JP2002224676A - Method for treating waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste water treating method by which citric acid and ions of heavy metals contained in waste water can be reduced easily at the same time. SOLUTION: This waste water treating method comprises a step to add iron ion, copper ion or both iron ion and copper ion of 2-10 times of the citric acid amount in waste water by weight to the waste water containing citric acid and ions of heavy metals, a step to make the waste water alkaline so that precipitates containing citric acid and heavy metals are produced and a step to subject the precipitate-containing waste water to solid-liquid separation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating wastewater containing citric acid and heavy metal ions.

[0002]

2. Description of the Related Art Citric acid is widely used as a useful additive in the plating industry because it forms stable complexes with various heavy metal ions. For example, for the purpose of improving the heat resistance of a printed circuit board, Ni-
Although a plating process made of a Mo-Co alloy is performed,
If the plating solution does not contain citric acid, the desired heat resistance cannot be obtained. The primary rinsing water obtained by rinsing the plating solution attached to the copper foil surface contains heavy metal ions such as Ni, Mo, and Co in an amount of 3 to 300 mg / l, and 30 to 3,000, respectively.
It contains 0 mg / l citric acid.

As a method for treating wastewater containing heavy metal ions, it is common practice to make the wastewater alkaline and to precipitate the heavy metal ions contained therein as metal hydroxides, but the complex of citric acid and heavy metal ions is alkaline. However, because of its stability, wastewater containing citric acid and heavy metal ions is difficult to treat by the above method.

JP-A-61-192386 discloses that an iron salt, a calcium salt or a magnesium salt is added to waste water containing citric acid and heavy metal ions to form a citrate complex of these metal ions. Next, it is described that the discharged heavy metal ions are precipitated as metal hydroxide by making the wastewater alkaline. However, the above citric acid complex of metal ions has a high solubility.
Which corresponds to about 700 mg / l as citric acid.
Therefore, although the heavy metal ions are reduced by the above method, the reduction of citric acid is limited to about 500 mg / l. The allowable value of COD for industrial wastewater differs depending on agreements with local governments, but is generally 10 mg / l or less, whereas, for example, the COD of wastewater containing 100 mg / l citric acid is 75 mg / l. To satisfy the value,
Further, a treatment such as an activated sludge method is required, and the treatment becomes complicated.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for treating wastewater containing citric acid and heavy metal ions, which can easily reduce both citric acid and heavy metal ions.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above-mentioned object, and as a result, have found that in wastewater containing citric acid and heavy metal ions, an excess amount of iron ion By adding copper ion or iron ion and copper ion to make iron hydroxide or copper hydroxide as alkaline, or by adding iron hydroxide or copper hydroxide, citric acid in the wastewater is changed to iron hydroxide Alternatively, they have found that they are efficiently adsorbed and precipitated on copper hydroxide, and have completed the present invention based on this finding. That is, the present invention provides a wastewater containing citric acid and heavy metal ions, by adding iron ion, copper ion or iron ion and copper ion in an amount of 2 to 10 times the weight of citric acid in the wastewater, The present invention relates to a method for treating wastewater, which comprises forming a precipitate containing an acid and a heavy metal, followed by solid-liquid separation.

The present invention still further relates to the above-mentioned method for treating wastewater, wherein 0.01 to 1 times by weight of alkaline earth metal ions is added to citric acid in the wastewater.

[0008] The present invention also relates to the above-mentioned method for treating wastewater, wherein the concentration of citric acid in the wastewater is measured, and the amount of iron ion, copper ion or iron ion and copper ion added is controlled based on the measured value.

The present invention also relates to a method of making a wastewater containing citric acid and heavy metal ions alkaline to form a precipitate containing citric acid and heavy metals, adding a copper or iron hydroxide and mixing the solid and liquid. The present invention relates to a method for treating wastewater, which is characterized by being separated.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The concentration of citric acid in waste water in the present invention is preferably 1000 mg / l or less.
The treatment is possible even if the concentration of citric acid exceeds 1000 mg / l, but the precipitation amount of copper hydroxide and iron hydroxide generated during the treatment is large and separation becomes difficult. The following concentrations are preferred.

The heavy metal ions contained in the wastewater include Ni, Mo, Co, Zn, Cu, Cr, In, and Sn.
And the like, and the concentration is preferably 300 mg / l or less. When heavy metal ions do not precipitate as metal hydroxide in a highly oxidized state, it is preferable to reduce the state to a low oxidized state with an appropriate reducing agent.

In the treatment, iron ions or copper ions to be added to the wastewater may be those existing from the beginning of the wastewater. If not present in the wastewater, an iron ion source or copper ion is added to the wastewater. Add ion source. When an iron ion derived from ferrous sulfate is used as the iron ion, the iron ion itself acts as a reducing agent, so that it is not necessary to use the reducing agent in advance.

