JP5143790B2 - Cyanogen-contaminated groundwater treatment method - Google Patents

Description

  The present invention relates to a method for treating groundwater contaminated with cyanide. Specifically, the present invention relates to a method for removing an iron cyano complex from groundwater containing a cyanide compound.

  As a method for treating groundwater contaminated with cyanide contained in factory wastewater, for example, Japanese Patent Application Laid-Open No. 2004-81979 (the following Patent Document 1) is a method of treating groundwater contaminated with cyan by a zinc white method. The first step of pumping ground water to the ground in an environment shielded from the atmosphere, the second step of adding zinc salt to the pumped ground water to generate zinc white, the pH within the range of 8.5-10 Adjust to produce zinc hydroxide to separate and remove the third step of precipitating the cyan component bound to the humic colloid along with the zinc white and colloidal zinc cyanide suspension, and the precipitated suspension, etc. A cyan-contaminated groundwater treatment method characterized in that it includes a fourth step, which can pump up groundwater contaminated with cyanide and perform purification treatment efficiently and economically on the ground. Processing methods and apparatus for emission contaminated groundwater has been proposed.

Further, typical cyanide treatment methods include the following.
1) Alkaline chlorine method 2) Ozone oxidation method 3) Bitumen method Hereinafter, each method will be described.
1) Alkaline chlorine method This is the most typical cyanide treatment method. After the pH is adjusted to 10 to 13 using an alkali, an oxidizing agent such as chlorine, hypochlorous acid or potassium permanganate is added to oxidatively decompose cyanide ions.

However, the alkali chlorine method can be applied to the decomposition of a cyanide having a relatively low concentration, but is not applicable to the decomposition of a cyanide having a high concentration. It is also difficult to apply to cyanide complex ions with iron, nickel, cadmium and the like. Moreover, application to soil purification is actually difficult from the viewpoints of difficulty of raising the pH to 10 to 13, consumption of hypochlorite, environmental impact, and the like.
2) Ozone oxidation method This method directly oxidizes cyanide compounds by the oxidizing power of ozone. This method requires a special ozone generating facility and has a cost problem. Moreover, the oxidative decomposition efficiency is not necessarily high. It is also difficult to apply to cyanide complex ions such as iron.
3) Bituminous process Cyanide from factory wastewater leaks into the ground and mixes with groundwater often forms iron cyano complexes with iron in the ground. An iron cyano complex reacts as follows by adding an iron salt to form a hardly soluble salt.

3 [Fe (CN) ₆ ] ^4- + 4Fe ³⁺ → Fe ₄ [Fe (CN) ₆ ] ₃ Ferriferro type (Prussian blue)
2 [Fe (CN) ₆ ] ^3- + 3Fe ²⁺ → Fe ₃ [Fe (CN) ₆ ] ₂ Ferroferri type (turnable blue)
[Fe (CN) ₆ ] ^4- + 2Fe ²⁺ → Fe ₂ [Fe (CN) ₆ ] Ferroferro type (Berlin White)
In this case, if iron ions are insufficient, Fe [Fe (CN) ₆ ] ^- (soluble Prussian blue) will be formed, and soluble cyanoiron (II) ions will remain. Become imperfect.

Therefore, normally, ferrous sulfate is excessively added and agglomerated and precipitated as a hardly soluble cyano compound. However, since divalent iron (Fe ²⁺ ) is excessively required, there are the following problems.

  1) Chemical cost increases because ferrous sulfate must be added in excess.

  2) In addition to the above inorganic flocculant, a polymer flocculant is required.

  3) The amount of generated sludge is large, and the treatment cost of sludge increases.

JP 2004-81979 A

  The present invention solves the problems of the prior art as described above, a method for treating cyan-contaminated groundwater with low Fe addition, no polymer flocculant, low sludge generation, and low running cost. It is an issue to provide.

As a result of intensive studies to solve the above-mentioned problems, the present invention has a pH of groundwater contaminated with cyanide.
Was found to be able to remove the iron cyano complex by solid-liquid separation after adding and stirring polyferric sulfate and adjusting the content to 5.5 or less. It is the following contents as described in the range.
(1) After adjusting the pH of groundwater contaminated with iron cyano complex which cyanide leaked into the groundwater and combined with the Fe content in the ground to 5.5 or lower, added polyferric sulfate and stirred, Cyanogen-contaminated groundwater treatment method characterized by solid-liquid separation.
(2) The method for treating cyan-contaminated groundwater according to (1), wherein a filtration device is used for the solid-liquid separation.
(3) The method for treating cyan-contaminated groundwater according to (2), wherein a laminated filtration device is used as the filtration device.
According to the invention of (1), ferrocyanine [Fe (CN) ₆ ] ^4- reacts with Fe ³⁺ of polyferric sulfate to produce Fe ₄ [Fe (CN) ₆ ] ₃ (Prussian blue). In addition, ferricyan [Fe (CN) ₆ ] ^3- reacts with iron hydroxide in polyferric sulfate and is coprecipitated and removed by adjusting the pH to 5.5 or lower. can do.
According to the invention of (2), the efficiency of solid-liquid separation can be remarkably enhanced by using a filtration device in the solid-liquid separation step.
According to invention of (3), the following effect can be show | played by using a laminated filtration apparatus as a filtration apparatus.
-Since a cake layer is made and filtered, it can be processed even if the SS concentration (Suspended Solid concentration) of the treatment liquid is high.
・ The amount of backwash water for removing the separated solid can be reduced.
-Less clogging with mud balls.
・ Easy to clean.
-Since the filter itself is made of SUS, it is easy to clean.

