CN103241894A - Method for dechlorinating and neutralizing waste liquor with bromine extracted - Google Patents

Abstract

The invention relates to a treatment method for waste liquid after bromine extraction from brine. The method uses sulfur dioxide as a reducing agent to treat free chlorine in concentrated brine after bromine extraction, so as to reduce the chlorine content to a certain index, and treat the concentrated brine after chlorine removal. Neutralize with limestone, and then add biological populations to the buffer pool to restore the biological system. The invention has low production cost, zero discharge and no pollution, and the concentrated seawater obtained from the treatment can be directly discharged into the seawater, and is suitable for industrial batch production.

Description

A method for dechlorinating and neutralizing bromine wastewater

technical field

The invention belongs to the technical field of inorganic chemical industry, and in particular relates to the treatment of waste water after bromine extraction from seawater and brine. Specifically, sulfur dioxide and limestone are used to treat acid and chlorine-containing waste liquid, and finally adding biological populations to the buffer pool to repair the biological system and reach the standard. method of emission.

Background technique

At present, the bromine extraction process from brine at home and abroad includes the traditional steam distillation method and air blowing method, two mainstream processes, and new bromine extraction processes such as resin adsorption method, gaseous membrane method, and emulsion liquid membrane method. my country's bromine resources are mainly distributed in the eastern coastal areas. The raw materials for production are generally obtained from concentrated seawater and underground brine in the process of drying salt. The bromine content is about 0.2g/L-0.3g/L, which is compared with the bromine content in raw materials in the United States and Israel. Much lower, only suitable for large-scale extraction of bromine by air blowing method.

The air blowing method includes acidification, oxidation, blowing, absorption, distillation, condensation, separation and other processes. According to the different absorbents in the absorption process, the air blowing method is divided into air blowing acid absorption method and air blowing lye absorption method. Due to the disadvantages of low bromine content in the absorption liquid and large consumption of electric steam and acid and alkali in the lye absorption method, more than 90% of bromine has been produced by the acid solution absorption method blown out by air so far. In the 1880s, my country introduced the advanced process of "air-blown tail gas closed cycle acid bromine production" from the United Kingdom, and has made many improvements to the process technology, and now it has become the most mature and widely used bromine extraction process. The production process of this process is as follows: after the brine with low bromine content is acidified to a pH value of about 3 to 3.5, it is oxidized by chlorine gas in a tubular static mixer, and bromide ions are oxidized into free bromine; Blown out by a large amount of air in the absorption tower, the sulfuric acid mist in the absorption tower absorbs the free bromine in the air and is reduced to misty hydrobromic _acid ; Bromine is finally concentrated and condensed under the stripping action of water vapor in the lower part of the packed tower to obtain crude bromine. Among them, the tail gas of the absorption tower is returned to the blowing process through a closed circulation system for recycling.

The wastewater after bromine extraction contains a large amount of chlorine, which has a strong ability to kill pathogenic microorganisms, so it is widely used in many sewage treatment plants. However, while chlorine disinfection kills pathogenic microorganisms in water, chlorine easily reacts with organic matter in water to produce mutagenic and carcinogenic DBPs (D-infection By products), such as trihalomethanes, which have long-term effects on humans and aquatic organisms. Toxic effects. In addition, if the chlorine disinfection water is directly discharged into the water body, the residual chlorine will have a toxic effect on fish or aquatic organisms. In order to protect aquatic organisms from the toxic effects of residual chlorine in the disinfection tail water, it is necessary to strictly control the amount of residual chlorine in the tail water discharged into the water body. The U.S. National Environmental Protection Agency stipulates that the total chlorine in the tail water should be less than 0.16mol/L (0.011mg Cl/L). There is no such standard in my country, and the residual chlorine in hospital sewage that is chlorinated and disinfected is only included in the Comprehensive Wastewater Discharge Standard (GB89781996). It is stipulated that it is 0.5mg Cl/L.

Chlorine-containing wastewater after bromine extraction has high pungent odor and corrosiveness. If it is not treated, it may react with organic matter in water to generate organic chloride and cause secondary pollution. Chlorine water has a strong ability to kill microorganisms, destroy the water ecosystem, produce strong pollution to the environment, corrode pipelines, equipment and ships, and cause economic losses.

The pH of concentrated brine after dechlorination is about 4, and the discharge standard pH=6~9 stipulated by the environmental protection department (bureau), so there is a problem of neutralization of acidic wastewater.

Contents of the invention

The technical problem to be solved by the present invention is to provide a treatment method for waste liquid after bromine extraction in brine, by using a reducing agent to treat free chlorine in concentrated brine after bromine extraction, so as to reduce the chlorine content to a certain index, and to reduce the chlorine content. The final concentrated brine is neutralized, and then the biological population is added to the buffer pool to restore the biological system. This method overcomes the shortcomings of high energy consumption, large investment and low benefit in the existing bromine extraction wastewater treatment.