The iron ion sources to be added include ferrous sulfate, ferric sulfate or iron chloride, hydroxide, oxide,
As the copper ion source, copper sulfate, copper nitrate, hydroxides and oxides of copper, and the like are used, but not limited to these. Ferrous sulfate is preferably used as an iron ion source, and copper sulfate is preferably used as a copper ion source because it is inexpensive and has little toxicity problem.

The amount of various metal ions to be added may be constant if the concentration of citric acid or the like is controlled, but the citric acid concentration is measured by a citric acid analyzer such as a high-performance liquid chromatograph. It is preferable to control the addition amount of iron ion, copper ion or iron ion and copper ion based on the measured value.

When these metal ions are added, the metal ion source may be added directly in a solid state, but it is preferable to add the metal ion source in advance as an aqueous solution because the treatment result is stable.

The amount of iron ions or copper ions to be added is 2 to 10 times the weight of citric acid in the waste water. When the addition amount is less than twice, the reduction of citric acid and heavy metal ions becomes insufficient, and when the addition amount exceeds 10 times, it becomes difficult to treat a large amount of metal hydroxide.

In the present invention, alkaline earth metal ions may be added to the wastewater together with iron ions and copper ions. As the alkaline earth metal ion, magnesium ion is preferably used. The amount of addition is preferably 0.01 to 1 times the weight of citric acid in the waste water. Addition of alkaline earth metal ions can further reduce citric acid and heavy metal ions.

An alkali such as sodium hydroxide is added to the wastewater to which iron ions or copper ions are added, and the wastewater is preferably adjusted to pH 8 to 12, more preferably to pH 9 to 12.
When alkalinized, heavy metal ions precipitate as metal hydroxides along with iron ions and copper ions. Citric acid is adsorbed by the precipitated iron hydroxide or copper hydroxide and its concentration decreases. If the pH is high, the adsorption of citric acid tends to decrease. At this time, if necessary, by using a polymer flocculant such as sodium polyacrylate, solid-liquid separation between the precipitate and the supernatant is facilitated.

According to another treatment method of the present invention, instead of adding iron ions or copper ions to the wastewater, the wastewater is made alkaline to cause precipitation containing citric acid and heavy metals, and further, a hydroxide of iron or copper. Is added and mixed, followed by solid-liquid separation. As the iron or copper hydroxide, wastewater containing hydroxide obtained by making wastewater containing iron ions or copper ions alkaline may be used. The citric acid can be efficiently adsorbed on the iron or copper hydroxide to reduce the concentration of citric acid in the wastewater. The amount of iron hydroxide or copper hydroxide to be added is the same as the amount of iron ions or copper ions described above in terms of ions.

The treatment according to the present invention can be carried out continuously or batchwise. However, in the continuous treatment, the residence time in the treatment layer needs to be longer than that in the batch treatment.

FIG. 1 shows an example of a processing apparatus for carrying out the processing method of the present invention. The wastewater containing citric acid and heavy metal ions is stored in the drain tank 1, then sent from the drain tank 1 to the mixing tank 2, and the iron ions or the iron ions sent from the processing liquid tank 5 by the processing liquid pump 4. It is mixed with a processing solution containing copper ions. Drain tank 1 and mixing tank 2
The flow path to is branched, and a citric acid analyzer 3 for measuring the concentration of citric acid in the wastewater is provided. Based on the measurement result of the citric acid analyzer 3, the flow rate of the processing liquid by the processing liquid pump 4 is controlled. As the citric acid analyzer, various analyzers can be used. For example, a high-performance liquid chromatograph is 1 mg / mg.
1 can be easily measured in a short time, and can be automated using an automatic sampling method using a valve switching method.

The wastewater mixed in the mixing tank 2 is transferred to a neutralization tank 6, and sodium hydroxide is added by a sodium hydroxide pump 8. The addition of sodium hydroxide is performed by controlling the sodium hydroxide pump 8 based on the output of the pH meter 7.

Next, the waste water is transferred from the neutralization tank 8 to the sedimentation basin 9 to settle the sediment, and the supernatant is transferred to the adjustment tank 10 and adjusted to pH 6 to 8, and then discharged to a river or the like. . Removal of fine sediment by filtration treatment for wastewater before discharge
Various treatments such as reduction of heavy metal ions by ion exchange treatment may be performed. The sedimented sediment is reduced in water content by the dewatering device 11 and disposed of as industrial waste. The wastewater generated in this step is preferably sent to the wastewater tank 1 for treatment.

[0024]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

Example 1 Nickel ion 10 mg / l, cobalt ion 30 mg
To 1 liter of waste water containing 200 mg / l and citric acid 200 mg / l, 4.5 g of ferrous sulfate heptahydrate was added, and the pH of the waste water was adjusted to 10.5 with a 40% aqueous sodium hydroxide solution.
To produce a precipitate. Further, 1 mg of sodium polyacrylate was added, and the coagulated and precipitated metal hydroxide was separated by filtration.

