A method and device for reducing, detoxifying and recycling fly ash from incineration of domestic waste

Abstract

The invention relates to the field of waste incineration fly ash treatment, and discloses a method and device for reducing, detoxifying and recycling fly ash from domestic waste incineration, comprising the following steps: alkali washing the fly ash from domestic waste incineration; precipitating the slurry after alkali washing to obtain alkali washed fly ash, performing step-by-step electrodeposition on the supernatant, and recovering Pb and Zn to obtain an alkaline salt solution; acid leaching the obtained alkali washed fly ash, and purifying and separating the high calcium and high salt fly ash acid leaching solution by a neutralization precipitation method step by step to obtain NaCl, KCl and CaCl 2 The present invention uses step-by-step electrodeposition to recover Pb and Zn in fly ash alkali washing slurry in steps, and uses neutralization precipitation method to purify and separate the high-calcium and high-salt fly ash acid leaching solution step by step, so as to remove the heavy metals in the fly ash and recover the valuable metals at the same time, thereby achieving the ultimate reduction of fly ash and reducing the medium and low temperature thermal desorption treatment amount and treatment energy consumption.

Description

Technical Field

[0001] The invention relates to the technical field of waste incineration fly ash treatment, and in particular to a method and device for reducing, detoxifying and recycling fly ash from domestic waste incineration. Background Art

[0002] During the incineration of domestic waste, the boiling points of the single element and chloride of heavy metals Pb and Zn are low, and they are easy to volatilize and migrate to fly ash with the flue gas. In addition, the pollution sources of Pb and Zn are extensive, and the amount of Pb and Zn in domestic waste is high. Therefore, the content of Pb and Zn in fly ash from domestic waste incineration is generally high. If appropriate treatment methods can be used to recover lead and zinc, the obtained heavy metal slag can provide good raw materials for lead and zinc smelting, which will greatly improve the value of fly ash resource utilization.

[0003] The traditional fly ash leaching process uses an acidic solvent washing method to dissolve a large amount of heavy metals in the fly ash, and then uses a chemical method to remove the heavy metals in the solution to obtain sludge containing heavy metals. This increases the disposal cost of the sludge, and secondly, a large amount of valuable metals in the fly ash are not properly disposed of, resulting in a waste of resources.

[0004] Patent CN102618725A discloses a method for extracting amphoteric heavy metals from incineration fly ash as a low-grade heavy metal ore, wherein an inorganic chlorine-containing medium is added to the incineration fly ash, and under the conditions of appropriate roasting temperature and time, amphoteric heavy metals such as Pb, Cd, Cu and Zn are selectively and efficiently extracted from the incineration fly ash by adjusting the inorganic chlorine-containing medium and roasting temperature. However, it requires the addition of an inorganic chlorine-containing medium and high-temperature roasting, resulting in high recovery costs and energy consumption, which is not conducive to large-scale application; and it is unable to separate and recover other non-amphoteric metals in the incineration fly ash. Summary of the invention

[0005] The present invention aims to overcome the above-mentioned problems existing in the resource utilization method of fly ash from incineration of domestic waste in the prior art, and provides a method and device for reducing, detoxifying and resource utilization of fly ash from incineration of domestic waste. Step-by-step electrodeposition is used to recover Pb and Zn in fly ash alkali washing slurry in steps, and neutralization precipitation method is used step by step to purify and desalinate high-calcium and high-salt fly ash acid leaching solution, so that valuable metals are recovered while removing heavy metals from fly ash, thereby achieving the ultimate reduction of fly ash and reducing the medium and low temperature thermal desorption disposal amount and processing energy consumption.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for reducing, detoxifying and recycling fly ash from incineration of domestic waste, the steps comprising:

[0008] 1) Alkaline washing of fly ash from incineration of domestic waste;

[0009] 2) The slurry after alkali washing is precipitated to obtain alkali washed fly ash, and the supernatant is subjected to electrodeposition at voltages of 1-5 V and 6-10 V, respectively, to recover Pb and Zn to obtain an alkaline salt solution;

[0010] 3) The obtained alkali-washed fly ash is subjected to acid leaching, and solid-liquid separation is performed to obtain acid-leached ash residue and acidic high calcium solution; the acid-leached ash residue is subjected to medium-low temperature thermal desorption at a temperature below 600°C;

[0011] 4) Using lime milk to adjust the pH value of the acidic high calcium solution to 5.5-7.5, and precipitate to obtain sludge A and magnesium-rich calcium chloride solution;

[0012] 5) adjusting the pH value of the magnesium-rich calcium chloride solution to 9-11 with the alkaline salt solution obtained in step 2), and precipitating to obtain sludge B and a high-calcium polychloride salt solution;

[0013] 6) Evaporate and concentrate the high calcium polychloride salt solution to a CaCl2 concentration of 30-35wt%, separate and precipitate NaCl while hot, and then cool the liquid phase to separate KCl and CaCl2 solutions.

[0014] The present invention first performs alkali washing on the fly ash through step 1), and then performs electrodeposition on the supernatant after precipitating the alkali-washed fly ash in step 2. Since the electrode potential of Pb (-0.126 V) is higher than that of Zn (-0.762 V), it will deposit faster at the cathode than Zn, so the step-by-step recovery of Pb and Zn can be achieved at different voltages; at the same time, the fly ash contains soluble chloride salts, which enter the liquid phase during the alkali washing process, increase the conductivity of the solution, reduce the internal resistance of the electrolytic cell, avoid concentration polarization during the electrodeposition process, and improve the recovery effect of Pb and Zn. Step 3) Acid leaching is performed on the precipitated alkali-washed fly ash to leach the heavy metals in the fly ash into the solution, and a large amount of calcium is dissolved at the same time to form an acidic high-calcium slurry system; the acid-leached ash residue can be subjected to medium-low temperature thermal desorption to complete dioxin detoxification; the acidic high-calcium solution continues to recover Fe, Al, and Mg resources. Step 4) After adjusting the pH value of the acidic high calcium solution to 5.5-7.5 with lime milk, the Fe 2+ / Fe 3+ 、Al 3+The sludge A obtained by precipitation in the form of hydroxides is mainly composed of Fe(OH)3, Fe(OH)2, Al(OH)3 and a small amount of Ca(OH)2 carried during the precipitation process, which can be used as a neutralizer for treating acidic mine wastewater produced by mineral resource mining, thus achieving waste treatment. Step 5) The pH value of the magnesium-rich calcium chloride solution is adjusted to 9-11 with an alkaline salt solution, which can completely precipitate magnesium, and the obtained sludge B is Mg(OH)2 sludge, which can be used as a flame retardant or a raw material for making magnesium oxide. Step 6) According to the change in the solubility of chloride salts in the three-salt quaternary aqueous solution system (CaCl2-KCl-NaCl-H2O), and the solubility of sodium chloride does not change much with temperature, and the solubility of potassium chloride increases with increasing temperature, the high-calcium polychloride salt solution is separated and purified by evaporation and concentration, and NaCl salt, KCl salt and CaCl2 solution are recovered, realizing the resource recovery of salts.

