Washing method and washing system for chlorine-containing powder

Abstract

To provide a flushing method and flushing system for chlorine-containing fine particles for stably satisfying the control reference value of waste water in the discharge of cleaning water generating in the flushing desalination treatment of the above fine particles.SOLUTION: A flushing method for chlorine-containing fine particles comprises: a slurrying process of slurrying chlorine-containing fine particles by adding water; a first solid-liquid separation process of separating the slurry into a solid and a liquid to collect a discharge water after flushing as a liquid phase; a conditioner addition process of adding an oxidation-reduction potential conditioner to the above discharge water; a first coagulation process of forming a first coagulation slurry in which the oxidation-reduction potential is controlled within a specific range while adding a ferrous inorganic coagulant to the discharge water to which the above conditioner is added; a second coagulation process of adding a high molecular coagulant to the first coagulation slurry to form a second coagulation slurry; and a second solid-liquid separation process of separating the second coagulation slurry into a solid and a liquid to collect noble metals as a solid phase.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a water washing method and a water washing system for desalting chlorine-containing powders such as incineration ash generated by incineration of municipal waste and extraction dust from the kiln end of a cement kiln.

Background Art

[0002] When recycling chlorine-containing powders containing high concentrations of chlorine such as municipal waste incineration fly ash as cement raw materials, it is necessary to remove the chlorine in advance. Therefore, after performing a water washing desalting treatment to remove water-soluble chlorine compounds, it is used as a cement raw material.

[0003] The washing wastewater generated when the chlorine-containing powder is subjected to a water washing desalting treatment contains various heavy metals derived from the chlorine-containing powder, together with the chlorine eluted from the chlorine-containing powder. Therefore, it is necessary to remove the heavy metals from such washing wastewater before discharging it outside the system.

[0004] Regarding the technology for removing heavy metals from washing wastewater, for example, in Patent Document 1 and Patent Document 2, a method capable of insolubilizing various heavy metals and excellent in reducing the chemical cost used is sodium hydrogen sulfide (NaSH), which is an oxidation-reduction potential regulator, and ferrous chloride (FeCl 2 ), and a method of treating washing wastewater using a polymer flocculant is disclosed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, according to the study by the present inventors, it has been found that even when treated with a theoretically equivalent amount of flocculant with respect to the amount of heavy metals contained in the washing wastewater, it often exceeds the drainage control standard value.

[0007] Therefore, an object of the present invention is to provide a method and a system for washing chlorine-containing powder for the washing wastewater generated by the water washing and desalting treatment of chlorine-containing powder so as to stably satisfy the drainage control standard value.

Means for Solving the Problems

[0008] In order to achieve the above object, in a first aspect of the present invention, A method for washing chlorine-containing powder for the purpose of desalting chlorine-containing powder, A slurrying step of adding water to the chlorine-containing powder to form a slurry; A first solid-liquid separation step of subjecting the slurry to solid-liquid separation and recovering washing wastewater as a liquid phase; An oxidation-reduction potential regulator addition step of adding an oxidation-reduction potential regulator to the washing wastewater; A first flocculation step of adding an iron-based inorganic flocculant to the washing wastewater to which the oxidation-reduction potential regulator has been added while controlling the oxidation-reduction potential within a specific range to form a first flocculant slurry; A second flocculation step of adding a polymer flocculant to the first flocculant slurry to form a second flocculant slurry; A second solid-liquid separation step of subjecting the second flocculant slurry to solid-liquid separation and recovering heavy metals as a solid phase, and provides a method for washing chlorine-containing powder characterized by comprising the above steps.

[0009] According to the method for washing chlorine-containing powder of the present invention, water is added to the chlorine-containing powder to form a slurry, and then solid-liquid separation is performed. Therefore, the chlorine content of the chlorine-containing powder is reduced, and it can have properties suitable for reuse as a cement raw material. Further, in the generated washing wastewater, an oxidation-reduction potential adjuster, an iron-based inorganic flocculant, and a polymer flocculant are added to form an aggregate slurry, and then solid-liquid separation is performed. Thus, heavy metals can be recovered as the solid phase. Thereby, the heavy metal content of the treated washing wastewater is reduced, and it can have properties suitable for discharging outside the system. In addition, when adding the iron-based inorganic flocculant, the oxidation-reduction potential of the first aggregate slurry in the first flocculation step is controlled within a specific range. Thereby, it is possible to avoid the generation of non-insoluble heavy metals due to insufficient addition amount of the iron-based inorganic flocculant and the increase in chemical oxygen demand (COD) due to excessive addition, and there is no waste in the amount of chemicals used. As a result, it is possible to more stably satisfy the drainage management standard values.

[0010] In the method for washing chlorine-containing powder of the present invention, it is preferable that the specific range of the oxidation-reduction potential of the first aggregate slurry in the first flocculation step is -400 mV to -100 mV.

[0011] According to this, heavy metals dissolved in the liquid phase of the washing wastewater are more likely to aggregate, and thus, heavy metals are more easily recovered from the washing wastewater.

[0012] Also, in the method for washing chlorine-containing powder of the present invention, it is preferable that the pH of the slurry in the slurrying step is 9 to 10.5.

[0013] According to this, by dissolving chlorine while avoiding the dissolution of heavy metals into the slurry liquid phase as much as possible, the amount of chemicals such as the oxidation-reduction potential adjuster can be reduced in the subsequent heavy metal removal step from the washing wastewater.

