CN116790887A - Method for separating iron, silicon, gallium, aluminum and calcium from fly ash - Google Patents
Method for separating iron, silicon, gallium, aluminum and calcium from fly ash Download PDFInfo
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- CN116790887A CN116790887A CN202310720692.6A CN202310720692A CN116790887A CN 116790887 A CN116790887 A CN 116790887A CN 202310720692 A CN202310720692 A CN 202310720692A CN 116790887 A CN116790887 A CN 116790887A
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims abstract description 145
- 229910052742 iron Inorganic materials 0.000 title claims abstract description 67
- 238000000034 method Methods 0.000 title claims abstract description 59
- 229910052782 aluminium Inorganic materials 0.000 title claims abstract description 48
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 title claims abstract description 48
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 title claims abstract description 42
- 229910052791 calcium Inorganic materials 0.000 title claims abstract description 42
- 239000011575 calcium Substances 0.000 title claims abstract description 42
- 239000010881 fly ash Substances 0.000 title claims abstract description 39
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 title claims abstract description 22
- 229910052733 gallium Inorganic materials 0.000 title claims abstract description 22
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 18
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 18
- 239000010703 silicon Substances 0.000 title claims abstract description 18
- 238000002386 leaching Methods 0.000 claims abstract description 53
- 238000001556 precipitation Methods 0.000 claims abstract description 39
- 238000006243 chemical reaction Methods 0.000 claims abstract description 30
- 239000007788 liquid Substances 0.000 claims abstract description 30
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 claims abstract description 26
- 239000000047 product Substances 0.000 claims abstract description 25
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 claims abstract description 24
- 239000000706 filtrate Substances 0.000 claims abstract description 20
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims abstract description 18
- 229910017604 nitric acid Inorganic materials 0.000 claims abstract description 18
- 238000001914 filtration Methods 0.000 claims abstract description 16
- 235000010344 sodium nitrate Nutrition 0.000 claims abstract description 12
- 239000004317 sodium nitrate Substances 0.000 claims abstract description 12
- WNROFYMDJYEPJX-UHFFFAOYSA-K aluminium hydroxide Chemical compound [OH-].[OH-].[OH-].[Al+3] WNROFYMDJYEPJX-UHFFFAOYSA-K 0.000 claims abstract description 9
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims abstract description 8
- 238000000605 extraction Methods 0.000 claims abstract description 8
- 229910052749 magnesium Inorganic materials 0.000 claims abstract description 8
- 239000011777 magnesium Substances 0.000 claims abstract description 8
- 239000012074 organic phase Substances 0.000 claims abstract description 8
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims abstract description 7
- 229910052938 sodium sulfate Inorganic materials 0.000 claims abstract description 7
- 235000011152 sodium sulphate Nutrition 0.000 claims abstract description 7
- 239000000126 substance Substances 0.000 claims abstract description 7
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims abstract description 6
- 238000005406 washing Methods 0.000 claims abstract description 6
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 5
- 239000007800 oxidant agent Substances 0.000 claims abstract description 5
- 230000001590 oxidative effect Effects 0.000 claims abstract description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 33
- CDBYLPFSWZWCQE-UHFFFAOYSA-L sodium carbonate Substances [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 20
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 10
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 claims description 8
- 238000003756 stirring Methods 0.000 claims description 7
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 6
- 238000001704 evaporation Methods 0.000 claims description 6
- 238000002425 crystallisation Methods 0.000 claims description 5
- 230000008025 crystallization Effects 0.000 claims description 5
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims description 4
- 230000008020 evaporation Effects 0.000 claims description 4
- 235000010265 sodium sulphite Nutrition 0.000 claims description 4
- 230000005484 gravity Effects 0.000 claims description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 2
- 229910052729 chemical element Inorganic materials 0.000 claims description 2
- 229910052760 oxygen Inorganic materials 0.000 claims description 2
- 239000001301 oxygen Substances 0.000 claims description 2
- 230000035484 reaction time Effects 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims 1
- 239000002253 acid Substances 0.000 description 10
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 8
- 239000012535 impurity Substances 0.000 description 4
- 239000002893 slag Substances 0.000 description 4
- 239000003513 alkali Substances 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 229910052598 goethite Inorganic materials 0.000 description 3
- AEIXRCIKZIZYPM-UHFFFAOYSA-M hydroxy(oxo)iron Chemical compound [O][Fe]O AEIXRCIKZIZYPM-UHFFFAOYSA-M 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 238000011084 recovery Methods 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- -1 metallurgy Substances 0.000 description 2
