Nitrate decomposition catalyst and application thereof

Abstract

The invention provides a nitrate decomposition catalyst and application thereof, and relates to the technical field of waste sludge and wastewater treatment. The method comprises the following steps: firstly, preparing a nitrate decomposition catalyst from iron-containing acid pickling sludge powder as iron-containing activated carbon and a transition metal salt solution; when the catalyst is used for treating iron-containing waste liquid, nitrate in the waste liquid is effectively decomposed, and a ferric chloride water purifying agent is prepared. The method not only improves the removal efficiency of nitrate, but also realizes resource utilization of wastes, and has the technical effects of simplicity and convenience in operation, low cost and environmental friendliness.

Description

Technical Field

[0001] The invention relates to the technical field of waste sludge and wastewater treatment, and more specifically, to a nitrate decomposition catalyst and application thereof. Background Art

[0002] Stainless steel has been widely used as a new type of material with excellent performance. In the processing and production of stainless steel, it is usually necessary to use mixed acids such as nitric acid, sulfuric acid and hydrofluoric acid for surface pickling to remove the oxide scale, rust and passivation groups on the surface of the stainless steel. However, this process will produce a large amount of iron-containing pickling waste liquid and iron-containing pickling sludge containing nitrate ions. If these waste liquids and sludges are discharged directly, they will not only cause serious environmental pollution, but also threaten human health. Nitrate ions (NO3 - ) may undergo a reduction reaction under strong acid conditions or high temperatures and decompose into nitrogen oxides (NO x ), mainly including nitric oxide (NO) and nitrogen dioxide (NO2). The emission of these gases will lead to the formation of photochemical smog and acid rain, which will cause great harm to the environment and human health.

[0003] At present, there are three main methods for removing nitrate from waste liquid or sludge: biological method, physical and chemical method and chemical reduction method. The biological method usually uses microbial action, but its treatment speed is slow, the effect is unstable, and the treatment upper limit is low. Although physical and chemical methods, such as ion exchange, reverse osmosis, electrodialysis, etc., can effectively remove nitrate, they are often costly and complicated to operate. The chemical reduction method reduces nitrate to ammonia nitrogen and nitrogen by adding active metals such as iron, zinc and aluminum as reducing agents to the water body. The catalytic reduction method has a high treatment rate and is easy to operate. It can completely convert nitrate into nitrogen, but the dosage is large, the cost is expensive, and it cannot be recycled for secondary use.

[0004] The prior art discloses a method of treating water containing low concentrations of nitrate and nitrite by combining transition metal (iron, manganese, copper) compounds and reducing water treatment agents in an anaerobic environment, and denitrifying under sunlight. However, the pH of the water that can be treated requires alkalinity, the reaction time is long, and it is a combination of biological and chemical methods, which has uncertainty in biological effects.

[0005] Therefore, the development of a nitrate decomposition catalyst prepared from iron-containing pickling sludge and its application in treating iron-containing wastewater have important research significance and application value. Summary of the invention

[0006] The present invention aims to overcome the shortcomings of the prior art, namely, high cost and the ability to process only low-concentration nitrates, and to provide a nitrate decomposition catalyst and its application, which not only improves the removal efficiency of nitrates but also realizes the resource utilization of waste.

[0007] Therefore, the primary object of the present invention is to provide a nitrate decomposition catalyst prepared by acidic iron-containing sludge.

[0008] Another object of the present invention is to provide a method for treating acidic iron-containing waste liquid using the above nitrate decomposition catalyst.

[0009] Another object of the present invention is to protect the use of the above-mentioned nitrate decomposition catalyst To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a nitrate decomposition catalyst, which is prepared by the following steps: S1. The iron-containing pickling sludge powder is anaerobic pyrolyzed at 400-600℃ for 2-4h to obtain iron-containing activated carbon; S2. The iron-containing activated carbon is added to the mixed transition metal salt solution and immersed for 1 to 3 hours to obtain the nitrate decomposition catalyst; The mixed transition metal salt is selected from at least two soluble salts of copper, iron, aluminum, cobalt, manganese, zinc, nickel or palladium.

