JP5468945B2 - How to remove selenium - Google Patents

Description

  The present invention relates to a method for removing selenium, and more particularly, to a method for removing selenium contained in a filtrate or the like obtained by washing chlorine bypass dust collected by a chlorine bypass system attached to a cement manufacturing facility.

  Conventionally, a chlorine bypass system for removing chlorine that causes problems such as blockage of a preheater in a cement manufacturing facility has been used. In recent years, recycling of waste by converting to cement raw material or fuel has been promoted, and as the amount of waste processed increases, the amount of volatile components such as chlorine brought into the cement kiln also increases, and the amount of chlorine bypass dust generated also increases. It has increased. Therefore, development of an effective utilization method of chlorine bypass dust has been demanded.

  From this viewpoint, in the cement raw material processing method described in Patent Document 1, water is added to waste containing chlorine to elute and filter out chlorine in the waste, and the obtained desalted cake is used as a cement raw material. In addition to using it, the wastewater is purified and discharged as it is, or the salinity is recovered, so that the chlorine bypass dust is effectively used without causing environmental pollution.

However, in this method, when desalinating chlorine bypass dust, the selenium concentration in the waste water is removed to a safe standard, for example, 0.1 mg-Se / l in the case of sewage discharge. As a result, ferrous chloride (FeCl ₂ ) of 8000 mg-Fe ²⁺ / l or more is required, and a large amount of reducing agent is consumed in removing selenium, resulting in a problem of increased operating costs.

  In order to solve the above problem, the present applicant has proposed a method for treating cement kiln combustion gas bleed dust as shown in FIG.

  This treatment method is roughly divided into a water washing process for removing chlorine by washing chlorine bypass dust, a waste water treatment process for removing heavy metals such as selenium from the filtrate, and industrial recovery by collecting salt from concentrated salt water. It is divided into a salt recovery process for obtaining raw materials.

  In the water washing step, warm water generated in the boiler 61 is supplied to the dissolution tank 63 through the warm water tank 62 and mixed with chlorine bypass dust. Thereby, the water-soluble chlorine content contained in the chlorine bypass dust is dissolved in the warm water. The slurry discharged from the dissolution tank 63 is solid-liquid separated by the belt filter 64, and the primary cake from which the chlorine content has been removed is returned to the cement kiln and used as a cement raw material. On the other hand, the primary filtrate containing heavy metals such as chlorine and selenium is temporarily stored in the storage tank 65.

  In the waste water treatment process, the primary filtrate containing chlorine, heavy metals such as selenium, and calcium stored in the storage tank 65 is supplied to the chemical reaction tank 66, and hydrochloric acid as a pH adjuster is added to the chemical reaction. The pH in the tank 66 is adjusted to 4 or less. After reducing and precipitating selenium as a heavy metal contained in the wastewater with ferrous sulfate, calcium hydroxide is added to raise the pH to 8-11, and ferrous hydroxide produced by addition of ferrous sulfate Iron is condensed and deposited.

  And the slurry discharged | emitted from the chemical | medical solution reaction tank 66 is solid-liquid separated by the filter press 67, a secondary cake is returned to a cement kiln etc. and used as a cement raw material, and a secondary filtrate is potassium carbonate in the chemical | medical solution reaction tank 68. And the calcium in the secondary filtrate is removed.

  Next, the slurry discharged from the chemical reaction tank 68 is solid-liquid separated by the filter press 69, the tertiary cake is returned to the cement kiln and used as a cement raw material, and the tertiary filtrate is added with hydrochloric acid in the storage tank 70. After the pH is adjusted, iron, residual heavy metal, and suspended substances (SS) are removed by the iron removal tower 71, the chelate resin tower 72, and the filtration device 73.

The waste water from the filtration device 73 is supplied to the electrodialysis device 74. In the electrodialysis device 74, selenic acid (SeO ₄ ²⁻ ) in the waste water is contained in the desalted water and the chlorine content is contained in the concentrated salt water. The desalinated water from the electrodialyzer 74 is returned to the hot water tank 62 in the water washing step via a circulation route (not shown) (see reference A).