- 238000005272 metallurgy Methods 0.000 description 2
- 238000006386 neutralization reaction Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 2
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 1
- 235000011941 Tilia x europaea Nutrition 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 239000004571 lime Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 230000003472 neutralizing effect Effects 0.000 description 1
- 235000021110 pickles Nutrition 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
- 238000000638 solvent extraction Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
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- Manufacture And Refinement Of Metals (AREA)
Abstract
The invention provides a method for separating iron, silicon, gallium, aluminum and calcium from fly ash, which comprises the following steps: step S1: carrying out nitric acid pressurizing two-stage leaching reaction on the fly ash, carrying out second-stage leaching on the first filtrate, and processing the first filter residue into silicon-containing and iron-containing products; step S2: adding a reducing agent into the second filtrate for reaction to obtain a reduced liquid; step S3: extracting the reduced liquid to obtain an organic phase and raffinate, and carrying out back extraction on the organic phase to obtain a gallium product; step S4: adding alkaline substances into the raffinate to adjust the pH value for carrying out aluminum precipitation reaction to obtain aluminum hydroxide and aluminum precipitation post-liquid, and washing and roasting the aluminum hydroxide to obtain an aluminum oxide product; step S5: adding an oxidant into the solution after aluminum precipitation for reaction, and filtering to obtain solution after iron removal; step S6: adding sodium sulfate into the solution after iron removal, fully reacting, and filtering to obtain a calcium sulfate product and a solution after calcium precipitation; step S7: and (5) deeply removing calcium and magnesium from the solution after calcium precipitation, and concentrating and crystallizing to obtain a sodium nitrate product. The method has low equipment requirement and simple process.
Description
Technical Field
The invention relates to the technical field of chemical metallurgy, in particular to a method for separating iron, silicon, gallium, aluminum and calcium from fly ash.
Background
At present, coal is used in thermal power generation and northern heating plants in China to generate a large amount of fly ash. The fly ash is widely applied to the industrial fields of construction, building materials, metallurgy, chemical industry, environmental protection, backfill, high-performance ceramic materials and the like, and can be applied to the agricultural fields of soil improvement, field building and the like. The fly ash contains a large amount of rare metals such as alumina, silicon dioxide, iron, gallium, germanium and the like, and the aluminum resources in China are very lack, so the resource utilization of the fly ash has important research significance and wide market prospect.
Methods for extracting alumina from fly ash can be classified into an acid method and an alkali method. The alkali recovery process is mature, but the process flow is long, and the recovery cost is high. The existing acid method comprises a hydrochloric acid method and a sulfuric acid method, the iron content in the fly ash is high, the fly ash is directly leached by acid by the existing acid method recovery process, the metal elements in the fly ash almost completely enter the leaching solution, the acid consumption is high, the leaching cost is high, the impurity content in the leaching solution is high, and the impurity removal cost is high.
Currently, there are many methods for removing iron in the process of producing alumina by acid leaching, for example, the goethite method is industrially used for removing iron. Patent document CN103805779A discloses a method for removing iron in an acid aluminum extraction process, wherein the temperature of a reaction tank is controlled to be 60-100 ℃, the aging time is controlled to be 30-120min, and Na is used 2 CO 3 The pH value is regulated to be less than 3.0, and the method can effectively solve the problem of separation of gallium and iron. However, the method needs to prepare goethite seed crystal, the concentration of the goethite seed crystal reaches 0.9-3.0g/L, and Na is needed to be added in the reaction 2 CO 3 The pH value of the solution is controlled, and the process is complex. Qi Dong and the like report a method for removing iron by a precipitation method, wherein the pH value of a solution is controlled to be 2 by adopting a lime neutralization precipitation method, part of iron in pickle liquor is removed in advance, and then the purpose of separating vanadium and iron is achieved by reducing solvent extraction. The method can also effectively remove iron, but the loss of vanadium is reduced in a multi-stage washing mode in the neutralization process, so that the process is longer, the technology is complex, and the method is not suitable for separating iron from aluminum in aluminum oxide. In addition, the iron removal process also comprises a magnetizing roasting method, an extraction method, a recrystallization method and the like, and although the iron removal effect is good, the process flow is complex, the production cost is high, and industrialization is difficult to realize.
