JP4920932B2 - Treatment method for wastewater containing heavy metals - Google Patents

Description

  The present invention relates to a method for treating wastewater containing heavy metals such as copper, and more particularly to a method for treating wastewater containing heavy metals suitable for treating wastewater containing low-concentration heavy metals.

As a method of treating wastewater containing heavy metals such as copper, a method of adding a hydrating agent (alkali agent) or a sulfiding agent to precipitate heavy metals in the form of hydroxides or sulfides, aggregating them, and solid-liquid separation Is known (see Patent Document 1).
However, when treating wastewater containing relatively low concentrations of heavy metals, the resulting metal hydroxides and metal sulfides are extremely poor in cohesiveness and often cannot be easily treated simply by using a polymer flocculant in combination. . For this reason, an iron salt such as an iron chloride aqueous solution or an aluminum salt such as a polyaluminum chloride aqueous solution is usually added as an agglomeration aid to enhance the coagulation property.
In addition, when an alkali metal hydroxide such as sodium hydroxide is used as a hydroxylating agent or pH adjuster, it does not lead to any improvement in cohesion, but an alkaline earth metal hydroxide such as calcium hydroxide. Since the improvement of cohesiveness is seen when using, alkaline earth metal hydroxides are frequently used as the alkali agent.

However, the amount of sludge recovered by solid-liquid separation of wastewater treated by these methods will increase depending on the amount of agglomeration aid such as iron salt or aluminum salt or calcium hydroxide added. As a result, the content of valuable metals such as copper in the sludge decreases.
When the content of valuable metals in the sludge is high, it is possible to recycle valuable metals by taking it to a smelter, but sludge with a low content of valuable metals as mentioned above is difficult to recycle and is expensive. In most cases, the landfill is disposed after paying the processing cost. In addition to the cost, there is also a problem of exhaustion of the treatment plant, and its disposal is expected to become a bigger social problem in the future.

As a method of processing without increasing the valuable metal content in the sludge without increasing the cohesiveness of the sludge, if the heavy metal species is copper, in the printed circuit board manufacturing industry, etc. A method has been proposed in which waste liquid (aqueous solution of cupric chloride or copper sulfate) contained in a high concentration is added to increase the concentration of copper in the waste water (see Patent Document 2).
This method is effective in that copper can be recovered in sludge at a relatively high content without being affected by other metal species. However, by adding new copper, such as a hydroxylating agent or a sulfiding agent. The processing cost is increased, for example, the processing chemical is consumed unnecessarily and the sludge to be generated is increased. In addition, since this high concentration copper-containing waste liquid contains a high concentration of chelating agents, organic acids, etc., the addition of the high concentration copper-containing waste liquid may cause processing failure, increase the COD of the processing liquid, and bad odor. In many cases, it is accompanied by malfunctions. Furthermore, when there is no waste liquid containing appropriate copper, chemicals such as cupric chloride and copper sulfate have to be procured separately, which is difficult to say from the viewpoint of processing cost.

Further, a method has been proposed in which the sludge after treatment is returned and mixed during the treatment reaction to increase the concentration of heavy metals in the sludge while ensuring cohesiveness (see Patent Document 3).
This method is effective in that coagulation can be improved by recycling sludge and sludge having a high heavy metal concentration can be recovered. However, in this method, since a step of sending once generated sludge from the sedimentation tank to the reaction tank is added, the cost is increased due to maintenance and maintenance of the process. Furthermore, with regard to treated water, heavy metals such as copper may be re-eluted from the returned sludge due to the chelate component coexisting in the wastewater in the reaction tank. As a result, the heavy metal concentration in the treated water meets the wastewater standards. In some cases, the concentration cannot be sufficiently reduced to 1 mg / liter or less, which is a concentration guideline for biological treatment. For these reasons, it is preferable to solid-liquid-separate the sludge once produced as soon as possible, and avoid using it after returning it.

