JPS58186495A - Neutralization treatment of waste water - Google Patents

Abstract

PURPOSE:To reduce the cost for neutralization treatment of waste water of pickling considerably, by adding a mixed soln. of the dust produced in the stage of desulfurizing molten iron to waste water contg. acid thereby making effective use of the above-described dust which is heretofore discarded. CONSTITUTION:Molten iron is contained in an iron pouring ladle, and a desulfurizer contg. limestone and quicklime at 1:1 ratio and compounded with about 5% soda ash is added thereto. The molten iron is desulfurized by agitation with an impeller, then slag is discharged therefrom. Dust is generated together with a generated gas in this stage; therefore, a hood is put on the powdery dust and the dust is sucked and collected with a dust collector. When such dust is added to waste water contg. acid as a neutralizer, the neutralization capacity equivalent to the capacity of conventional neutralizers such as caustic soda, soda ash or the like is provided. If the above-descirbed dust is added as a neutralizer to the waste water contg. acid and further contg. metallic salts, the settling speed of the formed sludge is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for neutralizing acid-containing wastewater such as steel pickling wastewater.

For surface RFI cleaning of hot-rolled steel sheets, steel bars, and other steel materials, pickling treatment with hydrochloric acid, sulfuric acid, or the like is performed.

This pickling wastewater is rounded and neutralized with a neutralizing agent that contains acid, the generated sludge and the like are allowed to settle, and the supernatant liquid is discarded.

As neutralizing agents, caustic soda (NaOH), soda ash (NmlCO3), quicklime (CaO), slaked lime (C
a (OH)*) is used, and limestone (C@COs) is known as a naturally occurring material.

However, a large amount of pickling wastewater is generated, and the use of such a neutralizing agent increases the processing time accordingly.In particular, quicklime or limestone needs to be crushed, and the disadvantage is that the Vc: 2 stroke is high. There is.

This invention was developed for the purpose of low-cost neutralization treatment of pickling wastewater, and its gist is that a mixture of dust generated during hot metal desulfurization treatment is added to acid-containing wastewater. That is.

The inventors conducted various studies and experiments on neutralizing agents for acid-containing wastewater, and as a result, they discovered that a mixed solution of dust F generated during hot metal desulfurization treatment is most suitable as a neutralizing agent.

Hot metal desulfurization treatment includes ■ desulfurization method or soda ash desulfurization method.

■The general desulfurization treatment method involves placing hot metal in poured steel, adding a desulfurizing agent, stirring in an in-vehicle to desulfurize, and then draining the slag. As a desulfurizing agent, limestone (C, Co,
N,,GO,), etc. are used. The desulfurization reaction is based on the following formula.

2CaωB + 35 →2Ca S + So, ↑+
2ωs4 − (1)2 Cm O+ 38 →2Ca
S + sOg small - (2) As seen in this reaction equation, ω, gas or button, gas is generated and dust is generated along with the generated gas.

This dust is collected by a dust collector after it is sucked in with a hood. The concentrated dust is a fine powder, and its components include limestone and quicklime. An example of the particle size distribution is shown in the first example.
An example of the ingredients is shown in Table 2.

4$1 Table 2 Table 2 As is clear from Tables 1 and 2, the dust during the KKR desulfurization treatment is a very fine powder, and the main components are caco and CaO. As a result of experiments using this dust as a neutralizing agent for acid-containing wastewater, it was found that this dust has a neutralizing ability comparable to that of the above-mentioned neutralizing agent. In addition, gold-salt (iron chloride or iron sulfate) is used for pickling wastewater, etc.
However, the reaction formula in which sludge (iron hydroxide) is generated when an acid containing such a metal salt is neutralized is according to the following formula.

2F @Cjm+ 3Ca■s” 3H1O→2F6
(OH)s↓+3CaC1m+3CO...(3) 2FgC1m + 3CaO+ 3810→2Fe (
OH)s↓+3C@cl, ++ (4)F, SO4
+C,Q), +H* O→F* (OH) t↓+C
, SO.

+ co,,,7-...(5) Fe 804 + CaO+ I[,O→F *(
OH) m↓+C,SO4・(6) The sludge generated by this reaction is allowed to settle and the supernatant liquid is discarded, but if the dust generated during hot metal desulfurization is used as a neutralizing agent, the rate of settling is extremely fast. I actually confirmed this.

As mentioned above, dust is a very fine powder and has good paper reactivity and can be used as is without the need for pulverization, so it is less expensive and more effective than using conventional neutralizing agents.
This method greatly reduces the cost of neutralizing wastewater.

A more detailed explanation will be given based on examples.

Example 1 A neutralization test was conducted on pickling wastewater from hot-rolled steel sheets.

