A mechanical activation combined with oxygen pressure leaching method for extracting alumina from fly ash

Abstract

The invention discloses a mechanical activation combined with oxygen pressure leaching method for extracting aluminum oxide from fly ash, and relates to a resource utilization technology for solid waste. The specific method includes the steps of calcining and crushing fly ash, ball milling activation of fly ash mixed with sodium pyrosulfate, heating reaction of activated material mixed with sodium persulfate and deionized water, solid-liquid separation and detection. The invention has the advantages of low energy consumption, mild reaction conditions, no polluting gas generation, etc. The maximum extraction rate of Al obtained is 98.92%. The invention provides new technical support for recovering useful elements from solid waste.

Description

Technical Field

[0001] The invention relates to a resource utilization technology of solid waste, and in particular to a mechanical activation combined with oxygen pressure leaching method for extracting aluminum oxide from fly ash. Background Art

[0002] Fly ash produced by coal-fired power plants is a type of industrial solid waste that is small in size, light in weight, and rich in heavy metal elements. Long-term accumulation will pollute the atmosphere, soil, and water resources. Therefore, the resource utilization of fly ash has become a focus of attention worldwide. It is worth mentioning that fly ash contains a large number of valuable elements, such as aluminum, silicon, iron, and gallium. Among them, the content of alumina in high-aluminum fly ash is as high as more than 50%, which is a precious potential aluminum resource. However, inappropriate recycling methods may cause serious environmental and waste disposal problems. Based on this, it is very meaningful to develop a clean and efficient technology for recovering aluminum from fly ash.

[0003] The existing typical metallurgical methods for extracting alumina from fly ash generally include sodium-calcium roasting method, acid method and molten salt method (ammonium sulfate / ammonium bisulfate), which have both advantages and disadvantages. For example, the sodium-calcium roasting method shows the flexibility of operation and the maturity of technology, but it requires a higher roasting temperature and produces a large amount of waste slag. Secondly, the sodium-calcium roasting method easily dissolves a large amount of amorphous silicon dioxide in the fly ash, making it difficult to separate silicon and aluminum, and requires a complex process to further separate and purify the leachate, resulting in high recovery costs; although the acid method has low energy consumption, produces less waste slag, and silicon is insoluble in acid, the reaction system has high requirements for equipment and requires strong anti-corrosion treatment equipment; in the molten salt method, ammonium sulfate is used as an extractant. Although the recovery efficiency is high, ammonia will be produced during the sintering process, polluting the atmosphere. Therefore, developing a new method that can efficiently and cleanly recover alumina under mild conditions is a key and hot issue that researchers are currently concerned about. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a mechanical activation combined with oxygen pressure leaching method for extracting aluminum oxide from fly ash. The fly ash is mechanically activated by sodium pyrosulfate, and then the stable crystalline phases such as mullite and corundum in the fly ash are effectively destroyed by sodium persulfate high-pressure leaching, thereby obtaining a higher Al extraction rate under relatively mild conditions. The technology is suitable for the industrial production of extracting aluminum oxide from fly ash.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented through the following technical solutions:

[0006] A persulfate high-pressure leaching method for extracting aluminum oxide from fly ash comprises the following steps:

[0007] 1) calcining fly ash at 800° C. and then grinding it to obtain pretreated fly ash;

[0008] 2) putting the pretreated fly ash and sodium pyrosulfate into a ball mill, and ball milling them for activation to obtain activated clinker;

[0009] 3) adding sodium persulfate and deionized water to the activated clinker, stirring and mixing, and then transferring all of the mixture to a high-pressure reactor for reaction;

[0010] 4) After the reaction is completed, the clinker is subjected to solid-liquid separation to obtain a filtrate and a filter residue containing aluminum ions;

[0011] 5) Take 2-5 g of the filtrate and dilute it to 50 g. Use inductively coupled plasma-mass spectrometry to determine the Al content in the filtrate. 3+ The content is then converted into the content of aluminum oxide.

