Method for synergistically preparing and purifying sodium fluosilicate by using fluorine-containing waste acid and fly ash

Abstract

The invention discloses a method for synergistically preparing and purifying sodium fluosilicate by using fluorine-containing waste acid and fly ash. The method comprises the following steps: crushing household garbage incineration fly ash, pulping, pickling, and carrying out solid-liquid separation to obtain crude calcium water; sequentially carrying out heavy metal removal, denitrification, oxidation and neutralization treatment on the crude calcium water, and carrying out solid-liquid separation to obtain refined calcium water; carrying out primary calcium removal treatment on the obtained refined calcium water, and carrying out solid-liquid separation to obtain crude brine; carrying out deep calcium removal treatment on the crude brine to obtain refined brine mainly containing sodium chloride; pretreating the fluorine-containing waste acid to obtain a fluosilicic acid solution; mixing and reacting the fluosilicic acid solution with refined salt water, controlling the pH value of a reaction system to be less than 2, and performing solid-liquid separation to obtain crude sodium fluosilicate; and carrying out multistage countercurrent oxidation washing on the crude sodium fluosilicate, and drying to obtain a sodium fluosilicate product. And resource comprehensive utilization of the fluorine-containing waste acid and the fly ash is realized.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment and resource utilization technology, specifically to a method for preparing and purifying sodium fluorosilicate by co-processing fluorine-containing waste acid and fly ash. Background Technology

[0002] Waste acid is classified as hazardous waste (HW34), and its effective recycling and disposal is a crucial issue in the environmental protection field. Waste acid from glass etching mainly contains hydrofluoric acid, fluorosilicic acid, and metal ions, and is therefore classified as hazardous waste (HW34). Improper handling pollutes the environment and wastes resources. Fluorine-containing waste acid mainly originates from polysilicon production and the glass etching industry. It contains high concentrations of fluoride ions and may also contain other components such as silicon and nitrate, thus exhibiting strong acidity and high corrosiveness. Improper handling of this waste also pollutes the environment and wastes resources.

[0003] Municipal solid waste incineration fly ash refers to the ash collected by the flue gas purification system of municipal solid waste incineration facilities and the bottom ash settling at the bottom of the flue and chimney. Municipal solid waste incineration fly ash is characterized by high salt content and contains pollutants such as heavy metals and dioxins, and is listed in the "National Hazardous Waste List".

[0004] Sodium fluorosilicate (Na₂SiF₆), commonly known as sodium hexafluorosilicate or sodium fluorosilicide, is a white crystalline powder, slightly soluble in water, and decomposes into an acidic state in hot water. It is mainly produced as a byproduct of superphosphate production and has wide applications in industry, construction, agriculture, and public utilities. In industrial manufacturing, it is used as an enamel opacifier, glass opacifier, flux in metal smelting, and filler for plastics and rubber. In the construction industry, it is a key additive in acid-resistant cement, concrete, and mortar. In agriculture, it is a major component of pesticides, defoliants, and wood preservatives. In public utilities, it is used as a fluoride source for drinking water fluoridation.

[0005] Currently, the main methods for recovering fluorine-containing waste acid include crystallization, distillation, and ion exchange. Crystallization involves dissolving waste fluorosilicic acid and then using crystallization to precipitate it from the solution, thus obtaining a high-purity fluorosilicic acid product. Its advantage is the efficient extraction of fluorosilicic acid from wastewater. Its disadvantage is the need for strict control of crystallization conditions to ensure product purity and quality. Distillation utilizes the fact that the distillation temperature of fluorosilicic acid is lower than that of water to extract it from wastewater. Its advantages are simple operation and high efficiency. Its disadvantage is the need for strict temperature control during distillation to prevent the decomposition or volatilization of fluorosilicic acid. Ion exchange uses ion exchange resins to adsorb and desorb fluorosilicic acid from wastewater, achieving fluorosilicic acid recovery. Its disadvantage is the high cost of regenerating and replacing ion exchange resins, requiring regular maintenance and replacement. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing and purifying sodium fluorosilicate by using fluorine-containing waste acid and fly ash in synergistic process.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing and purifying sodium fluorosilicate using fluorine-containing waste acid and fly ash, comprising the following steps:

[0008] (1) The fly ash from municipal solid waste incineration is crushed and pulped, then acid washed, and the solid-liquid separation is performed to obtain crude calcium water; the crude calcium water is subjected to heavy metal removal, denitrification, oxidation and neutralization treatment in sequence, and the solid-liquid separation is performed to obtain refined calcium water;

[0009] (2) The obtained refined calcium water is subjected to preliminary decalcification treatment, and after solid-liquid separation, crude brine is obtained; then the crude brine is subjected to deep decalcification treatment to obtain refined brine mainly composed of sodium chloride.

