CN114804396B

CN114804396B - High-salinity lye pool wastewater treatment process

Info

Publication number: CN114804396B
Application number: CN202110118396.XA
Authority: CN
Inventors: 仲亚洲; 虞恺
Original assignee: WUXI ZHONGTIAN SOLID WASTE DISPOSAL CO Ltd
Current assignee: WUXI ZHONGTIAN SOLID WASTE DISPOSAL CO Ltd
Priority date: 2021-01-28
Filing date: 2021-01-28
Publication date: 2023-04-07
Anticipated expiration: 2041-01-28
Also published as: CN114804396A

Abstract

The invention provides a high-salinity alkali liquor pool wastewater treatment process, and belongs to the technical field of waste liquid treatment. The method comprises the following steps: adding hydrogen peroxide into the wastewater and stirring; adding a fluorine removal agent into the obtained reaction liquid, and carrying out solid-liquid separation after the reaction is finished to obtain a filtrate 1 and solid calcium fluoride; adding a calcium removal agent into the filtrate 1, and carrying out mixed reaction and solid-liquid separation to obtain a precipitate and a filtrate 2; carrying out activated carbon adsorption and decoloration on the filtrate 2 to obtain a sodium sulfate solution, and regenerating and recycling the activated carbon subjected to adsorption and decoloration; carrying out negative pressure concentration on the sodium sulfate solution, and then carrying out solid-liquid separation to obtain a concentrated solution and sodium sulfate crystals; pretreating the concentrated solution with sulfuric acid, carrying out solid-liquid separation after reaction to obtain solid impurities and filtrate 3, carrying out negative pressure concentration on the filtrate 3, adding sulfuric acid into the concentrated solution to adjust acidity, supplementing water, continuing negative pressure concentration to obtain hydrochloric acid fraction water and the concentrated solution, and crystallizing the concentrated solution to obtain sodium sulfate. The method changes the salt content in the alkali liquor pool into valuable, relieves the salt content pressure of the alkali liquor pool, and reduces the outsourcing landfill amount.

Description

High-salinity lye pool wastewater treatment process

Technical Field

The invention belongs to the technical field of waste liquid treatment, and particularly relates to a high-salinity alkali liquor pool wastewater treatment process.

Background

With the rapid development of economy in China, the quantity of solid wastes in China is huge, the solid wastes are various, and related subdivision industries are also numerous, wherein incineration and hazardous waste disposal are mainly taken as two important sub-industries. In the incineration industry, household garbage incineration, organic sundry material incineration and the like exist; part danger is useless handles company and can select the comparatively single material of component to burn when burning the material, if: the material mainly contains sulfur elements and hardly contains other ions, so that after incineration, the waste gas is sprayed, absorbed and settled by an alkali liquor spray tower and then treated to prepare a pure sodium sulfite product, or the sulfur dioxide waste gas is introduced into lime water to prepare qualified calcium sulfite. However, for a more complex material system, after incineration, various anions can be mixed in the alkali liquor pool after generated waste gas is sprayed, absorbed and settled by the alkali liquor spray tower, such as: sulfite, nitrite, phosphate, fluoride, chloride ions, and the like. And the salt content of the alkali liquor pool is high, and impurities are difficult to be completely stripped by a conventional means to recover qualified sodium sulfite products.

The method aims at the problems existing between the recovery of the waste water of the alkali liquor pool which mainly comprises sodium sulfite (the content is 15-33%) and also comprises impurity ions such as fluorine chloride ions, phosphate radicals and the like and the method:

1. the raw water contains fluorine ions, and the raw water is directly subjected to fluorine removal, so that the fluorine content is difficult to be reduced to below 30 ppm.

2. Other impurity ions exist in the raw water, qualified sodium sulfite products cannot be directly recycled, and the crystallization color is yellow.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a high-salinity alkali liquor pool wastewater treatment process. The method treats the salt in the alkali liquor pool, changes waste into valuable, relieves the salt pressure of the alkali liquor pool, and reduces outsourcing landfill quantity; simple process, low equipment requirement and capability of treating complex wastewater in the alkali liquor pool. The single prior scheme has the following problems:

1, the solution is gradually changed into acid by adding hydrogen peroxide, the sodium sulfite is accelerated to decompose, and if the pH is controlled to be more than 7, the hydrogen peroxide is largely decomposed to cause resource waste;

2, the product distilled by the sodium sulfate solution turns yellow and gray.

