 20% higher than that of neodymium carbonate and neodymium chloride Ti-Nd, respectively, and organic matter removal rates of 4.78% and 5.0% higher, respectively. The difference may be due to the different coordination abilities of nitrate, carbonate, and chloride ions, leading to variations in the properties of the synthesized materials. Therefore, lanthanide gel coagulants are synthesized using nitrate-based rare earth metals as rare earth sources.

[0061] Example 3: Determination of Rare Earth Ion Species in Rare Earth Metal Salts

[0062] In this embodiment, nitrate-based light rare earth metals (La, Ce, Nd, Y, Sm, Gd, Pr, Eu) and nitrate-based heavy rare earth metals (Ho) were used to modify Ti-based dry gel (TXC).

[0063] The only difference between the method for modifying TXC and step (1) in Example 1 is that the rare earth metal salts in this example are nitrate-type light rare earth metals (La, Ce, Nd, Y, Sm, Gd, Pr, Eu) and nitrate-type heavy rare earth metals (Ho), while the other parameters are the same.

[0064] At 25℃, 300 mL of wastewater sample (cotton pulp black liquor) was placed in a beaker, and the dry gel coagulant prepared in this example was added. After treatment according to step (2) of Example 1, the water sample to be tested was taken 2 cm below the surface of the liquid after stirring and settling with a syringe, and the water quality index was determined. The results are shown in Table 3.

[0065] Table 3. Coagulation properties of different Ti-Re dry gels

[0066] Types of coagulants <![CDATA[UV 254 Removal rate / % Turbidity removal rate / % Y-TXC 79.2 78.0 Pr-TXC 90.2 82.0 Eu-TXC 91.7 82.5 Gd-TXC 93.0 83.0 Nd-TXC 95.0 85.0 Ce-TXC 95.6 87.3 Sm-TXC 96.6 87.7 La-TXC 98.3 88.7 Ho-TXC 98.8 98.5

[0067] Experimental results show that the prepared Ti-Re dry gel coagulants can significantly improve the coagulation effect. Except for the Ti-Y dry gel prepared with yttrium nitrate, the coagulation efficiency is above 90%. Since the atomic radius of rare earth elements gradually decreases with increasing atomic number, and holmium has the smallest atomic radius, Ti is more easily incorporated into the framework of Ho hydrolysates, forming Ho-O-Ti bonds. Furthermore, the floc properties indicate that Ho-Ti gel, compared to other Re-Ti gels, promotes the formation of larger and denser flocs. Among them, the coagulant Ti-Ho, composed of rare earth metal holmium and titanium, achieved a turbidity removal rate of 98.5% and an organic matter removal rate of 98.8%, exhibiting the best coagulation performance compared to other rare earth metal modified TXCs. Therefore, the Ti-Ho dry gel, modified with rare earth metal Ho, was selected for the experiment to optimize the raw material ratio.

[0068] Example 4: Determination of the Ho / Ti molar ratio

[0069] The only difference between the method for preparing Ti-Ho dry gel coagulant in this embodiment and step (1) of Example 1 is that the molar ratio of rare earth element Ho in rare earth metal salt to titanium element Ti in titanium tetrachloride in this embodiment is: Ho / Ti=(0.01-0.05):1 (see Table 4 for details). Other parameters are the same as step (1) of Example 1.

[0070] ① At 25℃, take 300mL of wastewater sample (cotton pulp black liquor) into a beaker, add the Ti-Ho dry gel coagulant prepared in this example, and treat it according to the method of step (2) in Example 1. Then, use a syringe to take the water sample 2cm below the surface of the liquid after stirring and settling, and measure the water quality index. The results are shown in Table 4.

[0071] ② At 25℃, take 300mL of wastewater sample (dyeing and printing wastewater) into a beaker, add the Ti-Ho dry gel coagulant prepared in this example, and treat it according to the method of step (2) in Example 1. Then, use a syringe to take the water sample 2cm below the surface of the liquid after stirring and settling, and measure the water quality index. The results are shown in Table 5.

