Method for preparing calcium peroxide based on dicyandiamide waste residue and application thereof

Abstract

This invention provides a method for preparing calcium peroxide from dicyandiamide waste residue. Using dicyandiamide waste residue as raw material, calcium is extracted using concentrated hydrochloric acid to prepare CaO2. The Fenton catalytic degradation effect of CaO2 combined with Fe(II) catalyst on methylene blue, methyl orange, rhodamine B, and tetracycline hydrochloride was investigated. The addition of Fe(II) Fenton catalyst showed a significant catalytic degradation effect on methylene blue, with a degradation rate of 94.19%; the degradation rate of rhodamine B was 78.56%; and the degradation rate of methyl orange was 74.77%. The calcium peroxide combined with ferrous ion catalyst of this invention forms a Fenton system, exhibiting excellent Fenton catalytic degradation effects on methylene blue, methyl orange, and rhodamine B. This method not only allows for the secondary utilization of dicyandiamide waste residue but also provides a new approach for the degradation of dyeing and printing wastewater and antibiotics. It not only turns waste into treasure but is also more environmentally friendly.

Description

Technical Field

[0001] This invention relates to a method for preparing calcium peroxide based on dicyandiamide waste residue, and also to the Fenton catalytic degradation effect of CaO2 composite Fe(II) catalyst on methylene blue, methyl orange and rhodamine B, belonging to the field of waste utilization and degradation catalysis technology. Background Technology

[0002] Dicyandiamide (C2H4N4), also known as dicyandiamide, is typically a white, needle-like, rhomboid, or powdery crystal with highly reactive chemical properties. It is commonly used in the production of melamine guanidine, guanidine salts, pharmaceuticals, and as an industrial intermediate in dyeing and printing. It is also used in the production of agricultural nitrogen fertilizer synergists and pesticides, as well as as a raw material for polymer coagulants, epoxy resin adhesives, coatings, and cationic surfactants. Due to its wide range of applications, dicyandiamide production is increasing year by year, leading to a continuous rise in its price. Dicyandiamide is produced through calcium cyanamide hydrolysis, decalcification, polymerization, crystallization, filtration, and drying. The hydrolysis and decalcification stages generate a large amount of waste residue. The main component of dicyandiamide waste residue is CaCO3, and the dry residue (anhydrous state) has a particle size of 0–0.1 mm and is a grayish-black powder. The stockpiling of dicyandiamide waste residue not only wastes land resources but also poses a serious environmental pollution problem due to the toxicity of the dicyandiamide component. Currently, common treatment methods for dicyandiamide waste residue include landfilling, open-air storage, road paving, and cement production. Among these, the production of cement from dicyandiamide waste residue is the most widely used. Xu Xiaoyun et al. used dicyandiamide waste residue to produce amine slag plastic cement; Ding Aihua et al. used dicyandiamide waste residue as raw material to prepare ordinary silicate cement.

[0003] Calcium peroxide (CaO2) is an important inorganic peroxide with a molecular weight of 72.08 g·mol⁻¹. -1 It is a white tetragonal crystal with a specific gravity of 2.92 g·cm³. -3(25 ℃), with a refractive index of 1.895, CaO2 is a white to pale yellow powder at room temperature, odorless, non-toxic, and almost tasteless in the form of powdery crystals or granules. Due to its strong oxidizing properties and the significant characteristic of decomposing to form calcium hydroxide and oxygen, CaO2 possesses strong bleaching, bactericidal, and disinfecting effects, and is considered an excellent environmentally friendly product with high application value and promising development prospects. In agriculture and animal husbandry, CaO2 can be applied to rice cultivation, edible fungi production, soil improvement, aquaculture, and food preservation. Dong Chunhua et al. investigated the slow-release technology of CaO2 and its effects on the physicochemical properties, soil microorganisms, soil enzyme activity, and crop yield and quality of gleyed paddy soil. Their findings showed that applying CaO2 to gleyed paddy soil increases soil redox potential, reduces reducing substances, and provides a good opportunity to improve soil nutrients, reduce greenhouse gas emissions, and increase rice yield and quality. Industrially, it can be used to produce bleaching agents and detergents, as a raw material for the production of calcium formate and calcium superoxide, and as a catalyst and emulsifier. In wastewater treatment, CaO2, combined with other technologies, can treat various types of wastewater. Ning Fangrui et al. used CaO2 as a precipitant, employing chemical precipitation or neutralization precipitation methods to treat heavy metal industrial wastewater; and combined it with ozone to treat dye wastewater. Furthermore, CaO2 has a certain effect on eliminating red tides and can also be used to prepare high-concentration fragrances.

