JPH06182344A - Decomposition and utilization method and device for salt and inorganic nitrogen compound-containing solution - Google Patents

Abstract

PURPOSE:To make harmless effectively waste water containing salt harmful to animals and vegetables and an inorganic nitrogen compound such as nitric acid and ammonia causing problems of the enrichmet of a water area by means of chemical and electrical method and also provide a method of recovering and reusing hypochlorite having sterlization force or the like. CONSTITUTION:Nitric acid or the like is formed by (a) electrolyzing water solution 1 containing salt and an inorganic nitrogen compound in a single electrolytic cell or (b) the electrolysis cell is divided by an ion exchange membrane or a diaphragm into two cells, and water solution is introduced into a first cell 7 provided with an anode 3 to electroytically oxidize ammonia and salt or the like to form nitric acid, and then introduced into a second cell 11 provided with a cathode 5 and nitric acid is electrolytically reduced to form a harmless nitrogen gas or the like. (c) Chlorine gas 10 formed in the first cell and caustic soda formed in the second cell are introduced into a reaction tank in which hypochlorite and chloramine with sterilization force are formed and recovered. (d) Chemical reduction is performed by using metal, and can be treated and recovered in the process of (a)-(c).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention electrolyzes a solution containing salt and / or nitric acid, nitrous acid, ammonia, etc., in a single electrolytic cell, or in the first tank (and third tank).
Chlorine gas by electrolytically oxidizing salt and ammonia at the anode of
Nitric acid, chloramine, nitrogen gas, etc. are generated, and nitric acid is electrolytically reduced to nitrogen gas etc. in the second tank (and the fourth tank) in which the cathode is installed, and the generated chlorine gas and alkaline solution are mixed in the fifth gas.
It is a method of mixing hypochlorite and / or chloramine by mixing in a tank and using it for sterilizing bacteria. Therefore, treatment of an aqueous solution containing a high concentration of salt, nitric acid or ammonia. It is particularly effective in the fields of clean water, sewage and industrial wastewater treatment.

[0002]

2. Description of the Related Art Conventionally, there is no effective treatment method for an aqueous solution containing a high concentration of salt, and it has been concentrated to a solid or diluted and then discharged into a sewer or a public water area. On the other hand, although there was an ammonium stripping method for the solution containing ammonium, there was no suitable method for the solution containing nitric acid.

In recent years, biological denitrification methods for nitric acid- and ammonium-containing aqueous solutions have been developed and applied in various fields. However, in the case of an aqueous solution that does not contain organic substances at the same time, there is a drawback that it is necessary to add appropriate organic substances. Moreover, this method is ineffective for salt removal. Therefore, there is still no suitable treatment method for an inorganic aqueous solution containing salt and nitric acid, nitrous acid, ammonia and the like.

[0004]

Aqueous solutions containing salt at a high concentration and further containing nitric acid and / or ammonium have been generated in various places in the field of wastewater treatment. High concentrations of salt are harmful to plants and animals, and nitrogen components cause the problem of nutrient eutrophication in water bodies, so both must be properly treated. However, the operation of the biological denitrification method for the inorganic aqueous solution containing nitric acid and / or ammonia requires the addition of organic matter, but the organic matter to be used may be devised depending on the intended use of the treated water, such as drinking water. In addition, the problem of the amount of residual organic matter in the treated water and the harmfulness of the produced organic matter in the biological treatment process occurs. Further, there is still no treatment method for the salt-containing solution as described above. On the other hand, in small and medium-sized wastewater treatment facilities, sterilization is insufficient, and there are many places that discharge wastewater containing a large amount of bacteria such as Escherichia coli, which solves problems related to supply of bactericides and maintenance of sterilizers. There is a need to.

Therefore, there is provided a method and apparatus for removing nitrogen components contained in wastewater into harmless nitrogen gas from an aqueous system and producing hypochlorite having a bactericidal activity from the coexisting salt to recover and utilize it. It is intended to be provided.

