Cooperative treatment method for sulfur dioxide-containing waste gas and sulfate ion-containing wastewater

Abstract

The invention discloses a cooperative treatment method of sulfur dioxide-containing waste gas and sulfate ion-containing wastewater, which comprises the following steps: (1) dispersing a catalyst containing metal Ni nanoparticles into the sulfate ion-containing wastewater, introducing the sulfur dioxide-containing waste gas, controlling the pH value to be 2-5, and reacting; (2) adding salt or alkali containing calcium ions, adjusting the pH value to 9-10, and stirring for reaction to generate calcium sulfite precipitate; sulfate wastewater is directly treated by using SO2 waste gas, so that waste cooperative treatment is achieved, and waste is treated with waste.

Description

Technical Field

[0001] This invention belongs to the field of environmental pollution control or resource recycling, and in particular relates to a method for the synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater. Background Technology

[0002] Industrial wastewater (such as mine drainage and metallurgical wastewater) contains high concentrations of sulfate. Traditional treatment methods include membrane processes and evaporation processes. Membrane processes only transfer sulfate ions from the water, while evaporation processes have high investment and operating costs. Existing sulfate reduction technologies (such as biological reduction) are inefficient and require an external carbon source.

[0003] Sulfur dioxide is a common industrial waste gas (such as coal-fired flue gas), which usually requires oxidative desulfurization treatment (such as generating sulfates), but it has not been effectively utilized as a resource.

[0004] Existing technologies involve the oxidation of SO2 (such as in the production of sulfuric acid) or the chemical reduction of sulfates (such as using H2S), but lack direct utilization of SO2 gas to reduce SO4. 2- Collaborative methods. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above and to provide a method for the synergistic treatment of sulfur dioxide waste gas and sulfate ion wastewater.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for the synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater includes the following steps: (1) The catalyst containing Ni nanoparticles is dispersed in wastewater containing sulfate ions, and waste gas containing sulfur dioxide is introduced and the pH is controlled between 2 and 5 to carry out the reaction. (2) Add a salt or alkali containing calcium ions and adjust the pH to between 9 and 10. Stir the reaction to generate calcium sulfite precipitate.

[0007] As a further improvement, the method for preparing the catalyst containing Ni nanoparticles includes: (1') Ni-containing 2+ and La 3+ The metal salt solution was mixed with boehmite powder to form a paste, and then allowed to stand and dry. (2') The dried product is calcined in air, so that Ni 2+ and La 3+ It is converted into oxide, and pseudoboehmite is converted into γ-Al2O3 to obtain the catalyst precursor; (3') The catalyst precursor is reduced in a reducing atmosphere to reduce the nickel oxide to metallic nickel to obtain the catalyst containing metallic Ni nanoparticles.

[0008] As a further improvement, the catalyst containing Ni nanoparticles has a Ni mass fraction of 13-18% and a La2O3 mass fraction of 2-4%.

[0009] As a further improvement, the metal salt solution is an aqueous solution prepared from Ni(NO3)2·6H2O and La(NO3)3·6H2O, with a mass ratio of Ni(NO3)2·6H2O to La(NO3)3·6H2O of (5~6):(0.6~1).

[0010] As a further improvement, the roasting includes: (a) Heat to 110~130℃ and hold for 20~40 minutes; (b) Raise the temperature to 450~550℃ and keep it warm for 2~4 hours; (c) Heat to 750~800℃ and keep warm for 3~5 hours.

[0011] As a further improvement, the reduction temperature is 350~450℃.

[0012] As a further improvement, the catalyst addition amount is 90~110g / L, and the flow rate of the sulfur dioxide-containing waste gas is 0.1~0.2L / min.

[0013] As a further improvement, calcium hydroxide is added in step (1) to control the pH between 2 and 5.

[0014] As a further improvement, the calcium-containing salt or alkali in step (2) is calcium hydroxide.