[0015] According to the amphoteric characteristics of heavy metal ions, the present invention firstly adopts alkali washing-electrodeposition to step-by-step recover Pb and Zn in fly ash, then adopts acid leaching to extract calcium salt and other heavy metal ions in fly ash, and further adopts step-by-step precipitation to recover Fe, Al and Mg in the form of hydroxide, thereby achieving the extreme reduction of fly ash and the recycling of heavy metals, reducing the medium and low temperature thermal desorption disposal amount and processing energy consumption. Furthermore, NaCl is obtained by thermal separation through evaporation concentration and KCl and CaCl2 solutions are obtained by cooling crystallization separation, thereby achieving the separation and purification of high calcium polychloride salt solution. The present invention realizes the reduction, detoxification and recycling of fly ash from the incineration of domestic waste, and is simple to operate, low in cost and large in market benefits.

[0016] Preferably, the alkali solution used in the alkali washing in step 1) is a mixed solution of NaOH and KOH, and the molar ratio of NaOH to KOH is 1:3-7; the solid-liquid mass ratio of the domestic waste incineration fly ash and the alkali solution during the alkali washing is 1:1-3, and the total concentration of NaOH and KOH in the alkali solution is 1-10 mol / L. The present invention prepares the alkali solution used in the alkali washing in a specific proportion, and the potassium ion content in the alkaline salt solution generated by the alkali washing of the fly ash with the alkali solution is about 3 times more than the sodium ion content. The alkaline salt solution is used in step 5) to adjust the pH value of the magnesium-rich calcium chloride solution, which can ensure the purity of the sodium salt obtained by evaporation, concentration and separation of the high-calcium polychloride salt solution.

[0017] Preferably, in step 3), hydrochloric acid is used to acid-leach the alkali-washed fly ash, the mass ratio of the alkali-washed fly ash to the hydrochloric acid during the acid-leach is 1:0.6-1.3, and the acid-leach time is 45-90 min.

[0018] Preferably, after precipitation in step 4), sodium sulfide solution is added to the supernatant for reaction and sand filtration is performed to obtain a magnesium-rich calcium chloride solution; the concentration of the sodium sulfide solution is 0.1-2 mol / L, and the concentration of the added sodium sulfide is 0.25-4 mmol / L. Adding sodium sulfide solution to the supernatant can remove trace heavy metal impurities, and then sand filtration is performed to remove fine suspended matter, which can improve the purity of the salts finally recovered.

[0019] Preferably, in step 6), the temperature for separating NaCl is 110-115°C, the liquid phase is cooled to -5-15°C, and centrifuged to obtain KCl and CaCl2 solutions.

[0020] Preferably, in step 6), the separated KCl is further refined and purified by: dissolving KCl and passing it through a Na-type ion exchange resin, and then evaporating and crystallizing it to obtain the refined and purified KCl. The KCl obtained by cooling and crystallization contains a small amount of calcium ions carried by water. In order to make its quality reach the premium product standard, the present invention dissolves KCl, passes it through a Na-type ion exchange resin, removes the calcium ions therein, and then evaporates and crystallizes it to obtain premium KCl. NaCl has a better dehydration effect in the process of hot centrifugal separation, carries less water, contains fewer impurity ions, and does not need to be refined.

[0021] In the second aspect, the present invention provides a device for reducing, detoxifying and recycling fly ash from incineration of domestic waste used for the above-mentioned method for reducing, detoxifying and recycling fly ash from incineration of domestic waste, comprising an alkali washing reaction tank, a separate electrodeposition reaction tank, an acid leaching reaction tank, a filter press, a primary sedimentation tank, a secondary sedimentation tank, a primary MVR evaporator, a constant temperature separator, a NaCl heat-insulating centrifuge, a cooling kettle and a KCl centrifuge connected in sequence through pipelines; the separate electrodeposition reaction tank comprises a gravity sedimentation zone, a stirring and cleaning zone and an electrodeposition zone connected in sequence; an ash hopper is provided at the bottom of the gravity sedimentation zone and the stirring and cleaning zone, and the top is separated by a sedimentation baffle; a stirring device is provided in the stirring and cleaning zone; the electrodeposition zone is divided into a plurality of electrolytic cells by a plurality of insulating baffles, each electrolytic cell is provided with a pair of electrode plates, and the electrode plates are connected to a rectifier; the top of the gravity sedimentation zone is connected to the alkali washing reaction tank, the ash hopper is connected to the acid leaching reaction tank, and the outermost electrolytic cell is connected to the secondary sedimentation tank.

