A method for long-term stabilization of heavy metals in household waste incineration fly ash by acid washing and water phase reaction

Abstract

The application discloses a long-term stabilization method for heavy metal pickling and water-phase reaction of household garbage incineration fly ash. The method comprises the following steps: S1, adding sulfuric acid solution to the household garbage incineration fly ash and stirring; S2, adding phosphoric acid solution, and obtaining solid products containing insoluble heavy metal phosphate and liquid products containing soluble salt through centrifugal separation; S3, carrying out first precipitation on the liquid products, discharging supernatant, adding sulfuric acid solution to the supernatant for acidification treatment, then adding a mixed solution of 5% ferrous sulfate and 5% ferric chloride for reduction flocculation treatment, and then carrying out second precipitation and subsequent third precipitation; and S4, collecting flocculation precipitates and combining into the fly ash after acidification treatment in step S1. The method can realize long-term stabilization treatment of mercury, copper, lead, zinc, cadmium, nickel, total chromium, hexavalent chromium, arsenic and selenium which are stipulated in the household garbage landfill pollution control standard (GB 16889-2008).

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of household garbage incineration fly ash disposal, in particular, especially relates to a long-term stabilization method for heavy metal pickling and water phase reaction of household garbage incineration fly ash. BACKGROUND

[0002] Garbage incineration fly ash usually adopts simple mixing + landfill treatment of stabilizer. However, not only the treatment process produces pungent smell, but also two kinds of key attention metalloid arsenic and selenium cannot be effectively disposed, at the same time, the stabilizing treatment agent itself is easy to decompose, and cannot long-term stabilize heavy metals after entering the landfill, still having great environmental risk. SUMMARY

[0003] In view of the above problems, the present application provides a household garbage incineration fly ash heavy metal and metalloid graded stabilization method, and suggests using waste sulfuric acid to pickling fly ash, so as to reduce cost by waste treating waste, and realize long-term stabilization treatment of mercury, copper, lead, zinc, cadmium, nickel, total chromium, hexavalent chromium, arsenic and selenium specified in the 'Standard for Pollution Control on Domestic Waste Landfill Site' (GB 16889-2008). The leaching toxicity of fly ash after stabilization treatment is lower than the limit value specified in GB 16889-2008, and the treated fly ash has no pungent smell, and no wastewater is generated in the treatment process.

[0004] In order to achieve the above object, the present application provides the following technical scheme:

[0005] A long-term stabilization method for heavy metal pickling and water phase reaction of household garbage incineration fly ash, comprising the following steps:

[0006] S1, adding sulfuric acid solution to household garbage incineration fly ash and stirring;

[0007] S2, adding phosphoric acid solution to the fly ash treated by sulfuric acid in step S1, and obtaining solid product containing insoluble heavy metal phosphate and liquid product containing soluble salt after centrifugal separation, and then adding slaked lime to the solid product, mixing uniformly, bagging and curing, and sending to the garbage landfill site for landfill;

[0008] S3, performing first precipitation on the liquid product containing soluble salt obtained in step S2, adding sulfuric acid solution to the supernatant for acidification treatment, then adding mixed solution of iron salt with mass fraction of 5% ferrous sulfate and 5% ferric chloride for reduction flocculation treatment, and then performing second precipitation and subsequent third precipitation;

[0009] S4, collecting the flocculation precipitates at the bottom of the first precipitation tank, the second precipitation tank, the third precipitation tank and the iron salt mixed solution storage tank, and combining into the fly ash after acidification treatment in step S1.

[0010] In the technical scheme, further, in the step S1 and the step S3, the mass concentration of the sulfuric acid solution is 0.83-2.5%.

[0011] In the technical scheme, further, in the step S1, the mass of the sulfuric acid is 3-5% of the mass of the fly ash.

[0012] In the technical scheme, further, in the step S1, the stirring time is 5-10 minutes, and the pH of the solution after the reaction is 11-11.5.

[0013] In the technical scheme, further, in the step S2, the mass concentration of the phosphoric acid solution is 2.125-8.5%.

[0014] In the technical scheme, further, in the step S2, the mass of the phosphoric acid is 1.5-3% of the mass of the fly ash.

[0015] In the technical scheme, further, in the step S2, the stirring time is 5-10 minutes, and the pH of the solution after the reaction is 9.5-11.

[0016] In the technical scheme, further, in the step S2, the mass of the slaked lime is 10% of the mass of the fly ash.