[0015] As a further improvement, the sulfate content in the wastewater was reduced to <160 mg / L.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: In the presence of calcium ions, catalyzed by the catalyst of this invention, sulfur dioxide gas reduces sulfate ions in the solution to sulfite ions, forming calcium sulfite precipitate which is then separated. The chemical equation is as follows: 2SO4 2- +2SO2+4Ca 2+ +4OH - →4CaSO3+O2+2H2O The specific mechanism is as follows: Under acidic (pH=2~5) and catalytic conditions, SO2 and SO4... 2- A redox reaction occurs, producing bisulfite ions (HSO3).- ), E under acidic conditions 0 (SO2 / HSO3 - = -0.25V < E 0 (SO4 2- / HSO3 - With a voltage of approximately +0.17V, the catalyst of this invention accelerates electron transfer through catalytic reduction. Bisulfite ions become sulfite ions (SO32-) at elevated pH (pH=9~10). 2- Sulfite ions rapidly react with calcium ions to form calcium sulfite precipitate, thereby reducing the amount of sulfate ions in the water. This reaction is thermodynamically spontaneous (ΔG < 0).

[0017] This invention utilizes SO2 waste gas to directly treat sulfate wastewater, achieving co-treatment of waste and realizing "waste-to-waste" technology. The catalyst in this invention has high reduction efficiency and avoids the generation of byproducts. This invention simultaneously recovers sulfur and calcium, reducing treatment costs. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 It is an X-ray photoelectron spectrum; Figure 2 It is the H2- temperature-programmed reduction spectrum. Detailed Implementation

[0020] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0021] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0023] In some specific embodiments, the preparation method of the catalyst (pseudo-boehmite supported nickel metal catalyst) used in this invention includes the following steps: (1') Ni-containing2+ The metal salt solution is mixed with the carrier powder to form a paste, and then left to stand and dry.

[0024] In some embodiments, the carrier is pseudoboehmite (AlOOH· n H2O).

[0025] In some embodiments, the metal salt solution also contains La 3+ .

[0026] In some embodiments, the metal salt solution is an aqueous solution prepared from Ni(NO3)2·6H2O and La(NO3)3·6H2O. The mass ratio of Ni(NO3)2·6H2O to La(NO3)3·6H2O is (5~6):(0.6~1). The mass ratio of Ni(NO3)2·6H2O to boehmite is (5~6):(8~12).

[0027] In some embodiments, the sample is sealed and left to stand at room temperature for 10-15 hours. This helps to distribute metal ions more evenly within the pores of the support.

[0028] In some embodiments, drying is performed at 110-130°C for 10-15 hours.

[0029] (2') The dried product is calcined in air, so that Ni 2+ and La 3+ It is converted into an oxide, and pseudoboehmite is converted into γ-Al2O3 to obtain the catalyst precursor (denoted as NiO-La2O3 / γ-Al2O3).

[0030] In some embodiments, the calcination process is as follows: (a) Heat to 110~130℃ and keep warm for 20~40 minutes to completely remove residual moisture; (b) Raise the temperature to 450~550℃ and keep it for 2~4 hours to decompose the metal nitrates, so that the pseudoboehmite is dehydrated and dehydroxylated to convert into γ-Al2O3; (c) Raise the temperature to 750~800℃ and keep warm for 3~5 hours.

[0031] At 750–800 °C, the specific surface area of ​​γ-Al₂O₃ remains relatively high, but it begins to transform into the δ / θ phase with a lower specific surface area, resulting in significantly enhanced thermal stability. At this temperature, NiO interacts strongly with the support, which helps prevent the sintering and growth of metal particles during subsequent use. At this temperature, all impurity ions such as nitrate and ammonium ions in the precursor are completely decomposed and burned off.

[0032] In some embodiments, the heating rate is 2-5°C / min. Slow heating prevents damage to the pore structure.

[0033] (3') The catalyst precursor is reduced under a reducing atmosphere to reduce the nickel oxide to metallic nickel to obtain the catalyst of the present invention (denoted as Ni-La2O3 / γ-Al2O3).

[0034] In some embodiments, the reducing atmosphere is a hydrogen atmosphere.

[0035] In some embodiments, the reduction temperature is 350~450℃ and the reduction time is 1.5~2.5 hours.