[0012] Furthermore, the calcination of fly ash in step 1) needs to be carried out in a muffle furnace for 3 hours, and after grinding, the fly ash is sieved through a 200-mesh sieve to ensure that the particle size of the fly ash is below 45 um.

[0013] Furthermore, in the step 2), the pretreated fly ash and sodium pyrosulfate are mixed according to the molar ratio of sodium pyrosulfate to alumina in the pretreated fly ash (0-20):1, more preferably (0-4):1; and the ball milling time is 0-10h, more preferably 0-4h.

[0014] Furthermore, in step 2), a planetary ball mill is used to ball mill the activated fly ash, the mass ratio of agate balls to materials is 3:1, and a forward and reverse alternating ball milling method is adopted, with a replacement time of 15 minutes per time.

[0015] Among them, in step 2), the main principle of using sodium pyrosulfate to activate fly ash is that sodium pyrosulfate is an ionic compound and its sulfur anion is oxidizing. 2 O 7 2- is a dimer of sulfate anion, and SO 4 2- There is a bridging oxygen atom in the 3+ Connected to form a complex three-dimensional network, and almost tetrahedral SO 4 2- All oxygen atoms in the group can be bonded to Al 3+ The oxygen atom is not combined with the aluminum end but further connected to the sulfur atom (Al-OS structure), thus destroying part of the Al-O-Si structure. + It shows that it is an electron acceptor that interacts with oxygen atoms in aluminosilicates, promoting Al 3+ It is expected to destroy the constraints of the original crystal lattice to form an anionic sulfate complex. The equation for the reaction process is as follows:

[0016] Na 2 S 2 O 7 →Na 2 SO 4 +SO 3 (1)

[0017] Al 2 O 3 (Corundum)+3Na 2 S 2 O 7 →2Na 3 Al(SO 4 ) 3 (2)

[0018] Al 6 Si 2 O1 3 (Mullite)+9Na 2 S 2 O 7 →6Na 3 Al(SO 4 ) 3 +2SiO 2 (3)

[0019] Al 2 O 3 (Glass phase)+3Na 2 S 2 O 7 →2Na 3 Al(SO 4 ) 3 (4)

[0020] Furthermore, in step 3), the amount of sodium persulfate added is based on the molar ratio of sodium persulfate to alumina in the fly ash of (0-20):1, more preferably (0-4):1; the amount of deionized water added is based on the liquid-solid ratio of deionized water to (activated clinker + sodium persulfate) of (1-20):1, more preferably (2-8):1;

[0021] Among them, the main principle of using sodium persulfate to leach fly ash under high pressure is that sodium persulfate will decompose into HSO when it comes into contact with water. 4 - and O 2 , HSO 4 - The generated H +It can form interfacial hydroxyl groups with a large amount of unsaturated oxygen in the solution, resulting in interfacial oxygen deficiency, lattice vacancies, and lattice defects in the aluminosilicate crystals in fly ash, weakening the bondage of oxygen atoms to aluminum atoms, thereby freeing aluminum atoms from lattice bondage and entering the solution. The equation for the reaction process is as follows:

[0022] Na 2 S 2 O 8 +H 2 O→2NaHSO 4 +1 / 2O 2 (pH = 3-7) (1)

[0023] Al 2 O 3 +6NaHSO 4 →Al 2 (SO 4 ) 3 +3Na 2 SO 4 +3H 2 O (2)

[0024] Further, in step 3), the stirring speed of the reaction process in step 3) is set to 300 rpm, and the reaction temperature range is 140-240°C; the leaching temperature range is preferably selected to be 140-240°C mainly to create a subcritical water environment. When the temperature and pressure of water are lower than its critical temperature Tc (374.3°C) and critical pressure Pc (22.1Mpa), and in the vicinity of the near state, it is called subcritical water. Studies have shown that subcritical water is an excellent reaction medium that can promote the reaction rate, thereby promoting the recovery of aluminum.