[0022] When the device of the present invention is used to treat fly ash from the incineration of domestic waste, the alkali washing step of step 1) is carried out in the alkali washing reaction tank, and the slurry after alkali washing enters the separate electrodeposition reaction tank to carry out the precipitation and step-by-step electrodeposition of step 2) to recover Pb and Zn; the alkali washed fly ash precipitated in the ash hopper enters the acid leaching reaction tank, and hydrochloric acid is added to carry out the acid leaching of step 3), and after the acid leaching, the solid-liquid separation is carried out by the filter press, and the acid leached ash is subjected to medium-low temperature thermal desorption, and the acidic high calcium solution enters the primary sedimentation tank, and lime milk is added to adjust the pH value to carry out the precipitation of step 4); the effluent of the primary sedimentation tank enters In the secondary sedimentation tank, the effluent from the separation electrodeposition reaction tank is added to adjust the pH value, and the precipitation in step 5) is carried out; the effluent from the secondary sedimentation tank enters the primary MVR evaporator for evaporation and concentration, and then enters the constant temperature separator for separation, the bottom discharge port of the constant temperature separator is connected to the NaCl insulation centrifuge, and the slag outlet of the NaCl insulation centrifuge is the precipitated NaCl crystalline salt; the liquid outlet of the NaCl insulation centrifuge is connected to the cooling kettle, and the liquid phase is cooled and then enters the KCl centrifuge for centrifugal separation, the slag outlet is the KCl crystalline salt, and the liquid outlet is the CaCl2 solution.

[0023] When the separate electrodeposition reaction cell of the present invention is working, the alkali-washed slurry enters from the top of the gravity settling zone, the alkali-washed fly ash is precipitated into the ash hopper, the supernatant enters the electrodeposition zone through the stirring and cleaning zone, the rectifier power supply is turned on, and the supernatant is subjected to electrodeposition to recover Pb and Zn step by step. Since the Pb electrode potential is higher than that of Zn, it will precipitate at the cathode faster than Zn, so several electrolytic cells close to the stirring and cleaning zone are Pb recovery electrolytic cells, and the remaining electrolytic cells are Zn recovery electrolytic cells. The rectifier voltage connected to the electrode plate in the Pb recovery electrolytic cell is set to 1~5 V, and the rectifier voltage connected to the electrode plate in the Zn recovery electrolytic cell is set to 6~10 V. Each electrolytic cell of the present invention is separated by an insulating baffle, and the baffled flow mode can make each electrolytic cell form an up-and-down tumbling electrolytic cell, ensuring that the liquid has enough electrodeposition time in each electrolytic cell, and ensuring the recovery effect of Pb and Zn. After one round of recovery is completed, the stirring device in the stirring and washing area is started to stir and wash the mud precipitated in the ash bucket, and the Pb and Zn deposited in the ash due to the adhesion effect are washed into the liquid phase for secondary recovery of Pb and Zn. This greatly improves the dissolution and recovery efficiency of Pb and Zn in fly ash.

[0024] Preferably, an online ion analysis probe is provided at the outlet of the separate electrodeposition reaction tank, and the content of lead ions and zinc ions in the outlet water is detected by the online ion analysis probe. When the content of the two reaches the requirement, the separate electrodeposition reaction tank enters the sludge discharge stage, and the alkali-washed fly ash in the ash hopper is sent to the acid leaching reaction tank for acid leaching.

[0025] Preferably, the electrode plates in the electrolytic cell are divided into cathode plates and anode plates, the cathode plates are made of copper, iron or stainless steel, and the anode plates are made of graphite or titanium.

[0026] Preferably, the method further comprises a Na-type ion exchange resin tank, a secondary MVR evaporator and a crystallizer connected in sequence, wherein the Na-type ion exchange resin tank is connected to a KCl centrifuge.

[0027] Therefore, the present invention has the following beneficial effects:

[0028] (1) Based on the amphoteric characteristics of heavy metal ions, alkaline washing-electrolytic deposition is first used to recover Pb and Zn in fly ash in steps, and then acid leaching is used to extract calcium salts and other heavy metal ions in fly ash. Fe, Al and Mg are further recovered in the form of hydroxides by precipitation. They can be used as neutralizers and flame retardants, achieving the ultimate reduction of fly ash and resource recovery of heavy metals. NaCl salt is obtained by thermal separation through evaporation and concentration, and KCl salt and CaCl2 solution are obtained by cold crystallization separation, achieving resource recovery of salts at the same time.

[0029] (2) The various indicators of the KCl finally obtained meet the standards of the superior product in "Industrial Potassium Chloride" (GB / T 7118-2008), the various indicators of the NaCl salt meet the secondary standards of industrial dry salt in "Industrial Salt" (GB / T 5462-2015), and the various indicators of the CaCl2 solution meet the standards of liquid calcium chloride in "Industrial Calcium Chloride" (GB / T 26520-2011), and all of them can be used as resources;

[0030] (3) The alkaline salt solution produced after electrolytic recovery of Pb and Zn is used to adjust the pH value of the magnesium-rich calcium chloride solution. Firstly, it saves the use of reagents. Secondly, the potassium ion content in the alkaline salt solution produced by treating fly ash with alkali solution prepared in a specific ratio is about 3 times the sodium ion content, which ensures the purity of the sodium salt obtained by evaporation, concentration and separation of the high-calcium polychloride salt solution;

[0031] (4) A separate electrodeposition reaction pool with sedimentation, stirring and electrodeposition functions is used to utilize the gravity sedimentation performance of fly ash to separate the solid and liquid of the alkaline washing slurry; then a multi-stage tumbling electrolytic cell is used to partition the alkaline salt solution containing Pb and Zn and electrolyze the metal Pb and Zn in steps; at the same time, the stirring effect can cause the settled bottom residue to be washed with alkaline solution for the second time, fully dissolving and extracting the Pb and Zn in the fly ash, so that the discharged ash contains almost no Pb and Zn. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the connection structure of the device for reducing, detoxifying and recycling fly ash from incineration of domestic waste of the present invention.

[0033] Figure 2It is a schematic structural diagram of a separate electrodeposition reaction cell of the present invention.

[0034] Figure 3 This is a graph showing the solubility change of chloride salt in a three-salt quaternary aqueous solution system (CaCl2-KCl-NaCl-H2O) at 25°C.

