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CN114751429B - Treatment process for preparing baking soda from desulfurized fly ash - Google Patents

Treatment process for preparing baking soda from desulfurized fly ash Download PDF

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CN114751429B
CN114751429B CN202210338340.XA CN202210338340A CN114751429B CN 114751429 B CN114751429 B CN 114751429B CN 202210338340 A CN202210338340 A CN 202210338340A CN 114751429 B CN114751429 B CN 114751429B
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sodium bicarbonate
salt
filtrate
crystallization
oxidation
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CN114751429A (en
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李保震
李雅
王美娇
赵宇靖
韦凤密
王天慧
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Beijing Saike Kanglun Environmental Science & Technology Co ltd
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Beijing Saike Kanglun Environmental Science & Technology Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D7/00—Carbonates of sodium, potassium or alkali metals in general
    • C01D7/02—Preparation by double decomposition
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C1/00—Ammonia; Compounds thereof
    • C01C1/24—Sulfates of ammonium
    • C01C1/244—Preparation by double decomposition of ammonium salts with sulfates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
    • C01D5/04—Preparation of sulfates with the aid of sulfurous acid or sulfites, e.g. Hargreaves process
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
    • C01D5/16—Purification
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D7/00—Carbonates of sodium, potassium or alkali metals in general
    • C01D7/10—Preparation of bicarbonates from carbonates
    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05C—NITROGENOUS FERTILISERS
    • C05C3/00—Fertilisers containing other salts of ammonia or ammonia itself, e.g. gas liquor
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity

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Abstract

A treatment process for preparing baking soda from desulfurization ash belongs to the technical field of desulfurization ash treatment. One technical scheme comprises the following steps: (1) dissolving and filtering; (2) removing organic matters; (3) aeration impurity removal; (4) defluorination; (5) salt separation; (6) sodium sulfate to prepare sodium bicarbonate; and (7) treating the crystallization mother liquor. Another technical proposal replaces the step (1) with saturated Na 2 SO 4 The solution was rinsed and filtered. According to the invention, a large amount of sodium bicarbonate in the system is firstly transferred out, then sodium sulfate in the system is converted into sodium bicarbonate, the usage amount of a conversion reagent for converting sodium sulfate into sodium bicarbonate is reduced, and the recycling of the desulfurization ash is fully realized.

Description

Treatment process for preparing baking soda from desulfurized fly ash
Technical Field
The invention belongs to the technical field of desulfurization ash treatment, and relates to a treatment process for preparing baking soda from desulfurization ash.
Background
The flue gas desulfurization ash is first-grade dangerous solid waste generated in the flue gas desulfurization process of the coke oven by taking sodium carbonate and sodium bicarbonate as desulfurizing agents, wherein the main components are sodium carbonate, sodium bicarbonate, sodium sulfate and the like, and the flue gas desulfurization ash contains impurity ions in a certain proportion. In general, na in the desulfurized fly ash 2 SO 3 10-20 percent of NaF accounting for 0.5-1 percent of Na 2 CO 3 The ratio of the sodium bicarbonate to the sodium sulfate is 5-15%, and the sodium bicarbonate and the sodium sulfate are the rest. The desulfurized fly ash is easy to dissolve in water, and when being piled up or buried, the desulfurized fly ash can infiltrate into soil after being drifted by rainwater, thereby causing serious pollution to soil and underground water.
CN11207363a proposes a method for recycling sodium bicarbonate desulfurization ash, after the desulfurization ash is dissolved by pure water, clarifying solid-liquid separation is performed, sodium bicarbonate crystals are added into the clarified liquid, and evaporation concentration is performed to obtain a sodium bicarbonate product, but the technology does not mention a technology for removing impurity ions in the desulfurization ash, and the purity of the obtained sodium bicarbonate and sodium sulfate products cannot be ensured.
CN109850922a proposes a method and a device for recycling baking soda desulfurization ash, which are based on the dissolution and filtration of desulfurization ash, and provides a method for converting carbonate in solution into bicarbonate by adopting the combined action of lime milk and carbon dioxide and oxygen, so that the purity of baking soda is improved, and byproduct calcium sulfate is recovered, but the added value of the calcium sulfate is lower than that of the baking soda. And the purity of the recovered calcium sulfate cannot be ensured due to the existence of organic matters and fluoride ions in the desulfurized fly ash.
