JPS60118288A - Water treating method - Google Patents

Abstract

PURPOSE:To efficiently remove an iron or calcium complex and a noxious metal ion, by adjusting the pH of metal complex-containing water discharged from a chemical plating process to 8 or less and, thereafter, adding a calcium compound and an iron compound to perform flocculation treatment at pH of 10-12. CONSTITUTION:The pH of water containing metal complex of a noxious metal ion such as nickel, zinc or copper and a complexing agent such as ethylenediamine tetraacstic acid or trinitrilotriacetate is adjusted to 8 or less and, on the basis of the metal complex, 2mol or more of a calcium compound and 3mol or more of an iron compound are added to the pH controlled water. Subsequently, an alkali agent is added to said water under stirring to adjust the pH thereof to 9.0 or more, pref, 10-11.5 and flocculation treatment is performed to remove an iron or calcium complex and the noxious metal ion from water. The adding order of the aforementioned calcium compound and iron compound is not especially limited. Further, as the alkali agent, sodium hydroxide or potassium hydroxide is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating water, and more particularly to a method for treating water containing metal complexes.

Various chelating agents are used in the plating process employed at plating factories. In particular, electroless plating (chemical plating), which has excellent surface properties, is increasingly being used.
citric acid, tartaric acid, citric acid,
Complexing agents such as oxycarboxylic acids such as gluconic acid and malic acid, and cardinic acids such as malonic acid, succinic acid and acetic acid are used.

Among these, aminocarginic acid and oxycarzenic acid form stable complexes with heavy metal ions in water, so it has been difficult to treat them by coagulation and sedimentation, which is commonly used in wastewater treatment.

Conventionally, substitution treatment involves adding iron salts or calcium salts to water containing harmful heavy metal complexes, converting the harmful heavy metals into iron or calcium complexes, and precipitating the released harmful heavy metals into hydroxides. method; and a method in which harmful heavy metal complexes are directly adsorbed onto activated carbon have been proposed, but their treatment effects are not always satisfactory, and in particular, KD
Almost no treatment effect was observed for TA-Ni complexes and the like.

In order to solve the drawbacks of the prior art, the present inventors have made extensive research and have discovered a method for efficiently removing metal, and have completed the present invention.

That is, the present invention is a water treatment method characterized by adding a calcium compound and an iron compound to metal complex-containing water and then performing a coagulation treatment.

The metal complexes targeted by this invention include nickel, zinc, copper,
It is a complex of harmful metal ions such as cadmium, lead, and cobalt with various complexing agents, and the complexing agents include aminocarzenic acids such as EDTA (ethylenediaminetetraacetic acid), nitritetraacetic acid, and iminodiacetic acid, citric acid, and tartaric acid. Examples include oxycaldic acid such as. However, depending on the type of metal in the complex, in the case of EDTA, the desired effect may not be obtained unless the amount added is significantly increased, and the target complex of the present invention preferably has 3 carzexyl groups. less than or equal to 1.

A calcium compound and an iron compound are added to such metal complex-containing water.

The calcium compound to be used is not particularly limited as long as it generates calcium ions in water, such as calcium chloride, calcium oxide, calcium hydroxide, etc., and one or two types can be used.
Use more than one species.

On the other hand, the iron compound may be any water-soluble iron salt such as ferric chloride, ferric sulfate, ferrous chloride, or ferrous sulfate, but ferrous salts are preferred from the viewpoint of cost and effectiveness. Furthermore, as the iron compound, pickling waste liquid containing abundant iron ions can also be used depending on the case.

The calcium compound and the iron compound may be added so that they coexist in the system, and the order of addition is not limited. Therefore, the iron compound may be added first and then the calcium compound may be added, or vice versa, or may be added at the same time. However, it is preferable to first add the iron compound and then add the calcium compound because the treatment effect becomes better.

When adding a calcium compound and an iron compound to metal complex-containing water, the pH of the water to be treated is adjusted in advance to 8 or less, preferably in the range of 2 to 6.

As described later, when calcium compounds and iron compounds are added to metal complexes and potted water, they cause a substitution reaction between the metal ions in the complex and calcium and iron ions. During the reaction, there is a core that keeps the calcium and iron compounds in ionic form in the water.

Therefore, when the p)I of the liquid to be treated exceeds 8, the added calcium compounds and iron compounds have a strong tendency to form hydroxides and become insolubilized, and eventually become completely useless.

On the other hand, the lower the p)I, the better, but if it is less than 2, the improvement in the effect will not be significant considering the amount of the pH adjuster added, and the result will be poor.

The pI required to adjust the pH to 8 or less (a known acid or alkaline agent can be used as the adjuster).

The amount of the calcium compound added varies depending on the content of all the complexing agents being treated, but is usually 2 moles or more of the content.

On the other hand, the amount of iron compounds added is 3 moles or more.

