CN111484117B - Method and device for reducing nitrate radical in acid solution - Google Patents
Method and device for reducing nitrate radical in acid solution Download PDFInfo
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- CN111484117B CN111484117B CN202010304279.8A CN202010304279A CN111484117B CN 111484117 B CN111484117 B CN 111484117B CN 202010304279 A CN202010304279 A CN 202010304279A CN 111484117 B CN111484117 B CN 111484117B
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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
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- C02F2101/16—Nitrogen compounds, e.g. ammonia
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Abstract
The invention provides a method for reducing nitrate radical in acid solution, which comprises the steps of pre-reducing the acid solution containing nitrate radical to reduce the nitrate radical into nitrite radical state, then carrying out catalytic reduction to directly reduce the nitrite radical into nitrogen gas, thereby not only removing nitrate radical ions in the acid solution, but also generating gas with low content of nitrogen oxide, having no pollution to air and no harm to human body; meanwhile, the method has the advantages of simple operation condition and process; the invention also provides a device for reducing nitrate radicals in the acid solution, which is simple and easy to operate and has greater industrial application value.
Description
Technical Field
The invention relates to the technical field of industrial wastewater treatment, in particular to a method and a device for reducing nitrate radicals in an acid solution.
Background
There are three main methods for removing nitrate from industrial wastewater: physical methods, biological denitrification methods, and chemical reduction methods. The physical methods mainly comprise electrodialysis, reverse osmosis, distillation, ion exchange and the like, and because the physical methods are high in cost for removing nitrate nitrogen in water, and are not selective, the removal is not thorough, only the transfer or concentration of pollutants occurs, and the methods are not suitable for waste acid. The biological method converts nitrate into other forms through the action of microorganisms, and has the defects of long time required for degrading nitrate, poor impact resistance, obvious environmental influence and acid resistance depending on the action of the microorganisms. Chemical reduction processes use reducing agents or utilize electrocatalytic reduction techniques to convert nitrate to nitrogen oxides, nitrogen and ammonia nitrogen. However, the chemical reduction technology has many disadvantages, such as easy inactivation of the catalyst, long catalytic reaction time, generation of toxic gas, non-corrosion resistance of the electrode plate, especially acidic wastewater, and the like.
CN107519868A discloses a nano palladium-silver alloy catalytic material for catalytic reduction of nitrate in water, and the material is applied in the reduction process of nitrate, and uses nano metal particles as a catalyst, formic acid as a reducing agent, so as to improve the reaction rate and selectivity of catalytic reduction, but the catalyst is easy to deactivate and has long catalytic reaction time, and toxic gas is generated in the reaction process.
CN103193298A discloses a method for the combined internal electrolysis catalytic reduction of nitrate nitrogen in water by using zero-valent metal and carbon, which utilizes the reducibility of a zero-valent metal simple substance and the internal electrolysis effect of the zero-valent metal simple substance and conductive substances such as active carbon and the like to accelerate the transfer of electrons on a solid-liquid phase interface, thereby reducing and removing the nitrate nitrogen more rapidly. However, the electrode plate used in the electrocatalysis of the method is not corrosion-resistant, especially to acidic wastewater and the like.
CN107640814A discloses a method for in-situ reduction and degradation of nitrate in water, which uses metal sodium borohydride or potassium borohydride and metal alkali solution to reduce nitrate in the solution into ammonia, but the ammonia generated by the method still needs to be reprocessed.
In summary, the conventional methods for treating nitrate in wastewater have various problems that the catalyst is easily deactivated, the electrode plate is easily corroded, or the reduction product needs to be treated again.
Therefore, developing a new method for treating nitrate in acid solution to reduce the nitrate completely, and generating no toxic gas is the key of the existing treatment of the waste water containing nitrate solution.
Disclosure of Invention
In view of the problems in the prior art, the invention provides a method for reducing nitrate radical in acid solution, which comprises the steps of pre-reduction and catalytic reduction, wherein nitrate radical is firstly converted into nitrite radical, nitrite radical is then converted into nitrogen, the generated reducing gas is harmless, and meanwhile, high-concentration acid product can be further obtained; the invention also provides a device for reducing nitrate radicals in the acid solution, which comprises a concentration unit, a pre-reduction unit and a catalytic reduction unit, and has the advantages of simple device and higher industrial application value.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a process for the reduction of nitrate in an acid solution, the process comprising the steps of:
(1) carrying out pre-reduction reaction on an acid solution containing nitrate radicals to obtain a pre-reduction solution containing nitrite radicals;
(2) and carrying out catalytic reduction on the pre-reduction solution to generate nitrogen and obtain a nitric acid removal solution.