The technical scheme of the invention is as follows:

a high-salinity alkali liquor pool wastewater treatment process comprises the following steps:

(1) Adding hydrogen peroxide into the high-salinity alkali liquor wastewater, stirring, and adjusting the pH value of the solution to 5-6;

(2) Adding a fluorine removal agent into the reaction liquid obtained in the step (1), controlling the temperature of the solution at 40-50 ℃, and performing solid-liquid separation after the reaction is finished to obtain a filtrate 1 and solid calcium fluoride;

(3) Adjusting the pH value of the filtrate 1 obtained in the step (2) to 7-8, adding a calcium removal agent, stirring, mixing and reacting, and performing solid-liquid separation to obtain a precipitate and a filtrate 2;

(4) Performing activated carbon adsorption and decoloration on the filtrate 2 prepared in the step (3) to obtain a sodium sulfate solution, and performing high-temperature regeneration and recycling on the activated carbon subjected to adsorption and decoloration;

(5) Concentrating the sodium sulfate solution in the step (4) under negative pressure, and then carrying out solid-liquid separation to obtain a concentrated solution and sodium sulfate crystals;

(6) Pretreating the concentrated solution prepared in the step (5) by using sulfuric acid to enable the pH value of the solution to be 2-3, carrying out solid-liquid separation after reaction to obtain solid impurities and filtrate 3, carrying out negative pressure concentration on the filtrate 3 to improve the content of chloride ions in the solution, and adding sulfuric acid into the concentrated solution to adjust the acidity of the concentrated solution to 15-25% when the concentration ratio is more than or equal to 3; adding water into the obtained concentrated solution, then carrying out negative pressure concentration to obtain hydrochloric acid distillate water and concentrated solution, carrying out crystallization treatment on the concentrated solution, and finally carrying out solid-liquid separation to obtain sodium sulfate crystals.

Further, the mass concentration of sodium sulfite in the high-salinity alkali liquor wastewater in the step (1) is 15-33%, and fluorine: 150-950ppm, chlorine: 20-65g/L.

Further, in the step (1), the mass concentration of hydrogen peroxide is 30-36.5%, the reaction temperature is 40-60 ℃, the dropping speed of the hydrogen peroxide is 30L-60L/h, and the usage amount of the hydrogen peroxide is 115-255L/T.

Further, in the step (2), the defluorinating agent is lime or calcium chloride, and the mass ratio of the defluorinating agent to the total amount of the waste liquid is as follows: 6.8X 10 ^-4 ：1-6.85×10 ^-3 ：1。

Further, the calcium removing agent in the step (3) is sodium carbonate or sodium oxalate, and the reaction time is 40-60min.

Further, the iodine adsorption value of the activated carbon in the step (4) is more than 500mg/g.

Further, the weight of the calcium removal agent in the step (3) is 0.27kg/T relative to the total mass concentration of the waste liquid.

Further, the negative pressure concentration condition in the step (5) is that the pressure is-0.055 MPa to-0.06 MPa, and the temperature is 80-90 ℃; the concentration ratio is 4.

Further, the concentration of the sulfuric acid in the step (6) is 50%; the negative pressure concentration condition is that the pressure is between-0.08 MPa and-0.09 MPa, and the temperature is between 90 and 100 ℃; the concentration ratio is 3.

Further, the water adding frequency in the step (6): the volume ratio of the water added to the concentrated solution in the kettle each time is 2:3-1:2, adding 9-11 times in total; the negative pressure concentration conditions are as follows: the temperature is 90-100 ℃, and the pressure is-0.08 MPa to-0.09 MPa.

The invention uses hydrogen peroxide to oxidize sodium sulfite into sodium sulfate with higher solubility through redox reaction, removes fluorinion by lime defluorination, removes residual calcium ion by sodium carbonate, removes organic impurities by active carbon adsorption decoloration method to obtain qualified sodium sulfate solution, and prepares sodium sulfate product by distillation and concentration.

The high-salinity alkali liquor pool wastewater is formed by that organic waste liquid generates a large amount of waste gas after being incinerated at high temperature, and the waste gas is absorbed and settled by a condensation system and an alkali liquor spray tower.

The beneficial technical effects of the invention are as follows:

(1) Because the Ksp of calcium sulfite and calcium fluoride are very close and are very difficult to dissolve, the Ksp of the substance is more crystallized and is more difficult to remove one component, so that fluorine is difficult to remove in a sodium sulfite solution; therefore, sodium sulfite is oxidized into sodium sulfate with high solubility, and the Ksp of calcium sulfate is smaller than that of calcium fluoride, so that the calcium fluoride which is more difficult to dissolve is preferentially precipitated, and the fluorine ions can be well reduced to below 30 ppm.

