Environment-friendly treatment method of cationic dye wastewater

Abstract

The invention discloses an environment-friendly treatment method for cationic dye wastewater, and belongs to the technical field of environmental protection. The method comprises the following steps: preparing diatom shells, carrying out hydroxylation treatment on the diatom shells, and treating cationic dye wastewater by using the hydroxylated diatom shells, specifically, soaking the diatom shells in absolute ethyl alcohol, then washing the diatom shells with deionized water, soaking the diatom shells in hydrochloric acid for 8 hours, soaking the diatom shells at room temperature in the first 2-6 hours, then washing the diatom shells with deionized water, then soaking the diatom shells in hydrochloric acid for 2-6 hours, and finally drying the diatom shells to obtain the cationic dye wastewater. And soaking in the oven in the remaining time, washing with deionized water again, and drying to obtain the hydroxylated diatom shell with the zero charge point of less than 5. The method has the beneficial effects that the hydroxylated diatom shells can give full play to the adsorption capacity under the low-pH condition, the amount of acid and alkali needed in the wastewater treatment process can be reduced, even cationic dyes in the wastewater can be effectively removed without adjusting the pH value with acid and alkali, the use amount of acid and alkali is saved, and the environment is protected.

Description

Technical Field

[0001] The invention relates to a wastewater treatment method, in particular to an environmentally friendly treatment method for cationic dye wastewater, and belongs to the technical field of environmental protection. Background Art

[0002] Cationic dyes are a type of textile dye. Cationic dyes are highly water-soluble and are dissolved in water in a cationic state. They have a small molecular weight, high salt content, and low pH value. Due to the particularity of cationic dye wastewater, it has a great impact on the environment, and it is difficult to achieve the treatment effect using traditional treatment processes. Therefore, it is very important to effectively remove cationic dyes from wastewater.

[0003] The main treatment methods for cationic dye wastewater are: adsorption, membrane separation, chemical coagulation, Fenton oxidation, photocatalytic oxidation, electrochemical method, etc. Among them, membrane separation requires special operating conditions and membrane pollution is difficult to clean, chemical coagulation has poor decolorization effect on hydrophilic cationic dyes, Fenton oxidation is highly dependent on pH conditions, photocatalytic oxidation requires specific conditions and the catalyst is difficult to recover, electrochemical reaction speed is slow, reaction column is easy to clog, adsorption is simple to operate, low cost, does not introduce new pollutants, and is very suitable for the treatment of cationic dye wastewater. Because cationic dye wastewater has the characteristics of low pH value and positive charge, it is particularly important to select suitable adsorption materials.

[0004] Diatom frustules have a porous structure and carry a negative charge in solutions with a pH value greater than their zero charge point, which makes them suitable for use as cationic dye adsorption materials. However, a single species of diatom frustules has only one zero charge point, and most diatom frustules have zero charge points between 5 and 8, which limits the application of diatom frustules in the adsorption of cationic dyes.

[0005] Essam A. Mohamed used calcination and thermochemical methods to modify diatomite (Essam A. Mohamed, et al; Enhancing adsorption capacity of Egyptian diatomaceous earth by thermo-chemical purification: Methylene blue uptake; Journal of Colloid and Interface Science, 2019, 534: 408-419), and then used the modified diatomite to conduct an adsorption experiment on the cationic dye methylene blue. The zero charge point of the modified diatomite is 6.21. To ensure its adsorption effect on methylene blue, the adsorption experiment was carried out at pH = 8 (the pH value was adjusted higher with alkali). According to the experiment, the adsorption amount of methylene blue by the modified diatomite was 48.56 mg / g, and it only had excellent adsorption effect in solutions with a pH value greater than 6.21, which limited its application in treating methylene blue wastewater. Summary of the invention

[0006] To address the deficiencies of the prior art, the present invention aims to provide a method for effectively removing cationic dyes from wastewater without using acid or alkali to adjust the pH value, which can reduce the amount of acid or alkali required in the wastewater treatment process.

