CN113480056B - A method for treating high-concentration fluorine-containing wastewater by two-stage iron-carbon adsorption-complexation-co-precipitation process - Google Patents

Abstract

The invention discloses a method for treating high-concentration fluorine-containing wastewater by a two-stage iron-carbon adsorption-complexation-co-coprecipitation process. The method realizes the synergistic effect of multiple fluorine removal ways such as adsorption fluorine removal, complex fluorine removal, coagulating sedimentation fluorine removal and the like, can efficiently remove fluorine from high-concentration fluorine-containing wastewater, has the advantages of simple process, simple and convenient operation, stable operation, economy, high efficiency and the like, and is beneficial to large-scale industrial production and application.

Description

A two-stage iron-carbon adsorption-complexation-co-precipitation process for the treatment of high-concentration fluorine-containing waste water method

technical field

The invention relates to a method for treating fluorine-containing wastewater, in particular to a method for treating high-concentration fluorine-containing wastewater by a two-stage iron-carbon adsorption-complexing-co-precipitation process, which belongs to the technical field of wastewater treatment.

Background technique

Industrial processes such as iron and steel smelting, fluorine-containing ores mining, semiconductors, electronics, chemicals, pesticides, and fluoride processing and manufacturing will all produce large amounts of fluorine-containing wastewater. Fluorinated wastewater has the characteristics of wide distribution, strong electronegativity, complex composition, and difficult treatment, which is very harmful to animals, plants and humans in the environment.

At present, the treatment methods of fluorine-containing wastewater include chemical precipitation, coagulation precipitation, adsorption, electrochemistry, ion exchange, membrane separation, induced crystallization, etc. Among them, the three methods of chemical precipitation, coagulation precipitation and adsorption are the most widely used. The chemical precipitation method is to add chemical reagents, usually calcium salts and magnesium salts, to the fluorine-containing wastewater to form fluoride precipitation with fluoride ions in the wastewater, and finally use natural sedimentation or filtration to separate solid-liquid, In order to achieve the purpose of defluorination. However, the fluorine content in the wastewater treated by this method is difficult to meet the discharge standard, and there are problems such as large amount of sludge and serious secondary pollution. In industry, the precipitation of calcium salts and magnesium salts will cause boiler scale, hinder heat conduction, and due to the problem of hard water, the industry will spend a lot of money every year due to the maintenance and replacement of equipment and pipelines. The coagulation sedimentation method is to add various coagulants to the fluorine-containing wastewater to form precipitation to remove fluoride. The disadvantage of these methods is that the effluent quality is not stable enough, and the amount of sludge produced is large, which makes subsequent treatment difficult. The adsorption method uses adsorbents to adsorb fluorine in fluorine-containing wastewater to achieve the purpose of reducing fluoride. However, there are also some shortcomings such as only low concentration, high requirements for adsorbents, and difficulty in desorption and regeneration. Usually high-concentration fluorine-containing wastewater is treated by a combination of methods, that is, two or more process methods are used to jointly treat and remove fluoride.

Therefore, it is of great practical significance to develop an efficient, cheap and easy process for the treatment of high-concentration fluorine-containing wastewater.

SUMMARY OF THE INVENTION

For the treatment of high-concentration fluorine-containing wastewater in the prior art, it is usually necessary to use two or more technical means in combination, which has the disadvantages of complex process, low treatment efficiency, and high cost. The method of adsorption-complexation-co-precipitation defluorination, this method realizes the synergistic effect of adsorption defluorination, complexation defluorination and coagulation precipitation defluorination, etc. Defluorination.

In order to achieve the above technical purpose, the present invention provides a method for treating high-concentration fluorine-containing wastewater by a two-stage iron-carbon adsorption-complexation-co-precipitation process. The method adjusts the pH of the fluorine-containing wastewater to acidity, and then enters the primary iron The carbon bed is subjected to micro-electrolysis reaction I, the effluent from the primary iron-carbon bed enters the secondary iron-carbon bed and the pH is adjusted to perform micro-electrolysis reaction II under alkaline conditions, and the effluent from the secondary iron-carbon bed undergoes solid-liquid separation to obtain defluorinated water. .