CN111701419a proposes a cyclic utilization method of sodium-alkali dry desulfurization ash, firstly mixing desulfurization ash with evaporation condensate water for dissolution, then introducing compressed air to oxidize sodium sulfite into sodium sulfate, then adding sulfuric acid solution to fully convert sodium bicarbonate and sodium carbonate into sodium sulfate, then filtering out impurities, then through double decomposition reaction, adding ammonium bicarbonate to convert sodium sulfate into sodium bicarbonate and ammonium sulfate, but firstly converting sodium carbonate and sodium bicarbonate into sodium sulfate by adding sulfuric acid to release a large amount of carbon dioxide, consuming a large amount of sulfuric acid, then converting sodium sulfate back into sodium bicarbonate by adding ammonium bicarbonate (removing carbonate and bicarbonate firstly, supplementing bicarbonate again, causing resource waste), repeating operation, causing waste of medicament and resource, failing to truly realize recycling utilization of waste.
CN110697738A proposes a method for recycling baking soda dry desulfurization ash, wherein desulfurization ash is recovered as sodium sulfate solid, but the added value of sodium sulfate is lower than that of baking soda for enterprises, and the sodium sulfate cannot be recycled in the enterprises.
The treatment process of the desulfurization ash is urgently needed, so that the desulfurization ash can be recycled, and environmental pollution is avoided.
Disclosure of Invention
The invention aims to provide a treatment process for preparing sodium bicarbonate from desulfurization ash, which optimizes and perfects a impurity removal process in the process of recycling sodium bicarbonate from desulfurization ash, firstly transfers a large amount of sodium bicarbonate in a system, then converts sodium sulfate in the system into sodium bicarbonate, reduces the usage amount of a conversion reagent for converting sodium sulfate into sodium bicarbonate, and fully realizes recycling of desulfurization ash.
The invention provides two technical schemes for preparing baking soda from desulfurized fly ash, wherein one technical scheme comprises the following steps:
(1) Dissolving and filtering: dissolving the desulfurized fly ash with water, filtering, and removing insoluble substances to obtain filtrate;
(2) Removing organic matters: removing the organic matters in the filtrate obtained in the step (1) by adopting an adsorption method or an oxidation method;
(3) Aeration impurity removal: introducing air or oxygen into the filtrate after removing the organic matters in the step (2) to lead Na to be 2 SO 3 All oxidation to Na 2 SO 4 Introducing CO into the solution 2 So thatThe pH value of the solution is less than or equal to 8.3, and CO is added 3 2- All conversion to HCO 3 - At the moment, by utilizing the principle that the solubility of sodium bicarbonate is obviously reduced compared with that of sodium carbonate at the same temperature, the sodium bicarbonate in the solution is saturated and separated out, and filtrate and solid are obtained after filtration;
(4) Defluorination: removing fluorine ions from the filtrate obtained in the step (3);
(5) Separating salt: separating salt from the filtrate obtained after removing fluoride ions in the step (4) by adopting one or more of evaporation crystallization, freezing crystallization and nanofiltration processes to obtain crystal salt and crystal mother liquor;
(6) Sodium sulfate sodium bicarbonate: dissolving the crystal salt obtained in the step (5) in water, adding ammonium bicarbonate, and converting sodium sulfate into sodium bicarbonate and ammonium sulfate, wherein the supersaturation of the sodium bicarbonate is separated out; mixing the separated sodium bicarbonate with the sodium bicarbonate separated in the step (3) and then entering a drying system to prepare a baking soda product, wherein the purity of the baking soda is more than 95%, and ammonium sulfate can be used as a nitrogenous fertilizer;
(7) And (3) treatment of crystallization mother liquor: and (3) continuously concentrating the crystallization mother liquor in the step (5) until the crystallization is completed, and drying to obtain a very small amount of mixed salt, wherein the mixed salt comprises sodium chloride, sodium nitrate, sodium fluoride and other small components.