[0007] In order to achieve the above object, the present invention adopts the following technical solution: An environmentally friendly method for treating cationic dye wastewater comprises the following steps: (1) Preparation of diatom frustules: centrifuge the cultured diatoms, add concentrated nitric acid and hydrogen peroxide to the algae cells, let them stand and heat them in a water bath, then drop hydrogen peroxide into the water bath during heating, and finally wash them repeatedly with deionized water and centrifuge until the supernatant is neutral, freeze-dry the precipitate, and obtain the diatom frustules; (2) Hydroxylating the diatom shells: soak the diatom shells in anhydrous ethanol, then wash with deionized water, and then soak them in hydrochloric acid for 8 hours. The first 2 to 6 hours are soaked at room temperature, and the remaining time is soaked in an oven to allow the hydrochloric acid to etch the diatom shells. The diatom shells are washed with deionized water again, and finally dried to obtain hydroxylated diatom shells with a zero charge point less than 5. (3) Treating cationic dye wastewater with hydroxylated diatom frustules: Detect the pH value of the cationic dye wastewater. If the pH value is less than the zero charge point of the hydroxylated diatom frustules, first use alkali to adjust the pH value to a value greater than or equal to the zero charge point of the hydroxylated diatom frustules. If the pH value is greater than or equal to the zero charge point of the hydroxylated diatom frustules, there is no need to adjust the pH value with acid or alkali. Then, add the hydroxylated diatom frustules into the cationic dye wastewater for adsorption.

[0008] Preferably, in step (1), the diatom is ovate algae or Skeletonema costatum; before heating in a water bath, the dosage ratio of algal cells, concentrated nitric acid and hydrogen peroxide is 2.7×10 8 Pieces: 3mL: 0.5mL.

[0009] Preferably, in step (2), the concentration of the hydrochloric acid is 0.5 mol / L to 1.0 mol / L; and the temperature of the oven is 80°C.

[0010] Preferably, in step (3), the ratio of the hydroxylated diatom frustules to the cationic dye wastewater is 0.06 g:30 mL.

[0011] The benefit of the present invention lies in that under low pH conditions, hydroxylated diatom shells (for example, ovate shells and mid-rib shells) are negatively charged and attract positively charged cationic dyes. Under low pH conditions, the adsorption capacity of diatom shells can be fully exerted, which broadens its application scenarios, reduces the amount of acid and alkali required in the wastewater treatment process, and can even effectively remove cationic dyes in wastewater without the need to adjust the pH value with acid and alkali, thereby saving acid and alkali usage and protecting the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is the FTIR spectrum of the egg-shaped algae shell before and after hydroxylation treatment; Figure 2 This is the FTIR spectrum of the crust of Skeletonema midrib before and after hydroxylation treatment; Figure 3 is the inert electrolyte titration curve of the oval algae frustules before hydroxylation; Figure 4 is the inert electrolyte titration curve of Skeletonema midi shell before hydroxylation treatment; Figure 5 is the inert electrolyte titration curve of the oval algae shell after hydroxylation treatment; Figure 6 is the inert electrolyte titration curve of the Skeletonium ribatum shell after hydroxylation treatment; Figure 7 is the effect of time on the adsorption of methylene blue by ovate algae frustules and hydroxylated ovate algae frustules; Figure 8 is the effect curve of time on the adsorption of methylene blue by Skeletonium costatum and hydroxylated Skeletonium costatum. Fig. 9 is the effect of the number of cycles on the adsorption of methylene blue by hydroxylated ovate algae frustules; Fig.10 This is a graph showing the effect of cycle number on the adsorption of methylene blue by the mid-rib algae shells. DETAILED DESCRIPTION

[0013] Diatoms have many unique morphologies, among which Oval algae ( Cocconeis sp. ) are mostly slightly rounded ellipsoids, which have high structural stability and are easy to recycle. In addition, the ovoid algae have low nutritional requirements and are easy to cultivate. Skeletonema costatum ) is widely distributed and reproduces rapidly, and can reproduce to a very high density in a short time. At the same time, the shape of the middle costal algae is cylindrical, which makes the middle costal algae shell have a high stability. Therefore, the egg-shaped algae and the middle costal algae are preferably used as adsorption materials.

[0014] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0015] 1. Cultivation of diatoms F / 2 culture medium (basal culture medium) was prepared with artificial seawater (made of sea crystal and deionized water) with a salinity of 3%, and NaNO3, NaH2PO4.H2O, NaSiO3.9H2O and trace element stock solution were added thereto, with the addition amounts of the four being 40 mg / L, 6 mg / L, 20 mg / L and 1.0 mL / L respectively. The culture medium was then packaged and sterilized under high pressure, and then vitamin stock solution was added at an amount of 0.1 mL / 100 mL to obtain the optimized F / 2 culture medium.