[0010] The present invention adopts discarded iron-containing pickling sludge to prepare nitrate decomposition catalyst, and can recycle the discarded iron-containing pickling sludge, avoiding pollution to the environment caused by discharging iron-containing pickling sludge. The present invention first pyrolyzes the iron-containing sludge under high temperature and anaerobic conditions to generate iron-containing activated carbon, and then uniformly loads the transition metal salt onto the iron-containing activated carbon by a wet impregnation method, thereby obtaining a nitrate decomposition catalyst. The nitrate decomposition catalyst prepared by the present invention can reduce nitrate ions in wastewater to nitrogen by a chemical catalytic reduction method. Transition metal ions of copper, iron, aluminum, cobalt, manganese, zinc, nickel or palladium have a catalytic reaction in the reaction of reducing nitrate, can improve the removal effect of nitrate, select two of the ions for combined use, play a synergistic effect, and more efficiently realize the process of catalytic reduction.

[0011] Anaerobic pyrolysis refers to the process of decomposing organic matter by heating in an oxygen-free or low-oxygen environment. After the organic matter in the sludge is decomposed, the remaining carbon elements will form activated carbon with a porous structure under certain temperature and anaerobic conditions. The pore structure makes the activated carbon have a strong adsorption capacity, making the transition metal compounds highly dispersed on the activated carbon.

[0012] Specifically, the mixed transition metal salt is selected from copper, iron, aluminum, cobalt, manganese, zinc, nickel or palladium, the valence state of copper is +2, the valence state of iron is +3, the valence state of aluminum is +3, the valence state of cobalt is +2, the valence state of manganese is +2, the valence state of zinc is +2, the valence state of nickel is +2, and the valence state of palladium is +2.

[0013] Preferably, the mixed transition metal salt solution in step S2 is a mixed solution of at least two of copper chloride, ferric chloride, aluminum chloride, cobalt chloride, manganese chloride, zinc chloride, nickel chloride or palladium chloride.

[0014] Specifically, the preparation method of the mixed transition metal salt solution comprises the following steps: Take a corresponding proportion of transition metal salts, dissolve them in water as a solvent, and obtain a mixed transition metal salt solution.

[0015] More preferably, the method for preparing the mixed transition metal salt solution comprises the following steps: Take a corresponding proportion of transition metal salt, dissolve it in water as solvent, add hydrochloric acid to obtain a transition metal salt solution.

[0016] Adding hydrochloric acid can assist in dissolving the transition metal salt.

[0017] Specifically, the mass fraction of the hydrochloric acid is 30%.

[0018] Specifically, the mass fraction of hydrochloric acid in the transition metal salt solution is 3wt%.

[0019] Preferably, the iron-containing pickling sludge powder in step S1 is obtained by pretreating the iron-containing pickling sludge, wherein the mass fraction of Fe2O3 is 20-60%.

[0020] Specifically, the pretreatment includes the following steps: drying and crushing.

[0021] Specifically, the iron-containing pickling sludge is derived from the pickling sludge of a stainless steel plant.

[0022] Specifically, the iron-containing pickling sludge includes the following components: Fe2O3 with a mass fraction of 20-60%, and other impurities.

[0023] Preferably, the mass ratio of the total mass of the mixed transition metal salt to the iron-containing activated carbon is 1-5:1.

[0024] Preferably, the molar ratio of each transition metal salt contained in the mixed transition metal salt solution is 1.

[0025] The present invention also provides a method for removing nitrate ions from acidic iron-containing waste liquid, comprising the following steps: The above-mentioned nitrate decomposition catalyst is added to the acidic iron-containing waste liquid to be treated, a hydrogen gas flow is introduced, and the reaction is carried out at 40-100° C. for 1-3 hours.

[0026] Preferably, the mass ratio of the nitrate decomposition catalyst to the acidic iron-containing waste liquid to be treated is 1:2-10.

[0027] Preferably, the nitrate mass concentration of the acidic iron-containing waste liquid to be treated is 1000 mg / L~10000 mg / L.

[0028] Preferably, the flow rate of the hydrogen gas flow is 40-60 mL / min.

[0029] More preferably, the flow rate of the hydrogen gas flow is 50 mL / min.

[0030] Preferably, the method for removing nitrate ions from the above-mentioned acidic iron-containing waste liquid further comprises the step of: adding ferrous sulfate to the solution after the reaction.