The other technical scheme is different from the previous technical scheme in that the sodium sulfate in the filter cake reaches more than 99% in purity after the desulfurization ash is leached by saturated sodium sulfate solution and filtered, and the sodium sulfate can be directly used for preparing sodium bicarbonate; the subsequent treatment mode of the leaching filtrate is the same as the subsequent treatment mode of the filtrate obtained by dissolving and filtering in the previous technical scheme, and the specific technical scheme comprises the following steps:
(1) Leaching and filtering: with saturated Na 2 SO 4 The solution is leached to remove the desulfurized fly ash, and a great deal of sodium sulfate solid is separated out due to leaching by saturated sodium sulfate, and the solid is dried to obtain Na 2 SO 4 The content is more than 99 percent, and sodium sulfate is mixed with sodium sulfate and sodium bicarbonate after subsequent crystallization and salt separation to prepare sodium bicarbonate; filtering the leached desulfurization ash to remove insoluble substances to obtain filtrate;
(2) Removing organic matters: removing the organic matters in the filtrate obtained in the step (1) by adopting an adsorption method or an oxidation method;
(3) Aeration impurity removal: introducing air or oxygen into the filtrate after removing the organic matters in the step (2) to lead Na to be 2 SO 3 All oxidation to Na 2 SO 4 Introducing CO into the solution 2 So that the pH value of the solution is less than or equal to 8.3, and CO is added 3 2- All conversion to HCO 3 - At the moment, by utilizing the principle that the solubility of sodium bicarbonate is obviously reduced compared with that of sodium carbonate at the same temperature, the sodium bicarbonate in the solution is saturated and separated out, and filtrate and solid are obtained after filtration;
(4) Defluorination: removing fluorine ions from the filtrate obtained in the step (3);
(5) Separating salt: separating salt from the filtrate obtained after removing fluoride ions in the step (4) by adopting one or more of evaporation crystallization, freezing crystallization and nanofiltration processes to obtain crystal salt and crystal mother liquor;
(6) Sodium sulfate sodium bicarbonate: dissolving the crystal salt obtained in the step (5) in water, adding ammonium bicarbonate, and converting sodium sulfate into sodium bicarbonate and ammonium sulfate, wherein the supersaturation of the sodium bicarbonate is separated out; mixing the separated sodium bicarbonate with the sodium bicarbonate separated in the step (3) and then entering a drying system to prepare a baking soda product, wherein the purity of the baking soda is more than 95%, and ammonium sulfate can be used as a nitrogenous fertilizer;
(7) And (3) treatment of crystallization mother liquor: and (3) continuously concentrating the crystallization mother liquor in the step (5) until the crystallization is completed, and drying to obtain a very small amount of mixed salt, wherein the mixed salt comprises sodium chloride, sodium nitrate, sodium fluoride and other small components.
Further, in the first technical scheme, the dissolution temperature of the step (1) is 20-40 ℃, and the mass ratio of the desulfurization ash to the water is 1:1-1:5.
Further, in the second technical scheme, the leaching temperature in the step (1) is 20-40 ℃, and the mass ratio of leaching solid to liquid is 1:1-1:5.
Further, removing the organic matters in the filtrate obtained in the step (1) by adopting an adsorption method in the step (2), wherein the adsorption material is one or more selected from carbon-based materials (such as walnut shells, fruit shells, sawdust, anthracite, fly ash and activated carbon), inorganic materials (such as diatomite, kaolin, bentonite, expanded shale, alumina and natural zeolite), fiber materials (such as fiber balls and sponge) and adsorption resins; when static adsorption is adopted, the adding amount of the adsorbent is 0.01-20 g/L, and the adsorption time is 0.5-1.5h; when dynamic adsorption is adopted, the height-diameter ratio of the adsorbent bed is 1:1-3:1, and the water inflow flow rate is 1-12BV/h. The organic matter removal rate of the filtrate after adsorption is more than 90 percent.
Further, the step (2) adopts an oxidation method to remove the organic matters in the filtrate obtained in the step (1), and the oxidation process comprises one or a combination of more of medicament oxidation, wet oxidation, fenton oxidation, ozone catalytic oxidation, photocatalytic oxidation and electrochemical oxidation.
