Method for treating heavy metal-containing waste and method for producing recycled materials

Abstract

The present invention provides a waste treatment method that can sufficiently reduce the heavy metal content of waste containing heavy metals. [Solution] A method for treating heavy metal-containing waste, comprising a preparation step of preparing a mixture by mixing a member containing polyvinyl chloride resin and a calcium compound with heavy metal-containing waste, and a heating step of heating the mixture to generate a gas containing volatile heavy metal chloride, wherein the member used in the preparation step is crushed material and / or fragments of at least one of carpet tiles and wallpaper, the temperature at which the mixture is heated in the heating step is set according to the volatilization temperature of heavy metal chloride, and a treated material that can be reused as part of cement raw materials is obtained from the mixture by heating at the said temperature in the heating step.

Description

Technical Field

[0001] The present disclosure relates to a method for treating heavy metal-containing waste and a recycling method. The present disclosure also relates to a method for producing a resource product from heavy metal-containing waste by the above treatment method. This resource product is a material with a reduced heavy metal content by the treatment method according to the present disclosure, and for example, it is assumed to be used as a Ca source or a cement raw material.

Background Art

[0002] Patent Document 1 discloses an apparatus and method for removing mercury from combustion exhaust gas discharged from a cement kiln constituting a cement firing facility.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present disclosure provides a method for treating waste that can sufficiently reduce the heavy metal content of waste containing heavy metals. The present disclosure also provides a method for producing a resource product and a recycling method for recycling the resource product.

Means for Solving the Problems

[0005] One aspect of the present disclosure relates to a method for treating heavy metal-containing waste. This treatment method includes a step of generating a gas containing a volatile matter of heavy metal chloride by heating a mixture including a member containing a polyvinyl chloride resin and a calcium compound and the heavy metal-containing waste, wherein the member is a crushed product having a particle size of 5 mm or less and / or a fragment having a thickness of 1 mm or less.

[0006] One aspect of this disclosure relates to a recycling method for reusing treated materials containing resources whose heavy metal content has been reduced by the above-mentioned heavy metal-containing waste treatment method. Another aspect of this disclosure relates to a method for producing resources whose heavy metal content has been reduced by the above-mentioned heavy metal-containing waste treatment method. [Effects of the Invention]

[0007] This disclosure provides a waste treatment method that can sufficiently reduce the heavy metal content of heavy metal-containing waste. Furthermore, this disclosure provides a method for producing a resource material with reduced heavy metal content by this treatment method, and a recycling method for reusing a treated material containing said resource material. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a carpet tile. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described in detail below with reference to the drawings. However, this disclosure is not limited to the embodiments described below.

[0010] <Disposal methods for heavy metal-containing waste> The method for treating heavy metal-containing waste according to this embodiment includes a step of generating a gas containing volatile heavy metal chloride by heating a mixture containing a member containing polyvinyl chloride resin and a calcium compound, and the heavy metal-containing waste, wherein the member is crushed material with a particle size of 5 mm or less and / or fragments with a thickness of 1 mm or less.

[0011] By heating the above mixture, heavy metals contained in the waste are converted into heavy metal chlorides (chlorides of heavy metals). Specifically, it is presumed that first, the chlorine in the polyvinyl chloride resin contained in the above material reacts with the calcium in the calcium compound to produce calcium chloride (CaCl2), and then the calcium chloride reacts with the heavy metal to produce heavy metal chlorides. Since heavy metal chlorides volatilize at relatively low temperatures, the gas generated by heating contains volatile components of heavy metal chlorides. For this reason, the heavy metal content of the waste can be reduced by going through the above process. Because the above material is crushed material with a particle size of 5 mm or less and / or fragments with a thickness of 1 mm or less, the reaction with heavy metals contained in the heavy metal-containing waste proceeds easily, and the processing time can be shortened.

