JP4823192B2 - Wastewater treatment method - Google Patents

Description

  The present invention relates to a wastewater treatment method for purifying hazardous wastewater containing heavy metals and organic matter, and more particularly to a method for removing the heavy metals and organic matter in the wastewater and detoxifying the wastewater.

  Focusing on chlorine, sulfur, alkali, etc., which causes problems such as blockage of preheaters in cement manufacturing facilities, from the bottom of the kiln of the cement kiln to the bottom cyclone A chlorine bypass system for extracting a part of combustion gas and removing chlorine from the kiln exhaust gas flow path is used.

  In this chlorine bypass system, chlorine is unevenly distributed on the fine powder side of the dust generated by cooling the extracted combustion gas. At the same time, the fine powder (chlorine bypass dust) containing the separated potassium chloride and the like was recovered.

  However, the extracted combustion gas contains heavy metals such as lead and cadmium in addition to chlorine and the like, and it is appropriate whether the recovered chlorine bypass dust is discarded or returned to the raw material system. Need to be processed.

  Therefore, in Patent Document 1, in order to remove lead from chlorine bypass dust, water and sulfuric acid are mixed with chlorine bypass dust to adjust the liquidity to pH 1 to 4, and after producing a slurry containing calcium sulfate, There has been proposed a method in which a sulfide is added to a slurry to produce lead sulfide, and then a collector is added to the slurry to perform flotation, and lead sulfide is floated and recovered.

  Further, in Patent Document 2, for the same purpose as described above, chlorine bypass dust is mixed with water and sulfuric acid to adjust the liquidity to pH 4 or less, and after producing a slurry containing calcium sulfate and lead sulfate, the slurry There has been proposed a method in which an alkali agent is added to adjust the liquidity to pH 5 or higher, and then a trapping agent or the like is added to the slurry to perform flotation, and lead sulfate is precipitated to be recovered.

JP 2006-346512 A JP 2006-299394 A

  According to the processing methods described in Patent Documents 1 and 2, lead contained in the chlorine bypass dust can be effectively removed, but some of the heavy metals that could not be completely removed are subjected to flotation. It remains in the discharged wastewater. On the other hand, in recent years, the amount of heavy metals such as lead brought into cement kilns has increased as the recycling of wastes into cement raw materials or fuels has been promoted and the amount of waste processed has increased.

  In the above processing method, as a pretreatment for flotation, a hydrophobizing agent (eg, xanthate) or the like as a collecting agent is added to the slurry, and the organic compound such as the hydrophobizing agent is added during the flotation. However, when the wastewater is discharged, it is also required to remove these components.

  These problems are not limited to the flotation wastewater generated when flotation of chlorine bypass dust slurry is generated, but also occurs when flotation of wastewater generated by flotation of soot and slurries and polluted soil slurry. In the case of drainage, etc., it occurs almost in the same way, and it is necessary to appropriately detoxify it.

  Therefore, the present invention has been made in view of the problems in the conventional technology described above, and purifies harmful wastewater containing heavy metals and organic matter, and renders the wastewater harmless to a state where it can be discharged. It aims at providing the waste water treatment method which can be.

In order to achieve the above object, the present invention provides a flotation wastewater comprising a filtrate obtained by solid-liquid separation of floss generated during flotation and / or a filtrate obtained by solid-liquid separation of a tail. a waste water treatment method for purifying process, after adjusting the pH of the wastewater to a predetermined value, pH and solid-liquid separation drainage adjusted, and heavy metals treatment step of removing the heavy metals of the exhaust water, the heavy metal And an organic matter treatment step of adding an oxidant to the wastewater from which the kind has been removed and oxidizing the organic matter in the wastewater.

  According to the present invention, it is possible to remove heavy metals and organic compounds contained in the wastewater, and it is possible to render the wastewater harmless to a state where it can be discharged.

  In the wastewater treatment method, in the heavy metal treatment step, the pH of the wastewater can be adjusted to 10 or more and 12 or less, and according to this, it is possible to effectively remove heavy metals contained in the wastewater. .

In the wastewater treatment method, the oxidizing agent is at least one selected from the group consisting of hydrogen peroxide (H ₂ O ₂ ), sodium hypochlorite (NaClO), ozone (O ₃ ), and oxygen (O ₂ ). Seeds can be used.