[0016] Among them, the preparation methods of trace element reserve solution and vitamin reserve solution are as follows: (1) Trace element stock solution: Mix 1 mL of 0.98 g / 100 mL CuSO4.5H2O solution, 1 mL of 2.20 g / 100 mL ZnSO4.7H2O solution, 1 mL of 1.00 g / 100 mL CoCl.6H2O solution, 1 mL of 18.00 g / 100 mL MnCl2.4H2O solution, 1 mL of 0.63 g / 100 mL Na2MoO4.2H2O solution, 4.36 g Na2EDTA and 3.00 g FeCl3.6H2O, and then make up to 1000 mL with deionized water.

[0017] (2) Vitamin stock solution: 20 mg vitamin B1, 0.1 mg vitamin H and 0.05 mg vitamin B 12 Mix, then dilute to 100 mL with deionized water, and filter with a 0.22 μm filter membrane.

[0018] In an ultra-clean workbench, algae species (ovate algae or mid-costal algae) were inoculated into the optimized F / 2 medium, and then cultured under continuous light and a temperature of 25±2°C for 9 days to allow the diatoms to grow to the logarithmic phase. The ovate algae liquid (9×10 6 / mL) and Skeletonema costatum algae solution (6.3×10 6 / mL).

[0019] 2. Preparation of Diatom Frustules Take 30mL of algae liquid (ovate algae liquid or middle rib strip algae liquid) and divide it into 50mL centrifuge tubes. Centrifuge (speed 5000r / min, 5min) to collect algae cells. Put the collected algae cells into a beaker, first add 3mL of concentrated nitric acid with a concentration of 15.2mol / L, then drip 0.5mL of hydrogen peroxide with a concentration of 9.79mol / L at a rate of 1 drop / 3 seconds (drop operation in a fume hood). When a large number of bubbles are violently generated in the beaker, stop dripping immediately, and continue dripping after the number of bubbles decreases and stabilizes. After the sample is allowed to stand for 5min, put it in a constant temperature water bath at 85℃ and heat it for 10min. During heating, drip 0.5mL of hydrogen peroxide with a concentration of 9.79mol / L at a rate of 1 drop / 3 seconds (drop operation in a fume hood). Finally, wash repeatedly with deionized water and centrifuge until the supernatant is neutral, discard the supernatant, freeze-dry the precipitate, and obtain the ovate algae shell and middle rib strip algae shell respectively.

[0020] The obtained egg-shaped algae shells and mid-rib algae shells were subjected to infrared spectroscopy (FTIR) detection and zero charge point detection. The zero charge point detection method is as follows: Add 0.1g of algae shells to each of 6 50mL centrifuge tubes, and then add deionized water and 0.1mol / L HNO3 solution or 0.1mol / L NaOH solution to make the final volume of the solution in the centrifuge tube 20mL, and make the pH values ​​of the solutions in each centrifuge tube 2, 3, 4, 5, 6, and 7, respectively. Use a constant temperature oscillator to balance the solutions in each centrifuge tube for 1d, the temperature is 25℃, and the stirring speed is 250rpm, and then the pH value of the solution in each centrifuge tube is measured and recorded as pH0. Then add 0.5mL of 2mol / L NaNO3 solution to each centrifuge tube, oscillate for 3h, and then measure the pH value of the solution in each centrifuge tube, and record it as pH1. Plotting ΔpH (i.e. pH1-pH0) against pH1 will give the inert electrolyte titration curve. The pH value corresponding to ΔpH=0 is the zero charge point (pH PZC value).

[0021] After testing, the FTIR spectrum of the egg-shaped algae shell prepared above is shown in Figure 1 (solid line), the FTIR spectrum of the mid-costal algae shell is shown in Figure 2 (solid line); the titration curve of inert electrolyte for oval algal shells is shown in Figure 3 The titration curve of inert electrolyte of the mid-costal algae shell is shown in Figure 4 .Depend on Figure 3 and Figure 4 It can be seen that the zero charge point of the oval algae shell is 5.80, and the zero charge point of the mid-rib algae shell is 5.12.