There is also a method using electrolysis as another wastewater treatment method, and this method is effective in that heavy metals can be recovered relatively efficiently with respect to the treatment of waste liquid containing a high concentration of heavy metals to be recovered. However, it is disadvantageous in terms of cost because it requires installation of a new electrolyzer and a large amount of energy is consumed. Therefore, it is not suitable as a treatment method for dilute wastewater having a heavy metal concentration of less than 500 mg / liter.
In addition, there is a method of concentrating and recovering valuable metals in wastewater using ion exchange membranes or reverse osmosis membranes, and these are particularly effective treatment methods for wastewater treatment in which metals are relatively lean. However, in the case of these methods, it is necessary to install each membrane separation device, and there is a problem in the maintenance of the device, particularly the membrane, and in order to perform stable processing, it takes a large amount every fixed period. Maintenance is required.

JP 2002-282867 A JP 2003-260475 A JP 2003-251369 A

  In the case of treating heavy metal-containing wastewater, particularly wastewater containing a heavy metal at a relatively low concentration, the present invention facilitates solid-liquid separation by increasing cohesion while suppressing the amount of sludge generated after treatment, To provide a wastewater treatment method capable of treating the quality of water to below the wastewater standard value (and not causing any obstacle to biological treatment) and at the same time increasing the concentration of valuable metals in the sludge to an extent that it can be easily recovered. Objective.

  As a result of diligent research on a method for treating heavy metal-containing wastewater to solve the above-mentioned problems, the present inventors have converted a heavy metal in wastewater to sulfide using a sulfurizing agent, and then added an oxidizing agent to the wastewater. The solid metal-liquid separation can be facilitated by quickly improving the cohesiveness of the generated heavy metal sulfide. As a result, the sludge recovered after the treatment is reduced, and at the same time the content of valuable metals in the sludge is increased. The present inventors have found that the recyclability can be improved, and have arrived at the present invention based on this knowledge. That is, the present invention has the following configurations (1) to (6).

(1) adding a sulfurizing agent to heavy metal containing waste water, a first step for precipitating heavy metals as sulphides, the first step processing wastewater hypochlorite, chlorite, perchlorate, permanganate and, At least one oxidizing agent selected from the group consisting of these water-soluble salts is added while adjusting the addition amount by ORP control, or quantitatively added to increase the cohesiveness of sludge containing heavy metal sulfide. A method for treating heavy metal-containing wastewater, comprising two steps and a third step of solid-liquid separation of the wastewater treated in the second step into sludge containing heavy metal sulfide and treated water.
(2) The method for treating heavy metal-containing wastewater according to (1), wherein the heavy metal-containing wastewater is wastewater containing copper having a concentration of 500 mg / liter or less.
(3) In the first step, at least one selected from the group consisting of alkali metal hydrosulfides, alkali metal sulfides, and alkali metal polysulfides is used as the sulfiding agent, and the sulfiding agent is subjected to ORP control. The method for treating wastewater containing heavy metal according to (1) or (2) above, wherein the addition is carried out while adjusting the amount of addition or by quantitative addition.

(4) The method for treating heavy metal-containing wastewater according to any one of (1) to (3), wherein the first step is performed while controlling the pH to 1 to 5.
( 5 ) The method for treating heavy metal-containing wastewater according to any one of (1) to ( 4 ), wherein the second step is performed while controlling the pH to 7 or less.

  According to the wastewater treatment method of the present invention, in wastewater treatment for separating heavy metals in wastewater containing heavy metal as sulfides, the cohesiveness of sludge containing heavy metal sulfides is improved, and the amount of sludge generated after treatment is suppressed. Solid-liquid separation can be performed easily, and the quality of treated water is treated below the wastewater standard value (and does not interfere with biological treatment), and at the same time, the concentration of valuable metals in sludge is easily recovered. Can be increased. In particular, the method of the present invention is effective for treating wastewater containing heavy metals at a relatively low concentration (for example, 500 mg / liter or less), and its industrial value is extremely large.