In conclusion, the method for separating iron, silicon, gallium, aluminum and calcium from the fly ash has important research value, and has the advantages of low equipment requirement, simple process, low energy consumption and high added value of products.
Disclosure of Invention
The method can recover the useful elements in the fly ash step by step and obtain industrial alumina, calcium sulfate and sodium nitrate products.
Specifically, the invention provides the following technical scheme: a method for separating iron, silicon, gallium, aluminum and calcium from fly ash, comprising the following steps:
step S1: carrying out nitric acid pressurizing two-stage leaching reaction on the fly ash, adding excessive acid into the first-stage leached fly ash or the second filter residue to improve the leaching rate of aluminum, filtering after the reaction is finished to obtain first filtrate and first filter residue, and processing the first filter residue into silicon-containing and iron-containing products; mixing the first filtrate with the fly ash for second-stage leaching, neutralizing acid in the first filtrate, improving the pH value of the solution, filtering after the reaction is finished to obtain second filtrate and second filter residues, and returning the second filter residues to the first-stage leaching;
step S2: adding a reducing agent into the second filtrate for reaction to obtain a reduced liquid; fe in this step 3+ Reduction to Fe 2+ ，Fe 2+ With Ga 3+ The difference of distribution coefficients in the extractant is large, which is favorable for the separation of iron and gallium, and meanwhile, because of Fe 2+ The pH value of the hydrolysis is higher, which is favorable for separating iron from aluminum;
step S3: extracting the reduced liquid to obtain an organic phase and raffinate, and carrying out back extraction on the organic phase to obtain a gallium product;
step S4: adding alkaline substances into the raffinate to adjust the pH value for carrying out aluminum precipitation reaction, filtering after full reaction to obtain aluminum hydroxide and aluminum precipitation solution, and washing and roasting the aluminum hydroxide to obtain an aluminum oxide product;
step S5: adding an oxidant into the aluminum-precipitated liquid to react, and filtering to obtain an iron-removed liquid; fe in this step 2+ Oxidation to Fe 3+ ；
Step S6: adding sodium sulfate into the deironing solution, fully reacting, and filtering to obtain a high-purity calcium sulfate product and a calcium precipitation solution;
step S7: adding sodium hydroxide and sodium carbonate into the calcium-precipitating solution, removing trace calcium and magnesium remained in the calcium-precipitating solution in the form of carbonate under the condition of higher pH to obtain sodium nitrate solution with higher purity, and then carrying out negative pressure evaporation concentration crystallization to obtain sodium nitrate products.
Preferably, in step S1, the first stage leaching conditions include: the solid-liquid ratio of the fly ash or the second filter residue and the nitric acid is 1:2-1:5 (g/mL), the concentration of the nitric acid is 300-500g/L, the leaching temperature is 160-220 ℃, the stirring speed is 55-85rpm, and the leaching time is 0.5-5h.
The second stage leaching conditions include: the solid-liquid ratio of the fly ash and the first filtrate is 1:2-1:5 (g/mL), the leaching temperature is 160-220 ℃, the stirring speed is 55-85rpm, and the leaching time is 0.5-3h. Preferably, the fly ash comprises the following main chemical elements in percentage by mass: fe is 1-5%; 16-30% of Al; si is 18-25%; ca is 2-8%; mg is 0.2-0.8%.
Preferably, the concentration of the nitric acid in the first stage leaching reaction is 300-500g/L, and the leaching temperature is 160-200 ℃.
Preferably, in the second stage leaching reaction, the leaching temperature is 180-220 ℃ and the leaching time is 1-3h.
In the preferred nitric acid pressurized two-stage leaching scheme, a large amount of iron in the fly ash can be fed into slag through the step, and more than 90% of iron can be removed.
Preferably, in step S2, the reducing agent is at least one of iron powder and sodium sulfite.
Preferably, in step S4, the alkaline substance is one of sodium carbonate and sodium hydroxide.
