Method for treating heavy metal-containing plastic waste

Abstract

To provide a method for treating heavy metal-containing plastic waste, which can separate heavy metals from the heavy metal-containing plastic waste and also recover other useful substances.SOLUTION: A method for treating heavy metal-containing plastic waste includes: a step of mixing the heavy metal-containing plastic waste (a) and a chlorine-containing material (b) in such a ratio that a molar ratio (chlorine / heavy metal) of the heavy metals in the heavy metal-containing plastic waste (a) to the chlorine in the chlorine-containing material (b) is 3 or more; and a heating step in which the mixture is heated under conditions where an oxygen concentration in an atmosphere is 3% by volume or less and the temperature is between 500°C and 700°C to promote a volatilization of the heavy metals and an embrittlement of plastics.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating heavy metal-containing plastic waste. [Background technology]

[0002] Shredder dust generated after the dismantling and crushing of used electrical appliances and automobiles is heated and crushed, and then the crushed material is physically separated to recover combustible materials as fuel for cement calcination, and valuable metals such as iron, copper, and aluminum are recovered individually. However, heavy metals such as zinc, lead, and cadmium have not been recovered individually using conventional methods, and many of them are contained in the cement calcination fuel and dissipated directly into the cement clinker. Shredder dust contains a high proportion of galvanized steel sheets, which are a source of zinc, and also contains heavy metals and alloys added to resins, making it difficult to recover heavy metals using physical separation alone.

[0003] Conventionally, as a method for recovering heavy metals such as zinc, it has been reported that, for example, by supplying shredder dust as a reducing agent together with zinc-containing iron oxide to a reduction furnace and heat-treating them at 800 to 1,080°C, zinc can be separated from the zinc-containing iron oxide and the iron oxide can be reduced to recover metallic iron (Patent Document 1). It has also been reported that zinc can be removed from zinc-plated steel sheet scrap by preheating the zinc-plated steel sheet scrap to 400 to 450°C at atmospheric pressure, heating the preheated zinc-plated steel sheet scrap to 500 to 900°C in a vacuum of 0.16 Torr or less to evaporate the zinc and separate it into steel sheet scrap and zinc, and then cooling the evaporated zinc to 400°C or less while maintaining the vacuum to obtain metallic zinc (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5079222 specification [Patent Document 2] Patent No. 3050720 specification Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method described in Patent Document 1 requires high-temperature conditions of 800°C or higher to volatilize zinc, and when applied to waste containing low-melting-point metals such as copper alloys and aluminum alloys, the low-melting-point metals melt when heated and fuse with other components or form slag, making it difficult to recover the low-melting-point metals. Furthermore, the method described in Patent Document 2 requires heating and cooling in a vacuum, consuming a great deal of energy, which inevitably increases costs. An object of the present invention is to provide a method for treating heavy metal-containing plastic waste, which is capable of separating heavy metals from the heavy metal-containing plastic waste and recovering other useful substances. [Means for solving the problem]

[0006] The inventors of the present invention conducted research to develop a method for recovering heavy metals that does not require excessive heating, which is a cost-intensive process, and found that heavy metals can be volatilized and removed from raw materials by heating the raw materials at a temperature of 700°C or less in a low-oxygen atmosphere in the presence of chlorine in an amount three times or more molar relative to the heavy metals contained in the raw materials. Furthermore, because the heating temperature is 700°C or less, low-melting-point metals do not melt, and it was found that combustibles can be recovered as fuel for cement calcination by physical separation, and valuable metals such as iron, copper, and aluminum can be recovered individually.