  The method of the present invention is effective for the treatment of wastewater containing heavy metals such as iron, cobalt, nickel, copper, zinc, molybdenum, silver, cadmium, tin, mercury, lead and the like, which can be applied with a treatment with a sulfurizing agent. In particular, it is suitable as a method for treating copper-containing wastewater.

In the method of the present invention, as a first step, a sulfiding agent is first added to the heavy metal-containing wastewater to precipitate the heavy metal in the wastewater as a sulfide.
Examples of the sulfiding agent used in the present invention include alkali metal hydrosulfides such as sodium hydrosulfide, alkali metal sulfides such as sodium sulfide, alkali metal polysulfides such as sodium polysulfide, alkaline earth metal hydrosulfides, alkaline earths. And at least one aqueous solution selected from the group consisting of metal sulfides, alkaline earth metal polysulfides, and hydrogen sulfide.
The wastewater pH at the time of adding the sulfiding agent is preferably maintained at 5 or less, and more preferably from 1 to 5 in view of reactivity. When the pH is less than 1, the pH is adjusted to the above range with an alkaline agent (for example, sodium hydroxide, potassium hydroxide, etc.), and when the pH exceeds 5, with a mineral acid (for example, sulfuric acid, nitric acid, hydrochloric acid, etc.) It is preferable to do. At this time, if calcium hydroxide, magnesium hydroxide, or the like is used as the alkaline agent, the concentration of valuable metals in the sludge recovered after the treatment is lowered.

As a method for adding the sulfiding agent, either a method of adding while controlling the amount of the sulfiding agent by ORP control or a method of quantitatively adding a preset amount may be used. At this time, the sulfurizing agent is preferably added to the waste water. When dripping onto the liquid level of waste water, part of the sulfiding agent may be scattered as hydrogen sulfide gas depending on the conditions, which may cause safety problems and increase the consumption of the sulfiding agent, which may be disadvantageous in terms of cost. Because there is.
The ORP control method is particularly preferable because the sulfurizing agent can be added without excess or deficiency even when the concentration of heavy metals in the raw wastewater varies. As described above, since the addition of the sulfiding agent is performed on the acidic side, the ORP initial value of the raw wastewater containing heavy metal ions is on the plus side, but when the sulfiding agent (reducing substance) is added thereto, the ORP value goes to the minus side. Transition. When heavy metal ions are present in the wastewater, the sulfurizing agent is consumed, so the ORP value returns to the positive side again. In a state where all the heavy metal ions contained are sulfides and the added sulfurizing agent is no longer consumed by heavy metal ions, the ORP value completely shifts to the negative side and does not return. If a sulfiding agent is added so that the ORP value is maintained on the negative side, even if the heavy metal concentration in the wastewater fluctuates, a sufficient amount of the sulfiding agent can be added to completely convert the heavy metal to sulfide. .

In the case of a method of adding a fixed amount, if the sulfurizing agent is insufficient, the properties of the treated water will deteriorate, so the amount of addition should be set in advance according to the fluctuation range of the heavy metal concentration in the raw wastewater so that it will not be insufficient. Added. Even if the sulfurizing agent is added excessively, the amount of the oxidizing agent added in the second step is increased, which is disadvantageous in terms of cost, but there is no problem with the properties of the treated water.
Since the reaction between the heavy metal and the sulfiding agent proceeds promptly, the reaction time after the addition of the sulfiding agent may be until the ORP value is stabilized if ORP control. In the case of quantitative addition, the liquid is sufficiently stirred. It may be the time until it becomes uniform. Even if the reaction time becomes longer depending on the working conditions, there is no effect on the workability of processing, the heavy metal residual concentration, and the like.

