Method for preparing medical shielding material from hazardous wastes containing heavy metals

Abstract

The invention belongs to the technical field of hazardous waste resource utilization, and relates to a method for preparing a medical shielding material from hazardous waste containing heavy metal. Hazardous waste containing heavy metal (electroplating sludge, smelting waste residues and incineration fly ash) is selected, the leaching toxicity index of the hazardous waste does not need to be limited, and the shielding performance is improved by fully utilizing the high-density characteristic of the heavy metal. Impurity components do not need to be removed in advance, hazardous waste primary components are directly reserved, and cooperative forming of heavy metal and impurities is achieved through process regulation and control. According to the method, the heavy metal leaching process in a traditional technology is avoided, efficient and harmless utilization of the hazardous waste is directly achieved through the forming technology, and a green and efficient method is provided for treatment of the hazardous waste containing heavy metal and preparation of medical shielding materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource utilization of hazardous waste containing heavy metals, and relates to a method for preparing medical shielding materials from hazardous waste containing heavy metals. The hazardous waste containing heavy metals is pretreated, and then through a specific forming process, the treated hazardous waste is made into the shape required for medical shielding materials; finally, the performance of the materials is detected and optimized to ensure that their shielding performance, safety and other indicators meet medical standards. Background Art

[0002] With the rapid development of industry, the generation amount of hazardous waste containing heavy metals is increasing day by day. As defined in the National List of Hazardous Wastes, hazardous waste containing heavy metals contains various heavy metal components such as lead (Pb), mercury (Hg), cadmium (Cd), chromium (Cr), etc., and has dangerous characteristics such as toxicity and corrosiveness. If these hazardous wastes are not properly disposed of, they will cause serious pollution to soil, water bodies and the atmosphere, threatening human health and the ecological environment.

[0003] From the perspective of the industrial production system and the field of urban solid waste treatment, the main sources of hazardous waste containing heavy metals show diversified characteristics. In the traditional industrial field, the non-ferrous metal smelting industry (such as copper, lead, zinc, nickel smelting) is a typical source. The smelting slag, soot and wastewater treatment sludge generated during its production process are rich in heavy metals such as Cu, Zn, Pb, Cd, etc., and are often accompanied by complex impurities such as SiO2, Al2O3; the chemical industry and electroplating industry generate a large amount of Cr 6+ , Ni 2+ , Cu 2+Electroplating sludge, chemical precipitates, and waste catalysts; in the field of electronic waste treatment, fluorescent powders, welding slag, and etching waste liquids containing Hg, Pb, and Cd released during circuit board disassembly and display recycling, as well as electrode waste and electrolyte residues generated in the battery manufacturing industry (lead-acid batteries, lithium batteries), are all classified as high-risk wastes due to their high heavy metal concentrations and strong toxicity. In the field of municipal solid waste treatment, fly ash generated from waste incineration (covering industrial waste incineration plants and domestic waste incineration power generation facilities) is an important new source. Among them, industrial waste incineration fly ash (such as coal chemical slag and industrial waste incineration ash) contains characteristic pollutants such as Cr and Hg, while domestic waste incineration fly ash is enriched with heavy metals such as Pb, Cd, and Zn due to the incineration of plastics and electronic components, and its leaching toxicity is significantly affected by the incineration temperature and flue gas purification process. These hazardous wastes containing heavy metals from industrial production and urban metabolism generally have the characteristics of complex chemical compositions and unstable heavy metal occurrence forms (such as soluble ionic states and easily leachable compounds). If not properly disposed of, they are extremely likely to cause ecological risks through soil infiltration, surface runoff, etc., becoming the key difficulties in global environmental governance. For example, copper smelting produces copper slag and soot containing Cu, Zn, Pb, etc.; the electroplating industry produces electroplating sludge rich in metal hydroxides such as Cu, Ni, Cr, and Zn. The chemical compositions of these hazardous wastes are complex. In addition to heavy metal oxides or sulfides in the smelting slag, they also contain components such as SiO2 and Al2O3, and soluble heavy metal ions such as Cr 6+ , Cd 2+ and other soluble heavy metal ions are easily released; the metal hydroxides in electroplating sludge have poor stability and are easily dissolved to release heavy metal ions under acidic conditions.