[0007] That is, the present invention provides the following [1] to [5]. [1] A process of mixing a heavy metal-containing plastic waste (a) and a chlorine-containing substance (b) in such a ratio that the molar ratio (chlorine / heavy metal) of the heavy metals in the heavy metal-containing plastic waste (a) to the chlorine in the chlorine-containing substance (b) is 3 or more; A heating process in which the mixture is heated under conditions where the oxygen concentration in the atmosphere is 3% by volume or less and the temperature is between 500°C and 700°C to promote the volatilization of heavy metals and the embrittlement of plastics. A method for treating heavy metal-containing plastic waste, comprising: [2] The treatment method according to [1], wherein the heating device used in the heating step has a first zone that promotes the volatilization of heavy metals and the embrittlement of plastics in a low-oxygen atmosphere, and a second zone that brings the combustible gas and volatilized heavy metals generated in the first zone into contact with a high-temperature oxidizing atmosphere, promoting the complete combustion of the combustible gas and the oxidation of the volatilized heavy metals. [3] The treatment method according to [1] or [2] above, wherein the heavy metal is one or more selected from zinc, lead, and cadmium. [4] After the heating process, a wind sorting process in which the embrittled plastic waste is crushed and the crushed material is separated into heavy and light items by wind sorting; A magnetic separation process in which heavy objects separated by wind separation are magnetically separated to separate magnetic and non-magnetic objects. The processing method according to any one of [1] to [3] above, [5] The treatment method according to [4], further comprising a gravity separation step of separating the non-magnetic materials separated by magnetic separation into heavy products and light products. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for treating heavy metal-containing plastic waste, which is capable of separating heavy metals from heavy metal-containing plastic waste and recovering other useful substances. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a flowchart according to an embodiment of the method for treating plastic waste containing heavy metals of the present invention. [Figure 2] 1 is a schematic diagram showing an example of an apparatus applicable to the method for treating heavy metal-containing plastic waste of the present invention. [Figure 3] FIG. 1 is a schematic diagram showing another example of an apparatus applicable to the method for treating plastic waste containing heavy metals of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the method for treating plastic waste containing heavy metals of the present invention will be described with reference to the accompanying drawings. Figure 1 is a flow chart showing an embodiment of the method for treating plastic waste containing heavy metals of the present invention.

[0011] The method for treating heavy metal-containing plastic waste of the present invention comprises at least a mixing step and a heating step, as shown in Figure 1. Each step will be described below.

[0012] <Mixing process> In this process, heavy metal-containing plastic waste (a) and chlorine-containing material (b) are mixed in such a ratio that the molar ratio (chlorine / heavy metal) of the heavy metals in the heavy metal-containing plastic waste (a) to the chlorine in the chlorine-containing material (b) is 3 or more. This can promote the volatilization of heavy metals in the heating process.

[0013] Heavy metal-containing plastic waste is not particularly limited as long as it contains plastic, but examples include shredder dust, automobile shredder dust, construction waste plastic, agricultural waste plastic, fishing waste plastic, and marine waste plastic. These wastes typically contain heavy metals such as zinc, lead, and cadmium. Here, "shredder dust" as used herein refers to the mixture of debris discarded after industrial or municipal waste is crushed using an industrial shredder and metals are recovered. Examples of such waste include discarded automobiles, discarded home appliances, vending machines, and office equipment. Plastic-containing waste may be a mixture of two or more types of waste, and may contain foreign matter other than plastic, such as soil, metal, glass, paper, and wood chips.

[0014] The size of the plastic-containing waste is not particularly limited, but from the viewpoint of mixing efficiency and heat transfer during heating, the maximum particle size is preferably 30 mm or less, more preferably 20 mm or less, even more preferably 10 mm or less, and even more preferably 5 mm or less. Here, in this specification, the "maximum particle size" refers to the particle size represented by the smallest sieve opening of a sieve through which the entire sample passes.

[0015] The chlorine-containing substance is not particularly limited as long as it contains a chlorine source, and examples thereof include inorganic chlorides and chlorine-containing resins. Examples of inorganic chlorides include alkali metal chlorides such as potassium chloride and sodium chloride, and alkaline earth metal chlorides such as calcium chloride and magnesium chloride. Examples of chlorine-containing resins include polyvinyl chloride, polyvinylidene chloride, and chloroprene rubber, and waste or crushed materials of these resins may also be used.