[0072] Table 4. Coagulation properties of Ti-Ho dry gels prepared with different Ho / Ti molar ratios on cotton pulp black liquor

[0073] Ho / Ti molar ratio <![CDATA[UV 254 Removal rate / % Turbidity removal rate / % 0.01 90.8 71.5 0.02 93.1 84.2 0.03 97.8 89.7 0.04 98.8 98.5 0.05 93.9 89.5

[0074] Table 5. Coagulation performance of Ti-Ho dry gels prepared with different Ti / Ho molar ratios on dyeing and printing wastewater.

[0075] Ho / Ti molar ratio <![CDATA[UV 254 Removal rate / % Turbidity removal rate / % 0.01 79.6 61.2 0.02 83.7 74.2 0.03 87.2 79.6 0.04 88.8 82.3 0.05 83.9 79.5

[0076] Table 4 shows that the coagulation efficiency improves with increasing Ho / Ti molar ratio. The highest turbidity removal rate (98.5%) and organic matter removal rate (98.8%) are achieved when the Ho / Ti molar ratio is 0.04. With further increases in the molar ratio, the coagulation efficiency decreases, with the optimal Ho / Ti molar ratio being 0.04. Analysis indicates that the Re content affects the hydrolysis and polymerization processes of Ti and Re. If the Re / Ti ratio is too low, the proportion of mononuclear and medium-sized polymers increases while the proportion of colloidal hydrolysates decreases, resulting in poor coagulation efficiency. If the Re / Ti ratio is too high, excess Re forms Re-AcAc complexes through complexation, thus limiting the polymerization of Re / Ti-based hydrolysates. This invention plays a crucial role in the coagulation mechanism by controlling the Re / Ti ratio, thereby influencing the degree of hydrolysis of Re and Ti.

[0077] As shown in Table 5, the coagulation efficiency improves with the increase of the Ti-Ho molar ratio, especially in terms of color removal, where dye particles are removed. The coagulation efficiency reaches its highest level at a Ti-Ho molar ratio of 0.04, with a turbidity removal rate of 82.3% and an organic matter removal rate of 88.8%. As the molar ratio continues to increase, the coagulation efficiency decreases, and the optimal Ti-Ho molar ratio is 0.04.

[0078] Figure 1The images show the XRD patterns of Ti-Ho dry gel coagulants with different Ho / Ti molar ratios in this embodiment and the Ti gel (titanium tetrachloride) in Comparative Example 1. Figure 1 It can be seen that the composite Ti-Ho dry gel did not significantly change the basic structure of the titanium gel. XRD analysis results proved that the structure of the hydrolysate after composite was the same, still exhibiting an amorphous structure. The XRD spectra all contained relatively broad Ti-O structural peaks located at 2θ=5°.

[0079] In summary, different wastewater components exhibit varying reactivity to coagulants. Due to the different molecular structures and reactivity characteristics of pollutants in cotton pulp black liquor and dyeing wastewater, the same coagulant will have different UV effects when treating these two types of wastewater. 254 The removal rates for both turbidity and turbidity differed. Cotton pulp black liquor from the textile industry typically contains organic substances such as fulvic acid and humic acid. These substances have strong colloidal properties and are easily removed by coagulants through processes like charge neutralization, adsorption, and coagulation. In contrast, dyeing wastewater containing dyes is removed primarily through charge neutralization and adsorption by the coagulant. Furthermore, optimizing coagulation conditions can further improve the coagulation effect for better wastewater treatment. Appropriately adjusting these parameters for different types of textile dyeing wastewater can ensure that the optimal performance of the coagulant is fully realized.