[0012] (Waste containing heavy metals) Specific examples of heavy metal-containing waste include dust generated from combustion in cement kilns, sludge obtained from wastewater from waste treatment plants, and coal ash generated in boilers of coal-fired power plants. Of these, dust generated from combustion in cement kilns has the advantage that heavy metals are easily volatilized by relatively low-temperature heat treatment. It is presumed that the ease of volatilization depends on the type of waste, even if the type of heavy metal contained is the same, because the form in which heavy metals exist in the waste differs depending on the type of waste.

[0013] The volatilization temperatures (boiling points) of typical heavy metal chlorides are as follows: • Mercury chloride (HgCl2): 302℃ Lead chloride (PbCl2): 950℃ Cadmium chloride (CdCl2): 964℃ Cobalt chloride (CoCl2): 1088℃ Nickel chloride (NiCl2): 972℃ Chromium chloride (CrCl2): 1294℃ • Tin chloride (SnCl2): 608℃ • Molybdenum chloride (MoCl4): 406℃ • Vanadium chloride (VCl2): 1061℃ Tungsten chloride (WCl4): 342℃ Silver chloride (AgCl): 1550℃ Zinc chloride (ZnCl2): 746℃

[0014] (Methods containing polyvinyl chloride resin and calcium compounds) As an example of the above-mentioned component, crushed material from carpet tiles can be cited. As described later, carpet tiles contain both a calcium source (e.g., calcium carbonate) and a chlorine source (polyvinyl chloride resin) necessary for producing calcium chloride. Therefore, there is an advantage in that it does not need to prepare the calcium source and chlorine source separately. In addition, by using crushed material from discarded carpet tiles, it is useful in that one waste material (carpet tiles) can be used to detoxify another waste material (remove heavy metals). Below, this embodiment will be specifically described using the case in which crushed material obtained from carpet tiles is used as the above-mentioned component.

[0015] The tile carpet 10 shown in Figure 1 comprises a pile layer 1 composed of pile yarns and a base layer 3 in which a portion of the pile yarns are embedded. In this embodiment, the base layer 3 has a two-layer structure and is composed of an intermediate layer 3a in contact with the pile layer 1 and a base material layer 3b. The thickness of the intermediate layer 3a is, for example, 1 to 2 mm. The thickness of the base material layer 3b is, for example, 1 to 2 mm. The thickness of the base layer 3 (the sum of the thicknesses of the intermediate layer 3a and the base material layer 3b) is, for example, 2 to 4 mm. The tile carpet 10 may be made from cutting scraps generated during the manufacturing process, or from used materials disposed of as waste from ordinary households or offices.

[0016] The pile layer 1 is composed of pile yarns made of a fiber material. The fiber material may be a synthetic fiber or a natural fiber. Examples of synthetic fibers include polyester fibers, nylon fibers, polypropylene fibers, and acrylic fibers. Examples of natural fibers include hemp, cotton, and wool. The pile layer 1 is formed, for example, by weaving in a warp pile weave or a weft pile weave. The pile layer 1 may be formed, for example, by implanting pile yarns using a tufting machine, or by adhering pile yarns using an adhesive. The pile form may be either cut pile or loop pile.

[0017] The intermediate layer 3a is sandwiched between the pile layer 1 and the base material layer 3b. The intermediate layer 3a serves to fix the pile layer 1 with a part of the pile yarns embedded therein, and to bond the pile layer 1 and the base material layer 3b. The intermediate layer 3a is made of a composition containing polyvinyl chloride resin, a plasticizer, and a filler, and contains resin fibers (for example, PET fibers). The plasticizer is for imparting flexibility to the polyvinyl chloride resin. The filler is, for example, for improving the dimensional stability of the tile carpet 10. The resin fibers are for tying the pile yarns of the pile layer 1.

