JP2017159194A - Treatment equipment and treatment method for heavy metal-containing water - Google Patents

Abstract

An object of the present invention is to provide a heavy metal-containing water treatment apparatus and a treatment method that suppress the amount of sludge generated while maintaining a high heavy metal removal rate when removing heavy metals from heavy metal-containing water using a ferrous salt. SOLUTION: A reaction vessel 10 as a reaction means for carrying out a reduction reaction and an aggregation reaction of heavy metals in heavy metal-containing water at a temperature of 60° C. or more and less than 100° C. and a pH of 7 or more in the presence of a ferrous salt, and a reduction reaction and an aggregation reaction. A circulation means for circulating a part of the reaction water in which the is being carried out through a circulation line 38, an ejector 24 as a mixing means for supplying and mixing an oxygen-containing gas into the reaction water in the circulation line 38, and aggregating heavy metals Solid-liquid separation means for separating aggregates from reacted aggregation reaction water. [Selection drawing] Fig. 1

Description

  The present invention relates to a technique for treating heavy metal-containing water and a method for treating heavy metal-containing water.

  In coal-fired power generation, a desulfurization facility is installed to purify the exhaust gas generated by burning coal, and the sulfur content in the exhaust gas and the dust collector are not removed by water in which calcium hydroxide or magnesium hydroxide is dissolved. Removes dust and so on. Water that has absorbed sulfur, dust, etc. is appropriately discharged from the desulfurization facility as desulfurization effluent, treated to a level below the effluent standard, and discharged to the ocean. This desulfurization wastewater often contains heavy metals such as selenium, and it may be present at a value exceeding the wastewater standard depending on the production area and type of coal used. Also, in coal gasification power generation, heavy metals such as selenium may exist in wastewater discharged from gas purification equipment attached to power generation equipment (hereinafter referred to as coal gasification wastewater) at a value exceeding the wastewater standard value. It is supposed to be.

  Other than power generation facility wastewater, for example, selenium and the like may be present in glass manufacturing wastewater, and mine wastewater and the like, in addition to selenium, heavy metals such as arsenic and chromium may be present at values exceeding the wastewater standard value .

  A treatment apparatus or treatment method for removing heavy metals from these heavy metal-containing waters to below the drainage standard value has been considered and put into practical use. For example, there are an alkali coagulation precipitation method for producing a heavy metal hydroxide with alkali, a method of coagulating heavy metal with a ferric salt or the like by adding a heavy metal collector. However, in the case of wastewater containing a plurality of types of heavy metals, the alkali coagulation sedimentation method may differ in the appropriate pH for aggregation depending on each heavy metal, and the batch treatment of each heavy metal may be difficult. In addition, heavy metal scavengers cannot collect elements such as selenium and are expensive, so that the cost of treatment may be high depending on the properties of drainage.

  Among heavy metals, selenium is particularly difficult to agglomerate and separate. In the case of hexavalent selenium, it is difficult to remove the selenium as it is by agglomeration. Aggregates and the aggregates are removed by solid-liquid separation.

  Conventionally, there has been known a method of reducing selenium or the like with ferrous salt, adjusting pH to insolubilize the iron salt, and agglomerating solid-liquid separation of the reduced selenium and other heavy metals. An improved invention for the coagulation sediment removal of selenium with ferrous salts is disclosed.

  The method of removing heavy metals from water containing heavy metals with ferrous salts has the advantage that a plurality of types of heavy metals can be treated at once, and ferrous salts are relatively inexpensive and easily available as industrial chemicals. However, in order to reduce selenium to a low concentration, for example, less than the wastewater standard value of less than 0.1 mg / L, the amount of ferrous salt required increases, so a large amount of iron hydroxide aggregates (sludge) are generated. In addition, there is a problem that the processing efficiency is lowered, for example, the sedimentation concentration property of the aggregate is poor and the equipment capacity must be increased.

  On the other hand, in Non-Patent Document 1, ferrous salt and air are added in a state where the heavy metal-containing water is at a high temperature of 60 to 70 ° C., thereby agglomerating the metal and partially converting iron hydroxide to ferrite. A method of treating a plurality of types of heavy metals at once by changing to the above is disclosed.

  However, Non-Patent Document 1 discloses a reaction condition for efficiently improving the sedimentation concentration of aggregates and reducing the amount of sludge generation while reducing each heavy metal from the heavy metal-containing water containing selenium to below the drainage standard value. Etc. are not specified.