[0010] (3) Fluorine-containing waste acid is pretreated to obtain fluorosilicic acid solution; the fluorosilicic acid solution is mixed with refined salt water and reacted, the pH of the reaction system is controlled to be <2, and crude sodium fluorosilicate is obtained after solid-liquid separation;

[0011] (4) The crude sodium fluorosilicate is subjected to multi-stage countercurrent oxidation washing and drying to obtain the sodium fluorosilicate product.

[0012] Preferably, in step (1), the mass ratio of fly ash to water in the crushing and pulping process is 1:2~4; the pickling process uses 8~15% industrial waste hydrochloric acid; the pH of the crude calcium water is 1~2, wherein the calcium ion concentration is 20~40 g / L and the magnesium ion concentration is 2~10 g / L.

[0013] Preferably, in step (1), the heavy metal removal treatment is carried out by adding a heavy metal removal agent, the dosage of which is 1-2 grams per liter of crude calcium water; the pH value of the reaction endpoint system is 4-5; the heavy metal removal agent is prepared as a solution with a mass fraction of 5%-15% and added dropwise under stirring conditions, with the addition time controlled at 30-60 minutes.

[0014] Preferably, the deweighting agent is one or more combinations of sodium sulfide, ammonium dithiocarbamate, sodium dithiocarbamate, and diisopropyl disulfide xanthate.

[0015] Preferably, in step (1), the crude calcium water undergoes denitrification, oxidation, and neutralization treatment, specifically as follows: First, a denitrification agent is added, with the amount of denitrification agent added being 0.5%~2% of the mass of the crude calcium water, and the reaction is carried out for 30~60 minutes; then, an oxidant is added, with the amount of oxidant added being 0.5%~2% of the mass of the crude calcium water; finally, a sodium hydroxide solution with a mass fraction of 30%~40% is added for neutralization, and the solution is slowly added dropwise while stirring for 30 minutes. After the neutralization reaction, the pH is 7~8.5; after stepwise dosing, solid-liquid separation is carried out to obtain colorless and transparent refined calcium water.

[0016] Preferably, the denitrifying agent is one or more of sodium hypochlorite, hypochlorous acid, sodium phosphate, and disodium hydrogen phosphate, and the oxidizing agent is one or more of hydrogen peroxide, sodium metabisulfite, and ozone.

[0017] Preferably, in step (2), the specific process of the preliminary decalcification treatment of the refined calcium water is as follows: the refined calcium water is added to the reaction vessel, acidified with hydrochloric acid, stirred, and the stirring temperature is 20~40℃; then sodium sulfate solution is added, and the feeding time is 30~60min; after the feeding is completed, the mixture is stirred for 20~45min and left to stand for 1~2h; finally, solid-liquid separation is performed, the solid is calcium sulfate dihydrate whiskers, and the liquid is crude brine.

[0018] Preferably, the volume ratio of hydrochloric acid to refined calcium water is 1~5:10.

[0019] Preferably, in step (2), the specific process of deep decalcification treatment of the crude brine is as follows: add sodium carbonate solution to the crude brine, adjust the pH value to 9~11, and after precipitation, obtain refined brine mainly composed of sodium chloride.

[0020] Preferably, in step (4), the crude sodium fluorosilicate undergoes multi-stage countercurrent oxidation washing, and the mass ratio of the crude sodium fluorosilicate to the washing liquid is 1:3~5. The specific process is as follows: the crude sodium fluorosilicate enters the primary washing unit, and after washing and solid-liquid separation, the obtained solid enters the secondary washing unit, and the obtained wastewater is discharged from the system; washing liquid and oxidant are added to the secondary washing unit for washing and solid-liquid separation, and the obtained solid is dried to obtain sodium fluorosilicate product; the obtained washing effluent is returned to the primary washing unit.

[0021] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention achieves efficient recovery and resource utilization of fluorosilicate and sodium ions from two types of hazardous waste through the co-treatment of fluorinated waste acid and fly ash, successfully producing sodium fluorosilicate products that meet national standards, providing a new approach for the resource utilization of fluorinated waste acid. Furthermore, through acid dissolution, deep impurity removal, and two-stage calcium removal processes, high-purity sodium chloride brine is obtained from the complex fly ash system, providing qualified raw materials for the synthesis reaction. Precise control of the synthesis pH and multi-stage countercurrent oxidation washing ensures that the purity of the final product meets standards. This invention treats waste with waste, significantly reducing treatment costs and secondary pollution, and has outstanding environmental and economic benefits. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] In this embodiment of the invention, sodium fluorosilicate is prepared by co-processing fluorine-containing waste acid from an environmental protection company in Yancheng, Jiangsu Province, fly ash from municipal solid waste incineration at a waste-to-energy plant in Yancheng, Jiangsu Province, and waste hydrochloric acid from a chemical plant in Yancheng, Jiangsu Province.