The components and properties of the pickling wastewater are shown in Table 3. iJa Table 800cc of this pickling wastewater was placed in a 1j beaker, stirred on a magnetic shoe, and adjusted to a weight concentration of 211 while blowing air.Ca(OH) *Neutralization titration comparison was performed by adding the emulsion and the Das F emulsion obtained during KR desulfurization treatment. FIG. 1 is a diagram showing an embodiment of the first embodiment. (1) is a beaker, (2) is pickling wastewater, and (3) is PH1t.

(4) is an air blowing bud, (5) is a titration tube for neutralizing agent, (
6) is a magnetic metallizer that stirs the waste water in the beaker. FIG. 2 is a diagram showing the relationship between the amount of neutralizing emulsion added and the pH value of wastewater. The horizontal axis is the amount of neutralizing emulsion added, and the vertical axis is the pH value. In the figure, the solid line shows the change in Cm(OH) and the OPH value when the emulsion is added, and the broken line shows the change in the PH value when the dust emulsion in the KR desulfurization treatment is added. + *Washing wastewater needs to be neutralized to a pH value of 6.8 to 8.6 and then disposed of, but as shown in Figure 2, 3 to 4 f/l of emulsion (Dus during desulfurization treatment) is added. Then, the pH value becomes 6.8 to &6, and when 4f/1 or more is added, the pH value can be raised to about 10.

Example 2 FIG. 3 is a diagram showing an embodiment of the second embodiment.

In Fig. 3(a), pickling wastewater shown in Table 3 was taken from 11 beakers K 500cc and placed in a magnetic stub (
6) While stirring and blowing air, 9 Cm(OH)s emulsion and 32/l of dust emulsion from KR desulfurization treatment were added with careful adjustment twice, and the change in box value over time was measured. did. FIG. 4 shows the transition of the P■ value of the wastewater with the elapsed time. The horizontal axis shows the elapsed time, and the vertical axis shows the PH value.The solid line in the diagram shows Cm (
OH) is the one with the addition of emulsion, and the broken line is the one with the addition of dust emulsion in the KR desulfurization process. After adding 2 as shown in the figure
In ~3 minutes, the pH value rose to within the specified range of 6.8 to 8.6.

In addition, in Example 2, a sedimentation test of sludge generated in this waste water was also conducted. In Fig. 3(b), 0.2 ppm of polymer flocculant was added to this waste water and a jar tester (7
) for 1 minute with rapid stirring (rotation speed 15 Orpm), and then slow stirring (rotation speed 5 Orpm) in Figure 3 (-C).
pm) for 5 minutes, and as shown in FIG. 3(d), the water was packed for 25 minutes to measure the drain height V and sludge height V, and the sludge volume ratio V/V. Figure 5 shows elapsed time and sludge volume ratio V/V. FIG. The horizontal axis shows elapsed time, and the vertical axis shows sludge volume ratio. In the figure, the solid line is ca (OH), - for emulsion neutralization, and the broken line is n
This is due to neutralization of dust emulsion during desulfurization treatment. As shown in the figure, the dust emulsion neutralized sediments quickly, and
This indicates that sedimentation occurs after a sedation time of about minutes.

Table 4 shows the results of investigating the supernatant.

Table 4 As is clear from Table 4, the water neutralized by the method of the present invention has a lower COD d degree and shows better results than the neutralized water obtained by the conventional method.

Example 3 The neutralization treatment method of the present invention was implemented in a neutralization treatment facility that combines 400 m/brim of pickling process wastewater from a hot rolling mill, pickling process wastewater from a fertilizing plant, and alkali pickling process wastewater from a cold rolling factory. . The implementation results are shown in Table 5.

Table 5 As shown in Table 5, good results were also obtained in the neutralization treatment facility.

As described above, this inventive method effectively utilizes the dust generated during desulfurization of hot metal, which was conventionally discarded, as a neutralizing agent for acid-containing wastewater such as cleaning wastewater, thereby reducing the cost of neutralizing pickling wastewater. There is a remarkable effect of a significant reduction.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the embodiment of Example 1, and FIG. 2 is a diagram showing the relationship between the addition of a neutralizing agent emulsion and the PR value of wastewater. Figure j3 is a diagram showing the embodiment of Example 2, Figure 4 is a diagram showing the elapsed time and the transition of the pH value of the wastewater, and Figure 5 is a diagram showing the relationship between the elapsed time and the sludge volume ratio v, 'v0. It is. In the figure, 1...beaker, 2...pickling wastewater, 3...
PH meter, 4...Air blowing tube, 5 River titration tube, 6...
Magnetex Stub-17...Jar tester. Source: Sumitomo Metal Industries, Ltd. Figure 1 Figure 3 (α) (b) (c)
(d) Figure 4

Claims (1)

[Claims] A method for neutralizing wastewater, which is characterized by adding a mixture of dust generated during hot metal desulfurization treatment to acidic wastewater.