A method for synergistically removing heavy metals in fly ash acidic leaching solution wastewater by using hexavalent chromium as a trigger

Abstract

The application discloses a method for removing heavy metals in fly ash acidic leaching solution wastewater with hexavalent chromium as a trigger agent, which comprises the following steps: (1) adjusting the content of hexavalent chromium in the fly ash acidic leaching solution, and adjusting the pH to 3-6 to obtain treated wastewater; (2) pumping the treated wastewater into a fixed bed filled with sponge iron through a peristaltic pump, and further treating the effluent through sodium sulfide, then performing precipitation and filtration; introducing Cr(VI) into the acid leaching solution of medical waste incineration fly ash (FA), and revealing the space-time migration law of multiple target heavy metals (HMs) through an s-Fe0 packed bed column reactor; the results verify that most residual heavy metals can be efficiently removed, accompanied by the cooperative regeneration of passivated sponge iron; the research enriches the basic theory of ZVI packed bed reactor cooperative regeneration, and provides a novel, economical and sustainable strategy for the harmless treatment of fly ash leaching solution.

Description

Technical Field

[0001] This invention relates to the field of heavy metal wastewater treatment technology, specifically a method for the synergistic removal of heavy metals from acidic wastewater using hexavalent chromium as a trigger. Background Technology

[0002] Medical waste and municipal solid waste are mostly treated by high-temperature incineration to achieve volume reduction and harmlessness. The solids produced after incineration mainly consist of bottom ash and fly ash. Fly ash refers to the residue collected in the flue gas purification system and heat recovery system. During incineration, a large amount of heavy metals volatilize into the flue gas due to high temperatures, resulting in a high concentration of volatile heavy metals in the fly ash. Therefore, fly ash is classified as hazardous waste, and stabilizing it to transform it into a safer form is a meaningful approach. Acid washing transfers the exchangeable heavy metal ions remaining in the fly ash to the pickling solution. Typically, pickling solutions contain large amounts of heavy metal ions (copper, zinc, lead, cadmium, aluminum, silver, etc.). These pollutants are non-biodegradable and easily accumulate in ecosystems and food chains, posing a serious threat to human health. Therefore, it is urgent to deeply treat the heavy metal ions in the pickling solution to meet wastewater discharge standards. Various technologies have been developed for the treatment of heavy metal wastewater, including reduction-precipitation, ion exchange, physical adsorption, membrane separation, electrochemical methods, and biosorption. While effective, these methods are often costly. This highlights the necessity of developing more sustainable and economical remediation technologies, among which chemical reduction has attracted attention due to its high efficiency and low cost.

[0003] Zero-valent iron (ZVI) can donate electrons and act as a highly efficient reducing agent, simultaneously removing heavy metal ions such as Pb(II) and Cr(VI), representing a promising technological approach. In terms of reaction mechanism, ZVI, as an electron donor, can reduce toxic heavy metal ions to less soluble forms (e.g., Cr(VI) → Cr(III), Pb(II) → Pb(O)), while iron corrosion products can further enhance the removal effect through adsorption and co-precipitation. In engineering applications (such as packed bed reactors and permeable reaction walls), millimeter-sized sponge iron (s-Fe)... 0 It exhibits significant advantages: compared to nanoscale ZVI (nZVI, 500–5000 RMB / kg), it is less expensive (approximately 4 RMB / kg), has strong reducibility, is environmentally friendly, and is easily magnetically separable. However, its long-term performance is limited by spontaneous surface passivation, a process accompanied by Fe 2+ / Fe 3+ The release of ions and the formation of iron hydroxides and oxides. These passivation products can hinder electron transfer or fix contaminants through adsorption and co-precipitation, thereby reducing reactivity. Therefore, developing regeneration methods for ZVI passivation layers is crucial for their sustainable application, especially in the presence of coexisting ions.

