KR100291899B1 - METHOD OF ELIMINATING FLUORINE ION(F¬-) AND HEXAVALENT CHROMIUM ION(Cr¬6+) FROM INDUSTRIAL WASTEWATER - Google Patents

Abstract

PURPOSE: The present method for eliminating fluorine ion(F¬-) and hexavalent chromium ion(Cr¬6+) from industrial wastewater produce less amount of sludge, because sodium carbonate is far more soluble into water than lime ever been used. CONSTITUTION: The method includes the steps of (i) into a reduction reactor, injecting a chemical composition comprising, on the 100mL of chemical composition basis, CaCO3 0.50-1.00g, LiCO3 0.10-0.30g, NaHSO3 0.05-0.20g, CH3COOH(1+1) 25-50mL, and a balance of water so as to convert fluorine ion into insoluble fluoride as well as convert hexavalent chromium into trivalent chromium; (ii) introducing the wastewater into a neutralization tank containing 10-20% Na2CO3 to eliminate trivalent chromium ion.

Description

Wastewater treatment method to reduce fluorine and chromium hexavalent ions in wastewater

In the present invention, fluorine ions and chromium (Cr ⁺⁶ ) ions contained in plant wastewater generated during the process of making a product using hydrofluoric acid reagent, fluorine compound, chromium ore, chromium-containing compound, etc. To treat or treat wastewater to remove or reduce wastewater and discharge it below the levels specified in the Environmental Conservation Act.

Conventionally, the neutralization treatment method by adding slaked lime is generally used as a crime prevention method for removing fluorine ions and chromium ions in the plant wastewater, and the wastewater generated in the plant shown in FIG. When the pH of the wastewater is in an acidic state, sodium bisulfite (NaHSO ₃ ), which is a reducing agent, is added immediately, and in a neutral or alkaline state, sulfuric acid (H ₂ SO ₄ ) is added to make the pH less than 2, and then sodium sulfite (NaHSO), which is a reducing agent, is added. ₃ ) is added to reduce chromium from Cr ⁺⁶ to Cr ⁺³ .

After the reduction reaction is sent to the neutralization tank, the solution of calcium hydroxide (Ca (OH)) ₂ ) is added to the neutralization reaction. The neutralization tank is equipped with a pH meter (manual or automatic) inside, and neutralized by adding strongly alkaline slaked lime to the strongly acidic wastewater introduced from the reduction tank within the measurement range (8.5 ± 0.5) of the pH meter. The waste water neutralized by repeating this reaction is sent to the sedimentation tank, the flocculant is added to the sedimentation tank to separate the water and the sediment, and the sediment is sludge-treated to the bottom of the sedimentation tank. Wastewater separated from the sediment is discharged after filtering the suspended solids in the wastewater in the filter press and adjusting to the pH range (5.8 -8.6) specified in the Environmental Conservation Act before final discharge.

However, the following problems exist in the conventional wastewater treatment process as described above.

That is, due to the property that the slaked lime injected into the neutralization tank is almost insoluble in water, precipitation occurs, and accordingly, a large amount of sludge is generated and the neutralization power of the wastewater and reactivity with fluorine ions are not good. In addition, in the neutralization tank, pH control is not easy because strong acidic wastewater and strong alkaline hydrated lime from the reaction tank react, and the unreacted substances generated when the acid-alkali state is repeated are not completely neutralized. Do not.

In addition, sulfuric acid (H ₂ SO ₄ ), which is added to make acidic pH before reacting with calcium hydroxide (CaSO ₄ ), reacts with hydrated lime in the neutralization tank before adding a reducing agent to convert chromium hexavalent to chromium trivalent. made of an insoluble material in the waste water fluorine ions (F ^-) it interferes with the reaction of.

Due to these problems, wastewater without complete neutralization is finally discharged, causing fluorine ions and chromium hexavalent ions to exceed the limits prescribed by the Environmental Conservation Act, which is a major cause of pollution and has many difficulties in the treatment of wastewater. It was.

The present invention has been made to solve the problems of the prior art described above, a composition prepared from calcium carbonate, lithium carbonate, sodium bisulfite, acetic acid, and the like, which is not conventionally used in a reduction tank (hereinafter referred to as A drug) as a reducing agent. By using this product, fluorine ions and chromium 6 satisfy the conditions for easy removal of ions in the post process, and the neutralization reaction tank uses a weakly alkaline sodium carbonate (Na ₂ CO ₃ ) neutralization solution to fluorine ion (F ^-) and hexavalent chromium ions (Cr ⁺⁶⁾ and at the same time a markedly reduced Sikkim fluorine, chromium 6 in the waste water that can be easily processed by the environmental protection and waste water according to this effective pH adjusting ion It is an object of the present invention to provide a wastewater treatment ice method for reducing.

1 is a view showing a process for removing fluorine and chromium hexavalent ions in conventional wastewater;

2 is a view showing a process for generating fluorine and chromium hexavalent ions in wastewater according to the present invention.