The reduction method of nitrate radical in acid solution provided by the invention comprises two steps of pre-reduction and catalytic reduction, wherein nitrate radical in the acid solution containing nitrate radical is converted into nitrite radical after the pre-reduction reaction, and the nitrite radical can be directly reduced into nitrogen gas through the catalytic reduction, the content of the generated nitrogen oxide is lower, the air pollution is small, and the method is harmless to human body; the nitric acid removing solution finally obtained by the method has low nitrate content, and acid products with high purity can be further recovered. Compared with the traditional biological denitration method, the method of pre-reducing and then catalytic reducing has the advantages of high reaction speed, controllable reaction and the like; compared with the traditional chemical method, the method has the advantages of single reducing substance, no secondary pollution and the like; the operation condition and the process technology are simple, the method is suitable for any harsh condition reaction, and the method can be applied to the process for removing nitrate radical from most industrial waste acid.
Preferably, the mass concentration of nitrate in the nitrate-containing acid solution in the step (1) is 1000-50000 mg/L, 1000mg/L, 2000mg/L, 5000mg/L, 10000mg/L, 20000mg/L, 30000mg/L, 40000mg/L or 50000mg/L and the like.
Preferably, the pre-reduction reaction in step (1) comprises: and (3) carrying out pre-reduction reaction on the acid solution containing the nitrate radical under the action of a first reducing agent to obtain pre-reduced solution containing nitrite radical.
Preferably, the first reducing agent comprises any one of ascorbic acid, glucose, isopropanol or oxalic acid or a combination of at least two of them, with a typical but non-limiting combination being: a combination of ascorbic acid and glucose, a combination of ascorbic acid and isopropanol, a combination of glucose and isopropanol, a combination of isopropanol and oxalic acid, preferably ascorbic acid.
Preferably, the first reducing agent accounts for 2 to 10% by mass of the nitrate-containing acid solution, and may be, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or the like.
Preferably, the temperature of the pre-reduction reaction is 10 to 30 ℃, for example, 10 ℃, 12 ℃, 15 ℃, 18 ℃, 20 ℃, 22 ℃, 25 ℃, 28 ℃ or 30 ℃.
Preferably, the time of the pre-reduction reaction is 10-30 min, for example, 10min, 12min, 15min, 18min, 20min, 22min, 25min, 28min or 30 min.
Preferably, the pre-reduction solution in step (2) is subjected to catalytic reduction by the action of a catalyst.
Preferably, a catalyst is added to the pre-reduction solution.
Preferably, the catalyst comprises an acid other than nitric acid.
The acid type is not particularly limited in the present invention, and an acid other than nitric acid may be used, and preferably, a high-concentration acid of the acid originally present in the acid solution is used, which is more advantageous for subsequent recovery of the acid product.
Preferably, the catalyst comprises any one or a combination of at least two of hydrochloric acid, sulfuric acid, fluorosilicic acid, or phosphoric acid, with typical but non-limiting combinations being: a combination of hydrochloric acid and sulfuric acid, a combination of hydrochloric acid and fluorosilicic acid, a combination of hydrochloric acid and phosphoric acid, a combination of sulfuric acid and fluorosilicic acid, a combination of fluorosilicic acid and phosphoric acid.
Preferably, the molar concentration of hydrogen ions in the pre-reduction solution containing the catalyst is 8-15 mol/L, and can be 8mol/L, 9mol/L, 10mol/L, 11mol/L, 12mol/L, 13mol/L, 14mol/L or 15mol/L, and the like.
According to the invention, the molar concentration of hydrogen ions needs to be controlled within 8-15 mol/L, and the acidity needs to be controlled, so that the strong oxidizing property of nitrite can be activated, the reducing property of a reducing agent is relatively improved, and the highly-oxidizing nitrite is rapidly reduced into nitrogen without generating harmful gases such as nitrogen oxide.
Preferably, the catalytic reduction in step (2) comprises: and carrying out catalytic reduction reaction on the pre-reduction solution under the action of a catalyst and a second reducing agent to generate nitrogen and obtain the nitric acid removal solution.
Preferably, the second reducing agent comprises an organic reducing agent or an inorganic reducing agent.
Preferably, the organic reducing agent comprises formaldehyde and/or formic acid.