[0017] In the technical scheme, further, in the step S3, the time of the reduction flocculation treatment is 5-10 minutes.

[0018] In the technical scheme, further, in the step S3, during the acidification treatment, the pH value is 4-5.5.

[0019] In the step S1, the sulfuric acid reacts with the calcium oxide and calcium hydroxide in the fly ash generated from waste incineration to generate calcium sulfate, effectively reducing the consumption of phosphoric acid by the calcium oxide and calcium hydroxide in the fly ash.

[0020] In the step S2, in the aqueous phase, the phosphoric acid reacts with the heavy metal ions to form heavy metal-phosphate salt complex, and part of the heavy metal-phosphate salt complex is converted into hydroxyapatite structure. Meanwhile, the addition of phosphoric acid releases the metalloid arsenic and selenium into the liquid phase. After solid-liquid separation, most of the heavy metals are stably present in the solid product. The solid product and lime are mixed and then fed into a bagging machine, and the solid product is bagged, cured and landfilled. The main components of lime are Ca(OH)2 and CaO, which are highly alkaline substances. The addition of lime to the solid product after the heavy metal-phosphate salt solid phase stabilization of fly ash can keep the fly ash highly alkaline and improve its acid buffering solubility. In an alkaline condition, lime reacts with phosphoric acid and phosphate to form calcium phosphate salt, and even hydroxyapatite. Meanwhile, the calcium phosphate salt reacts with heavy metal ions to form insoluble double salt, i.e., part of the calcium ions are replaced by other heavy metal ions, thereby realizing the long-term stabilization of heavy metal ions. In addition, the addition of lime reduces the water content of the treated fly ash to less than 30%, which meets the requirements of the landfill site.

[0021] In the step S3, in addition to the high content of Cl - , Na + , K + and Ca 2+ ions, the liquid product after the heavy metal-phosphate salt stabilization treatment also contains a large amount of dissolved and released SeO4 2- , SeO3 2- , AsO4 2- , AsO3 2- and CrO4 2- ions. Since Cr, Se and As are the control indexes of the leaching toxicity of fly ash, the liquid product after the heavy metal-phosphate salt stabilization is sequentially added with a mixed solution of iron salts of sulfuric acid, ferrous sulfate and ferric chloride, and the solution is acidified by the sulfuric acid solution to keep the solution acidic. The ferrous sulfate reduces the hexavalent chromium in CrO4 2- to Cr 3+ , and the ferric chloride and ferrous sulfate make SeO4 2- , SeO3 2- , AsO4 2- and AsO3 2- generate flocculation and precipitation, thereby realizing the long-term stabilization of total chromium, hexavalent chromium, arsenic and selenium in accordance with the Pollution Control Standard for Domestic Waste Landfill Sites (GB 16889-2008).

[0022] In the step S4, the flocculation and precipitation are combined with the fly ash after the sulfuric acid acidification treatment in the step S1, and the remaining heavy metals are further stabilized using phosphoric acid, thereby realizing the long-term stable disposal and zero emission of heavy metals in the waste incineration fly ash. The supernatant obtained after the third precipitation is the acid-containing waste liquid after the complete heavy metal and metalloid stabilization treatment of fly ash, which is recycled.

[0023] The beneficial effects of the present application are:

[0024] The household garbage incineration fly ash heavy metal pickling and water phase reaction long-term stabilization method provided by the present application not only stabilizes the heavy metals in the fly ash for a long time, but also considers the disposal of two kinds of metals, arsenic and selenium, and comprehensively realizes the long-term stabilization treatment of mercury, copper, lead, zinc, cadmium, nickel, total chromium, hexavalent chromium, arsenic and selenium specified in the Standard for Pollution Control on Domestic Waste Landfill Sites (GB 16889-2008). At the same time, by suggesting the use of waste sulfuric acid and waste phosphoric acid for acid pickling and heavy metal stabilization of fly ash, the disposal cost of fly ash is reduced, the industrial application conditions of fly ash disposal are better, and the purpose of waste treatment by waste is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0026] Figure 1 The process flow chart of the method of the present application is shown in the figure;

[0027] Figure 2 The structure schematic diagram of the device used in embodiment 1 of the present application is shown in the figure;

[0028] In the figure: 1, reaction tank I, 2, reaction tank II, 3, horizontal screw centrifuge, 4, acidification and reduction treatment tank, 5, iron salt mixed solution storage tank, 6, first sedimentation tank, 7, second sedimentation tank, 8, third sedimentation tank, 9, bagging machine, 10, mixer, 11, fly ash storage bin, 12, sulfuric acid storage tank, 13, phosphoric acid storage tank, 14, lime milk storage bin, 15, screw metering scale. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0030] Embodiment 1