(2) In the invention, when the pH value of the solution is adjusted to be 5-6 by using the liquid caustic soda, the effects of slowing down the decomposition of sodium sulfite and improving the utilization rate of hydrogen peroxide can be achieved. Due to the respective properties of hydrogen peroxide and sodium sulfite: hydrogen peroxide is stable under acidic conditions, but decomposes more rapidly as the pH is higher; sodium sulfite can be decomposed into sulfur dioxide gas under acidic condition, which causes pollution to the environment. When the pH value is selected to be 5-6, the decomposition speed of sodium sulfite and hydrogen peroxide is relatively slow, and the recovery rate of the product and the utilization rate of the hydrogen peroxide are improved.

Drawings

FIG. 1 is a schematic view of the process of the present invention.

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings and examples.

Example 1

Taking 500mL of wastewater in the alkali liquor pool, wherein fluorine: 240ppm, 3.4g/L of chlorine, 21.6 percent of sodium sulfite and 35.3 percent of hydrogen peroxide; and calculating the usage amount of the hydrogen peroxide to be 82.5mL and the addition amount of the lime to be 0.508g. Slowly adding hydrogen peroxide dropwise at a speed of 5mL/min, controlling the reaction temperature to be less than 60 ℃, detecting the change of pH value, adding liquid alkali after the solution becomes acidic to adjust the pH to be =5.5, stirring for 10min after the dropwise addition of the hydrogen peroxide is finished, detecting the sodium sulfite content to be 0% (not detected), weighing lime, dissolving the lime in 50mL of water, slowly adding the lime into the solution, fully stirring for reaction for 1h, sampling and detecting the fluorine ion content to be 22ppm, weighing 0.3g of sodium carbonate, adding the sodium carbonate into the solution, fully stirring for reaction for 40min, sampling and detecting the calcium ion content to be 47ppm, determining the calcium ion content to be qualified, starting suction filtration, detecting the filtrate at a temperature of 37 ℃, and adsorbing and decoloring by using an activated carbon column. Taking 400ml of filtrate for negative pressure concentration (90 ℃, under-0.06 MPa), wherein the concentration ratio is 4: 96.3 percent, and the chlorine content of the product: 0.071% and the chlorine content in the concentrated solution 25.65g/L.

Example 2

Taking 300mL of wastewater in an alkali liquor pool, wherein the fluorine: 500ppm, 7.8g/L of chlorine, 15.7 percent of sodium sulfite and 34.7 percent of hydrogen peroxide; and calculating the usage amount of the hydrogen peroxide to be 36.6mL and the addition amount of the lime to be 0.602g. Slowly adding hydrogen peroxide dropwise at a speed of 5mL/min, controlling the reaction temperature to be less than 60 ℃, detecting the change of pH value, supplementing liquid alkali to regulate the pH to be =5.3 after the solution becomes acidic, stirring for 10min after the hydrogen peroxide dropwise addition is finished, detecting the sodium sulfite content to be 0% (not detected), weighing lime, dissolving in 50mL of water, slowly adding the solution, fully stirring for reaction for 1h, sampling to detect the fluorine ion content to be 11ppm, weighing 0.27g of sodium carbonate, adding the sodium carbonate into the solution, fully stirring for reaction for 40min, sampling to detect the calcium ion content to be 59ppm, determining the calcium ion content to be qualified, starting suction filtration, detecting the filtrate temperature to be 48 ℃, and adsorbing and decoloring by an activated carbon column. Taking 300mL of filtrate for negative pressure concentration (85 ℃, minus 0.06 MPa), wherein the concentration ratio is 5: 93.7%, chlorine content of the product: 0.043 percent and the chlorine content in the concentrated solution is 33.2g/L.