[0080] Example 5: Determination of the Dosage of Ti-Ho Dry Gel Coagulant

[0081] The method for preparing Ti-Ho dry gel coagulant in this embodiment is the same as step (1) in Example 1. The difference from Example 1 is that when treating cotton pulp black liquor, the mass ratio of Ti-Ho dry gel coagulant to the volume ratio of cotton pulp black liquor in step (2) of this embodiment is (0.8-1.05) g:1L (see Table 6 for details); when treating dyeing and printing wastewater, the mass ratio of Ti-Ho dry gel coagulant to the volume ratio of dyeing and printing wastewater is 0.25-0.45 g:1L (see Table 7 for details), and other parameters are the same.

[0082] ① At 25℃, take 300mL of wastewater sample (cotton pulp black liquor) into a beaker. According to the dosage of this embodiment, other process parameters are the same as step (2) of embodiment 1. After treatment, use a syringe to take the water sample to be tested 2cm below the liquid surface after stirring and standing, and measure the water quality index. The results are shown in Table 6.

[0083] ② At 25℃, take 300mL of wastewater sample (dyeing and printing wastewater) in a beaker. According to the dosage of this embodiment, other process parameters are the same as in step (2) of embodiment 1. After treatment, use a syringe to take the water sample to be tested 2cm below the liquid surface after stirring and standing, and measure the water quality index. The results are shown in Table 7.

[0084] Table 6. Coagulation performance of Ti-Ho dry gel at different dosages on cotton pulp black liquor

[0085] Dosage (g / L) <![CDATA[UV 254 Removal rate / % Turbidity removal rate / % 0.8 10.0 12.5 0.85 91.9 92.9 0.9 96.6 97.0 0.95 98.8 98.5 1 96.9 97.4 1.05 96.6 97.1

[0086] Table 7. Coagulation performance of Ti-Ho dry gel at different dosages on dyeing and printing wastewater.

[0087] Dosage (g / L) <![CDATA[UV 254 Removal rate / % Turbidity removal rate / % 0.25 40.0 52.5 0.30 71.9 72.9 0.35 88.8 82.3 0.40 78.8 78.5 0.45 72.9 75.4

[0088] As shown in Table 6, the coagulation efficiency increases with the increase of coagulant dosage. The coagulation effect is optimal when the coagulant dosage is 0.95g. Further increases in coagulant dosage lead to a decrease in coagulation efficiency. 0.95g is the optimal dosage.

[0089] As shown in Table 7, the coagulation efficiency increases with the increase of coagulant dosage. The coagulation effect is optimal when the coagulant dosage is 0.35g. Further increases in coagulant dosage lead to a decrease in coagulation efficiency. 0.35g is the optimal dosage.

[0090] Analysis shows that if the dosage is insufficient, it will not be enough to bridge and connect the organic matter, and some suspended particles will remain suspended without being affected by the coagulant, resulting in poor coagulation effect. If the dosage is too high, the suspended particles will undergo electroreversal due to excessive adsorption of the coagulant, which may cause the colloid to re-stabilize. On the other hand, the adsorption surface of the suspended particles will be covered by the coagulant, producing a "colloidal protection" effect, which will reduce the coagulation effect.

[0091] Example 6: pH study of treated water samples

[0092] The method for preparing Ti-Ho dry gel coagulant in this embodiment differs from step (1) of Example 1 only in that the molar ratio of rare earth element Ho in the rare earth metal salt to titanium element Ti in titanium tetrachloride in this embodiment is Ho / Ti = (0.01-0.05):1 (see Table 8 for details). Other parameters are the same as step (1) of Example 1. When treating cotton pulp black liquor, the mass ratio of Ti-Ho dry gel coagulant to the volume ratio of cotton pulp black liquor in step (2) of this embodiment is (0.8-1.05) g:1 L (see Table 8 for details). Other parameters are the same as step (2) of Example 1.

