Method for preparing calcium peroxide from oyster shells and application of calcium peroxide

Abstract

The invention discloses a method for preparing calcium peroxide from oyster shells and application of the calcium peroxide, and belongs to the technical field of oyster shell recycling. The method comprises the following steps: 1) cleaning oyster shells, drying in the sun and grinding into powder; 2) dissolving the oyster shell powder with hydrochloric acid, adjusting the pH value of the reaction solution to be alkaline with sodium hydroxide, then adding ammonia water, and slowly dropwise adding H2O2; and (3) filtering after dropwise adding, and drying a solid product to obtain CaO2. Compared with CaO2 prepared by a traditional preparation method taking calcium chloride as a substrate and commercially available CaO2, the CaO2 prepared by the method disclosed by the invention has a longer H2O2 release period; the purity of the CaO2 prepared by the method is high and can reach more than 80%, while the purity of the commercially available CaO2 is 65-75%; the specific surface area of the CaO2 prepared by the method is far lower than that of commercially available CaO2. In addition, cheap and easily available starting raw materials are adopted, the synthesis process is green and environment-friendly, the operation is simple and convenient, the product purity is high, the process is stable, and the method is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, specifically relating to a method for preparing calcium peroxide using oyster shells and its application. Background Technology

[0002] Oysters are the world's most farmed shellfish and my country's most important marine economic shellfish. Currently, oyster production and processing mainly utilize the oyster meat, while the oyster shells, which account for over 60% of the shell's weight and are inedible, are not effectively utilized. Most oyster shells are discarded as solid waste, accumulating in mudflats and other areas. However, the remaining meat and juices in these discarded shells decompose and rot, attracting flies and mosquitoes and producing toxic substances and harmful gases, directly or indirectly causing serious pollution to the terrestrial and marine environments. Therefore, developing high-value utilization technologies for oyster shells, improving their resource utilization efficiency and added value, and reducing environmental pollution have become critical issues urgently needing to be addressed in the fields of environmental protection and resource recycling.

[0003] Oyster shells are composed of a highly ordered, multi-layered structure made up of inorganic substances, proteins, and polysaccharides. The main inorganic component of oyster shells is calcium carbonate (CaCO3), accounting for over 90% of their mass. In recent years, due to their rich calcium content, oyster shells have been extensively studied as a raw material for preparing calcium-based environmental functional materials, which have found applications in water purification and soil improvement.

[0004] Calcium peroxide (CaO2) is a white or yellow crystalline powder, odorless, tasteless, non-toxic, and harmless, and has wide applications in many fields. CaO2 shows promising application prospects in environmental pollution remediation due to its controllable release of O2 and H2O2, thermal stability, and non-polluting reaction products. Furthermore, CaO2 reacts with H2O to directly release H2O2, and is therefore considered solid H2O2. Recent studies have shown that, compared to traditional hydrogen peroxide, CaO2, as a source of H2O2, is more effective than Fe... 2+ Constructing Fenton-like systems to sustainably generate highly oxidizing free radicals has significantly improved the degradation efficiency of organic pollutants and has become a research hotspot in the field of environmental pollution remediation.

[0005] Currently, there are three main categories of methods for synthesizing calcium peroxide: the calcium salt method, the calcium oxide method, and the calcium hydroxide method. The principle is to use a calcium source (calcium chloride, calcium oxide, calcium hydroxide, etc.) to react with H₂O₂ to produce CaO₂. However, the nCaO₂ prepared by existing methods both domestically and internationally is characterized by small particle size and large specific surface area. This results in a relatively fast reaction rate between CaO₂ and H₂O, making it difficult to sustain the slow release of H₂O₂. Consequently, it is challenging to achieve stable and long-lasting remediation effects in practical environmental pollution remediation projects.