[0004] This invention proposes an innovative approach: utilizing acidic leachate from incinerated fly ash of medical or municipal waste with a low-concentration Cr(VI) oxidant to achieve synergistic removal of the ZVI surface passivation layer and simultaneous removal of heavy metals. The underlying mechanism lies in the coupling effect of the acidic leachate and the Cr(VI) oxidant, which jointly promotes the efficient stripping of the passivation layer, thereby achieving the synergistic removal of Cr(VI) and other target heavy metals in the acidic system. This provides technical support for the harmless treatment and resource utilization of fly ash. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the synergistic removal of heavy metals from acidic fly ash wastewater using hexavalent chromium as a trigger, thereby solving the problems mentioned in the background section. This invention utilizes an acidic heavy metal leaching solution and a low-concentration Cr(VI) oxidant to achieve synergistic removal of the ZVI surface passivation layer and simultaneous removal of heavy metals.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for the synergistic removal of heavy metals from acidic wastewater using hexavalent chromium as a trigger, comprising the following steps:

[0008] (1) Adjust the hexavalent chromium content in the acidic heavy metal wastewater and adjust the pH to 3-6 to obtain the wastewater to be treated;

[0009] (2) The wastewater to be treated is pumped into a fixed bed filled with one or more layers of sponge iron through a peristaltic pump. Sodium sulfide is added to the effluent, and then sedimentation and filtration are carried out.

[0010] Furthermore, step (1) also includes the following steps: adjusting the hexavalent chromium content in the acidic heavy metal wastewater to 10-90 mg / L.

[0011] Further, in step (2), the particle size of the sponge iron is 0-8 mm, preferably 1-3 mm.

[0012] Further, in step (2), the wastewater to be treated is pumped into a fixed bed containing sponge iron at a flow rate of 0.5-2.5 mL / min.

[0013] Furthermore, in step (2), the amount of sponge iron added to each layer is 2.0 g / cm³. 2 -15 g / cm 2 .

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] This invention is the first to apply sponge iron s-Fe0 The introduction of Cr(VI) ion inducers into a packed bed reactor simultaneously promotes the removal of most target heavy metal ions from acidic fly ash leachate wastewater and synergistically removes millimeter-sized s-Fe. 0 The passivation layer on the surface achieves a synergistic improvement in reaction performance.

[0016] Millimeter-scale low-cost s-Fe 0 Packed bed reactors can efficiently remove Cu, Cd, Ag, Al, and Pb ions in acidic fly ash leachate, and also achieve the removal of s-Fe. 0 Efficient peeling and in-situ regeneration of the interface passivation layer. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a fixed-bed reactor. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] sponge iron (s-Fe) 0 The samples were divided into four different particle sizes: <1 mm, 1-3 mm, 3-5 mm and 5-8 mm. After verification, 1-3 mm was finally selected for further fixed-bed reactor experiments.

[0020] A 100 mg / L Cr(VI) stock solution was prepared by dissolving 0.2829 g of K₂Cr₂O₇ dried at 120 °C for 2 hours in 1000 mL of deionized water (resistivity 18.3 MΩ·cm). The working solution was obtained by diluting the stock solution to the desired concentration, and the initial pH was adjusted by 0.1 M HCl and 0.1 M NaOH.

[0021] Before use, s-Fe 0 Activation treatment is required: s-Fe 0 Mix with 2% (v / v) dilute hydrochloric acid solution and react under sonication for 3 minutes, then rinse with ultrapure water to neutral pH to remove surface impurities and expose active sites.

[0022] To investigate the effect of coexisting ions on the removal of Cr(VI), the reduction reaction of the ZVI system was found to be easily modulated by environmental factors, such as the type and concentration of coexisting cations. The effects of ionic strength (IS, using NaCl as a simulated electrolyte) and the presence of different cations (K+) were investigated. + Ca2+ Mg 2+ The effect of ) on the Cr(VI) removal rate constant.

[0023] The results showed that as the ionic strength increased from 10 mM to 100 mM, the rate constant of Cr(VI) increased from 4.29 × 10⁻⁶ mM to 100 mM. -2 min -1 Rising to 7.29×10 -2 min -1 This indicates that moderate ionic strength can promote the reaction. Furthermore, Ca... 2+ Mg 2+ The presence of [elements] significantly improved the removal efficiency of Cr(VI), possibly due to altering the solution charge distribution, promoting flocculation, or enhancing the surface charge of ZVI, while K [elements]... + The impact is relatively small.

[0024] In summary, Ca 2+ Mg 2+ The presence of isocations facilitates the reduction of Cr(VI). Therefore, it can be inferred that in subsequent s-Fe... 0 In packed bed reactors, these coexisting ions have a significant impact on heavy metal removal behavior.