  Further, in Non-Patent Document 1, oxygen (air) is supplied to the reaction tank by a compressor or the like in order to change a part of iron hydroxide to ferrite, but excessive aeration increases the power cost, Depending on the supply method, a part of the reduced tetravalent selenium may be oxidized to hexavalent selenium which is not easily aggregated, and the quality of the treated water may be deteriorated.

Japanese Patent No. 395978

New Civil Engineering 90 Water Treatment-Unit Operation and Industrial Water / Waste Water-March 20, 1982, Mitsumi Kaneko and Kenji Fujita, published by Gihodo Publishing Co., pp. 62-63

  An object of the present invention is to provide a treatment apparatus and treatment method for heavy metal-containing water that suppresses sludge generation while maintaining a high heavy metal removal rate when removing heavy metal from heavy metal-containing water using ferrous salt. There is to do.

  In the present invention, in the presence of a ferrous salt, a reaction means for performing a reduction reaction and an agglomeration reaction of heavy metal in heavy metal-containing water at a temperature of 60 ° C. to less than 100 ° C. and a pH of 7 or more, and the reduction reaction and the aggregation reaction are performed. A circulation means for circulating a part of the reaction water through the circulation line, a mixing means for supplying and mixing the oxygen-containing gas to the reaction water in the circulation line, and agglomeration from the agglutination reaction water obtained by agglomeration reaction of the heavy metal And a solid-liquid separation means for separating an object.

  The amount of oxygen supplied in the mixing means in the heavy metal-containing water treatment apparatus is 0.01 to 0.11 L (ntp) / g-Fe with respect to the addition amount of the ferrous salt converted to iron concentration. A range is preferable.

  In the apparatus for treating heavy metal-containing water, the mixing means is preferably an ejector or a compressor and a line mixer.

  The present invention also includes a reaction step for performing a reduction reaction and an agglomeration reaction of heavy metal in heavy metal-containing water, and a reduction reaction and an aggregation reaction in the presence of a ferrous salt at a temperature of 60 ° C. to less than 100 ° C. and pH 7 or higher. A circulation step of circulating a part of the reaction water through a circulation line, a mixing step of supplying and mixing oxygen-containing gas to the reaction water in the circulation line, and agglomeration reaction water obtained by agglomeration reaction of the heavy metal And a solid-liquid separation step of separating the agglomerates from the heavy metal-containing water treatment method.

  The amount of oxygen supplied in the mixing step in the method for treating heavy metal-containing water is 0.01 to 0.11 L (ntp) / g-Fe with respect to the added amount of the ferrous salt converted to iron concentration. A range is preferable.

  In the mixing step in the method for treating heavy metal-containing water, it is preferable that the oxygen-containing gas is supplied to the reaction water and mixed using an ejector, a compressor, and a line mixer.

  ADVANTAGE OF THE INVENTION According to this invention, when removing heavy metal using ferrous salt from heavy metal containing water, the heavy metal containing water processing apparatus and the processing method which suppress sludge generation amount are maintained, maintaining a high heavy metal removal rate. can do.

It is a schematic block diagram which shows an example of the processing apparatus of the heavy metal containing water which concerns on embodiment of this invention. It is a schematic block diagram which shows the processing apparatus of the heavy metal containing water used by the Example and the comparative example.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  The schematic structure of an example of the processing apparatus of the heavy metal containing water which concerns on embodiment of this invention is shown in FIG. 1, and the structure is demonstrated.

The heavy metal-containing water treatment apparatus 1 includes a reaction tank 10 as a reaction means. The reaction vessel 10 may function as a solid-liquid separation unit. The reaction tank 10 is provided with a stirrer 12 as stirring means, a pH meter 14 as pH measuring means, a thermometer 16 as temperature measuring means, and a heater 18 as heating means. In the upper part of the reaction tank 10, a heavy metal-containing water supply line 30 and
A ferrous salt addition line 32 as a ferrous salt addition means, a pH adjuster addition line 34 as a pH adjustment means, a polymer flocculant addition line 36 as an aggregate coarsening means, and an exhaust gas line 46 It is connected. A lower part and an upper part of the reaction tank 10 are connected by a circulation line 38 via a circulation pump 20 as a circulation means. The circulation line 38 is, for example, a pipe made of a metal such as stainless steel or a heat resistant resin such as heat resistant vinyl chloride. From the viewpoint of preventing sedimentation of suspended substances in the pipe, the pipe diameter is The diameter is preferably such that the pipe flow velocity is 0.5 m / sec or more. Between the circulation pump 20 and the upper connection part of the reaction tank 10 in the circulation line 38, a flow meter 22 and an ejector 24 as a mixing means are installed. A gas line 48 that is sucked by the ejector 24 is connected to the ejector 24, and a gas flow meter 26 is installed in the gas line 48. A treated water line 40 is connected between the circulation pump 20 and the flow meter 22 in the circulation line 38 via a valve 28, and the treated water line 40 is connected to the treated water discharge line 42 and sludge downstream of the valve 28. Branches to a discharge line 44.

