JP4959977B2 - Cadmium recovery facility and recovery method - Google Patents

Description

The present invention relates to a facility and a method for efficiently recovering cadmium.

In recent years, phytoremediation is known in which plants that absorb and accumulate cadmium in soil are cultivated (growth) in soil contaminated with cadmium and the plant absorbs cadmium in soil and removes it from soil. (For example, see Patent Documents 1 to 3). Also, in order to safely treat cadmium without re-diffusion, cadmium-absorbed plants are incinerated, cadmium alone or compounds are vaporized, cooled and precipitated, and the precipitated cadmium is collected in a dust collector (bug A method of collecting and recovering with a filter) has also been developed (see, for example, Patent Document 4).

JP-A-57-190 JP 7-508206 A JP 2000-288529 A JP 2005-76970 A

However, in the method described in Patent Document 4, when the filter cloth of the bag filter is covered with inorganic fine particles such as slaked lime, the cadmium collection rate is improved, but the filter cloth has nitrogen oxide or the like. Are adsorbed simultaneously, and there is a problem that cadmium cannot be recovered at a high concentration.

The present invention has been made in view of such circumstances, and an object thereof is to provide a cadmium recovery facility for efficiently recovering cadmium from a plant that has absorbed cadmium and a method for recovering the same.

The cadmium recovery facility according to the present invention that meets the above-mentioned object is an incinerator that incinerates a plant containing cadmium at a temperature of 765 ° C. or more and 900 ° C. or less, and vaporizes the cadmium as a simple substance and / or a compound,
A cooling means for cooling and depositing the vaporized cadmium to 250 ° C. or lower, which is a temperature lower than the boiling point of the cadmium alone and / or the compound;
A first collecting means for collecting a powdery substance containing a simple substance and / or a compound of cadmium precipitated by the cooling means;
Wherein provided on the downstream side of the first collecting means, have a second collecting means comprising a bag filter with activated carbon and one coated at one or both braze cloth slaked lime,
And, a gas containing vaporized cadmium discharged from the incinerator, the oxygen-containing gas supply means for supplying an oxygen-containing gas that has is provided. Air, pure oxygen, etc. can be used as the oxygen-containing gas.

The plant containing cadmium used in the present invention has a property of taking cadmium in soil into the plant body, for example, Brassicaceae, Mallow, Legume, Solanum, Asteraceae, Amaraceae, Gramineae, etc. is there. Among them, Obata kana, kenaf, okra and sorghum are preferable in terms of cadmium absorption and accumulation ability, and rice is preferable in terms of high production technology from seedlings to harvesting and widespread use. Further, the higher the concentration of cadmium contained in the plant to be incinerated, the better the recovery rate, and 0.2 ppm or higher, preferably 1 ppm or higher and 1000 ppm or lower is used. The cadmium concentration in the plant is a concentration (weight ratio) when the water content in the plant is zero.

Plants containing cadmium are incinerated at 500 ° C. or higher, preferably at 765 ° C. or higher, more preferably 900 ° C. or higher, which is the boiling point of cadmium. Cadmium absorbed by the plant is incinerated at high temperature, reduced by the organic matter of the plant body and carbon monoxide generated by combustion, and is almost volatilized (vaporized) as metal cadmium. As an incinerator, what is necessary is just to be able to make the temperature of an incinerator into more than the combustion temperature mentioned above, and a fluidized-bed furnace, a kiln stoker furnace, a stoker furnace, a fixed bed furnace, an electric furnace etc. can be used.