[0018] Examples of the plasticizer include include dioctyl phthalate (DOP), di-n-butyl phthalate (DBP), di-2-ethylhexyl adipate (DOA), diisononyl adipate (DINA), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), tri-2-ethylhexyl trimellitate (TOTM), and tricresyl phosphate (TCP). Among them, at least one selected from the group consisting of dioctyl phthalate, di-n-butyl phthalate, di-2-ethylhexyl adipate, and diisononyl adipate is preferable, and dioctyl phthalate or di-2-ethylhexyl adipate is more preferable. Note that the dioctyl phthalate may be either di-n-octyl phthalate or di-2-ethylhexyl phthalate.

[0019] Examples of the filler include calcium carbonate, magnesium carbonate, magnesium sulfate, barium sulfate, magnesium hydroxide, aluminum hydroxide, and glass powder. Among these, calcium carbonate is preferred from the viewpoints of economy and processability.

[0020] The base material layer 3b constitutes the back surface of the tile carpet 10. The base material layer 3b is made of a composition containing a polyvinyl chloride resin, a plasticizer, and a filler. The plasticizer may be the same as that contained in the intermediate layer 3a.

[0021] In the present embodiment, the polyvinyl chloride resin contained in the tile carpet 10 serves as a chlorine source. On the other hand, the calcium carbonate contained in the tile carpet 10 serves as a calcium source. The calcium carbonate content in the tile carpet 10 is, for example, 45 to 60% by mass based on the total mass of the tile carpet 10.

[0022] The crushed material of the tile carpet 10 can be obtained through the following steps. (a1) A step of crushing the tile carpet 10. (a2) A step of sorting out the crushed material of the base layer 3 from the crushed material of the tile carpet 10.

[0023] The crushing of the carpet tiles 10 in step (a1) can be carried out using a known crushing or cutting device. If the crushed material is in the form of fragments, its thickness is 1 mm or less. There is no particular lower limit, but considering the capacity of known crushing or cutting devices, 0.1 mm or more is preferred. There is no particular limit to the area circle equivalent diameter of the fragments of the carpet tiles 10 in a plan view, but from the viewpoint of handling in the manufacturing equipment, it is preferably 12 mm or less, more preferably 8 mm or less, and even more preferably 5 mm or less. When the area circle equivalent diameter of the fragments is 12 mm or less, the reaction with heavy metals contained in the heavy metal-containing waste proceeds easily, and the processing time can be shortened. From the viewpoint of improving the efficiency of the crushing process of the carpet tiles 10, the lower limit of the area circle equivalent diameter is preferably 0.5 mm. The thickness of the fragments is less than or equal to the thickness of the base layer 3 (for example, 4 mm or less), preferably 0.5 to 3 mm, and more preferably 0.5 to 2 mm.

[0024] In step (a1), the tile carpet 10 may be further crushed (pulverized) to prepare a powdered or granular material. The tile carpet 10 can be crushed using a known crushing device. In this case, the particle size of the crushed material is 5 mm or less, preferably 3 mm or less, and more preferably 2 mm or less. In particular, a particle size of 2 mm or less allows for easier reaction with heavy metals contained in heavy metal-containing waste, further shortening the processing time. The lower limit of the particle size of the crushed material is, for example, 0.5 mm. A particle size of 0.5 mm or more tends to prevent the crushed material from becoming excessively bulky and difficult to handle. The particle size of the crushed material can be determined by preparing several sieves with different mesh sizes and observing whether or not the crushed material passes through the sieves.

[0025] The sorting of the crushed material from the sublayer 3 in step (a2) can be carried out, for example, by wind separation. This allows for sufficient removal of fibrous material from the crushed material.

[0026] (Preparation of mixtures) A mixture (material to be treated) is prepared by mixing heavy metal-containing waste with crushed material obtained from carpet tiles. If the mass of the crushed material in the mixture is 100 parts by mass, the amount of heavy metal in the mixture is preferably 40 parts by mass or less, more preferably 30 parts by mass or less. This amount of 40 parts by mass or less tends to significantly reduce the amount of heavy metal in the heavy metal-containing waste. The amount of heavy metal in the mixture (based on 100 parts by mass of crushed material) should be greater than 0 parts by mass, and from the viewpoint of efficiently carrying out the heavy metal reduction treatment, it may be greater than, for example, 0.001 parts by mass or 0.002 parts by mass or more. The mixing ratio may be set according to the type of heavy metal to be reduced.