  Operation | movement of the processing method 1 of the heavy metal containing water processing apparatus and heavy metal containing water which concern on this embodiment is demonstrated.

  The heavy metal-containing water to be treated by the heavy metal-containing water treatment method and treatment apparatus according to the present embodiment is not particularly limited as long as the heavy metal-containing water is used, and includes, for example, desulfurization wastewater from a coal-fired power plant, In addition to coal gasification wastewater from coal gasification power generation, glass production wastewater, mine wastewater and the like can be mentioned.

  The heavy metal to be removed is at least one of selenium, chromium, copper, zinc, arsenic, cadmium, lead and the like. The method and apparatus for treating heavy metal-containing water according to the present embodiment is suitably applied to heavy metal-containing water containing two or more heavy metals, and includes selenium, chromium, copper, zinc, arsenic, cadmium, lead, and the like. It is suitably applied to heavy metal-containing water containing at least one of them.

  Content of the heavy metal in the heavy metal containing water used as a process target is the range of 0.1 mg / L-10 mg / L, for example.

  First, the heavy metal-containing water that is the water to be treated is supplied to the reaction tank 10 through the heavy metal-containing water supply line 30. The stirrer 12 is operated, and the heavy metal-containing water is heated to a predetermined temperature by the heater 18 or the like (heating step). A predetermined amount of ferrous salt is added to the reaction tank 10 through the ferrous salt addition line 32 (a ferrous salt addition step). Further, a predetermined amount of acid or alkali is added as a pH adjuster through the pH adjuster addition line 34, the pH is adjusted to an alkaline predetermined pH (pH adjustment step), and a reduction reaction and an aggregation reaction are performed (reaction step).

  After the addition of the ferrous salt and the pH adjuster, the circulation pump 20 is started, and a part of the reaction water in which the reduction reaction and the aggregation reaction are performed is circulated from the lower part to the upper part of the reaction tank 10 through the circulation line 38. (Circulation process). When passing through the ejector 24 in the circulation line 38, air is sucked as an oxygen-containing gas, and the sucked air is turned into fine bubbles, supplied to the reaction water, mixed and dissolved (mixing step).

In the reaction tank 10 and the circulation line 38, when the heavy metal-containing water contains selenium, the ferrous iron reduces hexavalent selenium to tetravalent selenium and tetravalent selenium to zero-valent selenium. It is considered that most of the ferrous iron is changed into a form of insoluble matter called ferrite by the sucked air. Reduced tetravalent selenium, zero-valent selenium and other heavy metals are adsorbed and aggregated on the insoluble ferrite. Some of the added ferrous salt may exist as divalent dissolved iron ions, but it can be insolubilized by adjusting the pH of the reaction water to 7 or more, preferably in the range of pH 8-10. . Aggregates containing iron ferrite and iron hydroxide have higher sedimentation and concentration than aggregates containing only iron hydroxide. In addition, although the main component of the ferrite formed by reaction is considered to be Fe ₃ O ₄ or the like, the detailed chemical composition is unknown.

  The undissolved air (mainly nitrogen or the like) is transferred from the aqueous phase to the gas phase in the reaction tank 10 and discharged out of the system through the exhaust gas line 46.

  Next, after the circulation pump 20 is stopped and the circulation of the reaction water is completed, the polymer flocculant addition line is added to the reaction water (including heavy metals adsorbed and aggregated on iron insoluble matter such as ferrite) as necessary. Through 36, a polymeric flocculant may be added. The aggregate is coarsened by the polymer flocculant, and further changed into an aggregate having high sedimentation and concentration (aggregate coarsening step).

  Thereafter, the stirrer 12 in the reaction vessel 10 is stopped, the agglomerated water is allowed to stand for a predetermined time, and the agglomerate on which heavy metals are adsorbed and agglomerated is precipitated. The precipitated agglomerates are withdrawn by the circulation pump 20 with the valve 28 opened, and sent to the sludge storage tank as sludge through the treated water line 40 and the treated water discharge line 42, while the supernatant water is treated with the treated water line. 40, It is discharged from the reaction tank 10 as treated water through the treated water discharge line 42 (solid-liquid separation step).

