JPS61174990A - Water treatment - Google Patents

Abstract

PURPOSE:To decolorize water contg. metallic ions at a small treating expense and to prevent the deposition of scales by using a chemical agent such as ethylenediaminetetraacetic acid or its derivative in the water treatment. CONSTITUTION:In the treatment of water such as city water, a chemical agent such as etylenediaminetetraacetic acid (hereinafter referred to as EDTA) and its derivative is used in the treatment of water contg. metallic ions at the rate of 1-100mg per liter of water. Consequently, the metallic ions causing the coloration of water combine rapidly with EDTA to form a chelate compd., and the water is decolored. Accordingly, the method is extremely economical. In a heat exchanger troubled by the deposition of scales, the water contg. EDTA is heated, and the deposition of scales can be easily prevented in addition to the decolorization of the water.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a water treatment method for decolorizing municipal water, particularly tap water.

[Prior Art] Regarding the color of drinking water, in Japan, Article 4 of the Water Supply Law stipulates that drinking water should be colorless in appearance. For industrial water, the chromaticity is defined as 20-70. The quality of the raw water that becomes tap water varies greatly depending on the region, and methods for decolorizing it include chemical oxidation, activated carbon adsorption, and biological oxidation. Regarding chemical oxidation methods, there are phosphate-based agents and silicate-based agents as typical water treatment agents that are permitted to be added to tap water. Nitrite-based chemicals are also used in non-potable water systems.

[Problems to be solved by the invention] However, all three conventional methods, activated carbon adsorption and biological oxidation, require expensive equipment and operating costs, and the most economical chemical oxidation method does not work well as a water treatment agent. Phosphate-based chemicals have problems such as not being expected to be effective in water with low hardness components, and Kei I-based chemicals having little effect when added in small amounts, and causing swool to accumulate in pipes when added in large amounts. had.

Therefore, when using these chemicals as water treatment agents, cleaning the pipes with chemicals or mechanical treatment is necessary to prevent the accumulation of high-grade components and scale components in the water, especially in heat exchangers, to prevent a decrease in heat transfer. It is necessary to perform extensive cleaning, which also leads to increased costs due to wear and tear on piping materials and wastewater treatment.

SUMMARY OF THE INVENTION An object of the present invention is to provide a water treatment method that eliminates the drawbacks of the prior art described above, requires less treatment cost, has an excellent decolorizing effect, and is free from scale deposition.

[Means for Solving the Problems] The gist of the present invention is to use ethylenediaminetetraacetic acid (hereinafter referred to as EDT) as a metal ion sequestering agent, that is, a coloring preventive agent in service water.
A) or its derivatives.

That is, the water treatment method is characterized by using a chemical such as ethylenediaminetetraacetic acid or its derivatives in the water containing metal ions, and the amount of the chemical used is 1 u per 1 Jl of the water. ~1.00010 is effective, and is particularly effective for tap water.

The following drugs are derivatives of EDTA.

Ethylenediaminetetraacetic acid sodium salt (EDTA-2N
a), ethylenediaminetetraacetic acid potassium salt (EDTA-
2K), ethylenediaminetetraacetic acid calcium salt (EDT
A-2Ca), magnesium ethylenediaminetetraacetate m
(EDTA-2Mg> and other EDTΔ metal salts.

[Function] EDTA used in the present invention reacts with most metal ions in water to form a stable chelate compound. This chelate compound has very high solubility in water and decolorizes water. The structural formula of EDTA is EDTA and metal ion M2+ Which reaction is as follows: + (EDTA)' - + M2 M (EDTA)2 - The stability constant at that time is the metal chelate stability constant given by the following formula. Table 1 Shown below.

Table 1 In this way, it can be seen that stable compounds are created with all metal ions and water coloring is prevented. Similarly, drugs that are derivatives of EDTA exhibit similar effects.

Example] (1) Fe3 + in a white container with a depth of 1 m,
Cu2 + 'IrNN water to pH 10 and 1.2 each
, 4.6°B, 10 (llo/J) was added,
The amount of EDTA added is 1 g/l necessary to eliminate the coloring.
The results are shown in Figure 1.

It was shown that in the case of metal ions of 1 o/J, 2 to 5 mg/l of EDTA is required, but when the metal ions are about 1 oppi+, 40 to 50 on of EDTA is required.

In addition, the metal ion concentration is 1l1+II/J! Normally, the coloration of water cannot be detected, but when detergent, which is an alkaline ingredient, is mixed in, even metal ions of 1l1l0/Jl form hydroxides, and the color can be detected with the naked eye.This experiment also shows this point. The pH of the distilled water was adjusted to 10.

■ Tap water containing 50 ppn+ of Ca2+ is circulated in a closed circuit of steel pipes, and the steel pipes are heated with hot water from the outside to create an environment where scale containing Ca is easily formed inside the copper pipes.This tap water is free of EDTA. Addition.

25.50,100,200.300 <llQ/I!
) was measured and compared for the amount of scale in the tubes after 30 days with the addition of EDTA. In this case, the experimental conditions are:
Steel pipe size outer diameter 15.88. Thickness 0.7, length 500
Average flow velocity in the pipe is 0.5 m/sec.

The temperature of the hot water for heating was 60°C, and the pH was 7.5. Figure 2 shows the results. Under conditions without EDTA, the inner tube area is 1
While 200+no scale was attached to C12,
No scale was generated when 300 mg/Il of EDTA was added. Even with the addition of 25+++o/Il, the scale generation was reduced to less than half. This effect is EDT
This effect is due to the fact that A adsorbs to the inner surface of the steel pipe under high temperature conditions and forms a film, which acts as an inhibitor that prevents direct contact between the metal and the inorganic substance.

[Effect of the Invention J According to the present invention, by simply adding EDTA to the water, the metal ions in the water, which are the cause of coloring the water, quickly form a chelate compound with EDTA to decolorize the water. This is a very economical method. In addition, in a heat exchanger where there is a concern about scale accumulation, by heating service water containing EDTA, not only decolorization but also the effect of preventing scale accumulation can be easily obtained.

[Brief explanation of drawings]

Figure 1 shows the EDTA required for decolorization depending on the metal ion concentration.
A diagram of one example showing the relationship with the concentration of EDTA.
FIG. 2 is a diagram of one example showing the relationship between the concentration of and the amount of scale deposited. 1st child: 2 mouths of EDTA not added>/.

Claims (3)

[Claims] (1) A water treatment method for industrial water, characterized in that a chemical agent such as ethylenediaminetetraacetic acid or a derivative thereof is used in water containing metal ions. (2) The amount of ethylenediaminetetraacetic acid or its derivatives used is 1 mg or more per 1 liter of water for 1,000 m
The water treatment method according to claim 1, wherein the water treatment amount is less than or equal to g. (3) The water treatment method according to claims 1 and 2, wherein the water used is tap water.