Preferably, the inorganic reducing agent comprises thiourea dioxide, phosphorous acid, ferrous sulfate or iron powder.
Preferably, the second reducing agent accounts for 2-10% of the mass fraction of the pre-reduction solution, and may be, for example, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or the like.
Preferably, the temperature of the catalytic reduction reaction is 40 to 60 ℃, for example, 40 ℃, 42 ℃, 45 ℃, 48 ℃, 50 ℃, 52 ℃, 55 ℃, 58 ℃ or 60 ℃.
Preferably, the time of the catalytic reduction reaction is 30-60 min, for example, 30min, 35min, 40min, 45min, 50min, 55min or 60 min.
Preferably, the mass concentration of nitrate in the nitric acid removing solution in the step (2) is less than 100mg/L, and may be 99mg/L, 95mg/L, 90mg/L, 85mg/L, 80mg/L, 75mg/L, 70mg/L, 60mg/L, 50mg/L, 40mg/L, 30mg/L, 20mg/L, 10mg/L, 5mg/L, or the like, without exceeding the detection limit.
Preferably, the nitric acid-removed solution obtained by the catalytic reduction is concentrated to obtain an acid product.
Preferably, before step (1), comprising: and (3) concentrating the acid solution containing nitrate radicals to obtain a concentrated solution.
In the invention, a concentration treatment step is further added before the pre-reduction to supplement the pre-reduction and the reduction steps, and the concentration step improves the hydrogen ion concentration, namely the acidity, in the acid solution to a higher range and then carries out the pre-reduction treatment, thereby generating better reduction effect.
Preferably, the concentration treatment mode comprises reduced pressure evaporation concentration or normal pressure evaporation concentration.
Preferably, the concentration treatment temperature is 50-70 ℃, for example, 50 ℃, 52 ℃, 55 ℃, 58 ℃, 60 ℃, 62 ℃, 65 ℃, 68 ℃ or 70 ℃.
Preferably, the molar concentration of hydrogen ions in the concentrated solution is 2-4 mol/L, for example, 2mol/L, 2.2mol/L, 2.5mol/L, 2.7mol/L, 2.8mol/L, 3mol/L, 3.2mol/L, 3.5mol/L, 3.8mol/L or 4 mol/L.
According to the invention, through controlling the molar concentration of hydrogen ions in the concentrated solution to be 2-4 mol/L and further controlling the temperature and time, nitrate radicals in the acid solution can be reduced to nitrite radicals, and a reactant is provided for subsequent catalytic reduction.
Preferably, when the molar concentration of hydrogen ions in the pre-reduction solution in the step (1) is less than 2mol/L, the pre-reduction solution is returned to the concentration treatment.
According to the invention, after pre-reduction, the hydrogen ion molar concentration in the pre-reduction solution may be less than 2mol/L, and at this time, the hydrogen ion molar concentration is preferably returned to the concentration step for concentration, and does not enter the next catalytic reduction reaction, so that a better reduction effect can be achieved, and the addition amount of the catalyst is reduced.
As a preferable technical scheme of the invention, the method comprises the following steps:
(1) concentrating an acid solution containing nitrate radicals at 50-70 ℃ to obtain a concentrated solution with the hydrogen ion molar concentration of 2-4 mol/L;
(2) adding a first reducing agent into the concentrated solution, carrying out pre-reduction reaction at 10-30 ℃ for 10-30 min to obtain a pre-reduction solution containing nitrite, and returning to the concentration treatment in the step (1) when the molar concentration of hydrogen ions in the pre-reduction solution is less than 2 mol/L; the first reducing agent comprises any one or a combination of at least two of ascorbic acid, glucose, isopropanol and oxalic acid, and accounts for 2-10% of the mass fraction of the concentrated solution;
(3) Adding a catalyst into the pre-reduction solution until the molar concentration of hydrogen ions in the pre-reduction solution is 8-15 mol/L, adding a second reducing agent, and performing catalytic reduction reaction at 40-60 ℃ for 30-60 min to generate nitrogen gas to obtain a nitric acid removal solution; the catalyst comprises any one or a combination of at least two of hydrochloric acid, sulfuric acid, fluosilicic acid and phosphoric acid, the second reducing agent comprises any one or a combination of at least two of formaldehyde, thiourea dioxide, phosphorous acid, formic acid, ferrous sulfate or iron powder, and the second reducing agent accounts for 2-10% of the mass fraction of the pre-reduction solution.