The key of the technical solution of the present invention is to realize the deep defluorination of high-concentration fluorine-containing wastewater by utilizing the micro-electrolysis reaction of iron-carbon materials under different pH conditions. First control the pH of the fluorine-containing wastewater to carry out the micro-electrolysis reaction of the iron-carbon material under acidic conditions. The iron-carbon material can release iron ions to complex the fluoride ions in the fluorine-containing wastewater to form a variety of iron-fluoride complexes. It is a porous material with good adsorption, which can efficiently adsorb some fluoride ions and iron-fluoride complexes, so as to achieve the purpose of defluorination, while the fluoride ions and iron-fluoride complexes remaining in the fluorine-containing wastewater enter the secondary Iron-carbon bed, and in the secondary iron-carbon bed, the pH of the solution is mainly adjusted to alkaline to carry out the micro-electrolysis reaction of iron-carbon materials. Under alkaline conditions, iron-fluorine complexes can be further converted into iron-fluorine complexes At the same time, iron ions are easily hydrolyzed to form ferric hydroxide with colloidal properties, which has certain adsorption properties, and ferric hydroxide colloid can promote the formation of large particles and the occurrence of coagulation, synergistic precipitation, etc. In addition, iron The carbon material can adsorb residual fluoride ions. Therefore, during the two micro-electrolysis reactions of iron-carbon materials, various defluorination pathways act synergistically to achieve a better defluorination effect.

The technical scheme of the present invention utilizes the micro-electrolysis of two-stage iron-carbon to realize the main principle of the defluorination process of high-concentration fluorine-containing wastewater, which is briefly described as follows:

a) Iron-carbon micro-electrolysis process: Based on the reaction principle of metal corrosion electrochemistry, under acidic conditions, the potential difference generated by low-potential metal iron and high-potential carbon material in fluorine-containing wastewater is used to form numerous galvanic cells. The metal iron loses electrons as the anode and releases iron ions into the fluorine-containing wastewater environment.

b) The complex reaction process of iron ions and fluoride ions: the iron ions released by the micro-electrolysis process undergo complex reactions with the fluoride ions in the fluorine-containing wastewater to form various iron-fluoride complexes, which exist in the liquid phase environment.

c) The adsorption process of iron-carbon materials: due to the large porosity and specific surface area of iron-carbon materials, they have strong adsorption capacity. Negatively charged fluoride ions have strong electrostatic interaction, and realize efficient adsorption of fluoride and/or iron-fluoride complex in fluorine-containing wastewater.

d) Alkali precipitation process: there are iron-fluoride complexes and iron ions in the solution, and after adjusting and mixing, the iron-fluorine complexes form iron-fluoride complex precipitates, and iron ions also form colloids such as ferric hydroxide, which promotes the formation of iron-fluoride complexes. The formation of particulate matter and the occurrence of coagulation.

e) Synergistic co-precipitation process: colloids and large particles such as iron-carbon materials, iron-fluorine complex precipitates and iron hydroxides mixed in the reaction system have a synergistic co-precipitation defluorination effect under alkaline conditions. to improve the separation and removal rate of fluoride.

As a preferred solution, the pH of the fluorine-containing wastewater is adjusted to <4. More preferred pH=2～3. On the one hand, when the pH is 2-3, the iron-carbon material will release a large amount of iron ions through the electrochemical reaction to participate in the removal of fluorine. When the pH is greater than 4, the micro-electrolysis reaction is weak, and the amount of dissolved iron in the system is very small. The contribution of iron ions to the removal of fluoride decreases; on the other hand, pH affects the degree of protonation. With the increase of pH, the degree of protonation on the surface of iron-carbon materials gradually decreases. The less positive charge on the surface of iron-carbon, the greater the electronegativity. The weaker the interaction with negatively charged F- ^, the less ability to remove fluorine.

As a preferred solution, in the process of micro-electrolysis reaction I, the dosage of iron-carbon material in the fluorine-containing wastewater is 20-40 g/L, the reaction residence time is 1-2 h, and the reaction temperature is 20-25 °C.

As a preferred solution, the pH of the effluent from the primary iron-carbon bed is adjusted to 8-10. The pH is adjusted by common alkaline compounds such as sodium hydroxide, potassium hydroxide, and ammonia.

As a preferred solution, in the process of micro-electrolysis reaction II, the dosage of the iron-carbon material relative to the effluent of the first-level iron-carbon bed is 20-40g/L, the reaction residence time is 1-2h, and the reaction temperature is 20℃～25℃ .

As a preferred solution, the micro-electrolysis reaction II process is assisted by aeration and/or ultrasound. It is used to wash and separate the alkaline iron sludge generated on the surface of the secondary iron-carbon bed from the surface of the secondary iron-carbon bed, so as to maintain its long-term use.