[0024] Example 1

[0025] The main parameters of fluoride-containing waste acid are shown in Table 1;

[0026] Table 1. Composition parameters of fluorine-containing waste acid

[0027]

[0028] Acid dissolution of waste hydrochloric acid and fly ash: The reaction is carried out at a water-to-ash ratio of 1:4. 300g of fly ash is placed in a beaker, 400ml of pure water is added, and the mixture is stirred until a slurry is formed. Then, 750mL of waste hydrochloric acid is slowly added dropwise while stirring. Simultaneously, the solution is heated to 40℃. Another 50mL of pure water is added, and the mixture is stirred for 30 minutes. Vacuum filtration is performed to separate the solid and liquid phases, yielding 900mL of pickling solution, i.e., crude calcium water. The crude calcium water mainly contains calcium chloride, sodium chloride, magnesium chloride, potassium chloride, and other salts, as well as small amounts of polluting elements. Basic process parameters: Appearance: orange-yellow solution, pH=1.5, TOC: 66mg / L, calcium ions: 36g / L, magnesium ions: 2.5g / L;

[0029] (2) Weight removal: Take 900ml of crude calcium water from step (1), slowly add sodium sulfide solution while stirring. Stop adding when pH=4. Add a total of 22ml of 5% sodium sulfide solution. The reaction time is 30min. A brown precipitate is formed. Let stand for 1h, then vacuum filter to obtain a brown precipitate with a dry weight of 5.8g. The solution after weight removal is light yellow.

[0030] (3) Oxidation and impurity removal: Add 10 ml of sodium hypochlorite solution to the filtrate obtained in step (2), stir and react for 30 min, a blue-brown precipitate is formed, then add 10 ml of hydrogen peroxide, the precipitate color turns yellow, aerate with ozone for 1 h, add 30% sodium hydroxide solution, adjust the pH to neutral, filter, and obtain a yellow precipitate with a dry weight of 6.1 g and a clear and transparent solution, i.e., refined calcium water, and proceed to the calcium sulfate whisker preparation step. Basic process parameters of refined calcium water: Appearance: colorless and transparent solution, pH=7, TOC: 2 mg / L, calcium ions: 36 g / L, magnesium ions: 2.2 g / L; heavy metal pollutants are basically removed.

[0031] (4) Preliminary calcium removal from refined calcium water: Add 500 mL of refined calcium water to a constant temperature reaction vessel, keep the temperature constant at 20 °C, add hydrochloric acid solution, control pH=1, take 260 mL of sodium sulfate solution with a concentration of 250 g / L, slowly drip it into the reaction vessel while stirring, add it dropwise for 45 min, let it stand for 1 h, filter, and obtain 82 g of wet calcium sulfate whiskers. The crude brine enters the next step.

[0032] (5) Deep calcium removal from crude brine: Add 50 ml of 20% sodium carbonate solution to the crude brine obtained in step (4), adjust the pH to 9, and filter to obtain refined brine, which mainly contains sodium chloride.

[0033] (6) Preparation of sodium fluorosilicate: The fluorine-containing waste acid was filtered to remove insoluble matter and obtain a clear solution. 1L of the filtered fluorine-containing waste acid was added to 240ml of the refined salt water obtained in step (4), and the mixture was stirred and reacted for 1h. After precipitation and filtration, 50g of crude sodium fluorosilicate was obtained.

[0034] (7) Take the crude sodium fluorosilicate obtained in step (6) and perform a two-stage countercurrent washing at a mass ratio of crude sodium fluorosilicate to washing solution of 1:3. Take 50g of crude calcium sulfate and add it to 200mL of saturated sodium fluorosilicate solution for a first wash. Stir thoroughly for 30min, filter, and add a small amount of hydrochloric acid to control the pH=1.5. After the first wash, add another 200ml of saturated sodium fluorosilicate solution for a second wash to further remove the salt on the surface of the whiskers. Filter and dry the obtained sodium fluorosilicate in an oven at 160℃. The obtained sodium fluorosilicate is tested, and the product indicators meet the superior grade standard in "Industrial Sodium Fluorosilicate" (GB / T23936), as shown in Table 2.

[0035] Table 2 Quality Indicators of Sodium Fluorosilicate

[0036]

[0037] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A method for the synergistic preparation and purification of sodium fluorosilicate using fluorine-containing waste acid and fly ash, characterized in that: Includes the following steps: (1) The fly ash from municipal solid waste incineration is crushed and pulped, then acid washed, and the solid-liquid separation is performed to obtain crude calcium water; the crude calcium water is subjected to heavy metal removal, denitrification, oxidation and neutralization treatment in sequence, and the solid-liquid separation is performed to obtain refined calcium water; (2) The obtained refined calcium water is subjected to preliminary decalcification treatment, and after solid-liquid separation, crude brine is obtained; then the crude brine is subjected to deep decalcification treatment to obtain refined brine mainly composed of sodium chloride. (3) Fluorine-containing waste acid is pretreated to obtain fluorosilicic acid solution; the fluorosilicic acid solution is mixed with refined salt water and reacted, the pH of the reaction system is controlled to be <2, and crude sodium fluorosilicate is obtained after solid-liquid separation; (4) The crude sodium fluorosilicate is subjected to multi-stage countercurrent oxidation washing and drying to obtain the sodium fluorosilicate product.