The technical solution adopted by the present invention to solve the technical problem is:

A kind of treatment method of waste liquid after the brine extracts bromine, comprises the following steps:

The first step, dechlorination

Pass sulfur dioxide into the waste water after bromine extraction for dechlorination, the ratio is molar ratio chlorine: sulfur dioxide=1:0.9～1.5, react at 30～60°C for 20～30min;

The second step, neutralize

Pass the dechlorinated waste water after bromine extraction into the neutralization tank filled with limestone, the flow rate is 4.0-7.5m/h, and the residence time is 16-30min; the neutralized concentrated seawater is obtained, and its pH value is 6.0- 6.9;

The third step, biological system recovery

The concentrated seawater after neutralization is passed into the buffer pool, and then the original seawater is added to obtain mixed seawater, and the pool is filled with oxygen to repair the biological system; among them, the original seawater is 9-12% of the volume of the concentrated seawater after neutralization. The oxygenation time is 30 minutes, and the amount of oxygenation reaches 6-8 cm ³ /dm ³ of the oxygen content in the seawater in the buffer pool.

The filling height of the limestone in the tank is 40-65 mm, and the average particle size of the limestone is 20-30 mm.

The bromine-extracted waste water in the first step is the chlorine-containing acidic waste water after bromine-extracted concentrated sea water is blown out by air, wherein the chlorine content is 2-8 mg/L, and the pH value is 3.5-5.0.

The beneficial effects of the present invention are: compared with the prior art, the inventive method has the following obvious advantages and progress:

(1) Using sulfur dioxide with high reducibility as a reducing agent overcomes the defect of insufficient reaction between sodium hydroxide and calcium hydroxide and chlorine in the prior art; in addition, the production cost of sodium hydroxide is high; cheap and easy-to-obtain limestone As a neutralizing agent, it has low production cost, zero discharge and no pollution, and is suitable for industrial mass production.

(2) The method of the present invention restores the biological system of the treated concentrated seawater without affecting the marine ecosystem, and the treated concentrated seawater can be directly discharged into the seawater.

(3) The chlorine-containing wastewater treated in the present invention is different from the common chlorine-containing wastewater after bleaching. The chlorine-containing wastewater in the present invention not only has certain acidity, but also has a large amount of salts and some harmful substances. The first and second step reactions use chemical methods, and the third step uses biological treatment methods to successfully solve the pollution problem of chlorine-containing concentrated brine after bromine extraction.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is the schematic diagram of the experimental device used for the neutralization reaction in the second step of the present invention.

Among them, 1. Plastic bucket, 2. Peristaltic pump 1, 3. Neutralization tank, 4. Initial measurement point, 5. Measurement point 1, 6. Measurement point 2, 7. End measurement point, 8. Peristaltic pump 2, 9. Buffer pool.

Detailed ways

The embodiments of the present invention are only used to describe the present invention in detail, and are not regarded as limiting the protection scope of the claims of the present invention.

What is not mentioned in the present invention is applicable to the prior art.

The second step reaction process of the present invention is as shown in Figure 1, the waste water after dechlorination after bromine extraction is put into plastic bucket 1, and the waste water after dechlorination after bromine extraction is passed into the groove 3 filled with limestone by peristaltic pump 2 Inside, the specification of tank 3 is 2000mm×100mm×70mm, the filling height of limestone in the tank is 40-65mm, the average particle size of limestone is 20-30mm, and the waste water after dechlorination and bromine extraction flows through the initial measuring point 4, Measuring point one 5, measuring point two 6 and ending measuring point 7, wherein the initial measuring point 4 and the ending measuring point 7 are respectively located at both ends of the tank, measuring point one 5 and measuring point two 6 are located at the measuring point of the neutralization tank At the third equal point; finally the neutralized concentrated seawater is moved into the buffer pool 9 through the peristaltic pump 28, and then the original seawater is added to the buffer pool 9 and oxygenated.

The amount of limestone in the neutralization tank must maintain a certain filling height; as the neutralization reaction proceeds, the filled limestone will react with the acid, and the product will be dissolved in the waste water in the form of calcium sulfate, and it will be replenished to the original filling height in time Just do it;

The waste water after extracting bromine used in the experiment of the present invention is the chlorine-containing acidic waste water after the bromine is extracted by Tianjin Changlu Haijing Group by using the concentrated seawater of Bohai Sea through the air blowing method. The chlorine content in the acidic waste water is 2～8mg/L, and the pH is 3.5～ 5.0; the original seawater is Bohai seawater.