[0031] Preferably, the added amount of ferrous sulfate is 5-10g.

[0032] Preferably, the total iron content in the acidic iron-containing waste liquid to be treated is 2-10wt%, and the hydrochloric acid acidity is 1-5%.

[0033] Preferably, the above method for removing nitrate ions from acidic iron-containing waste liquid further comprises the following steps: In the solution obtained by the above removal method, ferrous ions are oxidized into ferric ions to prepare a ferric chloride water purifier.

[0034] The present invention firstly degrades nitrate ions in acidic iron-containing waste liquid by using the prepared nitrate decomposition catalyst, and then further removes the residual nitrate ions by using a small amount of ferrous sulfate, thereby obtaining a solution that is almost free of nitrate ions, which can be further used to prepare ferric chloride water purifier. Ferrous sulfate (FeSO4) can react with nitrate (NO3 - ) undergoes an oxidation-reduction reaction to generate nitric oxide in the presence of dilute nitric acid. After the above-mentioned method for removing nitrate ions from acidic iron-containing waste liquid, the concentration of nitrate ions contained in the solution is low, and after reacting with ferrous sulfate, the obtained nitric oxide is extremely low. Compared with the prior art of using ferrous sulfate to directly remove nitrates, on the one hand, the amount of ferrous sulfate added is reduced, reducing costs, and on the other hand, less nitric oxide is obtained by the reaction, reducing the impact on the environment.

[0035] Preferably, the specific preparation method of the above-mentioned ferric chloride water purifier is: adding waste hydrochloric acid and sodium chlorate to mix and react to prepare the ferric chloride water purifier.

[0036] Specifically, the waste hydrochloric acid is a hydrochloric acid solution containing metal ions and other impurities used in an industrial pickling process.

[0037] Preferably, the mass concentration of the waste hydrochloric acid is 33wt%.

[0038] Preferably, the mass ratio of the purified liquid, waste hydrochloric acid and sodium chlorate is 250-300:70-80:10-15.

[0039] The use of the above nitrate decomposition catalyst in treating nitrate in acidic wastewater is also within the protection scope of the present invention.

[0040] Specifically, the ferric chloride water purifier is a liquid containing ferric chloride, various transition metal salt solutions, other insoluble particles and ionic impurities.

[0041] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a nitrate decomposition catalyst, which is prepared from iron-containing sludge, pyrolyzed to prepare activated carbon as a carrier of transition metal, and catalyzed the reaction process of reducing nitrate to nitrogen by a reducing agent, thereby achieving the effect of treating waste with waste; 2. The present invention provides a method for treating nitrate in iron-containing wastewater using the above-mentioned nitrate decomposition catalyst, with a nitrate removal rate of more than 99%, and a ferric chloride water purifier is prepared, which is resource-efficient and cost-saving. DETAILED DESCRIPTION

[0042] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0043] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0044] Test indicators: Iron-containing pickling sludge: It comes from the pickling sludge of the stainless steel plant, and contains 50% Fe2O3 by mass; Acidic iron-containing waste liquid to be treated: The total iron content is 5wt%, the hydrochloric acid acidity is 4%, and the nitrate mass concentration is 5000mg / L; The total iron content is 7wt%, the hydrochloric acid acidity is 5%, and the nitrate mass concentration is 10000mg / L.

[0045] (1) Nitrate removal rate of nitrate decomposition catalyst for acidic iron-containing wastewater (%): The nitrate removal rate is used to evaluate the performance of the catalyst and the nitrate removal effect, namely: R(NO3 - )=[C(NO3 - )0-C(NO3 - ) t ] / C(NO3 - )0 Among them, R(NO3 -) represents the removal rate of nitrate, C(NO3 - )0 represents the initial content of nitrate, C(NO3 - ) t Represents the content of nitrate after reaction at time t; Nitrate concentration test: "Determination of Nitrate Nitrogen in Water Quality - Ultraviolet Spectrophotometry (Trial)" (Standard No.: HJ / T346-2007); (2) Acidity of ferric chloride water purifier (%); (3) Iron content of ferric chloride water purifier (expressed as Fe 3+ Calculation): "Water Purifier Ferric Chloride (GB 4482-1993)".