As a preferred solution, the porosity of the iron-carbon material is greater than or equal to 55%, and the specific surface area is greater than or equal to 1.4 m ² /g. The preferred iron-carbon material has higher porosity and larger specific surface area, and has higher reactivity and better adsorption performance.

As a preferred solution, the main components of the iron-carbon material are zero-valent iron and carbon material. The zero-valent iron can be iron filings, zero-valent iron powder, nano zero-valent iron, etc.; the carbon material can be activated carbon, coke, and the like.

As a preferred solution, the iron-carbon material includes a transition metal-based catalyst. Specifically, catalysts containing copper, aluminum and other transition metal elements. Iron-carbon materials directly purchase commercial iron-carbon materials on the market.

As a preferred solution, the fluorine concentration of the fluorine-containing wastewater is not greater than 2000 mg/L. Generally speaking, the higher the concentration of fluorine-containing wastewater, the worse the fluorine removal effect in the prior art, and the more complicated the means. 1000～2000mg/L, another example is 1500～2000mg/L. The fluorine-containing wastewater mainly comes from fluorine-containing wastewater generated in industrial processes such as iron and steel smelting, fluorine-containing ores mining, semiconductors, electronics, chemicals, pesticides, and fluoride processing and manufacturing.

As a preferred solution, the solid-liquid separation can adopt common filtration means, or can achieve the purpose of solid-liquid separation through a settling device, and the settling device can be a settling tank, including a conical settling tank, an inclined plate settling tank, a radial flow Sedimentation tank, etc.

Relative to the prior art, the beneficial technical effects brought by the technical solution of the present invention:

(1) In the method for treating high-concentration fluorine-containing wastewater provided by the present invention, the two-stage iron-carbon adsorption-complex-co-co-precipitation defluorination process is used to simultaneously include the adsorption and defluorination of iron-carbon materials on fluoride, iron ions and The complex defluorination effect of fluoride ions and the coagulation and synergistic precipitation defluorination effect of iron gel and other fluoride removal effects show a better comprehensive defluorination effect, which can realize the depth of high-concentration fluorine-containing wastewater. Fluoride removal.

(2) In the method for treating high-concentration fluorine-containing wastewater provided by the present invention, by reasonably adjusting the pH in the micro-electrolysis reaction process of the two-stage iron-carbon material, high-efficiency defluorination in the micro-electrolysis reaction process is realized, and in the initial stage, adjusting The pH value of the influent water is adjusted to be acidic, which is more suitable for the release and dissolution of iron ions during the micro-electrolysis process to achieve the effect of complex defluorination. In the later stage, the pH of the solution system is adjusted to alkaline, which can realize coagulation and synergistic precipitation, etc. Comprehensive fluoride removal. The method is more suitable for the treatment of acidic fluorine-containing wastewater, and the acidity of the wastewater itself can be used to reduce the acid consumption of the initial pH adjustment of the reaction. At the same time, the separation of fluorides can be improved without adding coagulants in the post-reaction stage removal rate.

(3) In the method for treating high-concentration fluorine-containing wastewater provided by the present invention, it is mainly realized based on iron-carbon materials. Iron-carbon materials are common cheap and environmentally friendly materials, and their safety is high, and they remain in the solution during use. The iron element in the system can be easily separated and removed from the system by adjusting the pH and precipitation, which can solve the calcium salt and magnesium salt used in the conventional defluorination method in the prior art. problem with flaws.

(4) The method for treating high-concentration fluorine-containing wastewater provided by the present invention has the advantages of simple process, simple and convenient operation, stable operation, economical efficiency, and is beneficial to large-scale industrial production and application.

Description of drawings

Fig. 1 is the process flow diagram of the two-stage iron-carbon adsorption-complexation-co-precipitation process of the present invention for treating high-concentration fluorine-containing wastewater.

Figure 2 shows the comparison of the fluoride removal effects of three different processes for the treatment of high-concentration fluorine-containing wastewater using one-stage acidic iron-carbon micro-electrolysis, one-stage iron-carbon complex adsorption alkali precipitation, and two-stage iron-carbon adsorption-complexation-co-precipitation.

Fig. 3 is the influence of the dosage of iron-carbon material on the fluorine removal effect in the process of treating high-concentration fluorine-containing wastewater by the two-stage iron-carbon adsorption-complexation-co-precipitation process of the present invention.

Fig. 4 is the influence of influent fluoride concentration in the process of treating high-concentration fluorine-containing wastewater by the two-stage iron-carbon adsorption-complexation-co-precipitation process of the present invention.