[0035] In the figure: 1 alkali washing reaction tank, 1-1 fly ash storage tank, 1-2 alkali agent preparation tank, 1-3 three-way pipeline, 1-4 closed pipeline spiral, 2 separate electrodeposition reaction tank, 2-1 gravity sedimentation zone, 2-1-1 sedimentation baffle, 2-1-2 ash hopper, 2-2 stirring and washing zone, 2-3 electrodeposition zone, 2-4 stirring shaft, 2-4-1 triangular stirring paddle, 2-5 shaftless screw conveyor, 2-6 first rectifier, 2-7 Pb recovery electrolytic cell, 2-8 Zn recovery electrolytic cell, 2-9 second rectifier, 2-10 online ion analysis probe, 2-11 insulating baffle, 2-12 electrode plate, 3 alkaline salt solution storage tank, 4 acid leaching reaction tank, 4-1 hydrochloric acid storage tank, 5 plate and frame filter press, 6 primary sedimentation tank, 6-1 lime milk storage tank, 6-2 primary sedimentation tank sludge outlet, 7 buffer tank, 7-1 Na2S solution mixing tank, 8 sand filter tank, 9 secondary sedimentation tank, 9-1 secondary sedimentation tank sludge outlet, 10 regulating tank, 11 primary MVR evaporator, 12 constant temperature separator, 13 NaCl heat preservation centrifuge, 14 cooling kettle, 15 KCl centrifuge, 16 Na type ion exchange resin tank, 17 secondary MVR evaporator, 18 crystallizer. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0037] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art.

[0038] Overall embodiment:

[0039] like Figure 1As shown in, a device for reducing, detoxifying and recycling fly ash from incineration of domestic waste used in an embodiment of the present invention comprises an alkali washing reaction tank 1, a fly ash storage tank 1-1 and an alkali agent preparation tank 1-2 are connected to the feed port of the alkali washing reaction tank 1 through a three-way pipe 1-3; the discharge port of the alkali washing reaction tank 1 is connected to the feed port of the separate electrodeposition reaction tank 2 through a mud pump, the liquid outlet of the separate electrodeposition reaction tank 2 is connected to the water inlet of the alkaline salt solution storage tank 3 through a metering pump, the slag outlet at the bottom of the separate electrodeposition reaction tank 2 is connected to the feed port of the acid leaching reaction tank 4; the liquid inlet at the bottom of the acid leaching reaction tank 4 is connected to the hydrochloric acid storage tank 4- 1, the discharge port of the acid leaching reaction tank 4 is connected to the feed port of the plate and frame filter press 5 through a mud pump; the liquid outlet of the plate and frame filter press 5 is connected to the feed port of the primary sedimentation tank 6 through a lifting pump, the dosing port of the primary sedimentation tank 6 is connected to the discharge port of the lime milk storage tank 6-1 through a metering pump, the sludge of the primary sedimentation tank 6 is discharged through the primary sedimentation tank mud discharge port 6-2, the supernatant overflowing from the primary sedimentation tank 6 flows into the buffer tank 7 through a pipeline, the dosing port of the buffer tank 7 is connected to the liquid outlet of the Na2S solution preparation tank 7-1 through a metering pump, the liquid outlet of the buffer tank 7 is connected to the liquid inlet of the sand filter tank 8 through a lifting pump, and the sand filter tank 8 is connected to the liquid outlet of the Na2S solution preparation tank 7-1 through a metering pump. The liquid outlet of the tank 8 is connected to the liquid inlet of the secondary sedimentation tank 9 through a lifting pump, the sludge in the secondary sedimentation tank 9 is discharged through the secondary sedimentation tank sludge outlet 9-1, and the overflow supernatant of the secondary sedimentation tank 9 flows into the regulating tank 10 through a pipeline; the liquid outlet of the regulating tank 10 is connected to the liquid inlet of the primary MVR evaporator 11, the discharge port of the primary MVR evaporator 11 is connected to the feed port of the constant temperature separator 12, the supernatant outlet of the constant temperature separator 12 is connected to the cooling kettle 14, the discharge port at the bottom of the constant temperature separator 12 is connected to the feed port of the NaCl insulation centrifuge 13 through a circulating pump, and the NaCl insulation centrifuge 13 is connected to the cooling kettle 14. The liquid outlet is connected to the cooling kettle 14, the slag outlet of the NaCl insulation centrifuge 13 is NaCl crystal salt, the material outlet of the cooling kettle 14 is connected to the KCl centrifuge 15 through a circulating pump, the liquid outlet of the KCl centrifuge 15 is CaCl2 solution, the slag outlet of the KCl centrifuge 15 is connected to the condensate outlet of the primary MVR evaporator 11, and the KCl crystal salt is dissolved and transported to the Na type ion exchange resin tank 16 through the circulating pump, the liquid outlet of the Na type ion exchange resin tank 16 is connected to the liquid inlet of the secondary MVR evaporator 17, and the material outlet of the secondary MVR evaporator 17 is connected to the crystallizer 18.

[0040] like Figure 2As shown in the figure, the separated electrodeposition reaction pool includes a gravity sedimentation zone 2-1, a stirring and cleaning zone 2-2 and an electrodeposition zone 2-3 which are connected in sequence; an ash hopper 2-1-2 is provided at the bottom of the gravity sedimentation zone and the stirring and cleaning zone, and the top is separated by a sedimentation baffle 2-1-1; a stirring device is provided in the stirring and cleaning zone, and the stirring device includes a stirring shaft 2-4 and a triangular stirring paddle 2-4-1 located in the ash hopper, and the triangular stirring paddle is gradually reduced from top to bottom along with the structure of the ash hopper; the electrodeposition zone is divided into five electrolytic cells by four insulating baffles 2-11, the two on the left are Pb recovery electrolytic cells 2-7, and the three on the right are Zn recovery electrolytic cells 2-8, A pair of electrode plates 2-12 is respectively provided in each electrolytic cell. The electrode plates in the Pb recovery electrolytic cell are connected to the first rectifier 2-6, and the electrode plates in the Zn recovery electrolytic cell are connected to the second rectifier 2-9. The electrode plates are divided into cathode plates and anode plates. The cathode plates are made of stainless steel, and the anode plates are made of graphite. The electrode plates are fixed in a suspended manner and do not contact the cell wall. The top of the gravity sedimentation zone is connected to the discharge port of the alkaline washing reaction tank 1 through a mud pump; the discharge port at the bottom of the ash hopper is connected to the acid leaching reaction tank 4, and the liquid outlet of the rightmost electrolytic cell is connected to the water inlet of the alkaline salt solution storage tank 3 through a metering pump, and an online ion analysis probe 2-10 is provided at the liquid outlet.

