JP5241988B2 - Method and apparatus for preventing elution of heavy metals from slag - Google Patents

Description

  The present invention relates to a technique for suppressing elution of heavy metals from slag.

  In general, incineration ash and fly ash (incineration residue) generated when incineration of waste contains dioxins (DXNs) and toxic heavy metals. Melt solidification, which is one of the methods for treating these incineration residues, is an effective means that can be rendered harmless, long-term stabilized, reduced in volume, reduced in weight, and further recycled slag. Melting methods include gasification melting furnace using pyrolysis gas, electric plasma melting furnace, fuel type surface melting furnace, coke head type melting furnace, etc., but heavy metals are contained in the molten slag. In addition, elution of heavy metals from granulated slag may be observed. Moreover, elution of heavy metals resulting from the attachment of cooling water containing heavy metals to the surface of the slag may cause a problem.

  Conventionally, as a method for preventing the elution of such heavy metals, a method of washing slag with cooling water and washing with chelate washing water (see, for example, Patent Document 1), washing with a washing water added with a dispersant, and a coagulant There has been proposed a method (for example, see Patent Document 2) that combines washing with washing water to which is added.

  FIG. 5: shows the outline | summary of an example of the waste melting processing equipment provided with the slag washing | cleaning apparatus in patent document 1. As shown in FIG. The cleaning tank 51 that receives and cleans the slag S discharged from the waste melting furnace F, the cleaning water supply unit 52 that receives the supply of cleaning water, the slag discharge mechanism 53 that can discharge the slag after cleaning, In the molten slag cleaning device including a cleaning water discharge mechanism 54 that extracts and discharges a part of the cleaning water supplied from the cleaning water supply unit 52, the chelate cleaning in which a chelating agent is added from the cleaning water supply unit 52 It is configured to supply water, and further, the chelate washing water after being used for the washing is used as a treatment agent for detoxification treatment of fly ash recovered from the waste treatment furnace, so that the waste melting treatment While facilitating the treatment of waste water after washing the slag discharged from the furnace F, heavy metals that can be easily eluted from the slag are removed.

Moreover, FIG. 6 illustrates the block diagram for implementing the waste-melting-processing method provided with the slag washing | cleaning apparatus in patent document 2. As shown in FIG. In a melt processing method in which waste is melted in a waste melting furnace 61, and the discharged melt is rapidly cooled and granulated and solidified. The amount of elution of heavy metals can be further reduced with a small amount of additive by performing a washing process in the cooling water washing tank 65 to which is added and agglomerating the fine particles in the washing tank 68 to which the melt flocculant is added. The present invention is intended to provide a method and apparatus for treating slag in the waste melting furnace 61 capable of performing the above.
Japanese Patent Laid-Open No. 10-5616 JP 2000-263015 A

  However, in the method for preventing the elution of heavy metals as described above, when the cooling water is circulated and used, the heavy metals are gradually concentrated, and the water remaining in the slag or the suspended matter generated during the granulation process Due to the adhesion to the slag, heavy metals such as lead may be exposed mainly on the surface of the slag. Such slag may cause elution of heavy metals in subsequent processing steps or use after processing, and may hinder the effective use of slag.

  Also, many chemicals such as chelating agents, oxidizing agents, and dispersing agents used in the above elution prevention methods are expensive, and it is also necessary to work on these agents with heavy metals bound and aggregated. There are also many practical issues.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to enable elution prevention of heavy metals from slag efficiently and with minimum energy in a system for processing slag generated based on waste or the like. .

  As a result of intensive studies, the present inventors have found that the above object can be achieved by the processing method and apparatus shown below, and have completed the present invention.