  In the salt recovery step, the concentrated salt water is heated in the heater 76 by steam from the boiler 75 and crystallized by the crystallizer 77. In the crystallizer 77, the solute in the concentrated salt water is precipitated as crystals, and industrial salts mainly composed of potassium chloride (KCl) are recovered through the centrifuge 80 and can be used as industrial raw materials. On the other hand, the water evaporated in the crystal unit 77 is cooled in the condenser 78 to recover the drain, and this drain is returned to the water washing step. The filtrate separated by the centrifuge 80 is returned to the crystallizer 77 through the filtrate tank 79. In addition, it is also possible to discharge the salt without recovering the salt from the concentrated salt water.

Japanese Patent Laid-Open No. 11-100343 JP 2004-330148 A

  However, in the conventional cement kiln combustion gas bleed dust treatment method, an electrodialyzer is installed to remove selenium. Therefore, in addition to equipment costs, energy costs are incurred, and heavy metals such as lead are used. Since the calcium is removed after the removal, there is a problem that the cost of the treatment chemical increases and the operation cost increases.

  Therefore, the present invention has been made in view of the problems in the above-described conventional technology, and does not require electrodialysis or the like, and also reduces facility costs and operation costs by reducing the amount of medicine used. An object of the present invention is to provide a selenium removal method that can be used.

To achieve the above object, the present invention provides a method for removing selenium, wherein a solution containing SO ₄ and selenium and regenerated water for regenerating the ion exchange resin are alternately supplied to the ion exchange resin, and the ion exchange is performed. Of the effluent discharged gradually and continuously from the resin, a solution having a high concentration of both SO ₄ and selenium is selectively recovered .

Then, according to the present invention, it is possible to both concentrations of concentration and selenium SO ₄ is selectively recovering high solution using an ion exchange resin, electrical to remove selenium as traditional There is no need to install a dialysis machine, and the equipment cost and energy cost can be greatly reduced.

In the selenium removal method, the solution may contain at least one of NaCl, KCl, and CaCl ₂ , and SO ₄ and selenium can be simultaneously separated from salt water.

Further, in the selenium removal method, the effluent discharged from the ion exchange resin may be selected from the group consisting of measurement results of Cl, SO ₄ , K, Na or Ca, electrical conductivity and pH. Based on this , it is possible to selectively recover a solution having a high concentration of both SO ₄ and selenium .

  Furthermore, the said solution can be made into the filtrate obtained by washing with water the chlorine bypass dust which generate | occur | produced at the cement baking process, and can process a chlorine bypass dust at low cost.

  Moreover, the said solution can be used as the leachate of a final disposal site, and the process of harmful leachate in a final disposal site and the stabilization promotion of a final disposal site can be performed at low cost.

  As described above, according to the present invention, it is possible to provide a method for removing selenium and the like having low equipment costs and low operating costs by not requiring electrodialysis or the like and reducing the amount of drug used.

It is a flowchart which shows an example of the processing system of the cement kiln combustion gas extraction dust using the selenium removal method concerning this invention. It is the schematic for demonstrating operation | movement of the ion exchange resin used for the processing system shown in FIG. It is a graph which shows the Example of the ion exchange resin shown in FIG. It is a flowchart which shows the case where the leachate of a final disposal site is processed using the ion exchange resin shown in FIG. It is a flowchart which shows an example of the processing system of the conventional cement kiln combustion gas extraction dust.

  Next, modes for carrying out the present invention will be described with reference to the drawings.

FIG. 1 shows a case where the present invention is applied to a cement kiln combustion gas extraction dust processing system as a first embodiment of a selenium removal method according to the present invention. This processing system 1 extracts air from a kiln bottom of a cement kiln. After the chlorine bypass dust contained in the combustion exhaust gas is washed with water, it is composed of a water washing device 2, a heavy metal removing device 3 for removing heavy metals and SO _4, and a drying device 4.