Example 3

Taking 1000mL of wastewater from an alkali liquor pool, wherein fluorine: 877ppm, 17.9g/L of chlorine, 30.8 percent of sodium sulfite and 35.9 percent of hydrogen peroxide; 231.5mL of hydrogen peroxide and 4.01g of lime are calculated. Slowly adding hydrogen peroxide dropwise at a speed of 5mL/min, controlling the reaction temperature to be less than 60 ℃, detecting the change of pH value, supplementing liquid alkali to regulate the pH to be =5.9 after the solution becomes acidic, stirring for 10min after the hydrogen peroxide dropwise addition is finished, detecting the sodium sulfite content to be 0% (not detected), weighing lime, dissolving in 50mL of water, slowly adding the solution, fully stirring for reaction for 1h, sampling to detect the fluorine ion content to be 25ppm, weighing 1.1g of sodium carbonate, adding the sodium carbonate into the solution, fully stirring for reaction for 40min, sampling to detect the calcium ion content to be 22ppm, determining the calcium ion content to be qualified, starting suction filtration, detecting the filtrate temperature to be 51 ℃, and adsorbing and decoloring by an activated carbon column. And (2) carrying out negative pressure concentration (80 ℃ and-0.06 MPa) on 1000mL of filtrate, wherein the concentration ratio is 4: 97.8%, chlorine content of the product: 0.039% and the chlorine content in the concentrate was 63.4g/L.

Example 4

Mixing and taking 1000mL of concentrated solution, wherein the content of chlorine is as follows: 43.6g/L, pH =6, salt content 30%, theoretical addition of 86mL of sulfuric acid (degree of sulfate 50%). Pretreating the concentrated solution, adding 200mL of water for dilution, adding sulfuric acid for adjusting the pH to be =2.3, filtering out impurities, taking 1200mL of filtrate for negative pressure concentration, and when 850mL of distillate water is taken out, adding chlorine: 185ppm, adding sulfuric acid to acidify the concentrated solution, collecting distillate water for circularly replenishing water, replenishing 100mL of water each time, replenishing water after 80-90mL of hydrochloric acid is discharged, and adding chlorine in hydrochloric acid: 4.1g/L and 18% acidity, discharging after the distillate water is supplemented, stirring, cooling and crystallizing, wherein the centrifugal sodium sulfate product is 98.1%, the chlorine content in the product is 0.033%, and the chlorine content in the concentrated solution is as follows: 47g/L, and the acidity of the concentrated solution is 3.7 percent.

Comparative example 1

(1) 300mL of stock solution of the lye pool (pH = 7.8) was measured, and the stock solution fluorine: 500ppm; lime (0.763 g) in an amount 3 times the theoretical amount was added to the solution, stirred well for 1h, sampled to detect fluorine: 173ppm; then, 2 times of theoretical amount of lime (0.509 g) as the stock solution was added thereto, and the mixture was sufficiently stirred for 1 hour, and then sampled to detect fluorine: 117ppm;

(2) the same alkali solution pool stock solution was measured 300mL (pH = 7.8), stock solution fluorine: 500ppm; to the solution was added 1.5 times the theoretical amount of calcium chloride (0.543 g), stirred well for 40min, sampled to detect fluorine: 110ppm; then, 1.5 times of the theoretical amount of calcium chloride (0.543 g) was added to the solution, and the mixture was stirred sufficiently for 40 hours, and then sampled to detect fluorine: 85ppm;

(3) measuring and measuring 300mL (pH = 7.5) of stock solution of the same alkali solution pool, adding hydrogen peroxide into the stock solution to ensure that sodium sulfite is completely changed into sodium sulfate, sampling and measuring fluorine: 423ppm; to this was added 2 times the theoretical amount of lime (0.502 g), stirred well for 1h, sampled to detect fluorine: 52ppm; 0.4 times of theoretical amount of lime (0.1 g) was further added thereto, sufficiently stirred for 1 hour, sampled to detect fluorine: 11ppm;

(4) measuring and measuring 300mL (pH = 7.9) of stock solution of the same alkali solution pool, adding hydrogen peroxide into the stock solution to completely change sodium sulfite into sodium sulfate, sampling and measuring fluorine: 401ppm; to this was added 2 times the theoretical amount of calcium chloride (0.677 g), stirred well for 40min, sampled to detect fluorine: 39ppm; further, 0.2 times the theoretical amount of lime (0.068 g) was added thereto, and the mixture was stirred well for 40min, and sampled to detect fluorine: 5ppm of the total amount of the reaction product.

And (4) conclusion:

1. when the stock solution of the alkali solution pool is directly subjected to fluorine removal, fluorine is difficult to be removed to be below 30ppm, the dosage is large, and the disposal cost is high; but after the sodium sulfite is oxidized into the sodium sulfate, the fluorine removal effect is obviously improved, and the addition amount of the agent is also obviously reduced; therefore, the invention improves the impurity removal effect after oxidizing sodium sulfite into sodium sulfate through oxidation-reduction reaction.