[0041] When the device of the present invention is in operation, fly ash is transported from the discharge port of the fly ash storage tank 1-1 by the closed pipe spiral 1-4 to the intersection of the three-way pipe 1-3 and slurried with the alkali solution in the alkali agent preparation tank 1-2 to avoid the generation of dust in the alkali washing reaction tank; after slurrying, it is transported to the alkali washing reaction tank 1 for stirring reaction, and the pH value of the alkali washing slurry is monitored online to be ≥14. After stirring and reacting for 30 to 60 minutes for sufficient reaction, the slurry is transported to the separation electrodeposition reaction tank 2 for solid-liquid separation and recovery of Pb and Zn.

[0042] The alkali-washed slurry is transported to the gravity sedimentation zone 2-1 of the separate electrodeposition reaction tank 2 by a slurry pump, the alkali-washed fly ash is precipitated in the ash hopper 2-1-2, and the supernatant enters the electrodeposition zone 2-3. When the liquid level rises to half of the Pb recovery electrolytic cell 2-7, the first rectifier 2-6 power supply is turned on, and the power supply voltage is set to 1~5 V, and the Pb ion reduction deposition is carried out. As the liquid level gradually rises and exceeds the insulating baffle 2-11 of the Pb recovery electrolytic cell 2-7, the solution overflows into the Zn recovery electrolytic cell 2-8, and gradually fills the first two Zn recovery electrolytic cells. When the liquid level of the last Zn recovery electrolytic cell reaches half, the second rectifier 2-9 power supply is turned on, and the power supply voltage is set to 6~10 V, and the solution that has completed the Pb recovery is reduced and deposited with Zn ions, thereby realizing the step-by-step recovery of Pb and Zn; after the electrodeposition reaction is 45~120 min later, the stirring motor is started to stir and wash the sludge deposited in the ash hopper 2-1-2 for 3-7 min at a stirring speed of 200-1000 r / min, and the Pb and Zn deposited in the ash due to the attachment effect are washed into the liquid phase for secondary recovery of Pb and Zn until the online ion analysis probe 2-10 at the outlet end of the separation electrodeposition reaction cell detects Pb in the solution. 2+ Concentration below 5 mg / L, Zn 2+ When the concentration is lower than 15 mg / L, the separate electrodeposition reaction tank 2 enters the sludge discharge stage, and the alkali-washed fly ash is quantitatively sent to the acid leaching reaction tank 4 by the shaftless screw conveyor 2-5 at the sludge discharge port at the bottom of the ash hopper. Then the slurry pump is turned on to send the slurry of the alkali-washing reaction tank 1 to the gravity sedimentation area 2-1 of the separate electrodeposition reaction tank 2. The supernatant after recovering Pb and Zn overflows into the alkaline salt solution storage tank 3 for standby use. This cycle is repeated to complete the recovery of Pb and Zn in the fly ash.

[0043] After the alkali-washed fly ash quantitatively enters the acid leaching reaction tank 4, start the stirred reactor, turn on the metering pump of the hydrochloric acid storage tank 4-1, and slowly add hydrochloric acid while stirring to make the alkali-washed fly ash and hydrochloric acid fully react. When the pH value of the slurry is ≤3, stop adding hydrochloric acid, continue stirring and reacting for 15 min~30 min, and the heavy metals in the fly ash are leached into the solution. At the same time, a large amount of calcium is dissolved to form an acidic high-calcium slurry system. Subsequently, after solid-liquid separation by the plate and frame filter press 5, the final reduction of the fly ash is 65%~85%, and the acid leaching ash enters the medium-low temperature pyrolysis desorption unit to complete dioxin detoxification (the structure and method of the medium-low temperature pyrolysis desorption unit are detailed in patent CN202311429849.6), and the acidic high-calcium solution enters the primary sedimentation tank 6 for Fe, Al, and Mg resource recovery.

[0044] The acidic high calcium solution is pumped into the primary sedimentation tank 6 through a lifting pump. The metering valve of the lime milk storage tank 6-1 is opened, and lime milk is added while stirring to adjust the pH value of the acidic high calcium solution to 5.5-7.5.2+ / Fe 3+ 、Al 3+ It precipitates in the form of hydroxide and is discharged from the mud outlet 6-2 of the first-level sedimentation tank at the bottom. The main components of the obtained sludge are Fe(OH)3, Fe(OH)2, Al(OH)3 and a small amount of Ca(OH)2 carried during the precipitation process. It can be used as a neutralizer for treating acidic mine wastewater generated by mineral resource mining, thus achieving waste treatment. After static precipitation, the supernatant enters the buffer tank 7, the metering valve of the Na2S solution preparation tank 7-1 is opened, the sodium sulfide solution is added, the agitator is turned on, and after low-speed stirring for 10 minutes, the solution is sent to the sand filter tank 8 by the lifting pump to remove fine suspended impurities, filtered to obtain a magnesium-rich calcium chloride solution, and sent to the secondary sedimentation tank 9 by the lifting pump, the metering valve of the alkaline salt solution storage tank 3 is opened, and the alkaline salt solution is added while stirring, and the pH value of the magnesium-rich calcium chloride solution is adjusted to 9-11 to completely precipitate magnesium to obtain Mg(OH)2 sludge, which is discharged through the mud outlet 9-1 of the secondary sedimentation tank at the bottom. It can be used as a flame retardant or a raw material for making magnesium oxide. The supernatant is a high-calcium polychloride salt solution containing 15%-20% calcium chloride. The pH value is adjusted to 8-9 by the regulating tank 10 for subsequent purification and salt separation.