The main components are as follows: NaCl: 4.94%, KCl: 0.14%, CaSO ₄ : 0.22%, MgCl ₂ : 0.59% and MgSO ₄ : 0.40%.

Example 1

Take 10L of bromine-extracted wastewater, the chlorine content of which is 4.87mg/L (0.03mmol/L), pass 25.0mg of sulfur dioxide (0.39mmol) into it, and react at 30°C for 20min to obtain dechlorinated bromine-extracted wastewater , the pH of the wastewater after dechlorination and bromine extraction is the initial measurement point 4, the concentrated brine after dechlorination is passed into the plastic bucket 1, and the wastewater after dechlorination and bromine extraction is passed into the filled limestone through a peristaltic pump 2 In the neutralization tank 3, flow through the flow velocity 6.5m/h of the neutralization tank 3, and flow through the initial measuring point 4, the measuring point one 5, the measuring point two 6 and the dechlorination of the ending measuring point 7 to extract bromine The pH values of the post-waste water were 4.50, 6.54, 6.56 and 6.57 in sequence.

After testing, the content of free chlorine in the treated waste liquid was reduced to 0.15mg/L, and the pH increased to 6.57. The chlorine content detection method is the common silver nitrate titration method, and this data is in line with the national discharge standard.

Collect the treated concentrated seawater (the processed concentrated seawater is still about 10L) into the buffer pool 9, add 1L of raw seawater, and oxygenate for ³⁰ minutes ^. After standing still for 72 hours, it was found that the number of bacteria in the concentrated seawater after treatment reached 10 ⁶ /ml, and the bacteria mainly included Escherichia coli, Vibrio and pseudoalteromonas and other organisms grew, indicating that the biological system has been restored .

Example 2

Take 10L of bromine-extracted wastewater, the chlorine content of which is 5.74mg/L (0.035mmol/L), pass 34.0mg of sulfur dioxide (0.53mmol) into it, and react at 30°C for 20min to obtain dechlorinated bromine-extracted wastewater , the pH of the wastewater after dechlorination and bromine extraction is the initial measurement point 4, the concentrated brine after dechlorination is passed into the plastic bucket 1, and the wastewater after dechlorination and bromine extraction is passed into the filled limestone through a peristaltic pump 2 In the neutralization tank 3, the flow rate of the neutralization tank 3 is 6.2m/h, and the bromine after dechlorination after flowing through the initial determination point 4, the determination point one 5, the determination point two 6 and the final determination point 7 The pH value of the wastewater is 4.28, 6.32, 6.35, 6.36 in turn.

The content of free chlorine in the waste liquid after detection and treatment was reduced to 0.10 mg/L, and the pH increased to 6.36. The detection method of chlorine content is the common silver nitrate titration method, and this data is in line with the emission standard of the national standard.

Collect the treated concentrated seawater (the processed concentrated seawater is still about 10L) into the buffer pool 9, add 1L of raw seawater, and oxygenate for ³⁰ minutes ^. After standing still for 72 hours, it was found that the number of bacteria in the concentrated seawater after treatment reached 10 ⁶ /ml, and the bacteria mainly included Escherichia coli, Vibrio and pseudoalteromonas and other organisms grew, indicating that the biological system has been restored .

Claims (3)

1. the processing method of waste liquid after a kind of bittern extracts bromine, it is characterized in that comprising the following steps: The first step, dechlorination Pass sulfur dioxide into the waste water after bromine extraction for dechlorination, the ratio is molar ratio chlorine: sulfur dioxide=1:0.9～1.5, react at 30～60°C for 20～30min; The second step, neutralize Pass the dechlorinated waste water after bromine extraction into the neutralization tank filled with limestone, the flow rate is 4.0-7.5m/h, and the residence time is 16-30 minutes; the neutralized concentrated seawater is obtained, and its pH value is 6.0 ~6.9; The third step, biological system recovery The concentrated seawater after neutralization is passed into the buffer pool, and then the original seawater is added to obtain mixed seawater, and the pool is filled with oxygen to repair the biological system; among them, the original seawater is 9-12% of the volume of the concentrated seawater after neutralization. The oxygenation time is 30 minutes, and the amount of oxygenation reaches 6-8 cm ³ /dm ³ of the oxygen content in the seawater in the buffer pool. 2. The method for treating waste liquid after extracting bromine from brine as claimed in claim 1, characterized in that the filling height of limestone in the tank is 40-65 mm, and the average particle size of limestone is 20-30 mm. 3. the processing method of waste liquid after the brine extracts bromine as claimed in claim 1, it is characterized in that the waste water after extracting bromine in the described first step is the chlorine-containing acidic waste water after the bromine extraction of concentrated seawater through the air blowing method, Among them, the chlorine content is 2-8 mg/L, and the pH value is 3.5-5.0.

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