[0014] Also, in the method for washing chlorine-containing powder of the present invention, it is preferable that the pH adjustment of the slurry in the slurrying step is performed using a gas containing a high concentration of carbon dioxide.

[0015] According to this, exhaust gas from a cement kiln or the like can be effectively utilized for the purpose of pH adjustment, and for example, stirring of slurry in a water washing system using this method or generation of scale can be suppressed.

[0016] Further, in the method for washing a chlorine-containing powder of the present invention, it is preferable to adjust the oxidation-reduction potential of the washing waste water to -300 mV to -100 mV by adding the oxidation-reduction potential adjuster in the oxidation-reduction potential adjuster addition step.

[0017] According to this, even if chlorine is contained at a high concentration, dissolved heavy metals can be efficiently insolubilized, and in the subsequent first flocculation step, heavy metals dissolved in the liquid phase of the washing waste water are more likely to flocculate, and as a result, it becomes easier to recover heavy metals from the washing waste water.

[0018] Further, in the method for washing a chlorine-containing powder of the present invention, it is preferable that the oxidation-reduction potential adjuster is sodium hydrogen sulfide.

[0019] Further, in the method for washing a chlorine-containing powder of the present invention, it is preferable that the iron-based inorganic flocculant is ferrous chloride.

[0020] In order to achieve the above object, in a second aspect of the present invention, a water washing system for performing the above-described method for washing a chlorine-containing powder, a powder dissolution tank for adding water to the contained chlorine-containing powder to form a slurry, a first solid-liquid separation device for solid-liquid separating the slurry discharged from the powder dissolution tank, an oxidation-reduction potential adjuster mixing tank for containing the washing waste water recovered as a liquid phase from the first solid-liquid separation device and adding and mixing an oxidation-reduction potential adjuster to the washing waste water, A first flocculation tank that stores the washing wastewater after mixing the redox potential adjuster discharged from the redox potential adjuster mixing tank, and adds an iron-based inorganic flocculant to the washing wastewater to form a first floc slurry. A second flocculation tank that stores the first floc slurry discharged from the first flocculation tank, and adds a polymer flocculant to the first floc slurry to form a second floc slurry. A second solid-liquid separation device for solid-liquid separation of the second floc slurry discharged from the second flocculation tank, and a water washing system characterized by comprising the same is provided.

[0021] According to the configuration of the water washing system provided by the present invention, the above-described method for washing chlorine-containing powder can be preferably implemented.

[0022] In the water washing system of the present invention, it is further preferable to further include a first redox potential measuring device for measuring the redox potential of the first floc slurry in the first flocculation tank, and an iron-based inorganic flocculant addition device capable of automatically controlling the addition amount of the iron-based inorganic flocculant based on the measurement result of the first redox potential measuring device.

[0023] According to this, the management of the addition amount of the iron-based inorganic flocculant can be performed more stably, and as a result, the drainage management standard value can be satisfied more stably.

[0024] Further, in the water washing system of the present invention, it is further preferable to further include a second redox potential measuring device for measuring the redox potential of the washing wastewater in the redox potential adjuster mixing tank, and a redox potential adjuster addition device capable of automatically controlling the addition amount of the redox potential adjuster based on the measurement result of the second redox potential measuring device.

[0025] According to this, the management of the addition amount of the redox potential adjuster can be performed more stably, and as a result, the drainage management standard value can be satisfied more stably.

[0026] Further, in the water washing system of the present invention, it is preferable that the powder dissolution tank is provided with a gas blowing device for diffusing a gas containing carbon dioxide at a high concentration into the slurry in the tank.

[0027] According to this, exhaust gas from a cement kiln or the like can be effectively utilized for the purpose of pH adjustment, and the generation of scale in the present water washing system can be suppressed.

[0028] Further, in the water washing system of the present invention, it is preferable that the gas blowing device is a cylindrical diffusing device.

[0029] According to this, the slurry can be stirred using the exhaust gas from the cement kiln or the like described above.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0031] Hereinafter, with reference to the drawings, a water washing system for chlorine-containing powder according to the present invention will be described.

[0032] Figure 1 shows an embodiment of a water washing system for chlorine-containing powder according to the present invention. In Figure 1, the solid and liquid flows such as the chlorine-containing powder and the washing wastewater are indicated by the solid arrows, and the signal path is indicated by the dotted line. The water washing system 1 of chlorine-containing powder in this embodiment (hereinafter referred to as "water washing system 1") includes a powder dissolution tank 2 for generating a slurry S1 composed of a chlorine-containing powder P1 and water W1, a first solid-liquid separation device 3 for solid-liquid separating the slurry S1 discharged from the powder dissolution tank 2, a redox potential adjuster mixing tank 4 for accommodating the washing wastewater W2 recovered as a liquid phase from the first solid-liquid separation device 3 and adding and mixing a redox potential adjuster A1 to the washing wastewater W2, a first coagulation tank 5 for accommodating the washing wastewater W3 discharged from the redox potential adjuster mixing tank 4 and adding an iron-based inorganic flocculant A2 to the washing wastewater W3 to form a first floc slurry S2, a second coagulation tank 6 for accommodating the first floc slurry S2 discharged from the first coagulation tank 5 and adding a polymer flocculant A3 to the first floc slurry S2 to form a second floc slurry, and a second solid-liquid separation device 7 for solid-liquid separating the second floc slurry S3 discharged from the second coagulation tank 6.

[0033] In the powder dissolution tank 2, a process of mixing and stirring the chlorine-containing powder P1 and water W1 to generate a slurry S1, and a process of eluting chlorine from the chlorine-containing powder P1 in the slurry S1 into the liquid phase are performed.