[0025] Example 1

[0026] To evaluate s-Fe 0 (1-3 mm) In a packed bed reactor (column inner diameter 3 cm, each layer height 10 cm, 3 layers of sponge iron particles sequentially packed, each layer containing 40 g s-Fe), 0 Scale-up feasibility in (1–3 mm) was assessed by using acidic leachate from medical waste incineration fly ash (FA) as influent (K). + 1430 mg / L; Na + 11800 mg / L; Ca 2+ 264.4 mg / L; Zn 2+ 488.97 mg / L; Cu 2+ 12.34 mg / L; Pb 2+ 7.68 mg / L; Cd 2+ 1.24 mg / L; Al 3+ 2.73 mg / L; Ag + 0.087 mg / L; Mg 2+12.8 mg / L; Si 3.7 mg / L; initial pH=4.5); flow rate V=1.5 mL / min; top-down flow, aeration rate of 0.8 L / min (enhancing oxidation reaction, promoting iron corrosion and enhancing redox-driven metal precipitation), Cr(VI) content adjusted to 20 mg / L. This influent is used for both removing s-Fe 0 The surface passivation layer is also used to simultaneously remove residual target heavy metals (HMs).

[0027] Table 1 compares the effects of adding Cr(VI) inducer to acidic fly ash leachate on the spatiotemporal behavior of various HMs and physicochemical parameters. The results show that the addition of 20 mg / L Cr(VI) and the use of a three-layer modified s-Fe... 0 After the packed bed (40 g per layer), the removal efficiency of Cu, Pb, Al, and Cd was significantly improved (except for Zn), and the effluent met the discharge standards of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) (e.g., Cu: 0.5-2.0 mg / L, Pb: 1.0 mg / L, Ag: 0.5 mg / L, Cd: 0.1 mg / L, Zn: 2-5 mg / L, Cr(VI): 0.5 mg / L, Cr...). total (1.5 mg / L, pH: 6-8). This indicates that the addition of Cr(VI) inducer to the acidic leachate promoted the removal of target HMs and s-Fe. 0 Effective removal of the corrosion passivation layer was achieved; the enhanced Cd removal may be related to the fact that the presence of Cr(VI) strengthened the removal of the iron-containing oxide passivation layer and improved its interfacial adsorption properties. For residual Zn in the column chromatography solution... 2+ Continue adding Na2S solution (2 mol / L). This advanced treatment can significantly improve the removal efficiency (final concentration 1.89 mg / L) and meet the discharge standard requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0028] Table 1. Effect of adding 20 mg / L hexavalent chromium on metal ion removal (40 g / layer, 3 layers in total)

[0029] Time (h) 5 10 15 20 Cu 4.35 2.56 1.78 0.963 Pb 6.59 4.32 1.23 0.685 Ag 0.0437 0.0385 0.0341 0.0296 Al 2.49 2.38 2.27 1.05 Cd 0.057 0.063 0.051 0.024 <![CDATA[Cr 6+ ]]> 0.11 0.17 0.06 0.02 <![CDATA[Cr total ]]> 0.19 0.14 0.15 0.13

[0030] Example 2

[0031] s-Fe 0 (1-3 mm) packed bed reactor (3 cm inner diameter of column, 10 cm height of each layer, 3 layers packed, 25 gs-Fe per layer) 0 In (1–3 mm) samples, acidic leachate from medical waste incineration fly ash (FA) was selected as the influent (K). +1430 mg / L; Na + 11800 mg / L; Ca 2+ 264.4 mg / L; Zn 2+ 488.97 mg / L; Cu 2+ 12.34 mg / L; Pb 2+ 7.68 mg / L; Cd 2+ 1.24 mg / L; Al 3+ 2.73 mg / L; Ag + 0.087 mg / L; Mg 2+ 12.8 mg / L; Si 3.7 mg / L; initial pH=4.5); flow rate V=1.5 mL / min; top-down flow, aeration rate of 0.8 L / min, Cr(VI) content adjusted to 20 mg / L.