  According to the present invention, it is possible to provide a method for treating cyan-contaminated groundwater with a small amount of Fe added, no polymer flocculant, and a small amount of sludge generation, and low running costs. There is an effect.

It is a figure which shows the processing flow of cyan pollution groundwater using the conventional bitumen method. It is a figure which shows the processing flow of the cyan pollution groundwater of this invention. It is a figure which shows the effect of the processing method of cyan pollution groundwater of this invention. It is a figure which shows the Example of the processing method of the conventional cyan pollution groundwater. It is a figure which shows the Example of the processing method of the conventional cyan pollution groundwater. It is a figure which shows the Example of the processing method of the conventional cyan pollution groundwater. It is a figure which shows the Example of the processing method of the conventional cyan pollution groundwater.

  The form for implementing this invention is demonstrated in detail using FIGS. 1-3.

  FIG. 1 is a diagram showing a treatment flow of cyan-contaminated groundwater using a conventional bitumen method.

Cyanogen-contaminated groundwater is pumped up from the well, transferred to the raw water tank, sulfuric acid (H ₂ SO ₄ ) is added to adjust the pH to 5.6 or more, and ferrous sulfate (FeSO ₄ · 7H ₂₎ O) is added excessively and stirred to form a hardly soluble salt. In order to agglomerate and precipitate this hardly soluble salt, in addition to the above-mentioned inorganic aggregating agent, it is necessary to add a polymer aggregating agent, and there is a problem that the amount of generated sludge is large and the sludge treatment cost increases. there were.

  FIG. 2 is a diagram showing a treatment flow of the cyan-contaminated groundwater of the present invention.

Cyanogen-contaminated groundwater is pumped up from the well, transferred to the raw water tank, sulfuric acid (H ₂ SO ₄ ) is added to adjust the pH to 5.5 or lower, and polyferric sulfate is added and stirred. By doing, the amount of Fe required for the production | generation of a hardly soluble salt can be reduced. In addition, since ferric sulfate is an iron-based polymer flocculant, it is not necessary to add a polymer flocculant separately as in the prior art in order to agglomerate and precipitate this sparingly soluble salt. Since the amount is small, sludge treatment costs can be significantly reduced.

Polyferric sulfate is an inorganic flocculant having a composition of the general formula [Fe ₂ (OH) _n (SO ₄ ) _{3 -n / 2} ] _m and also called polyiron. The aggregation mechanism of cyanide compounds by polyferric sulfate is not necessarily clear, but ferrocyanate [Fe (CN) ₆ ] ^4- reacts with Fe ^{3+ of} ferric sulfate and Fe ₄ [Fe ( CN) ₆ ] ₃ (Prussian blue) can be removed by precipitation, and ferricyan [Fe (CN) ₆ ] ^3- can be hydroxylated in polyferric sulfate by adjusting the pH to 5.5 or lower. Since it reacts with iron and can be coprecipitated and removed, it is considered that the amount of Fe necessary for producing a hardly soluble salt can be reduced. The stirring speed during the coagulation precipitation is preferably 30 to 100 rpm.

The processing flow in FIG. 2 shows a method of solid-liquid separation by coagulating sedimentation in a sedimentation site, but it is necessary because the equipment can be made compact by performing solid-liquid separation using a filter. The space can be reduced and can be unitized, so that the equipment can be relocated and used.
However, when the SS concentration is high, the frequency of backwashing is increased and the amount of backwashing water is increased in the case of normal sand filtration, which increases the cost of sludge treatment.

  Further, when SS is mainly composed of iron hydroxide, mudballs are easily generated and clogged, and since sludge containing cyan is difficult to clean the filter medium, it is necessary to treat it as waste.

  Furthermore, since the pH of the wastewater is 5.5 or less, it is necessary to use a material with high corrosion resistance such as SUS as the material of the filtration device.

  Therefore, it is preferable to use a laminated filtration device as the filtration device.

