JPS6178491A - Treatment of pickling rinse waste liquid - Google Patents

Abstract

PURPOSE:To attain cost reduction, by measuring Cl<-> in a pickling rinse waste liquid and adding an oxidizing agent in an amount proportional to the concn. of a Cl<-> ion. CONSTITUTION:A pickling rinse waste liquid is introduced into an absorbing tower 2 and an oxidizing tower 3 from a raw water tank 1 by a pump and Fe<2+> is oxidized to Fe<3+> by an oxidizing agent such as sodium nitrite. The concn. of Cl<-> in the waste liquid is measured by a measuring instrument 5 and the oxidizing agent 4 corresponding to the concn. of Cl<-> is charged in the oxidizing tower 3. The oxidized waste liquid is neutralized by a neutralizing agent 8 such as calcium carbonate in a neutralization tank 7 to form hydroxide. Iron oxide is flocculated by a flocculant 9, and sedimented and removed in a thickener 10.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a method for treating pickling rinse waste liquid.

<Prior art and its problems> The cold rolling process differs from other rolling processes in that a large amount of waste liquid is discharged from the zero process, which includes pickling and alkali cleaning processes, and the processing process is complicated. This requires a lot of processing costs.

Among them, the pickling rinse waste liquid contains a large amount of soluble iron (iron ions, ferric ions), and if untreated, the water pollution control law (sea area pH 5-9°, river pH) l 5.8~
B, 8, Fe 10 PP @ or less), some kind of treatment is required.

Ferrous ion (Fe2+) and ferric ion7 (li e
3+), as shown in the table below, there is a large difference in solubility product and a large difference in precipitate p)I.

When removing iron ions from waste liquid containing iron ions by neutralization and precipitation, in order to meet the discharge standards, PH8 is required for PE2+.
, it is necessary to adjust the pH to 4 for Fe3+.

For this reason, Fe2+ requires expensive slaked lime as a neutralizing agent, but Fe2+ can be treated with inexpensive calcium carbonate.

On the other hand, regarding pickling rinse waste liquid, metallic iron and ugly (H+)
When reacting, hydrogen gas is generated, but this hydrogen gas is extremely active and reduces even Fe3+ in the pickling rinse waste solution, so Fe2+ in the waste solution accounts for 80% of the total dissolved outer iron.
% or more.

Therefore, when treating pickling rinse waste, Fe2+ is oxidized using an oxidizing agent such as sodium nitrite, as shown in the formula below.
After oxidizing to e3+, neutralization and precipitate are removed.

2FeC12+4)IC1+2NaNO2-42FeC
l3÷2 NaC1+2 H20+2 NOAs this reaction formula shows, the amount of oxidizing agent required for oxidation is Fe2+
It is related to the concentration, and it is sufficient to inject an amount of oxidizing agent corresponding to the Fe2+ concentration.

For this reason, continuous analysis of Fe2+ was difficult in the past.
The first decision to inject the oxidizer was made by periodically measuring Fe2+.

The Fe2+ concentration in the pickling rinse waste fluid fluctuates widely.

An example of this is shown in FIG.

(1) The Fe”13 degree of the pickling rinse waste fluid fluctuates significantly as shown in Figure 1, so in the conventional method, it is necessary to add an excessive amount of oxidizing agent such as sodium nitrite, which poses a cost problem. was there.

(2) If high-concentration waste liquid of Fe2+ was generated due to unavoidable reasons on the source side, there was a possibility that it could not be treated.

(3) By using more sodium nitrite than the theoretically required amount, the nitrogen concentration in the treated water (effluent water) increases. Nitrogen in wastewater, along with phosphorus, is thought to be a cause of eutrophication of public water bodies.

<Objective of the Invention> The present invention was made in view of the above-mentioned circumstances, and its object is to provide a method that can inexpensively process pickling rinse waste liquid so as to satisfy water quality standards. There is something to do.

<Structure of the Invention> The present invention is characterized in that Fe"8 degree is about 50 to 2000 PPs and p
Regarding the treatment of pickling and rinsing waste liquid with H of 1 to 3, C in the waste liquid
Continuously measure the I-concentration using a measurement base such as an ion electrode method,
By adding an oxidizing agent, such as sodium nitrite, in an amount proportional to the Cl concentration, the amount of oxidizing agent used can be optimized to stabilize costs and processing.

The present invention will be explained in detail with reference to the accompanying drawings.