[0022] For cationic dye wastewater with a pH value lower than 5.0, the adsorption effects of the oval algae shells (zero charge point of 5.80) and the mid-rib algae shells (zero charge point of 5.12) prepared previously are both poor, which limits the application of the oval algae shells and the mid-rib algae shells in low pH cationic dye wastewater.

[0023] 3. Hydroxylation of diatom shells In order to enhance the adsorption capacity of diatom frustules for cationic dyes under low pH conditions (eg pH = 5), diatom frustules (ovate frustules, mid-rib frustules) were hydroxylated to increase the number of hydroxyl groups on their surfaces and reduce their zero charge point.

[0024] Example 1

[0025] The oval algae shells obtained above were first soaked in anhydrous ethanol for 12 h, then washed with deionized water, and then soaked in 1.0 mol / L hydrochloric acid for 8 h, the first 2 h of soaking was at room temperature, and the last 6 h were immersed in an oven at 80 ° C (hydrochloric acid etches the oval algae shells), washed again with deionized water, and finally dried to obtain hydroxylated oval algae shells.

[0026] The obtained hydroxylated egg-shaped algal shells were subjected to FTIR detection and zero charge point detection.

[0027] After testing, the FTIR spectrum of the hydroxylated egg-shaped algae shell is shown in Figure 1 (dashed line), the titration curve of inert electrolyte is shown in Figure 5 .

[0028] Depend on Figure 1 It can be seen that after hydroxylation, the oval algae shells have a -1 The Si—OH characteristic peak at the hydroxylation site is significantly larger than that before hydroxylation, indicating that the oval algal shell has been successfully hydroxylated.

[0029] Depend on Figure 5 It can be seen that the zero charge point of the hydroxylated ovate algal frustule is 4.46.

[0030] Example 2

[0031] The skeleton algae shell obtained above was first soaked in anhydrous ethanol for 12 hours, then washed with deionized water, and then soaked in 1.0 mol / L hydrochloric acid for 8 hours, the first 2 hours of soaking was at room temperature, and the last 6 hours were immersed in an oven at 80°C (hydrochloric acid etches the skeleton algae shell), washed with deionized water again, and finally dried to obtain hydroxylated skeleton algae shell.

[0032] The obtained hydroxylated Skeletonium costatum shells were subjected to FTIR detection and zero charge point detection.

[0033] After testing, the FTIR spectrum of the hydroxylated Skeletonium shell is shown in Figure 2 (dashed line), the titration curve of inert electrolyte is shown in Figure 6 .

[0034] Depend on Figure 2 It can be seen that after hydroxylation, the mid-rib algae shells have a -1 The Si—OH characteristic peak at the hydroxylation site is significantly larger than that before hydroxylation, indicating that the crust of the mid-costal algae has been successfully hydroxylated.

[0035] Depend on Figure 6 It can be seen that the zero charge point of the hydroxylated Skeletonema costatum shell is 4.60.

[0036] It can be seen from Examples 1 and 2 that after hydroxylation treatment, the zero charge point of the diatom shells decreased significantly (the zero charge point of the ovate shells decreased from 5.80 before hydroxylation treatment to 4.46, and the zero charge point of the mid-rib shells decreased from 5.12 before hydroxylation treatment to 4.60), which greatly enhanced the adsorption capacity of the diatom shells for cationic dyes, expanded the applicable pH range of the diatom shells, and can reduce the amount of acid and alkali required in the wastewater treatment process. Even without the use of acid and alkali to adjust the pH value, the cationic dyes in the wastewater can be effectively removed, thereby enhancing the application potential of diatom shells in actual wastewater treatment, especially in the scene of treating wastewater containing low pH values.

[0037] During the hydroxylation of diatom shells, the concentration of hydrochloric acid and etching time need to be strictly controlled. If the concentration of hydrochloric acid is too low or the etching time is too short, the change of zero charge point will not be obvious enough. The following takes the egg-shaped algae shell as an example to explore the effect of hydrochloric acid concentration and etching time on the change of zero charge point.

[0038] Example 3

[0039] The oval algae shells obtained above were first soaked in anhydrous ethanol for 12 h, then washed with deionized water, and then soaked in 0.1 mol / L hydrochloric acid for 8 h, the first 6 h of soaking was at room temperature, and the next 2 h were immersed in an oven at 80°C, washed again with deionized water, and finally dried to obtain hydroxylated oval algae shells.