The metal ions in the filtrate were measured by the ICP method. Citrate ion is available from Showa Denko KK
It was measured by a high performance liquid chromatograph method using an organic acid analysis column KC-811 column. The column temperature was 70 ° C., a 0.1% by weight phosphoric acid aqueous solution was used as an eluent, and the measurement was performed at a wavelength of 214 nm by an ultraviolet absorption spectrometer type detector. The results are shown in Table 1.

Example 2 The procedure of Example 1 was repeated except that 6.0 g of ferrous sulfate heptahydrate was used instead of 4.5 g of ferrous sulfate heptahydrate.
The results are shown in Table 1.

Example 3 The procedure of Example 1 was repeated, except that 6.0 g of copper sulfate pentahydrate was used instead of 4.5 g of ferrous sulfate heptahydrate. The results are shown in Table 1.

Example 4 Example 1 was repeated except that 1.5 g of ferrous sulfate heptahydrate and 4.0 g of copper sulfate pentahydrate were used instead of 4.5 g of ferrous sulfate heptahydrate. The same treatment was performed. The results are shown in Table 1.

Example 5 In the same manner as in Example 1 except that 1.0 g of magnesium sulfate was used in addition to 4.5 g of ferrous sulfate heptahydrate. The results are shown in Table 1.

Example 6 10 liters of wastewater containing 150 mg / l of copper ions was adjusted to pH 9 with sodium hydroxide to convert the copper ions to copper hydroxide and concentrated to 1 liter by decantation. Nickel ion 10mg / l, cobalt ion 30
1 liter of wastewater containing 200 mg / l of citric acid and 200 mg / l of citric acid was adjusted to pH 10.5 with sodium hydroxide, and these heavy metal ions were precipitated as hydroxide. Mixed. After the mixture was adjusted to pH 10.5 with sodium hydroxide, 1 mg of sodium polyacrylate was added, and the precipitate was filtered off. Table 1 shows the measurement results of metals and citric acid in the filtrate.

Comparative Example 1 The procedure of Example 1 was repeated, except that 1.5 g of ferrous sulfate heptahydrate was used instead of 4.5 g of ferrous sulfate heptahydrate. The results are shown in the table.

Comparative Example 2 Example 1 was repeated except that 4.5 g of ferrous sulfate heptahydrate was not used.
The same treatment was performed. The results are shown in the table. Comparative Example 3 The procedure of Example 1 was repeated except that 2.5 g of magnesium sulfate heptahydrate was used instead of 4.5 g of ferrous sulfate heptahydrate. The results are shown in the table.

[0034]

[Table 1] * Copper ion equivalent

From the above results, when the amount of iron ion is 1.5 times the amount of citric acid, the effect of reducing citric acid is not sufficient.
It is clear that citric acid is sufficiently reduced by using 2 to 10 times the amount.

[0036]

According to the present invention, citric acid-containing wastewater is
By adding excess iron ions or copper ions to citric acid in the wastewater and making it alkaline, it is easy to simultaneously reduce citric acid and heavy metal ions,
It is extremely effective as a wastewater treatment method.

[0037]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a processing apparatus for performing a processing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drain tank 2 Mixing tank 3 Citric acid analyzer 4 Processing liquid pump 5 Processing liquid tank 6 Neutralization tank 7 pH meter 8 Sodium hydroxide pump 9 Settling tank 10 Adjustment tank 11 Dehydration device

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[Procedure amendment]

[Submission date] March 22, 2001 (2001.3.2)
2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

Next, the waste water is transferred from the neutralization tank 6 to the sedimentation basin 9 to settle the sediment. . Removal of fine sediment by filtration treatment for wastewater before discharge
Various treatments such as reduction of heavy metal ions by ion exchange treatment may be performed. The sedimented sediment is reduced in water content by the dewatering device 11 and disposed of as industrial waste. The wastewater generated in this step is preferably sent to the wastewater tank 1 for treatment.

Claims (4)

[Claims] 1. A wastewater containing citric acid and heavy metal ions is added with iron ion, copper ion or iron ion and copper ion in an amount of 2 to 10 times the weight of citric acid in the wastewater,
A method for treating wastewater, comprising making the wastewater alkaline to form a precipitate containing citric acid and heavy metals, and then performing solid-liquid separation. 2. The method according to claim 1, further comprising adding 0.01 to 1 times by weight of alkaline earth metal ion to citric acid in the waste water. 3. The method for treating wastewater according to claim 1, wherein the concentration of citric acid in the wastewater is measured, and the addition amount of iron ions, copper ions or iron ions and copper ions is controlled based on the measured value. . 4. A wastewater containing citric acid and heavy metal ions is made alkaline to form a precipitate containing citric acid and heavy metal, and a hydroxide of copper or iron is added and mixed, followed by solid-liquid separation. A method for treating wastewater.