[0006]

Means for Solving the Problems The means of the present invention for solving the above-mentioned problems are as follows: (a) Water containing salt and / or inorganic nitrogen compound salt in one electrolytic water tank provided with an anode and a cathode. Or, to the aqueous solution containing ammonium, introduce water containing an electrolyte such as carbonate, sulfate, or salt as necessary to enhance the conductivity and decomposability, and perform electrolytic oxidation under the condition of pH = 1 to 14. And electrolytic reduction to produce chloramine, sodium hypochlorite, nitrogen gas or the like, or (b) the first tank and the second tank are separated by an ion exchange membrane or a diaphragm. An anode is installed in the tank, and water containing a salt and / or an inorganic nitrogen compound is continuously added thereto, or an aqueous solution containing an ammonia is added, if necessary, to improve the conductivity and decomposability, carbonate, Sulfate, salt, etc. The first step (c) and the first step in which water with an electrolyte added is introduced, and ammonia and salt are electrolytically oxidized under the condition of pH = 1 to 14 to generate chloramine, nitric acid, nitrogen gas, chlorine gas, etc. The resulting solution is introduced into a heated water tank, and the solution is subjected to the second step and (d) the first or second step, in which the partially generated ammonium nitrate or ammonium nitrite is thermally decomposed into nitrogen gas, and the cathode is installed. In an aqueous solution that is made alkaline by the OH ⁻ ions generated as a result of electrolysis, or by introducing PH into the second tank.
= 1 to 14, in the third step in which nitric acid is electrolytically reduced to nitrogen gas and (e) the third step, if ammonia or the like remains, it is refluxed again to the first tank. Oxidize it to nitric acid, etc. and lead it to the second tank again, and electrolytically reduce the generated nitric acid to nitrogen gas, or separate the third tank and the fourth tank with an ion exchange membrane or diaphragm. , The ammonia-containing solution from the second tank is introduced into the third tank in which the anode is installed for electrolytic oxidation,
The fourth step of electrolytically reducing to nitrogen gas in the fourth tank equipped with a cathode, and (f) the chlorine gas generated in the first tank (or the first tank and the fourth tank) and the second tank (or the second tank). 2nd and 4th tanks) The fifth step of mixing the alkaline solutions formed in the 5th tank to form hypochlorite, and (g) the hypochlorite formed in the 5th step. And / or pooling an aqueous solution containing chloramine, or
It is characterized by being equipped with a sixth stage used for sterilizing bacteria by injecting it into the treated water of an adjacent treatment facility, and a reaction accelerating device such as stirring installed in each stage if necessary. A method and apparatus for decomposing a solution containing salt, nitric acid, nitrous acid, ammonia and the like.

Further, means other than the above are as follows: (a) In the preceding stage of the steps (a) and (b) described in "Claim 1", aluminum, iron, zinc, manganese, vanadium, palladium and other metals are used. Powder, metal salt,
A metal oxide is added under a predetermined pH condition (pH 1 to 9) and stirred for 1 to 120 minutes to reduce nitric acid in raw water,
The first stage such as nitrogen gas, nitrous acid, ammonia, etc., (b) the second stage for filtering unreacted metal by filtering the mixed liquid of the first stage, and (c) the second stage of filtering liquid Electrolyze in a single electrolysis tank or lead to the first tank and electrolytically oxidize and decompose ammonia, nitrous acid and / or salt at the anode to produce chloramine, hypochlorite, nitrogen gas, nitric acid, etc. , The third step of oxidizing the eluted metal to insolubilize it by oxidizing the metal (partially by further adjusting the pH), (d) filtering the third step Lead to the second tank with the cathode installed, and electrolytically reduce the remaining nitric acid to produce nitrogen gas in the fourth step (e) The metals recovered in the second and third steps are converted into the nitric acid in the first step. And a fifth step of utilizing the salt and / or the glass according to claim 1 or 2, characterized in that A method and apparatus for decomposing a solution containing acid, nitrous acid, ammonia, etc.

[0008]

Function Nitrogen forms a +5 to -3 valent compound. Therefore, theoretically, N ₂ O ₅ (5
+) Or N ₂ O ₃ (3+) can be electrically reduced to give N
₂ (0) NH ₃ (3-), etc., and if NH ₃ (3-) is oxidized, N ₂ O ₅ (5+), N ₂ O ₃ (3+), N
₂ (0) will be formed.