[0025] Furthermore, in the step 3), the initial heating rate of the reactor is set to 5°C / min, and the heating rate is set to 3°C / min after approaching 80% of the target temperature, in order to prevent the reactor from overheating;

[0026] Furthermore, in step 4), the solid-liquid separation is performed by suction filtration, and the filter residue can be further recycled after being dried at 105° C., such as preparing molecular sieves or porous materials.

[0027] Furthermore, in step 5), three parallel samples of the filtrate are taken each time, and the content of the elements is determined using an inductively coupled plasma-mass spectrometer to ensure that the confidence interval of the test result is between 90% and 95%.

[0028] Further, in step 5), Al in the solution 3+ The formula for converting concentration to alumina is: Among them, M Al2O3 and MAl Al 2 O 3 and the relative molecular mass of Al, g·mol-1; m is the mass of fly ash in a single test, g; V is the volume of aluminum leaching solution, mL; W Al2O3 Al in fly ash 2 O 3 Mass fraction, %.

[0029] The present invention has the following beneficial effects:

[0030] 1. Compared with the prior art, the present invention firstly adopts a ball milling activation method to fully mix sodium pyrosulfate with fly ash, and firstly uses pyrosulfate ions to destroy Si-O-Al bonds and Al-O bonds on the surface of fly ash, so that Al3+ is expected to destroy the constraints of the original crystal lattice to form anionic sulfate complexes, and then uses sodium persulfate high-pressure leaching method to further destroy the mullite structure inside the fly ash, resulting in lattice defects of aluminosilicate crystals, weakening the constraints of oxygen atoms on aluminum atoms, so that aluminum atoms get rid of the lattice constraints and enter the solution.

[0031] 2. The process adopted by the present invention is relatively mild, and a higher leaching rate can be obtained at a leaching temperature of 200°C. Compared with the traditional sodium carbonate or ammonium sulfate / ammonium bisulfate roasting method which requires a temperature of 800°C or even higher to obtain a higher Al extraction rate, the present invention has low energy consumption and high efficiency.

[0032] 3. The reagents used in the present invention are mild and non-corrosive, and no polluting gas is generated during the reaction. There is no need to consider the treatment of waste acid, waste alkali and other solutions. At the same time, the aluminum recovery rate is high, up to 98.92%, which is a clean and efficient method for recovering valuable elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the process flow of the present invention; DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention is clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1

[0036] Extraction of alumina from fly ash:

[0037] 1. Fly ash calcination: Low-aluminum fly ash was selected from Pingxu coal-fired power plant in Huainan, Anhui Province, and calcined at 800°C in a muffle furnace for 3 hours. Then, it was taken out and crushed through a 200-mesh sieve to obtain pretreated fly ash;

[0038] 2. Accurately weigh 5g of pretreated fly ash and 8.6314g of sodium pyrosulfate (CFA / Na 2 S 2 O 7 =1:3) In an agate jar containing 65g of agate balls, the speed of the ball mill was set to 300rpm, the time interval of forward and reverse rotation was 15min / time, and the ball milling was carried out for 2h.

[0039] 3. After the ball milling is completed, transfer the material into a 250 ml beaker and weigh 12.3384 g of sodium persulfate (CFA / Na 2 S 2 O 8 =1:4) in a beaker, add 104 ml of deionized water (liquid-to-solid ratio is 4:1), stir evenly and transfer the mixture to the reactor, set the speed to 300 rpm, first increase the temperature to 160 °C at a heating rate of 5 °C / min, then adjust the heating rate to 3 °C / min to increase the temperature to 200 °C, and keep the temperature constant for 120 min.

[0040] 4. After the reaction is completed, the solid-liquid separation is carried out by suction filtration to obtain the leaching solution.

[0041] Embodiment 2:

[0042] Extraction of alumina from fly ash:

[0043] 1. Fly ash calcination: Low-aluminum fly ash was selected from Pingxu coal-fired power plant in Huainan, Anhui Province, and calcined at 800°C in a muffle furnace for 3 hours. Then, it was taken out and crushed through a 200-mesh sieve to obtain pretreated fly ash;

[0044] 2. Accurately weigh 5g of pretreated fly ash into an agate jar containing 65g of agate balls, set the speed of the ball mill to 300rpm, the time interval of forward and reverse rotation to 15min / time, and ball mill for 2h.