[0006] Therefore, how to utilize oyster shells as a calcium source to prepare CaO2 with long-lasting H2O2 mitigation properties, thereby increasing its added value and protecting the environment, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing calcium peroxide using oyster shells and its application.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for preparing calcium peroxide using oyster shells includes the following steps performed sequentially:

[0010] 1) After washing and drying the oyster shells, crush them and then sieve them to obtain oyster shell powder with a particle size of 50-150μm;

[0011] 2) Place the oyster shell powder obtained in step 1) into a beaker, slowly add hydrochloric acid solution and stir continuously until no bubbles are present to obtain the acid hydrolysate;

[0012] 3) Adjust the pH of the acid hydrolysate obtained in step 2) to alkaline using sodium hydroxide solution, filter to remove solid impurities, and obtain the filtrate;

[0013] 4) At room temperature, add 30 mL of ammonia water to the filtrate obtained in step 3) and stir to mix well. Then slowly add 30 mL of hydrogen peroxide solution while stirring continuously. After the addition is complete, filter immediately to complete the solid-liquid separation. The solid product is dried and ground to obtain calcium peroxide.

[0014] Preferably, in step 2), the concentration of the hydrochloric acid solution is 3-5 mol / L, and the solid-liquid ratio of oyster shell powder to hydrochloric acid solution is 1:4-10 g / mL;

[0015] Preferably, in step 3), the concentration of the sodium hydroxide solution is 1.0 mol / L, and the alkaline pH value range is 11-12;

[0016] Preferably, in step 4), the concentration of the ammonia solution is 25%–28%, and the concentration of the hydrogen peroxide solution is 15%–30%.

[0017] Preferably, in step 4), the drying temperature is 80-100°C.

[0018] This invention provides a calcium peroxide prepared by the above method.

[0019] In one embodiment of the present invention, the nano-calcium peroxide has a particle size of 0.5–1.2 μm, a purity of over 80%, and a specific surface area of ​​less than 3 m². 2 / g.

[0020] This invention provides an application of the above-mentioned calcium peroxide in the field of environmental protection.

[0021] In one embodiment of the present invention, applications in environmental protection include the remediation of organically contaminated soil and water.

[0022] In one embodiment of the present invention, the application uses the above-mentioned calcium peroxide and Fe. 2+ A Fenton-like system was constructed for pollution remediation.

[0023] In one embodiment of the present invention, the application is carried out using calcium peroxide / citric acid-Fe. 2+ The Fenton-like system generates hydroxyl radicals with strong oxidizing power to efficiently degrade phenanthrene.

[0024] In one embodiment of the present invention, the calcium peroxide, citric acid and Fe 2+ The molar ratio is 2:1:1.

[0025] In one embodiment of the present invention, the Fe 2+ It is either ferrous sulfate or ferrous chloride.

[0026] The present invention has achieved the following beneficial technical effects:

[0027] (1) Oyster shells, whose main component is CaCO3, are almost completely decomposed into calcium chloride, carbon dioxide and water after the addition of hydrochloric acid solution, resulting in high utilization rate and virtually no waste generation. Among them, the calcium chloride produced is a commonly used calcium source for the preparation of calcium peroxide. This is one of the main reasons for using oyster shells to prepare calcium peroxide in this application.

[0028] (2) The calcium peroxide obtained by the method of the present invention has a high purity, which can reach more than 80%, while the purity of commercially available calcium peroxide is 65-75%.

[0029] (3) The calcium peroxide prepared by the method of the present invention has a smaller specific surface area, which is much lower than that of commercially available calcium peroxide. The reduction in specific surface area can reduce the probability of contact with H2O, thereby reducing the reaction rate and prolonging the release cycle of H2O2.

[0030] (4) The H2O2 release cycle of calcium peroxide prepared by the method of the present invention is significantly longer than that of commercially available calcium peroxide.

[0031] (5) The calcium peroxide prepared by the method of the present invention has a slower H2O2 release rate, which makes the calcium peroxide / citric acid-Fe 2+ The reaction time of the Fenton-like system is extended, thereby improving the degradation efficiency of pollutants. Attached Figure Description

[0032] Figure 1 The image shows the XRD pattern of CaO2 prepared in Example 1.