In a second aspect, the present invention provides an apparatus for the method for reducing nitrate nitrogen in an acid solution according to the first aspect, the apparatus comprising a concentration unit, a pre-reduction unit and a catalytic reduction unit connected in series.
The reduction device for nitrate radicals in acid solution provided by the invention can better realize reduction of nitrate radicals in nitrate radical-containing acid solution through the concentration unit, the pre-reduction unit and the catalytic reduction unit, and has higher industrial application value.
Preferably, the outlet of the pre-reduction unit is connected to both the inlet of the catalytic reduction unit and the inlet of the concentration unit.
According to the invention, the outlet of the pre-reduction unit is connected with the inlet of the concentration unit, so that the hydrogen ion concentration can be further concentrated and improved when the hydrogen ion concentration in the pre-reduction solution is low, and a better reduction effect can be achieved.
Preferably, the outlet of the catalytic reduction unit is connected to the inlet of the concentration unit.
The invention leads the nitric acid removing solution after catalytic reduction to be capable of recycling acid products after further concentration by connecting the outlet of the catalytic reduction unit with the inlet of the concentration unit.
Compared with the prior art, the invention at least has the following beneficial effects:
(1) the method for reducing nitrate radicals in acid solution provided by the invention adopts a reduction-concentration combined technology, and the reduction and concentration combined technology supplement each other; the reduction technology thoroughly removes nitrate radicals in the acid solution, finally improves the purity of acid products, and the concentration technology provides reaction conditions for the reduction technology, controls the temperature and the acidity and strengthens the reduction reaction;
(2) the method for reducing nitrate radical in acid solution provided by the invention has the advantages of high reaction speed, controllable reaction, single reducing substance, no secondary pollution and the like, and the content of nitrogen oxide in the generated gas is low and is 5mg/m3The following; and the used raw materials have wide sources, The concentration of the recovered acid product is high;
(3) the reduction device for nitrate radicals in acid solution provided by the invention has simple operating conditions and process technology, is suitable for any harsh conditions, can be applied to most industrial waste acid nitrate radical removal processes, and has a nitrate radical removal rate of more than 99% for different acid solutions.
Drawings
FIG. 1 is a schematic view of a reduction apparatus for nitrate nitrogen in an acid solution according to the present invention.
FIG. 2 is a schematic flow diagram of a process for reducing nitrate in an acid solution provided by the present invention.
In the figure: 1-a concentration unit; 2-a pre-reduction unit; 3-a catalytic reduction unit.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
The present invention is described in further detail below. The following examples are merely illustrative of the present invention and do not represent or limit the scope of the claims, which are defined by the claims.
The following examples employ an apparatus for reducing nitrate nitrogen in an acid solution as shown in fig. 1, which comprises a concentration unit 1, a pre-reduction unit 2 and a catalytic reduction unit 3 connected in sequence.
The outlet of the pre-reduction unit 2 is simultaneously connected with the inlet of the catalytic reduction unit 3 and the inlet of the concentration unit 1; the outlet of the catalytic reduction unit 3 is connected with the inlet of the concentration unit 1.
The flow chart of the method for reducing nitrate nitrogen in acid solution provided by the invention is shown in figure 2, and the method comprises the following steps:
(1) concentrating an acid solution containing nitrate radicals to obtain a concentrated solution with the hydrogen ion molar concentration of 2-4 mol/L;
(2) adding a first reducing agent into the concentrated solution, carrying out pre-reduction reaction to obtain a pre-reduction solution containing nitrite, and returning to the concentration treatment in the step (1) when the molar concentration of hydrogen ions in the pre-reduction solution is less than 2 mol/L;
(3) adding a catalyst into the pre-reduction solution until the molar concentration of hydrogen ions in the pre-reduction solution is 8-15 mol/L, adding a second reducing agent, and performing catalytic reduction reaction to generate nitrogen gas to obtain a nitric acid removal solution;
(4) and concentrating the nitric acid removing solution to obtain an acid product.
Example 1
The composition of the nitrate nitrogen-containing acid solution in this example included: the nitrate content is 50000mg/L, the COD value is 5000mg/L, and the mass content of the sulfuric acid is 5 percent.