[0027] In preparing the mixture, in addition to the crushed carpet tiles, at least one of a calcium source and a chlorine source may be added as needed.

[0028] (Heat treatment) The heating temperature of the mixture can be appropriately set according to the volatilization temperature of the heavy metal chloride to be reduced, for example, between 350 and 1100°C. A heating temperature of 350°C or higher allows the dechlorination reaction of the polyvinyl chloride resin to proceed sufficiently, while a temperature of 1100°C or lower tends to reduce the costs required for the construction and operation of the heating equipment. For example, if the heavy metal to be reduced is mercury, the heating temperature is preferably 300 to 500°C, and more preferably 350 to 450°C. For example, if the heavy metal to be reduced is lead, the heating temperature is preferably 800 to 1100°C, and more preferably 850 to 1000°C. When heat-treating a mixture containing an excess amount of crushed material relative to a trace amount of heavy metal, it is not always necessary to heat it above the volatilization temperature of the heavy metal chloride to sufficiently volatilize the heavy metal chloride. This is presumed to be because the heavy metal chloride has a low partial pressure.

[0029] Depending on the type of heavy metal to be reduced, the upper limit of the heating temperature for the mixture containing it may be 2000°C. When the heavy metal to be reduced is tin(II), the heating temperature is preferably 1400 to 1600°C, more preferably 1450 to 1550°C. When the heavy metal to be reduced is tungsten(VI), the heating temperature is preferably 1750 to 1950°C, more preferably 1800 to 1900°C.

[0030] Depending on the type of heavy metal to be reduced, the heating temperature can be lowered by reacting the mixture in the presence of carbon. When the heavy metal to be reduced is chromium, the heating temperature is preferably 1300 to 1900°C, and more preferably 1350 to 1850°C. When the heavy metal to be reduced is tin(IV), the heating temperature is preferably 950 to 1150°C, and more preferably 1000 to 1100°C. When the heavy metal to be reduced is vanadium, the heating temperature is preferably 1900 to 2000°C, and more preferably 1950 to 2000°C.

[0031] Depending on the type of heavy metal to be reduced, the heating temperature can be lowered by reacting the mixture in the presence of oxygen. When the heavy metal to be reduced is molybdenum, the heating temperature is preferably 800 to 1000°C, and more preferably 850 to 950°C. When the heavy metal to be reduced is tungsten(IV), the heating temperature is preferably 500 to 700°C, and more preferably 550 to 650°C.

[0032] The vaporization rate of heavy metals by heat treatment is preferably 87-98%. That is, if the mass of heavy metals contained in the mixture is 100 parts by mass, the mass of heavy metal chlorides contained in the gas, converted to heavy metals, is preferably 87-98 parts by mass. This makes it possible to obtain a resource material with sufficiently reduced heavy metals. This resource material can be recycled by adding other components as needed. The treated material (resource material) obtained through the heavy metal-containing waste treatment method according to this embodiment contains, for example, calcium oxide (CaO) produced by the oxidation of calcium chloride. Such a treated material can be reused, for example, as part of a cement raw material.

[0033] Although embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above embodiments. For example, in the above embodiments, a tile carpet having a two-layer base layer was exemplified, but the base layer may be a single layer or a laminated structure of three or more layers.

[0034] In the above embodiment, a method for reducing heavy metals contained in other waste was illustrated using crushed carpet tiles, but any material containing a calcium source and a chlorine source may be used instead of crushed carpet tiles. A specific example of such material is residential wallpaper. [Examples]

[0035] The present disclosure will be described below based on practical examples and comparative examples. The present invention is not limited to the following embodiments.