The present invention is a method for preventing elution of heavy metals from slag, wherein cooling water used for slag water granulation treatment is stored in a predetermined cooling water tank after the water granulation treatment, and then cooled and the particle size is 500 μm by a strainer. after removal process more suspended solids were made, having a circulation system for water-granulated treatment with the water again granulated processing, and one of the cooling water after the removal treatment of the suspended solids has been carried out For the cleaning treatment , the suspended matter having a particle size of less than 500 μm contained in the treated cooling water is removed using agglomeration means or / and filtration means and then returned to the cooling water tank again. The circulatory system of this is comprised. The present inventor has found that in the slag treatment process, a large amount of heavy metals are contained in the suspended matter produced when the water granulation treatment is performed. In other words, for example, 90% or more of the lead contained in the cooling water treated with incineration residue is contained in the suspended matter, and the elution of heavy metals from the suspended matter adhering to the slag after the water granulation treatment It was a major factor in the elution of heavy metals from slag, and it was devised that treating this suspended solid from the circulating water system is very effective in preventing the elution of heavy metals. This allows slag to be processed efficiently and with minimal energy without using expensive chelating agents or other chemicals, and it is possible to effectively suppress elution of heavy metals, which is a major issue in the system. It became possible to provide a method. In addition, about a part of the cooling water delivered from the storage tank, after performing the removal process of suspended solids, by constituting a circulation system that recirculates to the cooling water stored again, It is washed with cooling water from a cooling water tank that has always been treated cleanly, and is transported to the slag pit with little elution of heavy metals. It is also possible to reduce the size of the equipment, which is advantageous in terms of cost and high efficiency. Processing becomes possible. Furthermore, in the present invention, among the suspended matter generated in the slag granulation treatment, the suspended matter having a particle size of less than 500 μm contains a large amount of heavy metals in particular, so that the particle size of the first-stage strainer is 500 μm. The above suspended substances are treated, and the most important suspended particles having a particle size of less than 500 μm are efficiently treated using agglomeration means or filtration means, thereby appropriately removing the entire suspended substances in the circulating water system. be able to. As a result, elution of heavy metals, which is a major problem in the system, can be effectively suppressed.

Moreover, the method for preventing elution of heavy metals from the slag according to the present invention is such that the cooling water used for the slag water granulation treatment is stored in a predetermined cooling water tank after the water granulation treatment, and then cooled and used again for the water granulation treatment. A part of the cooling water that is a circulation system and is supplied from the cooling water tank to form the circulation system is subjected to a removal treatment of suspended substances having a predetermined particle size contained in the treated cooling water, and then the cooling water tank again. A circulation system for cleaning treatment that recirculates to the cooling water, and forming the circulation system for cleaning treatment only with respect to the cooling water stored in the cooling water tank. Without changing, the processing capacity can be adjusted so that clean cooling water is always stored in the cooling water tank . The above suspended substance has a minute particle size, and it is difficult to remove the suspended substance from the circulating water system only with a commonly used strainer. By providing the filtering means, it was possible to effectively remove such suspended substances and to effectively prevent elution of heavy metals by using the wash water treated in the circulating water system. In addition, by circulating only the water in the cooling water tank, the processing capacity is adjusted according to the state of the cooling water without changing the amount of cooling water supplied in the circulation system for granulation treatment, so that clean cooling water is always supplied to the cooling water tank. It can be stored. It became possible to effectively prevent elution of heavy metals by using the clean water treated in the circulating water system and subjecting the slag to the water granulation treatment.

Further, in the method for preventing elution of heavy metals from the slag , in the circulation system for the cleaning treatment , after a suspended substance having a particle size of 500 μm or more is removed by a strainer, the aggregation means or / And removing the suspended solids having a particle size of less than 500 μm using a filtering means. Among the above suspended substances, the suspended substances having a predetermined particle diameter or less have been found to contain a large amount of heavy metals. In the first stage strainer, the suspended substance having a particle diameter of, for example, 500 μm or more is treated. The most important suspended particle having a particle size of less than 500 μm is efficiently processed using agglomeration means and / or filtration means, so that the entire suspended substance in the circulating water system can be appropriately removed. As a result, elution of heavy metals, which is a major problem in the system, can be effectively suppressed. In other words, among the suspended solids generated in the slag granulation treatment, the suspended solids having a particle size of less than 500 μm contain a lot of heavy metals. By treating the substance and efficiently treating the suspended substance having the most important particle size of less than 500 μm using the aggregating means or the filtering means, the entire suspended substance in the circulating water system can be appropriately removed. As a result, elution of heavy metals, which is a major problem in the system, can be effectively suppressed.

The present invention is an apparatus for preventing elution of heavy metals from slag, which is characterized by being used in any of the processing methods described above. Since any of the above treatment methods can effectively suppress elution of heavy metals, it has means for granulating slag, and means for removing suspended substances having a predetermined particle size in cooling water. By having it, the heavy metal elution prevention apparatus from the slag very excellent can be comprised.

  As described above, according to the present invention, slag can be processed efficiently and with minimal energy without using expensive chemicals such as chelating agents, thereby effectively suppressing elution of heavy metals, which is a major problem in the system. It has become possible to provide a method for preventing elution of heavy metals from slag and an apparatus therefor. In addition, the reliability of removal of heavy metals is high, safe slag can be effectively used, and the use of circulating wash water can save water treatment equipment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 illustrates the overall structure of an incineration residue according to the present embodiment, specifically, a slag treatment apparatus. A material to be melted 1 such as an incineration residue is supplied to a melting furnace 2 and melted at a high temperature of 1200 to 1600 ° C. The melt is subjected to a water granulation process in a slag conveyor 3 filled with cooling water to form granular slag, and is carried out to the slag pit 4 by the slag conveyor 3. At this time, the used cooling water is once stored in the cooling water tank 5 and then pumped by the pump 9, and sequentially subjected to the water granulation treatment again via the strainer 6, the suspended matter removing means 8 and the cooler 7. . The suspended substance in the cooling water is removed by the strainer 6 after a predetermined particle size (for example, 500 μm) or more is removed, and then the suspended substance removing means 8 removes the suspended substance. As a result, the molten slag is always subjected to a water granulation treatment with the cooling water that has been treated cleanly, and is carried out to the slag pit 4 with little elution of heavy metals.