[0046] Example 1 A nitrate decomposition catalyst and its application S1. The pickling sludge from the stainless steel plant was dried and crushed to remove moisture and large particles to obtain iron-containing sludge powder. The sludge powder was pyrolyzed and carbonized at 500℃ for 3 h under anaerobic conditions to obtain iron-containing sludge activated carbon; S2. Dissolve mixed transition metal salts: copper chloride, iron chloride, aluminum chloride, cobalt chloride, manganese chloride, zinc chloride, nickel chloride and palladium chloride (the molar ratio of each transition metal salt contained in the mixed transition metal salt solution is 1) in water to form a 5wt% mixed transition metal salt solution, add 30% hydrochloric acid and iron-containing sludge activated carbon, the mass fraction of hydrochloric acid in the obtained solution is 3wt%, and the mass fraction of iron-containing sludge activated carbon is 1wt%. The mass ratio of the total mass of the mixed transition metal salt to the iron-containing activated carbon is 5:1, mechanically stir at 250 rpm for 3 h, filter to obtain solid particles, wash with ethanol and pure water, and dry to obtain a nitrate decomposition catalyst; S3. Add the nitrate decomposition catalyst described in S2 to the iron-containing waste liquid containing 10000 mg / L nitrate, the mass ratio of the nitrate decomposition catalyst to the acidic iron-containing waste liquid to be treated is 1:6, introduce a hydrogen flow of 50 mL / min, raise the temperature to 70° C., react for 1 h, prepare the iron-containing waste liquid with nitrate removed, and perform solid-liquid separation; S4. Determine the nitrate content in the pretreated iron-containing waste liquid in S3, add 6 g of ferrous sulfate solid to remove the residual nitrate to obtain the pretreated iron-containing waste liquid, and measure the nitrate removal rate of the treated iron-containing waste liquid to be 99.9%; S5. 300g of iron-containing waste liquid after S3 treatment was added with 80g of waste hydrochloric acid having a mass concentration of 33%, 11.2g of sodium chlorate was added, mixed and stirred to dissolve, and a ferric chloride water purifier was prepared. The acidity of the ferric chloride water purifier was measured to be 0.45%, and Fe 3+The calculated iron content is 15.21%, which is a qualified ferric chloride water purifier product.

[0047] Example 2 A nitrate decomposition catalyst and its application S1. The pickling sludge from the stainless steel plant was dried and crushed to remove moisture and large particles to obtain iron-containing sludge powder. The sludge powder was pyrolyzed and carbonized at 500℃ for 3 h under anaerobic conditions to obtain iron-containing sludge activated carbon; S2. Dissolve a mixed transition metal salt: copper chloride, iron chloride, aluminum chloride (the molar ratio of each transition metal salt contained in the mixed transition metal salt solution is 1) in water to form a 4wt% mixed transition metal salt solution, add 30% hydrochloric acid and iron-containing sludge activated carbon, wherein the mass fraction of hydrochloric acid in the obtained solution is 3wt%, the mass fraction of iron-containing sludge activated carbon is 1wt%, and the mass ratio of the total mass of the mixed transition metal salt to the iron-containing activated carbon is 4:1, mechanically stir at a speed of 250 rpm for 3 h, filter to obtain solid particles, wash with ethanol and pure water, and dry to obtain a nitrate decomposition catalyst; S3. Add the nitrate decomposition catalyst described in S2 to the iron-containing waste liquid containing 5000 mg / L nitrate, the mass ratio of the nitrate decomposition catalyst to the acidic iron-containing waste liquid to be treated is 1:5, introduce a hydrogen flow of 60 mL / min, raise the temperature to 60° C., and react for 1.5 h to prepare the iron-containing waste liquid with nitrate removed, and perform solid-liquid separation; S4. Determine the nitrate content in the pretreated iron-containing waste liquid in S3, add 7g of ferrous sulfate solid to remove the residual nitrate to obtain the pretreated iron-containing waste liquid, and the nitrate removal rate of the treated iron-containing waste liquid is measured to be 99.7%; S5. Add 100g of 33% waste hydrochloric acid and 12.5g of sodium chlorate to 350g of iron-containing waste liquid treated in S3, stir and dissolve them to prepare ferric chloride water purifier. The acidity of ferric chloride water purifier was measured to be 0.41%, based on Fe 3+ The calculated iron content is 15.03%, which is a qualified ferric chloride water purifier product.