This example provides a method for reducing nitrate in an acid solution, the method comprising the steps of:
(1) sending acid solution containing nitrate radicals into a reduction device, and carrying out evaporation concentration treatment at 70 ℃ under normal pressure to obtain concentrated solution with the hydrogen ion molar concentration of 2 mol/L;
(2) Adding glucose into the concentrated solution, wherein the mass of the glucose accounts for 10% of the total mass of the concentrated solution, and carrying out pre-reduction reaction at 10 ℃ for 10min to obtain a pre-reduction solution containing nitrite;
(3) adding concentrated sulfuric acid into the pre-reduction solution until the molar concentration of hydrogen ions in the pre-reduction solution is 8mol/L, adding formic acid, wherein the mass of the formic acid accounts for 2% of the total mass of the pre-reduction solution, and performing catalytic reduction reaction at 40 ℃ for 30min to generate nitrogen gas to obtain a nitric acid-removed solution;
(4) and concentrating the nitric acid-removed solution at 100 ℃ for 1h to obtain a sulfuric acid product.
Comparative example 1
The nitrate nitrogen-containing acid solution treated in this comparative example was the same as in example 1.
This comparative example provides a method for reducing nitrate nitrogen in an acid solution, which is the same as example 1 except that the concentration and pre-reduction treatment of step (1) and step (2) and the catalytic reduction of step (3) are not performed, and specifically includes the following steps:
adding concentrated sulfuric acid into the nitrate-containing acid solution until the molar concentration of hydrogen ions in the acid solution is 8mol/L, and concentrating at 100 ℃ for 1h to obtain a sulfuric acid product.
The mass concentration of nitrate, the mass concentration of sulfuric acid, and the COD value in the sulfuric acid products of example 1 and comparative example 1 were measured, and the nitrate removal rate in example 1 was calculated, with the results shown in table 1.
TABLE 1
As can be seen from table 1, in example 1, by sequentially concentrating, pre-reducing, catalytically reducing and re-concentrating the nitrate-containing acid solution, the removal rate of nitrate in example 1 is as high as 99.5% compared to the concentration treatment of the nitrate-containing acid solution directly in comparative example 1, the mass concentration of sulfuric acid can be increased from 45 wt% to 72 wt% in comparative example 1 at the same concentration time and temperature, and most of organic matters can also be removed, thereby showing that the present invention can remove not only nitrate and organic matters but also product concentration of acid by concentrating, pre-reducing and catalytically reducing the nitrate-containing acid solution.
Example 2
The nitrate-containing acid solution treated in this example was: an aqueous nitrate-containing fluorosilicic acid solution having a composition comprising: the nitrate content is 25000mg/L, and the mass content of the fluosilicic acid is 10 percent.
This example provides a method for reducing nitrate nitrogen in an acid solution, comprising the steps of:
(1) sending the acid solution containing nitrate radicals into a reduction device, and carrying out evaporation concentration treatment at 60 ℃ and normal pressure to obtain a concentrated solution with the hydrogen ion molar concentration of 3 mol/L;
(2) adding ascorbic acid into the concentrated solution, wherein the mass of the ascorbic acid accounts for 2% of the total mass of the concentrated solution, and carrying out pre-reduction reaction at 20 ℃ for 20min to obtain a pre-reduction solution containing nitrite;
(3) Adding fluosilicic acid with high concentration into the pre-reduction solution until the molar concentration of hydrogen ions in the pre-reduction solution is 12mol/L, then adding formaldehyde, wherein the mass of the formaldehyde accounts for 6% of the total mass of the pre-reduction solution, and carrying out catalytic reduction reaction at 50 ℃ for 45min to generate nitrogen gas and obtain a nitric acid removal solution;
(4) and concentrating the nitric acid removing solution at 70 ℃ for 1h to obtain a fluosilicic acid product.
Example 3
The nitrate nitrogen-containing acid solution treated in this example was the same as that of example 2.
This example provides a method for reducing nitrate in an acid solution, which is the same as in example 2 except that "ascorbic acid" in step (2) is replaced with "isopropyl alcohol".
Example 4
The nitrate-containing acid solution treated in this example was the same as in example 2.
This example provides a method for reducing nitrate in an acid solution, which is the same as in example 2 except that "ascorbic acid" in step (2) is replaced with "oxalic acid".
The mass concentration of nitrate radicals and the mass concentration of fluorosilicic acid in the fluorosilicic acid products of examples 2 to 4 were measured, and the nitrate radical removal rate was calculated, and the results are shown in table 2.