[0033] Figure 2 This is a scanning electron microscope image of commercially available CaO2.

[0034] Figure 3 This is a scanning electron microscope image of the CaO2 prepared in Example 1.

[0035] Figure 4 The image shows a scanning electron microscope (SEM) image of the CaO2 prepared in Comparative Example 1.

[0036] Figure 5 The ability of three types of CaO2 to release H2O2 was measured using ultraviolet spectrophotometry.

[0037] Figure 6 The degradation effect of phenanthrene under different conditions. Detailed Implementation

[0038] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0039] 1. Surface morphology test of calcium peroxide: The surface morphology of commercially available calcium peroxide and prepared calcium peroxide was compared using an S-4800 field emission scanning electron microscope (SEM).

[0040] 2. The diffraction pattern of the prepared calcium peroxide was determined using an X'Pert Pro X-ray diffractometer (XRD), with a scanning range of 5–90° and a scanning speed of 10° / min.

[0041] 3. Specific surface area test: The specific surface area of ​​calcium peroxide was determined using an ASAP 2020M+C fully automatic three-station specific surface area and pore size distribution instrument. Before the test, the sample was placed at 120℃ and degassed under vacuum for 3 hours. Then, the treated sample was placed under liquid nitrogen temperature (-196℃) to measure the N2 adsorption and desorption isotherms. Finally, the specific surface area was calculated using the BET (Brunauer-Emmett-Tellr) equation.

[0042] 4. Method for determining the purity of CaO2: The purity of CaO2 is determined by potassium permanganate titration. The specific steps are as follows: Accurately weigh 0.05g of the sample to be tested and place it in a 250mL Erlenmeyer flask. Add 10mL of phosphoric acid (4mol / L) and 10mL of sulfuric acid (4mol / L) successively. After dissolution, titrate with 0.02mol / L potassium permanganate until a red solution appears. The purity of CaO2 is calculated using the following formula:

[0043] W = (5CVM / 2m) × 100%

[0044] In the formula, C: concentration of potassium permanganate, mol / L; V: volume of potassium permanganate titration, L; M: relative molecular weight of calcium peroxide, g / mol; m: mass of calcium peroxide weighed, g.

[0045] 5. Method for determining the concentration of H2O2 released by calcium peroxide: The method uses potassium titanate spectrophotometry. The specific steps are as follows: Add 0.02g of CaO2 prepared by different methods to 200mL of deionized water. At regular time intervals, take 1.0mL of the sample and filter it through a 0.22μm filter membrane into a 25mL colorimetric tube. Add 1.0mL of potassium titanate solution (0.08mol / L) and 1.0mL of sulfuric acid solution (4mol / L) respectively. After color development for 10min, measure the absorbance at 358nm using a UV spectrophotometer. Then calculate the corresponding concentration based on the calibration curve.

[0046] 6. Determination of phenanthrene concentration in solution: High performance liquid chromatography (HPLC) was used. The specific procedure was as follows: Take 1.0 mL of sample, add 0.1 mL of methanol to quench the reaction, filter with a 0.22 μm polytetrafluoroethylene membrane, and then determine the concentration of phenanthrene in the filtrate using HPLC.

[0047] Comparative Example 1

[0048] Calcium peroxide was prepared according to the method in Example 1, except that the calcium source was calcium chloride. The specific steps of the method are as follows:

[0049] 1) Weigh 5.0g of calcium chloride into a 500mL beaker, then add 50mL of deionized water and stir continuously until completely dissolved to obtain a calcium chloride solution;

[0050] 2) At room temperature, add 30 mL of 26% ammonia water to the calcium chloride solution prepared in step 1), stir and mix well, then slowly add 30 mL of 20% hydrogen peroxide while stirring continuously. After the addition is complete, filter immediately to complete the solid-liquid separation. Dry the solid product at 80℃ for 4 hours, grind it, and seal it for storage.