[0036] To manufacture processed products from heavy metal-containing waste, the following waste carpet tiles and heavy metal-containing samples were prepared. <Recycled Tile Carpet> • Layer composition: Pile layer / Intermediate layer (underlayment layer) / Base material layer (underlayment layer) • Composition of carpet tiles Polyvinyl chloride resin (PVC): 20 parts by mass (chlorine content: 10 parts by mass) Plasticizer (dioctyl phthalate, DOP): 15 parts by mass Nylon fibers: small amount Calcium carbonate (CaCO3): 60 parts by mass Other fillers besides calcium carbonate: small amounts <Heavy metal-containing sample> • Composition of heavy metal-containing samples Calcium oxide (CaO): 20 parts by mass Iron oxide (Fe2O3): 50 parts by mass Sulfate: 15 parts by mass Mercury (form of existence unknown): Small amount Lead (form of existence unknown): Small amount

[0037] <Preparation of raw materials> We prepared crushed carpet tiles (particle size: approximately 0.1-2 mm). We prepared pulverized samples containing heavy metals (particle size: approximately 0.1-1 mm).

[0038] <Determination of mercury> Quantitative analysis was performed using a heated vaporized mercury analyzer. The amount of mercury is shown in Table 1. <Determination of lead> The sample was heated and decomposed with acid, then diluted to a fixed volume with ultrapure water to prepare the test solution. Quantitative analysis of lead in the test solution was performed using inductively coupled plasma mass spectrometry. The lead content is shown in Table 2.

[0039] (Preparation of mixed products) 1 g of crushed carpet tiles and 1 g of heavy metal-containing sample were placed in a container and shaken to mix.

[0040] (Example 1) Two grams of the above mixture were heated at 450°C for five minutes using a heated mercury vaporization analyzer to volatilize the mercury. The amount of mercury after heating is shown in Table 1. The mercury vaporization rate due to heating was calculated from the amount of mercury before heating. The mercury vaporization rates are shown in Table 1.

[0041] (Comparative Example 1) Two grams of heavy metal-containing samples were heated at 450°C for five minutes using a heated mercury vaporization analyzer to volatilize the mercury. The amount of mercury after heating is shown in Table 1. The mercury vaporization rate due to heating was calculated from the amount of mercury before heating. The mercury vaporization rates are shown in Table 1.

[0042] (Example 2) Two grams of the above mixture were heated at 850°C for five minutes using a heated mercury vaporization analyzer to volatilize the lead. The amount of lead after heating is shown in Table 2. The lead vaporization rate due to heating was calculated from the amount of lead before heating. The lead vaporization rate is shown in Table 2.

[0043] (Comparative Example 2) Two grams of heavy metal-containing samples were heated at 850°C for five minutes using a heated mercury vaporization analyzer to volatilize the lead. The amount of lead after heating is shown in Table 2. The lead vaporization rate due to heating was calculated from the amount of lead before heating. The lead vaporization rates are shown in Table 2.

[0044] <Evaluation of vaporization rate> Table 1 shows the mercury vaporization rates for Example 1 and Comparative Example 1. The mercury amounts in the table were measured using a heated vaporization mercury analyzer. The vaporization rates were calculated using the following formula. Mercury vaporization rate (%) = (Amount of mercury before heating - Amount of mercury after heating) / (Amount of mercury before heating) × 100

[0045] [Table 1]

[0046] Table 2 shows the lead vaporization rates for Example 2 and Comparative Example 2. The lead amounts in the table were measured using an inductively coupled plasma mass spectrometer. The vaporization rates were calculated using the following formula. Lead vaporization rate (%) = (Amount of lead before heating - Amount of lead after heating) / (Amount of lead before heating) × 100

[0047] [Table 2]

