KR20020014445A - Waste water treatment agent and a method for treating waste water using it - Google Patents

Abstract

PURPOSE: Provided is a wastewater treatment agent and method for treating wastewater using the same. The agent is applicable to the stainless manufacturing plant. Generally, Waste acids containing heavy metals are produced in the stainless cleaning process using many acids. When waste acids are treated by using wastewater treatment agent, much sludge cake is produced. Therefore, provided wastewater treatment agent is used for treating waste acids without producing much sludge cake. CONSTITUTION: The agent is composed of KOH of 10-40 wt.%, Lanthanum of 0.5-5.0 wt.%, and hydroxylamine chloride of 0.05-1.5 wt.%. According to the method for treating wastewater using the agent, the agent of 1-6L is injected into the waste acids of 1L.

Description

Wastewater treatment agent and wastewater treatment method using same {WASTE WATER TREATMENT AGENT AND A METHOD FOR TREATING WASTE WATER USING IT}

The present invention relates to wastewater treatment, and more particularly, to a treatment agent for treating various wastewater generated in the production of stainless products and a treatment method thereof.

In general, stainless hot rolled and cold rolled mills use a large amount of acid such as sulfuric acid and mixed acid (HNO ₃ / HF) to wash the surface of the product to show the unique luster of stainless steel. During this pickling process, waste acid containing heavy metals such as Fe, Cr, and Ni melted from the surface of the stainless strip is generated. In addition, the acid and strip react during pickling, producing NOx, SOx, and F ^- gases, which are highly corrosive and toxic from the acid. These harmful gases are removed by adding absorbing solution to prevent them from scattering into the atmosphere. At this time, the waste absorbing solution should be treated with wastewater using wastewater treatment agent together with waste acid.

On the other hand, when the waste acid is treated using a wastewater treatment agent, a large amount of sludge cake is generated, which is expensive when landfilling it. In the heavy metal contained in waste water generated Mn, T-Cr, Cr ^+6, and fluorine (F ^-), COD, etc. The fluorine-regulation level of the plant water quality conservation methods: 15ppm or less, Mn: 10ppm or less, T-Cr: 2.0ppm It should be less than or equal to Cr ^{+ 6} : 0.50ppm.

As such, in order to remove fluorine and heavy metal ions contained in the wastewater, a wastewater treatment apparatus as shown in FIG. 1 has been widely used. As a representative conventional method using the wastewater treatment apparatus as shown in FIG. This method first collects the waste acid and waste absorbent liquid into the waste acid collection tank (1), transfers it to the primary neutralization tank (2) by a certain amount, and adjusts it to neutral (pH 7.0 ~ 8.0) by adding 10% lime solution. Fluoride ions are formed as precipitates of calcium fluoride, and heavy metals as hydroxide precipitates. In the first neutralization treatment, unreacted fluorine ions and heavy metals, especially hydroxide hydrates, are formed at pH 9.5 or higher to remove Mn, and 10% slaked lime solution is added to the secondary neutralization tank (3). ~ 10.5). Subsequently, the reaction time is given in the 3rd neutralization tank 4 to make a complete reactant. Thereafter, since the calcium fluoride precipitation type and the hydroxide precipitation type are very unstable, a certain amount of flocculant (polyaluminum chloride) is added and then sent to the flocculation tank 5. Wastewater coagulated in the coagulation tank (5) is sent to the settling tank (6) to separate the supernatant and sludge, and the supernatant is filtered through a sand filter (7), and the filtrate is de-neutralized to pH 5.8-8.6. After adjusting to the outlet, discharge it to the discharge tank (8). At this time, the sludge settled in the settling tank is pressed into a cake state is sent to the landfill.

