JP2000202461A - Treatment of heavy metal complex-containing waste liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently separate heavy metal with less use quantity of chemical and to unnecessitate neutralization after the treatment, since the treatment enables at a lower pH region. SOLUTION: In this treatment method, a magnesium compound more than a reaction equivalent with respect to the heavy metal complex is added to the waste water containing heavy metal complex, and besides 50-5000 mg/l of an iron- and/or an aluminum compound are added, and the solid is separated from the solution at pH 5.5-9.5. Thus, the heavy metal can be efficiently separated with less chemical use quantity, and neutralization after the treatment is unnecessary and a synergetic effect can be obtained compared to separate treatments of respective compounds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating heavy metals from wastewater containing heavy metal complexes.

[0002]

2. Description of the Related Art Heavy metal wastewater containing a chelating agent is difficult to treat because heavy metals form a complex. Conventionally, as a treatment of wastewater containing a heavy metal complex, a method of adding calcium salts such as slaked lime and calcium chloride to carry out coagulation precipitation treatment, and adding iron salts such as iron chloride and iron sulfate to carry out coagulation precipitation. Or a method in which a heavy metal collector such as diethylcarbamate is used in combination with an iron or aluminum salt. However, the above-described treatment methods have problems in that the treatment efficiency is low, there are cases where there is no effect depending on the type of chelating agent, and there are cases where iron salts may remain in the treated water.

[0003] As a processing method for improving such a point,
Add magnesium compound to wastewater containing heavy metal complex
A method of performing solid-liquid separation at H10 to H12 has been proposed (JP-A-61-192386). This method can efficiently separate heavy metals with a smaller amount of drug used as compared to the above method,
Stable processing can be performed regardless of the types of heavy metals and chelating agents. However, since the treatment is carried out in a high pH region, a large amount of an alkali agent for adjusting the pH is required, and it is necessary to neutralize again with an acid to discharge the solution, which is not always efficient.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to carry out the treatment in a low pH range, whereby it is possible to efficiently separate heavy metals with a small amount of chemicals, and to neutralize after treatment. An object of the present invention is to provide a method for treating a heavy metal complex-containing effluent that is not required and has a synergistic effect.

[0005]

According to the present invention, a magnesium compound is added to a wastewater containing a heavy metal complex in an amount equivalent to or more than the reaction equivalent of the heavy metal complex, and an iron and / or aluminum compound is added in an amount of 50 to 5000 mg / l and a pH of 5 .5-
9.5 A method for treating wastewater containing a heavy metal complex, comprising performing solid-liquid separation in 9.5.

The wastewater to be treated in the present invention is wastewater containing a heavy metal and a chelating agent as a heavy metal complex, such as plating wastewater. Heavy metals include copper, chromium, zinc, lead, manganese, iron, nickel, cadmium and the like. Gluconic acid, citric acid,
Organic acids such as tartaric acid and malonic acid; and amines such as triethanolamine.

Magnesium compounds added to these wastewaters include magnesium oxide, magnesium hydroxide,
Any compound that releases magnesium ions, such as magnesium carbonate, magnesium chloride, and magnesium sulfate, may be used. These magnesium compounds have a reaction equivalent of at least a heavy metal complex (generally 20 to 500 m as Mg).
g / l), preferably 1 to 3 times the reaction equivalent.

[0008] Examples of the iron compound include ferric salts such as ferric chloride and ferric sulfate and polyiron, and a combination of a ferrous salt such as ferrous chloride and ferrous sulfate with an oxidizing agent. For example, any compound that releases ferric ion may be used. These iron compounds are contained in the wastewater in an amount of 50 to 5000 mg / l, preferably 20 to 5000 mg / l.
Add 0-3000 mg / l.

As aluminum compounds, aluminum sulfate, aluminum chloride, polyaluminum chloride (P
Compounds that release aluminum ions such as AC) can be used. These aluminum compounds contribute 5 to wastewater.
0 to 5000 mg / l, preferably 200 to 3000 m
g / l.

In the treatment method of the present invention, a magnesium compound is added to a wastewater containing a heavy metal complex with stirring, and after adding an iron and / or aluminum compound, the pH is adjusted to 5.5.
To 9.5, preferably 6 to 9, and insoluble matter is subjected to solid-liquid separation. It is preferred to add the iron and / or aluminum compound after adding the magnesium compound, but in some cases they may be added simultaneously or in the reverse order.

When the above-mentioned pH range is attained by these additions, it is not necessary to add a pH adjuster. In general, an alkali agent such as sodium hydroxide or calcium hydroxide can be used as the pH adjuster, but an acid such as hydrochloric acid or sulfuric acid can be used if necessary.