[0004] In recent years, ecological and environmental issues have become a major concern, with severe environmental pollution threatening the survival and development of humans, animals, and plants. With industrial development, antibiotics and dyes are widely used in people's production and daily lives, providing convenience but also causing serious environmental problems. Dyeing and printing wastewater is a difficult-to-treat industrial wastewater, with very high concentrations of organic pollutants and color indicators. Without effective treatment, it will severely pollute the aquatic environment. Advanced oxidation processes are an effective method for treating recalcitrant wastewater. Fenton oxidation is a commonly used advanced oxidation technology. Compared to other oxidation methods, it can destroy organic matter in the dark, and features simple operation, readily available reactions, low operating costs, and environmental friendliness. In Fenton oxidation technology, the catalyst can efficiently decompose to generate ·OH, which has strong oxidizing power and high electronegativity or electrophilicity (electron affinity 569.3 KJ). This oxidizes and degrades organic pollutants in water, ultimately breaking them down into smaller molecules or CO2 and H2O. Calculations show that in a solution with pH=3, its oxidation potential reaches as high as 2.73 V, making its oxidizing power second only to hydrofluoric acid in solution. Therefore, the Fenton oxidation method can oxidize and degrade the vast majority of organic pollutants. The mechanism diagram is shown below. Figure 1 . Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing calcium peroxide based on dicyandiamide waste residue, and to study the Fenton catalytic degradation effect of CaO2 composite Fe(II) catalyst on methylene blue, methyl orange and rhodamine B.

[0006] I. Preparation of Calcium Peroxide A method for preparing calcium peroxide based on dicyandiamide waste residue includes the following steps: (1) Thoroughly wet the dicyandiamide waste residue with deionized water, and slowly drip concentrated hydrochloric acid into the wetted dicyandiamide waste residue. React at 90~110 ℃ for 1~2 h. After cooling, filter to remove the remaining waste residue. The filtrate is used as an intermediate product. During the reaction, the toxic substance dicyandiamide in the dicyandiamide waste residue will be converted into non-toxic and harmless urea under the action of concentrated hydrochloric acid. The mass-volume ratio of dicyandiamide waste residue to concentrated hydrochloric acid is 0.5~0.8 g / mL.

[0007] (2) The mixed solution of H2O2 and NH3·H2O was cooled to 0 ℃ in an ice-water bath and slowly added dropwise to the intermediate product obtained in step (1) while stirring at 300~500 r / min. The mixture was kept in an ice-water bath at 0~4 ℃ for 1~2 h. After white crystals appeared, the mixture was filtered, washed, and dried to obtain calcium peroxide. The volume ratio of H2O2 to NH3·H2O in the mixed solution of H2O2 and NH3·H2O was 1:2~1:2.5. The volume ratio of the mixed solution of H2O2 and NH3·H2O to the intermediate product was 1:1~1:3.

[0008] II. Characterization of CaO2 1. Scanning electron micrographs of raw material dicyandiamide waste residue and product CaO2. Figure 5 These are scanning electron microscope (SEM) images of the raw material dicyandiamide waste residue and the product CaO2. Images a and b show the dicyandiamide waste residue, which is composed of many large particles aggregated together. Images c and d show the CaO2, which is entirely granular and relatively dispersed. Compared to the raw material dicyandiamide waste residue, the CaO2 particles are significantly smaller, resulting in a larger specific surface area. This allows for better contact with pollutants, leading to excellent adsorption and achieving the goal of dye degradation.