Generally, waste acid (H ₂ SO ₄ : 120g / l, HNO ₃ / HF mixed acid: 75 / 20g / l) and waste absorbing liquid (KMnO ₄ + NaOH + NOx) generated in stainless hot rolled and cold rolled mills are at high concentrations. The liquidity of the wastewater collection tank which collects this waste acid and waste absorption liquid is strong acid with pH below 1.5. When this waste acid is treated by the slaked lime neutralizing method, a high concentration of slaked lime of about 10%, which is used as a neutralizing agent, should be used. However, in general, hydrated lime is almost insoluble in water, and thus, hydrated lime is used in the form of lime milk, and when the heavy metal in the waste acid reacts with solid acid, solid hydrated lime is deposited on the hydroxide precipitate. As it forms and solidifies, much larger amounts of sludge are produced than actual sludge produced during waste acid and wastewater treatment. Moreover, in the milked slaked lime, undissolved slaked lime in the slaked lime solution tank solidifies at the bottom of the tank unless the stirring is intensified. In addition, when delaying the transfer or stopping the wastewater treatment for a short time due to the pH rise of the solution inside the tertiary neutralization tank 4 and the repair of the neutralization tank, there is a problem in that the transfer pipe is clogged because the lime is solidified inside the transfer pipe. In addition, the sulfuric acid contained in the waste acid reacts with hydrated lime to turn into an insoluble substance (calcium sulfate), which is more reactive than hydrofluoric acid, which prevents the waste hydrofluoric acid from forming a precipitate of calcium fluoride, thus causing a complete reaction, and thus, in the final discharged water. In some cases, the fluorine plant contained water is outside the regulations of the Conservation Act.

The present invention has been proposed to solve such a conventional problem, by efficiently treating the waste acid generated in the stainless manufacturing plant to reduce the amount of sludge cake generated at this time, and also each anion and heavy metals generated during waste acid treatment plant water quality It is an object of the present invention to provide a wastewater treatment agent and a wastewater treatment method using the same, which can be managed within the regulation of the Environmental Conservation Act.

1 is a schematic configuration diagram of a general wastewater treatment apparatus

Explanation of symbols on the main parts of the drawings

1 ..... waste acid collection tank, 2 ..... 1st neutralization tank, 3 ..... 2nd neutralization tank,

4 ..... tertiary neutralization tank, 5 ..... flocculation tank, 6 ..... sedimentation tank,

7 ..... sand filter, 8 ..... drain

The present invention for achieving the above object relates to a wastewater treatment agent comprising, by weight, KOH: 10-40%, lanthanum ion: 0.5-5.0%, and hydroxylamine chloride: 0.05-1.5%.

The present invention also relates to a wastewater treatment method in which the wastewater treatment agent is added in a range of about 1000 to 6000 ml per 1000 ml of wastewater.

First, the wastewater treatment agent of the present invention will be described in detail.

Potassium hydroxide contained in the wastewater treatment agent of the present invention serves to convert the waste acid to neutral by reacting the OH ⁻ group with H ⁺ in the waste acid. At this time, when the concentration of potassium hydroxide is 10% by weight or less, the amount of the wastewater treatment agent is relatively increased, and when the concentration of potassium hydroxide is more than 40% by weight, it is difficult to control the amount of the treatment agent.

In addition, the lanthanum ions combine with fluorine ions in hydrofluoric acid contained in the waste acid to form lanthanum fluoride precipitates. In the case of the present invention, any of the lanthanum compounds containing lanthanum ions can be used. Preferably, fluorine ions are not contained in the lanthanum compound, and examples thereof include La (NO ₃ ) ₃ and LaCl ₂ . If the content of the lanthanum ion is less than 0.5% by weight, the effect of the hydrofluoric acid in the waste acid is high, and the effect is insignificant.

The hydroxyl chloride chlorine is added to the waste gas absorption liquid with waste acid, potassium permanganate (KMnO ₄ ) chromium, which is a heavy metal in the waste acid is converted into a hexavalent state, so it is not removed by the hydroxide precipitate, put a hydroxyl chloride as a reducing agent give. Thus, hydroxylamine chloride serves as an adjuvant to completely reduce the oxidation of the oxidized heavy metals by the reduction of hexavalent chromium in the waste water to trivalent chromium. For this purpose, it is necessary to add at least 0.05% by weight of hydroxylamine chloride, but when 0.5% by weight or more is added, hexavalent chromium is no longer detected, which is uneconomical.