In the second step, an oxidant is added to the wastewater treated in the first step. This enhances the cohesiveness of the sludge containing heavy metal sulfide that is generated, facilitates solid-liquid separation in the subsequent third step, and increases the content of valuable metals in the sludge, facilitating subsequent recovery operations. Has the effect of The reason why the cohesiveness of the sludge is improved by the addition of the oxidizing agent is not clear, but it is presumed that the oxidizing agent acts on the charge on the surface of the sludge particles to eliminate the repulsive force between the particles.
Examples of the oxidizing agent used in the present invention include chlorine-based oxidizing agents such as hypochlorous acid, chlorous acid, perchloric acid, and water-soluble salts thereof, permanganic acid and water-soluble salts thereof, peroxodisulfuric acid and Examples thereof include at least one selected from the water-soluble salt and hydrogen peroxide. Among these, chlorine-based oxidants, permanganic acid and their water-soluble salts are preferable from the viewpoint of effects, and the use of sodium hypochlorite, which is a chlorine-based oxidant, is particularly important from the viewpoint of procurement and economy. preferable.

Although the addition amount of the oxidizing agent varies depending on the wastewater, it is preferable to add the ORP value so that the ORP value becomes about +210 mV or more by ORP control. This ORP value is considered to be a redox potential necessary for maintaining the state in which the repelling force between particles is eliminated by the action of the oxidizing agent on the sludge particle surface as described above. An oxidizer may be quantitatively added based on an addition amount set value obtained in advance according to the fluctuation of waste water. For example, in a single processing method, addition can be performed while visually confirming the cohesiveness.
If the oxidizing agent is insufficient, the cohesiveness becomes insufficient, and as a result, heavy metals may remain in the treated water after solid-liquid separation. In addition, when an oxidizing agent is added excessively, although the tendency for a processing result to deteriorate is not seen, since a chemical | medical agent is consumed unnecessarily, it is disadvantageous in cost.

The pH during or during the addition of the oxidizing agent is preferably 7 or less, and more preferably 5 or less. If the pH is 7 or less, sufficient cohesiveness can be obtained, and the heavy metal concentration in the treated water after solid-liquid separation can be 1 mg / liter or less. Even if the pH exceeds 7 by keeping the pH during addition constant, the concentration of heavy metals in the treated water can be reduced to 1 mg / liter or less, but the lower the pH, the better the cohesiveness and the higher the retained pH. As a result, the cohesiveness and solid-liquid separation tend to deteriorate.
Since the effect of improving the cohesiveness due to the addition of the oxidant is manifested relatively quickly, the reaction time after the addition of the oxidant may be until the ORP value stabilizes if ORP control. The time until the liquid becomes uniform after is performed. Increasing the reaction time has little effect on the workability of the treatment and the heavy metal residual concentration in the treated water.

  Throughout the first to third steps, the lower the reaction temperature, the better the results. That is, the heavy metal residual concentration in the treated water could be treated to 1 mg / liter or less at 0 ° C. or 60 ° C., but the effect of improving the cohesiveness of the sludge containing heavy metal sulfide by the addition of the oxidizing agent is best at 0 ° C. If the temperature exceeds 40 ° C., the effect of improving cohesion tends to be reduced. However, normal heavy metal-containing wastewater is treated at room temperature and does not exceed 40 ° C., so there is no particular problem.

In the third step, the waste water that has been flocculated by adding an oxidizer in the second step is adjusted to a pH that can be biologically treated or discharged (depending on the establishment where the wastewater treatment is carried out, it is discharged into public waters) In this case, the pH is adjusted within the range of 5.0 to 9.0 in the sea area and 5.8 to 8.6 in the case of rivers and lakes), and if necessary, a polymer flocculant is added to perform solid-liquid separation. As the polymer flocculant, any one or more of cationic, nonionic, anionic and amphoteric polymers can be used.
By the treatment in the first to third steps, the concentration of heavy metals in the treated water after the solid-liquid separation can be reduced to 1 mg / liter or less. The amount of sludge thus produced is reduced, and the concentration of valuable metals in the sludge is high, so that there is an effect that workability in the subsequent recovery process is improved.