[0034] The powder dissolution tank 2 is provided with a powder supply device 21 for supplying the chlorine-containing powder P1 to the powder dissolution tank 2 and a liquid supply device 22 for supplying water W1 to the powder dissolution tank 2. Further, a slurry stirring device 23 is provided for mixing the chlorine-containing powder P1 and water W1 and stirring the slurry S1 generated by the mixing. In the embodiment of Figure 1, a cylindrical air diffuser is used as the slurry stirring device 23, and the combustion exhaust gas G1 containing a high concentration of carbon dioxide supplied from the cement manufacturing facility K is diffused into the slurry S1.

[0035] As the slurry stirring device 23, for example, a general slurry stirring device such as a paddle type or a screw type may be used.

[0036] Here, by using a cylindrical air diffuser that diffuses the combustion exhaust gas G1 containing a high concentration of carbon dioxide as the slurry stirring device 23, a state in which the chlorine-containing powder P1 is well dispersed throughout the slurry S1 in the powder dissolution tank 2 is formed. Therefore, in the solid-liquid separation step in the subsequent first solid-liquid separation device 3, a cake through which the liquid phase can easily pass is formed, and the time required for solid-liquid separation can be shortened. In addition to this, the pH of the slurry S1 changes to the acidic side due to the carbon dioxide in the combustion exhaust gas G1, and calcium ions eluted in the liquid phase of the slurry S1 are precipitated as calcium carbonate and can be recovered as the dehydration cake C1 in the subsequent first solid-liquid separation device 3. As a result, an effect of suppressing the formation of scale (calcium sulfate) in the present water washing system is brought about. Thus, from the viewpoint of suppressing the formation of scale, it is preferable to adjust the pH of the slurry S1 to 9 to 10.5 by diffusing a gas containing a high concentration of carbon dioxide.

[0037] The sufficiently mixed and stirred slurry S1 is transported from the powder dissolution tank 2 to the first solid-liquid separation device 3. For the transportation of the slurry S1, a normal slurry liquid transportation device (not shown) such as a slurry centrifugal pump, a piston pump, and a mono pump may be used.

[0038] The first solid-liquid separation device 3 separates the transported slurry S1 into the washing waste water W2 (liquid phase) containing chlorine eluted from the chlorine-containing powder P1 and the dehydration cake C1 (solid phase) composed of the chlorine-containing powder P1 from which chlorine has been eluted and calcium carbonate derived from calcium ions in the liquid phase.

[0039] As the first solid-liquid separation device 3, a normal filtration device such as a filter press, a pressure leaf filter, a screw press, a belt press, or a belt filter may be used.

[0040] In the first solid-liquid separation device 3, the dewatered cake C1 (solid phase) separated and recovered is transported to the cement manufacturing facility K and recycled as a cement raw material. For transporting the dewatered cake C1 (solid phase), for example, a general cake transport device (not shown) such as a belt conveyor, a screw conveyor, or a pipe conveyor may be used.

[0041] The washing waste water W2 (liquid phase) separated and recovered in the first solid-liquid separation device 3 is transported to a liquid supply device 41 attached to the redox potential adjuster mixing tank 4. For transporting the washing waste water W2, for example, a general liquid transport pump (not shown) such as a piston pump, a plunger pump, a diaphragm pump, a gear pump, a screw pump, a centrifugal pump, or a cascade pump may be used.

[0042] In the redox potential adjuster mixing tank 4, a treatment is performed in which the redox potential adjuster A1 is added to the washing waste water W2 (liquid phase) to make the washing waste water W2 into washing waste water W3 (liquid phase) having a predetermined redox potential.

[0043] Attached to the redox potential adjuster mixing tank 4 are a liquid supply device 41 for supplying the washing waste water W2 to the redox potential adjuster mixing tank 4 and a liquid supply device 42 for supplying the redox potential adjuster A1 to the redox potential adjuster mixing tank 4. Further, a stirring device 43 is attached for mixing the washing waste water W2 and the redox potential adjuster mixing tank 4 and for stirring the washing waste water W3 generated by the mixing. In the embodiment of FIG. 1, a stirring blade is used as the stirring device 43.

[0044] As the stirring device 43, a general paddle type or screw type one may be used.

[0045] Attached to the redox potential adjuster mixing tank 4 is a redox potential meter (hereinafter referred to as an "ORP measuring device") 44 for continuously measuring the redox potential of the washing waste water W3. And the measurement result of the ORP measuring device 44 is transmitted to the control device 10 at any time.

[0046] As the ORP measurement device 44, a known oxidation-reduction potential measurement device may be used.

[0047] Based on the signal from the control device 10, the liquid supply device 42 supplies the liquid oxidation-reduction potential regulator A1 to the oxidation-reduction potential regulator mixing tank 4. That is, in the present embodiment, the oxidation-reduction potential of the washing wastewater W3 generated in the oxidation-reduction potential regulator mixing tank 4 is adjusted by the oxidation-reduction potential regulator A1 supplied from the liquid supply device 42, and the control device 10 automatically controls the supply amount of the oxidation-reduction potential regulator A1 based on the measurement result of the ORP measurement device 44. Thereby, stable treatment can be performed regardless of the type of the chlorine-containing powder P1.