When the wastewater treatment agent prepared as described above is added to the neutralization treatment apparatus as shown in FIG. 1, the wastewater discharged from the stainless hot rolling process is regulated to environmental pollution, that is, COD: 90 ppm or less, Mn: 10.0 ppm or less, T-Cr: 2.0 ppm or less, Cr ^+6: 0.05ppm or less, and F ^-: can be controlled to less than 15.0ppm. At this time, the input amount is preferably in the range of about 1000 ~ 6000ml, the reason is that if the input amount of the treatment agent is too small, waste water treatment is insufficient, if too large, the amount of the discharged water is rather large, which is not preferable.

In the wastewater treatment according to the present invention, the main reaction occurs as in Chemical Formulas 1 to 11.

HNO ₃ + KOH → KNO ₃ + H ₂ O

HF + KOH → KF + H ₂ O

H ₂ SO ₄ + 2KOH → K ₂ SO ₄ + 2H ₂ O

The reactions of Chemical Formulas 1 to 3 neutralize strongly acidic waste acid with alkali. In addition, heavy metals such as Fe, Cr, Ni, and Mn dissolved in the waste acid are reacted as follows.

Fe (NO ₃ ) ₂ + 2KOH → Fe (OH) ₂ ↓ + 2KNO ₃

CrSO ₄ + 2KOH → Cr (OH) ₂ ↓ + K ₂ SO ₄

NiSO ₄ + 2KOH → Ni (OH) ₂ ↓ + K ₂ SO ₄

NiFNO ₃ + 2KOH → Ni (OH) ₂ ↓ + KF + KNO ₃

MnO + 2KOH → Mn (OH) ₂ ↓ + K ₂ O

Cr (NO ₃ ) ₂ + 2KOH → Cr (OH) ₂ ↓ + 2KNO ₃

That is, the reaction of Chemical Formulas 4 to 9 is a reaction scheme showing a process in which heavy metal in waste acid is converted into hydroxide precipitated sludge by OH groups. By neutralizing the waste acid in this way, the heavy metal contained in the waste acid can be sludged immediately. In addition, the fluorine ion in the waste acid reacts with the lanthanum compound as in Chemical Formulas 10 to 11.

3HF + La (NO ₃ ) ₃ → 3LaF ↓ + 3HNO ₃

3FeF + La (NO ₃ ) ₃ → 3LaF + 3FeNO ₃ ↓

The reactions of Formulas 10 and 11 make fluorine ions a lanthanum fluoride precipitate to increase the removal efficiency by causing the precipitates produced in the above reaction to co-precipitate together, and these precipitates are separated from the supernatant in the settling tank (6). It becomes a neutralized sludge cake. In addition, the elution of other environmental pollutants from the landfill sludge cake can be prevented.

In this case, the sludge cake generated by the heavy metal component contained in the waste acid and the waste gas absorption liquid to be treated in the present invention is greatly reduced compared to the conventional method.

Hereinafter, the present invention will be described in detail through examples.

Example 1

In this example, the waste acid generated in the stainless hot rolling process, the B5.2 solution, which is a NOx absorbing solution, and the waste sulfuric acid were collected as samples, and used in the laboratory as close to the field process as shown in Table 1. The waste acid used in the present invention was a mixture of 50 ml of waste sulfuric acid, 10 ml of waste mixed acid, and 10 ml of B5.2 solution.

sample H ₂ SO ₄ HNO ₃ HF Fe Waste acid Spent sulfuric acid 120 g / ℓ - - 25 g / ℓ Waste mixed acid - 75 g / ℓ 20g / ℓ 35 g / ℓ B5.2 Solution Including NOx gas and Mn, pH 2.0 or less

70 ml of waste mixed acid as shown in Table 1 was added to the neutralization tank, and the treatment agent, as shown in Table 2, was added thereto in a range of 60 to 380 ml, stirred to pH 7.0 to 8.0, and then to the first neutralized treated water. The treatment agent was added again to maintain wastewater at pH 9.5 to 10.0.