At the time of solid-liquid separation, a heavy metal collector such as diethyldithiocarbamate and other additives may be added, or a polymer coagulant may be added to perform coagulation precipitation. As the solid-liquid separation means, ordinary solid-liquid separation means such as sedimentation separation, flotation separation, centrifugation, and filtration can be used.

The stirring and mixing can be performed by stirring and mixing using a rotary stirrer, stirring and mixing using a pump, stirring and mixing using a line mixer, and the like. 10-300 in case of stirrer
rpm, preferably 20 to 150 rpm.

The above treatment will be described in the case of an organic acid. When an organic acid such as sodium gluconate and a metal ion such as trivalent chromium coexist, they form a complex and form an insoluble pH range of chromium (pH 8 to 9). ), No precipitate of chromium hydroxide is formed, and the chromium hydroxide is maintained in a dissolved state as shown in the equation (1).

^{Embedded image} Mg ³⁺ + L ^3- → ML [1] Metal ion Organic acid dissolved state

This becomes unstable on the alkaline side,
Although a hydroxide is generated as shown in the formula [2], this reaction is extremely slow and cannot be directly applied to wastewater treatment.

## STR2 ## ^{ML + 3OH - → M (OH} ) 3 + L 3- [2]

On the other hand, magnesium also forms a complex with an organic acid as shown in formula [3].

Embedded image 3Mg ²⁺ + 2L ^3- → Mg ₃ L ₂ [3]

For this reason, when making alkaline in the presence of magnesium ion, magnesium ion acts as an acceptor of an organic acid, and precipitation of a heavy metal hydroxide immediately occurs as shown in the formula (4).

Embedded image 2ML + 3Mg ²⁺ + 6OH ⁻ → Mg ₃ L ₂ + 2M (OH) ₃ ↓ [4] The amount of the magnesium compound to be added is appropriately from the reaction equivalent to the heavy metal complex in the formula [4] to 3 equivalents. Can be confirmed experimentally for each case.

In the reaction of the formula [4], precipitation of heavy metal hydroxide occurs rapidly in the pH range of 10 to 12,
Solid-liquid separation is difficult in the lower pH range. On the other hand, when iron and / or aluminum ions coexist, hydroxides of iron and / or aluminum and hydroxides of heavy metals are co-precipitated, so that the pH is 5.5 to 9.5.
Solid-liquid separation becomes possible even in a relatively low pH range.

[0019]

According to the present invention, a magnesium compound and an iron and / or aluminum compound are added to wastewater containing a heavy metal complex, and solid-liquid separation is performed at a pH of 5.5 to 9.5, thereby treating in a low pH range. This makes it possible to separate heavy metals efficiently with a small amount of drug used, eliminating the need for neutralization after treatment and achieving a synergistic effect compared to treatment with each compound alone. Can be

[0020]

Embodiments of the present invention will be described below.

Examples 1 to 3 and Comparative Examples 1 to 5 Each of chromium (III), copper and manganese was 50 mg / l.
Magnesium chloride was added to a solution containing 100 mg / l of gluconic acid and gluconic acid, and then ferric chloride was added thereto. Then, the pH was adjusted with calcium hydroxide or sodium hydroxide, and the mixture was reacted for 15 minutes to precipitate and separate. Filter paper no. Table 1 shows the results of the 5A filtrate analysis. The case where magnesium chloride is not added and the case where only magnesium chloride is added are shown as comparative examples. From the results in Table 1,
Gluconic acid complex has poor treatment effect only by adding iron salt and calcium salt, but magnesium salt and iron salt are added,
It can be seen that a stable treatment effect can be obtained by adjusting the pH with calcium oxide or sodium hydroxide.

[0022]

[Table 1]

Examples 4 to 8, Comparative Examples 6 to 9 Plating drainage of electronic parts (pH 2.2, Cu 92 mg /
l, containing 100 mg / l of citric acid), a conventional diethyldithiocarbamate-based heavy metal scavenger and an iron salt or an aluminum salt were added thereto, and the pH was adjusted with sodium hydroxide for coagulation precipitation treatment. The rate was poor (Comparative Example). By adding magnesium chloride to the system before adding the iron salt, a good removal effect was obtained. Also processing p
H showed a stable effect in the range of 6 to 9. Table 2 shows the results
Shown in

[0024]

[Table 2]

From the above results, all of the examples in which a magnesium compound and an iron or aluminum compound are used together have excellent treated water quality in a low pH range. This shows that a synergistic effect is obtained.

Claims (1)

[Claims] 1. A magnesium compound is added to a wastewater containing a heavy metal complex in an amount of at least a reaction equivalent of the heavy metal complex, and an iron and / or aluminum compound is added in an amount of 50 to 5000 m.
g / l, and solid-liquid separation at pH 5.5 to 9.5.