[0093] At 25℃, 300mL of wastewater sample (cotton pulp black liquor) was placed in a beaker. The dosage was the same as in this embodiment, and other process parameters were the same as in step (2) of Example 1. After treatment, the water sample to be tested was taken 2cm below the surface of the liquid after stirring and settling with a syringe, and the pH of the treated water sample was measured. The results are shown in Table 8.

[0094] Table 8. pH changes in the effluent from Ti-Ho dry gels prepared with different Ho / Ti molar ratios.

[0095]

[0096] As shown in Table 8, the actual effluent pH of the coagulants prepared with different molar ratios, after coagulation at the optimal dosage, stabilized at 6.0-6.3, indicating a slightly acidic pH. Furthermore, the pH after Ti-Ho coagulation did not decrease significantly, avoiding corrosion problems caused by low pH.

[0097] Example 7: Stability Test of Ti-Ho Dry Gel Coagulant

[0098] Following the method for treating cotton pulp black liquor in Example 1, the coagulation performance of the Ti-Ho dry gel coagulant obtained in Example 1 was tested for three months, and the results are shown in Table 9.

[0099] Table 9. Effect of time on the coagulation performance of Ti-Ho dry gel coagulant in cotton spinning black liquor treatment.

[0100] time <![CDATA[UV 254 Removal rate / % Turbidity removal rate / % 1 day 98.8 98.5 2 days 98.8 98.5 4 days 98.6 98.4 8 days 98.1 98.0 16 days 98.0 98.0 32 days 97.5 97.0 64 days 97.0 96.0 90 days 95.1 94.5

[0101] In summary, the wastewater treated by the method of this invention complies with the "Integrated Wastewater Discharge Standard" (GB 8978-1996) and the "Water Pollutant Discharge Standard for Textile Dyeing and Finishing Industry" (GB 4287-2012).

[0102] Comparative Example 1

[0103] This comparative example provides a Ti-based dry gel coagulant, comprising the following steps:

[0104] Add 0.028 mol of titanium source (titanium tetrachloride, tetrabutyl titanate, isobutyl titanate, or titanium sulfate) dropwise to a mixture of ethanol A (20 mL) and acetylacetone; then add a mixture of ethanol B (10 mL) and distilled water dropwise. Stir for 90 min to obtain a homogeneous sol. Dry in a vacuum drying oven at 50 °C until the sol becomes a dry gel of constant weight, and then dry and store.

[0105] The molar ratio of acetylacetone (AcAc) to titanium tetrachloride (Ti) is 1:4; the molar ratio of distilled water (H2O) to titanium tetrachloride (Ti) is 4:1; the volume ratio of ethanol A to ethanol B is 2:1; and the mixed volume ratio of ethanol B to distilled water is 5:1.

[0106] ① At 25℃, 300 mL of wastewater sample (cotton pulp black liquor) was placed in a beaker, and different Ti-based dry gel coagulants prepared in this comparative example were added. After treatment according to step (2) of Example 1, the water sample to be tested was taken 2 cm below the surface of the liquid after stirring and standing with a syringe, and the water quality indicators were measured. The results are shown in Table 10.

[0107] ② At 25℃, take 300mL of wastewater sample (dyeing and printing wastewater) into a beaker, add different Ti-based dry gel coagulants prepared in this comparative example, and treat them according to the method of step (2) in Example 1. Then, use a syringe to take the water sample 2cm below the surface of the liquid after stirring and settling, and measure the water quality indicators. The results are shown in Table 11.

[0108] Table 10. Coagulation performance of different titanium-based dry gel coagulants on cotton black liquor.