In order to achieve the above object, in the present disclosure, when preparing 100 ml of the composition, calcium carbonate (CaCO ₃ ): 0.50 -1.00 g. Lithium tinate (LiCO ₃ ): 0.10 -0.30 g, sodium bisulfite (NaHSO ₃ ): 0.05 -0.20 g, acetic acid (CH ₃ COOH) (1 + 1): 25 -50 ml. The remainder is made up of a composition composed of water (H ₂ O) in a reduction reaction tank to precipitate and remove fluorine as an insoluble fluorine compound, and chromium is easily removed from the neutralization reactor by converting Cr ^{+ 6} to Cr ^{+ 3} . To facilitate pH adjustment; Neutralizing the reaction vessel is 10-20% of the Na ₂ fluorine ions in the waste water charged into the CO ₃ (F ^-), and chromium (VI) ion (Cr ⁺⁶⁾ fluorine and chromium 6 in the waste water, comprising a step of removing or reducing the A wastewater treatment ice cream for removing or reducing ions is provided.

The following describes the present invention in detail in connection with the preferred embodiment.

The process of the present invention is shown in Figure 2, the wastewater generated in the manufacturing process is primarily collected in the collection tank and sent to the reduction reaction tank, A chemicals capable of chromium reduction and fluorine precipitation at the same time in the neutralization reaction tank To facilitate the removal of fluorine and chromium, fluorine ions (F ⁻ ) are reacted with precipitates of calcium fluoride and lithium fluoride, and chromium ions are subjected to a reduction reaction tank for reducing chromium hexavalent ions to chromium trivalent ions which are difficult to precipitate hydroxide. Pass the wastewater introduced into the reduction reaction tank with a 10% aqueous solution of sodium carbonate (Na ₂ CO ₃ ) to pass through a neutralization tank to form hydroxide and calcium fluoride precipitates, and add a flocculant to the precipitates of hydroxide and calcium fluoride in the waste water after the neutralization reaction is completed. To increase the rate of sedimentation and to settle the sediment from wastewater Which is removed by adjusting the pH, and then when the suspended solids in a filter press apparatus in a range (pH 5.8 -8.6) specified in environmental conservation laws consists in finally discharged from the discharge part.

In this process, the chemicals introduced in the reduction reaction tank are adjusted to pH 2 or less by adding sulfuric acid to increase the reduction reaction rate as shown in FIG. 1, and chromium 6 is easily removed so that Cr is easily removed from the neutralization reaction tank. Sodium bisulfite was added to make isone (Cr ⁺⁶ ) into chromium trivalent ions (Cr ⁺³ ), but in the present invention, A drug is added to the reduction bath.

The composition of this A drug was calcium carbonate (CaCO ₃ ): 0.50 -1.00 g when prepared with 100 mL of drug. Lithium tinate (LiCO ₃ ): 0.10 -0.30 g, sodium bisulfite (NaHSO ₃ ): 0.05 -0.20 g, acetic acid (CH ₃ COOH) (1 + 1): 25-50 ml, namiji water (H ₂ O) To manufacture.

By introducing the above-mentioned drug A into the reduction reaction tank, Cr is made into Cr ⁺³ state which can react with Cr (OH) _{2 which} is a hydroxide precipitate in Cr ⁺⁶ state, which is difficult to form hydroxide precipitate, and fluorine is calcium fluoride (CaF ₂ ). It is made of (insoluble) precipitate and treated first.

In addition, as shown in Fig. 1, the chemical introduced into the neutralization tank is conventionally added with hydrated lime, but hydrated lime is almost insoluble in water, requiring continuous stirring and decreasing reactivity, and insoluble by reacting with sulfuric acid added during reduction. Phosphorus calcium sulfate (CaSO4) is made to interfere with the reaction with fluorine ions. In the present invention, as shown in Figure 2, by adding 10% sodium carbonate, Ca (OH) ₂ , Li (OH) ₂ , Cr A precipitate such as (OH) ₂ and CaF ₂ was made to remove Cr and F to maximize the neutralization effect.

Hereinafter, referring to FIG. 2, the application and effects of the first reaction in which the A drug used in the present invention is added to the reduction reaction tank and the secondary reaction in which 10% aqueous sodium carbonate solution is added to the neutralization reaction tank will be described. If the wastewater containing fluorine and chromium collected is sent to a reduction reaction tank, A drug of the present invention is introduced.

At this time, the reaction process of fluorine and chromium in waste water by A drug is as follows.

Reaction to Fluorine Ion in Reduction Reactor

H ₂ F ₂ + 3LiCO ₃ H + 3LiCO ₃ → 2LiF ↓ + CH ₃ COOLi + 3HCO ₃

H ₂ F ₂ + CH ₃ COOH + ₂ CaCO ₃ → CaF ₂ : ↓ + CH ₃ COOCa + CO ₂ + H ₂ O + HCO ₃

Reaction to Chromium Ion in Reduction Reactor

2H ₂ CrO ₄ + 3CH ₃ COOH + 3NaHSO ₃ → Cr ₂ (SO ₄ ) ₃ + 3CH ₃ COONa + 5H ₂ O

As described above, fluorine ions in the reaction vessel are formed of fine precipitates insoluble in calcium fluoride and lithium fluoride, and chromium is converted from Cr ⁺⁶ to Cr ⁺³ by reaction with SO ₃ , a reducing agent.