[0048] The washing wastewater W3 (liquid phase) adjusted to a predetermined oxidation-reduction potential in the oxidation-reduction potential regulator mixing tank 4 is transported to the liquid supply device 51 attached to the first coagulation tank 5. For the transportation of the washing wastewater W3, for example, a general liquid transportation pump (not shown) such as a piston pump, a plunger pump, a diaphragm pump, a gear pump, a screw pump, a centrifugal pump, a cascade pump, etc. may be used.

[0049] In the first coagulation tank 5, an iron-based inorganic coagulant A2 is added to the washing wastewater W3 (liquid phase) to generate aggregates of heavy metals, and the washing wastewater W3 is processed into the first aggregate slurry S2.

[0050] The first coagulation tank 5 is provided with a liquid supply device 51 for supplying the washing wastewater W3 to the first coagulation tank 5 and a liquid supply device 52 for supplying the iron-based inorganic coagulant A2 to the first coagulation tank 5. Further, a stirring device 53 is provided for mixing the washing wastewater W3 and the iron-based inorganic coagulant A2 and for stirring the first aggregate slurry S2 generated by the mixing. In the embodiment of FIG. 1, a stirring blade is used as the stirring device 53.

[0051] As the stirring device 53, a general paddle type or screw type one may be used.

[0052] An ORP measuring device 54 for continuously measuring the oxidation-reduction potential of the first aggregate slurry S2 is attached to the first flocculation tank 5. And the measurement result of the ORP measuring device 54 is transmitted to the control device 10 at any time.

[0053] As the ORP measuring device 54, a known oxidation-reduction potential measuring instrument may be used.

[0054] The liquid supply device 52 supplies the liquid iron-based inorganic flocculant A2 to the first flocculation tank 5 based on a signal from the control device 10. This is done because the oxidation-reduction potential of the first aggregate slurry S2 changes due to the addition of the iron-based inorganic flocculant A2. In this embodiment, the oxidation-reduction potential of the first aggregate slurry S2 is adjusted by the iron-based inorganic flocculant A2 supplied from the liquid supply device 52, and the control device 10 automatically controls the supply amount of the iron-based inorganic flocculant A2 based on the measurement result of the ORP measuring device 54.

[0055] The management range of the oxidation-reduction potential of the first aggregate slurry S2 in the first flocculation tank 5 is such that almost all heavy metals in the first aggregate slurry S2 form aggregates within that range, and a specific range can be set so that the amount of the iron-based inorganic flocculant A2 used for the formation of the aggregates is minimized.

[0056] The first aggregate slurry S2 formed by adding the minimum necessary amount of the iron-based inorganic flocculant A2 in the first flocculation tank 5 is transported to the liquid supply device 61 attached to the second flocculation tank 6. For the transportation of the first aggregate slurry S2, for example, a general liquid transportation pump (not shown) such as a piston pump, a plunger pump, a diaphragm pump, a gear pump, a screw pump, a centrifugal pump, a cascade pump, etc. may be used.

[0057] In the second flocculation tank 6, a treatment is performed to change the first aggregate slurry S2 into a second aggregate slurry S3 containing large aggregates by adding the polymer flocculant A3 to the first aggregate slurry S2 to generate large aggregates of heavy metals and effectively recover the heavy metals in the subsequent solid-liquid separation.

[0058] In the second agglomeration tank 6, a liquid supply device 61 for supplying the first agglomerate slurry S2 to the second agglomeration tank 6 and a powder supply device 62 for supplying the polymer flocculant A3 to the second agglomeration tank 6 are attached. Further, a stirring device 63 is attached for mixing the first agglomerate slurry S2 and the polymer flocculant A3 and for stirring the second agglomerate slurry S3 generated by the mixing. In the embodiment of FIG. 1, a stirring blade is used as the stirring device 63.

[0059] As the stirring device 63, a general paddle type or screw type one may be used.

[0060] The well-mixed second agglomerate slurry S3 is transported from the second agglomeration tank 6 to the second solid-liquid separation device 7. For the transportation of the second agglomerate slurry S3, for example, a general liquid transportation pump (not shown) such as a piston pump, a plunger pump, a diaphragm pump, a gear pump, a screw pump, a centrifugal pump, a cascade pump, etc. may be used.

[0061] The second solid-liquid separation device 7 separates the transported second agglomerate slurry S3 into drained water W4 (liquid phase) from which heavy metals have been effectively removed and dehydrated cake C2 (solid phase) composed of aggregates of heavy metals.

[0062] As the second solid-liquid separation device 7, a normal filtration device such as a filter press, a pressure leaf filter device, a screw press, a belt press, a belt filter, etc. may be used.

[0063] The dehydrated cake C2 (solid phase) separated and recovered in the second solid-liquid separation device 7 is transported to the cement manufacturing facility K and recycled as a cement raw material. For the transportation of the dehydrated cake C2 (solid phase), for example, a general cake transportation device (not shown) such as a belt conveyor, a screw conveyor, a pipe conveyor, etc. may be used.

[0064] The drained water W4 (liquid phase) separated and recovered by the second solid-liquid separation device 7 meets the drainage management standard values and can be discharged outside the system.

[0065] Next, with reference to FIG. 2 together with FIG. 1, a method for washing chlorine-containing powder performed in the washing system 1 will be described.

[0066] The chlorine-containing powder to be washed in the present invention is not particularly limited as long as it is a powder containing water-soluble chlorine. Examples include incineration fly ash, molten fly ash, cement clinker dust, etc. These are wastes that have been effectively utilized as cement raw materials after desalination treatment by washing. Typically, typical municipal solid waste incineration fly ash contains about 10% to 30% by mass of chlorine, and fly ash generated from a gasification melting furnace generally contains about 10% to 40% by mass of chlorine. Also, cement clinker dust, which is the dust contained in the cement kiln extraction gas, generally contains about 10% to 40% by mass of chlorine.