[0031] The household garbage incineration fly ash heavy metal pickling and water phase reaction long-term stabilization method provided by the present application is shown in the figure, which comprises the following steps: Figure 2As shown, the device used includes: fly ash storage bin 11, sulfuric acid storage tank 12, phosphoric acid storage tank 13, reaction tank I 1, horizontal screw centrifuge 3, reaction tank II 2, spiral weighing scale 15, lime storage bin 14, iron salt mixed solution storage tank 5, acidification and reduction treatment tank 4, mixing blender 10, first sedimentation tank 6, second sedimentation tank 7, third sedimentation tank 8, bagging machine 9;

[0032] The sulfuric acid storage tank 12 is provided with a supernatant inlet of the third sedimentation tank 8 and a sulfuric acid solution outlet, and the sulfuric acid solution outlet is connected with the inlet of the reaction tank I 1; the reaction tank I 1 is provided with a fly ash inlet and a reaction slurry outlet at the same time, and the reaction slurry outlet is connected with the inlet of the reaction tank II 2;

[0033] The phosphoric acid storage tank 13 is provided with a supernatant inlet of the third sedimentation tank 8 and a phosphoric acid solution outlet, and the phosphoric acid solution outlet is connected with the inlet of the reaction tank II 2; the reaction tank II 2 is provided with a reaction slurry outlet at the same time, and the reaction slurry outlet transmits the reaction slurry to the horizontal screw centrifuge 3 for solid-liquid separation;

[0034] The horizontal screw centrifuge 3 includes a liquid outlet and a solid outlet, wherein the solid outlet is connected with the mixing blender 10, and the mixing blender 10 is provided with a lime inlet and a product outlet at the same time; the lime inlet is used for adding lime, the outlet is weighed with the solid product through the spiral weighing scale 15, and the product outlet is connected with the bagging machine 9 for bagging and landfill;

[0035] The liquid outlet of the horizontal screw centrifuge 3 is connected with the first sedimentation tank 6, and the first sedimentation tank 6 is provided with a liquid outlet and a sediment collection port at the same time; the liquid outlet of the first sedimentation tank 6 is connected with the acidification and reduction treatment tank 4, and the acidification and reduction treatment tank 4 is provided with an iron salt solution inlet, a sulfuric acid solution inlet, a liquid product outlet and a sediment collection port at the same time; the iron salt solution inlet is connected with the iron salt mixed solution storage tank 5, the sulfuric acid solution inlet is connected with the sulfuric acid solution outlet of the sulfuric acid storage tank 12, and the liquid product outlet of the acidification and reduction treatment tank 4 is connected with the inlet of the second sedimentation tank 7;

[0036] The second sedimentation tank 7 is provided with a liquid outlet and a sediment collection port in addition to the inlet; the liquid outlet of the second sedimentation tank 7 is connected with the liquid inlet of the third sedimentation tank 8, and the third sedimentation tank 8 is provided with a supernatant outlet and a sediment collection port at the same time; the supernatant of the third sedimentation tank 8 is pumped back to the sulfuric acid storage tank 12 and / or the phosphoric acid storage tank 13 for recycling, so that there is no waste liquid discharge in the whole fly ash treatment process;

[0037] The iron salt mixed solution storage tank 5 is provided with a flocculation outlet at the same time, and collects the flocculation precipitates of the primary sedimentation tank, the secondary sedimentation tank, the tertiary sedimentation tank and the bottom of the iron salt mixed solution storage tank 5, and is added to the reaction tank II 2 to ensure that all heavy metals and metalloids in the fly ash are converted into solid phase and are long-term stabilized.