As a result of analyzing the treated water thus treated, it was as shown in Table 3.

division Chemical composition (% by weight) KOH La (NO ₃ ) ₃ Hydroxylamine chloride water Comparative Material 1 10 0.3 0.5 Balance Invention 1 10 0.5 0.5 Invention 2 10 1.0 0.5 Invention 3 10 3.0 0.5 Invention 4 10 5.0 0.5 Comparative Material 2 10 7.0 0.5 Comparative Material 3 30 0.3 0.1 Invention 5 30 0.5 0.5 Invention 6 30 1.0 0.5 Invention 7 30 3.0 0.5 Invention Material 8 30 5.0 0.5 Comparative Material 4 30 7.0 0.5 Comparative Material 5 50 0.1 0.05

division Type of treatment Input amount of treatment agent (ml) Analysis value (ppm) Sludge Generation (g) Input amount of discharged water (ml) COD F Mn T-Cr Target 90 or less 15.0 or less 10.0 or less 2.0 or less - - Comparative Example 1 Comparative Material 1 270 25 21.4 5.1 1.0 43 205 Inventive Example 1 Invention 1 290 26 12.0 5.8 0.6 44 220 Inventive Example 2 Invention 2 300 25 8.2 7.0 0.6 44 245 Inventive Example 3 Invention 3 330 20 3.0 7.3 0.6 45 250 Inventive Example 4 Invention 4 350 21 2.3 6.0 0.7 45 260 Comparative Example 2 Comparative Material 2 380 25 tr. 6.8 0.6 47 270 Comparative Example 3 Comparative Material 3 125 28 20.4 5.1 0.5 43 105 Inventive Example 5 Invention 5 130 26 11.0 5.8 0.4 43 105 Inventive Example 6 Invention 6 140 25 4.2 5.0 0.3 44 105 Inventive Example 7 Invention 7 145 22 2.8 7.3 0.4 45 110 Inventive Example 8 Invention Material 8 150 25 2.0 4.0 0.3 45 110 Comparative Example 4 Comparative Material 4 155 24 tr. 6.8 0.5 48 120 Comparative Example 5 Comparative Material 5 60 27 47.2 13.5 0.2 42 50

As can be seen from the results of Table 3, the wastewater treatment agent that satisfies the composition range of the present invention is shown to significantly reduce the amount of sludge generated while managing the concentration of waste acid below the regulated value.

Example 2

Conventional example

Add 70 ml of waste acid as shown in Table 1 to the neutralization tank and add 120 ml of 10% slaked lime to pH 7.0 ~ 8.0 with stirring. Was maintained at pH 9.5 ~ 10.0 and treated with wastewater.

This treatment was repeated six times to analyze the treated water, as shown in Table 4.

division Analysis result of treated water (unit: ppm) COD T-Cr Mn F ^- Amount of sludge (g) Quantity of discharged water (ml) Target 90 or less 2.0 or less 10.0 or less 15.0 or less - - Conventional example 6.8 0.13 0.3 7.1 71.9 140

Inventive Example (9)

70 ml of waste acid as shown in Table 1 was added to the neutralization tank, and 80 ml of the treatment agent of the present invention (7) was added while stirring to bring the pH to 7.0 to 8.0. 5ml was added and maintained at pH 9.5 ~ 10.0 to treat wastewater.

As a result of analyzing the treated water thus treated, it was as shown in Table 5.

division Analysis result of treated water (unit: ppm) COD T-Cr Mn F ^- Amount of sludge (g) Quantity of discharged water (ml) Target 90 or less 2.0 or less 10.0 or less 15.0 or less - - Inventive Example 23.3 0.1 5.1 4.8 45.8 100

As can be seen from Tables 4 and 5, when the treatment agent of the present invention is used, not only the wastewater can be treated below the environmental management regulation range, but also the input amount of the treatment agent is greatly reduced as compared to the conventional treatment method, and thus the sludge and The amount of effluent is also shown to be greatly reduced.

As described above, by treating the waste acid generated in the stainless manufacturing plant with the treatment agent of the present invention, each anion and heavy metals generated during the waste acid treatment can also be managed within the factory water quality preservation law regulation, and the sludge cake and There is also a very useful effect that can significantly reduce the amount of effluent.

Claims (2)

By weight%, KOH: 10 to 40%, lanthanum ion: 0.5 to 5.0%, and hydroxylamine chloride: 0.05 to 1.5%. In the wastewater treatment method, A wastewater treatment method comprising introducing the wastewater treatment agent of claim 1 into the wastewater in a range of 1000 to 6000 ml.