Detailed ways

The following is intended to further describe the content of the present invention in detail with reference to the accompanying drawings and embodiments, rather than limiting the protection scope of the claims of the present invention.

The detection methods used in the following examples are all conventional detection methods in the industry, and the iron-carbon materials and chemical reagents used are obtained from commercial sources.

The commercial iron-carbon material is pretreated by grinding, with a specific surface area of 1.2 m ² /g and a porosity of 55%.

Example 1

(1) Prepare 1000mg/L simulated fluorine-containing wastewater, adjust pH=2, and take 100 mL of the above simulated wastewater in a conical flask;

(2) add 2g to the conical flask, shake it up gently, then move the conical flask to a shaker with a temperature of 25°C, a shaking speed of 140rpm, and a first-level iron-carbon microelectrolysis complex adsorption reaction for 120min;

(3) After the reaction is completed, take out the conical flask, stand for precipitation, filter out the supernatant, measure and analyze the content of fluoride and calculate the fluorine removal rate of the first-level iron-carbon micro-electrolysis complex adsorption.

(4) take the filtrate after the first-step iron-carbon micro-electrolysis complex adsorption, adjust the pH of the solution to 10 with NaOH, stand for precipitation, filter out the supernatant, analyze the content of fluoride and calculate the first-level iron-carbon Fluorine removal rate of complex adsorption alkali precipitation;

(5) Repeat the above steps, and get the filtrate after the first-level iron-carbon micro-electrolysis complexation adsorption, pass into another conical flask, add 2g iron-carbon material, and adjust the pH of the mixed solution to 10 with NaOH, and leave it to stand still Precipitate and filter out the supernatant to determine the content of fluoride and calculate the fluorine removal rate of the two-stage iron-carbon adsorption complex co-precipitation synergistic co-precipitation.

The experimental results are shown in the following table and Figure 2:

Reaction volume: 100mL, raw water fluoride concentration 1000mg/L

As can be seen from Figure 2 and the above table, when the reaction volume is 100mL, the pH of the influent water is 2, 2g iron carbon, and the reaction time is 2h, the fluorine removal rate of the first-grade iron-carbon is about 50.92%. The fluorine removal rate of first-grade iron-carbon complex adsorption and alkali precipitation was about 59.54%, and the removal rate increased by about 8.6%; while the fluorine removal rate of two-stage iron-carbon adsorption and complex co-precipitation was about 97.07%. It can be seen from the comparison that the fluorine removal rate of the two-stage iron-carbon adsorption complex co-precipitation is much higher than that of the first-level iron-carbon complex adsorption alkali precipitation, about 37.5% higher. The two-stage iron-carbon has a synergistic co-precipitation fluoride removal effect, which greatly improves the separation and removal rate of fluoride.

Example 2

The fluorine-containing wastewater used in this example is a simulated wastewater of 1000 mg/L configured. Influent pH=2.5, first-grade iron-carbon reaction time 2h, second-stage precipitation time 1h, shaker rotation speed 140rpm, temperature 25°C. The specific implementation steps are as follows:

(1) Take the simulated wastewater with a fluoride concentration of 1000 mg/L in a beaker, and adjust the pH to 2.5;

(2) respectively take 100mL of above-mentioned simulated waste water in 5 conical flasks with measuring cylinder;

(3) Add 0.5g, 1g, 1.5g, 2g, 2.5g of iron-carbon material to the conical flask, and shake gently;

(4) the Erlenmeyer flask was moved to a shaker with a temperature of 25°C and a shaking speed of 140rpm, and the reaction was performed for 120min;

(5) after the reaction is completed, take out the conical flask, filter out the supernatant respectively;

(6) Add 0.5g, 1g, 1.5g, 2g, 2.5g of iron-carbon material to the above-mentioned filtered supernatant, and shake gently;

(7) The pH of the solution was adjusted to 10 with NaOH, and after 1 h of aeration-assisted reaction, the solution was left to stand for 1 h;

(8) Filter the supernatant, measure and analyze the content of fluoride and calculate the removal rate.

The experimental results are shown in Figure 3.

It can be seen from Figure 3 that the dosage of two-stage iron-carbon has a great influence on the removal of fluoride. The removal rate of fluoride in the simulated fluoride-containing wastewater increased gradually with the increase of iron-carbon dosage. The removal rate of fluoride increased greatly in the initial stage, and then with the increase of the dosage, the increasing trend tended to be gentle. When the dosage is 1.5g, the fluorine removal rate tends to be gentle.