  In the waste water treatment method, in the heavy metal treatment step, secondary filtration by sand filtration of the filtrate discharged by the solid-liquid separation and / or chelate of heavy metals in the filtrate discharged by the solid-liquid separation Adsorption removal by resin can be performed. According to this, heavy metals that could not be completely removed by solid-liquid separation can be removed, and it becomes possible to further purify the waste water.

In the waste water treatment method, the heavy metal treatment step comprises ferrous chloride (FeCl ₂ ), ferrous sulfate (FeSO ₄ ), and sodium hydrosulfide (NaHS) with respect to waste water containing the heavy metals and organic matter. At least one reducing agent selected from the group can be further added. According to this, since it is possible to reduce the selenium compound in the wastewater to produce a poorly soluble selenium compound, and the produced poorly soluble selenium compound can be separated from the wastewater by solid-liquid separation. It becomes possible to reduce the selenium content in the waste water.

  As described above, according to the present invention, it is possible to purify harmful wastewater containing heavy metals and organic matter, and to render the wastewater harmless to a state where it can be discharged.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a first embodiment of a system to which a wastewater treatment method according to the present invention is applied. This wastewater treatment system 1 is roughly composed of a lead recovery facility 2 and a wastewater treatment facility 3.

  The lead recovery facility 2 is a facility for recovering lead in dust (chlorine bypass dust) contained in the combustion gas extracted from the kiln exhaust gas passage from the kiln bottom of the cement kiln to the bottom cyclone. Pretreatment equipment 4 for performing pH adjustment, sulfidation, addition of a collecting agent, and the like, and slurry S1 supplied from the pretreatment equipment 4 are subjected to flotation, and lead sulfide is removed from the slurry S1. It comprises a flotation equipment 5 for separation and solid-liquid separators 6 and 7 for separating the floss F and tail T collected by the flotation equipment 5 from each other.

The pretreatment facility 4 adds lead sulfide to the slurryed chlorine bypass dust to produce lead sulfide, and adds sulfuric acid to react with calcium in the slurry to produce calcium sulfate. It is provided for adding agents and foaming agents. As the sulfiding agent, sodium hydrosulfide (NaSH), sodium sulfide (Na ₂ S), hydrogen sulfide gas (H ₂ S), or the like can be used.

  In addition, as a collecting agent, xanthate, acidic dithiophosphates (trade name: Elofloat), alkyl sulfates such as sodium n-dodecyl sulfate, unsaturated aliphatic carboxylates such as sodium oleate, etc. should be used. Can do.

  Furthermore, as a foaming agent, methyl isobutyl carbinol (MIBC; 4-methyl-2-pentanol), methyl isobutyl ketone, pine oil, ethylene glycol, propylene glycol methyl ether, cresolic acid, or the like can be used.

  The flotation equipment 5 is provided for flotation of the slurry S1 supplied from the pretreatment equipment 4 and separating lead sulfide from the slurry S1. In the flotation beneficiation equipment 5, the lead sulfide in the slurry S <b> 1 adheres to the bubbles generated inside and floats, and is recovered as floss F. The calcium sulfate in the slurry S1 settles at the bottom of the liquid in the flotation equipment 5 and is discharged together with the tail T.

  The solid-liquid separator 6 is provided for solid-liquid separation of the floss F collected by the flotation equipment 5, and separates the floss F into a cake C1 and a filtrate W1. The solid-liquid separator 7 is provided for solid-liquid separation of the tail T supplied from the flotation beneficiation equipment 5, and separates the tail T into cake C2 and filtrate W2.

  The wastewater treatment facility 3 is a facility for detoxifying industrial wastewater generated in the lead recovery facility 2, and includes a slurry tank 11, a filter press 12, a regulating tank 13, a sand filter 14, and a chelate resin tower. 15 and an organic matter treatment tank 16.

  The slurry tank 11 is provided for adjusting the pH of the filtrate W3 by adding an alkaline agent to the filtrate (floating beneficiation wastewater) W3 (W1 + W2) discharged from the solid-liquid separators 6 and 7. In addition, as an alkali agent, slaked lime slurry, caustic soda, sodium carbonate, etc. can be used, These 1 type may be used independently and 2 or more types may be used together.

  The filter press 12 is provided for solid-liquid separation of the slurry S2 generated in the slurry tank 11 and recovering heavy metals remaining in the slurry S2. The cake C3 generated by the filter press 12 is reused as a cement raw material or the like.