Further, the method for removing fluorine in the step (4) is one or more of calcium method fluorine removal, aluminum salt fluorine removal and resin adsorption fluorine removal, and the calcium method fluorine removal specifically comprises the following steps: according to mole ratio Ca 2+ ：F - =1:1 to 6:1 CaSO was added 4 Reacting 0.5-4. 4 h, precipitating, filtering to obtain filtered liquid and CaF 2 Precipitating; the aluminum salt defluorination specifically comprises the following steps: adding aluminum sulfate according to the molar ratio Al: F=1:1-9:1, reacting for 0.5-4 h, precipitating, and filtering to obtain filtrate and AlF 3 Precipitating; the resin adsorption defluorination concretely comprises: and (3) adsorbing the filtrate by using fluorine-removing resin for 0.5-4 hours. After defluorination, na in the solute of the filtrate 2 SO 4 And NaHCO 3 The total ratio is more than 93%.
Further, the evaporation crystallization process in the step (5) specifically comprises the following steps: evaporating the filtrate obtained in the step (4) at the temperature of 60-90 ℃ under negative pressure, and concentrating to Na 2 SO 4 Stopping evaporating when the saturated state is approached, precipitating crystal salt at the moment, and centrifugally separating the crystallized salt at the temperature of more than 50 ℃ to obtain crystal salt and crystal mother liquor; the nanofiltration process comprises the following steps: and (3) firstly, the filtrate obtained in the step (4) enters a nanofiltration membrane component, salt separation is carried out to obtain nanofiltration concentrated water and nanofiltration fresh water, the nanofiltration concentrated water is evaporated and crystallized to obtain crystallization salt and crystallization mother liquor, and the nanofiltration fresh water and the crystallization mother liquor are mixed.
Further, in the step (6), ammonium bicarbonate is added according to the molar ratio of 1:1-1:10 of ammonium bicarbonate to sodium sulfate.
The invention has the following beneficial technical effects:
1) The invention adopts an effective process to prepare the industrial desulfurization ash into the baking soda with high added value, and the baking soda is reused in the desulfurization process, thereby realizing the recycling of the industrial desulfurization ash. And for impurities in the desulfurized fly ash: COD, sulfite, carbonate, fluoride ions, chloride ions, nitrate and the like are comprehensively removed, and compared with the traditional process, the purity of the recovered baking soda is higher and the recovery rate is higher through the combined process.
2) Sodium sulfite is converted into sodium carbonate by air aeration or oxygen introduced into the sodium carbonate and CO is introduced into the sodium carbonate by utilizing the solubility difference of sodium carbonate and sodium bicarbonate at the same temperature in the impurity removal process 2 The sodium carbonate is completely converted into sodium bicarbonate and is saturated and separated out, so that not only is the sodium bicarbonate primarily purified and recovered, but also the influence of carbonate on the subsequent defluorination effect is effectively avoided. Adding various impurity removing agents which are the same ions of valuable ions in the solution, and ensuring the purity of the subsequent products without introducing other impurity ions.
3) In the evaporation, crystallization and salt separation process, according to Na 2 SO 4 -NaCl-H 2 O ternary phase diagram, reasonable control of temperature, ensuring precipitated Na 2 SO 4 Takes up Na in the solution 2 SO 4 The total content is more than 85%, and the mixture of anhydrous sodium sulfate with the purity of more than 98% and sodium bicarbonate is obtained.
4) By Na 2 SO 4 At a certain temperature with NaHCO 3 Solubility difference, na is added when ammonia bicarbonate is added 2 SO 4 All conversion to NaHCO 3 After NaHCO 3 Precipitation starts, the conversion rate reaches 90%, and two industrial products of sodium bicarbonate solid and ammonium sulfate are obtained.
5) The desulfurization ash is leached by saturated sodium sulfate, so that sodium sulfate solid with the purity of more than 99 percent can be obtained, and the purity can be directly used for preparing sodium bicarbonate.
Drawings
Fig. 1 is a schematic flow chart of a first technical solution.
Fig. 2 is a schematic flow chart of a second embodiment.
Detailed Description
The technical scheme of the invention is clearly and completely described below by means of examples in combination with the drawings of the specification. It will be apparent that the described embodiments are only some, but not all, of the embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, are intended to fall within the scope of the present invention. The terms "first," "second," and the like in this disclosure are used for descriptive purposes only and are not to be construed as indicating or implying any relative importance or quantity or position.
Example 1
The analysis of the desulfurization ash composition of a certain coal coking enterprise is shown in table 1.