[0109] Different titanium sources <![CDATA[UV 254 Removal rate / % Turbidity removal rate / % effluent pH Titanium tetrachloride 70.0 42.5 5.0 n-Butyl titanate 41.9 22.9 4.9 Isobutyl titanate 58.8 32.3 4.8 Titanium sulfate 62.4 38.5 4.9

[0110] Table 11 Coagulation performance of different titanium-based dry gel coagulants on dyeing and printing wastewater

[0111] Different titanium sources <![CDATA[UV 254 Removal rate / % Turbidity removal rate / % effluent pH Titanium tetrachloride 65.0 40.5 5.2 n-Butyl titanate 34.9 20.2 5.1 Isobutyl titanate 45.8 30.9 5.0 Titanium sulfate 58.4 36.5 5.0

[0112] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for treating textile printing and dyeing wastewater by using a rare earth modified Ti-based dry gel coagulant, characterized in that, The method comprises the following steps: (1) Preparation of the rare earth modified Ti-based dry gel coagulant: The rare earth metal salt is added into the mixture of ethanol A and acetylacetone, and then titanium tetrachloride is added dropwise after complete dissolution. Subsequently, the mixture of ethanol B and distilled water is added dropwise, and then stirring is performed until uniformity. Finally, drying is performed to obtain the product. The rare earth metal salt is a rare earth metal nitrate. The rare earth element in the rare earth metal salt is Ho. (2) The rare earth modified Ti-based dry gel coagulant is added into the textile printing and dyeing wastewater, and then stirring is performed and then standing is performed.

2. The method of claim 1, wherein, In step (1), the molar ratio of the rare earth element Re in the rare earth metal salt to the titanium element Ti in the titanium tetrachloride is Re / Ti=(0.01-0.05):

1.

3. The method of claim 2, wherein, In step (1), the molar ratio of the rare earth element Re in the rare earth metal salt to the titanium element Ti in the titanium tetrachloride is Re / Ti=0.04:

1.

4. The method of claim 1, wherein, In step (1), the molar ratio of acetylacetone AcAc to the titanium element Ti in the titanium tetrachloride is AcAc / Ti=1:4, and the molar ratio of distilled water H2O to the titanium element Ti in the titanium tetrachloride is H2O / Ti=4:

1. The volume ratio of ethanol A to ethanol B is 2:1, the mixed volume ratio of ethanol B to distilled water is 5:1, the stirring time is 90 min, and the drying temperature is 50 ℃ until the constant weight of the dry gel is obtained.

5. The method of claim 1, wherein, In step (2), the textile printing and dyeing wastewater is first stirred at a speed of 200-300 rpm for 30-40 s, and then the rare earth modified Ti-based dry gel coagulant is added into the textile printing and dyeing wastewater. The stirring is performed at a speed of 200-300 rpm for 1-2 min, and then the stirring is performed at a speed of 40 rpm for 15-20 min. Finally, standing is performed for 20-30 min.

6. The method of claim 1, wherein, In step (2), the textile printing and dyeing wastewater is textile wastewater or printing and dyeing wastewater. The mass of the rare earth modified Ti-based dry gel coagulant to the volume of the textile printing and dyeing wastewater is (0.25-1.05) g:1 L.

7. The method of claim 6, wherein, In step (2), when the textile printing and dyeing wastewater is textile wastewater, the mass of the rare earth modified Ti-based dry gel coagulant to the volume of the textile wastewater is (0.8-1.05) g:1 L. Or, when the textile printing and dyeing wastewater is printing and dyeing wastewater, the mass of the rare earth modified Ti-based dry gel coagulant to the volume of the printing and dyeing wastewater is (0.25-0.45) g:1 L.

8. The method of claim 6, wherein, In step (2), the turbidity of the textile printing and dyeing wastewater before treatment is ≥ 35 NTU, the pH is 8-12, and the absorbance UV 254 ≥ 2.5; When the textile printing and dyeing wastewater is textile wastewater, the turbidity of the treated textile wastewater is ≤0.56 NTU, the pH is 6-6.3, the absorbance UV 254 ≤0.05; or, when the textile printing and dyeing wastewater is printing and dyeing wastewater, the turbidity of the treated printing and dyeing wastewater is ≤15 NTU, the pH is 6.2-6.5, the absorbance UV 254 ≤0.32.

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