Preferably, in step S4, the pH value of the precipitation reaction is 4-6, the reaction temperature is 60-100 ℃, the reaction time is 0.5-3.5h, and the feeding mode is homogeneous precipitation. Under the preferred scheme, the aluminum precipitation rate is more than 99% through the step, and the filterability is good.
Preferably, in step S5, the oxidizing agent is one of hydrogen peroxide or oxygen. In this preferred embodiment, the iron content of the solution is less than 0.01g/L by this step.
Preferably, in step S6, sodium sulfate is added in an amount of 0.8 to 1.0 times the theoretical amount of calcium sulfate produced. Under the preferred scheme, the calcium precipitation rate is more than 95% through the step, and the filterability is good.
Preferably, in the step S7, the addition amount of sodium hydroxide is adjusted to 11-14 of the pH value of the solution, and the addition amount of sodium carbonate is 1-1.5 times of the theoretical amount of carbonate generated by calcium and magnesium in the solution after calcium precipitation; preferably, in step S7, sodium hydroxide is added to adjust the pH of the solution, and then sodium carbonate is added. By this step the solution has a calcium content of less than 0.005g/L and a magnesium content of less than 0.0005g/L.
Preferably, in step S7, the negative pressure evaporation concentration temperature is 60-100 ℃, the concentration end specific gravity is 1.500-1.600, and the crystallization temperature is 20-40 ℃. Under the preferred scheme, the single crystallization rate of sodium nitrate can reach more than 50 percent, and the crystals are uniform and granular. The technical scheme provided by the invention has the beneficial effects that at least:
the method takes fly ash as a raw material, adopts nitric acid to carry out pressurization two-stage leaching, silicon and iron enter slag, and the leached slag can be further processed into iron and silicon products; reducing a small amount of iron in the leachate to Fe 2+ Extracting gallium, regulating pH value, precipitating aluminum, and removing iron by oxidation; washing and roasting precipitated aluminum hydroxide to obtain an aluminum oxide product; adding sodium sulfate into the iron-removing liquid to obtain a calcium sulfate product, removing calcium and magnesium from the liquid after removing calcium by double alkali depth, and evaporating, concentrating and crystallizing to obtain a sodium nitrate product. The method can recover iron, silicon, gallium, aluminum, calcium and other elements in the fly ash step by step, leach a large amount of iron slag by pressurizing with nitric acid in two stages, and initially separate iron and aluminum; reducing and oxidizing a small amount of iron in the solution to thoroughly separate iron from gallium and iron from aluminum; the whole process has the advantages of low acid consumption, low impurity content in the leaching solution, low impurity removal cost, low equipment requirement, simple process and the like.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a process flow diagram of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.
The analytical results of each component of the fly ash raw material used in the following examples are shown in Table 1.
TABLE 1 analysis results of principal components of fly ash
Example 1
As shown in fig. 1, the method for separating iron, silicon, gallium, aluminum and calcium from the fly ash specifically comprises the following steps:
s1: the first stage leaching conditions include: the solid-liquid ratio of the fly ash to the nitric acid is 1:4 (g/mL), the concentration of the nitric acid is 400g/L, the leaching temperature is 180 ℃, the stirring speed is 60rpm, and the leaching time is 2h; the second stage leaching conditions include: the solid-liquid ratio of the fly ash to the first filtrate is 1:3 (g/mL), the leaching temperature is 190 ℃, the stirring speed is 60rpm, and the leaching time is 1h.
The iron content in the obtained second filtrate is 0.75g/L, the leaching rate of the nitric acid pressurized secondary leached aluminum is 94 percent, and the leaching rate of the iron is 8.22 percent
S2: adding sodium sulfite and Fe into the second filtrate 3+ Reduction to Fe 2+ And obtaining a reduced liquid.
S3: and extracting the reduced liquid to obtain an organic phase and raffinate, and carrying out back extraction on the organic phase to obtain a back extraction liquid, wherein the back extraction liquid is further processed into a gallium product.
S4: and adding sodium carbonate into the raffinate to adjust the pH value to 5, carrying out aluminum precipitation at the reaction temperature of 60 ℃ for 1h, filtering after full reaction to obtain aluminum hydroxide and aluminum precipitation solution, and washing and roasting the aluminum hydroxide to obtain an aluminum oxide product.
The content of aluminum in the obtained aluminum-precipitated liquid is 0.0015g/L, and the aluminum precipitation rate is 99.99%.