[0032] Table 2 compares the effects of adding Cr(VI) inducer to acidic fly ash leachate on the spatiotemporal behavior of various HMs and physicochemical parameters. The results show that the addition of 20 mg / L Cr(VI) and the use of a three-layer modified s-Fe... 0 After the packed bed (25 g per layer), the removal efficiency of Cu, Pb, Al, and Cd was significantly improved (except for Zn), and the effluent met the discharge standards of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) (e.g., Cu: 0.5-2.0 mg / L, Pb: 1.0 mg / L, Ag: 0.5 mg / L, Cd: 0.1 mg / L, Zn: 2-5 mg / L, Cr(VI): 0.5 mg / L, Cr...). total (1.5 mg / L, pH: 6-8). This indicates that the addition of Cr(VI) inducer to the acidic leachate promoted the removal of target HMs and s-Fe. 0 Effective removal of the corrosion passivation layer was achieved; the enhanced Cd removal may be related to the fact that the presence of Cr(VI) strengthened the removal of the iron-containing oxide passivation layer and improved its interfacial adsorption properties. For residual Zn in the column chromatography solution... 2+ Continue adding Na2S solution (2 mol / L). This advanced treatment can significantly improve the removal efficiency (final concentration 2.36 mg / L) and meet the discharge standard requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0033] Table 2 Effect of adding 20 mg / L hexavalent chromium on metal ion removal (25 g / layer, 3 layers in total)

[0034] Time (h) 5 10 15 20 Cu 4.69 2.68 1.89 1.25 Pb 5.98 3.88 1.58 0.871 Ag 0.0405 0.0363 0.0327 0.0239 Al 0.396 0.278 0.188 0.216 Cd 0.011 0.013 0.012 0.008 <![CDATA[Cr 6+ ]]> 0.049 0.055 0.029 0.037 <![CDATA[Cr total ]]> 0.115 0.081 0.071 0.069

[0035] Example 3

[0036] s-Fe 0 (1–3 mm) packed bed reactor (3 cm inner diameter of column, 10 cm height per layer, 3 layers packed, 50 gs-Fe per layer) 0 In (1–3 mm) samples, acidic leachate from medical waste incineration fly ash (FA) was selected as the influent (K). + 1430 mg / L; Na + 11800 mg / L; Ca 2+ 264.4 mg / L; Zn 2+ 488.97 mg / L; Cu 2+ 12.34 mg / L; Pb 2+ 7.68 mg / L; Cd 2+ 1.24 mg / L; Al 3+ 2.73 mg / L; Ag + 0.087 mg / L; Mg 2+ 12.8 mg / L; Si 3.7 mg / L; initial pH=4.5); flow rate V=1.5 mL / min; top-down flow, aeration rate of 0.8 L / min, Cr(VI) content adjusted to 20 mg / L. This influent is used for both removing s-Fe 0 The surface passivation layer is also used to simultaneously remove residual target heavy metals (HMs).

[0037] Table 3 compares the effects of adding Cr(VI) inducer to acidic fly ash leachate on the spatiotemporal behavior of various HMs and physicochemical parameters. The results show that the addition of 20 mg / L Cr(VI) and the use of a three-layer modified s-Fe... 0 After the packed bed (50 g per layer) was used, the removal efficiency of Cu, Pb, Al, and Cd was significantly improved (except for Zn). The effluent all met the discharge standards of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) (e.g., Cu: 0.5-2.0 mg / L, Pb: 1.0 mg / L, Ag: 0.5 mg / L, Cd: 0.1 mg / L, Zn: 2-5 mg / L, Cr(VI): 0.5 mg / L, Cr...). total (1.5 mg / L, pH: 6-8). This indicates that the addition of Cr(VI) inducer to the acidic leachate promoted the removal of target HMs and s-Fe. 0 Effective removal of the corrosion passivation layer was achieved; the enhanced Cd removal may be related to the fact that the presence of Cr(VI) strengthened the removal of the iron-containing oxide passivation layer and improved its interfacial adsorption properties. For residual Zn in the column chromatography solution... 2+Continue adding Na2S solution (2 mol / L). This advanced treatment can significantly improve the removal efficiency (final concentration 2.59 mg / L) and meet the discharge standard requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0038] Table 3 Effect of adding 20 mg / L hexavalent chromium on metal ion removal (50 g / layer, 3 layers in total)

[0039] Time (h) 5 10 15 20 Cu 4.38 1.97 1.23 0.664 Pb 5.78 2.56 1.89 0.263 Ag 0.0382 0.0341 0.0308 0.0225 Al 0.376 0.262 0.177 0.203 Cd 0.0104 0.0122 0.0113 0.0075 <![CDATA[Cr 6+ ]]> 0.0464 0.0518 0.0274 0.0349 <![CDATA[Cr total ]]> 0.108 0.076 0.067 0.065