[0048] Using FactSage (GTT-Technologies, Germany), we predicted the temperature at which a reaction proceeds spontaneously based on the change in the free energy (Gibbs free energy, G), which is a thermodynamic function. FactSage is commercial software that contains thermodynamic data for chemical substances, including Gibbs free energy, and has the function to calculate the change in Gibbs free energy for any given reaction equation. △G = G(products) - G(reactants) △G<0: The reaction proceeds spontaneously. △G=0: Equilibrium state △G>0: The reaction does not proceed spontaneously. Tables 3 to 14 show the results of determining the lowest temperature at which ΔG < 0 in the reaction equation for the volatilization of heavy metals into chlorides, and using this as the volatilization temperature. Since the measured values ​​of mercury vaporization rate and lead vaporization rate shown in Tables 1 and 2 show a good correlation with the calculated values ​​below, this method can be applied to metals other than mercury and lead.

[0049] [Table 3]

[0050] [Table 4]

[0051] [Table 5]

[0052] [Table 6]

[0053] [Table 7]

[0054] [Table 8]

[0055] [Table 9]

[0056] [Table 10]

[0057] [Table 11]

[0058] [Table 12]

[0059] [Table 13]

[0060] [Table 14] [Explanation of Symbols]

[0061] 1...Pile layer, 3...Underlayment layer, 3a...Intermediate layer, 3b...Base material layer, 10...Tile carpet

Claims

1. A preparation step involves mixing a component containing polyvinyl chloride resin and a calcium compound with heavy metal-containing waste to prepare a mixture. A heating step in which the mixture is heated to generate a gas containing volatile heavy metal chlorides, Includes, The member used in the preparation step is crushed material and / or fragments of at least one of tile carpet and wallpaper. A method for treating heavy metal-containing waste, comprising setting a temperature for heating the mixture in the heating step according to the volatilization temperature of the heavy metal chloride, and obtaining a treated material from the mixture that can be reused as part of cement raw materials by heating at the said temperature in the heating step.

2. The method for treating heavy metal-containing waste according to claim 1, wherein the heavy metal-containing waste is dust generated by combustion in a cement kiln.

3. The method for treating heavy metal-containing waste according to claim 1 or 2, wherein the treated material contains calcium oxide.

4. A method for treating heavy metal-containing waste according to any one of claims 1 to 3, wherein the heavy metal-containing waste contains mercury, the heavy metal to be reduced from the heavy metal-containing waste is mercury, and the mixture is heated to 300 to 500°C.

5. A method for treating heavy metal-containing waste according to any one of claims 1 to 3, wherein the heavy metal-containing waste contains lead, the heavy metal to be reduced from the heavy metal-containing waste is lead, and the mixture is heated to 800 to 1100°C.

6. The tile carpet comprises a pile layer composed of pile yarns and a base layer in which a portion of the pile yarns are embedded, and the base layer contains both polyvinyl chloride resin and calcium carbonate. The method for processing heavy metal-containing waste according to any one of claims 1 to 5, wherein the preparation step includes the step of crushing the tile carpet and the step of selecting the crushed material of the base layer from the crushed material of the tile carpet, and the crushed material of the base layer is used as the member.

7. A method for treating heavy metal-containing waste according to any one of claims 1 to 6, wherein in the preparation step, crushed material with a particle size of 0.5 mm to 2.0 mm is used as the member.

8. A method for treating heavy metal-containing waste according to any one of claims 1 to 7, wherein in the preparation step, crushed carpet tiles with a particle size of 0.1 mm to 2 mm are mixed with the heavy metal-containing waste with a particle size of 0.1 mm to 1 mm.

9. A method for treating heavy metal-containing waste according to any one of claims 1 to 8, wherein the vaporization rate of heavy metals by heating in the heating step is 87% to 98%.

10. A method for producing a resource material in which the heavy metal content has been reduced by the method for treating heavy metal-containing waste described in any one of claims 1 to 9, A method for producing a resource product, wherein the resource product is a processed product that can be reused as part of a cement raw material.

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