[0045] like Figure 3As shown, according to the solubility changes of sodium chloride and potassium chloride in the three-salt quaternary aqueous solution system (CaCl2-KCl-NaCl-H2O) at 25°C with different percentages of calcium chloride solution system, when the calcium chloride concentration reaches 30wt%, the amount of sodium chloride and potassium chloride that can be dissolved in the system is small, and the solubility of potassium chloride increases with increasing temperature. Therefore, under high temperature conditions, the solubility of potassium chloride is much greater than that of sodium chloride. In the secondary sedimentation tank, the proportion of potassium chloride in the high-calcium polychloride salt solution system is about 3 times that of sodium chloride, which greatly improves the purity of NaCl salt separated by evaporation and concentration. Therefore, the present invention first sends the high-calcium polychloride salt solution into the first-level MVR evaporator 11 for evaporation and concentration until the concentration of calcium chloride is 30wt%~35wt%, and the boiling point temperature rise is controlled at 15°C. Then the hot solution enters the constant temperature separation chamber 12 for preliminary sedimentation separation, the temperature of the constant temperature separation chamber is controlled at 110~115°C, the supernatant after standing enters the cooling kettle 14, the mother liquor containing NaCl crystallized salt precipitated from the bottom by heat is separated into solid and liquid by the NaCl insulation centrifuge 13, the NaCl salt is separated by centrifugation while hot, the liquid phase separated by the NaCl insulation centrifuge 13 is sent to the cooling kettle 14 by a lifting pump, the temperature of the cooling kettle 14 is controlled at -5°C~15°C, KCl is precipitated by cold crystallization, and solid-liquid separation is carried out by the KCl centrifuge 15 to obtain KCl crystallized salt and CaCl2 solution. KCl salt is discharged from the slag outlet of KCl centrifuge 15, mixed and dissolved with the condensed water produced by the first-stage MVR evaporator in the pipeline, and then sent to the Na-type ion exchange resin tank 16 through a circulating pump. The solid-liquid ratio is controlled at 1:1~1:2. The calcium ions are removed in the Na-type ion exchange resin tank 16, and then sent to the second-stage MVR evaporator 17 for evaporation and crystallization, and KCl refined salt is obtained through a crystallizer 18. The various indicators of the KCl finally obtained meet the standards of the superior products in "Industrial Potassium Chloride" (GB / T7118-2008), the various indicators of NaCl meet the second-level standards of industrial dry salt in "Industrial Salt" (GB / T 5462-2015), and the various indicators of CaCl2 solution meet the standards of liquid calcium chloride in "Industrial Calcium Chloride" (GB / T 26520-2011).

[0046] Embodiment 1:

[0047] A method for reducing, detoxifying and recycling fly ash from incineration of domestic waste, comprising the following steps:

[0048] 1) Using alkali solution to wash the fly ash from the incineration of domestic waste (high chlorine ash from a domestic waste incineration plant in Hangzhou, with a moisture content of 1.1wt%, in the form of loose powder, and its main element composition by mass percentage is: Na 7.30%, K 5.05%, Cl21.65%, Ca 32.28%, Zn 3.98%, Pb 2.46%, Fe 2.35%, Al 4.38%, Mg 2.88%, Cu 0.45%, Si2.51%, O 14.71%); the alkali solution is a mixed solution of NaOH and KOH, and the molar ratio of NaOH to KOH is 1:5; during alkali washing, the solid-liquid mass ratio of the fly ash from the incineration of domestic waste and the alkali solution is 1:2, and the total concentration of NaOH and KOH in the alkali solution is 3 mol / L; the pH value of the alkali washing slurry is monitored online to be ≥14, and the slurry is transported to the separate electrodeposition reaction tank after stirring and reacting in the alkali washing reaction tank for 45 min to fully react;

[0049] 2) The slurry after alkali washing is precipitated in the gravity sedimentation zone of the separate electrodeposition reaction cell to obtain alkali-washed fly ash, and the supernatant enters the electrodeposition zone. The power supply voltages of the first rectifier and the second rectifier are set to 3.5 V and 7.8 V, respectively, and Pb and Zn are recovered step by step until the online ion analysis probe at the outlet of the separate electrodeposition reaction cell detects Pb in the solution. 2+ Concentration below 5 mg / L, Zn 2+ When the concentration is lower than 15 mg / L, the sludge discharge stage begins, the alkali-washed fly ash in the ash hopper enters the acid leaching reaction tank, and the supernatant overflows into the alkaline salt solution storage tank for standby use;

[0050] 3) After the alkali-washed fly ash is quantitatively fed into the acid leaching reaction tank, the stirred reactor is started, the metering pump of the hydrochloric acid storage tank is turned on, and hydrochloric acid is slowly added while stirring, and the ratio of alkali-washed wet ash to hydrochloric acid is controlled to be 1:1, and the reaction is fully carried out. When the pH value of the slurry is ≤3, the addition of hydrochloric acid is stopped, and the stirring reaction is continued for 20 min. The acid leaching ash residue and the acidic high calcium solution are obtained by solid-liquid separation through a plate and frame filter press, and the acid leaching ash residue is subjected to medium-low temperature thermal desorption at a temperature below 600°C;

[0051] 4) In the primary sedimentation tank, adjust the pH value of the acidic high calcium solution to 6.5 with lime milk, precipitate to obtain sludge A, and the supernatant enters the buffer tank, add 0.5 mol / L sodium sulfide solution to a sodium sulfide concentration of 1 mmol / L, turn on the stirrer, stir at a low speed for 10 minutes, and then send the solution to the sand filter tank through the lift pump to remove fine suspended impurities, and filter to obtain a magnesium-rich calcium chloride solution;

[0052] 5) The magnesium-rich calcium chloride solution enters the secondary sedimentation tank, the metering valve of the alkaline salt solution storage tank is opened, the alkaline salt solution is added while stirring, the pH value of the magnesium-rich calcium chloride solution is adjusted to 10, and sludge B and high-calcium polychloride salt solution are precipitated;