  According to the method and apparatus for treating heavy metal-containing water according to the present embodiment, when removing heavy metal from heavy metal-containing water using ferrous salt, the amount of sludge generated is suppressed while maintaining a high heavy metal removal rate. can do. By supplying and mixing oxygen-containing gas to the reaction water in the circulation line, and adding the ferrous iron into the form of ferrite with high sedimentation concentration, there are multiple types of heavy metals contained in the heavy metal-containing water. Moreover, sludge generation amount can be suppressed while maintaining a high removal rate with respect to heavy metals. In addition, since the oxygen-containing gas is supplied to the reaction water and mixed in the circulation line, the oxygen dissolution efficiency is high, and the power required for supplying the oxygen-containing gas can be reduced. Can be suppressed. In addition, the running cost is reduced accordingly.

  When the heavy metal-containing water contains selenium, ferrous salt is added to the heavy metal-containing water containing selenium to reduce selenium at a pH suitable for the reduction of hexavalent selenium, and the circulation of the reaction water and the circulation line Ferritification is promoted by mixing of oxygen-containing gas (oxygen supply) in, and agglomerates heavy metals such as selenium. Then, by adjusting the pH to a higher level, the dissolved iron remaining in the water is insolubilized, so that heavy metals such as selenium are effectively removed, and the sedimentation and concentration of aggregates are improved. The amount of discharged sludge is suppressed.

  Below, the conditions in each processing process, a modification, etc. are demonstrated.

<Heating process>
The heating time of the heavy metal-containing water that is the water to be treated may be any time when the ferrous salt is added, not only before the ferrous salt is added, but also during the addition of the ferrous salt, Also included after addition of ferrous salt. And the heating temperature of the heavy metal containing water in a heating process should just be the temperature of the grade which water does not boil, and should just be the range of 60 degreeC or more and less than 100 degreeC, but should be the range of 60 degreeC or more and 95 degrees C or less. Is preferable, and the range of 65 ° C. or higher and 75 ° C. or lower is more preferable. When the heavy metal-containing water contains selenium, if the water temperature is less than 50 ° C., the rate of reduction of selenium by the ferrous salt is slow, so the amount of ferrous salt added becomes large, and the formation of ferrite and the like through a series of reactions Therefore, a solid substance with a small amount of iron hydroxide is generated, and a large amount of sludge having poor sedimentation concentration is likely to be generated. Moreover, even if the temperature of the heavy metal-containing water containing selenium exceeds 95 ° C, the energy cost required for heating is almost the same as when the temperature is less than 95 ° C in terms of suppressing the amount of ferrous salt required and sludge generation. Only can be expensive.

  The heating means is not particularly limited as long as it can heat the heavy metal-containing water, which is the water to be treated, to a predetermined temperature, and examples thereof include a heater such as an electric heater and a steam injection pipe.

<Ferrous salt addition process>
The amount of ferrous salt greatly varies depending on the heavy metal concentration of heavy metal-containing water, the amount of coexisting ions, and the like. When the heavy metal-containing water contains hexavalent selenium, the addition amount of the ferrous salt that is likely to cause a reduction reaction is desirable. If the selenium concentration is approximately 1 mg / L or less, the addition amount of the ferrous salt is the iron concentration. If the range is 50 to 300 mg / L and the selenium concentration is 1 to 10 mg / L, the iron concentration range is 300 to 5000 mg / L.

Examples of the ferrous salt include ferrous chloride (FeCl ₂ ), ferrous sulfate (FeSO ₄ ), etc., which are previously dissolved in water, acid, etc. and added in the form of a ferrous ion solution. It is good to do.

  Here, the heavy metal concentration in the heavy metal-containing water that is the water to be treated is preferably measured by, for example, sampling periodically and using a hydride generation ICP emission method or ICP mass spectrometry method defined in JIS K0102.

<PH adjustment step>
The pH of the water to be treated in the reaction tank 10 shifts to the acidic side when the ferrous salt changes to iron hydroxide. To this, an alkali or an acid is added as a pH adjusting agent to adjust to a predetermined pH of pH 7 or more, preferably pH 7-10.

  Examples of the pH adjuster include sodium hydroxide and calcium hydroxide if they are alkaline, and examples include sulfuric acid and hydrochloric acid if they are acids.