  The adjustment tank 13 is provided for adding hydrochloric acid to the filtrate W4 discharged from the filter press 12 and adjusting the pH of the filtrate W4 to 4-6. The filtrate W4 whose pH is adjusted is secondarily filtered by the sand filter 14, and then the heavy metal is adsorbed and removed by the chelate resin in the chelate resin tower 15 to purify the filtrate W4.

The organic matter treatment tank 16 is provided to add an oxidizing agent to the filtrate W5 purified by the sand filter 14 and the chelate resin tower 15 and oxidize organic compounds dissolved in the filtrate W5. As the oxidizing agent, hydrogen peroxide water (H ₂ O ₂ ), sodium hypochlorite (NaClO), ozone (O ₃ ), oxygen (O ₂ ), etc. can be used, and one of these can be used alone. You may use, and may use 2 or more types together.

  Next, the waste water treatment method according to the present invention will be described with reference to FIG.

  Chlorine bypass dust is supplied to the pretreatment facility 4 and mixed with water to produce a slurry, and then a sulfiding agent and sulfuric acid are added to produce lead sulfide and calcium sulfate. Next, a hydrophobizing agent as a collecting agent and a foaming agent are added to the slurry.

  Next, the slurry S1 from the pretreatment facility 4 is supplied to the flotation beneficiation facility 5, and bubbles are generated in the flotation beneficiation facility 5, and lead sulfide in the slurry S1 is adhered to the bubbles. Thereafter, the air bubbles floating together with the lead sulfide are recovered, and the recovered froth F is supplied to the solid-liquid separator 6. The calcium sulfate contained in the slurry S1 settles without adhering to the bubbles and is supplied to the solid-liquid separator 7 together with the tail T.

  Next, the solid-liquid separator 6 performs solid-liquid separation of the froth F from the flotation equipment 5 to recover lead sulfide. Since the dehydrated lead sulfide has a low content of components other than lead sulfide, it is reused as a non-ferrous refining raw material by Yamamoto reduction.

  At the same time, the tail T from the flotation equipment 5 is solid-liquid separated by the solid-liquid separator 7 and calcium sulfate is recovered as gypsum. The collected gypsum is reused by adding it to a cement mill or the like.

  Next, the filtrate W3 of the solid-liquid separators 6 and 7 is supplied to the slurry tank 11, and in the slurry tank 11, an alkaline agent such as slaked lime slurry is added to the filtrate W3 to adjust the pH of the filtrate W3. . The pH of the filtrate W3 at this time is preferably adjusted to 10-12.

  Next, the pH-adjusted slurry S <b> 2 is supplied to the filter press 12, and solid-liquid separation is performed by the filter press 12. Then, the slurry S2 is separated into the filtrate W4 and the cake C3, and the separated cake C3 is recovered. Thereby, the heavy metals in the slurry S2, that is, the heavy metals remaining in the flotation wastewater W3 of the flotation equipment 5 are recovered.

  Next, the filtrate W4 of the filter press 12 is supplied to the adjustment tank 13, and in the adjustment tank 13, hydrochloric acid as a neutralizer is added to the filtrate W4 to adjust the pH of the filtrate W4 to 4-6. . Thereafter, the pH-adjusted filtrate W4 is supplied to the sand filter 14 for secondary filtration, and the chelate resin tower 15 adsorbs and removes heavy metals remaining in the filtrate W4.

  Next, the filtrate W5 from which heavy metals have been removed is supplied to the organic matter treatment tank 16, and in the organic matter treatment tank 16, hydrochloric acid is added to the filtrate W5 to adjust the pH of the filtrate W5 to 2-4. Thereafter, an oxidizing agent such as hydrogen peroxide is added to the filtrate W5 whose pH has been adjusted, and the organic compound dissolved in the filtrate W5 is oxidized and decomposed. At this time, for example, when 35% hydrogen peroxide is used as the oxidizing agent, the amount added is 0.5 to 2 ml / l with respect to 1 liter of the filtrate W5 in consideration of the chemical cost and the like. Is preferred.

  Finally, caustic soda (NaOH) is added to the filtrate W5 in which the organic compound has been decomposed, and the pH of the filtrate W5 is adjusted to the neutral range of 6-8. The pH-adjusted filtrate W6 can be discharged into the sewer.