[0045] 3. After the ball milling is completed, transfer the material into a 250 ml beaker and weigh 24.6773 g of sodium persulfate (CFA / Na 2 S 2 O 8 =1:8) in a beaker, add 119 ml of deionized water (liquid-to-solid ratio of 4:1), stir evenly and transfer the mixture to the reactor, set the speed to 300 rpm, first increase the temperature to 160 °C at a heating rate of 5 °C / min, then adjust the heating rate to 3 °C / min to increase the temperature to 200 °C, and keep the temperature constant for 120 min.

[0046] 4. After the reaction is completed, the solid-liquid separation is carried out by suction filtration to obtain the leaching solution.

[0047] Embodiment 3:

[0048] Extraction of alumina from fly ash:

[0049] 1. Fly ash calcination: Low-aluminum fly ash was selected from Pingxu coal-fired power plant in Huainan, Anhui Province, and calcined at 800°C in a muffle furnace for 3 hours. Then, it was taken out and crushed through a 200-mesh sieve to obtain pretreated fly ash;

[0050] 2. Accurately weigh 5g of pretreated fly ash and 8.6314g of sodium pyrosulfate (CFA / Na 2 S 2 O 7 =1:3) In an agate jar containing 65g of agate balls, the speed of the ball mill was set to 300rpm, the time interval of forward and reverse rotation was 15min / time, and the ball milling was carried out for 2h.

[0051] 3. After the ball milling is completed, transfer the material into a 250 ml beaker and weigh 24.6773 g of sodium persulfate (CFA / Na 2 S 2 O 8 =1:8) in a beaker, add 154 ml of deionized water (liquid-to-solid ratio of 4:1), stir evenly and transfer the mixture to the reactor, set the speed to 300 rpm, first increase the temperature to 160 °C at a heating rate of 5 °C / min, then adjust the heating rate to 3 °C / min to increase the temperature to 200 °C, and keep the temperature constant for 120 min.

[0052] 4. After the reaction is completed, the solid-liquid separation is carried out by suction filtration to obtain the leaching solution.

[0053] Embodiment 4:

[0054] Extraction of alumina from fly ash:

[0055] 1. Fly ash calcination: Low-aluminum fly ash was selected from Pingxu coal-fired power plant in Huainan, Anhui Province, and calcined at 800°C in a muffle furnace for 3 hours. Then, it was taken out and crushed through a 200-mesh sieve to obtain pretreated fly ash;

[0056] 2. Accurately weigh 5g of pretreated fly ash and 8.6314g of sodium pyrosulfate (CFA / Na 2 S 2 O 7 =1:3) In an agate jar containing 65g of agate balls, the speed of the ball mill was set to 300rpm, the time interval of forward and reverse rotation was 15min / time, and the ball milling was carried out for 1h.

[0057] 3. After the ball milling is completed, transfer the material into a 250 ml beaker and weigh 24.6773 g of sodium persulfate (CFA / Na 2 S 2 O 8 =1:8) in a beaker, add 154 ml of deionized water (liquid-to-solid ratio of 4:1), stir evenly and transfer the mixture to the reactor, set the speed to 300 rpm, first increase the temperature to 160 °C at a heating rate of 5 °C / min, then adjust the heating rate to 3 °C / min to increase the temperature to 200 °C, and keep the temperature constant for 120 min.

[0058] 4. After the reaction is completed, the solid-liquid separation is carried out by suction filtration to obtain the leaching solution.