[0040] Example 4

[0041] s-Fe 0 (1–3 mm) in a packed bed reactor (3 cm inner diameter column, 10 cm height per layer, 3 layers packed, 80 g s-Fe per layer) 0 In (1–3 mm) samples, acidic leachate from medical waste incineration fly ash (FA) was selected as the influent (K). + 1430 mg / L; Na + 11800 mg / L; Ca 2+ 264.4 mg / L; Zn 2+ 488.97 mg / L; Cu 2+ 12.34 mg / L; Pb 2+ 7.68 mg / L; Cd 2+ 1.24 mg / L; Al 3+ 2.73 mg / L; Ag + 0.087 mg / L; Mg 2+ 12.8 mg / L; Si 3.7 mg / L; initial pH=4.5); flow rate V=1.5 mL / min; top-down flow, aeration rate of 0.8 L / min, Cr(VI) content adjusted to 20 mg / L. This influent is used for both removing s-Fe 0 The surface passivation layer is also used to simultaneously remove residual target heavy metals (HMs).

[0042] Table 4 compares the effects of adding Cr(VI) inducer to acidic fly ash leachate on the spatiotemporal behavior of various HMs and physicochemical parameters. The results show that the addition of 20 mg / L Cr(VI) and the use of a three-layer modified s-Fe... 0After the packed bed (80 g per layer), the removal efficiency of Cu, Pb, Al, and Cd was significantly improved (except for Zn), and the effluent met the discharge standards of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) (e.g., Cu: 0.5-2.0 mg / L, Pb: 1.0 mg / L, Ag: 0.5 mg / L, Cd: 0.1 mg / L, Zn: 2-5 mg / L, Cr(VI): 0.5 mg / L, Cr...). total (1.5 mg / L, pH: 6-8). This indicates that the addition of Cr(VI) inducer to the acidic leachate promoted the removal of target HMs and s-Fe. 0 Effective removal of the corrosion passivation layer was achieved; the enhanced Cd removal may be related to the fact that the presence of Cr(VI) strengthened the removal of the iron-containing oxide passivation layer and improved its interfacial adsorption properties. For residual Zn in the column chromatography solution... 2+ Continue adding Na2S solution (2 mol / L). This advanced treatment can significantly improve the removal efficiency (final concentration 3.02 mg / L) and meet the discharge standard requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0043] Table 4. Effect of adding 20 mg / L hexavalent chromium on metal ion removal (80 g / layer, 3 layers in total)

[0044] Time (h) 5 10 15 20 Cu 4.05 2.42 1.71 0.637 Pb 5.34 2.26 1.02 0.252 Ag 0.0369 0.0329 0.0296 0.0216 Al 0.362 0.251 0.170 0.194 Cd 0.0100 0.0117 0.0108 0.0072 <![CDATA[Cr 6+ ]]> 0.0447 0.0494 0.0263 0.0336 <![CDATA[Cr total ]]> 0.104 0.073 0.064 0.062

[0045] Example 5

[0046] s-Fe 0 (1–3 mm) in a packed bed reactor (3 cm inner diameter column, 10 cm height per layer, 3 layers packed, 40 g s-Fe per layer) 0 In (1–3 mm) samples, acidic leachate from medical waste incineration fly ash (FA) was selected as the influent (K). + 1430 mg / L; Na + 11800 mg / L; Ca 2+ 264.4 mg / L; Zn 2+ 488.97 mg / L; Cu 2+ 12.34 mg / L; Pb 2+ 7.68 mg / L; Cd 2+ 1.24 mg / L; Al 3+ 2.73 mg / L; Ag + 0.087 mg / L; Mg 2+12.8 mg / L; Si 3.7 mg / L; initial pH=4.5); flow rate V=1.5 mL / min; top-down flow, aeration rate of 0.8 L / min, Cr(VI) content adjusted to 10 mg / L. This influent is used for both removing s-Fe2+ and... 0 The surface passivation layer is also used to simultaneously remove residual target heavy metals (HMs).