[0036] In some embodiments, NiO is reduced to catalytically active metallic Ni nanoparticles, the particle size of which is mainly distributed in the range of 3-9 nm, and the mass fraction of Ni in the catalyst is 13-18% and the mass fraction of La2O3 is 2-4%.

[0037] In some specific embodiments, the synergistic treatment method for sulfur dioxide-containing waste gas and sulfate-containing wastewater of the present invention includes the following steps: (1) The catalyst of the present invention is dispersed in wastewater containing sulfate ions, waste gas containing sulfur dioxide is introduced, and the pH is controlled between 2 and 5 to carry out the reaction.

[0038] In some embodiments, the catalyst addition amount is 90~110 g / L. The flow rate of the sulfur dioxide-containing waste gas is 0.1~0.2 L / min.

[0039] In some embodiments, an alkali (preferably calcium hydroxide) is added to adjust the pH to between 2 and 5, to avoid the pH dropping below 2 due to continuous introduction of sulfur dioxide.

[0040] In some embodiments, the reaction time is 5-10 minutes.

[0041] (2) Add a salt or alkali containing calcium ions and adjust the pH to between 9 and 10. Stir the reaction to generate calcium sulfite precipitate.

[0042] Preferably, calcium hydroxide is added. Depending on the amount of sulfate and sulfur dioxide, calcium ions should be added in excess.

[0043] In some embodiments, the reaction is stirred for 10-20 minutes, and then allowed to stand before filtration to obtain calcium sulfite precipitate (calcium sulfate content ≤0.5%), with sulfate content in the filtrate <160mg / L.

[0044] Example 1: Preparation of Catalyst (1) Add 5.84 g of Ni(NO3)2·6H2O and 0.80 g of La(NO3)3·6H2O to 8.8 mL of water, mix well, and obtain a metal salt solution.

[0045] (2) The metal salt solution was slowly added dropwise to the carrier powder (10.93 g of industrial pseudoboehmite) and stirred continuously to obtain a uniform paste. Then, it was sealed and left to stand at room temperature for 12 hours for aging.

[0046] (3) After drying the aged sample at 120°C for 12 hours, it was calcined in air. The calcination procedure was as follows: the temperature was increased to 120°C at a rate of 2-5°C / min and held for 30 min; the temperature was then increased to 500°C at the same rate and held for 3 hours; the temperature was then increased to 750°C at the same rate and held for 4 hours. The sample was then cooled to room temperature to obtain the catalyst precursor (denoted as NiO-La2O3 / γ-Al2O3).

[0047] (4) The catalyst precursor was reduced at 400℃ and under a 10% H2 / Ar atmosphere for 2 hours to obtain about 10.00 g of gray-black powder, which is the final catalyst (denoted as Ni-La2O3 / γ-Al2O3), in which the mass fraction of Ni is 15% and the mass fraction of La2O3 is 3%.

[0048] The obtained catalyst precursor and the final catalyst were characterized: (a) X-ray photoelectron spectroscopy (XPS) (Ni 2p region) Figure 1 For the reduced catalyst, a main peak was observed at a binding energy (BE) of approximately 852.8 eV, corresponding to metallic Ni. 0 The 2p3 / 2 energy level. This is direct evidence of the existence of the active metal Ni.

[0049] Compared to pure Ni foil, the Ni on the catalyst surface... 0 The 2p3 / 2 binding energy exhibits a positive shift of approximately 0.3 eV. This small change in binding energy suggests a reduction in the electron cloud density of the metallic Ni particles, which may be due to the electron-donating effect of La2O3 or the residual interaction between Ni and the support γ-Al2O3. This electronic effect contributes to enhanced catalytic activity.

[0050] (b) The H2-temperature programmed reduction (H2-TPR) spectrum of the catalyst precursor (NiO-La2O3 / γ-Al2O3) is shown below. Figure 2 The spectrum shows an asymmetric main reduction peak with a maximum hydrogen consumption temperature of 382℃, which is attributed to the reduction of free NiO species with weak interaction with the support. There is a tailed shoulder peak on the high-temperature side of the main peak (>600℃), which corresponds to the reduction of "difficult-to-reducible" NiO species with strong interaction with the support. These species may be embedded on the support surface or have close contact with La species.