[0059] Embodiment 5:

[0060] Extraction of alumina from fly ash:

[0061] 1. Fly ash calcination: Low-aluminum fly ash was selected from Pingxu coal-fired power plant in Huainan, Anhui Province, and calcined at 800°C in a muffle furnace for 3 hours. Then, it was taken out and crushed through a 200-mesh sieve to obtain pretreated fly ash;

[0062] 2. Accurately weigh 5g of pretreated fly ash and 8.6314g of sodium pyrosulfate (CFA / Na 2 S 2 O 7 =1:3) In an agate jar containing 65g of agate balls, the speed of the ball mill was set to 300rpm, the time interval of forward and reverse rotation was 15min / time, and the ball milling was carried out for 2h.

[0063] 3. After completion, transfer the material into a 250 ml beaker and weigh 24.6773 g of sodium persulfate (CFA / Na 2 S 2 O 8 =1:8) in a beaker, add 154 ml of deionized water (liquid-to-solid ratio of 4:1), stir evenly and transfer the mixture to the reactor, set the speed to 300 rpm, first increase the temperature to 160 °C at a heating rate of 5 °C / min, then adjust the heating rate to 3 °C / min to increase the temperature to 200 °C, and keep the temperature constant for 60 minutes.

[0064] 4. After the reaction is completed, the solid-liquid separation is carried out by suction filtration to obtain the leaching liquid

[0065] Embodiment 6:

[0066] Extraction of alumina from fly ash:

[0067] 1. Fly ash calcination: Low-aluminum fly ash was selected from Pingxu coal-fired power plant in Huainan, Anhui Province, and calcined at 800°C in a muffle furnace for 3 hours. Then, it was taken out and crushed through a 200-mesh sieve to obtain pretreated fly ash;

[0068] 2. Accurately weigh 5g of pretreated fly ash and 8.6314g of sodium pyrosulfate (CFA / Na 2 S 2 O 7 =1:3) In an agate jar containing 65g of agate balls, the speed of the ball mill was set to 300rpm, the time interval of forward and reverse rotation was 15min / time, and the ball milling was carried out for 2h.

[0069] 3. After the ball milling is completed, transfer the material into a 250 ml beaker and weigh 12.3384 g of sodium persulfate (CFA / Na 2 S 2 O 8 =1:4) in a beaker, add 104 ml of deionized water (liquid-to-solid ratio is 4:1), stir evenly and transfer the mixture to the reactor, set the speed to 300 rpm, first increase the temperature to 130 °C at a heating rate of 5 °C / min, then adjust the heating rate to 3 °C / min to increase the temperature to 160 °C, and keep the temperature constant for 120 min.

[0070] 4. After the reaction is completed, the solid-liquid separation is carried out by suction filtration to obtain the leaching solution.

[0071] Embodiment 7:

[0072] Extraction of alumina from fly ash:

[0073] 1. Fly ash calcination: Low-aluminum fly ash was selected from Pingxu coal-fired power plant in Huainan, Anhui Province, and calcined at 800°C in a muffle furnace for 3 hours. Then, it was taken out and crushed through a 200-mesh sieve to obtain pretreated fly ash;

[0074] 2. Accurately weigh 5g of pretreated fly ash and 8.6314g of sodium pyrosulfate (CFA / Na 2 S 2 O 7 =1:3) In an agate jar containing 65g of agate balls, the speed of the ball mill was set to 300rpm, the time interval of forward and reverse rotation was 15min / time, and the ball milling was carried out for 2h.

[0075] 3. After the ball milling is completed, transfer the material into a 250 ml beaker and weigh 12.3384 g of sodium persulfate (CFA / Na 2 S 2 O 8=1:4) in a beaker, add 77 ml of deionized water (liquid-to-solid ratio is 2:1), stir evenly and transfer the mixture to the reactor, set the speed to 300 rpm, first increase the temperature to 160 °C at a heating rate of 5 °C / min, then adjust the heating rate to 3 °C / min to increase the temperature to 200 °C, and keep the temperature constant for 120 min.

[0076] 4. After the reaction is completed, the solid-liquid separation is carried out by suction filtration to obtain the leaching solution.