[0047] Table 5 compares the effects of adding Cr(VI) inducer to acidic fly ash leachate on the spatiotemporal behavior of various HMs and physicochemical parameters. The results show that the addition of 10 mg / L Cr(VI) and the use of a three-layer modified s-Fe... 0 After the packed bed (40 g per layer), the removal efficiency of Cu, Pb, Al, and Cd was significantly improved (except for Zn), and the effluent met the discharge standards of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) (e.g., Cu: 0.5-2.0 mg / L, Pb: 1.0 mg / L, Ag: 0.5 mg / L, Cd: 0.1 mg / L, Zn: 2-5 mg / L, Cr(VI): 0.5 mg / L, Cr...). total (1.5 mg / L, pH: 6-8). This indicates that the addition of Cr(VI) inducer to the acidic leachate promoted the removal of target HMs and s-Fe. 0 Effective removal of the corrosion passivation layer was achieved; the enhanced Cd removal may be related to the fact that the presence of Cr(VI) strengthened the removal of the iron-containing oxide passivation layer and improved its interfacial adsorption properties. For residual Zn in the column chromatography solution... 2+ Continue adding Na2S solution (2 mol / L). This advanced treatment can significantly improve the removal efficiency (final concentration 3.91 mg / L) and meet the discharge standard requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0048] Table 5. Effect of adding 10 mg / L hexavalent chromium on metal ion removal (40 g / layer, 3 layers in total)

[0049] Time (h) 5 10 15 20 Cu 4.90 3.96 2.13 1.87 Pb 6.39 4.17 2.88 0.89 Ag 0.0486 0.0421 0.0373 0.0324 Al 2.75 2.59 2.53 1.16 Cd 0.0625 0.0701 0.0563 0.0266 <![CDATA[Cr 6+ ]]> 0.121 0.186 0.066 0.022 <![CDATA[Cr total ]]> 0.211 0.154 0.162 0.141

[0050] Example 6

[0051] s-Fe 0 (1–3 mm) in a packed bed reactor (3 cm inner diameter column, 10 cm height per layer, 3 layers packed, 40 g s-Fe per layer) 0 In (1–3 mm) samples, acidic leachate from medical waste incineration fly ash (FA) was selected as the influent (K). + 1430 mg / L; Na +11800 mg / L; Ca 2+ 264.4 mg / L; Zn 2+ 488.97 mg / L; Cu 2+ 12.34 mg / L; Pb 2+ 7.68 mg / L; Cd 2+ 1.24 mg / L; Al 3+ 2.73 mg / L; Ag + 0.087 mg / L; Mg 2+ 12.8 mg / L; Si 3.7 mg / L; initial pH=4.5); flow rate V=1.5 mL / min; top-down flow, aeration rate of 0.8 L / min, Cr(VI) content adjusted to 50 mg / L. This influent is used for both removing s-Fe 0 The surface passivation layer is also used to simultaneously remove residual target heavy metals (HMs).

[0052] Table 6 compares the effects of adding Cr(VI) inducer to acidic fly ash leachate on the spatiotemporal behavior of various HMs and physicochemical parameters. The results show that the addition of 50 mg / L Cr(VI) and the use of a three-layer modified s-Fe... 0 After the packed bed (40 g per layer), the removal efficiency of Cu, Pb, Al, and Cd was significantly improved (except for Zn), and the effluent met the discharge standards of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) (e.g., Cu: 0.5-2.0 mg / L, Pb: 1.0 mg / L, Ag: 0.5 mg / L, Cd: 0.1 mg / L, Zn: 2-5 mg / L, Cr(VI): 0.5 mg / L, Cr...). total (1.5 mg / L, pH: 6-8). This indicates that the addition of Cr(VI) inducer to the acidic leachate promoted the removal of target HMs and s-Fe. 0 Effective removal of the corrosion passivation layer was achieved; the enhanced Cd removal may be related to the fact that the presence of Cr(VI) strengthened the removal of the iron-containing oxide passivation layer and improved its interfacial adsorption properties. For residual Zn in the column chromatography solution... 2+ Continue adding Na2S solution (2 mol / L). This advanced treatment can significantly improve the removal efficiency (final concentration 2.69 mg / L) and meet the discharge standard requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0053] Table 6. Effect of adding 50 mg / L hexavalent chromium on metal ion removal (40 g / layer, 3 layers in total)

[0054] Time (h) 5 10 15 20 Cu 4.83 3.15 1.02 0.588 Pb 5.82 3.74 2.54 0.835 Ag 0.0397 0.0346 0.0302 0.0262 Al 2.18 2.12 2.02 0.93 Cd 0.050 0.055 0.045 0.021 <![CDATA[Cr 6+ ]]> 0.096 0.148 0.052 0.018 <![CDATA[Cr total ]]> 0.168 0.125 0.134 0.115