TABLE 2
As can be seen from Table 2, in examples 2 to 3, ascorbic acid, isopropanol and oxalic acid are respectively used as first reducing agents, so that the removal rate of nitrate radicals can reach more than 99%, and the mass concentration of the obtained fluosilicic acid is more than 29 wt%; and compared with isopropanol or oxalic acid as the first reducing agent, the ascorbic acid has the nitrate radical removal rate of 99.7 percent and has better reduction effect.
Example 5
The nitrate-containing acid solution treated in this example was: a nitrate-containing hydrochloric acid solution having a composition comprising: the nitrate content is 10000mg/L, the HCl mass content is 4 percent, and the COD value is 4500 mg/L.
This example provides a method for reducing nitrate in an acid solution, the method comprising the steps of:
(1) sending the acid solution containing nitrate radicals into a reduction device, and carrying out evaporation concentration treatment at 50 ℃ under reduced pressure to obtain a concentrated solution with the hydrogen ion molar concentration of 3 mol/L;
(2) adding ascorbic acid into the concentrated solution, wherein the mass of the ascorbic acid accounts for 6% of the total mass of the concentrated solution, and carrying out pre-reduction reaction at 30 ℃ for 30min to obtain a pre-reduction solution containing nitrite;
(3) adding concentrated hydrochloric acid into the pre-reduction solution until the molar concentration of hydrogen ions in the pre-reduction solution is 8mol/L, adding thiourea dioxide, wherein the mass of the thiourea dioxide accounts for 10% of the total mass of the pre-reduction solution, and performing catalytic reduction reaction at 40 ℃ for 60min to generate nitrogen and obtain a nitric acid removal solution;
(4) and concentrating the nitric acid-removed solution at 100 ℃ for 1h to obtain a hydrochloric acid product from the fraction.
Example 6
The nitrate-containing acid solution treated in this example was the same as in example 5.
This example provides a method for reducing nitrate in an acid solution, which is the same as that of example 5 except that "thiourea dioxide" in step (3) is replaced with "phosphorous acid".
Example 7
The nitrate nitrogen-containing acid solution treated in this example was the same as in example 5.
This example provides a process for the reduction of nitrate in an acid solution, which is the same as that of example 5 except that "thiourea dioxide" in step (3) is replaced with "ferrous sulfate".
Example 8
The nitrate nitrogen-containing acid solution treated in this example was the same as in example 5.
This example provides a method for reducing nitrate nitrogen in an acid solution, which is the same as that of example 5 except that "thiourea dioxide" in step (3) is replaced with "iron powder".
The mass concentration of nitrate and the mass concentration of hydrochloric acid in the hydrochloric acid products of examples 5 to 8 were measured, and the nitrate removal rate was calculated, and the results are shown in table 3.
TABLE 3
It can be seen from table 3 that in examples 5 to 8, different second reducing agents are respectively used for catalytic reduction, so that a better reduction effect can be obtained, the nitrate removal rate is over 99%, and the mass concentration of the finally obtained hydrochloric acid is increased by over 6 times compared with that of the hydrochloric acid in the original acid solution.
Example 9
The nitrate-containing acid solution treated in this example was: a nitrate-containing phosphoric acid solution having a composition comprising: the acid radical content is 1000mg/L, the phosphoric acid mass content is 5 percent, and the COD is 4500 mg/L.
This example provides a method for reducing nitrate nitrogen in an acid solution, comprising the steps of:
(1) sending the acid solution containing nitrate radicals into a reduction device, and carrying out evaporation concentration treatment at 70 ℃ and normal pressure to obtain a concentrated solution with the hydrogen ion molar concentration of 4 mol/L;
(2) adding ascorbic acid into the concentrated solution, wherein the mass of the ascorbic acid accounts for 10% of the total mass of the concentrated solution, and carrying out pre-reduction reaction at 30 ℃ for 20min to obtain a pre-reduction solution containing nitrite;
(3) adding concentrated phosphoric acid into the pre-reduction solution until the molar concentration of hydrogen ions in the pre-reduction solution is 15mol/L, then adding phosphorous acid, wherein the mass of the phosphorous acid accounts for 2% of the total mass of the pre-reduction solution, and carrying out catalytic reduction reaction at 60 ℃ for 60min to generate nitrogen gas, thereby obtaining a nitric acid removal solution;
(4) and concentrating the nitric acid removing solution at 100 ℃ for 1h to obtain a phosphoric acid product from the mother liquor.
Comparative example 2
The nitrate-containing acid solution treated in this comparative example was the same as in example 9.