<Reaction process>
In the reaction process, a part of the reaction water in which the reduction reaction and the aggregation reaction are performed is circulated, and the oxygen-containing gas is supplied in the circulation line 38 and mixed. The reaction time of the ferrous salt is preferably in the range of 5 minutes to 60 minutes. That is, the residence time of the reaction water in the reaction vessel 10 is preferably in the range of 5 minutes to 60 minutes. When the reaction time is less than 5 minutes, the ferritization reaction of iron and the agglomeration reaction of heavy metal are not sufficiently performed, and the removal rate of heavy metal may be reduced. Even if the reaction time exceeds 60 minutes, the removal rate of heavy metals hardly changes, and the amount of sludge hardly decreases any more.

  In the reaction vessel 10, the ferrous salt and the pH adjuster are added and then mixed immediately to ensure many contact opportunities between the heavy metal and the ferrous iron. Reduction reactions such as selenium, agglomeration of other heavy metals, In order to promote ferritization and the like, it is preferable to install a stirrer 12 or the like as a stirring means.

  When the heavy metal-containing water contains selenium, the pH may be changed by additionally adding an alkali such as sodium hydroxide from the pH adjuster addition line 34 during the reaction process. At first, in order to promote the reduction of hexavalent selenium to tetravalent selenium and zero valent selenium, the pH is adjusted in the range of 7.0 to 7.8, and the reaction is performed, for example, for about 5 to 30 minutes. Is added to increase the pH to the range of 8.2 to 10.0, for example, the reaction is performed for about 5 to 30 minutes, and the selenium is agglomerated and insolubilized in the ferrite while insolubilizing the dissolved iron remaining in the reaction. It is better to promote.

  The reaction time in the reaction step when the heavy metal-containing water contains selenium is preferably 5 minutes or more in total. If the reaction time is less than 5 minutes, sufficient ferritization is not performed, and the sedimentation and concentration of aggregates may not be improved. The reaction time should be long, but the processing rate of heavy metal-containing water containing selenium is reduced and the capacity of the apparatus is increased, so it is preferable to set the upper limit of about 60 minutes.

<Circulation process, mixing process>
During the reaction process, for example, the reaction water is circulated by the circulation pump 20 and the circulation line 38, and the oxygen-containing gas is supplied and mixed during the circulation.

  Ferritification is best promoted after the outlet of the mixing means to which oxygen-containing gas is supplied and mixed, so the circulation flow rate should be large, and the number of times of reaction water circulation in the reaction process (= flow rate × reaction time / reaction tank) A flow rate at which (capacity) is 3 times or more is preferable.

  Any mixing means may be used as long as it can supply and mix the oxygen-containing gas to the reaction water in the circulation line 38. The oxygen-containing gas is refined in the circulation line 38 and supplied to the reaction water and mixed. What can be done is preferred. The mixing means is preferably an ejector or a compressor and a line mixer. Oxygen-containing gas may be supplied to the reaction water in the circulation line 38 by an air self-priming ejector installed in the middle of the circulation line 38, mixed and dissolved, or oxygen is contained in the circulation line 38 by a compressor. You may carry out by press-fitting gas.

  The ability of the mixing means to refine and supply oxygen-containing gas to water and mix with water is, for example, 20 (less than 0.1 mg / L) water containing almost no iron salt (20% oxygen consumption by iron), 20 It can be expressed by an actual air dissolution rate (%) with respect to a saturated air amount in a steady state when air is continuously blown at ° C. As a mixing means, the air dissolution rate is preferably 20% or more, and more preferably 25% or more.

  In the case of an ejector, after sucking the oxygen-containing gas, the oxygen-containing gas temporarily becomes fine bubbles in the ejector, the gas-liquid contact area increases, and oxygen dissolves quickly in the reaction water, making it effective for ferritization of iron Contribute to. When the oxygen-containing gas is injected with a compressor, it is preferable to provide a line mixer after the injection point of the oxygen-containing gas, refine the oxygen-containing gas, and mix with the reaction water.

  Examples of the oxygen-containing gas include air, oxygen and the like, and air is preferable from the viewpoint of handleability.

  As the supply amount of the oxygen-containing gas, the amount of oxygen to be supplied is 0.01 to 0.11 L (ntp: 0 ° C., volume of gas at 1 atm with respect to the addition amount of ferrous salt converted to iron concentration) ) / G-Fe, and more preferably 0.03-0.11 L (ntp) / g-Fe. In this range, as the supply amount of the oxygen-containing gas increases as the oxygen amount, ferritization proceeds and the sludge volume after precipitation tends to decrease, but the oxygen amount is 0.11 L (ntp) / g-Fe. If it exceeds, the sludge volume is almost the same as in the case of 0.11 L (ntp) / g-Fe, and an ejector or a compressor having a large capacity may be required. Further, when the amount of oxygen is less than 0.01 L (ntp) / g-Fe, ferritization hardly proceeds and the sludge volume reducing effect may be small.