[0009] 2. Comparative analysis of X-ray diffraction patterns of four samples XRD is mainly used to determine the main components and crystal structure characteristics of a substance. For example... Figure 6As shown in Figure a, the X-ray diffraction patterns of pure dicyandiamide, calcium carbonate, dicyandiamide waste residue, and calcium peroxide are as follows: The figure shows that CaCO3 exhibits distinct characteristic diffraction peaks at diffraction angles 2θ = 23.21°, 29.51°, 31.82°, 36.14°, 39.59°, 43.62°, 47.94°, and 48.93°. These characteristic diffraction peaks also appear at the corresponding positions in the dicyandiamide waste residue, indicating a high CaCO3 content. Furthermore, a characteristic diffraction peak at dicyandiamide angle 2θ = 25.85° is also present in the corresponding position in the dicyandiamide waste residue, indicating that the waste residue contains dicyandiamide, but in a relatively low amount. Figure b shows the X-ray diffraction pattern of CaO2. As can be seen from the figure, the product exhibits strong diffraction peaks at 2θ = 30.1°, 35.6°, 47.3°, and 52.9°. Comparison with the CaO2 standard card JCPDS03-0865 confirms that these peaks are indeed CaO2 diffraction peaks. However, some other diffraction peaks also appear in the product's X-ray diffraction pattern; these are likely diffraction peaks of impurities. It is speculated that the vigorous reaction between H2O2 and the substrate CaCl2 increases the reaction temperature and reduces the stability of H2O2, leading to an increase in minor products such as CaO and CaCO3 during CaO2 synthesis, thus reducing the purity of CaO2.

[0010] 3. Infrared spectral characterization of CaO2, dicyandiamide residue, CaCO3, and C2H4N4 Figure 7 These are the infrared spectra of CaO2, dicyandiamide waste residue, CaCO3, and C2H4N4. The 1400 cm⁻¹ value in the spectrum... -1 876cm -1 The characteristic absorption peak of CaCO3 is located at 2160 cm⁻¹, which appears in dicyandiamide waste residue. Combined with the XRD diffraction pattern, this indicates that the waste residue contains CaCO3 in a relatively high concentration. -1 1260cm -1 926cm -1 The peak at 875 cm⁻¹ is characteristic of dicyandiamide, but it was not observed in the waste residue, presumably due to the low dicyandiamide content, resulting in a less prominent peak. −1 The absorption peak is provided by the O−O bond vibration in CaO2; the absorption peak is at 1502 cm⁻¹. −1 The absorption peak is caused by the bending vibration of O−Ca−O in CaO2, with a peak at 670 cm⁻¹. −1 This is caused by the O−Ca−O vibration in CaO2, indicating that CaO2 was successfully prepared in the experiment.

[0011] 4. Infrared spectral characterization of the intermediate product obtained from the reaction of dicyandiamide waste residue with concentrated hydrochloric acid. Depend on Figure 8 It can be known that 1640cm -1The absorption peak at 3330 cm⁻¹ is caused by the C=O stretching vibration; -1 The absorption peak at 1250 cm⁻¹ is caused by the stretching vibration of NH₃; the spectrum shows an absorption peak at 1250 cm⁻¹. -1 1360cm -1 The absorption peak at that point is attributed to the stretching absorption peak of CN, suggesting that a certain compound in the intermediate product contains CN bonds. Therefore, it can be inferred that the intermediate product obtained from the reaction of dicyandiamide waste with concentrated hydrochloric acid may contain urea. During the experiment, the concentrated hydrochloric acid may have converted the toxic substance dicyandiamide in the raw material into urea.

[0012] III. Investigation of Fenton Catalytic Degradation of Dyes and Antibiotics Using CaO2 Composite Fe(II) Catalysts 0.05 g of CaO2 was added to 100.0 mL of methylene blue, methyl orange, rhodamine B, and tetracycline hydrochloride solutions (all 10 mg / L), followed by 2.00 g of FeSO4. A Fenton-catalyzed dark reaction was then carried out, with absorbance and maximum absorption wavelength measured every 30 min until no further change was observed. CaO2 releases H2O2 in water, with a maximum yield of 0.47 g H2O2 from 1.00 g of CaO2. The Fenton-catalyzed degradation effect on dyes and antibiotics was investigated.