S5: adding hydrogen peroxide and Fe into the solution after aluminum precipitation 2+ Oxidation to Fe 3+ Filtering to obtain the deironing liquid.
The iron content in the solution after iron removal is 0.0020g/L, and the iron removal rate is 99.56%.
S6: adding sodium sulfate into the deironing solution, wherein the addition amount is 0.9 times of the theoretical amount of calcium sulfate, stirring at 70 ℃ for reaction for 1h, and filtering after full reaction to obtain a calcium sulfate product and a calcium precipitation solution;
the content of calcium in the obtained calcium precipitation solution is 1.76g/L, and the calcium precipitation rate is 95.06%.
S7: and adding sodium hydroxide into the calcium-precipitating solution to adjust the pH value of the solution to 13, adding calcium and magnesium to generate sodium carbonate with the theoretical amount of 1 time of carbonate, reacting at 70 ℃ for 1 hour, filtering after full reaction, evaporating, concentrating and crystallizing the solution at 100 ℃, and concentrating to obtain a sodium nitrate product with the final specific gravity of 1.550.
The purity of the alumina obtained in this example was 98.65%, the purity of calcium sulfate was 90%, and the purity of sodium nitrate was 99.5%.
Example 2
Method for separating iron, silicon, gallium, aluminum and calcium from fly ash is carried out according to the method described in example 1, except that:
in step S1, the leaching temperature of the second stage is 200 ℃.
In the step S1, the iron content of the obtained second filtrate is 0.45g/L, the leaching rate of the nitric acid pressurized secondary leached aluminum is 94.5%, and the leaching rate of the iron is 4.93%.
In the step S4, the content of aluminum in the obtained aluminum-precipitated liquid is 0.0020g/L, and the aluminum precipitation rate is 99.99%.
In the step S5, the iron content in the iron-removing liquid is 0.0015g/L, and the iron-removing rate is 99.40%.
In the step S6, the content of calcium in the obtained calcium precipitation solution is 1.81g/L, and the calcium precipitation rate is 94.91%.
The purity of the alumina obtained in this example was 98.72%, the purity of calcium sulfate was 90.04%, and the purity of sodium nitrate was 99.49%.
Example 3
Method for separating iron, silicon, gallium, aluminum and calcium from fly ash is carried out according to the method described in example 1, except that:
in step S4, the raffinate was added to sodium hydroxide to adjust pH to 4.5.
In the step S1, the iron content of the obtained second filtrate is 0.72g/L, the leaching rate of the nitric acid pressurized secondary leached aluminum is 94.1%, and the leaching rate of the iron is 7.89%.
In the step S4, the content of aluminum in the obtained aluminum-precipitated liquid is 0.12g/L, and the aluminum precipitation rate is 99.52%.
In the step S5, the iron content in the solution after iron removal is 0.0022g/L, and the iron removal rate is 99.69%.
In the step S6, the content of calcium in the obtained calcium precipitation solution is 1.75g/L, and the calcium precipitation rate is 95.07%.
The purity of the alumina obtained in this example was 98.62%, the purity of calcium sulfate was 88.37%, and the purity of sodium nitrate was 99.46%.
Comparative example 1
Method for separating iron, silicon, gallium, aluminum and calcium from fly ash is carried out according to the method described in example 1, except that:
in step S1, the leaching temperature of the second stage is 150 ℃.
In the step S1, the leaching temperature of the second stage is lower than that of the embodiment, the iron content in the obtained second filtrate is 3.24g/L, which is higher than that of the embodiment, so that the later iron removal cost is increased, the leaching rate of nitric acid pressurized secondary leached aluminum is 91.2%, and the leaching rate of iron is 35.51%.
In the step S4, the content of aluminum in the obtained aluminum-precipitated liquid is 0.0014g/L, and the aluminum precipitation rate is 99.99%.
In the step S5, the iron content in the solution after iron removal is 0.015g/L, and the iron removal rate is 99.23%.
In the step S6, the content of calcium in the obtained calcium precipitation solution is 1.85g/L, and the calcium precipitation rate is 94.79%.
The purity of the alumina obtained in this example was 98.42%, the purity of calcium sulfate was 89.75%, and the purity of sodium nitrate was 99.34%.