<Aggregate coarsening process>
The amount of the polymer flocculant added from the polymer flocculant addition line 36 as necessary is preferably in the range of 1 to 30 mg / L. When the amount of the polymer flocculant is less than 1 mg / L, there are many small particles with a slow sedimentation rate in the aggregate, and the outflow of the aggregate to the treated water may increase in the subsequent solid-liquid separation process. In addition, when the amount of the polymer flocculant exceeds 30 mg / L, the sedimentation property of the agglomerates is almost the same as in the case of 30 mg / L. In some cases, the viscosity of the sludge increases, causing problems such as blockage of the sludge piping.

  Examples of the polymer flocculant include anionic polyacrylamide.

  In the agglomerate coarsening step, a stirrer 12 or the like may be installed in the reaction vessel 10 as a stirring means in order to promote the floc formation in the reaction vessel 10 by immediately mixing in the water after adding the highly viscous polymer flocculant. preferable.

  The reaction time of the polymer flocculant is preferably in the range of 3 minutes to 15 minutes. That is, the residence time of the reaction water in the reaction vessel 10 is preferably in the range of 3 minutes to 15 minutes. When the reaction time is less than 3 minutes, sufficient agglomeration reaction is not performed, and a large number of small particles having a slow sedimentation rate are present in the agglomerate, and a large number of agglomerates may flow out into the treated water. On the other hand, when the reaction time exceeds 15 minutes, the large grown agglomerates are broken again by stirring, and many broken small agglomerates may flow into the treated water.

<Solid-liquid separation process>
The precipitation tank used in the solid-liquid separation step may be of any form of separation as long as it can be subjected to solid-liquid separation from agglomeration reaction water containing coarse aggregates (including ferrite and heavy metals). Separation is most effective. The agglomeration reaction water may be transferred to a sedimentation tank different from the reaction tank 10 to perform solid-liquid separation, or the agitation reaction water in the reaction tank 10 is stopped and the agglomeration reaction water is allowed to stand. Precipitation separation may be performed. In the latter case, the reaction tank 10 functions as a reaction means and also functions as a solid-liquid separation means (precipitation tank). The precipitation time depends on the size of the precipitation tank, but is preferably about 15 to 30 minutes, for example.

  The precipitated agglomerates may be pulled out from the sedimentation tank or reaction tank 10 as sludge by a pump, but this pump may utilize the circulation pump 20 or may be provided separately from the circulation pump 20. In this case, a branch pipe (for example, a treated water line 40, a treated water discharge line 42, and a sludge discharge line 44) with an automatic valve 28 attached to the discharge side of the circulation pump 20 is laid, and sludge is formed by opening and closing the valve 28. In addition, it is efficient to discharge the treated water out of the reaction tank 10.

  With the method and apparatus for treating heavy metal-containing water according to the present embodiment, the concentration of heavy metal in the treated water can be reduced to, for example, about 0.1 mg / L or less. Even when the heavy metal-containing water contains two or more types of heavy metals, the concentration of each heavy metal in the treated water can be reduced to, for example, about 0.1 mg / L or less.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

<Example>
A treatment apparatus 3 for heavy metal-containing water shown in FIG. 2 was produced. The heavy metal-containing water treatment apparatus 3 is mainly composed of a reaction tank 10 and a precipitation tank 54. The processing apparatus 3 includes a reaction tank 10 (with a stirrer 12, a pH meter 14, a thermometer 16, and an electric heater 18) 150L, a circulation line 38, a circulation pump 20, a motor operated valve, a flow meter 22, an air self-priming type. The ejector 24 (with pressure gauges installed in the front and rear) and a gas flow meter 26 are included. Further, the inner wall of the settling tank 54 has a volume scale so that the amount of sludge can be read.

  Heavy metals were added to the well water to prepare 600 L of water-containing heavy metal-containing water shown in Table 1. In the example, 100 L per condition was filled in the reaction tank 10 of the processing apparatus 3, and processing was performed with five levels of ejector intake air.