A multi-layer filtration device is a filter in which treated water guided to the inner side of a multi-layered laminated plate made of doughnut-shaped stainless steel plates is filtered through a gap (10-50 μm) formed between the stacked thin plates. It is an apparatus and can have the following effects.
-Since a cake layer is made and filtered, it can be processed even if the SS concentration (Suspended Solid concentration) of the treatment liquid is high.
・ The amount of backwash water for removing the separated solid can be reduced.
-Less clogging with mud balls.
・ Easy to clean.
-Since the filter itself is made of SUS, cleaning is easy.

  FIG. 3 is a diagram showing the effect of the method for treating cyan-contaminated groundwater of the present invention.

  The horizontal axis of Fig. 3 shows the amount of polyiron added (mg / l), and the vertical axis shows the treated water cyanide concentration T-CN (mg / l). Water cyanide concentration T-CN (mg / l) cannot be reduced to 2 mg / l or less, but after adjusting cyan-contaminated groundwater to pH 4 to 5.5, adding polyiron 350 mg / l or more and stirring It was found that the total cyan amount T-CN (mg / l) can be reduced to 2 mg / l or less by solid-liquid separation.

  Adjust the cyan contaminated groundwater to pH 4 to 5.5, add 700 mg / l or more of polyiron and stir, then separate the solid and liquid to treat cyanide concentration T-CN (mg / l) of 1 mg / l or less. It was found that it can be reduced.

  4 to 7 show examples of conventional methods for treating cyan-contaminated groundwater.

  As shown in FIG. 4, the raw water was subjected to cyan decomposition by the alkali chlorine method and then treated by the bitumen method. Further, as shown in FIG. 5, the test was also performed by a method of decomposing with hydrogen peroxide solution. Furthermore, as shown in FIG. 6, coagulation precipitation with ferrous sulfate was performed.

  FIG. 7 (a) shows the total cyan concentration analysis value of the treated water. FIG. 7 (b) shows the relationship between the ferrous sulfate injection amount and the total cyan concentration of treated water. As shown in Fig. 7 (a), the total cyanide concentration in treated water did not become 1 mg / l or less in the alkali chlorine method and hydrogen peroxide decomposition, but when ferrous sulfate was injected at 2000 mg / l, the total cyanide concentration in treated water was Was 0.8 mg / l. As described above, there is a problem that a large amount of ferrous sulfate is required, a polymer flocculant is required, and the amount of generated sludge is increased.

  Next, the result of conducting a beaker test as an example of the method for treating cyan-contaminated groundwater of the present invention will be described.

  Table 1 shows the results of analysis of cyan contaminated groundwater collected from the wells. The pH was 11.7 and the total cyan concentration T-CN was 9.5 mg / l.

このシアン汚染地下水に表３に示す使用量（mg/l）の100％硫酸（H₂SO₄）を添加してｐＨを４〜７の試料を作成し、ポリ鉄を350〜700mg/l添加して凝集処理試験を行った結果を表２に示す。

A sample with a pH of 4-7 is prepared by adding 100% sulfuric acid (H ₂ SO ₄ ) in the amount used (mg / l) shown in Table 3 to this cyan contaminated groundwater, and 350-700 mg / l of polyiron is added. Table 2 shows the results of the coagulation treatment test.

表２に示すように、ｐＨ５でポリ鉄を350mg/l添加すれば、合計シアン量T-CNは1.6（mg/ｌ）に低減することができ、ｐＨ４でポリ鉄を350mg/l添加すれば、処理水シアン濃度T-CNは0.9（mg/ｌ）に低減することができ、ｐＨ５でポリ鉄を700mg/l添加すれば、処理水シアン濃度T-CNは0.8（mg/ｌ）に低減することができ、ｐＨ４でポリ鉄を700mg/l添加すれば、処理水シアン濃度T-CNは0.8（mg/ｌ）に低減することができることが判明し、本発明の効果が確認された。

As shown in Table 2, if 350 mg / l of polyiron is added at pH 5, the total cyan amount T-CN can be reduced to 1.6 (mg / l), and if polyiron is added at 350 mg / l at pH 4. The treated water cyanide concentration T-CN can be reduced to 0.9 (mg / l). If polyiron is added at 700 mg / l at pH 5, the treated water cyanide concentration T-CN is reduced to 0.8 (mg / l). It was found that if polyiron was added at 700 mg / l at pH 4, the treated water cyanide concentration T-CN could be reduced to 0.8 (mg / l), confirming the effect of the present invention.

Claims (3)

After adjusting the pH of groundwater contaminated with iron cyano complex which cyanide leaked into the groundwater and combined with Fe content in the ground to less than 5.5, adding ferric sulfate and stirring, solid-liquid separation A method for treating cyan-contaminated groundwater.   The method for treating cyan-contaminated groundwater according to claim 1, wherein a filtration device is used for the solid-liquid separation.   The method for treating cyan-contaminated groundwater according to claim 2, wherein a laminated filtration device is used as the filtration device.

Images