[0013] 1. Calculation method for Fenton catalytic degradation rate of dyes and antibiotics by CaO2 composite Fe(II) catalyst Prepare 10 mg / L solutions of methylene blue, methyl orange, rhodamine B, and tetracycline hydrochloride respectively, and store them protected from light.

[0014] Depend on Figure 3 It is known that the maximum absorption wavelengths of methylene blue (MB), methyl orange (Mo), rhodamine B (RhB), and tetracycline hydrochloride (Tc) are 664 nm, 464 nm, 552 nm, and 358 nm, respectively.

[0015] like Figure 4 As shown, solutions of methylene blue, methyl orange, rhodamine B, and tetracycline hydrochloride at concentrations of 0, 5, 10, 15, and 20 mg / L were prepared, and their absorbance A was measured. The linear relationship between the absorbance of the four solutions and the standard concentration was plotted.

[0016] The concentration of the solution was calculated from the absorbance using the working curves of methylene blue (MB), methyl orange (Mo), rhodamine B (RhB), and tetracycline hydrochloride (Tc), and then the degradation rate (Dt%) was calculated using the following formula.

[0017] Dt % = (c0-c t ) / c0×100% 2. Fenton catalytic degradation rate of target analytes by CaO2 composite Fe(II) catalyst at different pH values Figure 9 Figures a, b, and c show the Fenton catalytic degradation rates of the target compounds by the CaO2 composite Fe(II) catalyst at pH values ​​of 3, 5, 7, 9, and 11, and the degradation rate curves under optimal pH conditions. Figures a, b, and c show that at pH 3, the CaO2 composite Fe(II) catalyst exhibits the best catalytic degradation effect on methyl orange (Mo), with a degradation rate of 74.77%. At pH 5, the CaO2 composite Fe(II) catalyst shows the best catalytic degradation effect on methylene blue (MB), with a degradation rate of 94.19%. The degradation effect on rhodamine B (RhB) is second best, with a degradation rate of 78.56%. Figure d shows that the CaO2 composite Fe(II) catalyst has a significant degradation effect on methylene blue, methyl orange, and rhodamine B within 30 min, but its degradation effect on tetracycline is not significant.

[0018] 3. Kinetic curves of Fenton catalytic degradation of dyes by CaO2 composite Fe(II) catalyst Figure 10 The Fenton-catalyzed degradation of three dyes—methylene blue (MB), methyl orange (Mo), and rhodamine B (RhB)—by a CaO2 composite Fe(II) catalyst using a CaO2 composite Fe(II) catalyst is described. t The linear relationship between Fenton catalytic degradation data and dark reaction time t was analyzed using the LH kinetic model. The data are shown in Table 3. As shown in the table above, ln(C0 / C) t The reaction showed a good linear relationship with the Fenton reaction time t, suggesting that the Fenton-catalyzed degradation of methylene blue (MB), methyl orange (Mo), and rhodamine B (RhB) by the CaO2 composite Fe(II) catalyst is a pseudo-first-order reaction.

[0019] In summary, this invention prepared CaO2 from dicyandiamide waste residue using a simple and easy-to-operate method, achieving a yield of 49.6% and a purity of 72.11%. Besides potentially containing urea, the product is presumably also contaminated with minor byproducts such as CaO and CaCO3, leading to a decrease in CaO2 purity. The Fenton catalytic degradation effects of CaO2 combined with Fe(II) catalyst on methylene blue (MB), methyl orange (Mo), rhodamine B (RhB), and tetracycline hydrochloride (Tc) solutions were investigated at different pH values. The results showed that the Fenton system exhibited the best catalytic degradation effect on methylene blue at pH 5, with a degradation rate of 94.19%; the degradation effect on rhodamine B was second best, with a degradation rate of 78.56%; the degradation effect on methyl orange was best at pH 3, with a degradation rate of 74.77%; and there was no significant degradation effect on tetracycline. This indicates that CaO2 can enhance Fenton oxidation and thus achieve effective degradation of dyes. This not only realizes the secondary utilization of waste residue, but also provides a new approach for the treatment of dyeing and printing wastewater.