[0055] Comparative Example 1

[0056] The continuous flow fixed bed experiment was conducted using an acrylic glass column with an inner diameter of 3 cm and a layer height of 10 cm. Four layers of sponge iron particles (40 g s-Fe per layer) were sequentially packed into the column. 0 (1–3 mm). Each layer is approximately 4.5 cm high, with sampling ports between layers. The influent is actual acid leachate from fly ash from medical waste incineration (initial pH=4.5), containing heavy metal ions such as Cu, Zn, Pb, Ag, and Al, as well as a high concentration of K. + Na + Ca 2+ Mg 2+ The main components of the cationic (medical fly ash acid leaching solution) are: K + 1430 mg / L; Na + 11800 mg / L; Ca 2+ 264.4 mg / L; Zn 2+ 488.97 mg / L; Cu 2+ 12.34 mg / L; Pb 2+ 7.68 mg / L; Cd 2+ 1.24 mg / L; Al 3+ 2.73 mg / L; Ag + 0.087 mg / L; Mg 2+ 12.8 mg / L; Si 3.7 mg / L; initial pH=4.5). Influent flowed downwards through four layers of sponge iron via a peristaltic pump at a flow rate of 1.5 mL / min, with an aeration rate of 0.8 L / min. Effluent from each layer was sampled periodically to determine the residual heavy metal concentration and calculate the removal efficiency.

[0057] Table 7 shows the spatiotemporal distribution of various HMs (Cu, Pb, Ag, Al, Cd, Zn) during long-term operation; after 20 hours, the effluent did not fully meet the discharge standards of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) (e.g., Cu: 0.5-2.0 mg / L, Pb: 1.0 mg / L, Ag: 0.5 mg / L, Cd: 0.1 mg / L, Zn: 2-5 mg / L, Cr(VI): 0.5 mg / L, Cr...). total : 1.5 mg / L, pH: 6-8). Specifically, the removal of Cu, Pb, and Ag was significant in the first layer, with smaller changes in subsequent layers, indicating rapid reduction at the inlet. This thermodynamic driving force is consistent with the standard electrode potential (e.g., E). 0 (Cu2+ / Cu)=0.34 V; E 0 (Pb 2+ / Pb)=−0.13 V;E 0 (Ag + / Ag)=0.798 V). In comparison, Al(E) 0 (Al 3+ / Al)=−1.662 V) decreases only slightly along the path, similar to s-Fe 0 (E) 0 (Fe 2+ / Fe)=−0.44 V) has limited direct reduction reactivity, and its removal is mainly attributed to co-precipitation (Al) 3+ +3OH⁻→Al(OH)₃) adsorption with newly formed FeOOH. Cd(E 0 (Cd 2+ / Cd)=−0.40 V) exhibits moderate removal, possibly dominated by co-precipitation of iron hydroxides; while the Zn concentration remains essentially unchanged. In this system, its effect on s-Fe 0 It has poor affinity and is reduced by (E 0 (Zn 2+ The removal efficiency of both the Zn ( / Zn) = −0.76 V and the adsorption pathway is low. The effluent does not fully meet the requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996), and the removal efficiency of the target metal ions in the third and fourth layers is not significantly improved.

[0058] The pH of each layer initially increased from 4.5 to 6-7 (due to the consumption of protons H⁺ in the redox reaction, resulting in a subsequent pH increase) and then stabilized. This weakly acidic environment was conducive to the continuous dissolution of the iron oxide passivation layer (the pH changes in the above examples were similar to those in Comparative Example 1). Among them, the ZVI fixed bed showed high removal efficiency for Cu, Pb, and Ag, moderate removal efficiency for Al and Cd, and minimal removal of Zn (Zn was subsequently removed using sodium sulfide).