[0016] The size of the chlorine-containing material is not particularly limited, but from the viewpoint of mixing efficiency and heat transfer during heating, the maximum particle size is preferably 30 mm or less, more preferably 20 mm or less, even more preferably 10 mm or less, and even more preferably 5 mm or less.

[0017] The mixing ratio of the heavy metal-containing plastic waste (a) and the chlorine-containing material (b) is not particularly limited as long as the molar ratio (chlorine / heavy metal) of the heavy metals in the heavy metal-containing plastic waste (a) to the chlorine in the chlorine-containing material (b) is 3 or more, but from the viewpoint of promoting the volatilization of the heavy metals, the molar ratio (chlorine / heavy metal) is more preferably 3.5 or more, and even more preferably 4.5 or more. Note that the upper limit of the molar ratio (chlorine / heavy metal) can be appropriately selected, but from the viewpoint of suppressing damage to equipment due to hydrogen chloride gas generated in the heating step and suppressing the amount of chlorine remaining in the solid fuel recovered in the crushing and sorting step, it is preferably 15 or less, and even more preferably 10 or less.

[0018] <Heating process> In this process, the mixture prepared in the mixing process is heated under conditions where the oxygen concentration in the atmosphere is 3% by volume or less and the temperature is 500°C to 700°C to promote the volatilization of heavy metals and the embrittlement of plastics. A heating furnace can be used for heating, preferably an externally heated furnace. Examples of externally heated furnaces include an externally heated kiln and an antler kiln. Alternatively, a heating device may be used that has a first zone that promotes the volatilization of heavy metals and embrittlement of plastics in a low-oxygen atmosphere, and a second zone that brings the combustible gases and volatilized heavy metals generated in the first zone into contact with a high-temperature oxidizing atmosphere to promote complete combustion of the combustible gases and oxidation of the volatilized heavy metals.

[0019] An example of such a heating apparatus having two zones is the heating apparatus shown in FIG. 2. The heating apparatus shown in FIG. 2(a) is an example of a fixed furnace type. This heating apparatus has a double structure in which a container with a gas vent is housed inside the heating furnace. It includes a first zone in which a mixture is introduced into the container with a gas vent to promote volatilization of heavy metals and embrittlement of plastics, and a second zone in which the combustible gas and volatilized heavy metals generated in the first zone are brought into contact with a high-temperature oxidizing atmosphere to promote complete combustion of the combustible gas and oxidation of the volatilized heavy metals. The heating apparatus shown in FIG. 2(b) is an example of a kiln type. This heating apparatus includes the first zone in which a mixture is introduced into a rotary kiln and fired to promote volatilization of metals and embrittlement of plastics, and the second zone connected to the first zone by a connecting pipe to promote complete combustion of the combustible gas and oxidation of the volatilized heavy metals.

[0020] The atmosphere during heating must have an oxygen concentration of 3% by volume or less, but from the viewpoint of preventing oxidation of heavy metals in the raw materials, the oxygen concentration in the atmosphere is preferably 2% by volume or less, and more preferably 1% by volume or less. Methods for reducing the oxygen content of the heating atmosphere include, for example, filling the furnace with nitrogen gas or water vapor, or filling the furnace with gas components (e.g., HO, CO, combustible gases such as lower hydrocarbons) generated mainly by thermal decomposition of the raw materials themselves.

[0021] The heating temperature is 500°C or higher and 700°C or lower, but from the viewpoint of promoting volatilization of heavy metals and embrittlement of plastics, it is preferably 530°C or higher, more preferably 570°C or higher, and is preferably 680°C or lower, and even more preferably 660°C or lower. From the viewpoint of promoting volatilization of heavy metals and embrittlement of plastics, the heating time is preferably 60 minutes or more, more preferably 70 minutes or more, even more preferably 80 minutes or more, and is preferably 180 minutes or less, more preferably 150 minutes or less, even more preferably 120 minutes or less.