The wastewater treatment method of the present invention is particularly difficult to ensure sludge cohesion unless an iron salt or aluminum salt such as an iron chloride aqueous solution or a polyaluminum chloride aqueous solution is used in combination, and wastewater containing a relatively low concentration of heavy metal (in the case of copper) The effect is large when applied to the treatment of dilute wastewater having a copper concentration of 500 mg / liter or less).
Moreover, as a result of using an alkaline earth metal hydroxide as a conventional iron salt or aluminum salt and / or a hydroxylating agent or a pH adjusting agent as a coagulation aid, valuable metals in sludge recovered after solid-liquid separation. It is also effective for the treatment of wastewater whose content has been reduced and sludge could not be recycled as a valuable resource.
In addition, in these series of steps (first step to third step), any of a continuous processing method and a single processing method can be applied.

The present invention will be described more specifically with reference to the following examples, comparative examples, and reference examples, but the present invention is not limited to these examples.
In the following examples, the comparison of the results mainly uses numerical values such as concentration and content rate, but since the amount of the additive agent is small compared to the amount of the wastewater to be treated in any of the examples, the relative values of these are compared. The effect of the present invention can be sufficiently estimated by comparing the values.
In the following examples, the chemicals, filter paper, and measuring equipment shown in Table 1 were used.

[Examples 1 to 5 / Comparative Examples 1 to 4] (Effects of adding an oxidizing agent)
Copper (II) sulfate was dissolved in ion-exchanged water to prepare a model wastewater containing copper at the concentrations shown in Table 2.
As a first step, a 2.5% by mass sodium hydrosulfide aqueous solution was added to the model wastewater at room temperature (about 20 ° C.) using a 0.4% by mass sodium hydroxide aqueous solution while maintaining the pH at 4. , Added so as to be equivalent to copper. The addition amount was adjusted by ORP control, and was added until ORP became constant at -50 mV. The addition time was about 3 minutes.

  In Examples 1 to 5, the model wastewater to which sodium hydrosulfide was added in the first step as the second step was added to an aqueous solution of sodium hypochlorite having an effective chlorine content of 1.2% by mass or 0.005 mol / liter as an oxidizing agent. An aqueous potassium permanganate solution was added so that the ORP value was +210 mV or more. The pH during addition was 4.0 (at the end of the first step) to 6.5 (at the end of the second step), the temperature was at room temperature (about 20 ° C.), and the addition time was about 3 minutes. Table 2 shows the type of oxidizing agent used and the final ORP value.

  Next, the third process was performed on the wastewater that ended the second process (in Comparative Examples 1 to 4, the second process was omitted and the first process was completed). That is, after adding 0.4 mass% sodium hydroxide aqueous solution to the waste water to adjust the pH to 9, an anionic polymer flocculant was added to a concentration of 5 mg / liter, and the back paper was used. Solid-liquid separation. Table 2 shows the aggregation state of sludge before solid-liquid separation, the filtration time, the observation results of the appearance of the treated water after solid-liquid separation, and the measurement results of the copper concentration in the treated water. The filtration time shown in Table 2 is the time required to pour 100 ml of the pre-solid-liquid treatment liquid onto the filter paper at once and filter the first 50 ml.

As shown in Table 2, in Examples 1 to 5 in which the second step of adding sodium hypochlorite or potassium permanganate as an oxidant was performed, both sludge cohesiveness and sedimentation were good, copper A clear treated water having a concentration of less than 1 mg / liter was obtained.
On the other hand, in Comparative Examples 1 to 4 in which the second step was not performed, the sludge cohesiveness was poor, and the copper concentration in the treated water exceeded 1 mg / liter.
Moreover, when the treatment rate of copper in the Example and the Comparative Example is compared, it is consistently 96% or more regardless of the copper concentration in the raw wastewater (96% in Example 1, 99 in Examples 2-5). In contrast, Comparative Example 1 had a concentration of about 9%, but Comparative Example 2 was 86%, Comparative Example 3 was 99%, and Comparative Example 4 was 99% or more. It is clear that the effect increases as the copper concentration in the raw wastewater decreases.
The “copper treatment rate” here is a numerical value represented by “100 × (copper concentration in raw wastewater−copper concentration in treated water) / (copper concentration in raw wastewater)”.