[0020] The beneficial effects of this invention are: This invention uses dicyandiamide waste residue as raw material to prepare calcium peroxide. CaO2 releases H2O2 in water. By combining this with a ferrous ion catalyst, a Fenton system is formed, exhibiting excellent Fenton catalytic degradation effects on methylene blue (MB), methyl orange (Mo), and rhodamine B (RhB). This method not only allows for the secondary utilization of dicyandiamide waste residue but also provides a new approach for the degradation of dyeing and printing wastewater and antibiotics. It not only turns waste into treasure but is also more environmentally friendly.

[0021] This invention uses dicyandiamide waste residue as raw material and extracts calcium using concentrated hydrochloric acid to prepare calcium peroxide, while simultaneously aiming to effectively remove the harmful substance dicyandiamide from the raw material. This invention also prepares CaO2 from dicyandiamide waste residue using a simple and easy-to-operate method with high yield and purity.

[0022] Based on the composition of dicyandiamide waste residue and the characteristics of dicyandiamide production, this invention utilizes acid hydrolysis to treat the waste residue and achieve its reuse, thereby reducing enterprise production costs, minimizing environmental pollution, and conserving land resources. Attached Figure Description

[0023] Figure 1 This is a diagram illustrating the oxidation mechanism of Fenton catalysts. Figure 2 Flow chart of liquid-phase recycling process for preparing calcium peroxide from dicyandiamide waste residue; Figure 3 The UV absorption spectra of methylene blue, methyl orange, rhodamine B, and tetracycline hydrochloride are shown. Figure 4 Linear relationship between absorbance and standard concentration for methylene blue, methyl orange, rhodamine B, and tetracycline hydrochloride; Figure 5 Scanning electron microscope images of dicyandiamide waste residue and CaO2; Figure 6 X-ray diffraction patterns of C2H4N4, CaCO3, dicyandiamide waste residue, and CaO2; Figure 7 The FTIR spectra of CaO2, dicyandiamide waste residue, CaCO3, and C2H4N4 are shown. Figure 8 The FTIR spectrum of the intermediate product; Figure 9 a, b, and c are Fenton catalytic degradation rate diagrams of the target analyte by the CaO2 composite Fe(II) catalyst at different pH values; d is the degradation rate curve of the target analyte at the optimal pH value. Figure 10 Kinetic curves of Fenton catalytic degradation of methylene blue, methyl orange and rhodamine B using CaO2 composite Fe(II) catalyst. Detailed Implementation

[0024] The present invention will be further described below through specific embodiments.

[0025] The reagents and instruments used in this invention are as follows: Example 1 (1) Elimination of dicyandiamide in raw materials Accurately weigh 25.00 g of dicyandiamide waste residue and add it to a 250 mL round-bottom flask. Thoroughly wet the waste residue with 50.0 mL of deionized water. Slowly add 40.0 mL of concentrated hydrochloric acid dropwise to the round-bottom flask. Incubate the mixture in a 100 ℃ water bath for 1.5 h. After cooling, filter the mixture to remove the remaining waste residue. The filtrate is kept as an intermediate product. During the reaction, the toxic dicyandiamide in the waste residue will be converted into non-toxic and harmless urea under the action of concentrated hydrochloric acid. The reaction equation is: CaCO3 + 2HCl = CaCl2 + H2O + CO2 C2H4N4 + 2H2O = 2CH4N2O (2) Preparation of CaO2 Measure 100.0 mL of the intermediate product and add it to a 250 mL round-bottom flask. Separately prepare a mixed solution of 22.0 mL H2O2 and 32.0 mL NH3·H2O, cool it to 0 °C in an ice-water bath, and slowly add it dropwise to the intermediate product while stirring at 350 r / min. Keep the round-bottom flask in an ice-water bath at 0~4 °C for 1 h. After observing the appearance of white crystals, filter the solution, wash it three times with low-temperature deionized water, dry it, weigh the product, and calculate the yield. Figure 2 The reaction flow diagram for preparing CaO2.