[0022] <Crushing process> The embrittlement product obtained by the heating process contains a mixture of combustibles suitable for fuel use and useful metals. In addition, the polymer compounds in the raw material are decomposed into smaller molecules by thermal decomposition during the heating process, which significantly reduces their mechanical strength, making them easily granular by impact or compression.

[0023] A crusher can be used for the crushing treatment. The type of crusher is preferably one that crushes using collision stress or compression force. Specific examples include a hammer crusher, impact mill, ball mill, rod mill, roller mill, and jaw crusher. Crushing may be carried out two or more times, and when carried out two or more times, the same crusher or crushers of different types may be used.

[0024] <Wind sorting> The crushing process separates the waste into finely granulated combustibles (solid fuel) and unrefined useful metals. Therefore, wind sorting can easily separate the finely granulated combustibles (solid fuel) as light materials and the unrefined useful metals as heavy materials. For the air sorting, an air sorter can be used. The type of the air sorter is not particularly limited, but examples include a circulation type, a suction type, and a zigzag type. The wind speed for wind sorting is preferably set so that the light materials are mainly composed of solid fuels. For example, the wind speed is preferably 3 m / s or more, more preferably 5 m / s or more, and is preferably 20 m / s or less, more preferably 15 m / s or less. If the type of crusher in the preceding process is, for example, a roller mill that recovers fine particles by wind power, there is no need to provide a separate wind sorter.

[0025] <Magnetic separation> The heavy products separated by wind separation are magnetically separated, and iron is recovered as magnetic particles. A magnetic separator can be used for magnetic separation. Any known magnetic separator can be used. The type of separator is not particularly limited and may be a drum type, pulley type, or hanging type. From the viewpoint of recovering iron as a magnetic material, the surface magnetic flux density of the magnetic separator is preferably 100 to 3000 gausses, more preferably 150 to 2000 gausses, and even more preferably 200 to 1000 gausses.

[0026] <Gravity sorting> The non-magnetic materials separated by magnetic separation can be subjected to gravity separation to separate metals with low specific gravity such as aluminum from metals with high specific gravity such as copper, gold, and silver. A gravity separator can be used for gravity separation. Any known gravity separator can be used, and the type may be either a dry type or a wet type, but a dry type table type gravity separator is preferred, and an air table is more preferred.

[0027] Although the present invention has been described in detail above based on the embodiments, the present invention is not limited to the above embodiments. Various modifications of the present invention are possible without departing from the spirit of the present invention. For example, after magnetic separation and before gravity separation, non-magnetic materials separated by magnetic separation may be sieved. Then, the oversized and undersized materials separated by sieving may be gravity separated, recovering aluminum as a light product and copper as a heavy product. Furthermore, if a large amount of chlorine from the chlorine source remains in the combustibles (solid fuel) recovered as light materials by wind separation, they may be washed with water separately. [Example]

[0028] The following examples will explain the present invention in more detail, but the present invention is not limited to the examples below.

[0029] 1. Raw materials used in this example (a) Plastic waste containing heavy metals Shredder dust collected from dismantling and crushing electrical appliances, furniture, etc. was crushed in a small crusher until the maximum particle size was 1 mm or less. (b) Chlorine-containing substances PVC pipes were crushed in a small crusher to a maximum particle size of 1 mm or less and used.

[0030] Examples 1 to 3 <Mixing process> Heavy metal-containing plastic waste (a) and chlorine-containing material (b) were mixed so that the molar ratio (chlorine / heavy metal) of the heavy metals in the heavy metal-containing plastic waste (a) to the chlorine in the chlorine-containing material (b) was adjusted to the ratio shown in Table 1, and the mixture was placed in a cylindrical stainless steel container (internal volume 0.6 L).