It is known here that the nitric acid concentration can be reduced by chemical and electrochemical methods.
(For example, W. Heilgeist "Reduction"
n des Mittelakiven abfall
es durch Salzfree Verfah
renshrite ”Kernforschung
s zentrum Karlsruhe Gmbh,
No. 2940, March 1980) However, according to an electrochemical experiment of the present inventor, pH = 1.
~ 14 is possible, but pH = 8-14, temperature = 30
It was confirmed that the efficiency was high when the treatment was carried out in the range of -100 ° C under alkaline conditions and high temperature as much as possible. Also,
The present discoverer found and confirmed that powders of aluminum, iron, zinc, manganese, and other metals and salts and oxides thereof reduce nitric acid to form nitrous acid and ammonium. On the other hand, ammonium nitrate and ammonium nitrite formed in the electrolytic reduction process of nitric acid are converted into
It is also known to decompose by ~ 3. (Sakae Tsuda; general theory of inorganic chemistry, Soo Ishikawa; detailed explanation of inorganic chemistry, etc.)

[0010]

[Chemical 1]

[0011]

[Chemical 2]

[0012]

On the other hand, the present inventor has discovered that when electrolytically oxidizing an aqueous solution in which ammonium and salt coexist, the ammonia concentration decreases and forms N ₂ , NH ₂ Cl, etc.
I'm confirming. Furthermore, it has been discovered and confirmed that the electrolytic oxidation of ammonia is promoted even in the presence of nitrate ions, bicarbonate ions, sulfate ions, etc. existing in natural water and waste water for various uses in addition to salinity. On the other hand, when salt water is electrolyzed, chlorine gas is used at the anode and alkali (Na
It is also known to produce OH) and has already been applied to various industries (Yoshida Shiro; Electrochemical Experimental Method, April 1979).

[0013]

[Chemical 4]

[0014]

It is also known that when the generated chlorine gas is reacted with caustic soda, sodium hypochlorite is formed as shown in Chemical formula 6 and it has a bactericidal action, which has already been applied in various fields. (Sakae Tsuda; General Theory of Inorganic Chemistry, May 1964).

[0015]

On the other hand, it is also known that when hypochlorite or chlorine gas reacts with ammonium ion, chloramine is formed as shown in Chemical formulas 7 to 9 and that this chloramine has a bactericidal action. (F. Wilson
& D. Barnes; Chemistry and
Unit Operations in Water
treatment, 1983).

[0016]

[Chemical 7]

[0017]

[Chemical 8]

[0018]

It is also known that when chlorine gas or hypochlorite is injected into an aqueous solution containing chloramine, the reaction as shown in Chemical formulas 10 to 13 causes chloramine to decompose and generate nitrogen gas. There is (F. Wilson & D. Bar
nes; Chemistry and Unit Ope
relations in Water treatmen
t, 1983).

[0019]

[Chemical 10]

[0020]

[Chemical 11]

[0021]

[Chemical 12]

[0022]

[Chemical 13]

Thus, (a) electroless reduction of nitric acid into harmless nitrogen gas or the like, (b) electrolysis of salt to form chlorine gas and caustic soda, (c) generated chlorine gas and caustic soda To form sodium hypochlorite having a bactericidal action, and (d) reacts with chlorine gas or sodium hypochlorite even if ammonium is present in the raw water or the electrolytically treated liquid to sterilize. It is known that chloramine having an action is formed, and that (e) chloramine reacts with chlorine gas or sodium hypochlorite to form nitrogen gas. Note that the present inventor, when carbonate is coexisted in a system containing a sulfate ion as an electrolyte and electrolyzed in the presence of ammonium, the ammonium is oxidized to reduce its concentration, forming nitric acid and nitrous acid, and chlorine ion. It has been discovered that chloramine is also formed when a system coexisting with is electrolyzed.

However, these reactions are individually utilized. Therefore, in order to treat the wastewater containing salt and / or nitric acid and / or ammonia, and utilize the produced active ingredient, these known facts and the electrolytic oxidation of the ammonia found and confirmed by the present inventor are required. The phenomena need to be combined effectively. The present inventor, as a result of studies to provide an improved method for engineeringly performing the above-mentioned known method and discovery phenomenon,

(A) Water containing salt and / or inorganic nitrogen compound salt is introduced into a single electrolytic water tank provided with an anode and a cathode, and electrolytic oxidation and electrolytic reduction are carried out under the condition of pH = 1 to 14. , Chloramine, sodium hypochlorite, nitrogen gas, etc., or aluminum in an aqueous solution containing salt, nitric acid, ammonia, etc.,
Powders of iron, zinc, manganese, other metals, metal salts, and metal oxides are added under predetermined pH conditions (pH 1 to 9) and stirred to reduce nitric acid in raw water to obtain nitrogen gas, nitrous acid, Post-electrolytic oxidation / reduction as ammonia, or

(B) The first tank and the second tank are separated by an ion exchange membrane or a diaphragm, and an anode is installed in the first tank, and water containing salt and / or an inorganic nitrogen compound is continuously added thereto. And a first step in which chloramine, nitric acid, nitrogen gas, chlorine gas, etc. are generated by electrolytically oxidizing ammonia and salt under the condition of pH = 1 to 14.