[0053] 6) The high calcium polychloride salt solution enters the regulating tank, and after the pH value is adjusted to 8.5, it enters the first-stage MVR evaporator for evaporation and concentration to a calcium chloride concentration of 32wt%. Then the hot solution enters the constant temperature separator, and the temperature is controlled at 112°C for preliminary sedimentation separation. The mother liquor containing NaCl crystal salt precipitated by heat is separated into solid and liquid by a NaCl insulation centrifuge to obtain NaCl; the supernatant separated by the constant temperature separator enters the cooling kettle, and the temperature of the cooling kettle is controlled at 0°C. The mother liquor precipitated by cold crystallization is separated into solid and liquid by a KCl centrifuge to obtain KCl crystal salt and CaCl2 solution; the KCl crystal salt and the condensed water generated by the first-stage MVR evaporator are mixed and dissolved in the pipeline (the dissolved solid-liquid ratio is controlled at 1:1.5), and then sent to the Na-type ion exchange resin tank through a circulating pump to complete the removal of calcium ions, and then sent to the second-stage MVR evaporator for evaporation and crystallization to obtain KCl refined salt.

[0054] Embodiment 2:

[0055] The difference between Example 2 and Example 1 is that the molar ratio of NaOH to KOH in the alkali solution during alkali washing in step 1) is 1:3, and the rest is the same as in Example 1.

[0056] Embodiment 3:

[0057] The difference between Example 3 and Example 1 is that the molar ratio of NaOH to KOH in the alkali solution during alkali washing in step 1) is 1:7, and the rest is the same as in Example 1.

[0058] Embodiment 4:

[0059] The difference between Example 4 and Example 1 is that the mass ratio of alkali-washed fly ash to hydrochloric acid in step 3) is 1:0.6, and the rest is the same as in Example 1.

[0060] Embodiment 5:

[0061] The difference between Example 5 and Example 1 is that the mass ratio of alkali-washed fly ash to hydrochloric acid in step 3) is 1:1.3, and the rest is the same as in Example 1.

[0062] Comparative Example 1:

[0063] The difference between Comparative Example 1 and Example 1 is that the alkali solution in step 1) alkali washing is NaOH solution, and the rest is the same as in Example 1.

[0064] Comparative Example 2:

[0065] The difference between Comparative Example 2 and Example 1 is that the alkali solution in step 1) alkali washing is KOH solution, and the rest is the same as in Example 1.

[0066] The fly ash reduction effects and heavy metal and salt recovery results in the above examples and comparative examples are shown in Table 1.

[0067] Among them, the calculation method of fly ash reduction rate is: β loss (%) = [(M0-M1) / M0]×100%, M0 is the dry mass of original fly ash (g), M1 is the dry mass of fly ash after acid leaching treatment (g).

[0068] The calculation method of Pb and Zn recovery rate is: Pb / Zn (%) = [(C0-C1) / C0] × 100%, C0 is the concentration of Pb / Zn in the supernatant of the alkaline washing reaction tank (mg / L), C1 is the concentration of Pb / Zn at the outlet of the separate electrodeposition reaction tank (mg / L).

[0069] The calculation method of Fe and Al recovery rate in sludge A is: Fe / Al (%) = [(a0-a1) / a0] × 100%, a0 is the concentration of Fe / Al in the acidic high calcium solution at the inlet of the primary sedimentation tank (mg / L), a1 is the concentration of Fe / Al in the acidic high calcium solution at the outlet of the primary sedimentation tank (mg / L).

[0070] The calculation method of sludge B recovery rate is: Mg (%) = [(b0-b1) / b0] × 100%, b0 is the Mg concentration in the magnesium-rich calcium chloride solution at the inlet of the secondary sedimentation tank (mg / L), b1 is the Mg concentration in the high-calcium polychloride solution at the outlet of the secondary sedimentation tank (mg / L).

[0071] The calculation method of NaCl recovery rate is: R (%) = [(X0-X1) / X0] × 100%, X0 is the concentration of NaCl in the regulating tank (mg / L), and X1 is the concentration of NaCl in the supernatant of the constant temperature separator (mg / L).

[0072] The calculation method of NaCl purity is: J (%) = (W1 / W0) × 100%, W1 is the mass of NaCl in the salt product (g), and W0 is the total dry mass of the salt product obtained by separation of NaCl insulated centrifuge (g).

[0073] The calculation method of KCl recovery rate is: λ (%) = [(Y0-Y1) / Y0] × 100%, Y0 is the concentration of KCl in the supernatant of the constant temperature separator (mg / L), and Y1 is the concentration of KCl in the supernatant of the KCl centrifuge separation (mg / L).

[0074] The calculation method of KCl purity is: θ (%) = (Z1 / Z0) × 100%, Z1 is the mass of KCl in the salt product (g), and Z0 is the total dry mass of the salt product obtained by evaporation and crystallization in the secondary MVR evaporator (g).

[0075] The calculation method of the purity of CaCl2 solution is: E (%) = [(u × 111 / 40) / (ρ × 10 -4 )]×100%, u is the concentration of Ca in the calcium chloride solution (mg / L), ρ is the density of the calcium chloride solution (g / cm 3 ).

[0076] Table 1: Results of reduction, detoxification and resource utilization of fly ash from incineration of domestic waste

[0077]

[0078] As can be seen from Table 1, the method of the present invention in Examples 1 to 5 can effectively recover Pb and Zn in fly ash from incineration of domestic waste, and can recover Fe, Al and Mg in fly ash in the form of hydroxides by step-by-step precipitation, which can be used as a neutralizer and flame retardant for resource utilization, achieving the ultimate reduction of fly ash and resource recovery of heavy metals. At the same time, salts such as NaCl, KCl and CaCl2 solution can be recovered, and the various indicators of the finally obtained KCl salt meet the standards of superior products in "Industrial Potassium Chloride" (GB / T7118-2008), the various indicators of NaCl salt meet the secondary standards of industrial dry salt in "Industrial Salt" (GB / T 5462-2015), and the various indicators of CaCl2 solution meet the standards of liquid calcium chloride (12~40%) in "Industrial Calcium Chloride" (GB / T 26520-2011), which can achieve resource utilization.