[0004] Currently, the treatment technologies for hazardous wastes containing heavy metals mainly include resource utilization and harmless disposal. Resource utilization technologies such as pyrometallurgical-hydrometallurgical coupling technology, mineral phase reconstruction and stabilization technology, biological leaching and recovery technology, etc., aim to recover valuable metals, but there may still be problems of partial heavy metal residues or secondary pollution after treatment. Harmless disposal technologies such as stabilization / solidification, high-temperature treatment, and safe landfill can reduce the harm of heavy metals, but they do not fully exploit the potential value of hazardous wastes.

[0005] Medical shielding materials play an important role in the medical field. For example, during radiotherapy, nuclear medicine examinations, etc., they are used to protect patients and medical staff from radiation damage. Traditional medical shielding materials mainly use heavy metals such as lead as the main raw materials, but there are certain environmental and health risks during their production and use. Converting hazardous wastes containing heavy metals into medical shielding materials can not only solve the disposal problems of hazardous wastes containing heavy metals but also meet the needs of medical shielding materials, realizing resource recycling and having significant social benefits. Summary of the Invention

[0006] The present invention provides a method for converting hazardous waste containing heavy metals into medical shielding materials, which avoids the heavy metal leaching process in traditional processes and directly realizes efficient and harmless utilization of hazardous waste through a molding process, thereby providing a green and efficient method for the treatment of hazardous waste containing heavy metals and the preparation of medical shielding materials.

[0007] The present invention selects hazardous waste materials containing heavy metals (Pb, Cd, Zn, Cr, etc.), and there is no need to limit its leaching toxicity index (such as lead and cadmium leaching concentration), and fully utilizes the high density characteristics of heavy metals themselves to improve shielding performance. Impurity components (such as SiO2, Al2O3, etc.) do not need to be removed in advance, and the original components of hazardous waste are directly retained, and the synergistic formation of heavy metals and impurities is achieved through process control. Common experimental raw materials include electroplating sludge (rich in heavy metal hydroxides), smelting waste (high concentration of metal oxides), incineration fly ash (containing heavy metal glass), etc. without deep treatment.

[0008] The technical solution adopted by the present invention is as follows:

[0009] A method for preparing medical shielding materials using hazardous waste containing heavy metals comprises the following steps:

[0010] Step 1: Pretreatment of hazardous waste containing heavy metals

[0011] Select hazardous wastes containing heavy metals, such as electroplating sludge, smelting waste residue, and incineration fly ash. The hazardous wastes containing heavy metals include electroplating sludge, smelting waste residue, incineration fly ash, etc.; among which electroplating sludge contains a variety of heavy metal hydroxides, smelting waste residue contains metal oxides and impurities, and incineration fly ash contains glassy heavy metal ions. Place these hazardous wastes in a drying oven and dry them at 105℃~120℃. The drying time is adjusted according to the initial moisture content of the hazardous waste until the moisture content is ≤5% to remove free water and avoid bubbles in subsequent molding. For example, use a blast drying oven, set the temperature to 110℃, and spread the hazardous waste evenly on the pallet with a thickness of 2 to 3 cm.

[0012] The dried hazardous waste is first crushed by a crusher, and then finely ground by a ball mill to a particle size of 100 to 300 meshes. For example, for smelting waste slag, the size of the crusher's discharge port is adjusted during coarse crushing to make the particle size of the crushed waste slag about 1 to 2 cm, and then put it into the ball mill for grinding for 2 to 3 hours. During this period, samples are taken regularly to test the particle size to ensure that it meets the requirements and ensures the uniformity of subsequent mixing with resin.

[0013] Step 2: Direct compounding and thermoplastic molding

[0014] Accurately select resin and determine the optimal ratio based on the characteristics of different hazardous waste materials and target product performance requirements.