As shown in Figure 2, the Fe”e degree is approximately 50 to 2000p.
The pickling and rinsing waste liquid of the p layer is transferred from the log tank 1 to the absorption tower 2. Water is introduced into the oxidation tower 3.

Fe2+ is oxidized to Fe3+ with an oxidizing agent 4 such as sodium nitrite.

At this time, instead of injecting the oxidizing agent appropriately, the cfL-e concentration in the waste liquid is measured using a measuring device 5 such as an ion electrode meter, since the Fe2+ concentration and the 0-mon- concentration in the waste liquid have a high correlation. Then, the oxidizing agent 4 corresponding to (proportional to) this concentration is introduced into the oxidizing tower 3 by the oxidizing agent injection control device 6.

The oxidized wastewater is neutralized in a neutralization tank 7 with a neutralizing agent 8 such as calcium carbonate, and hydroxide is generated. After the iron hydroxide is flocculated by flocculant 9, it is flocculated by thickener 1.
The precipitate is removed at 0. The supernatant liquid of the thickener 10 is discharged, and the precipitate is turned into a cake by a dehydrator 11 such as a belt filter, and then recycled or disposed of in a landfill.

Practical example The present invention will be specifically explained below with reference to examples.

Fe2+ concentration and C1− of pickling rinse waste liquid from cold rolling process
The relationship with concentration was investigated. A highly correlated regression equation, the results of which are shown in FIG. 3, was obtained.

In the pickling line, kMe# used as pickling liquid dissolves metal iron, but chemically 1d, theoretically J1! As the amount of acidic acid increases, the amount of iron that dissolves also increases, so the regression equation with this high correlation seems to have been ignored.

Pickling and rinsing waste liquid (pH 2, 1,
Regarding Fe2+ ion C degree 200rsg/l),
Using NaNO2 as an acid inhibitor, add 240 layers of NaNO2 to oxidize Fe2+ to Fe3+, and use G as a neutralizing agent.
When aCO3 was used and 55 hg/JL was added, the Fe concentration became lag/2 or less. The amount of oxidizing agent added was determined by measuring the carbon concentration using a measuring device (ion electrode meter).

With this method, the amount of oxidizing agent used was reduced by 30% compared to the conventional method. Furthermore, since nearly all of the Fe2+ ions are oxidized to Fe3'+ ions, inexpensive calcium carbonate can be used as a neutralizing agent, saving both the oxidizing agent and the neutralizing agent, resulting in cost reduction.

<Effects of the invention> (1) The amount of oxidizing agents such as sodium nitrite is optimized,
Cost reduction can be achieved.

(2) Even if high-concentration waste liquid of FeZ+ is generated due to unavoidable reasons at the source, it can be sufficiently oxidized and the treatment can be stabilized.

(3) When using an oxidizing agent containing N such as sodium nitrite, N content will migrate into the effluent water, but by optimizing the amount of sodium nitrite used, the amount of N content transferred can be minimized. It can be held down to

(4) In the neutralization stage, if the concentration of FeZ+ is high, expensive slaked lime is required as a neutralizing agent.

As in the present invention, Fe2+ is always close to 100% < Fe3
If it is oxidized to '+', it can be neutralized using only inexpensive calcium carbonate. Further, when calcium carbonate is used as a neutralizing agent, the compactability of the precipitate is higher than that of slaked lime, so the amount of cake generated is reduced and the cost of landfill disposal is reduced.

[Brief explanation of drawings]

FIG. 1 is a graph showing the change over time in the Fe2+ concentration in the pickling rinse waste liquid. Figure 2 is 1! for explaining the method for treating pickling and rinsing waste liquid of the present invention. It is a diagram. FIG. 3 is a graph showing the correlation between the Fe2+ concentration and the Cl- concentration in the pickling rinse waste liquid. Explanation of symbols■... Raw water tank, 2... Absorption tower, 3... Oxidation tower, 4
... Oxidizing agent, 5... C1-ion measuring device, 6...
Oxidizing agent injection control device, 7... Neutralization tank, 8... Neutralizing agent, 9... Coagulant. 10... Thickener, 11... Dehydrator FIG, 1 Days FIG, 2 FIG, 3 Cji Concentration 3 (mq/l)

Claims (1)

[Claims] A method for treating pickling and rinsing waste, characterized by continuously measuring Cl^- ions in the pickling and rinsing waste, and adding an oxidizing agent in an amount proportional to the Cl^- ion concentration. .