  Further, as the strainer 6, a corrosion-resistant metal filter medium is generally used, but specifically, it is appropriately selected depending on the type of slag. The position of the cooler is not limited to the position as shown in FIG. 1, but in consideration of contamination by suspended substances and the like, it is preferably downstream of the suspended substance removing means. This is because such suspended substances may reduce heat exchange efficiency due to adhesion to the inner wall of the cooler 7. The suspended substance removing means 8 will be described later.

  The feature of this apparatus is that the cooling water has a circulation system for the water granulation treatment and has a cleaning treatment means for removing suspended substances in multiple stages in the system. Specifically, in the waste melting process, many heavy metals are contained in the suspended matter that is generated when the water granulation process is performed, and heavy metals from the suspended substance adhering to the slag after the granulation process are contained. It was devised that the elution of slag is a major factor in the elution of heavy metals from the slag, and it is very effective to prevent the elution of heavy metals by treating this suspended material from the circulating water system. This makes it possible to efficiently control the elution of heavy metals, which is a major issue in the system, by efficiently treating slag with minimal energy without using expensive chelating agents. .

  The incineration residue slag contains, for example, about 10 ppm of lead, and the slag transported to the slag pit contains 5 to 10% of water. On the other hand, the present inventors have found that about 0 to 10 ppm of lead is contained in the cooling water after the water granulation treatment, and that 90% or more of the lead is contained in the suspended substance.

  FIG. 2 illustrates the correlation between the amount of lead in the cooling water and the amount of lead eluted from the slag. The inventor experimentally added lead to the cooling water and measured the amount eluted from the slag. As a result, an increase in the elution amount was observed as the amount of lead in the cooling water increased, and when the addition amount exceeded 3-5 mg / L, the elution amount tended to increase rapidly.

  However, this conversely means that it is very effective to keep the amount of lead contained in the cooling water below a certain value in order to suppress the amount of elution. In other words, as described above, most of the heavy metals contained in the cooling water are contained in the suspended solids. Therefore, by removing the suspended solids in the cooling water, the heavy metals present in the suspended solids, that is, The amount of heavy metals contained in the cooling water can be greatly reduced, and as a result, elution of heavy metals from the slag can be efficiently suppressed. The present invention has been devised based on these findings.

  Moreover, the schematic whole structure of the processing apparatus of the slag which concerns on another embodiment is illustrated to FIG. 3 (A). A part of the cooling water introduced into the slag conveyor 3 is to be treated, the cooling water stored in the cooling water tank 5 is pumped by the pump 9, and sequentially subjected to the water granulation treatment again via the strainer 6 and the cooler 7. At the same time, a part thereof is returned to the cooling water tank 5 through the suspended substance removing means 8. That is, for suspended substances in the cooling water, suspended substances having a predetermined particle diameter or larger are removed by the strainer 6 and then suspended in the cooling water by a suspended substance removing means 8 for a part of the cooling water. Material is removed. As a result, the crushed slag is always washed with the cooling water from the cooling water tank 5 that has been treated cleanly, and is carried out to the slag pit 4 with little elution of heavy metals.

  The feature of this apparatus is that the cooling water has a circulation system for a water granulation treatment and a circulation system for a cleaning treatment for removing suspended substances. In addition to the cooling water supply system as shown in FIG. 1, the flow shown in FIG. 3A can reduce the size of the equipment, which is advantageous in terms of cost and enables high-efficiency processing. .

  It is also possible to circulate only the water in the cooling water tank 5. As illustrated in FIG. 3B, the processing capacity is adjusted according to the state of the cooling water without changing the amount of cooling water supplied to the slag conveyor 3, and clean cooling water is always stored in the cooling water tank 5. Is possible. It became possible to effectively prevent elution of heavy metals by using the clean water treated in the circulating water system and subjecting the slag to the water granulation treatment.

  In addition, in this invention, after conveying to said slag pit, it is also possible to combine with the process by a chelating agent. Since elution before the addition of the chelating agent is greatly reduced, the amount of the chelating agent added can be greatly reduced, and the effect of fixing heavy metals by the chelating agent can be synergistically improved.