[0015] (I) Resin selection and ratio determination

[0016] For electroplating sludge containing a relatively large amount of metal hydroxides, epoxy resin becomes an ideal choice due to its good adhesiveness and chemical stability. The mass ratio of electroplating sludge to epoxy resin is 12:1 - 15:1. Within this ratio range, it can not only ensure that the epoxy resin fully wraps the heavy metal particles in the electroplating sludge to form a stable structure, but also ensure that the material has good mechanical properties. For smelting slag, considering its high hardness and complex composition, polyamide resin is adapted to it by virtue of its high melting point and excellent wear resistance. The mass ratio of the two is set at 8:1 - 10:1. This ratio can enable the polyamide resin to effectively fill the gaps between the slag particles at high temperatures, enhancing the overall density and stability of the material.

[0017] (2) Blending

[0018] Before blending, first preheat the resin to a certain temperature to enhance its fluidity, which is convenient for uniform mixing with the hazardous waste powder. For example, preheat the epoxy resin to 60°C - 70°C and use an oven or heating platform to achieve precise temperature control. Then, slowly add the ground hazardous waste powder to the resin, and at the same time turn on a high-speed mixer. The stirring speed is controlled at 800 - 1200 revolutions per minute, and the stirring time is maintained for 15 - 20 minutes. During the stirring process, ensure that the hazardous waste powder is evenly dispersed in the resin without obvious agglomeration.

[0019] (3) Hot pressing and forming

[0020] The mold material is selected as high-temperature resistant and high-strength steel, such as Cr12MoV steel, and the inner wall of the mold is polished. The surface roughness is controlled at Ra0.8 - Ra1.6μm to reduce the friction between the material and the mold and facilitate demolding. Spread the mixed material evenly in the mold, control the material thickness to be uniform, and the deviation does not exceed ±1mm.

[0021] During the hot pressing process, strictly control the temperature, pressure, and holding time. Taking polyamide resin as an example, first place the mold in a hot press and heat it to 220°C - 240°C at a rate of 5°C / min - 8°C / min. At the same time, apply an initial pressure of 5MPa - 8MPa to remove the air in the material. After reaching the target temperature, increase the pressure to 12MPa - 15MPa and hold the pressure for 20 - 30 minutes. During the holding pressure process, monitor the temperature and pressure changes in real time through the temperature control system and pressure sensor of the hot press to ensure that the parameters are stable, and the deviation is controlled within ±2°C and ±0.5MPa. After the holding pressure is over, naturally cool the mold to below 80°C before demolding to avoid product deformation due to excessive temperature.

[0022] (4) Injection molding

[0023] Before injection molding, set the temperature of each section of the barrel according to the resin characteristics. Taking high-purity polyethylene as an example, the temperature of the front section of the barrel is set at 230°C - 250°C, the middle section is 250°C - 270°C, and the rear section is 220°C - 240°C. At the same time, install the mold on the injection molding machine and preheat it to 60°C - 80°C to ensure that the material flows quickly and evenly in the mold.

[0024] Add the blended material to the hopper of the injection molding machine. Set the injection pressure at 10MPa - 13MPa, and adjust the injection speed according to the shape and size of the product, generally controlled at 30 - 50mm / s. During the injection process, the screw melts the material at a certain rotation speed and injects it into the mold cavity. Set the holding pressure at 8MPa - 10MPa and the holding time at 10 - 15 seconds to fully form the product. After injection molding, cool the product through the cooling system of the mold. The cooling medium is circulating water, and the water temperature is controlled at 15°C - 25°C. The cooling time is determined according to the thickness of the product, generally 20 - 40 seconds, to ensure uniform cooling of the product without warping or deformation.

[0025] Step Three: Post-treatment

[0026] There may be defects on the surface of the formed material or it may not meet the requirements of the medical environment, so post-treatment is required. Adopt spraying technology to evenly spray a protective coating on the material surface, such as a polyurethane coating, with a thickness controlled at 30 - 50 microns, to enhance the corrosion resistance and wear resistance of the material, enabling it to be used stably in the indoor medical environment for a long time.

[0027] For some application scenarios with specific requirements, such as a shielding device that needs to be sealed, encapsulate the material. Use a sealant or metal encapsulation material to ensure effective isolation of the material from the external environment and prevent heavy metal leakage.