Truth reaction of sodium carbonate aqueous solution in central tank

The wastewater passed through the reduction tank is sent to the neutralization tank, and the reaction process with the wastewater by the aqueous 10 5 sodium carbonate solution in the neutralization tank is true as soon as the sodium carbonate is dissolved in water.

NaCO ₃ + 2H ₂ O ₂ NaOH + H ₂ CO ₃

As in the ionization reaction, the aqueous sodium carbonate solution generates OH ⁻ , which is an alkali, and CO ₃ ⁻² , which is a weak carbonic acid. These ions react with the heavy metal ions upon neutralization, resulting in hydroxide precipitation, and the weak carbonic acid groups change to CO ₂ .

Reaction Process in Neutralization Reactor

The neutralization process is as follows.

2Ca + 2NaOH + H ₂ CO ₃ + H ₂ F ₂ CaF2 ↓ + Ca (OH) ₂ ↓ + CO ₂ ↑ + 2H ₂ O ... Reaction 1

2Li + ₂ NaOH + H ₂ CO ₃ + H ₂ F ₂ LiF ↓ + Li (OH) ₂ ↓ + CO ₂ ↑ + 2H ² O ... Reaction 2

Cn (SO ₄ ) ₃ +2 NaOH + H ₂ CO ₃ 2Cr (0H) ₂ ↓ + NaSO ₄ + CO ₂ + 2H ₂ O ... reaction 3

As described above, the neutralization reaction vessel allows the fluorine ions, which are anions, to react completely with the reaction vessels that do not react with the calcium fluoride salt in the reduction reaction vessel, in the reaction 1 and 2, and the chromium is in the range of pH 7.0 -8.5 It completely turns into hydroxide precipitation, making the liquid of the acidic wastewater alkaline.

In addition, chromium trivalent, which is a heavy metal ion, is removed in a hydroxide precipitate state as in reaction 3.

In the neutralization tank, the neutralized wastewater is returned to the sedimentation tank. In the sedimentation tank, the flocculating agent is added to increase the sedimentation rate by increasing the binding state of the sediment.

The wastewater passing through the settling tank is a filty press device that removes fine suspended matter generated during the reaction, and the wastewater passed through the filter press device is finally discharged after adjusting to the pH range 5.8 -8.6 specified in the Environmental Protection Act.

The following describes the present invention in more detail with reference to examples.

(Example)

The results of simulation tests on the fancy wastewaters having F ⁻ : 40 ppm and Cr ⁺⁶ : 2 ppm were performed according to the conventional method in Table 1, and Table 2 shows the results according to the present invention.

Table 1

As can be seen from Table 1, A does not contain sulfuric acid, pH is not adjusted, so sludge generation is small, but it is not applicable due to exceeding environmental regulations. Not applicable due to excess of regulation. C shows a significant increase in sludge production with increasing slaked lime input, and occasionally exceeds the F ^- environmental limit. In the conventional method, it is mainly applied in this range.

TABLE 2

As can be seen from Table 2, a) the sludge amount was significantly reduced compared to the conventional method, but it was impossible to apply due to the environmental regulations. The amount of sludge was higher than that of a), but it was considerably less than the conventional method, and it could be applied below the environmental limit. And, d) the amount of sludge generated is remarkably reduced compared to the conventional method, but c) anti - privatization, that receive a significant amount than anti-F ^-, Cr + ⁶ will not be significantly improved. But. Applicable below environmental regulations, but economically low.

Thus, treatment of waste water according to the present invention as described above, A is a drug because it was in the reducing reaction tank fluorine converts a water-insoluble precipitate of calcium fluoride at the same time chromium is in the Cr ⁺⁶ to Cr ⁺³ to simplify the medication process input It is easy to adjust pH because it doesn't use sulfuric acid. It can be completely removed by precipitation with insoluble fluorine compound. Sodium carbonate that is added to the neutralization tank is more soluble in water than conventional slaked lime, so it is water-soluble. Useful effects are achieved, such as significantly less sludge produced.

Claims (1)

Calcium carbonate (CaCO ₃ ): 0.50 -1.00 g. Lithium Tinate (LiCO3): 0.10 -0.30 g, Sodium bisulfite (NaHSO ₃ ): 0.05-0.20 g, Acetic acid (CH ₃ COOH) (1 + 1): 25-50 ml; A composition composed of the remaining water as a component is introduced into a reduction tank to precipitate and remove fluorine from the waste water with an insoluble fluorine compound, and simultaneously react chromium with a reducing agent to reduce chromium trivalent to chromium trivalent ions; Wastewater treatment to reduce fluorine and chromium hexavalent ions in the wastewater, characterized by reacting the wastewater in a neutralization reactor with 10-20% Na ₂ CO ₃ to precipitate chromium trivalent ions in the wastewater as a hydroxide precipitate. Way.