The vaporized cadmium is cooled by a cooling means such as a gas cooling device or a heat exchanger and deposited as a liquid or a solid, and is collected by the first collecting means. As the first collecting means, for example, a bag filter having an untreated filter cloth that is formed of polyester, nylon, polypropylene, acrylic, polyimide, glass or the like and is not covered with slaked lime, activated carbon, or the like, a cyclone, or the like Can be used. Here, when a bag filter is used as the first collecting means, the cooling means is predetermined in order to keep the gas discharged from the incinerator within the operating temperature of the bag filter (usually about 90 to 250 ° C.). When cooling to a temperature (250 ° C. or lower, preferably 150 ° C. or lower), but the bag filter is equipped with a heat-resistant filter cloth, the temperature at which cadmium is precipitated, that is, the boiling point of cadmium alone and / or compound What is necessary is just to cool to below, and the temperature of the gas supplied to a 1st collection means can be made high.

The filter cloth used for the bag filter of the second collecting means is, for example, a gas containing fine particles of activated carbon and slaked lime having an average particle diameter of 2 to 50 μm, preferably 5 to 20 μm. The filter cloth can be coated with fine particles by passing it through a treated filter cloth. Dioxins are adsorbed on the activated carbon, and nitrogen oxides and sulfur oxides are adsorbed on the slaked lime, and these substances can be removed by the second collecting means.

In the cadmium recovery facility according to the present invention, the first collection means is preferably a bag filter provided with a filter cloth.
In the cadmium recovery facility according to the present invention, it is preferable that the filter cloth of the first collecting means has a basis weight of 500 g / m ² or more and an opening degree of 10 μm or less.
Here, the basis weight is the weight of the filter cloth per 1 m ^{2. When} the basis weight of the filter cloth is less than 500 g / m ² or the opening degree exceeds 10 μm, the filter cloth is too coarse, The collected cadmium deposits may escape. The filter cloth used for the bag filter of the second collecting means preferably has a basis weight of 500 g / m ² or more and an opening degree of 10 μm or less.

The cadmium recovery method according to the present invention that meets the above-mentioned object is a first method in which a cadmium-containing plant is placed in an incinerator and incinerated at a temperature of 765 ° C. or higher and 900 ° C. or lower to vaporize the cadmium as a simple substance and / or a compound. Process,
A second step of depositing the vaporized cadmium by cooling to 250 ° C. or lower, which is a temperature below the boiling point of the cadmium alone and / or the compound;
A third step of collecting the powdered substance containing the precipitated cadmium alone and / or a compound by the first collecting means;
The first collecting means is provided by a second collecting means comprising a bag filter provided on the downstream side of the first collecting means and provided with a filter cloth covered with one or both of activated carbon and slaked lime. nitrogen oxides passing through the, have a fourth step of collecting sulfur oxides, and any one or more of the substances of dioxins,
Further, an oxygen-containing gas is supplied to the gas containing vaporized cadmium discharged from the incinerator .

In the cadmium recovery method according to the present invention, it is preferable to use a bag filter provided with a filter cloth in the first collecting means.

In the cadmium recovery facility according to any one of claims 1 to 3 and the cadmium recovery method according to claims 4 and 5 , a first trap that collects the precipitated cadmium alone and / or a powder containing a compound. Since it has a collection means and the 2nd collection means provided with the filter cloth coat | covered with either one or both of activated carbon and slaked lime, a 1st collection means can collect | recover cadmium by high concentration, 2nd Any one or two or more substances of nitrogen oxides, sulfur oxides, and dioxins can be efficiently separated and collected by the collecting means. Note that cadmium that could not be collected by the first collecting means is collected by the second collecting means, so that it is difficult for cadmium to be discharged into the environment. Further, since the oxygen-containing gas is supplied to the vaporized cadmium discharged from the incinerator, the vaporized metal cadmium is oxidized to become cadmium oxide, and the boiling point becomes high and the metal is easily deposited.

Particularly, in the cadmium recovery facility according to claim 2 and the cadmium recovery method according to claim 5 , since the first collection means is a bag filter provided with a filter cloth, the precipitated cadmium can be easily and efficiently It can be collected well.
In the cadmium recovery facility according to the third aspect, the filter cloth of the first collecting means has a basis weight of 500 g / m ² or more and an opening degree of 10 μm or less, so that the deposited cadmium is easily collected.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
Here, FIG. 1 is an explanatory diagram of a cadmium recovery facility according to the first and second embodiments of the present invention.