[0079] In Comparative Example 1, only sodium hydroxide solution was used to perform alkali washing on the fly ash. Since the addition of sodium hydroxide introduced a large amount of sodium ions, the proportion of sodium salt in the high-calcium polychloride solution was much higher than that of potassium salt, resulting in difficulty in separating sodium salt and potassium salt during the cooling crystallization salt separation process, and the final KCl salt could not meet the standard of superior grade in "Industrial Potassium Chloride" (GB / T 7118-2008); in Comparative Example 2, only potassium hydroxide solution was used to perform alkali washing on the fly ash. Since the addition of potassium hydroxide introduced a large amount of potassium ions, the high-calcium polychloride solution reached saturation faster during the evaporation and concentration process, and potassium salt precipitated together with sodium salt, resulting in a higher proportion of potassium salt in the final NaCl salt, which could not meet the secondary standard of industrial dry salt in "Industrial Salt" (GB / T 5462-2015).

Claims

1. A method for reducing, detoxifying and recycling fly ash from incineration of domestic waste, characterized in that the steps include: 1) Alkaline washing of fly ash from incineration of domestic waste; 2) The slurry after alkali washing is precipitated to obtain alkali washed fly ash, and the supernatant is subjected to electrodeposition at voltages of 1-5 V and 6-10 V, respectively, to recover Pb and Zn to obtain an alkaline salt solution; 3) acid leaching the obtained alkali-washed fly ash, and solid-liquid separation to obtain acid-leached ash residue and acidic high calcium solution; The acid leaching ash is subjected to medium-low temperature pyrolysis desorption at a temperature below 600°C; 4) Using lime milk to adjust the pH value of the acidic high calcium solution to 5.5-7.5, and precipitate to obtain sludge A and magnesium-rich calcium chloride solution; 5) adjusting the pH value of the magnesium-rich calcium chloride solution to 9-11 with the alkaline salt solution obtained in step 2), and precipitating to obtain sludge B and a high-calcium polychloride salt solution; 6) Evaporate and concentrate the high calcium polychloride salt solution to a CaCl2 concentration of 30-35wt%, separate and precipitate NaCl while hot, and then cool the liquid phase to separate KCl and CaCl2 solutions.

2. The method for reducing, detoxifying and recycling fly ash from incineration of domestic waste according to claim 1, characterized in that: The alkali solution used in the alkali washing in step 1) is a mixed solution of NaOH and KOH, and the molar ratio of NaOH to KOH is 1:3-7; the solid-liquid mass ratio of the domestic waste incineration fly ash and the alkali solution during the alkali washing is 1:1-3, and the total concentration of NaOH and KOH in the alkali solution is 1-10 mol / L.

3. The method for reducing, detoxifying and recycling fly ash from incineration of domestic waste according to claim 1, characterized in that: In step 3), hydrochloric acid is used to acid-leach the alkali-washed fly ash. During the acid-leach, the mass ratio of the alkali-washed fly ash to the hydrochloric acid is 1:0.6-1.3, and the acid-leach time is 45-90 min.

4. The method for reducing, detoxifying and recycling fly ash from incineration of domestic waste according to claim 1, characterized in that: After precipitation in step 4), sodium sulfide solution is added to the supernatant to react and sand filter to obtain a magnesium-rich calcium chloride solution; the concentration of the sodium sulfide solution is 0.1-2 mol / L, and the concentration of the added sodium sulfide is 0.25-4 mmol / L.

5. The method for reducing, detoxifying and recycling fly ash from incineration of domestic waste according to claim 1, characterized in that: In step 6), the temperature for separating NaCl is 110-115°C, the liquid phase is cooled to -5-15°C, and centrifuged to obtain KCl and CaCl2 solutions.

6. The method for reducing, detoxifying and recycling fly ash from incineration of domestic waste according to claim 1 or 5, characterized in that: In step 6), the separated KCl is further refined and purified by dissolving the KCl and passing it through a Na-type ion exchange resin, followed by evaporation and crystallization to obtain refined and purified KCl.

7. A device for reducing, detoxifying and recycling fly ash from incineration of domestic waste used in the method for reducing, detoxifying and recycling fly ash from incineration of domestic waste as claimed in any one of claims 1 to 6, characterized in that: It includes an alkaline washing reaction tank, a separate electrodeposition reaction tank, an acid leaching reaction tank, a filter press, a primary sedimentation tank, a secondary sedimentation tank, a primary MVR evaporator, a constant temperature separator, a NaCl heat preservation centrifuge, a cooling kettle and a KCl centrifuge which are sequentially connected through pipelines; The separated electrodeposition reaction pool includes a gravity sedimentation zone, a stirring and cleaning zone and an electrodeposition zone which are connected in sequence; an ash hopper is provided at the bottom of the gravity sedimentation zone and the stirring and cleaning zone, and the top is separated by a sedimentation baffle; a stirring device is provided in the stirring and cleaning zone; the electrodeposition zone is divided into a plurality of electrolytic cells by a plurality of insulating baffles, each of which is provided with a pair of electrode plates, which are connected to a rectifier; the top of the gravity sedimentation zone is connected to an alkaline washing reaction tank, the ash hopper is connected to an acid leaching reaction tank, and the outermost electrolytic cell is connected to a secondary sedimentation tank.

8. The device for reducing, detoxifying and recycling fly ash from incineration of domestic waste according to claim 7, characterized in that: An online ion analysis probe is provided at the water outlet of the separate electrodeposition reaction cell.

9. The device for reducing, detoxifying and recycling fly ash from incineration of domestic waste according to claim 7, characterized in that: The electrode plates in the electrolytic cell are divided into cathode plates and anode plates. The cathode plates are made of copper, iron or stainless steel, and the anode plates are made of graphite or titanium.

10. The device for reducing, detoxifying and recycling fly ash from incineration of domestic waste according to claim 7, characterized in that: It also includes a Na-type ion exchange resin tank, a secondary MVR evaporator and a crystallizer which are connected in sequence. The Na-type ion exchange resin tank is connected to a KCl centrifuge.

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