TABLE 1 analysis results of the content of desulfurized fly ash components in mass percent
Composition of the components Duty ratio of
NaCl 7.618%
Na 2 SO 3 0.512%
Na 2 SO 4 61.419%
Na 2 CO 3、 NaHCO 3 24.66~31.11%
NaF 0.612%
Sodium nitrate 0.809%
COD（TOC） 1.042%（0.137%）
Other substances such as water insoluble substances 0~3.82%
Step 1: desulfurizing ash according to mass under the constant temperature condition of 30 ℃: after dissolution in water=1:4 ratio, filtration was performed to remove insoluble solid impurities, and filtrate was obtained.
Step 2: adding 10g/L of powdered activated carbon into the filtrate, adsorbing for 1h, precipitating for 30min, and filtering to obtain pale yellow transparent filtrate.
Step 3: in terms of mole ratio O 2 :SO 3 2- =3:1 bubbling O into the post-adsorption filtrate 2 Detection of SO in water 3 2- After all are oxidized, sufficient CO is introduced 2 Until the pH is less than or equal to 8.3, a large amount of NaHCO exists 3 And (3) precipitation.
Step 4: adding Ca in the molar ratio into the solution separated in the step 3 2+ ：F - Caso=6:1 4 Reacting for 3h, precipitating for 30min, detecting F in the filtered liquid - The removal rate is reduced from 702.24mg/L to 104.15mg/L, and the removal rate reaches 85.17 percent.
Step 5: evaporating and concentrating the filtered solution obtained in the step 4 to 5.56% of the original solution volume by adopting negative pressure at 80 ℃, separating and drying the precipitated crystals at 60 ℃ to obtain powder with an analysis component of Na 2 SO 4 86% of NaHCO 3 The proportion is 13%.
Step 6: na obtained in step 5 2 SO 4 And NaHCO 3 Dissolving the mixture in water until Na 2 SO 4 Concentration of 20% by mole of ammonium bicarbonate and sodium sulfateAdding ammonium bicarbonate solid in the molar ratio of 1:1, and separating out supersaturated sodium bicarbonate; and (3) mixing the precipitated sodium bicarbonate with the sodium bicarbonate precipitated in the step (3) and entering a drying system to prepare a baking soda product, wherein the total recovery rate of the sodium bicarbonate is 89%.
Step 7: and (5) evaporating the mother solution in the step (5) until the mother solution is completely crystallized to obtain the mixed salt.
Example 2
The analysis of the desulfurization ash composition of a certain coal coking enterprise is shown in table 1.
Step 1: desulfurizing ash according to mass under the constant temperature condition of 30 ℃: after dissolution in water=1:3 ratio, filtration was carried out to remove insoluble solid impurities, resulting in a filtrate in dark yellow.
Step 2: the filtrate was passed through the resin adsorbing the organic matters at a flow rate of 3BV/h, and the effluent was colorless and transparent.
Step 3: in terms of mole ratio O 2 :SO 3 2- =2:1 bubbling O into the post-adsorption filtrate 2 Detection of SO in water 3 2- After all are oxidized, sufficient CO is introduced 2 Until the pH is less than or equal to 8.3, a large amount of NaHCO exists 3 And (3) precipitation.
Step 4: adding the mole ratio Al into the solution separated in the step 3: f (F) - Aluminum sulfate of=3:1 reacted for 1h, precipitated for 30min, and F in the filtered solution was detected - The removal rate is reduced from 702.24mg/L to 70.22 mg/L, and the removal rate reaches 90%.
Step 5: evaporating and concentrating the filtered solution obtained in the step 4 to 5.56% of the original solution volume by adopting negative pressure at 80 ℃, separating and drying the precipitated crystals at 50 ℃ to obtain powder with an analysis component of Na 2 SO 4 The ratio of NaHCO is 85 percent 3 The ratio is 14%.
Step 6: na obtained in step 5 2 SO 4 And NaHCO 3 Dissolving the mixture in water until Na 2 SO 4 Adding ammonium bicarbonate solid with the concentration of 20% and the molar ratio of ammonium bicarbonate to sodium sulfate of 1:2, and separating out supersaturated sodium bicarbonate; and (3) mixing the precipitated sodium bicarbonate with the sodium bicarbonate precipitated in the step (3) and entering a drying system to prepare a baking soda product, wherein the total recovery rate of the sodium bicarbonate is 91%.