[0051] Compared to Ni / γ-Al2O3 catalysts without La (where the main reduction peak is typically at 400-450℃), the main reduction peak of this catalyst shifts significantly towards lower temperatures. This demonstrates that the addition of rare earth element La significantly promotes the reduction of NiO, weakens the strong interaction between NiO and the γ-Al2O3 support, and allows the active metal Ni to be reduced under milder conditions.

[0052] Example 2: A method for the synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater (1) Take 500ml of raw water (the test data is shown in Table 1), add 50g of the catalyst prepared in Example 1, stir, and then directly introduce sulfur dioxide at a flow rate of 0.15L / min.

[0053] Table 1

[0054] (2) When the pH value is between 2 and 3, add calcium hydroxide solution (5wt%) to keep the pH between 2 and 5, and stop the introduction of sulfur dioxide after 5 minutes.

[0055] (3) Add calcium hydroxide solution (5wt%) again to raise the pH to between 9 and 10. Stir for 10 minutes, let stand for 10 minutes, take a sample of the supernatant and filter it. Test the various indicators of the supernatant (i.e., the quality of the effluent) as shown in Table 2.

[0056] Table 2

[0057] (4) The treated mixture was filtered to obtain precipitated sludge, which was dried to a total weight of 14.9g, including 13.5g of calcium sulfite (calcium sulfite detection method: redox titration method, GB / T15817-1995).

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for the synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater, characterized in that, Includes the following steps: (1) The catalyst containing Ni nanoparticles is dispersed in wastewater containing sulfate ions, and waste gas containing sulfur dioxide is introduced and the pH is controlled between 2 and 5 to carry out the reaction. (2) Add a salt or alkali containing calcium ions and adjust the pH to between 9 and 10. Stir the reaction to generate calcium sulfite precipitate.

2. The method for synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater according to claim 1, characterized in that, The method for preparing the catalyst containing Ni nanoparticles includes: (1') Ni-containing 2+ and La 3+ The metal salt solution was mixed with boehmite powder to form a paste, and then allowed to stand and dry. (2') The dried product is calcined in air, so that Ni 2+ and La 3+ It is converted into oxide, and pseudoboehmite is converted into γ-Al2O3 to obtain the catalyst precursor; (3') The catalyst precursor is reduced under a reducing atmosphere to reduce the nickel oxide to metallic nickel to obtain the catalyst containing metallic Ni nanoparticles.

3. The method for synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater according to claim 2, characterized in that, The catalyst containing Ni nanoparticles has a Ni mass fraction of 13-18% and a La2O3 mass fraction of 2-4%.

4. The method for synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater according to claim 2, characterized in that, The metal salt solution is an aqueous solution prepared from Ni(NO3)2·6H2O and La(NO3)3·6H2O, with a mass ratio of (5~6):(0.6~1).

5. The method for synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater according to claim 2, characterized in that, The roasting includes: (a) Heat to 110~130℃ and hold for 20~40 minutes; (b) Raise the temperature to 450~550℃ and keep it warm for 2~4 hours; (c) Heat to 750~800℃ and keep warm for 3~5 hours.

6. The method for synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater according to claim 2, characterized in that, The reduction temperature is 350~450℃.

7. The method for synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater according to any one of claims 1 to 6, characterized in that, The catalyst addition amount is 90~110g / L, and the flow rate of the sulfur dioxide-containing waste gas is 0.1~0.2L / min.

8. The method for synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater according to any one of claims 1 to 6, characterized in that, Step (1) Add calcium hydroxide to control the pH between 2 and 5.

9. The method for synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater according to any one of claims 1 to 6, characterized in that, The calcium-containing salt or alkali in step (2) is calcium hydroxide.

10. The method for synergistic treatment of sulfur dioxide-containing waste gas and sulfate-containing wastewater according to any one of claims 1 to 6, characterized in that, Reduce the sulfate content in the wastewater to <160mg / L.

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