Example 3

The fluorine-containing wastewater used in this embodiment is simulated wastewater with different concentrations. Influent pH=2.5, primary iron-carbon reaction time 2h, secondary precipitation time 1h, shaker rotation speed 140rpm, temperature 25°C, the specific steps are as follows:

(1) Configure fluorine-containing simulated wastewater with different concentrations: 100, 500, 1000, 1500, 2000 mg/L;

(2) Take 100 mL of the above-mentioned fluorine-containing simulated wastewater with different concentrations in each measuring cylinder into 5 conical flasks, and adjust the pH to 2.5;

(3) respectively add 2g iron carbon material to above-mentioned conical flask, shake gently;

(4) the Erlenmeyer flask was moved to a shaker with a temperature of 25°C and a shaking speed of 140rpm, and the reaction was performed for 120min;

(5) after the reaction is completed, take out the conical flask, filter out the supernatant respectively;

(6) in the above-mentioned filtered supernatant, add 2g iron carbon material respectively, shake up gently;

(7) The pH of the solution was adjusted to 10 with NaOH, and after 1 h of aeration-assisted reaction, the solution was left to stand for 1 h;

(8) Filter the supernatant, measure and analyze the content of fluoride and calculate the removal rate.

The experimental results are shown in Figure 4.

It can be seen from Figure 4 that with the increasing initial fluoride concentration, the fluoride content in the effluent after the two-stage iron-carbon treatment of the fluoride in the solution also increases; and the fluorine removal rate increases with the initial fluoride concentration. It first increased and then decreased, and the maximum was when the initial fluorine concentration was 500 mg/L. The two-stage iron-carbon treatment has high fluoride removal rates for fluorine-containing wastewater with different initial fluoride concentrations, and has strong adaptability. When the initial fluoride concentration is 500-2000 mg/L, the fluorine removal rate is maintained at 80%. above.

The above specific embodiments and examples are specific support for the technical idea of fluoride removal of a method for treating high-concentration fluorine-containing wastewater by a two-stage iron-carbon adsorption-complexation-co-precipitation process proposed by the present invention, and the present invention cannot be limited by this. In the protection scope of the invention, any equivalent changes or equivalent modifications made on the basis of the technical solution according to the technical idea proposed by the invention still belong to the protection scope of the technical solution of the invention.

Claims (7)

1. a method for two-stage iron-carbon adsorption-complexation-co-precipitation process to handle high-concentration fluorine-containing waste water, it is characterized in that: after the fluorine-containing waste water is adjusted to pH, enter one-level iron-carbon bed and carry out micro-electrolysis reaction

, the effluent from the primary iron-carbon bed enters the secondary iron-carbon bed and adjusts the pH to an alkaline condition for micro-electrolysis reaction

, the effluent from the secondary iron-carbon bed is separated from solid and liquid to obtain defluorinated water; The fluorine concentration of the fluorine-containing wastewater is not more than 2000 mg/L. 2. The method for treating high-concentration fluorine-containing wastewater by a two-stage iron-carbon adsorption-complexation-co-precipitation process according to claim 1, wherein the pH of the fluorine-containing wastewater is adjusted to <4. 3. a kind of two-stage iron-carbon adsorption-complex-co-co-precipitation process according to claim 1 is characterized in that: micro-electrolysis reaction

During the process, the dosage of iron-carbon material relative to the fluorine-containing wastewater is 20-40 g/L, the reaction residence time is 1-2 h, and the reaction temperature is 20-25 °C. 4. the method for a two-stage iron-carbon adsorption-complexation-co-precipitation process for treating high-concentration fluorine-containing wastewater according to claim 1, is characterized in that: the pH of the first-level iron-carbon bed effluent is adjusted to 8～10 . 5. a kind of two-stage iron-carbon adsorption-complex-co-co-precipitation process according to claim 1 is characterized in that: micro-electrolysis reaction

In the process, the dosage of iron-carbon material relative to the effluent of the primary iron-carbon bed is 20-40 g/L, the reaction residence time is 1-2 h, and the reaction temperature is 20-25°C. 6. a kind of two-stage iron-carbon adsorption-complex-co-co-precipitation process according to claim 1 or 5 is characterized in that: described micro-electrolysis reaction

The procedure is assisted by aeration and/or ultrasound. 7. the method for a kind of two-stage iron-carbon adsorption-complex-co-co-precipitation process treatment high-concentration fluorine-containing wastewater according to claim 3, is characterized in that: the porosity of described iron-carbon material ≥ 55%, the ratio Surface area ≥ 1.2 m ² /g.

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