[Example 6, Comparative Examples 5 and 6] (Comparison between the treatment method of the present invention and a general treatment method using a coagulant aid)
Example 6: Copper (II) sulfate was dissolved in ion exchange water to prepare a model wastewater containing copper at a concentration of 100 mg / liter.
As a first step, a 2.5 mass% sodium hydrosulfide aqueous solution was added to the model wastewater at room temperature (about 20 ° C) while maintaining a pH of 4 using a 0.4 mass% sodium hydroxide aqueous solution. It added so that it might become an equivalent with respect to copper. The addition amount was adjusted by ORP control, and was added until ORP became constant at -50 mV. The addition time was about 3 minutes.
As a second step, an aqueous sodium hypochlorite solution containing 12% by mass effective chlorine as an oxidizing agent was added to the model wastewater to which sodium hydrosulfide was added in the first step so as to be 100 ppm based on the wastewater. The temperature at this time was room temperature (about 20 ° C.), the pH was 4.0 (at the end of the first step) to 6.5 (at the end of the second step), and the treatment time was about 10 minutes.
Then, as a third step, 0.4% by weight aqueous sodium hydroxide solution is added to the wastewater to adjust the pH to 9, and then an anionic polymer flocculant is added to a concentration of 5 mg / liter, Solid-liquid separation was performed using filter paper.

Comparative Example 5: To the same model wastewater as in Example 6, a 40% by mass iron (III) chloride aqueous solution as a coagulant aid was added to 300 ppm with respect to the model wastewater. While maintaining this wastewater at pH 4, a 2.5 mass% sodium hydrosulfide aqueous solution was added by an ORP control (ORP: -50 mV) so as to be equivalent to copper and iron. At this time, a 0.4 mass% sodium hydroxide aqueous solution was used for pH adjustment.
Next, 0.4% by weight aqueous sodium hydroxide solution was added to the waste water to adjust the pH to 9, and then an anionic polymer flocculant was added to a concentration of 5 mg / liter, and the back paper was used. Solid-liquid separation.
Comparative Example 6: Comparative Example 5 is the same as that of Comparative Example 5 except that a 2.5% by mass sodium hydrosulfide aqueous solution was not added, and the 0.4% by mass sodium hydroxide aqueous solution was directly added so that the pH of the wastewater was 9. The same operation was performed.

  The results of Example 6 and Comparative Examples 5 and 6 are as shown in Table 3, and there is no problem with the cohesiveness of the treated water under any condition, and the treated water after the solid-liquid separation is a clear liquid and copper. It was processed enough. However, in Comparative Example 5 in which the second step using the oxidizing agent is not performed and in Comparative Example 6 in which only the hydroxide treatment is performed, the amount of sludge generated is increased as compared with Example 6, and the copper content in the sludge is increased. It can be seen that the rate is significantly reduced.

[Example 7] (Example 1 using actual waste water)
Etching cleaning water (pH = 5.6, copper concentration 20.9 mg / liter) discharged from Printed Circuit Board Manufacturing Company A at room temperature (about 20 ° C.) with 0.5 mass% sulfuric acid and 0.4 mass% While maintaining the pH at 4 using an aqueous sodium hydroxide solution, a 2.5 mass% sodium hydrosulfide aqueous solution was added so as to be equivalent to copper by ORP control (ORP: ± 0 mV).
Subsequently, 0.004 mol% (3.5 ppm as potassium permanganate) of 0.005 mol / liter potassium permanganate aqueous solution as an oxidant was added to the wastewater. The temperature at that time was room temperature (about 20 ° C.), pH was 3.9, and ORP was 220 mV. Thereafter, the pH was adjusted to 8 with a 0.4 mass% aqueous sodium hydroxide solution, an anionic polymer flocculant was added to a concentration of 2.5 mg / liter, and solid-liquid separation was performed with filter paper.
As a result, the generated sludge formed flocs and settled, confirming the cohesiveness. Moreover, the result of measuring the copper concentration in the treated water after the solid-liquid separation was 0.2 mg / liter, and the copper content in the recovered dry sludge was 48%, which could be recovered in a recyclable form.