[0031] <Heating process> Heat treatment was performed by raising the temperature inside the furnace to a range of 500 to 700°C and maintaining it for 90 minutes while flowing a gas in the SUS container, which was a mixture of nitrogen gas and air at a predetermined ratio and had an oxygen concentration in the atmosphere adjusted to the concentration shown in Table 1. The heating device used was a SUS cylindrical container equipped with a gas diffusion port and placed inside a box-type electric furnace (internal volume 9 L), as shown in Figure 3. After the heat treatment, nitrogen gas was passed through the furnace to cool it, and then the heat-treated product was recovered.

[0032] <Fracture> A small grinder was used to crush the heat-treated material.

[0033] <Wind sorting> The crushed material was separated into finely divided lightweight materials (solid fuel) and non-finely divided heavy materials (metal) using an air sorter. The wind speed during air sorting was set at 8.0 m / s.

[0034] <Magnetic separation> The heavy materials separated by the wind separator were subjected to magnetic separation, and iron was recovered as magnetic particles. The surface magnetic flux density of the magnetic separator was set to 1000 gauss.

[0035] <Gravity sorting> The non-magnetic materials recovered by magnetic separation were then gravity separated to recover copper as a heavy product and aluminum as a light product.

[0036] Comparative Examples 1 to 4 The same operations as in Example 1 were carried out, except that no mixing step was performed, heavy metal-containing plastic waste (a) was used as the raw material, and nitrogen gas and air were mixed in a predetermined ratio in the heating step to adjust the oxygen concentration in the atmosphere to the concentration shown in Table 1.

[0037] To evaluate the zinc removal rate by heat treatment, the sample before heating and the heat-treated product after cooling were each dissolved in hydrofluoric acid and aqua regia, and the zinc content was measured by ICP-OES.

[0038] The zinc removal rate by heating was calculated using the following formula:

[0039] Zinc removal rate (%) = [1-(amount of zinc in the heat-treated sample (g) ÷ amount of zinc in the sample before heating (g))] × 100

[0040] Table 1 shows the production conditions and analysis results for each of the examples and comparative examples.

[0041] [Table 1]

[0042] Table 1 shows that by heating the raw materials at a temperature of 700°C or less in a low-oxygen atmosphere in the presence of chlorine in an amount three times or more molar relative to the heavy metals contained in the raw materials, the heavy metals can be volatilized and removed from the raw materials, the combustible matter can be recovered as fuel for cement firing, and valuable metals such as iron, copper, and aluminum can be recovered individually.

Claims

1. a step of mixing a heavy metal-containing plastic waste (a) with a chlorine-containing substance (b) in such a ratio that the molar ratio (chlorine / heavy metal) of the heavy metals in the heavy metal-containing plastic waste (a) to the chlorine in the chlorine-containing substance (b) is 3 or more; A heating process in which the mixture is heated under conditions where the oxygen concentration in the atmosphere is 3% by volume or less and the temperature is 500°C or higher and 700°C or lower to promote the volatilization of heavy metals and the embrittlement of plastics. A method for treating heavy metal-containing plastic waste, comprising:

2. 2. The method of claim 1, wherein the heating device used in the heating step has a first zone that promotes the volatilization of heavy metals and embrittlement of plastics in a low-oxygen atmosphere, and a second zone that brings the combustible gases and volatilized heavy metals produced in the first zone into contact with a high-temperature oxidizing atmosphere to promote complete combustion of the combustible gases and oxidation of the volatilized heavy metals.

3. 3. The treatment method according to claim 1, wherein the heavy metal is one or more selected from the group consisting of zinc, lead, and cadmium.

4. After the heating process, a wind sorting process in which the embrittled plastic waste is crushed and the crushed material is separated into heavy and light items by wind sorting; A magnetic separation process in which heavy objects separated by wind separation are magnetically separated to separate magnetic and non-magnetic objects.

3. The method of claim 1 or 2, comprising:

5. 5. The method according to claim 4, further comprising a gravity separation step for separating the non-magnetic materials separated by magnetic separation into heavy products and light products.

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