  The water washing apparatus 2 includes a dissolution tank 22 that dissolves chlorine in the chlorine bypass dust D stored in the tank 21, and a filter 23 that separates the slurry S1 discharged from the dissolution tank 22 into a cake C1 and a filtrate L1. And a hot water tank 24 for supplying hot water H to the dissolution tank 22 and a storage tank 25 for storing the filtrate L1.

  The hot water tank 24 is used for industrial purposes in which the desalted water L3 stored in the desalted water tank 37 of the heavy metal etc. removing device 3 described later is heated with the hot gas G3 discharged from the bag filter 42 of the drying device 4. The warm water H is stored and used for circulation in the dissolution tank 22.

The heavy metal etc. removing device 3 cakes the chemical liquid reaction tank 32 (32A, 32B) for removing heavy metals other than selenium (Se) in the filtrate L1 supplied from the storage tank 25 and the slurry S2 discharged from the chemical liquid reaction tank 32. Filter press 33 for solid-liquid separation into C2 and filtrate L2, sand filter 34 for filtering filtrate L2 discharged from filter press 33, SO ₄ and selenium contained in filtrate L2 supplied from sand filter 34 The ion exchange resin 35 for removing water, and the reclaimed water tank 36 for storing the reclaimed water L5, demineralized water L3, and desulfurized water L4 discharged from the ion exchange resin 35, a demineralized water tank 37, and a desulfurized water tank 38, respectively.

The chemical reaction tank 32A is provided for adding sodium hydrosulfate (NaHS) to the filtrate L1 to generate lead sulfide (PbS), thallium sulfide (Tl ₂ S), and the like. In the chemical reaction tank 32B, ferric chloride (FeCl ₃ ) is added to the filtrate L1 supplied from the chemical reaction tank 32A to condense the produced lead sulfide, thallium sulfide and the like so as to facilitate solid-liquid separation. Provided.

  The filter press 33 is provided to separate the filtrate L1 discharged from the chemical reaction tank 32B into a cake C2 containing thallium sulfide and lead sulfide and the filtrate L2.

The ion exchange resin 35 is provided to remove SO ₄ and selenium contained in the filtrate L2 discharged from the sand filter 34, and an amphoteric ion exchange resin or the like can be used. The amphoteric ion exchange resin has a function of allowing ion exchange with both cation and anion by making the base material cross-linked polystyrene or the like and having a quaternary ammonium group and a carboxylic acid group in the same functional group chain. It is a resin. For example, amphoteric ion exchange resin, Diaion (registered trademark), AMP03 manufactured by Mitsubishi Chemical Corporation can be used. The ion exchange resin 35 can separate the electrolyte and the non-electrolyte in the aqueous solution, and can also separate the electrolytes from each other.

  The drying device 4 dries desulfurized water L4 stored in the desulfurized water tank 38 using hot gas (hereinafter referred to as “cooler exhaust gas”) G1 discharged from a clinker cooler (not shown) attached to the cement kiln. Spray dryer 41 for obtaining industrial salt SL, bag filter 42 for collecting industrial salt SL in exhaust gas G2 discharged from spray dryer 41, and granulating industrial salt SL recovered by spray dryer 41 and bag filter 42 And a granulator 43.

  The spray dryer 41 includes an atomizing device, a hot air introduction device, a drying chamber, a dry powder separation and collection device, an exhaust treatment device, and a product cooling device, which are not shown in the drawings, and are introduced into the drying chamber via the hot air introduction device. The desulfurized water L4 is sprayed and dried on the cooler exhaust gas G1 from the atomizer.

  Next, the operation of the processing system 1 having the above configuration will be described with reference to FIG.

  The chlorine bypass dust D stored in the tank 21 is supplied to the dissolution tank 22, and the water-soluble chlorine content contained in the chlorine bypass dust D is dissolved in the warm water H supplied from the warm water tank 24. The slurry S1 discharged from the dissolution tank 22 is solid-liquid separated into the filtrate L1 and the cake C1 by the filter 23, and the cake C1 from which the chlorine content has been removed is used as a cement raw material.