With reference to FIG. 1, a cadmium recovery facility 10 according to a first embodiment of the present invention will be described.
The cadmium recovery facility 10 is a fixed bed incinerator (fixed bed furnace) 12 that incinerates and vaporizes a plant 11 containing cadmium, and cooling water that is an example of cooling means that cools and deposits the vaporized cadmium. The first evaporating gas cooling device (gas cooler) 13 that cools the high-temperature gas and the first collecting means including the filter cloth 15 that collects the powdery substance 14 containing the deposited cadmium are examples of the first collecting means. A second filter provided with a filter cloth 17 that collects one or more substances of nitrogen oxide, sulfur oxide, and dioxins that have passed through the first bag filter 16 and the first bag filter 16. The second bag filter 18 constituting the collecting means, the fan 19 for moving the gas in the pipe 21 forming the passage of the cadmium recovery facility 10, cadmium, nitrogen oxide, sulfur oxide, and diode A discharge unit 20 for discharging the thin compound has been removed gas, and a pipe 21 connecting them. Each will be described in detail below.

In the fixed-bed incinerator 12, the plant 11 containing cadmium is incinerated at 500 ° C. or higher, preferably 765 ° C. or higher, more preferably 900 ° C. or higher, for example, 850 to 900 ° C., which is the boiling point of cadmium. A thermometer (not shown) is disposed in the incinerator 12, and the combustion temperature is controlled so that the inside of the incinerator 12 has a predetermined temperature. Cadmium absorbed by the plant is incinerated at a high temperature and reduced by organic matter of the plant body and carbon monoxide generated by combustion, and is almost vaporized as a simple substance and / or compound of metal cadmium.

The gas cooling device 13 provided on the downstream side of the gas discharge portion of the incinerator 12 through the pipe 21 injects water into a gas containing cadmium at a high temperature generated in the incinerator 12, for example, about 800 ° C., This is a device that cools the filter cloth 15 of the first bag filter 16 to a use (heat resistant) temperature, for example, 250 ° C. or lower, preferably 150 ° C. or lower (about 200 ° C. in the present embodiment). A thermometer (not shown) is disposed at the discharge port of the gas cooling device 13, and the amount of water jetted in the gas cooling device 13 so that the temperature of the gas supplied to the first bag filter 16 is about 200 ° C. Is controlling. The cadmium vaporized in the incinerator 12 is cooled by the gas cooling device 13 and deposited as a solid or a liquid. A heat exchanger may be used as the cooling means. In addition, when the first bag filter 16 includes a heat-resistant filter cloth, the cooling means may cool the gas to a temperature at which cadmium is precipitated, that is, below the boiling point of the cadmium alone and / or the compound, The temperature of the gas supplied to the first bag filter 16 can be increased.

The first bag filter 16 provided on the downstream side of the gas cooling device 13 via a pipe 21 is provided with a polyethylene filter cloth 15 having a basis weight of 500 g / m ² or more and an opening degree of 10 μm or less. The powdery substance 14 containing the simple substance and / or compound of cadmium deposited by the cooling device 13 can be collected. Valves 22 and 23 are provided on the upstream side and the downstream side of the first bag filter 16, respectively.

Further, the first bag filter 16 is provided with a not-shown removal device for removing the collected powder 14 from the filter cloth 15, and the powder 14 can be discharged from the cadmium recovery facility 10. . The first bag filter 16 is difficult to collect any one or more of nitrogen oxides, sulfur oxides, and dioxins, and can recover cadmium at a high concentration. In addition, the recovery rate of cadmium can be increased by providing the first bag filter 16 in a plurality of stages.