[0059] Table 7. Effect of not adding hexavalent chromium on metal ion removal (40g / layer, 4 layers in total)

[0060] Time (h) 5 10 15 20 Cu 7.82 7.78 7.68 8.31 Pb 4.65 4.62 4.68 4.83 Ag 0.0532 0.0405 0.0381 0.0338 Al 2.24 2.12 2.06 2.09 Cd 1.17 1.18 1.21 1.22

[0061] Comparative Example 2

[0062] s-Fe 0 (1–3 mm) in a packed bed reactor (3 cm inner diameter of column, 10 cm height per layer, 3 layers packed, 12 g s-Fe per layer) 0 In (1–3 mm) samples, acidic leachate from medical waste incineration fly ash (FA) was selected as the influent (K). + 1430 mg / L; Na+ 11800 mg / L; Ca 2+ 264.4 mg / L; Zn 2+ 488.97 mg / L; Cu 2+ 12.34 mg / L; Pb 2+ 7.68 mg / L; Cd 2+ 1.24 mg / L; Al 3+ 2.73 mg / L; Ag + 0.087 mg / L; Mg 2+ 12.8 mg / L; Si 3.7 mg / L; initial pH=4.5); flow rate V=1.5 mL / min, from top to bottom, aeration rate of 0.8 L / min, and Cr(VI) content adjusted to 20 mg / L.

[0063] Table 8 compares the effects of adding Cr(VI) inducer to acidic fly ash leachate on the spatiotemporal behavior of various HMs and physicochemical parameters. The results show that the addition of 20 mg / L Cr(VI) and the use of a three-layer modified s-Fe... 0 After the packed bed (12 g per layer; 3 layers in total), the removal efficiency of Cu, Pb, Al, and Cd was significantly improved (except for Zn, which can be removed subsequently using sodium sulfide). However, the effluent did not fully meet the discharge standards of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) (e.g., Cu: 0.5-2.0 mg / L, Pb: 1.0 mg / L, Ag: 0.5 mg / L, Cd: 0.1 mg / L, Zn: 2-5 mg / L, Cr(VI): 0.5 mg / L, Cr...). total (1.5 mg / L, pH: 6-8). This indicates that the addition of Cr(VI) inducer to the acidic leachate promoted the removal of target HMs and s-Fe. 0 The corrosion passivation layer was effectively stripped; among them, the enhanced Cd removal may be related to the fact that the presence of Cr(VI) strengthened the stripping of the iron oxide passivation layer and improved the interfacial adsorption performance of the passivation layer.

[0064] Table 8 Effect of adding 20 mg / L hexavalent chromium on metal ion removal (12 g / layer, 3 layers in total)

[0065] Time (h) 5 10 15 20 Cu 4.60 3.84 4.86 3.42 Pb 6.97 6.91 5.50 1.22 Ag 0.0462 0.0414 0.0363 0.0315 Al 2.63 2.52 2.43 1.11 Cd 0.0604 0.0671 0.0543 0.0256 <![CDATA[Cr 6+ ]]> 0.117 0.182 0.064 0.021 <![CDATA[Cr total ]]> 0.203 0.150 0.161 0.138

[0066] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0067] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A method for the synergistic removal of heavy metals from fly ash acidic leachate wastewater using hexavalent chromium as a trigger, characterized in that, The steps include: (1) adjusting the hexavalent chromium content in the fly ash acid leachate wastewater and adjusting the pH to 3-6 to obtain the wastewater to be treated; (2) The wastewater to be treated is pumped into a fixed bed filled with one or more layers of sponge iron through a peristaltic pump. Sodium sulfide is added to the effluent, and then sedimentation and filtration are carried out. In step (1), the acidic leachate of fly ash is an acidic leachate of fly ash from the incineration of medical waste or domestic waste; In step (2), the particle size of the sponge iron is 1-8 mm.

2. The method for synergistic removal of heavy metals from fly ash acidic leachate wastewater using hexavalent chromium as a trigger, as described in claim 1, is characterized in that... Step (1) also includes the following steps: adjusting the hexavalent chromium content in fly ash acid leachate wastewater to 10-90 mg / L.

3. The method for synergistic removal of heavy metals from fly ash acidic leachate wastewater using hexavalent chromium as a trigger, as described in claim 1, is characterized in that... In step (2), the particle size of the sponge iron is 1-3 mm.

4. The method for synergistic removal of heavy metals from fly ash acidic leachate wastewater using hexavalent chromium as a trigger, as described in claim 1, is characterized in that... In step (2), the wastewater to be treated is pumped into a fixed bed containing sponge iron at a flow rate of 0.5-2.5 mL / min.

5. The method for synergistic removal of heavy metals from fly ash acidic leachate wastewater using hexavalent chromium as a trigger, as described in claim 1, is characterized in that... In step (2), the amount of sponge iron added to each layer is 2.0 g / cm³. 2 -15 g / cm 2 .

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