[0048] Example 3 A nitrate decomposition catalyst and its application S1. Dry and crush the pickling sludge from the stainless steel plant to remove moisture and large particles to obtain iron-containing sludge powder. Heat the sludge powder to 600℃ for 2h under anaerobic conditions to obtain iron-containing sludge activated carbon. S2. Dissolve a mixed transition metal salt: manganese chloride and zinc chloride (the molar ratio of each transition metal salt contained in the mixed transition metal salt solution is 1) in water to form a 3wt% mixed transition metal salt solution, add 30% hydrochloric acid and iron-containing sludge activated carbon, wherein the mass fraction of hydrochloric acid in the obtained solution is 3wt%, the mass fraction of iron-containing sludge activated carbon is 1wt%, and the mass ratio of the total mass of the mixed transition metal salt to the iron-containing activated carbon is 3:1, mechanically stir at a speed of 250 rpm for 3 h, filter to obtain solid particles, wash with ethanol and pure water, and dry to obtain a nitrate decomposition catalyst; S3. Add the nitrate decomposition catalyst described in S2 to the iron-containing waste liquid containing 5000 mg / L nitrate, the mass ratio of the nitrate decomposition catalyst to the acidic iron-containing waste liquid to be treated is 1:8, introduce a hydrogen flow of 40 mL / min, raise the temperature to 55° C., and react for 2 h to prepare the iron-containing waste liquid with nitrate removed, and perform solid-liquid separation; S4. Determine the nitrate content in the pretreated iron-containing waste liquid in S3, add 6 g of ferrous sulfate solid to remove the residual nitrate to obtain the pretreated iron-containing waste liquid, and measure the nitrate removal rate of the treated iron-containing waste liquid to be 99.6%; 300g of iron-containing waste liquid after S3 treatment was added with 95g of waste hydrochloric acid with a mass concentration of 33%, and 13.5g of sodium chlorate, mixed and stirred to dissolve, and a ferric chloride water purifier was prepared. The acidity of the ferric chloride water purifier was measured to be 0.49%, based on Fe 3+ The calculated iron content is 15.29%, which is a qualified ferric chloride water purifier product.

[0049] Example 4 A nitrate decomposition catalyst and its application S1. Dry and crush the pickling sludge from the stainless steel plant to remove moisture and large particles to obtain iron-containing sludge powder. Heat the sludge powder to 600℃ for 2h under anaerobic conditions to obtain iron-containing sludge activated carbon. S2. Dissolve a mixed transition metal salt: nickel chloride and palladium chloride (the molar ratio of each transition metal salt contained in the mixed transition metal salt solution is 1) in water to form a mixed transition metal salt solution with a mass fraction of 2wt%, add 30% hydrochloric acid and iron-containing sludge activated carbon, wherein the mass fraction of hydrochloric acid in the obtained solution is 3wt%, the mass fraction of iron-containing sludge activated carbon is 1wt%, and the mass ratio of the total mass of the mixed transition metal salt to the iron-containing activated carbon is 2:1, mechanically stir at a speed of 250 rpm for 3 h, filter to obtain solid particles, wash with ethanol and pure water, and dry to obtain a nitrate decomposition catalyst; S3. Add the nitrate decomposition catalyst described in S2 to the iron-containing waste liquid containing 1000 mg / L nitrate, the mass ratio of the nitrate decomposition catalyst to the acidic iron-containing waste liquid to be treated is 1:8, introduce a hydrogen flow of 50 mL / min, raise the temperature to 50° C., and react for 3 h to prepare the iron-containing waste liquid with nitrate removed, and perform solid-liquid separation; S4. Determine the nitrate content in the pretreated iron-containing waste liquid in S3, add 10 g of ferrous sulfate solid to remove the residual nitrate to obtain the pretreated iron-containing waste liquid, and the nitrate removal rate of the treated iron-containing waste liquid is measured to be 99.5%; 300g of iron-containing waste liquid after S3 treatment was added with 95g of waste hydrochloric acid with a mass concentration of 33%, and 13.5g of sodium chlorate, mixed and stirred to dissolve, and a ferric chloride water purifier was prepared. The acidity of the ferric chloride water purifier was measured to be 0.49%, based on Fe 3+ The calculated iron content is 15.29%, which is a qualified ferric chloride water purifier product.