  As described above, according to the present embodiment, the filtrate W3 discharged from the lead recovery facility 2 is subjected to heavy metal removal treatment to remove heavy metals, and then to the filtrate W5 from which heavy metals have been removed. In order to decompose the organic compound in the filtrate W5 by adding an oxidizing agent, it is possible to remove heavy metals and organic compounds contained in the flotation wastewater W3 when the chlorine bypass dust is treated. It is possible to make it harmless to a state where it can be discharged.

  In the above embodiment, the precipitated heavy metals are removed after adding the alkaline agent to the filtrate W3. However, when the concentration of heavy metals in the filtrate W3 is low, these operations are replaced. Heavy metals can be adsorbed and removed by the chelate resin.

Further, when treating the filtrate W3, a flocculant such as ferric chloride (FeCl ₃ ) or sulfuric acid band (aluminum sulfate, Al ₂ (SO ₄ ) ₃ ) or a liquid chelate generally used in waste water treatment. An agent can also be used.

  Next, a second embodiment of the system to which the wastewater treatment method according to the present invention is applied will be described with reference to FIG. In addition, in the figure, the same code | symbol is attached | subjected about the component same as the waste water treatment system 1 shown in FIG. 1, and the description is abbreviate | omitted. The lead recovery facility is the same as the lead recovery facility 2 of FIG.

  The waste water treatment system 20 shown in FIG. 2 has a basic configuration substantially the same as that of the waste water treatment system 1 shown in FIG. 1, and is different in that the waste water treatment facility 3 includes an adjustment tank 21.

The adjustment tank 21 is arranged on the upstream side of the slurry tank 11 and is provided for removing selenium contained in the filtrate W3 from the solid-liquid separators 6 and 7 (see FIG. 1). In the adjustment tank 21, first, hydrochloric acid is added to the filtrate W3 to adjust the pH of the filtrate W3 to 4 or less, and then a reducing agent is added to the filtrate W3 whose liquidity has been adjusted. The selenium compound in the inside is reduced to produce a poorly soluble selenium compound. Here, ferrous chloride (FeCl ₂ ), ferrous sulfate (FeSO ₄ ), sodium hydrosulfide (NaHS), or the like can be used as the reducing agent.

  The produced poorly soluble selenium compound is separated from the slurry S2 by solid-liquid separation in the filter press 12, and thereby selenium contained in the flotation wastewater W3 is removed. The pH of the slurry S2 in the slurry tank 11 is preferably adjusted to 8 to 12, preferably 8 to 10.

  According to the wastewater treatment system 20, selenium contained in the flotation wastewater W3 when chlorine bypass dust is treated can be removed, and even if the wastewater W3 contains a large amount of selenium, Can be reduced below the discharge standard value.

  Hereinafter, the present invention will be described more specifically with reference to examples.

  Using the waste water treatment system 1 of FIG. 1, chlorine bypass dust was treated while changing the pH of the slurry S2 in the slurry tank 11 in the range of 8 to 12, and the filtrate W4 of the filter press 12 at that time was analyzed. . In addition, the filtrate W3 upstream of the slurry tank 11 was also analyzed.

  The analysis results are shown in Table 1. Here, each numerical value in Table 1 indicates the amount of heavy metals per liter of solution, and the unit is mg / l. In Table 1, “ND” indicates that the heavy metal to be detected was not detected.

  As shown in Table 1, when the pH of the slurry S2 is adjusted to 10 to 11, no heavy metals are detected, and the heavy metals in the filtrate W3 supplied to the slurry tank 11 are reliably removed. It turns out that you can. In addition, when the pH of the slurry S2 was adjusted to 12, iron (Fe) and zinc (Zn) were detected, but both are well below the discharge standard value and the filtrate W3 can be sufficiently purified. I understood. On the other hand, when the pH was adjusted to 8-9, the cadmium (Cd) content exceeded the discharge standard value, and the filtrate W3 could not be rendered harmless to a state where it could be discharged.

  Next, chlorine bypass dust having a high selenium content is treated using the wastewater treatment system 20 of FIG. 2, and the filtrate W3 upstream of the slurry tank 11 and the filtrate W6 discharged from the organic matter treatment tank 16 are obtained. Each was analyzed. Moreover, in the organic substance processing tank 16, the oxidizing agent was added, the organic compound was oxidized, and the iodine consumption in the filtrate W6 was measured.