[0051] The obtained CaO2 had a purity of 74.4% and a specific surface area of ​​30.69 m². 2 / g, with a particle size of 50-150nm.

[0052] Example 1

[0053] A method for preparing calcium peroxide using oyster shells includes the following steps performed sequentially:

[0054] 1) After washing and drying the oyster shells, crush them and then sieve them to obtain oyster shell powder with a particle size of 50-150μm;

[0055] 2) Place 5.0g of oyster shell powder obtained in step 1) into a 500mL beaker, slowly add 25mL of 4.0mol / L hydrochloric acid and stir continuously until no bubbles are present to obtain the acid hydrolysate;

[0056] 3) Adjust the pH of the acid hydrolysate obtained in step 2) to 11.0 using a 1.0 mol / L sodium hydroxide solution, filter to remove solid impurities, and obtain the filtrate;

[0057] 4) At room temperature, add 30 mL of 26% ammonia water to the filtrate obtained in step 3) and stir to mix well. Then slowly add 30 mL of 20% hydrogen peroxide while stirring continuously. After the addition is complete, filter immediately to complete the solid-liquid separation. Dry the solid product at 80°C for 4 hours, grind it, and seal it for storage.

[0058] The obtained CaO2 had a purity of 81.8% and a specific surface area of ​​2.20 m². 2 / g, with a particle size of 0.5–1.2 μm; while commercially available CaO2 has a purity of 72.1% and a specific surface area of ​​7.19 m². 2 / g, with a particle size of 50-150nm.

[0059] Figure 1 The XRD pattern of CaO2 prepared in Example 1 shows that strong diffraction peaks appear at 2θ = 30.1, 35.6, and 47.3. According to the standard diffraction (PDF) card of calcium peroxide (PDF#03-0865), these diffraction peaks all belong to CaO2.

[0060] Figure 2 This is a scanning electron microscope image of commercially available CaO2 (purchased from Thermo Fisher Scientific (China) Co., Ltd.). Figure 3 This is a scanning electron microscope image of the CaO2 prepared in Example 1. Figure 4 The image shows a scanning electron microscope (SEM) image of the CaO2 prepared in Comparative Example 1, illustrating that the CaO2 prepared in Example 1 has a larger size, resulting in a corresponding decrease in its specific surface area.

[0061] Figure 5 The ability of three types of CaO2 to release H2O2 was measured using ultraviolet spectrophotometry. It can be seen that the hydrogen peroxide release cycles of the CaO2 prepared in Example 1, commercially available CaO2, and the CaO2 prepared in Comparative Example 1 were 60, 60, and 300 min, respectively, with maximum cumulative H2O2 concentrations of 0.74, 0.86, and 1.02 mmol / L, respectively. This indicates that the CaO2 prepared in Example 1 has superior H2O2 slow-release performance. This is because the increased particle size and decreased specific surface area of ​​CaO2 significantly reduce the contact probability between solid particles and H2O, slowing down the reaction rate between them, thereby prolonging the H2O2 release cycle.

[0062] Figure 6 The degradation effect of phenanthrene under different conditions is shown. It can be seen that the CaO2 system prepared in Example 1 exhibits better phenanthrene removal effect compared with commercially available CaO2 and CaO2 prepared in Comparative Example 1.

[0063] Example 2

[0064] An application of calcium peroxide preparation using oyster shells

[0065] The remediation effect of calcium peroxide-based Fenton-like technology was studied using phenanthrene as the target pollutant.

[0066] The CaO2 prepared in Example 1 was used as the experimental group, while commercially available CaO2 and the CaO2 prepared in Comparative Example 1 were used as the control groups. The experiment was conducted at room temperature in a 250 mL glass bottle equipped with a magnetic stirrer. 200 mL of a 1.0 mg / L phenanthrene solution was added, followed by 1 mL of 0.1 mol / L citric acid-Fe2+ solution. 2+ The solution was then mixed with CaO2 prepared in Example 1 / commercial CaO2 / CaO2 prepared in Comparative Example 1 to start the reaction. After a certain time interval, a sample was taken and an excess of quencher was added to terminate the reaction. The mixture was then filtered through a 0.22 μm filter membrane and analyzed by high performance liquid chromatography (HPLC).