Step 7: and (5) evaporating the mother solution in the step (5) until the mother solution is completely crystallized to obtain the mixed salt.
Example 3:
the desulfurization ash composition of a certain coal-electricity-aluminum enterprise is shown in Table 2
TABLE 2 analysis results of the content of desulfurized fly ash components in mass percent
Composition of the components Duty ratio of
NaCl 2.31%
Na 2 SO 3 13.52%
Na 2 SO 4 70.74%
NaF 0.4639%
Sodium carbonate 13.1452%
Sodium nitrate 0.4232%
Ca 0.1093%
K、Fe、Al、Pb、Zn、 Mo Trace amount of
COD 0.2483%
Oil (oil) 0.03%
Water insoluble material 0.005%
Step 1: desulfurizing ash according to mass under the constant temperature condition of 30 ℃: saturated sodium sulfate solution=1:3, and Na after the filter cake is dried 2 SO 4 The content ratio was 99.18%, and the analysis of the composition of the filtrate after rinsing was shown in Table 3.
TABLE 3 results of component analysis of the leaching filtrate
Project Index (I)
SO 4 2- （mg/L） 172660
SO 3 2- （mg/L） 38452
Cl - （mg/L） 16213
F - （mg/L） 525
CO 3 2- （mg/L） 22701
NO 3 - （mg/L） 890
COD（mg/L） 2709
Oil (mg/L) 7.62
Step 2: adding 10g/L of powdered activated carbon into the filtrate, adsorbing for 1h, precipitating for 30min, and filtering.
Step 3: in terms of mole ratio O 2 :SO 3 2- =3:1 bubbling O into the adsorbed filtrate 2 Detection of SO in water 3 2- After all are oxidized, sufficient CO is introduced 2 Until the pH is less than or equal to 8.3, a large amount of NaHCO exists 3 And (3) precipitation.
Step 4: adding Ca in the molar ratio into the solution separated in the step 3 2+ ：F - Caso=6:1 4 Reacting for 3h, precipitating for 30min, detecting F in the filtered liquid - The removal rate is reduced from 525mg/L to 94.56mg/L, the removal rate reaches 81.99 percent, and the water F is adsorbed by aluminum-based resin at the rate of 4BV/h - The concentration is reduced to below 20 mg/L.
Step 5: evaporating and concentrating the solution treated in the step 4 to 4.54% of the original solution volume at a negative pressure of 80 ℃, separating and drying the precipitated crystals at 60 ℃ to obtain powder with an analysis component of Na 2 SO 4 88% of NaHCO 3 The ratio is 11%.
Step 6: na obtained in step 5 2 SO 4 And NaHCO 3 Dissolving the mixture in water until Na 2 SO 4 Concentration is 20 percent, the mole ratio of ammonium bicarbonate to sodium sulfateAdding ammonium bicarbonate solid into the solution in a ratio of 1:1, and separating out supersaturated sodium bicarbonate; and (3) mixing the precipitated sodium bicarbonate with the sodium bicarbonate precipitated in the step (3) and entering a drying system to prepare a baking soda product, wherein the recovery rate of the obtained sodium bicarbonate is 85%.
Step 7: and (5) evaporating the mother solution in the step (5) until the mother solution is completely crystallized to obtain the mixed salt.
Example 4
The desulfurization ash composition of a coke plant is shown in Table 4.
TABLE 4 analysis results of the content of desulfurized fly ash components in mass percent
Composition of the components Duty ratio of
NaCl 4.69%
Na 2 SO 3 11.36%
Na 2 SO 4 75.32%
NaF 0.3855%
Sodium carbonate 7.8498%
Sodium nitrate 0.3378%
Ca 0.0992%
K、Fe、Al、Pb、Zn、 Mo Trace amount of
COD 0.1808%
Oil (oil) 0.01%
Water insoluble material 0.004%
Step 1: desulfurizing ash according to mass under the constant temperature condition of 30 ℃: water=1:5, and insoluble matter was removed by filtration to obtain a filtrate.
Step 2: according to ozone: the addition amount of COD=2:1 is used for ozone catalytic oxidation, and the oxidized water is light yellow transparent.