[0040] The results show that the zero charge point of the hydroxylated egg-shaped algae shell is 5.62.

[0041] It can be seen from Example 3 that, due to the low concentration of hydrochloric acid (0.1 mol / L) and the short etching time (2 h), the change of the zero charge point of the oval algal shell is not obvious.

[0042] Example 4

[0043] The egg-shaped algae shells obtained above were first soaked in anhydrous ethanol for 12 hours, then washed with deionized water, and then soaked in 0.1 mol / L hydrochloric acid for 8 hours, the first 4 hours were soaked at room temperature, and the next 4 hours were soaked in an oven at 80°C, washed again with deionized water, and finally dried to obtain hydroxylated egg-shaped algae shells.

[0044] The results show that the zero charge point of the hydroxylated egg-shaped algae shell is 5.49.

[0045] It can be seen from Example 4 that although the etching time is longer than that of Example 3 (4 h), the change of the zero charge point of the oval algal shell is still not obvious due to the low concentration of hydrochloric acid (0.1 mol / L).

[0046] Example 5

[0047] The egg-shaped algae shells obtained above were first soaked in anhydrous ethanol for 12 hours, then washed with deionized water, and then soaked in 0.1 mol / L hydrochloric acid for 8 hours, the first 2 hours were soaked at room temperature, and the last 6 hours were soaked in an 80°C oven, washed again with deionized water, and finally dried to obtain hydroxylated egg-shaped algae shells.

[0048] The results show that the zero charge point of the hydroxylated egg-shaped algae shell is 5.41.

[0049] It can be seen from Example 5 that although the etching time is longer than that of Example 4 (6 h), the change of the zero charge point of the oval algal shell is still not obvious due to the low concentration of hydrochloric acid (0.1 mol / L).

[0050] It can be seen from Examples 3, 4 and 5 that if the concentration of hydrochloric acid is too low (for example, 0.1 mol / L), even if the etching time is extended, the zero charge point of the oval algal shell cannot be significantly changed. Therefore, the concentration of hydrochloric acid needs to be higher than 0.1 mol / L.

[0051] Example 6

[0052] The egg-shaped algae shells obtained above were first soaked in anhydrous ethanol for 12 hours, then washed with deionized water, and then soaked in 0.5 mol / L hydrochloric acid for 8 hours, the first 6 hours were soaked at room temperature, and the next 2 hours were soaked in an oven at 80°C, washed again with deionized water, and finally dried to obtain hydroxylated egg-shaped algae shells.

[0053] The zero charge point of the hydroxylated ovate algal shell was found to be 5.22.

[0054] It can be seen from Example 6 that after increasing the concentration of hydrochloric acid (0.5 mol / L), the change of the zero charge point of the oval algal shell is still not obvious due to the short etching time (2 h).

[0055] Example 7

[0056] The egg-shaped algae shells obtained above were first soaked in anhydrous ethanol for 12 hours, then washed with deionized water, and then soaked in 0.5 mol / L hydrochloric acid for 8 hours, the first 4 hours were soaked at room temperature, and the next 4 hours were soaked in an oven at 80°C, washed again with deionized water, and finally dried to obtain hydroxylated egg-shaped algae shells.

[0057] The results show that the zero charge point of the hydroxylated egg-shaped algae shell is 4.79.

[0058] It can be seen from Example 7 that increasing the concentration of hydrochloric acid (0.5 mol / L) and appropriately extending the etching time (4 h) can significantly change the zero charge point of the oval algal shell.

[0059] Example 8

[0060] The egg-shaped algae shells obtained above were first soaked in anhydrous ethanol for 12 hours, then washed with deionized water, and then soaked in 0.5 mol / L hydrochloric acid for 8 hours, the first 2 hours were soaked at room temperature, and the last 6 hours were soaked in an 80°C oven, washed again with deionized water, and finally dried to obtain hydroxylated egg-shaped algae shells.

[0061] The results show that the zero charge point of the hydroxylated egg-shaped algae shell is 4.53.

[0062] It can be seen from Example 8 that by increasing the concentration of hydrochloric acid (0.5 mol / L) and appropriately extending the etching time (6 h), the zero charge point of the oval algal shell can be significantly changed.