  On the other hand, the filtrate L1 containing chlorine is supplied to the chemical reaction tank 32A, sodium hydrosulfide is added as a sulfiding agent to the filtrate L1 in the chemical reaction tank 32A, and lead and thallium in the filtrate L1 are sulfided. Produces lead sulfide and thallium sulfide.

  Next, the filtrate L1 is supplied from the chemical reaction tank 32A to the chemical reaction tank 32B, ferric chloride is added to the filtrate L1, and the generated sulfide is aggregated.

  Next, the slurry S2 discharged from the chemical reaction tank 32B is solid-liquid separated into the cake C2 and the filtrate L2 by the filter press 33, and the cake C2 containing heavy metal such as lead sulfide and thallium sulfide is reused as a cement raw material or the like. To do. On the other hand, the filtrate L2 discharged from the filter press 33 is filtered using the sand filter 34.

Next, the filtrate L2 filtered by the sand filter 34 is supplied to the ion exchange resin 35, and SO ₄ and selenium contained in the filtrate L2 are removed. As shown in FIG. 2, the ion exchange resin 35 performs batch processing continuously, and is pre-filled with water (FIG. 2A), and then the ion exchange resin 35 is obtained from the sand filter 34. The filtrate (stock solution) L2 is introduced, and then reclaimed water for regenerating the ion exchange resin is introduced (FIG. 2B). Then, as shown in FIG. 2 (c), first, the demineralized water L3 is discharged, and then the desulfurized water L4 and the reclaimed water L5 are discharged in this order with the passage of time. Here, the switching timing of the demineralized water L3, desulfurized water L4, and reclaimed water L5 is controlled based on any one or more of the measurement results of Cl, SO ₄ , K, Na, or Ca, electrical conductivity, and pH. Can do.

  As shown in FIG. 1, the reclaimed water L5 discharged from the ion exchange resin 35 as described above is returned to the ion exchange resin 35, the demineralized water L3 is returned to the warm water tank 24, and the desulfurized water L4 is returned to the drying apparatus 4 at the subsequent stage. dry. Thereafter, after the introduction of the filtrate L2, the regenerated water L5 is filled in the ion exchange resin 35.

Next, the cooler exhaust gas G1 is introduced into the spray dryer 41, the desulfurized water L4 stored in the desulfurized water tank 38 is supplied to the spray dryer 41, the filtrate is sprayed at a predetermined nozzle pressure, and dried with the cooler exhaust gas G1. Let The hot gas G2 used for drying the industrial salt SL is collected by the bag filter 42, and the collected industrial salt SL is collected by the granulator 43 together with the industrial salt SL dried in the air stream by the spray dryer 41. Granulate. The industrial salt SL thus obtained contains trace amounts of K ₂ SO ₄ , Na ₂ SO ₄ and CaSO ₄ in addition to KCl, NaCl and CaCl ₂ . On the other hand, the temperature of the working water is raised by the hot gas G3 discharged from the bag filter 42, and the obtained hot water H is stored in the hot water tank 24.

  As described above, according to the present embodiment, since no conventional electrodeposition apparatus or crystallization apparatus is used, electric power used for electrodeposition or heavy oil used for crystallization is unnecessary, and calcium content is removed. Since the chemical | medical agent for doing becomes unnecessary, manufacturing cost can be reduced significantly. Moreover, since no crystallization is performed, no skill is required for the production of industrial salts, and processing in a short time is possible. Furthermore, since it cools using the cooler exhaust gas G1 and heats the hot water H for washing treatment using the exhaust gas G4 used for drying, the operating cost can be further reduced.

Next, an example of the ion exchange resin 35 used in the processing system 1 will be described. As the ion exchange resin 35, the above amphoteric ion exchange resin manufactured by Mitsubishi Chemical Corporation, Diaion AMP03 was used, and the filtrate obtained by washing the chlorine bypass dust having the components shown in Table 1 with water as the stock solution was ion exchanged. 0.5 times the amount of the resin is passed through the resin 35, fresh water is passed as reclaimed water, and the amount of the flow, chloride contained in the treatment liquid that has passed through the ion exchange resin 35, SO ₄ and The relationship of the selenium concentration is shown in FIG. In the graph, the amount of liquid flow / resin amount 0 to 0.6 is demineralized water, the amount of liquid flow / resin amount 0.6 to 1.1, and desulfurized water, the amount of liquid flow / resin amount 1.1 to 1. Up to 4 is reclaimed water.