Valves 24 and 25 are provided on the upstream side and the downstream side of the second bag filter 18 provided on the downstream side of the first bag filter 16 via the pipe 21, respectively. The pipe 21 between the first bag filter 16 and the second bag filter 18 is a storage tank 27 in which activated carbon and slaked lime fine particles 26 having an average particle diameter of 2 to 50 μm, preferably 5 to 20 μm are stored. Are connected via a rotary valve 28.

Here, for example, the same filter cloth as the filter cloth 15 used in the first bag filter 16 is arranged in the second bag filter 18, the fan 19 is operated, and the fine particles 26 in the storage tank 27 are collected. The containing gas is passed through the filter cloth through the rotary valve 28 to create the filter cloth 17 whose surface is coated with activated carbon and slaked lime. Dioxins can be adsorbed by activated carbon, and nitrogen oxides and sulfur oxides can be adsorbed by slaked lime.

As a result, the second bag filter 18 can collect substances containing any one or more of nitrogen oxides, sulfur oxides, and dioxins that have passed through the first bag filter 16. The second bag filter 18 can also collect cadmium that has not been collected by the first bag filter 16. Further, the second bug filter 18 is provided with a payout device (not shown).

Next, a method for recovering cadmium using the cadmium recovery facility 10 will be described.
First, the valves 22 and 23 of the first bag filter 16 and the valves 24 and 25 of the second bag filter 18 are opened, and the fan 19 is operated to generate an air flow from the upstream side to the downstream side of the pipe 21 while cadmium is generated. The plant 11 containing is incinerated at 850 to 900 ° C. in the incinerator 12 to vaporize cadmium as a simple substance and / or a compound (first step).

Next, the exhaust gas of about 800 ° C. discharged from the gas discharge section of the incinerator 12 is cooled to about 200 ° C. which is the operating temperature of the filter cloth 15 attached to the first bag filter 16 by the gas cooling device 13. The vaporized cadmium alone and / or the compound is precipitated as a solid or liquid (second step). The powdery substance 14 containing the precipitated cadmium alone and / or compound is collected by the filter cloth 15 of the first bag filter 16 (third step), and the nitrogen oxides and sulfur passing through the first bag filter 16 are collected. Substances containing oxides and dioxins are collected by the filter cloth 17 of the second bag filter 18 (fourth step).

Here, before the first bag filter 16 is clogged with the powdery material 14, the wiping device provided in the first bag filter 16 is operated to wipe off the powdery material 14 attached to the filter cloth 15. Drop and collect cadmium. In this way, the cadmium recovery facility 10 can be operated continuously. Further, the filter cloth 17 of the second bag filter 18 can be reproduced in the same manner.

A cadmium recovery facility 30 according to a second embodiment of the present invention will be described with reference to FIG. The same components as those of the cadmium recovery facility 10 are denoted by the same reference numerals, and detailed description thereof is omitted.
The cadmium recovery facility 30 includes a blower 31, which is an example of an oxygen-containing gas supply unit that supplies air, which is an example of an oxygen-containing gas, to a gas containing vaporized cadmium discharged from the incinerator 12. The point provided in the piping 21 between the gas cooling devices 13 is different from the cadmium recovery facility 10. By supplying air to the gas containing vaporized cadmium discharged from the incinerator 12, the vaporized metal cadmium is oxidized to cadmium oxide, the boiling point is increased, and the first bag filter 16 is easily precipitated. Makes it easier to collect. This improves the recovery rate of cadmium.

An incinerator for incinerating plants containing cadmium, a gas cooling device, a first bag filter (first collecting means) having a filter cloth made of polyester, and a filter cloth coated with activated carbon and slaked lime Cadmium in the plant was recovered using a cadmium recovery facility equipped with a second bag filter (second collection means). The results are shown in Table 1.

As shown in Table 1, 164.6 mg of cadmium is contained in 10.92 kg of plants. When this was incinerated, the cadmium in the incineration ash remaining in the incinerator was 0.08 mg, and it was found that the cadmium was almost vaporized by the incinerator. The vaporized cadmium was cooled and precipitated by a gas cooling device, and 63.0 mg of cadmium was collected by the first bag filter. The recovery rate with the first bug filter was 38.3%.