[0038] The application will be further described below in combination with specific embodiments:

[0039] The application provides a long-term stabilization method for heavy metal pickling and water phase reaction of household garbage incineration fly ash, comprising the following steps:

[0040] S1, tap water is used to dilute 50% sulfuric acid to obtain a sulfuric acid solution with a concentration of 0.83-2.5%, the sulfuric acid solution is injected into a reaction tank I1, fly ash is quantitatively added by a spiral metering scale (the sulfuric acid addition amount is 3-5% of the mass of the fly ash), the final pH of the solution in the reaction tank I1 is controlled at 11-11.5, the reaction time is 5-10 minutes, and the product after reaction is unloaded from the reaction tank I1 and enters a reaction tank II2;

[0041] S2, tap water is used to dilute 85% concentrated phosphoric acid to obtain a phosphoric acid solution with a concentration of 0.5-5%, the fly ash treated by sulfuric acid is added into the reaction tank II2 at the same time as the phosphoric acid solution (the phosphoric acid addition amount is 1.5-3% of the mass of the fly ash), stirring is performed for about 5-10 minutes, the final pH of the solution in the reaction tank is controlled at 9.5-11, and after the stirring is completed, the product is introduced into a horizontal screw centrifuge 3 for solid-liquid separation to obtain a solid product containing insoluble heavy metal phosphate and a liquid product containing soluble salt, wherein the solid product containing insoluble heavy metal phosphate and slaked lime (a mixture of CaO and Ca(OH)2) are simultaneously poured into a mixing stirrer 10, uniformly stirred and then bagged and landfilled, and the slaked lime addition amount is about 10% of the mass of the original fly ash;

[0042] S3, the liquid product containing soluble salt is discharged into a first sedimentation tank 6, supernatant is introduced into an acidification and reduction treatment tank 4 after sedimentation treatment, and a sulfuric acid solution with a concentration of 0.83-2.5% is injected, so that the pH value of the solution is controlled at 4-5.5, then a 5% ferrous sulfate and 5% ferric chloride iron salt mixed solution is added from an iron salt solution storage tank, and after continuous stirring and reaction for 5-10 minutes, the product is unloaded into a second sedimentation tank 7, and a third sedimentation tank 8 is connected in succession for continuous sedimentation;

[0043] S4, a small amount of flocculation precipitate at the bottom of the first sedimentation tank, the second sedimentation tank, the third sedimentation tank and the iron salt mixed solution storage tank 5 is collected and added into the reaction tank II2, and the supernatant at the outlet of the third sedimentation tank 8 is an acid-containing waste liquid after the complete heavy metal and metalloid stabilization treatment of the fly ash, which is pumped back to a sulfuric acid storage tank 12 and / or a phosphoric acid storage tank 13 for recycling, so that all heavy metals can be separated in the solid phase, and no waste acid is discharged.

[0044] In step S1, the sulfuric acid solution is added to convert Ca(OH)2 in the fly ash into CaSO4, reduce the consumption of phosphoric acid, and make the added phosphoric acid more fully react with heavy metal ions in the next step; in step S2, the fly ash slurry after acid washing is mixed with a phosphoric acid solution, and in the aqueous phase, heavy metal ions react with phosphoric acid to form heavy metal-phosphoric acid calcium salt complexes, part of which is converted into hydroxyapatite structures, so that the heavy metal solid phase is precipitated, and after solid-liquid separation, the solid phase is mixed with slaked lime to realize long-term stabilization of most of the heavy metals in the fly ash and landfill; in step S3, the chromium, arsenic, and selenium that have not been effectively disposed of in the liquid phase continue to be added with a sulfuric acid solution to keep the solution acidic, and a mixed solution of ferrous sulfate and ferric chloride is added to make the heavy metals be reduced or flocculated and precipitated, and after the supernatant and the precipitate are separated, the two phases are all returned to the fly ash and phosphoric acid reaction container for solidification again, and no waste liquid is discharged in the whole process, so that the heavy metals and metalloids are safely and effectively disposed of for long-term stabilization. Due to the large amount of sulfuric acid used, it is recommended to use waste sulfuric acid to reduce the system treatment cost, which is more conducive to industrial application.

[0045] Example 2

[0046] A fly ash from a certain waste incineration power plant, after analysis and testing, has a water content of about 2.7%, a pH of 12.4, and the main components of the fly ash are as follows:

[0047] Table 1 Element composition of fly ash from a certain waste incineration power plant (unit: %)

[0048] Item Ca O Cl Na K S Fly ash 30.16 28.61 16.53 9.01 2.72 5.73 Item Si Fe Al Mg Zn Pb Fly ash 1.91 1.38 0.71 0.54 0.48 0.17 Item Br Mn Cr Cd As Se Fly ash 0.24 0.03 0.02 0.02 0.01 0.001

[0049] The method for long-term stabilization of heavy metal acid washing and aqueous phase reaction of the fly ash from the waste incineration power plant comprises the following steps:

[0050] S1, mix the fly ash from the waste incineration power plant with 1% sulfuric acid solution (mass concentration) (water to fly ash ratio 5:1, the water to fly ash ratio is the volume of sulfuric acid to the mass of fly ash, the volume of sulfuric acid is ml, and the mass of fly ash is g), the amount of sulfuric acid added is 5% of the mass of fly ash, fully stir in the reaction kettle for at least 10 minutes to form a slurry, and adjust the pH range to 11-11.5;

[0051] S2, mix the fly ash slurry after sulfuric acid neutralization treatment with 0.6% phosphoric acid solution (mass concentration) (phosphoric acid solution to original ash ratio 5:1), the amount of phosphoric acid added is 3% of the fly ash, fully stir in the reaction kettle for at least 10 minutes, adjust the pH range to 11-11.5, and after solid-liquid separation, obtain a solid product containing insoluble heavy metal phosphate and a liquid product containing soluble salt, and mix the solid product with slaked lime;

[0052] S3, after the liquid product is rested, the lower precipitate is removed, 1% sulfuric acid solution (mass concentration) is added to adjust the pH to 4-5.5, then a mixed solution of iron salts with a mass concentration of 5% ferrous sulfate and 5% ferric chloride chloride is added at a ratio of 1:1, the mixture is uniformly mixed for half an hour, and then solid-liquid separation is performed again;

[0053] The solid product containing insoluble heavy metal phosphate and the lime mixture, and the liquid product containing soluble salt, and the precipitate after the reaction of the two with the sulfuric acid and the mixed solution of iron salts are successively subjected to leaching according to the “Solid Waste Toxicity Leaching Method Acetate Buffer Solution Method” (HJ300-2007), and the concentrations of all heavy metals and metalloids meet the “Standard for Pollution Control on Domestic Waste Landfill Sites” (GB 16889-2008).

[0054] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0055] The above description of the disclosed embodiments enables those skilled in the art to carry out or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for long-term stabilization of heavy metals in household waste incineration fly ash by acid washing and water phase reaction, characterized by, The method comprises the following steps: S1, adding sulfuric acid solution to household garbage incineration fly ash and stirring; S2, adding phosphoric acid solution to the fly ash treated by sulfuric acid in step S1, and centrifuging to obtain solid product containing insoluble heavy metal phosphate and liquid product containing soluble salt, and adding lime to the solid product, mixing uniformly, bagging and curing, and sending to landfill site for landfill; S3, the liquid product containing soluble salt obtained in step S2 is subjected to first precipitation, acidification treatment by adding sulfuric acid solution in supernatant, and reduction flocculation treatment by adding 5% ferrous sulfate and 5% ferric chloride mixed solution, and then second precipitation and subsequent third precipitation; S4, collecting the flocculation precipitate at the bottom of the first precipitation tank, the second precipitation tank, the third precipitation tank and the iron salt mixed solution storage tank, and combining into the fly ash after acidification treatment in step S1.

2. The long-term stabilization method of heavy metal pickling and water phase reaction according to claim 1, characterized by, In step S1 and step S3, the mass concentration of the sulfuric acid solution is 0.83-2.5%.

3. The long-term stabilization method of heavy metal pickling and water phase reaction according to claim 1, characterized by, In step S1, the mass of sulfuric acid is 3-5% of the mass of fly ash.

4. The long-term stabilization method of heavy metal pickling and water phase reaction according to claim 1, characterized by, In step S1, the stirring time is 5-10 minutes, and the pH of the solution after reaction is 11-11.

5.

5. The long-term stabilization method of heavy metal pickling and water phase reaction according to claim 1, characterized by, In step S2, the mass concentration of the phosphoric acid solution is 0.5-5%.

6. The long-term stabilization method of heavy metal pickling and water phase reaction according to claim 1, characterized by, In step S2, the mass of phosphoric acid is 1.5-3% of the mass of fly ash.

7. The long-term stabilization method of heavy metal pickling and water phase reaction according to claim 1, characterized by, In step S2, the stirring time is 5-10 minutes, and the pH of the solution after reaction is 9.5-11.

8. The long-term stabilization method of heavy metal pickling and water phase reaction according to claim 1, characterized by, In step S2, the mass of lime is 10% of the mass of fly ash.

9. The long-term stabilization method of heavy metal pickling and water phase reaction according to claim 1, characterized by, In step S3, the reduction flocculation treatment time is 5-10 minutes.

10. The method for long-term stabilization of heavy metal pickling and aqueous phase reactions according to claim 1, characterized in that, In step S3, the pH value during acidification treatment is 4-5.5.

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