[0028] The medical shielding material prepared by the above method needs to be tested for shielding performance using professional equipment. For example, use an X-ray machine of model MG324 from PHILIPS Company in Germany, equipped with a radiation meter. Place the sample vertically in front of the center of the X-ray tube target, and fix the detector on the horizontal axis 100 cm away from the center of the target. Set the counting time at 100 s, measure the intensity of the incident ray and the transmitted ray after being blocked by the sample, and calculate the shielding rate according to the following formula:

[0029] Shielding rate = (Intensity of incident ray - Intensity of transmitted ray) / Intensity of incident ray × 100%

[0030] According to the method of "Identification Standard for Toxicity of Hazardous Wastes Extracted" (GB 5085.3—2007), a heavy metal leaching experiment was carried out by simulating the human body environment (such as leaching solution with a pH value of 4.5 - 7.5). The heavy metal leaching concentration of the material was detected within a certain period of time to ensure that the lead leaching concentration ≤ 0.1 mg / L, the cadmium leaching concentration ≤ 0.01 mg / L, etc., which meet the safety standards of medical materials. If the leaching concentration exceeds the standard, analyze the reasons. It may be that the forming process is imperfect, resulting in an incompact structure. The forming parameters can be adjusted to re-prepare and detect. The method provided by the present invention for converting hazardous waste containing heavy metals into medical shielding materials has the advantages of harmless treatment, resource utilization, and simple process. Through steps such as pretreatment, chemical conversion, forming process, and performance detection optimization, the efficient conversion of hazardous waste containing heavy metals into medical shielding materials is realized, providing a new technical solution for the treatment of hazardous waste containing heavy metals and the field of medical materials. Moreover, this method is environmentally friendly and has good application prospects. Specific Embodiments

[0031] Example 1: Test Results of Shielding Performance

[0032] Multiple groups of comparative examples were set, and the variables included the types of hazardous waste containing heavy metals, forming process parameters, etc. The specific parameters are shown in the following table:

[0033] Table 1 Experimental Parameters

[0034] Parameter Value range Control method Hazardous waste type Electroplating sludge, smelting slag, incineration fly ash Source screening Hot pressing temperature (°C) 150～200 Temperature controller adjustment Hot pressing pressure (MPa) 5～10 Pressure sensor control Injection molding temperature (°C) 200～250 Temperature controller adjustment Injection molding pressure (MPa) 8～12 Pressure sensor control

[0035] In each group of materials, the treatment of hazardous waste containing heavy metals and the preparation of medical shielding materials were carried out according to the set parameters. An X-ray machine of type MG324 from PHILIPS Company in Germany (tube voltage 60 - 250 kVp) was used as the radiation source, and a SolidDose Model 400 radiation meter (equipped with a high-resolution semiconductor detector R100, serial number S / N: 3023) was used for shielding performance detection. During the test, the sample was vertically placed directly in front of the X-ray machine target center, and the detector was fixed on the horizontal axis 100 cm away from the target center, keeping the incident ray direction perpendicular to the sample surface. The counting time was set to 100 s, and the incident ray intensity without the sample and the transmitted ray intensity after the sample blocked were measured respectively. The shielding rate was calculated as shown in formula (3-1). This test system can accurately evaluate the shielding efficiency of the material for medical diagnostic X-rays by controlling the X-ray tube voltage to simulate different energy rays (60 - 250 keV).

[0036] The experimental results are shown in Table 2 below:

[0037]

[0038] As can be seen from the results, there are differences in the shielding performance of medical shielding materials prepared from different types of hazardous wastes containing heavy metals. Among them, the materials prepared from electroplating sludge have relatively good shielding performance. When hot-pressed and formed with a chemical conversion reagent dosage of 1.5:1, a forming temperature of 250 °C, and a pressure of 10 MPa, the shielding rate can reach 88%. Generally speaking, increasing the dosage of chemical conversion reagent, raising the forming temperature and pressure is beneficial to improving the shielding performance of the materials.