[0026] Indirect iodometric determination of product purity (1) Standardization of Na2S2O3 solution (K2Cr2O7 method) Accurately transfer three 25.00 mL aliquots of K₂Cr₂O₇ standard solution into iodine flasks. Add 5.0 mL of 1:1 HCl and 5.0 mL of 200 g / L KI solution. Incubate in the dark for 5 min. Titrate with Na₂S₂O₃ solution until a pale yellow solution is reached. Then add 2.0 mL of 5 g / L starch indicator and titrate with Na₂S₂O₃ solution until the endpoint is bright green. Calculate the concentration of Na₂S₂O₃.

[0027] (2) Determination of calcium content in the product Accurately weigh 0.05 g CaO2 and place it in a 250 mL Erlenmeyer flask. Add 30.0 mL of distilled water and 2.0 mL of hydrochloric acid, and stir until the solid turns yellow. Then add 2.0 mL of starch indicator and titrate with Na2S2O3 solution until the blue color disappears and remains unchanged for 30 seconds. Perform the determination in triplicate. Calculate the mass fraction of CaO2 in the sample using the following formula: Calculations showed that the yield of CaO2 prepared from dicyandiamide waste residue via acid hydrolysis was 49.6%. The purity of the CaO2 prepared in the experiment was determined by indirect iodometric titration, and the purity of CaO2 was 72.11% after three parallel determinations.

[0028] Example 2 0.05 g of CaO2 was added to 100.0 mL of methylene blue, methyl orange, rhodamine B, and tetracycline hydrochloride solutions (all 10 mg / L), followed by 2.00 g of FeSO4. A Fenton-catalyzed dark reaction was then carried out, with absorbance and maximum absorption wavelength measured every 30 min until no further change was observed. The Fenton-catalyzed degradation efficiency for dyes and antibiotics was investigated. At pH 5, the catalytic degradation efficiency for methylene blue was the best, reaching 94.19%; the degradation efficiency for rhodamine B was second best, at 78.56%; and at pH 3, the degradation efficiency for methyl orange was the best, at 74.77%.

Claims

1. A method for preparing calcium peroxide from dicyandiamide waste residue, comprising the following steps: (1) Wet the dicyandiamide waste residue thoroughly with deionized water, slowly drip concentrated hydrochloric acid into the wetted dicyandiamide waste residue, react at 90~110 ℃ for 1~2 h, cool and filter to remove the remaining waste residue, and use the filtrate as an intermediate product for later use. During the reaction, the toxic substance dicyandiamide in the dicyandiamide waste residue will be transformed into non-toxic and harmless urea under the action of concentrated hydrochloric acid. (2) Place the mixed solution of H2O2 and NH3·H2O in an ice-water bath and cool it to 0 ℃. Add it slowly dropwise to the intermediate product obtained in step (1) while stirring at 300-500 r / min. Keep it in an ice-water bath at 0-4 ℃ for 1-2 h. After white crystals appear, filter, wash and dry to obtain calcium peroxide.

2. The method for preparing calcium peroxide based on dicyandiamide waste residue according to claim 1, characterized in that: In step (1), the mass-to-volume ratio of dicyandiamide waste residue to concentrated hydrochloric acid is 0.5~0.8 g / mL.

3. The method for preparing calcium peroxide based on dicyandiamide waste residue according to claim 1, characterized in that: In step (2), the volume ratio of H2O2 to NH3·H2O in the mixed solution of H2O2 and NH3·H2O is 1:2 to 1:2.

5.

4. The method for preparing calcium peroxide based on dicyandiamide waste residue according to claim 1, characterized in that: In step (2), the volume ratio of the mixed solution of H2O2 and NH3·H2O to the intermediate product is 1:1 to 1:3.

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