2. The method for preparing and purifying sodium fluorosilicate using fluorine-containing waste acid and fly ash according to claim 1, characterized in that, In step (1), the mass ratio of fly ash to water in the crushing and pulping process is 1:2~4; the pickling process uses 8~15% industrial waste hydrochloric acid; and the pH of the crude calcium water is 1~2.

3. The method for preparing and purifying sodium fluorosilicate using fluorine-containing waste acid and fly ash according to claim 1, characterized in that, In step (1), the heavy metal removal treatment is carried out by adding a heavy metal removal agent. The amount of the heavy metal removal agent added is 1-2 grams per liter of crude calcium water. The pH value of the reaction endpoint system is 4-5. The heavy metal removal agent is prepared as a solution with a mass fraction of 5%-15% and added dropwise under stirring conditions. The dropwise addition time is controlled at 30-60 minutes.

4. The method for preparing and purifying sodium fluorosilicate by co-processing fluorine-containing waste acid and fly ash according to claim 3, characterized in that, The deweighting agent is one or more combinations of sodium sulfide, ammonium dithiocarbamate, sodium dithiocarbamate, and diisopropyl disulfide xanthate.

5. The method for preparing and purifying sodium fluorosilicate using fluorine-containing waste acid and fly ash according to claim 1, characterized in that, In step (1), the crude calcium water undergoes denitrification, oxidation, and neutralization treatment, specifically as follows: First, a denitrification agent is added at a dosage of 0.5% to 2% of the crude calcium water mass, and the reaction is carried out for 30 to 60 minutes; then, an oxidant is added at a dosage of 0.5% to 2% of the crude calcium water mass; finally, a sodium hydroxide solution with a mass fraction of 30% to 40% is added for neutralization, and the solution is slowly added dropwise while stirring for 30 minutes. After the neutralization reaction, the pH is 7 to 8.5; after stepwise dosing, solid-liquid separation is carried out to obtain colorless and transparent refined calcium water.

6. The method for preparing and purifying sodium fluorosilicate using fluorine-containing waste acid and fly ash according to claim 5, characterized in that, The denitrifying agent is one or more of sodium hypochlorite, hypochlorous acid, sodium phosphate, and disodium hydrogen phosphate, and the oxidizing agent is one or more of hydrogen peroxide, sodium metabisulfite, and ozone.

7. The method for preparing and purifying sodium fluorosilicate by co-processing fluorine-containing waste acid and fly ash according to claim 1, characterized in that, In step (2), the specific process of the preliminary decalcification treatment of the refined calcium water is as follows: the refined calcium water is added to the reaction vessel, acidified with hydrochloric acid, stirred, and the stirring temperature is 20~40℃; then sodium sulfate solution is added, and the feeding time is 30~60min; after the feeding is completed, the mixture is stirred for 20~45min and left to stand for 1~2h; finally, solid-liquid separation is carried out, the solid is calcium sulfate dihydrate whiskers, and the liquid is crude brine.

8. The method for preparing and purifying sodium fluorosilicate using fluorine-containing waste acid and fly ash according to claim 7, characterized in that, The volume ratio of hydrochloric acid to refined calcium water is 1~5:

10.

9. The method for preparing and purifying sodium fluorosilicate by co-processing fluorine-containing waste acid and fly ash according to claim 1, characterized in that, In step (2), the specific process of deep decalcification treatment of the crude brine is as follows: sodium carbonate solution is added to the crude brine, the pH value is adjusted to 9~11, and after precipitation, a refined brine mainly composed of sodium chloride is obtained.

10. The method for preparing and purifying sodium fluorosilicate by co-processing fluorine-containing waste acid and fly ash according to claim 1, characterized in that, In step (4), the crude sodium fluorosilicate undergoes multi-stage countercurrent oxidation washing, and the mass ratio of the crude sodium fluorosilicate to the washing liquid is 1:3~5. The specific process is as follows: the crude sodium fluorosilicate enters the first-stage washing unit, and after washing and solid-liquid separation, the obtained solid enters the second-stage washing unit, and the obtained wastewater is discharged from the system. The secondary washing unit is replenished with washing liquid and oxidant for washing and solid-liquid separation. The resulting solid is dried to obtain sodium fluorosilicate product. The resulting washing effluent is returned to the primary washing unit.

Images