[0067] According to the washing method of the present invention, the chlorine concentration of the chlorine-containing powder as described above can be reduced to, for example, typically a concentration of about 0.1% to 3% by mass, more typically a concentration of about 0.1% to 2% by mass, and this can be effectively utilized as, for example, a cement raw material. The chlorine concentration of the chlorine-containing powder can be measured by a well-known method. For example, fluorescence X-ray analysis methods such as those applied mutatis mutandis to ISO 29581-2 Cement - Test methods - Part 2: Chemical analysis by X-ray fluorescence, or the Cement Association Standard Test Method JCAS I-05 "Quantification method of chlorine in cement by X-ray fluorescence analysis" are preferably exemplified.

[0068] The method for washing a chlorine-containing powder of the present invention comprises a slurrying step of adding water W1 to the chlorine-containing powder P1 to form a slurry S1, a first solid-liquid separation step of subjecting the slurry S1 to solid-liquid separation and recovering washing wastewater W2 as a liquid phase, a redox potential regulator addition step of adding a redox potential regulator A1 to the washing wastewater W2, and a first aggregation step of forming a first aggregate slurry S2 in which the redox potential is controlled within a specific range while adding an iron-based inorganic flocculant A2 to the washing wastewater W3 to which the redox potential regulator A1 has been added, a second aggregation step of adding a polymer flocculant A3 to the first aggregate slurry S2 to form a second aggregate slurry S3, and a second solid-liquid separation step of subjecting the second aggregate slurry S3 to solid-liquid separation and recovering heavy metals as a solid phase.

[0069] In the slurrying step, inside the powder dissolution tank 2, the chlorine-containing powder P1 and water W1 are stirred to form a slurry S1. The mass ratio (W1 / P1) of the chlorine-containing powder P1 to water W1 in such a slurry S1 is preferably 4 to 10, more preferably 4 to 7, and particularly preferably 4 to 5. When the mass ratio (W1 / P1) is less than 4, the elution of chlorine from the chlorine-containing powder P1 may be insufficient. Further, when the mass ratio (W1 / P1) is greater than 10, the washing wastewater W2 (liquid phase) separated and recovered in the subsequent first solid-liquid separation step increases.

[0070] The chlorine ion concentration of the water W1 mixed with the chlorine-containing powder P1 in the powder dissolution tank 2 and constituting the slurry S1 is preferably 3 mass% or less, more preferably 2 mass% or less, and particularly preferably 1 mass% or less. The lower limit is not particularly set, but usually, the chlorine concentration of industrial water derived from river water, groundwater, etc. is about 0.005 mass%. When the chlorine ion concentration of the water W1 is greater than 3 mass%, depending on the chlorine content of the chlorine-containing powder P1, the elution efficiency of chlorine from the chlorine-containing powder P1 in the slurrying step may decrease.

[0071] In the continuously stirred slurry S1, the time required for the elution of chlorine from the chlorine-containing powder P1 into the water W1 is preferably 30 minutes or more, more preferably 45 minutes or more, in order to sufficiently elute chlorine.

[0072] In addition, the higher the temperature condition in the slurrying step, the greater the amount of chlorine eluted from the chlorine-containing powder P1. However, from the perspective of the cost involved in the treatment, it is preferably set at 5°C to 50°C, more preferably 25°C to 50°C. In that case, as in the embodiment of FIG. 1, it is sufficient to disperse high-temperature gas such as combustion exhaust gas G1 from the cement manufacturing facility into the slurry S1, or to provide a temperature control device such as a heater in the powder dissolution tank 2.

[0073] The pH of the slurry S1 in the slurrying step is preferably 9 to 10.5, more preferably 9 to 10.3, and particularly preferably 9 to 10. By setting the pH of the slurry S1 to 9 to 10.5, the concentration of heavy metals dissolved in the slurry S1 decreases, so that the amount of the redox potential adjuster A1 used in the subsequent step can be reduced. This pH adjustment can be achieved, for example, as in the embodiment of FIG. 1, by dispersing the combustion exhaust gas G1 containing a high concentration of carbon dioxide discharged from the cement manufacturing facility into the slurry S1, and lowering the pH by the dissolution of the carbon dioxide. Also, the addition of a pH adjuster such as dilute sulfuric acid or hydrochloric acid, which is a common method, to the slurry S1 may be used.

[0074] Next, the first solid-liquid separation device 3 proceeds to the first solid-liquid separation step of separating and recovering the slurry S1 supplied from the powder dissolution tank 2 into a dewatered cake C1 (solid phase) composed of the chlorine-containing powder P1 from which chlorine has been eluted and washing wastewater W2 (liquid phase).

[0075] The water content of the dewatered cake C1 separated and recovered in the first solid-liquid separation step is preferably 20% by mass to 70% by mass in order to prevent the chlorine eluted in the liquid phase from remaining in the dewatered cake C1 together with the liquid phase.

[0076] The pressure of the pressing for adjusting the water content of the dewatered cake C1 may be 0.2 MPa to 2 MPa, and the mesh opening of the filter cloth may be such that it can collect solid phases with a particle size of 0.1 μm or more.