Specifically, after heating the heavy metal-containing water which is the water to be treated to 65 ° C. by the heater 18, a ferrous chloride solution (aqueous solution, 31% by weight of FeCl ₂ ) is added, and a sodium hydroxide solution (aqueous solution, PH was adjusted to 7.5. Then, the circulation pump 20 was started, the reaction water in the reaction tank 10 was extracted, and the reaction water was returned to the reaction tank 10 via the ejector 24. The circulation flow rate was 780 L / h. The amount of air sucked by the ejector 24 is adjusted by a valve 56 installed in the gas line 48, and the amount of oxygen is 0.0105 (Example 1), 0.021 (Example 2), 0.0315 (Example 3). , 0.063 (Example 4), 0.105 (Example 5) L (ntp) / g-Fe was adjusted in 5 stages. After reacting for 15 minutes, a sodium hydroxide solution (aqueous solution, 20% by weight) was added to the reaction tank 10 to adjust the pH to 9.5 while continuing the circulation of the reaction water and the intake of the ejector 24. After a further 15 minutes of reaction, the circulation pump 20 was stopped, and the reaction water circulation and the intake of the ejector 24 were stopped. Before completion of this reaction, 300 mL of reaction water was collected, and the interfacial sedimentation rate (initial constant velocity) of the aggregate was measured. 20 mg / L of an anionic organic polymer flocculant (Orgoc, Olflock M-4020) was added to the reaction vessel 10 and stirred for 5 minutes. The drainage valve was opened, and the agglomeration reaction water containing the agglomerate was transferred to the precipitation tank 54 in its entirety. In the sedimentation tank 54, the aggregate was allowed to settle for 30 minutes, and the volume of the aggregate sludge accumulated at the bottom was measured. Further, after 30 minutes, the supernatant water of the precipitation tank 54 was collected, and the concentration of heavy metal contained in the supernatant water was measured. Heavy metals other than arsenic were measured by the ICP-MS method defined in JIS 0102, and arsenic was measured by the atomic emission method. The measurement results of the sludge volume and the measurement results of each heavy metal in the supernatant water are summarized in Table 2. The processing conditions are shown below.

(Processing conditions)
・ Water volume to be treated: 100L
・ Reaction temperature 65 ℃
Ferrous chloride (31 wt% FeCl ₂ aqueous solution): 5.0 g Fe / L
-Reaction pH and time: pH 7.5 x 15 minutes + pH 9.5 x 15 minutes (0.5 hours in total)
・ Reaction water circulation flow rate: 780 L / h × 0.5 hours ・ Air supply amount (Example only): 50 to 250 L (ntp) / 100 L raw water / 0.5 hours
Oxygen amount 0.0105 to 0.105 L (ntp) / g-Fe
-Polymer flocculant: manufactured by Organo, Olflock M-4020 20 mg / L
-Polymer flocculant reaction time: 5 minutes-Precipitation time: 30 minutes

<Comparative Example 1>
100 L of heavy metal-containing water was treated in the same manner as in the example except that the valve 56 installed in the gas line 48 was completely closed and air was not allowed to enter from the ejector 24. Water quality and sludge volume were measured. The results are also summarized in Table 2.

<Comparative example 2>
An aeration tube 52 was installed at the bottom of the reaction vessel 10 of the processing apparatus 3 in FIG. 2 and connected to the blower 50. After heating 100 L of heavy metal-containing water contained in the reaction vessel 10 to 65 ° C. with the heater 18, a ferrous chloride solution (aqueous solution, 31% by weight of FeCl ₂ ) was added, and a sodium hydroxide solution (aqueous solution, 20% by weight). %) To adjust the pH to 7.5. Thereafter, the blower 50 was activated and aerated from the diffuser tube 52 into the reaction tank 10 (the circulation pump 20 was not activated and the reaction water was not circulated). After reacting for 15 minutes, while continuing aeration, a sodium hydroxide solution (aqueous solution, 20% by weight) was added to the reaction vessel 10 to obtain an organic polymer flocculant having a pH of 9.5 (Orflock M-4020, manufactured by Organo). ) 20 mg / L was added. Thereafter, the same operation as in the example was performed. The supernatant water quality and the sludge volume after sedimentation for 30 minutes were measured. The results are also summarized in Table 2.

(Processing conditions)
・ Air supply amount (only Comparative Example 2): 150 L (ntp) / 100 L raw water / 0.5 hours
Oxygen amount 0.063L (ntp) / g-Fe

  Regarding the quality of the treated water, each heavy metal was significantly reduced in Example and Comparative Example 1, and the removal rate was high. In Comparative Example 2, the value of selenium was higher than that in Examples and Comparative Example 1.