This comparative example provides a method for reducing nitrate nitrogen in an acid solution, which is the same as in example 9 except that the pre-reduction reaction in step (2) is not performed, and specifically includes the steps of:
(1) Sending an acid solution containing nitrate radicals into a reduction device, and carrying out evaporation concentration treatment at 70 ℃ under normal pressure to obtain a concentrated solution with the hydrogen ion molar concentration of 4 mol/L;
(2) adding concentrated phosphoric acid into the concentrated solution until the molar concentration of hydrogen ions in the concentrated solution is 15mol/L, adding phosphorous acid, wherein the mass of the phosphorous acid accounts for 2% of the total mass of the pre-reduction solution, and performing catalytic reduction reaction at 60 ℃ for 60min to generate nitrogen gas to obtain a nitric acid removal solution;
(3) and concentrating the nitric acid removing solution at 100 ℃ for 1h to obtain a phosphoric acid product from the mother liquor.
In the catalytic reduction reaction processes of example 9 and comparative example 2, anhydrous acetic acid, sulfanilic acid, and naphthylenediamine hydrochloride were used to prepare an absorption solution, the gas above the reactor was collected, the concentration of nitrogen oxide was measured by a spectrophotometer, and the mass concentration of nitrate and the mass concentration of phosphoric acid in the phosphoric acid product were finally measured and the nitrate removal rate was calculated, and the results are shown in table 4.
TABLE 4
As can be seen from Table 4, in example 9, by adding a pre-reduction step between concentration and catalytic reduction, compared with the method of directly performing catalytic reduction after concentration in comparative example 2, although the difference between the final phosphoric acid product mass concentration and the nitrate removal rate is smaller in example 9 and comparative example 2, the nitrogen oxide concentration in the gas generated by catalytic reduction in example 9 is only 5mg/m 3Comparative example 2, however, produced a gas with a concentration of oxynitrides as high as 103mg/m3It is thus shown that the present invention, by using the concentration, pre-reduction and catalytic reduction methods, not only removes nitrate nitrogen, but alsoNitrogen oxide gas is not generated basically in the reduction process, so that the method is more environment-friendly and healthy.
The first reducing agent provided in the above embodiments may be used alone or in combination, so as to achieve similar technical effects, which are not described herein again.
The detection methods in the above examples and comparative examples are as follows:
sulfuric acid: the content of sulfate radical is measured by adopting a detection method in the national standard GB/T534-2002 and combining an ICS-5000Thermo ion chromatograph, and the concentration of the sulfuric acid is calculated.
Nitric acid: the detection method in the national standard GB/T337.1-2014 is adopted, and an ICS-5000Thermo ion chromatograph is combined to measure the content of nitrate and calculate the concentration of nitric acid.
Fluosilicic acid: the content of fluosilicic acid radical is measured by adopting a detection method in the chemical industry standard HG/T2832-2008 and combining an ICS-5000Thermo ion chromatograph, and the concentration of fluosilicic acid is calculated.
Hydrochloric acid: the content of chloride ions is measured by a titration method of total acidity in national standard GB320-2006 and an ICS-5000Thermo ion chromatograph, and the concentration of hydrochloric acid is calculated.
Phosphoric acid: measuring the content of phosphate radical and calculating the concentration of phosphoric acid by adopting a gravimetric method in the national standard GB/T2091-2003 and combining an ICS-5000Thermo ion chromatograph.
Chemical oxygen demand COD value: measured according to the dichromate method in the national standard GB 11914-89.
In summary, the method for reducing nitrate radical in acid solution provided by the invention reduces nitrate radical into nitrous acid state by pre-reducing acid solution containing nitrate radical, then carries out catalytic reduction to directly reduce nitrite radical into nitrogen gas, and provides reaction conditions for pre-reduction and reduction by integrating concentration treatment steps, thereby not only removing nitrate radical ions in acid solution, but also generating gas with low content of nitrogen oxide, wherein the content of nitrogen oxide is 5mg/m3In the following, the method can achieve better treatment effect aiming at different acid solutions, has the nitrate radical removal rate of more than 99 percent, and has higher industrial application value.