[0077] In addition, when a filter press is used as the first solid-liquid separation device 3, the dehydrated cake C1 once separated and recovered by solid-liquid separation may be washed with water W1. This can make desalination from the dehydrated cake C1 more reliable. The mass ratio (W1 / C1) of the dehydrated cake C1 to water W1 in this washing is preferably 4 to 10, more preferably 4 to 7, and particularly preferably 4 to 5 from the viewpoint of suppressing the generation amount of washing wastewater. Note that the generated washing wastewater can be reused as water W1.

[0078] The dehydrated cake C1 separated and recovered in the first solid-liquid separation step has its chlorine content effectively reduced to 3.0 mass% or less and can be used as a cement raw material without any problems.

[0079] Next, it shifts to a redox potential adjuster addition step for adding a redox potential adjuster A1 to the washing wastewater W2 separated and recovered from the first solid-liquid separation device 3 to obtain washing wastewater W3 having a predetermined redox potential.

[0080] In the redox potential adjuster addition step, the redox potential (ORP) of the supplied washing wastewater W2 is changed to -100 mV or less, preferably -300 mV to -100 mV. By setting the redox potential of the changed washing wastewater W3 to -100 mV or less, even if it contains a high concentration of chlorine, the dissolved heavy metals can be efficiently insolubilized while minimizing the usage amount of the redox potential adjuster A1 used.

[0081] As the redox potential adjuster A1 added to the washing wastewater W2, general-purpose ones can be used, but hydrogen sulfide sodium (sodium hydrosulfide) is particularly preferable.

[0082] In this redox potential adjuster addition step, the stirring time for changing the washing wastewater W2 containing heavy metals into the washing wastewater W3 in which the heavy metals are insolubilized is 1 minute or more, more preferably 3 minutes or more, and even more preferably 5 minutes or more. The above-mentioned redox potential is the measured value after the end of this stirring.

[0083] Subsequently, the washing wastewater W3 containing insolubilized heavy metals is transferred to a first flocculation step for changing it into a first floc slurry containing aggregates of insolubilized heavy metals by adding an iron-based inorganic flocculant A2 while controlling the oxidation-reduction potential within a specific range.

[0084] In this first flocculation step, by making the insolubilized heavy metals into small aggregates, the aggregates can be enlarged in the second flocculation step using a polymer flocculant in the next step, and the separation and recovery of heavy metals can be facilitated in the subsequent second solid-liquid separation step. From such a viewpoint, the iron-based inorganic flocculant A2 used in the first flocculation step can also be regarded as functioning as a flocculation aid.

[0085] As the iron-based inorganic flocculant A2 used in the first flocculation step, it is an iron-based flocculant that generates divalent iron ions of ferrous chloride (FeCl 2 ) and ferrous sulfate (FeSO 4 ).

[0086] Since the divalent iron ions generated from these iron-based inorganic flocculants A2 act as reducing agents, the oxidation-reduction potential of the first floc slurry S2 is lowered in the first flocculation step, and the degree of insolubilization of the heavy metals contained in the first floc slurry S2 is further promoted. Thus, the iron-based inorganic flocculant A2 contributes in a favorable direction to the separation and recovery of heavy metals. On the other hand, when a large amount of such an iron-based inorganic flocculant A2 is added, the amount of iron dissolved in the first floc slurry S2 increases, and the chemical oxygen demand (COD) of the first floc slurry S2 also increases.

[0087] Therefore, it is necessary to set an upper limit value for the addition amount of the iron-based inorganic flocculant A2 in the first flocculation step so that the amount of iron and the chemical oxygen demand contained in the final wastewater W4 in this water washing method satisfy the wastewater management standard values.

[0088] On the one hand, as can be seen from the results of the tests described below, when an iron-based inorganic flocculant is used in the washing wastewater generated during the water washing and desalination treatment of chlorine-containing powder, even if the addition amount of sodium hydrogen sulfide is an appropriate amount for insolubilizing heavy metals, heavy metals may exceed the drainage control standard value depending on the addition amount of the iron-based inorganic flocculant. This is considered to be due to the fact that a part of the iron-based inorganic flocculant reacts with sodium hydrogen sulfide and a part of sodium hydrogen sulfide is consumed.

[0089] Therefore, considering that a part of the redox potential regulator A1 added in the above-described redox potential adjustment step is consumed by the addition of the iron-based inorganic flocculant A2, it is necessary to set a necessary lower limit value for the addition amount of the iron-based inorganic flocculant A2 in the first flocculation step.

[0090] Therefore, in this water washing method, the addition amount of the iron-based inorganic flocculant A2 is adjusted according to the redox potential of the first flocculated slurry S2. Specifically, the iron-based inorganic flocculant A2 is added so that the redox potential of the first flocculated slurry S2 is within the range of -400 mV to -100 mV. By adding the iron-based inorganic flocculant A2 so that the redox potential is within this range, even for the first flocculated slurry S2 containing a high concentration of chlorine, the dissolved heavy metals can be efficiently insolubilized while minimizing the amount of the iron-based inorganic flocculant A2 used.

[0091] The change in the redox potential of the first flocculated slurry S2 in this first flocculation step is as follows: initially, when the iron-based inorganic flocculant A2 is added, the divalent iron ions generated from the iron-based inorganic flocculant A2 consume a part of the redox potential regulator A1 as described above and rise to about 0 mV, and then gradually decrease with the continuous addition of the iron-based inorganic flocculant A2.

[0092] Since the change in the redox potential by the iron-based inorganic flocculant A2 is a reaction that is completed within 1 minute, the stirring time for changing from the washing wastewater W3 to the first floc slurry S2 in this first flocculation step is 1 minute or more, more preferably 3 minutes or more, and even more preferably 5 minutes or more. The redox potential of the first floc slurry S2 is the measured value after the completion of this stirring.