[0063] Example 9

[0064] The egg-shaped algae shells obtained above were first soaked in anhydrous ethanol for 12 hours, then washed with deionized water, and then soaked in 1.0 mol / L hydrochloric acid for 8 hours, the first 6 hours were soaked at room temperature, and the last 2 hours were soaked in an oven at 80°C, washed again with deionized water, and finally dried to obtain hydroxylated egg-shaped algae shells.

[0065] The results show that the zero charge point of the hydroxylated egg-shaped algae shell is 4.97.

[0066] It can be seen from Example 9 that after further increasing the concentration of hydrochloric acid (1.0 mol / L), even with a shorter etching time (2 h), the zero charge point of the oval algal shell can be significantly changed.

[0067] Example 10

[0068] The egg-shaped algae shells obtained above were first soaked in anhydrous ethanol for 12 h, then washed with deionized water, and then soaked in 1.0 mol / L hydrochloric acid for 8 h, the first 4 h of soaking was at room temperature, and the next 4 h were immersed in an oven at 80°C, washed again with deionized water, and finally dried to obtain hydroxylated egg-shaped algae shells.

[0069] The results show that the zero charge point of the hydroxylated egg-shaped algae shell is 4.68.

[0070] It can be seen from Example 10 that by further increasing the concentration of hydrochloric acid (1.0 mol / L) and appropriately extending the etching time (4 h), the zero charge point of the oval algal shell can be significantly changed.

[0071] It can be seen from Examples 6 to 10 that when diatom frustules are subjected to hydroxylation treatment, the appropriate concentration of hydrochloric acid is 0.5 mol / L to 1.0 mol / L, and the etching time needs to be controlled within 2 h to 6 h.

[0072] 4. Detection of the adsorption effect of hydroxylated diatom shells Methylene blue (a type of cationic dye) was dissolved in water to prepare a methylene blue solution with a concentration of 100 mg / L, and the pH value of the methylene blue solution was adjusted to 5 with 1.0 mol / L hydrochloric acid.

[0073] 0.06 g of each of the previously prepared ovate algae shell (without hydroxylation treatment), middle rib-skeletalgae shell (without hydroxylation treatment), hydroxylated ovate algae shell (Example 1) and hydroxylated middle rib-skeletalgae shell (Example 2) were added to 30 mL of methylene blue solution, and an adsorption experiment was carried out at 25° C. Sampling was performed at 10 min, 30 min, 60 min, 120 min, 240 min, 480 min and 720 min after the start of the adsorption experiment, and the absorbance was measured at 664 nm using a UV-visible spectrophotometer. The concentration of methylene blue was first calculated according to the absorbance, and then the adsorption amount of methylene blue by the ovate algae shell, middle rib-skeletalgae shell, hydroxylated ovate algae shell and hydroxylated middle rib-skeletalgae shell was calculated according to the concentration of methylene blue, and the adsorption amount was plotted against the adsorption time to obtain the influence curves of time on the adsorption of methylene blue by the ovate algae shell, middle rib-skeletalgae shell, hydroxylated ovate algae shell and hydroxylated middle rib-skeletalgae shell.

[0074] After calculation, the effect curve of time on the adsorption of methylene blue by ovate algae shells and hydroxylated ovate algae shells is shown in Figure 7 The effect of time on the adsorption of methylene blue by Skeletonium costatum and hydroxylated Skeletonium costatum is shown in Figure 8 .

[0075] Depend on Figure 7 It can be seen that the adsorption capacity of methylene blue by the ovate algae shell in the methylene blue solution with a pH of 5 is 45.13 mg / g. Under the same conditions, the adsorption capacity of methylene blue by the hydroxylated ovate algae shell is increased to 54.27 mg / g.

[0076] Depend on Figure 8It can be seen that the adsorption capacity of methylene blue by the mid-costal algae shell in the methylene blue solution with a pH of 5 is 44.07 mg / g. Under the same conditions, the adsorption capacity of methylene blue by the hydroxylated mid-costal algae shell is increased to 49.41 mg / g.

[0077] It can be seen that hydroxylation treatment broadens the pH range of application of the two diatom frustules.