[0077] 2 g of the leaching solution was taken and diluted to 50 g, and the content of aluminum ions in the leaching solution was detected by inductively coupled plasma emission spectrometer, and the dissolution rate of aluminum oxide was 45%;

[0078] Detection:

[0079] 2 g of each of the leachates obtained in Examples 1-7 were taken and diluted to 50 g, and the content of aluminum ions in the leachate was detected by inductively coupled plasma emission spectrometry (ICP-MS). The specific results are shown in the following table:

[0080]

[0081] As can be seen from the above table, the extraction effect of Example 3 is the best.

[0082] Finally, it should be noted that the above examples are only for the purpose of clearly illustrating the technical solutions of the present invention, rather than limiting it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not mean that the essence of the corresponding technical solutions deviates from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A mechanical activation combined with oxygen pressure leaching method for extracting aluminum oxide from fly ash, characterized in that: The steps include: 1) calcining fly ash at 800°C and then grinding it to obtain pretreated fly ash; 2) Put the pretreated fly ash and sodium pyrosulfate into a ball mill, and activate them by ball milling to obtain activated clinker; The pretreated fly ash and sodium pyrosulfate are mixed in a molar ratio of sodium pyrosulfate to alumina in the pretreated fly ash (0-20):1, and the ball milling time is 0-10h; 3) Add sodium persulfate and deionized water to the activated clinker, stir and mix well, then transfer all of the mixture to a high-pressure reactor for reaction; the amount of sodium persulfate added is based on the molar ratio of sodium persulfate to pretreated fly ash alumina in the activated clinker (0-20):1; the amount of deionized water added is based on the liquid-solid ratio of deionized water to activated clinker + sodium persulfate (1-20):1; the reaction temperature range is 140-240°C; 4) After the reaction is completed, the clinker is separated into solid and liquid to obtain a filtrate and a residue containing aluminum ions.

2. The method of mechanical activation combined with oxygen pressure leaching for extracting aluminum oxide from fly ash according to claim 1, characterized in that: In the step 1), the fly ash is calcined in a muffle furnace for 3 h, and after grinding, it is sieved through a 200-mesh sieve to ensure that the particle size of the fly ash is below 45 μm.

3. The method of mechanical activation combined with oxygen pressure leaching for extracting aluminum oxide from fly ash according to claim 1, characterized in that: In the step 2), a planetary ball mill is used to ball mill the activated fly ash, the mass ratio of agate balls to materials is 3:1, and a forward and reverse alternating ball milling method is adopted, with a replacement time of 15 minutes per time.

4. The method of mechanical activation combined with oxygen pressure leaching for extracting aluminum oxide from fly ash according to claim 1, characterized in that: In the step 3), the stirring speed during the reaction is set to 300 rpm.

5. The method of mechanical activation combined with oxygen pressure leaching for extracting aluminum oxide from fly ash according to claim 1, characterized in that: In step 3), the initial heating rate of the reactor is set to 5°C / min, and after the temperature reaches 80% of the target temperature, the heating rate is set to 3°C / min.

6. The method of mechanical activation combined with oxygen pressure leaching for extracting aluminum oxide from fly ash according to claim 1, characterized in that: The solid-liquid separation in step 4) is carried out by suction filtration.

7. The method of mechanical activation combined with oxygen pressure leaching for extracting aluminum oxide from fly ash according to claim 1, characterized in that: In step 4), three parallel samples of the filtrate are taken each time, and the content of the elements is determined by inductively coupled plasma-mass spectrometry to ensure that the confidence interval of the test result is between 90% and 95%.

8. The method according to claim 1, characterized in that: After step 4), the filtrate is diluted and tested, that is, 2-5 g of the filtrate is diluted to 50 g, and the Al content in the filtrate is determined by inductively coupled plasma-mass spectrometry. 3+ The content of Al in the solution is converted into the content of aluminum oxide. 3+ The formula for converting concentration to alumina is: ； Where: M Al2O3 and M Al are the relative molecular masses of Al2O3 and Al, g·mol -1 ; m is the mass of fly ash in a single test, g; V is the volume of aluminum leaching solution, mL; W Al2O3 is the mass fraction of Al2O3 in fly ash, %.

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