2. Calcium chloride has a slightly better defluorination than lime, but lime is chosen for its defluorination in view of cost issues and the calcium chloride adds more chloride ions to the system.

Comparative example 2

From the above table, the following conclusions can be drawn:

when the pH value is less than 4, the sodium sulfite is decomposed more, and the recovery rate is lower;

when the pH value is more than 7, although the recovery rate is high, the hydrogen peroxide is decomposed more, so that the resource waste is caused, and the production cost is increased;

when the pH is 3,3 and 5-6, although the yield is slightly lower than that of the third group of experiments, the decomposition rates of the hydrogen peroxide and the sodium sulfite are lower under the pH by combining the characteristics of the hydrogen peroxide and the sodium sulfite, the utilization rate of the hydrogen peroxide is high, and the waste of resources is reduced; therefore, the invention selects to use liquid alkali to maintain the pH =5-6 of the solution for reaction.

Claims

1. The high-salinity alkali liquor pool wastewater treatment process is characterized by comprising the following steps of:

(3) Adjusting the pH value of the filtrate 1 obtained in the step (2) to 7-8, adding a calcium removal medicament, stirring, mixing and reacting, and performing solid-liquid separation to obtain a precipitate and a filtrate 2;

(6) Pretreating the concentrated solution prepared in the step (5) by using sulfuric acid to enable the pH value of the solution to be 2-3, carrying out solid-liquid separation after reaction to obtain solid impurities and filtrate 3, carrying out negative pressure concentration on the filtrate 3 to improve the content of chloride ions in the solution, and adding sulfuric acid into the concentrated solution to adjust the acidity of the concentrated solution to 15-25% when the concentration ratio is more than or equal to 3; and supplementing water into the obtained concentrated solution, then performing negative pressure concentration to obtain hydrochloric acid fraction water and concentrated solution, performing crystallization treatment on the concentrated solution, and finally performing solid-liquid separation to obtain sodium sulfate crystals.

2. The process for treating wastewater in a high-salt alkaline liquid pool according to claim 1, wherein the mass concentration of sodium sulfite in the wastewater in the high-salt alkaline liquid pool in the step (1) is 15-33%, and the mass concentration of fluorine: 150-950ppm, chlorine: 20-65g/L.

3. The high-salt alkali liquor pool wastewater treatment process according to claim 1, wherein the mass concentration of hydrogen peroxide in the step (1) is 30-36.5%, the reaction temperature is 40-60 ℃, the dropping speed of hydrogen peroxide is 30L-60L/h, and the usage amount of hydrogen peroxide is 115-255L/t.

4. The high-salt alkali liquor pool wastewater treatment process according to claim 1, wherein the defluorinating agent in step (2) is lime or calcium chloride, and the mass ratio of the defluorinating agent to the total amount of the wastewater is as follows: 6.8X 10 ^-4 ：1-6.85×10 ^-3 ：1。

5. The process for treating high-salt alkali liquor pool wastewater according to claim 1, wherein the calcium removal agent in step (3) is sodium carbonate or sodium oxalate, and the reaction time is 40-60min.

6. The process for treating wastewater in a high-salt alkaline pond according to claim 1, wherein the iodine adsorption value in the activated carbon in the step (4) is more than 500mg/g.

7. The process of claim 1, wherein the weight of the calcium removal agent in step (3) is 0.27kg/t relative to the total mass concentration of the waste liquid.

8. The high-salt content alkali pool wastewater treatment process of claim 1, wherein the negative pressure concentration condition in step (5) is a pressure of-0.055 MPa to-0.06 MPa and a temperature of 80-90 ℃; the concentration ratio is 4.

9. The process for treating wastewater in a high-salt alkaline pond according to claim 1, wherein the concentration of sulfuric acid in step (6) is 50%; the negative pressure concentration condition is that the pressure is between-0.08 MPa and-0.09 MPa, and the temperature is between 90 and 100 ℃; the concentration ratio is 3.

10. The process for treating wastewater in a high-salt alkaline pond according to claim 1, wherein the water adding frequency in the step (6) is as follows: the volume ratio of the water added to the concentrated solution in the kettle each time is 2:3-1:2, supplementing 9-11 times; the negative pressure concentration conditions are as follows: the temperature is 90-100 ℃, and the pressure is-0.08 MPa to-0.09 MPa.