[0050] Comparative Example 1 A nitrate decomposition catalyst and its application The experimental method is the same as in Example 1, except that the pyrolysis temperature of the iron-containing pickling sludge powder is 200°C; The nitrate removal rate of the treated iron-containing wastewater was measured to be 29.37%; The nitrate content is too high, and considering the safety and environmental risks, it is impossible to prepare qualified ferric chloride water purifier products.

[0051] Comparative Example 2 A nitrate decomposition catalyst and its application The experimental method is the same as in Example 1, except that the pyrolysis temperature of the iron-containing pickling sludge powder is 800°C; The nitrate removal rate of the treated iron-containing wastewater was measured to be 74.25%; The nitrate content is too high, and considering the safety and environmental risks, it is impossible to prepare qualified ferric chloride water purifier products.

[0052] Comparative Example 3 A nitrate decomposition catalyst and its application The experimental method was the same as in Example 1, except that the pyrolysis time of the iron-containing pickling sludge powder was 0.5 h; The nitrate removal rate of the treated iron-containing wastewater was measured to be 10.14%; The nitrate content is too high, and considering the safety and environmental risks, it is impossible to prepare qualified ferric chloride water purifier products.

[0053] Comparative Example 4 A nitrate decomposition catalyst and its application The experimental method was the same as in Example 1, except that the pyrolysis time of the iron-containing pickling sludge powder was 8 h; The nitrate removal rate of the treated iron-containing wastewater was measured to be 70.61%; The nitrate content is too high, and considering the safety and environmental risks, it is impossible to prepare qualified ferric chloride water purifier products.

[0054] Comparative Example 5 A nitrate decomposition catalyst and its application The experimental method is the same as in Example 1, except that the iron-containing sludge activated carbon is added to the transition metal salt solution and mixed and reacted for 0.5 h; The nitrate removal rate of the treated iron-containing wastewater was measured to be 34.81%; The nitrate content is too high, and considering the safety and environmental risks, it is impossible to prepare qualified ferric chloride water purifier products.

[0055] Comparative Example 6 A nitrate decomposition catalyst and its application The experimental method is the same as in Example 1, except that the iron-containing sludge activated carbon is added to the transition metal salt solution and mixed and reacted for 6 hours; The nitrate removal rate of the treated iron-containing wastewater was measured to be 67.98%; The nitrate content is too high, and considering the safety and environmental risks, it is impossible to prepare qualified ferric chloride water purifier products.

[0056] Comparative Example 7 Method for using ferrous sulfate in treating iron-containing wastewater The experimental method is the same as that of Example 1, except that no nitrate decomposition catalyst is used, and comprises the following steps: S1. Add 25 g of ferrous sulfate to the iron-containing waste liquid containing 10000 mg / L nitrate, heat to 70 ° C, react for 1 h, prepare the iron-containing waste liquid with nitrate removed, and perform solid-liquid separation; S2. Determine the nitrate content in the pretreated iron-containing waste liquid in S3, add ferrous sulfate solid to remove residual nitrate to obtain the pretreated iron-containing waste liquid, and measure the nitrate removal rate of the treated iron-containing waste liquid to be 33.9%.

[0057] The nitrate content is too high, and considering the safety and environmental risks, it is impossible to prepare qualified ferric chloride water purifier products.

[0058] Comparative Example 8 A nitrate decomposition catalyst and its application The experimental method is the same as that of Example 1, except that the mixed transition metal salt in S2 is cupric chloride.

[0059] The nitrate removal rate of the treated iron-containing wastewater was measured to be 70.64%; The nitrate content is too high, and considering the safety and environmental risks, it is impossible to prepare qualified ferric chloride water purifier products.

[0060] Comparative Example 9 A nitrate decomposition catalyst and its application The experimental method is the same as that of Example 1, except that the mixed transition metal salt in S2 is cobalt chloride.