It has been confirmed that the effects of both compounds are improved as the amount added increases, and there is no particular upper limit.

However, if both amounts exceed 10 times the amount by mole, the rate of improvement will be small relative to the cost, so normally the upper limit may be set to 10 times the amount by mole.

When adding calcium compounds and iron compounds to the water to be treated, stirring is performed to ensure that the reaction proceeds sufficiently. The reaction time depends on the complex content, but usually one hour or less is sufficient.

As a result of the above treatment, toxic metal complexes that are extremely difficult to treat become iron complexes and calcium complexes that are relatively easy to treat due to the reaction between calcium compounds and iron compounds.

Although it is not clear why the present invention, which uses a calcium compound or an iron compound alone, results in efficient treatment, whereas it cannot be treated efficiently when a calcium compound or iron compound is used alone.
First, calcium or iron ions undergo a substitution reaction with the target harmful metal.

Then, since iron or calcium ions cause an insolubilization reaction on the substituted complex, it is presumed that calcium and iron ions act synergistically to efficiently remove harmful metals.

Next, in the present invention, iron or calcium complexes and harmful heavy metal ions are removed by water evaporation through aggregation treatment.

Coagulation treatment is carried out by adding an alkaline agent to the above-mentioned treated water while stirring.
This is carried out by adjusting H to 9.0 or more, preferably 10 to 11.5.

As the alkali agent, known alkali agents such as sodium hydroxide, potassium hydroxide, calcium hydroxide, and calcium oxide are used.

The reaction time is about several minutes to 30 minutes. Note that during the flocculation treatment, if several my/min of a known organic polymer flocculant such as a partially hydrolyzed polyacrylamide is added, the flocculation and precipitation treatment can be carried out extremely efficiently.

The aggregate thus produced is then subjected to solid-liquid separation using a solid-liquid separator.

The solid-liquid separator is not particularly limited, and a known settling tank or coagulation-sedimentation device can be used.

While the aggregates separated in this way are treated separately,
Treated water is discharged outside the system.

Example 1 As shown in Table 1, Cd, Nl, Cr, Zn
20 each of heavy metal ions selected from , Pb, and Cu.
The method of the invention was carried out on a solution containing 1,000 η/L of NTA, EDTA, citric acid, and tartaric acid.

First, the pH was adjusted to 4 with hydrochloric acid, then 1,000 η/L (as Ca) of calcium chloride was added under stirring, and then 1,000 mp/L of ferrous sulfate was added, followed by a reaction for 30 minutes. .

The pH was then adjusted to 11.0 with an IJ solution (hydroxide), and the resulting precipitate was filtered and separated using F paper.

The results of water quality analysis of the treated water are shown in Table 1.

As a comparative example, a) Each test water was directly adjusted to pH 11 with sodium hydroxide solution, and then solid-liquid separation b) Calcium chloride (2,000 Ing/L (as Ca) was added at pI (4) and reacted for 30 minutes. After that, the pH was adjusted to 11 with sodium hydroxide solution.*c) At pH 4, 2.000 m9/L of ferrous sulfate (as Fe) was added, and after reacting for 30 minutes, hydroxide was added. Three methods were also tested: adjusting the pH to 11 with a sodium solution followed by solid-liquid separation.

The results of each comparative example are also shown in Table 1.

(Left below) In the case of the method of the present invention, the Fe concentration in the treated water is 0.1
5 m9/L, whereas in Comparative Example C, the Fe concentration was 155 m9/L. It can be seen from this that the residual Fe concentration is also extremely reduced in the method of the present invention.

Example 2 Actual plating factory wastewater was used for treatment. Raw water quality is as follows.

pH12, CODMn220m9/l, EDTA52.
8m9/l.

Tartarite e5omy/l*gA K-k acid 25 Ni/
l.

Nl 10.8m9/L, Cu 6.8m9/L
, Znl 4. 'Imp/L was added and reacted for 30 minutes with stirring.

Next, the pH was adjusted to 11 with sodium hydroxide, and the resulting precipitate was separated in a precipitation tank. The results of water quality analysis of the supernatant water are shown in Table 2.

Additionally, the results obtained when the pH was directly adjusted to 11 with sulfuric acid are also shown.

As is clear from Example 1.2 in Table 2, harmful metal complexes, especially nickel complexes, which were difficult to treat by conventional methods, can be treated extremely well.

Patent applicant: NEC Corporation

Claims (1)

[Claims] 1. A water treatment method characterized by adding a calcium compound and an iron compound to metal complex-containing water and then performing a flocculation treatment. 2. The calcium compound is 3 mol or more based on the complex; Treatment method 3 according to claim 1, in which 2 moles or more of metal complex is added to the complex, and claim 1 or 2, in which the metal complex-containing water is adjusted to pH 8 or less in advance. Treatment method 4 according to claim 1, wherein the aggregation treatment is carried out at a pH of 10 to 12.