  On the other hand, the sludge volume after settling for 30 minutes is 62L in Comparative Example 1 and 62% of the amount of water to be treated (100L), and Comparative Example 2 is 68L and 68% of the amount of water to be treated. It was 22% or less, and it was confirmed that the amount of sludge decreases as the air supply amount increases in the range of oxygen amount of 0.0105 to 0.063 L (ntp) / g-Fe.

  From this result, it was confirmed that the sludge generation amount was suppressed while maintaining a high heavy metal removal rate by the reaction water circulation and the supply and dissolution of the oxygen-containing gas in the circulation line.

<Reference example>
The amount of dissolved air when air was blown into the water using an ejector, a line mixer, and an air diffuser was compared.

  Air is blown continuously into well water (water with almost no oxygen consumption by iron) at 20 ° C using an ejector, a line mixer, and an air diffuser, respectively, to contain almost no iron salt (0.1 mg / L or less). The actual air dissolution rate relative to the saturated air amount in the steady state was measured. In the measurement, water in which air was dissolved was introduced into a transparent acrylic sealed container, the pressure was reduced to atmospheric pressure, the volume of precipitated air was measured, and the ratio to the amount of saturated air was determined as the air dissolution rate (%). The results are shown in Table 3.

When the gas-liquid mixing ratio was the same, that is, at the same air supply amount, the air dissolution rate of the ejector and line mixer was higher in the diffuser pipe, ejector, and line mixer than in the diffuser pipe. This is presumably because in the ejector and line mixer, the supplied air temporarily became finer than the bubbles supplied from the diffuser tube, and the surface area of the bubbles, that is, the contact area between water and air increased. When ferrous iron is contained in a large amount as in the reaction of the present invention, it is considered that fine bubbles immediately react with ferrous iron to promote the formation of ferrite such as Fe ₃ O _4. .

1,3 treatment device, 10 reaction tank, 12 stirrer, 14 pH meter, 16 thermometer, 18 heater, 20 circulation pump, 22 flow meter, 24 ejector, 26 gas flow meter, 28, 56 valve, 30 heavy metal water Supply line,
32 Ferrous salt addition line, 34 pH adjuster addition line, 36 Polymer flocculant addition line, 38 Circulation line, 40 Treated water line, 42 Treated water discharge line, 44 Sludge discharge line, 46 Exhaust gas line, 48 Gas line , 50 Blower, 52 Air diffuser, 54 Sedimentation tank.

Claims (6)

A reaction means for performing a reduction reaction and an agglomeration reaction of heavy metal in heavy metal-containing water at 60 ° C. or higher and lower than 100 ° C. and pH 7 or higher in the presence of a ferrous salt;
A circulation means for circulating a part of the reaction water in which the reduction reaction and the aggregation reaction are performed through a circulation line;
Mixing means for supplying and mixing oxygen-containing gas to the reaction water in the circulation line;
Solid-liquid separation means for separating agglomerates from agglomeration reaction water obtained by agglomeration reaction of the heavy metal;
An apparatus for treating heavy metal-containing water. The heavy metal-containing water treatment apparatus according to claim 1,
The amount of oxygen supplied in the mixing means is in the range of 0.01 to 0.11 L (ntp) / g-Fe with respect to the added amount of the ferrous salt converted to iron concentration. Equipment for treating heavy metal-containing water. The heavy metal-containing water treatment apparatus according to claim 1 or 2,
The apparatus for treating heavy metal-containing water, wherein the mixing means is an ejector or a compressor and a line mixer. A reaction step of performing a reduction reaction and an agglomeration reaction of heavy metals in heavy metal-containing water at 60 ° C. or higher and lower than 100 ° C. and pH 7 or higher in the presence of a ferrous salt;
A circulation step in which a part of the reaction water in which the reduction reaction and the aggregation reaction are performed is circulated through a circulation line;
A mixing step of supplying and mixing oxygen-containing gas to the reaction water in the circulation line;
A solid-liquid separation step of separating the agglomerate from the agglomeration reaction water obtained by aggregating the heavy metal;
A method for treating heavy metal-containing water, comprising: It is a processing method of the heavy metal containing water of Claim 4, Comprising:
The amount of oxygen supplied in the mixing step is in the range of 0.01 to 0.11 L (ntp) / g-Fe with respect to the added amount of the ferrous salt converted to iron concentration. A method for treating heavy metal-containing water. It is a processing method of the heavy metal containing water of Claim 4 or 5,
In the mixing step, the oxygen-containing gas is supplied to and mixed with the reaction water using an ejector or a compressor and a line mixer.

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