[0039] The heavy metal leaching experiment was carried out on the prepared medical shielding materials. Using the method in the "Identification Standard for Toxicity of Hazardous Wastes Leaching" (GB 5085.3—2007), simulating the human environment (such as leaching solution with a pH value of 4.5 - 7.5), the heavy metal leaching concentration of the materials within a certain period of time was detected. The results showed that the heavy metal leaching concentrations of all experimental materials were far lower than the safety standard requirements for medical materials (such as lead leaching concentration

[0040] ≤0.1 mg / L, cadmium leaching concentration ≤0.01 mg / L). Because the formed stable substances hardly decompose in the simulated human environment, the safety of the materials was further verified.

[0041] Assume that the annual treatment volume of hazardous wastes containing heavy metals is 50,000 tons, and the market price of the prepared medical shielding materials is 5,000 yuan / ton. After calculation, about 40,000 tons of medical shielding materials can be produced annually, and the output value can reach 200 million yuan. After deducting the production cost (including raw material treatment, chemical reagents, energy consumption, equipment depreciation, etc.) of about 120 million yuan, the annual net profit is about 80 million yuan, showing significant economic benefits.

[0042] In terms of environmental benefits, treating 50,000 tons of hazardous wastes containing heavy metals annually avoids the pollution of these hazardous wastes to the environment. Taking electroplating sludge as an example, if directly discharged without treatment, the heavy metals in it will pollute the soil and water bodies, causing ecological damage. Through this technology, it is transformed into medical shielding materials, realizing the harmless treatment and resource utilization of hazardous wastes, reducing the exploitation of natural resources, and reducing the potential risks of heavy metals to the environment, which is of great significance to ecological environment protection.

Claims

1. A method for preparing medical shielding materials using hazardous waste containing heavy metals, characterized in that: Step 1: Pretreatment of hazardous waste containing heavy metals The hazardous waste materials containing heavy metals are electroplating sludge, smelting waste residue or incineration fly ash; wherein, electroplating sludge contains a variety of heavy metal hydroxides, smelting waste residue contains metal oxides and impurities, and incineration fly ash contains glassy heavy metal ions; The hazardous waste containing heavy metals is placed in a drying oven and dried at 105℃~120℃; the drying time is adjusted according to the initial moisture content of the hazardous waste until the moisture content is ≤5% to remove free water and avoid bubbles in subsequent molding; the dried hazardous waste is first coarsely crushed by a crusher, and then finely ground by a ball mill to a particle size of 100~300 mesh; Step 2: Direct compounding and thermoplastic molding (I) Resin selection and ratio determination The mass ratio of electroplating sludge to epoxy resin is 12:1-15:1; the mass ratio of smelting waste residue to polyamide resin is 8:1-10:1; (ii) Blending Before blending, preheat the resin first; then, slowly add the ground hazardous waste powder into the resin, and start the high-speed mixer at the same time, control the stirring speed at 800-1200 rpm, and maintain the stirring time for 15-20 minutes; (3) Hot Pressing The mold material is made of high-temperature resistant and high-strength steel, such as Cr12MoV steel, and the inner wall of the mold is polished, and the roughness is controlled at Ra0.8~Ra1.6μm; the mixed material is evenly spread in the mold, and the material thickness is controlled to be uniform and the deviation does not exceed ±1mm; During the hot pressing process, the temperature, pressure and holding time are strictly controlled. Taking polyamide resin as an example, the mold is first placed in the hot press, and the temperature is raised to 220℃~240℃ at a rate of 5℃ / min~8℃ / min. At the same time, an initial pressure of 5MPa~8MPa is applied to remove the air in the material. After reaching the target temperature, the pressure is increased to 12MPa~15MPa and the pressure is maintained for 20~30 minutes. During the holding process, the temperature and pressure changes are monitored in real time through the temperature control system and pressure sensor of the hot press to ensure that the parameters are stable and the deviation is controlled within ±2℃ and ±0.5MPa. After the holding is completed, the mold is naturally cooled to below 80℃ before demolding to avoid product deformation due to excessive temperature. (IV) Injection molding Before injection molding, the temperature of each section of the barrel is set according to the characteristics of the resin. Taking high-purity polyethylene as an example, the temperature of the front section of the barrel is set to 230℃~250℃, the middle section is 250℃~270℃, and the rear section is 220℃~240℃. At the same time, the mold is installed on the injection molding machine and preheated to 60℃~80℃ to ensure that the material flows quickly and evenly in the mold. Add the blended material into the hopper of the injection molding machine, set the injection pressure at 10MPa~13MPa, and adjust the injection speed according to the shape and size of the product, and control it at 30~50mm / s; during the injection molding process, the screw melts the material and injects it into the mold cavity, and the holding pressure is set to 8MPa~10MPa, and the holding time is 10~15 seconds to fully mold the product; after the injection molding is completed, the product is cooled by the cooling system of the mold, and the cooling medium uses circulating water, and the water temperature is controlled at 15℃~25℃. The cooling time is determined according to the thickness of the product, and the time is 20~40 seconds to ensure that the product is cooled evenly without warping and deformation; Step 3: Post-processing Using spraying technology, a protective coating is evenly sprayed on the surface of the material with a thickness controlled at 30 to 50 microns to enhance the corrosion resistance and wear resistance of the material, so that it can be used stably and for a long time in indoor medical environments. If a sealed shielding device is required, use sealant or metal packaging materials to ensure that the material is effectively isolated from the external environment to prevent heavy metal leakage.