[0093] Next, a second flocculation step is carried out in which a polymer flocculant A3 is added to the first floc slurry S2 containing small flocs of insolubilized heavy metals to change it into a second floc slurry S3 containing enlarged flocs.

[0094] The polymer flocculant A3 is used to enlarge the small flocs containing heavy metals formed in the first flocculation step. As the polymer flocculant A3, a flocculant used for solid-liquid separation in an alkaline region, such as an anionic flocculant mainly composed of polyacrylamide, may be used. At this time, the addition amount of the polymer flocculant A3 to the first floc slurry S2 may be the standard addition amount of the flocculant used.

[0095] The stirring time of the second floc slurry S3 in the second flocculation step is 5 minutes or more, more preferably 10 minutes or more, and even more preferably 20 minutes or more.

[0096] Next, the second solid-liquid separation device 7 proceeds to a second solid-liquid separation step of separating and recovering the second floc slurry S3 supplied from the second flocculation tank 6 into a dewatered cake C2 (solid phase) composed of flocs of heavy metals and wastewater W4 (liquid phase).

[0097] The water content of the dewatered cake C2 separated and recovered in the second solid-liquid separation step is preferably 20% by mass to 70% by mass in order to prevent chlorine eluted in the liquid phase from remaining in the dewatered cake C2 together with the liquid phase.

[0098] The pressure of the pressing for adjusting the water content of the dewatered cake C2 may be 0.2 MPa to 2 MPa, and the mesh opening of the filter cloth may be such that it can collect a solid phase with a particle size of 0.1 μm or more.

[0099] Also, when a filter press is used as the second solid-liquid separation device 7, the dehydrated cake C2 once separated and recovered by solid-liquid separation may be washed with water W1. Thereby, desalination from the dehydrated cake C2 can be made more reliable. The mass ratio (W1 / C2) of the dehydrated cake C2 to the water W1 in this washing is preferably 4 to 10, more preferably 4 to 7, and particularly preferably 4 to 5 from the viewpoint of suppressing the generation amount of washing water. Note that the generated washing water can be discharged out of the system together with the waste water W4.

[0100] The chlorine content of the dehydrated cake C2 separated and recovered in the second solid-liquid separation step is effectively reduced to 3.0 mass% or less, and it can be used as a cement raw material without any problem.

[0101] Finally, the test of the method for washing chlorine-containing powder of the present invention will be described. The test evaluated the drainage control item values (Se, Pb, Cd, Fe, COD) of the final waste water W4 when the addition amount of the iron-based inorganic flocculant A2 in the first flocculation step was changed, with and without pH adjustment of the slurry S1 in the slurrying step.

[0102] For the chlorine-containing powder P1, refuse incineration fly ash (chlorine content: 21.2 mass%) was used, and for the water W1, tap water was used to prepare a slurry S1-A with P1:S1 = 1:4. The pH of the slurry S1-A was 13. This slurry S1-A was used for the test without pH adjustment of the slurry S1.

[0103] A slurry S1-B was prepared in the same manner as the slurry S1-A except that carbon dioxide gas was blown in during slurry stirring. The pH of the slurry S1-B was 10. This slurry S1-B was used for the test with pH adjustment of the slurry S1.

[0104] For the obtained slurries S1-A and S1-B, a first solid-liquid separation step using a Buchner funnel (suction filter) was respectively carried out. After obtaining washing wastewater W2-A from slurry S1-A and washing wastewater W2-B from slurry S1-B, sodium hydrogen sulfide (redox potential regulator A1) was added until the redox potential of each of washing wastewater W2-A and washing wastewater W2-B reached -100 mV, and washing wastewater W3-A was obtained from washing wastewater W2-A and washing wastewater W3-B was obtained from washing wastewater W2-B.

[0105] Ferrous chloride (iron-based inorganic flocculant A2) was added to the obtained washing wastewater W3-A and washing wastewater W3-B at (i) 50 mg / L, (ii) 100 mg / L, (iii) 300 mg / L, (iv) 500 mg / L, (v) 1000 mg / L, (vi) 3000 mg / L, (vii) 6000 mg / L, and first aggregate slurries S2 at seven levels were formed for each of the washing wastewaters W3. The measured values of the redox potential measured for each first aggregate slurry S2 using an ORP measuring device (D72S + ORP electrode manufactured by Horiba, Ltd.) are shown in Table 1 and Table 2.

[0106] For each of the obtained 14 first aggregate slurries S2, after adding the standard addition amount of FK-flock (trade name, manufactured by Kubota Chemical Co., Ltd., polymer flocculant A3) to form a second aggregate slurry S3, a second solid-liquid separation step was carried out using a Buchner funnel to obtain wastewater W4.

[0107] For the obtained 14 wastewaters W4, the concentrations of Se, Pb, Cd, and Fe were measured using ICP mass spectrometry (measurement device: Agilent 7900 ICP-MS (trade name) manufactured by Agilent Technologies), and the COD value was measured in accordance with the oxygen consumption by potassium permanganate at 100 °C (CODMn) in JIS K 0102:2019. The measurement results are shown in Table 1 and Table 2.

[0108] Incidentally, the salt content (Cl content) of the two dewatered cakes C1 obtained in the first solid-liquid separation step and the 14 dewatered cakes C2 obtained in the second solid-liquid separation step was 1.5 mass% or less for all specimens.