Step 3: detecting the content of residual sulfite and according to the mole ratio O 2 :SO 3 2- =2:1 bubbling O into the oxidation effluent 2 Detection of SO in water 3 2- After all are oxidized, sufficient CO is introduced 2 Until the pH is less than or equal to 8.3, a large amount of NaHCO exists 3 And (3) precipitation.
Step 4: adding the mole ratio Al into the solution separated in the step 3: f (F) - Aluminum sulfate of=3:1 reacted for 1h, precipitated for 30min, and F in the filtered solution was detected - The removal rate is reduced from 546.11mg/L to 65.22 mg/L, and the removal rate reaches 88.06%.
Step 5: and (4) the solution treated in the step (4) enters a nanofiltration membrane component, salt separation is carried out to obtain sodium sulfate concentrated water and nanofiltration fresh water, and the nanofiltration concentrated water is evaporated and crystallized to obtain a mixture of anhydrous sodium sulfate with the purity of more than 98% and sodium bicarbonate.
Step 6: na obtained in step 5 2 SO 4 And NaHCO 3 Dissolving the mixture in water until Na 2 SO 4 Adding ammonium bicarbonate solid with the concentration of 20% and the molar ratio of ammonium bicarbonate to sodium sulfate of 1:3, and separating out supersaturated sodium bicarbonate; and (3) mixing the precipitated sodium bicarbonate with the sodium bicarbonate precipitated in the step (3) and entering a drying system to prepare a baking soda product, wherein the recovery rate of the obtained sodium bicarbonate is 90%.
Step 7: and (5) evaporating the nanofiltration fresh water in the step (5) until the nanofiltration fresh water is completely crystallized to obtain the mixed salt.
Although embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives, and variations may be made in the above embodiments by those skilled in the art without departing from the spirit and principles of the invention. The protection scope of the present invention is defined by the claims and the equivalents thereof.

Claims (8)

1. The treatment process for preparing baking soda from the desulfurized fly ash is characterized by comprising the following steps of:
(1) Dissolving and filtering: dissolving the desulfurized fly ash with water, filtering, and removing insoluble substances to obtain filtrate;
(2) Removing organic matters: removing the organic matters in the filtrate obtained in the step (1) by adopting an adsorption method or an oxidation method;
(3) Aeration impurity removal: introducing air or oxygen into the filtrate after removing the organic matters in the step (2) to lead Na to be 2 SO 3 All oxidation to Na 2 SO 4 Introducing CO into the solution 2 So that the pH value of the solution is less than or equal to 8.3, and CO is added 3 2- All conversion to HCO 3 - Saturated precipitation of sodium bicarbonate in the solution, and filtering to obtain filtrate and solid;
(4) Defluorination: removing fluorine ions from the filtrate obtained in the step (3);
(5) Separating salt: separating salt from the filtrate obtained after removing fluoride ions in the step (4) by adopting one or more of evaporation crystallization, freezing crystallization and nanofiltration processes to obtain crystal salt and crystal mother liquor;
(6) Sodium sulfate sodium bicarbonate: dissolving the crystal salt obtained in the step (5) in water, adding ammonium bicarbonate, and converting sodium sulfate into sodium bicarbonate and ammonium sulfate, wherein the supersaturation of the sodium bicarbonate is separated out; mixing the separated sodium bicarbonate with the sodium bicarbonate separated in the step (3) and then entering a drying system to prepare sodium bicarbonate products;
(7) And (3) treatment of crystallization mother liquor: and (3) continuously concentrating the crystallization mother liquor in the step (5) until the crystallization is completed, and drying to obtain a very small amount of mixed salt.
2. The treatment process according to claim 1, wherein the dissolution temperature in the step (1) is 20-40 ℃, and the mass ratio of the desulfurization ash to the water is 1:1-1:5.