  Here, various means can be adopted as the suspended solid removal means in the slag treatment method, and examples thereof include coagulation sedimentation, sand filtration, and membrane filtration. In particular, the suspended matter produced when incineration residue is treated has a fine particle size, and removal of suspended matter from the circulating water system is difficult only with a commonly used strainer. It is preferred to carry out using agglomeration means or / and filtration means. Further, in a treatment system using a circulation system, clean cooling water can be more effectively secured by providing a filtration means together with a suspended substance aggregating means in the circulation path.

  Specifically, in view of maintenance and cost, sand filtration combined with a flocculant is preferable. Suspended substances in cooling water may contain a lot of fine particles of about several μm (Fig. 4), and can be efficiently coagulated with these coagulants, which is sufficient even when sand filtration is used in combination. Removal processing is possible, and removal efficiency of 90% or more can be secured for a long time. The flocculant is not particularly limited as long as it has the action, and iron-based or aluminum-based materials can be used. Specifically, ferric chloride or polyaluminum chloride (PAC) ) And the like.

In the method for preventing elution of heavy metals from the slag, it is preferable that the particle size of the suspended substance to be cleaned is less than 500 μm . In other words, among the suspended solids generated in the slag granulation process, suspended solids with a particle size of less than 500 μm contain a large amount of heavy metals in particular, and therefore the initial strainer has a particle size of 500 μm or more. It is possible to appropriately remove the suspended solids in the circulating water system by treating suspended substances and efficiently treating suspended substances with the most important particle size of less than 500 μm using agglomeration means or filtration means. it can. As a result, elution of heavy metals, which is a major problem in the system, can be effectively suppressed.

  Since all of the above processing methods can effectively suppress elution of heavy metals, the processing method has means for granulating slag and means for removing suspended substances having a predetermined particle size in cooling water. By having the above, it is possible to configure a very excellent heavy metal elution preventing device from slag. That is, with the apparatus of the present invention, clean slag can be generated efficiently and with minimal energy from slag generated based on waste or the like.

  As described above, the embodiment of the present invention has been described by taking waste as an example of the processing target. However, the target object to which the present invention can be applied is not limited to this, Slag, for example, copper slag generated during copper refining, may be used. That is, the present invention can be applied to a technical field that generates granulated slag in which elution of heavy metals is a concern, particularly to a melting technique.

Explanatory drawing which shows the processing method of the slag which concerns on one Embodiment of this invention. Explanatory drawing illustrating elution characteristics of heavy metals from slag Explanatory drawing which shows the processing method of the slag which concerns on other embodiment of this invention. Explanatory diagram illustrating the particle size distribution characteristics of suspension in slag cooling water Explanatory drawing which shows the processing method of one slag which concerns on a prior art Explanatory drawing which shows the processing method of the other slag which concerns on a prior art

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Melted material 2 Melting furnace 3 Slag conveyor 4 Slag pit 5 Cooling water tank 6 Strainer 7 Cooler 8 Suspended substance removal means 9 Pump

Claims (4)

Cooling water used for slag water granulation treatment is stored in a predetermined cooling water tank after the water granulation treatment, then cooled and subjected to removal of suspended substances having a particle size of 500 μm or more by a strainer, and then water granulation again. has a circulation system for water-granulated process used for the processing, and a portion of the cooling water after the removal treatment of the suspended solids has been carried out and processed, the particle size contained in the cooling water is less than 500μm A method for preventing elution of heavy metals from slag, characterized in that a circulatory system for cleaning treatment is formed in which suspended substances are removed using agglomeration means or / and filtration means and then recirculated to the cooling water tank. . Cooling water used for slag granulation treatment is stored in a predetermined cooling water tank after the water granulation treatment, and then cooled to form a circulation system used for the water granulation treatment again, and is supplied from the cooling water tank to form the circulation system. A part of the cooling water to be treated has a cleaning circulation system for removing the suspended substance having a predetermined particle size contained in the treated cooling water and then returning to the cooling water tank again . The circulating system is formed only with respect to the cooling water stored in the cooling water tank, and clean cooling water is always stored in the cooling water tank without changing the cooling water supply amount of the circulating system for the water granulation treatment. A method for preventing elution of heavy metals from slag , wherein the processing capacity is adjustable . In the circulatory system for the cleaning treatment, after a suspended substance having a particle diameter of 500 μm or more is removed by a strainer, the suspended substance having a particle diameter of less than 500 μm is used by using the aggregating means and / or the filtering means. 3. The method for preventing elution of heavy metals from slag according to claim 2 , wherein a removal treatment is performed. An apparatus for preventing elution of heavy metals from slag, which is used in the prevention method according to claim 1.

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