2. The method for preparing medical shielding materials using hazardous waste containing heavy metals according to claim 1, characterized in that: In step 1, use a forced air drying oven to dry the hazardous waste containing heavy metals, set the temperature to 110°C, and spread the hazardous waste evenly on a pallet with a thickness of 2 to 3 cm.

3. The method for preparing medical shielding materials using hazardous waste containing heavy metals according to claim 1, characterized in that: In step 1, for the smelting waste slag, the size of the crusher's discharge port is adjusted during coarse crushing so that the particle size of the crushed waste slag is about 1 to 2 cm, and then it is put into a ball mill for grinding for 2 to 3 hours. During this period, samples are taken regularly to detect the particle size to ensure that it meets the requirements and ensures the uniformity of subsequent mixing with the resin.

4. The method for preparing medical shielding materials using hazardous waste containing heavy metals according to claim 1, characterized in that: In hot pressing, the mold material is Cr12MoV steel.

5. The method for preparing medical shielding materials using hazardous waste containing heavy metals according to claim 4, characterized in that: In hot pressing, polyamide resin is used; the details are as follows: First, place the mold in the hot press, heat it to 220℃~240℃ at a rate of 5℃ / min~8℃ / min, and apply an initial pressure of 5MPa~8MPa to expel air from the material; after reaching the target temperature, increase the pressure to 12MPa~15MPa and maintain the pressure for 20~30 minutes; during the pressure holding process, monitor the temperature and pressure changes in real time through the temperature control system and pressure sensor of the hot press to ensure parameter stability and deviation within ±2℃ and ±0.5MPa; after the pressure holding is completed, naturally cool the mold to below 80℃ before demolding to avoid product deformation due to excessive temperature.

6. The method for preparing medical shielding materials using hazardous waste containing heavy metals according to claim 1, characterized in that: In injection molding, when high-purity polyethylene is used, the temperature of the front section of the barrel is set to 230℃~250℃, the middle section to 250℃~270℃, and the rear section to 220℃~240℃.

7. The method for preparing medical shielding materials using hazardous waste containing heavy metals according to claim 1, characterized in that: The medical shielding material prepared by the above method needs to be tested for shielding performance using professional equipment; use the MG324 X-ray machine of the German PHILIPS company with a radiation meter, place the sample vertically in front of the X-ray machine's bull's eye, and fix the detector on the horizontal axis 100 cm away from the bull's eye; set the counting time to 100s, measure the intensity of the incident ray and the intensity of the transmitted ray after the sample is shielded, and calculate the shielding rate according to the following formula: Shielding rate = (incident ray intensity - transmitted ray intensity) / incident ray intensity × 100%.

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