[0061] The nitrate removal rate of the treated iron-containing wastewater was measured to be 80.68%; The nitrate content is too high, and considering the safety and environmental risks, it is impossible to prepare qualified ferric chloride water purifier products.

[0062] According to the data of the above embodiments and comparative examples, the nitrate decomposition catalysts prepared in embodiments 1 to 4 are acid and alkali resistant, easy to separate, and can reduce the nitrate in the waste acid to less than 1%. The safety and environmental protection risks of the treated iron-containing waste liquid are reduced and can be used to prepare ferric chloride water purifiers, and the acidity is controlled below 0.5%. 3+ The iron content is calculated to be above 15%, and a ferric chloride water purifier that meets the relevant standards is prepared, achieving its effective treatment and resource utilization; while the reaction conditions of comparative examples 1 to 6 are beyond the range, the nitrate removal rate of the nitrate decomposition catalyst for the iron-containing waste liquid is less than 75%, the nitrate content is too high, and considering the safety and environmental protection risks, a qualified ferric chloride water purifier product cannot be prepared; comparative example 7 only uses ferrous sulfate to remove nitrate from the iron-containing waste liquid, and the effect is poor; comparative example 8 only adds cupric chloride as a component of the mixed transition metal salt, that is, the catalyst contains copper ions, and the catalytic activity is weak, and comparative example 9 only adds cobalt chloride as a component of the mixed transition metal salt, which cannot form a synergistic catalytic nitrate reduction effect with copper or iron or aluminum or manganese or zinc or nickel or palladium ions, thereby reducing the degradation rate of nitrates, that is, comparative examples 8 and 9 illustrate that the components of the mixed transition metal salt are at least two of cupric chloride, ferric chloride, aluminum chloride, cobalt chloride, manganese chloride, zinc chloride, nickel chloride or palladium chloride.

[0063] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A nitrate decomposition catalyst, characterized in that: Prepared by the following steps: S1. The iron-containing pickling sludge powder is anaerobic pyrolyzed at 400-600℃ for 2-4h to obtain iron-containing activated carbon; S2. The iron-containing activated carbon is added to the mixed transition metal salt solution and immersed for 1 to 3 hours to obtain the nitrate decomposition catalyst; The mixed transition metal salt is selected from at least two soluble salts of copper, iron, aluminum, cobalt, manganese, zinc, nickel or palladium.

2. The nitrate decomposition catalyst according to claim 1, characterized in that: The iron-containing pickling sludge powder in step S1 is obtained by pretreating the iron-containing pickling sludge, wherein the mass fraction of Fe2O3 is 20-60%.

3. The nitrate decomposition catalyst according to claim 1, characterized in that: The mixed transition metal salt solution in step S2 is a mixed solution of at least two of copper chloride, iron chloride, aluminum chloride, cobalt chloride, manganese chloride, zinc chloride, nickel chloride or palladium chloride.

4. The nitrate decomposition catalyst according to claim 1, characterized in that: The mass ratio of the total mass of the mixed transition metal salt to the iron-containing activated carbon is 1-5:

1.

5. A method for removing nitrate ions from acidic iron-containing waste liquid, characterized in that: The following steps are involved: The nitrate decomposition catalyst according to any one of claims 1 to 4 is added to the acidic iron-containing waste liquid to be treated, a hydrogen gas flow is introduced, and the reaction is carried out at 40 to 100° C. for 1 to 3 hours.

6. The removal method according to claim 5, characterized in that: The mass ratio of the nitrate decomposition catalyst to the acidic iron-containing waste liquid to be treated is 1:2-10.

7. The removal method according to claim 5, characterized in that: The nitrate mass concentration of the acidic iron-containing waste liquid to be treated is 1000 mg / L~10000 mg / L.

8. The removal method according to claim 5, characterized in that: The method also comprises the step of adding ferrous sulfate to the solution after the reaction.

9. The removal method according to claim 5, characterized in that: The following steps are also included: In the solution obtained by the removal method according to any one of claims 5 to 8, ferrous ions are oxidized to ferric ions to prepare a ferric chloride water purifier.

10. Use of the nitrate decomposition catalyst according to any one of claims 1 to 4 in treating nitrate in acidic wastewater.