Comparative example 2
Method for separating iron, silicon, gallium, aluminum and calcium from fly ash is carried out according to the method described in example 1, except that:
in step S4, the raffinate was added to sodium hydroxide to adjust pH to 3.5.
In the step S1, the iron content in the obtained second filtrate is 0.73g/L, the leaching rate of the nitric acid pressurized secondary leached aluminum is 94.05%, and the leaching rate of the iron is 8%.
In the step S4, the pH value is low, the content of aluminum in the obtained aluminum-precipitated liquid is 12.51g/L, which is higher than that of the embodiment, the aluminum precipitation rate is 49.96%, and the aluminum precipitation rate is too low.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (9)
1. A method for separating iron, silicon, gallium, aluminum and calcium from fly ash, which is characterized by comprising the following steps:
step S1: carrying out nitric acid pressurizing two-stage leaching reaction on the fly ash, filtering the first-stage leaching reaction to obtain a first filtrate and a first filter residue, processing the first filter residue into a silicon-containing and iron-containing product, carrying out second-stage leaching on the first filtrate, filtering to obtain a second filtrate and a second filter residue, and returning the second filter residue to the first-stage leaching reaction;
step S2: adding a reducing agent into the second filtrate for reaction to obtain a reduced liquid;
step S3: extracting the reduced liquid to obtain an organic phase and raffinate, and carrying out back extraction on the organic phase to obtain a gallium product;
step S4: adding alkaline substances into the raffinate to adjust the pH value for carrying out aluminum precipitation reaction, filtering after full reaction to obtain aluminum hydroxide and aluminum precipitation solution, and washing and roasting the aluminum hydroxide to obtain an aluminum oxide product;
step S5: adding an oxidant into the aluminum-precipitated liquid for reaction, and filtering to obtain an iron-removed liquid;
step S6: adding sodium sulfate into the solution after iron removal, fully reacting, and filtering to obtain a calcium sulfate product and a solution after calcium precipitation;
step S7: and (3) deeply removing calcium and magnesium from the calcium-precipitating solution by using sodium hydroxide and sodium carbonate, and then carrying out negative pressure evaporation concentration crystallization to obtain a sodium nitrate product.
2. The method according to claim 1, wherein in step S1, the first stage leaching conditions comprise: the solid-liquid ratio of the fly ash or the second filter residue and the nitric acid is 1:2-1:5, the concentration of the nitric acid is 300-500g/L, the leaching temperature is 160-220 ℃, the stirring speed is 55-85rpm, and the leaching time is 0.5-5h;
the second stage leaching conditions included: the solid-liquid ratio of the fly ash and the first filtrate is 1:2-1:5, the leaching temperature is 160-220 ℃, the stirring speed is 55-85rpm, and the leaching time is 0.5-3h.
3. The method according to claim 1, wherein in step S1, the mass percentage of the main chemical element composition of the fly ash includes: fe is 1-5%; 16-30% of Al; si is 18-25%; ca is 2-8%; mg is 0.2-0.8%.
4. The method according to claim 1, wherein in step S2, the reducing agent is at least one of iron powder and sodium sulfite: sodium sulfite is preferred.
5. The method according to claim 1, wherein in step S4, the alkaline substance is at least one of sodium carbonate and sodium hydroxide; the pH value of the precipitation reaction is 4-6, the reaction temperature is 60-100 ℃, the reaction time is 0.5-3.5h, and the feeding mode is homogeneous precipitation.
6. The method of claim 1, wherein in step S5, the oxidizing agent is at least one of hydrogen peroxide or oxygen.
7. The method according to claim 1, wherein sodium sulfate is added in an amount of 0.8 to 1.0 times the theoretical amount of calcium sulfate produced in step S6.
8. The method according to claim 1, wherein in the step S7, the added amount of sodium hydroxide is 11-14 of the pH value of the solution, and the added amount of sodium carbonate is 1-1.5 times of the theoretical amount of carbonate generated by calcium and magnesium in the solution after calcium precipitation; preferably, in step S7, sodium hydroxide is added to adjust the pH of the solution, and then sodium carbonate is added.
9. The method according to claim 1, wherein in step S7, the negative pressure evaporation concentration temperature is 60 to 100 ℃, the concentration end specific gravity is 1.500 to 1.600, and the crystallization temperature is 20 to 40 ℃.
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