In the second bag filter, 21 mg of cadmium is collected in addition to the substance containing any one or more of nitrogen oxides, sulfur oxides, and dioxins. The cadmium recovery rate was 12.8%. Therefore, in order to improve the recovery rate of the first bag filter, it is preferable that the first bag filter is, for example, multistage. In addition, since cadmium was not detected in the gas discharged from the discharge section, cadmium not collected by the first and second bag filters is attached to the passage of the cadmium recovery facility. It is understood.

The present invention is not limited to the above-described embodiment, and can be changed without changing the gist of the present invention. For example, some or all of the above-described embodiments and modifications are possible. The cadmium recovery facility and the recovery method of the present invention are combined to form the recovery scope of the present invention.
For example, although the fixed bed furnace is used as the combustion furnace in the cadmium recovery facility and the recovery method of the embodiment, a kiln / stoker furnace, a stoker furnace, a fluidized bed furnace, an electric furnace, or the like may be used. Moreover, although the bag filter provided with the filter cloth was used as the first collecting means, a cyclone may be used. Furthermore, although the first and second bag filters are provided with a filter cloth formed of polyester, a filter cloth formed of nylon, polypropylene, acrylic, polyimide, glass, or the like may be used.

It is explanatory drawing of the collection | recovery equipment of the cadmium which concerns on the 1st and 2nd embodiment of this invention.

10: Cadmium recovery equipment, 11: Plant, 12: Incinerator, 13: Gas cooling device, 14: Powdered material, 15: Filter cloth, 16: First bag filter, 17: Filter cloth, 18: Second Bag filter, 19: fan, 20: discharge part, 21: piping, 22-25: valve, 26: fine particles, 27: storage tank, 28: rotary valve, 30: cadmium recovery equipment, 31: blower

Claims (5)

An incinerator that incinerates a plant containing cadmium at a temperature of 765 ° C. or higher and 900 ° C. or lower, and vaporizes the cadmium as a simple substance and / or a compound;
A cooling means for cooling and depositing the vaporized cadmium to 250 ° C. or lower, which is a temperature lower than the boiling point of the cadmium alone and / or the compound;
A first collecting means for collecting a powdery substance containing a simple substance and / or a compound of cadmium precipitated by the cooling means;
Wherein provided on the downstream side of the first collecting means, have a second collecting means comprising a bag filter with activated carbon and one coated at one or both braze cloth slaked lime,
And, a gas containing vaporized cadmium discharged from the incinerator, recovery equipment cadmium oxygen-containing gas supply means for supplying an oxygen-containing gas, characterized that you have provided. The cadmium recovery facility according to claim 1, wherein the first collection means is a bag filter provided with a filter cloth. 3. The cadmium recovery facility according to claim 2, wherein the filter cloth of the first collecting means has a basis weight of 500 g / m ² or more and an opening degree of 10 μm or less. A first step of putting a plant containing cadmium in an incinerator, incinerating at a temperature of 765 ° C. or higher and 900 ° C. or lower, and vaporizing the cadmium as a simple substance and / or a compound;
A second step of depositing the vaporized cadmium by cooling to 250 ° C. or lower, which is a temperature below the boiling point of the cadmium alone and / or the compound;
A third step of collecting the powdered substance containing the precipitated cadmium alone and / or a compound by the first collecting means;
The first collecting means is provided by a second collecting means comprising a bag filter provided on the downstream side of the first collecting means and provided with a filter cloth covered with one or both of activated carbon and slaked lime. nitrogen oxides passing through the, have a fourth step of collecting sulfur oxides, and any one or more of the substances of dioxins,
Furthermore, a method for recovering cadmium you and supplying the gas to the oxygen-containing gas containing vaporized cadmium discharged from the incinerator. 5. The method for recovering cadmium according to claim 4 , wherein a bag filter provided with a filter cloth is used for the first collecting means.

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