  Here, the pH of the slurry S2 in the slurry tank 11 was adjusted to 9, and the pH of the filtrate W5 in the organic matter treatment tank 16 was adjusted to 3. Further, hydrogen peroxide water was used as an oxidizing agent in the organic matter treatment tank 16. The analysis results of the filtrates W3 and W6 are shown in Table 2, and the measurement results of iodine consumption are shown in Table 3. In addition, the unit of the analysis value etc. in both tables is mg / l.

  As shown in Table 2, lead (Pb), zinc (Zn), and selenium (Se) were detected in the filtrate W6 after the oxidation treatment, and all of them were 1/10 or less of the discharge standard value. It was confirmed that the amount of the waste water W3 from the lead recovery facility 2 can be made harmless by a small amount.

  Further, as shown in Table 3, it was confirmed that the iodine consumption in the filtrate W6 after the oxidation treatment was significantly lower than the legal standard value and there was no problem from the environmental aspect.

  Next, the organic compound in the filtrate W5 was processed using the wastewater treatment system 20 of FIG. 2 while adjusting the amount of the oxidizing agent. Here, 35% hydrogen peroxide water was used as the oxidizing agent. The relationship between the addition amount of 35% hydrogen peroxide water and the iodine consumption amount in the waste water W6 is shown in FIG.

  As shown in FIG. 3, when 35% hydrogen peroxide solution is not used, the iodine consumption is about 1100 mg / l, whereas to make the iodine consumption 0 mg / l, about 1.3 ml / L of 35% hydrogen peroxide solution was found to be required. Taking into account the release standard value of iodine consumption, it was found that an addition amount of 35% hydrogen peroxide water of 0.7 ml / l or more is preferable. Each value in FIG. 3 varies depending on the chlorine bypass dust to be treated and the conditions of the flotation treatment, etc. It is the test example about the waste_water | drain at the time of setting it as the addition amount of a foaming agent.

It is a flowchart which shows 1st Embodiment of the system to which the waste water treatment method concerning this invention is applied. It is a flowchart which shows 2nd Embodiment of the system to which the waste water treatment method concerning this invention is applied. It is a graph which shows the relationship between the addition amount of 35% hydrogen peroxide water in organic substance processing, and iodine consumption.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wastewater treatment system 2 Lead recovery equipment 3 Wastewater treatment equipment 4 Pretreatment equipment 5 Flotation equipment 6 Solid-liquid separator 7 Solid-liquid separator 11 Slurry tank 12 Filter press 13 Adjustment tank 14 Sand filter 15 Chelate resin tower 16 Organic substance treatment Tank 20 Wastewater treatment system 21 Adjustment tank

Claims (5)

A wastewater treatment method for purifying a flotation wastewater comprising a filtrate obtained by solid-liquid separation of floss generated during flotation and / or a filtrate obtained by solid-liquid separation of a tail ,
After adjusting the pH of the wastewater to a predetermined value, and heavy metals treatment step the pH was solid-liquid separated exhaust water adjusted to remove the heavy metals of the exhaust water,
A wastewater treatment method comprising: an organic matter treatment step of adding an oxidizing agent to the wastewater from which the heavy metals have been removed, and oxidizing organic matter in the wastewater. The wastewater treatment method according to claim 1, wherein, in the heavy metal treatment step, the pH of the wastewater is adjusted to 10 or more and 12 or less . The oxidizing agent is at least one selected from the group consisting of hydrogen peroxide (H ₂ O ₂ ), sodium hypochlorite (NaClO), ozone (O ₃ ), and oxygen (O ₂ ). The waste water treatment method according to claim 1 or 2.   In the heavy metal treatment step, secondary filtration by sand filtration of the filtrate discharged by the solid-liquid separation and / or adsorption removal of heavy metals in the filtrate discharged by the solid-liquid separation by a chelate resin are performed. The wastewater treatment method according to claim 1, 2, or 3. In the heavy metal treatment step, at least one selected from the group consisting of ferrous chloride (FeCl ₂ ), ferrous sulfate (FeSO ₄ ), and sodium hydrosulfide (NaHS) with respect to the wastewater containing the heavy metals and organic matter. The waste water treatment method according to any one of claims 1 to 4, wherein a seed reducing agent is further added.

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