[0109]

Table 1

[0110]

Table 2

[0111] From Table 1 and Table 2, it can be seen that if the oxidation-reduction potential of the first aggregate slurry S2 is in the range of -400 mV to -100 mV, the heavy metals and COD in the drainage W4 satisfy the drainage standards.

[0112] Also, when comparing the oxidation-reduction potential of the first aggregate slurry S2 with the same addition amount of ferric chloride, a lower oxidation-reduction potential is obtained when the pH of the slurry S1 is adjusted. That is, by adjusting the pH of the slurry S1, the usage amount of the iron-based flocculant when obtaining a predetermined oxidation-reduction potential can be reduced. Therefore, in addition to insolubilizing heavy metals excluding iron, it is possible to suppress the dissolution amount of iron and the increase in COD.

Explanation of Symbols

[0113] 1: Water washing system 2: Powder dissolution tank 21: Powder supply device 22: Liquid supply device 23: Slurry stirring device 3: First solid-liquid separation device 4: Oxidation-reduction potential adjuster mixing tank 41, 42: Liquid supply device 43: Stirring device 44: Oxidation-reduction potential meter 5: First flocculation tank 51, 52: Liquid supply device 53: Stirring device 54: Redox potential meter 6: Second flocculation tank 61: Liquid supply device 62: Powder supply device 63: Stirring device 7: Second solid-liquid separation device 10: Control device A1: Redox potential regulator A2: Iron-based inorganic flocculant A3: Polymer flocculant C1, C2: Dewatered cake G1: Combustion exhaust gas K: Cement manufacturing equipment P1: Chlorine-containing powder S1: Slurry S2, S3: Aggregate slurry W1: Water W2, W3: Washing wastewater

Claims

1. A method for washing a chlorine-containing powder for the purpose of removing chlorine from the chlorine-containing powder, comprising: a slurrying step of adding water to the chlorine-containing powder to form a slurry; a first solid-liquid separation step of solid-liquid separating the slurry and recovering washing wastewater as a liquid phase; a redox potential adjuster addition step of adding a redox potential adjuster to the washing wastewater; a first aggregation step of measuring the redox potential while adding an iron-based inorganic flocculant to the washing wastewater to which the redox potential adjuster has been added, and forming a first aggregate slurry in which the redox potential is controlled within a specific range by controlling the addition amount of the iron-based inorganic flocculant; a second aggregation step of adding a polymer flocculant to the first aggregate slurry to form a second aggregate slurry; a second solid-liquid separation step of solid-liquid separating the second aggregate slurry and recovering heavy metals as a solid phase. The method for washing a chlorine-containing powder is characterized by comprising the above steps.

2. The method for washing a chlorine-containing powder according to Claim 1, wherein the specific range of the redox potential of the first aggregate slurry in the first aggregation step is -400 mV to -100 mV.

3. The method for washing a chlorine-containing powder according to Claim 1 or Claim 2, wherein the pH of the slurry in the slurrying step is 9 to 10.

5.

4. The method for washing a chlorine-containing powder according to Claim 3, wherein the pH adjustment of the slurry in the slurrying step is performed using a gas containing a high concentration of carbon dioxide.

5. The method for washing a chlorine-containing powder according to any one of Claims 1 to 4, wherein the redox potential of the washing wastewater is adjusted to -300 mV to -100 mV by adding the redox potential adjuster in the redox potential adjuster addition step.

6. The method for washing a chlorine-containing powder according to any one of Claims 1 to 5, wherein the redox potential adjuster is sodium hydrogen sulfide.

7. The method for washing a chlorine-containing powder according to any one of Claims 1 to 6, wherein the iron-based inorganic flocculant is ferric chloride.

8. A washing system for performing the method for washing a chlorine-containing powder according to any one of Claims 1 to 7, comprising: a powder dissolution tank for adding water to the contained chlorine-containing powder to form a slurry; a first solid-liquid separation device for solid-liquid separating the slurry discharged from the powder dissolution tank; A redox potential adjuster mixing tank for storing the washing wastewater recovered as a liquid phase from the first solid-liquid separation device, adding a redox potential adjuster to the washing wastewater, and mixing them; A first coagulation tank for storing the washing wastewater after mixing with the redox potential adjuster discharged from the redox potential adjuster mixing tank, adding an iron-based inorganic coagulant to the washing wastewater to form a first aggregate slurry, and comprising a first redox potential measuring device for measuring the redox potential of the first aggregate slurry; A second coagulation tank for storing the first aggregate slurry discharged from the first coagulation tank and adding a polymer coagulant to the first aggregate slurry to form a second aggregate slurry; A second solid-liquid separation device for solid-liquid separating the second aggregate slurry discharged from the second coagulation tank, wherein the washing system is characterized by comprising the above components.

9. The washing system according to claim 8, further comprising an iron-based inorganic coagulant adding device capable of automatically controlling the addition amount of the iron-based inorganic coagulant based on the measurement result of the first redox potential measuring device.

10. The washing system according to claim 8 or claim 9, further comprising a second redox potential measuring device for measuring the redox potential of the washing wastewater in the redox potential adjuster mixing tank, and a redox potential adjuster adding device capable of automatically controlling the addition amount of the redox potential adjuster based on the measurement result of the second redox potential measuring device.

11. The washing system according to any one of claims 8 to 10, wherein the powder dissolution tank is provided with a gas blowing device for diffusing a gas containing a high concentration of carbon dioxide into the slurry in the tank.

12. The washing system according to claim 11, wherein the gas blowing device is a cylindrical diffusing device.

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