[Comparative Example 7] (Comparative Example 1 with Actual Waste Water)
The same operation as in Example 7 was conducted except that the potassium permanganate aqueous solution as an oxidizing agent was not added.
As a result, the produced sludge was not cohesive at all, the copper concentration in the treated water after filtration was 4.9 mg / liter, and the appearance was a brown opaque liquid.

[Example 8] (Example 2 with actual wastewater)
Etching cleaning water (pH = 5.6, copper concentration 28.7 mg / liter) discharged from Printed Circuit Board Manufacturing Company B, 0.5% by mass sulfuric acid and 0.4% by mass at room temperature (about 20 ° C.) While maintaining the pH at 4 using a sodium hydroxide aqueous solution, a 2.5 mass% sodium hydrosulfide aqueous solution was added so as to be equivalent to copper by ORP control (ORP: -100 mV).
Subsequently, 100 ppm of sodium hypochlorite aqueous solution containing 12% by mass of effective chlorine as an oxidizing agent was added to the waste water. The temperature at that time was room temperature (about 20 ° C.), the pH was 5.3, and the ORP was 240 mV. Thereafter, the pH was adjusted to 9 with a 0.4% by mass aqueous sodium hydroxide solution, 5 mg / liter of an anionic polymer flocculant was added, and solid-liquid separation was performed with filter paper.
As a result, the generated sludge formed flocs and settled, confirming the cohesiveness. The sludge concentration in the treated water was 74 mg / liter, the copper concentration in the treated water after solid-liquid separation was 0.3 mg / liter, and the copper content in the recovered dry sludge was 34%.

[Example 9] (Example 3 with actual wastewater)
As an oxidizing agent, 0.005 mol / liter potassium permanganate aqueous solution was added in an amount of 1% by volume based on waste water instead of sodium hypochlorite aqueous solution containing 12% by mass of effective chlorine (the temperature at that time was room temperature (about 20 ° C. ), PH was 5.2, and ORP was 220 mV. The others were operated in the same manner as in Example 8.
As a result, the generated sludge formed flocs and settled, confirming the cohesiveness. The sludge concentration in the treated water was 74 mg / liter, the copper concentration in the treated water after solid-liquid separation was 0.4 mg / liter, and the copper content in the recovered dry sludge was 34%.
From the results of Examples 8 and 9, the effect of the oxidizing agent on the actual waste water is the same for both sodium hypochlorite and potassium permanganate, and the copper concentration in the treated water after solid-liquid separation is 1 mg / liter or less. In view of the copper content in the sludge, it was recovered in a sufficiently recyclable form.

[Comparative Example 8] (Comparative Example 2 with Actual Waste Water)
The same operation as in Example 8 was carried out except that no sodium hypochlorite aqueous solution as an oxidizing agent was added.
As a result, the produced sludge was not cohesive at all, the copper concentration in the treated liquid after filtration was 13.2 mg / liter, and the appearance was a brown opaque liquid.

[Comparative Example 9] (Comparative Example 3 with Actual Waste Water)
Etching cleaning water (pH = 5.6, copper concentration 28.7 mg / liter) discharged from Printed Circuit Board Manufacturing Company B was treated by a general hydroxide method.
40% by mass of iron (III) chloride is added in advance to the waste water at 300 ppm, 10% by mass of calcium hydroxide slurry is added until the pH reaches 9, and anionic polymer flocculant is added at 5 mg / liter. Then, solid-liquid separation was performed with filter paper.
As a result, the generated sludge formed flocs and aggregated well, and the copper concentration in the treated water after solid-liquid separation was 0.1 mg / liter or less, but the sludge concentration in the treated water was 197 mg / liter. The amount of copper contained in the recovered dry sludge was as high as 16% and was not suitable for recycling.