[0067] The degradation effect of phenanthrene under different experimental conditions is as follows: Figure 6 As shown in the figure, the removal rate of phenanthrene in the Fenton-like system of CaO2 prepared in Comparative Example 1 was 69% after 40 min, while the removal rate of phenanthrene in the Fenton-like system of commercially available CaO2 was 85%. It can be clearly seen from the figure that in the early stage of the reaction, the reaction rate was faster in both the CaO2 prepared in Comparative Example 1 and the Fenton-like system of commercially available CaO2, and the reaction was almost complete within 5 min. This is due to the large amount of H2O2 released initially and reacting with Fe. 2+ The Fenton reaction occurs, producing a large number of hydroxyl radicals ( • OH), which leads to the rapid degradation of phenanthrene.

[0068] Compared to the CaO2 prepared in Comparative Example 1 and the commercially available CaO2 Fenton-like system, the CaO2-based Fenton-like system prepared in Example 1 showed better phenanthrene degradation, achieving a removal rate of 94%. This is because the CaO2 prepared in Example 1 slowly and continuously generates H2O2, resulting in a continuous generation of H2O2 in the reaction system. • OH, thus maintaining a longer oxidation reaction time, thereby improving the removal efficiency of phenanthrene. In addition, the CaO2 prepared in Example 1 has higher purity, which can generate more H2O2 for phenanthrene degradation.

[0069] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing calcium peroxide using oyster shells, characterized in that, Includes the following steps: 1) After washing and drying the oyster shells, crush them and then sieve them to obtain oyster shell powder with a particle size of 50-150μm; 2) Place the oyster shell powder obtained in step 1) into a beaker, slowly add hydrochloric acid solution and stir continuously until no bubbles are present to obtain the acid hydrolysate; 3) Adjust the pH of the acid hydrolysate obtained in step 2) to alkaline using sodium hydroxide solution, filter to remove solid impurities, and obtain the filtrate; 4) At room temperature, add 30 mL of ammonia water to the filtrate obtained in step 3) and stir to mix well. Then slowly add 30 mL of hydrogen peroxide solution while stirring continuously. After the addition is completed, filter immediately to complete the solid-liquid separation. The solid product is dried and ground to obtain calcium peroxide. In step 3), the concentration of sodium hydroxide is 1.0 mol / L; In step 4), the concentration of ammonia is 25%–28%, and the concentration of hydrogen peroxide is 15%–30%. In step 4), the drying temperature is 80-100°C.

2. The method for preparing calcium peroxide using oyster shells according to claim 1, characterized in that, The concentration of the hydrochloric acid solution is 3–5 mol / L.

3. The method for preparing calcium peroxide using oyster shells according to claim 1, characterized in that, The solid-liquid ratio of oyster shell powder to hydrochloric acid solution is 1:4 to 10 g / mL.

4. The method for preparing calcium peroxide using oyster shells according to claim 1, characterized in that, The alkaline pH range is 11 to 12.

5. A calcium peroxide prepared using the method of claim 1.

6. An application of calcium peroxide as described in claim 5 in the field of environmental protection, characterized in that, Using the calcium peroxide and citric acid-Fe as described in claim 5 2+ A Fenton-like system was constructed to generate hydroxyl radicals to degrade organic pollutants in soil and water.

7. The application according to claim 6, characterized in that, The organic pollutant in this application is phenanthrene.

8. The application according to claim 6, characterized in that, The calcium peroxide, citric acid and Fe 2+ The molar ratio is 2:1:

1.

9. The application according to claim 6, characterized in that, The Fe 2+ It is either ferrous sulfate or ferrous chloride.

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