3. The treatment process for preparing baking soda from the desulfurized fly ash is characterized by comprising the following steps of:
(1) Leaching and filtering: with saturated Na 2 SO 4 Leaching the desulfurization ash by using a solution to separate out a large amount of sodium sulfate solids, and mixing the sodium sulfate with sodium sulfate and sodium bicarbonate after salt separation by subsequent crystallization to prepare sodium bicarbonate; filtering the leached desulfurization ash to remove insoluble substances to obtain filtrate;
(2) Removing organic matters: removing the organic matters in the filtrate obtained in the step (1) by adopting an adsorption method or an oxidation method;
(3) Aeration impurity removal: introducing air or oxygen into the filtrate after removing the organic matters in the step (2) to lead Na to be 2 SO 3 All oxidation to Na 2 SO 4 Introducing CO into the solution 2 So that the pH value of the solution is less than or equal to 8.3, and CO is added 3 2- All conversion to HCO 3 - Saturated precipitation of sodium bicarbonate in the solution, and filtering to obtain filtrate and solid;
(4) Defluorination: removing fluorine ions from the filtrate obtained in the step (3);
(5) Separating salt: separating salt from the filtrate obtained after removing fluoride ions in the step (4) by adopting one or more of evaporation crystallization, freezing crystallization and nanofiltration processes to obtain crystal salt and crystal mother liquor;
(6) Sodium sulfate sodium bicarbonate: dissolving the crystal salt obtained in the step (5) in water, adding ammonium bicarbonate, and converting sodium sulfate into sodium bicarbonate and ammonium sulfate, wherein the supersaturation of the sodium bicarbonate is separated out; mixing the separated sodium bicarbonate with the sodium bicarbonate separated in the step (3) and then entering a drying system to prepare sodium bicarbonate products;
(7) And (3) treatment of crystallization mother liquor: and (3) continuously concentrating the crystallization mother liquor in the step (5) until the crystallization is completed, and drying to obtain a very small amount of mixed salt.
4. The treatment process according to claim 3, wherein the leaching temperature in the step (1) is 20-40 ℃, and the mass ratio of leaching solid to liquid is 1:1-1:5.
5. A treatment process according to claim 1 or 3, wherein the step (2) comprises removing the organic matter from the filtrate obtained in the step (1) by adsorption, wherein the adsorption material is one or more selected from the group consisting of carbon-based materials, inorganic materials, fibrous materials and adsorption resins; when static adsorption is adopted, the adding amount of the adsorbent is 0.01-20 g/L, and the adsorption time is 0.5-1.5h; when dynamic adsorption is adopted, the height-diameter ratio of the adsorbent bed is 1:1-3:1, and the water inflow flow rate is 1-12BV/h.
6. A treatment process according to claim 1 or 3, wherein the step (2) is carried out by removing the organic matter from the filtrate obtained in the step (1) by an oxidation process comprising one or a combination of several of chemical oxidation, wet oxidation, fenton oxidation, ozone catalytic oxidation, photocatalytic oxidation and electrochemical oxidation.
7. A treatment process according to claim 1 or 3, wherein the method of defluorination in step (4) is one or more of calcium defluorination, aluminium salt defluorination and resin adsorption defluorination, and the calcium defluorination specifically comprises: according to mole ratio Ca 2+ ：F - =1:1 to 6:1 CaSO was added 4 Reacting 0.5-4. 4 h, precipitating, filtering to obtain filtered liquid and CaF 2 Precipitating; the aluminum salt defluorination specifically comprises the following steps: adding aluminum sulfate according to the molar ratio Al: F=1:1-9:1, reacting for 0.5-4 h, precipitating, and filtering to obtain filtrate and a mixture of the filtrate and the mixtureAlF 3 Precipitating; the resin adsorption defluorination concretely comprises: and (3) adsorbing the filtrate by using fluorine-removing resin for 0.5-4 hours.
8. A process according to claim 1 or 3, wherein the evaporative crystallisation process in step (5) is specifically: evaporating the filtrate obtained in the step (4) at the temperature of 60-90 ℃ under negative pressure, and concentrating to Na 2 SO 4 Stopping evaporating when the saturated state is approached, precipitating crystal salt at the moment, and centrifugally separating the crystallized salt at the temperature of more than 50 ℃ to obtain crystal salt and crystal mother liquor; the nanofiltration process comprises the following steps: and (3) firstly, the filtrate obtained in the step (4) enters a nanofiltration membrane component, salt separation is carried out to obtain nanofiltration concentrated water and nanofiltration fresh water, the nanofiltration concentrated water is evaporated and crystallized to obtain crystallization salt and crystallization mother liquor, and the nanofiltration fresh water and the crystallization mother liquor are mixed.
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