The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (18)
1. A method for reducing nitrate nitrogen in an acid solution, comprising the steps of:
(1) concentrating an acid solution containing nitrate radicals to obtain a concentrated solution with the hydrogen ion molar concentration of 2-4 mol/L;
(2) carrying out pre-reduction reaction on the concentrated solution obtained in the step (1) by using a first reducing agent to obtain a pre-reduction solution containing nitrite;
the first reducing agent comprises any one of or a combination of at least two of ascorbic acid, glucose, isopropanol or oxalic acid;
(3) adding a catalyst into the pre-reduction solution obtained in the step (2) to obtain a pre-reduction solution containing the catalyst and having a hydrogen ion concentration of 8-15 mol/L, and then performing catalytic reduction by using a second reducing agent to generate nitrogen gas to obtain a nitric acid removal solution;
the second reducing agent comprises an organic reducing agent or an inorganic reducing agent; the organic reducing agent comprises formaldehyde and/or formic acid; the inorganic reducing agent comprises thiourea dioxide, phosphorous acid, ferrous sulfate or iron powder;
the catalyst is an acid other than nitric acid.
2. The method according to claim 1, wherein the mass concentration of nitrate in the nitrate-containing acid solution in the step (1) is 1000 to 50000 mg/L.
3. The method according to claim 1, wherein the first reducing agent in step (2) accounts for 2-10% by mass of the nitrate-containing acid solution.
4. The method according to claim 1, wherein the temperature of the pre-reduction reaction in the step (2) is 10-30 ℃.
5. The method according to claim 1, wherein the time of the pre-reduction reaction in the step (2) is 10-30 min.
6. The method of claim 1, wherein the catalyst of step (3) comprises any one of hydrochloric acid, sulfuric acid, fluorosilicic acid, or phosphoric acid, or a combination of at least two thereof.
7. The method according to claim 1, wherein the second reducing agent in the step (3) accounts for 2-10% of the mass fraction of the pre-reduction solution.
8. The method according to claim 1, wherein the temperature of the catalytic reduction reaction in the step (3) is 40 to 60 ℃.
9. The method of claim 1, wherein the time of the catalytic reduction reaction in the step (3) is 30-60 min.
10. The method of claim 1, wherein the denitrated solution obtained by the catalytic reduction in step (3) is concentrated to obtain an acid product.
11. The method of claim 1, wherein the mass concentration of nitrate in the denitrified solution in step (3) is less than 100 mg/L.
12. The method according to claim 1, wherein the concentration treatment in step (1) comprises vacuum evaporation concentration or atmospheric evaporation concentration.
13. The method according to claim 1, wherein the concentration treatment in step (1) is carried out at a temperature of 50 to 70 ℃.
14. The method according to claim 1, wherein when the molar concentration of hydrogen ions in the pre-reduced solution in the step (2) is less than 2mol/L, the pre-reduced solution is returned to the concentration treatment.
15. Method according to claim 1, characterized in that it comprises the following steps:
(1) concentrating an acid solution containing nitrate radicals at 50-70 ℃ to obtain a concentrated solution with the hydrogen ion molar concentration of 2-4 mol/L;
(2) adding a first reducing agent into the concentrated solution, carrying out pre-reduction reaction for 10-30 min at 10-30 ℃ to obtain a pre-reduction solution containing nitrite, and returning to the concentration treatment in the step (1) when the molar concentration of hydrogen ions in the pre-reduction solution is less than 2 mol/L; the first reducing agent comprises any one or a combination of at least two of ascorbic acid, glucose, isopropanol and oxalic acid, and accounts for 2-10% of the mass fraction of the concentrated solution;
(3) Adding a catalyst into the pre-reduction solution until the molar concentration of hydrogen ions in the pre-reduction solution is 8-15 mol/L, adding a second reducing agent, and performing catalytic reduction reaction at 40-60 ℃ for 30-60 min to generate nitrogen gas to obtain a nitric acid removal solution; the catalyst comprises any one or a combination of at least two of hydrochloric acid, sulfuric acid, fluosilicic acid and phosphoric acid, the second reducing agent comprises any one or a combination of at least two of formaldehyde, thiourea dioxide, phosphorous acid, formic acid, ferrous sulfate or iron powder, and the second reducing agent accounts for 2-10% of the mass fraction of the pre-reduction solution.
16. An apparatus for the method of reducing nitrate nitrogen in an acid solution according to any one of claims 1 to 15, which comprises a concentration unit, a pre-reduction unit and a catalytic reduction unit connected in series.
17. The apparatus of claim 16, wherein the outlet of the pre-reduction unit is connected to both the inlet of the catalytic reduction unit and the inlet of the concentration unit.
18. The apparatus of claim 16, wherein the outlet of the catalytic reduction unit is connected to the inlet of the concentration unit.
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