As is apparent from the graph, SO ₄ and selenium can be recovered in the demineralized water, and chloride can be recovered in the desulfurized water.

The concentrations of SO ₄ and selenium in the demineralized water L3, desulfurized water L4 and reclaimed water L5 obtained as described above are as shown in Table 2.

  Next, as a second embodiment of the method for removing selenium according to the present invention, a case where it is applied to the treatment of leachate in a final disposal site will be described with reference to FIG.

  This treatment system 51 is intended to remove heavy metals including selenium from the leachate 50a of the final disposal site 50, reduce the BOD, and discharge the same, and the same ion exchange resin 35 to that shown in FIG. A desulfurized water tank 38, a heavy metal removing device 52, and a BOD processing device 53 are provided.

  The heavy metal removing device 52 is provided for removing heavy metals such as lead other than selenium, and the chemical reaction tank 32, the filter press 33 and the like shown in FIG. 1 can be used, and other commonly used devices are used. You can also. A general removal device can be used for the BOD processing device 53 as well.

Also in the present embodiment, the ion exchange resin 35 to the desulfurized water tank 38 function in the same manner as the processing system 1 shown in FIG. 1, and SO ₄ contained in fly ash, fly ash, etc. brought into the final disposal site 50. And selenium are removed by the ion exchange resin 35, the reclaimed water L5 discharged from the ion exchange resin 35 is returned to the ion exchange resin 35, and the demineralized water L3 is returned to the final disposal site 50 to promote stabilization. Then, the heavy metal is removed using the heavy metal removing device 52, the BOD is further reduced by the BOD processing device 53, and then discharged.

As described above, in the present embodiment, selenium and SO ₄ are removed from the salt water 50a after treating the leachate from the final disposal site 50 using the ion-exchange resin 35, detoxified and then discharged. At the same time, the desalted water L3 containing SO ₄ can be returned to the final disposal site 50, and stabilization of the final disposal site 50 can be promoted.

DESCRIPTION OF SYMBOLS 1 Cement kiln combustion gas extraction dust processing system 2 Water washing device 3 Heavy metal etc. removal device 4 Drying device 21 Tank 22 Dissolution tank 23 Filter 24 Hot water tank 25 Storage tank 32 (32A, 32B) Chemical reaction tank 33 Filter press 34 Sand filter 35 ion exchange resin 36 reclaimed water tank 37 demineralized water tank 38 desulfurized water tank 41 spray dryer 42 bag filter 43 granulator 50 final disposal site 50a leachate 51 treatment system 52 heavy metal removal device 53 BOD treatment device

Claims (5)

Alternately supplying a solution containing SO ₄ and selenium and regenerated water for regenerating the ion exchange resin to the ion exchange resin;
A method for removing selenium, wherein a solution having a high SO ₄ concentration and a high selenium concentration is selectively recovered from the effluent discharged gradually and continuously from the ion exchange resin over time. . The method for removing selenium according to claim 1, wherein the solution contains at least one of NaCl, KCl, and CaCl ₂ . Based on one or more selected from the group consisting of measurement results of Cl, SO ₄ , K, Na or Ca of the effluent discharged from the ion exchange resin, electrical conductivity and pH, and the concentration of SO ₄ and The method for removing selenium according to claim 1 or 2, wherein a solution having a high selenium concentration is selectively recovered. The method for removing selenium according to claim 1, 2 or 3, wherein the solution is a filtrate obtained by washing the chlorine bypass dust generated in the cement firing step with water. The method for removing selenium according to claim 1, 2 or 3, wherein the solution is salt water generated when leachate in a final disposal site is treated.

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