[0078] 5. Testing the Cyclic Stability of Hydroxylated Diatom Frustules Anhydrous ethanol is used to regenerate the hydroxylated diatom shells (hydroxylated ovate shells, hydroxylated middle rib-skeletal shells) after adsorbing methylene blue and reaching adsorption equilibrium. Specifically, the hydroxylated ovate shells or hydroxylated middle rib-skeletal shells after adsorbing methylene blue and reaching adsorption equilibrium are eluted with anhydrous ethanol until the eluent is colorless, and then the hydroxylated ovate shells or hydroxylated middle rib-skeletal shells are washed with deionized water, and finally dried and reused, and the adsorption amount of methylene blue by the hydroxylated ovate shells or hydroxylated middle rib-skeletal shells after each reuse is calculated.

[0079] 0.06 g of regenerated hydroxylated ovate algae frustules or hydroxylated mid-rib algae frustules was added to 30 mL of methylene blue solution (100 mg / L), and a regeneration adsorption experiment was carried out at 25 °C and pH 5. The concentration of methylene blue in the methylene blue solution was detected 240 min after the adsorption experiment began. The hydroxylated ovate algae frustules or hydroxylated mid-rib algae frustules were regenerated before entering the next cycle, and the cycle was repeated 6 times.

[0080] After testing, the adsorption of methylene blue by hydroxylated egg-shaped algae shells after each reuse was found to be Fig. 9 After each reuse, the adsorption of methylene blue by the hydroxylated Skeletonema ribata shells was Fig.10 .

[0081] Depend on Fig. 9 It can be seen that the adsorption performance of hydroxylated ovate algae shells decreased significantly after 5 cycles, and the adsorption amount decreased by 18.5% after 6 cycles. Specifically, the adsorption amount decreased from 54.27 mg / g in the first cycle to 44.21 mg / g in the sixth cycle.

[0082] Depend on Fig.10 It can be seen that the adsorption performance of the hydroxylated Skeletonaria shell decreased significantly after 6 cycles, and the adsorption amount decreased by 24.2% after 6 cycles. Specifically, the adsorption amount decreased from 49.41 mg / g in the first cycle to 37.41 mg / g in the sixth cycle.

[0083] In general, the cyclic stability of hydroxylated ovate algae shells and hydroxylated medium-ribbed algae shells is better.

[0084] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the embodiments here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. An environmentally friendly treatment method for cationic dye wastewater, characterized in that: The following steps are involved: (1) Preparation of diatom frustules: centrifuge the cultured diatoms, add concentrated nitric acid and hydrogen peroxide to the algae cells, let them stand and heat them in a water bath, then drop hydrogen peroxide into the water bath during heating, and finally wash them repeatedly with deionized water and centrifuge until the supernatant is neutral, freeze-dry the precipitate, and obtain the diatom frustules; (2) Hydroxylating the diatom shells: soak the diatom shells in anhydrous ethanol, then wash with deionized water, and then soak them in hydrochloric acid for 8 hours. The first 2 to 6 hours are soaked at room temperature, and the remaining time is soaked in an oven to allow the hydrochloric acid to etch the diatom shells. The diatom shells are washed with deionized water again, and finally dried to obtain hydroxylated diatom shells with a zero charge point less than 5. (3) Treating cationic dye wastewater with hydroxylated diatom frustules: Detect the pH value of the cationic dye wastewater. If the pH value is less than the zero charge point of the hydroxylated diatom frustules, first use alkali to adjust the pH value to a value greater than or equal to the zero charge point of the hydroxylated diatom frustules. If the pH value is greater than or equal to the zero charge point of the hydroxylated diatom frustules, there is no need to adjust the pH value with acid or alkali. Then, add the hydroxylated diatom frustules into the cationic dye wastewater for adsorption.

2. The method according to claim 1, characterized in that In step (1), the diatom is ovate algae or Skeletonema costatum.

3. The method according to claim 1, characterized in that In step (1), before heating in a water bath, the ratio of algae cells, concentrated nitric acid and hydrogen peroxide was 2.7×10 8 Pieces: 3mL: 0.5mL.

4. The method according to claim 1, characterized in that: In step (2), the concentration of the hydrochloric acid is 0.5 mol / L to 1.0 mol / L.

5. The method according to claim 1, characterized in that In step (2), the temperature of the oven is 80°C.

6. The method according to claim 1, characterized in that In step (3), the ratio of the hydroxylated diatom shell to the cationic dye wastewater is 0.06 g:30 mL.

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