[Reference Example 1: Investigation of influence of reaction time after addition of sodium hypochlorite]
After adding sodium hydrosulfide to waste water in which copper hydrosulfide was added to model wastewater with a copper concentration of 100 mg / liter, sodium hypochlorite was added and reacted for 0 to 30 minutes to investigate the effect of reaction time. . As a result, the influence of the reaction time on the treatment result was small, and the treatment could be sufficiently performed even if the reaction time was short. Almost the same result was obtained for the cohesiveness and the treated aqueous state.

[Reference Example 2: Investigation of optimum amount of sodium hypochlorite]
Add sodium hydrosulfide to model wastewater with varying copper concentration, add sodium hypochlorite to wastewater containing copper sulfide, and investigate the optimum amount of sodium hypochlorite for each concentration. It was.
As a result, regardless of the copper concentration in the raw waste water, it was confirmed that the treatment property was sufficiently improved by adding sodium hypochlorite until the ORP value reached 210 mV or more. When sodium hypochlorite was insufficiently added, copper remained or coagulated. Even when sodium hypochlorite was added in excess, the processing properties were not deteriorated.

[Reference Example 3: Investigation of optimum pH when sodium hypochlorite is added]
A model wastewater having a copper concentration of 100 mg / liter is treated by the method of the present invention comprising a first step using sodium hydrosulfide, a second step using sodium hypochlorite, and a third step. The effect of pH was investigated by changing the pH of the two steps from 1 to 9.
As a result, when the pH was maintained at a constant value during the addition of sodium hypochlorite, the copper concentration in the treatment liquid could be treated to 1 mg / liter or less in all pH ranges of pH 1-9. . However, the higher the pH, the worse the cohesiveness and filterability.
In addition, when only the pH before addition of sodium hypochlorite was adjusted and the pH was not adjusted during the addition, when the pH exceeded 7, the copper concentration in the treatment liquid was 1 mg / liter or more, and the coagulation and filtration The deterioration of the property and coloring of the treated water were confirmed.
From the above, it is preferable that the pH of the second step is 7 or less. In addition, in the case where the pH is maintained or not, good results are obtained at pH 1 to 5, and the sulfide in the first step. Since the generation process is preferably about pH 1 to 5, it is particularly preferable to carry out in this pH range through the first step and the second step.

  The method for treating heavy metal-containing wastewater of the present invention includes cleaning water (etching cleaning water) discharged from an etching process in the printed circuit board manufacturing industry, drainage from a plating plant, mine mine wastewater, smelter wastewater, etc. The processing method has a wide range of applicability.

Claims (5)

A first step of adding a sulfiding agent to the heavy metal-containing wastewater and precipitating the heavy metal as a sulfide;
At least one oxidizing agent selected from the group consisting of hypochlorous acid, chlorous acid, perchloric acid, permanganic acid, and water-soluble salts thereof is added to the first process treatment wastewater by ORP control A second step of adding a fixed amount or adding a fixed amount to increase the cohesiveness of sludge containing heavy metal sulfide,
A third step for solid-liquid separation of the second step treated wastewater into sludge containing heavy metal sulfide and treated water ;
A method for treating heavy metal-containing wastewater.   The method for treating heavy metal-containing wastewater according to claim 1, wherein the heavy metal-containing wastewater is wastewater containing copper having a concentration of 500 mg / liter or less.   In the first step, at least one selected from the group consisting of alkali metal hydrosulfides, alkali metal sulfides, and alkali metal polysulfides is used as the sulfiding agent, and the amount of the sulfiding agent added by ORP control The method for treating heavy metal-containing wastewater according to claim 1, wherein the amount is added while adjusting or is added quantitatively.   The method for treating heavy metal-containing wastewater according to any one of claims 1 to 3, wherein the first step is performed while controlling the pH to 1 to 5. The method for treating heavy metal-containing wastewater according to any one of claims 1 to 4 , wherein the second step is performed while controlling the pH to 7 or less.