(C) The solution which has passed through the first step is introduced into a heated water tank, and the second step in which the ammonium nitrate or ammonium nitrite partially produced is pyrolyzed to nitrogen gas, and (d) the first or second The solution that has undergone the step of is introduced into a second tank in which a cathode is installed, and in an aqueous solution that is alkaline due to OH ⁻ ions generated as a result of electrolysis, or
= 1 to 14 and a third step of electrolytically reducing nitric acid to nitrogen gas,

(E) In the third step, if ammonia or the like remains, it is refluxed again in the first tank to be oxidized to nitric acid and the like, and then introduced into the second tank to electrolytically reduce the produced nitric acid. Or nitrogen gas or the like, or the third and fourth tanks are similarly separated by an ion exchange membrane or a diaphragm, and the ammonia-containing solution from the second tank is introduced into the third tank with an anode for electrolysis. It was found that a nitrogen compound such as nitric acid can be effectively decomposed into harmless nitrogen gas or the like by the fourth step of oxidizing and electrolytically reducing in a fourth tank equipped with a cathode to nitrogen gas. Also,

(F) The chlorine gas produced in the first tank (or the first tank and the fourth tank) and the alkaline solution produced in the second tank (or the second tank and the fourth tank) are mixed in the fifth tank. And a fifth step to form hypochlorite etc.

(G) The aqueous solution containing hypochlorite and / or chloramine produced in the fifth step is stored or injected into the treated water of the adjacent treatment facility to sterilize the bacteria. It has been found that the sixth step used for this purpose can reduce the cost of electrolytic treatment of nitrogen compounds and salts and measure effective use of resources.

[0031]

The present invention will now be described with reference to the accompanying drawings, but the present invention is not limited to these drawings and embodiments.

FIG. 1 is a conceptual diagram of "a method and apparatus for decomposing / utilizing a solution containing a salt and an inorganic nitrogen compound" of the present invention. The device is basically (a) equipped with an anode and a cathode 1
Electrolysis separated by two electrolyzed water tanks or a cation exchange membrane or diaphragm (8) into a first tank (7) with an anode (3) and a second tank (11) with a cathode (5). A water tank, (b) heating section (9) for the electrolytic solution from the first tank,
(C) The electrolytic solution from the second tank is mixed with chlorine gas (15) generated in the first tank to mix sodium hypochlorite and / or
Alternatively, it comprises three parts of the reaction tank (13) for forming chloramine.

The salt and / or inorganic nitrogen compound-containing solution (1) is introduced into the first tank (7), where ammonia and salt are electrolytically oxidized to nitric acid and nitrogen gas (a part of the ammonia becomes chloramine. Part is oxidized to nitrogen gas), and chlorine gas is generated.

Next, the electrolytic solution in the first tank is introduced into the heating section (9), and the partially formed ammonium nitrite or the like is thermally decomposed into nitrogen gas, and then introduced into the second tank (11). However, when the amount of ammonium nitrite produced is small due to the method of setting the electrolysis conditions, the electrolytic solution in the first tank is directly introduced into the second tank.

In the second tank (11) provided with a cathode, the nitric acid from the first tank is electrolytically reduced into nitrogen gas or the like in an aqueous solution which is alkaline due to OH ions generated as a result of electrolysis. Then, it is led to the reaction tank (fifth tank) (13). Here, the chlorine gas generated in the first tank and the alkali generated in the second tank are mixed and reacted to form hypochlorite and / or chloramine. However, the second tank (1
If there is a concentration of ammonia that cannot be overlooked in the electrolyte of 1), it is refluxed again in the first tank to oxidize it to nitric acid, etc., and then introduced again into the second tank to electrolytically reduce the generated nitric acid. Or use nitrogen gas or the like, or install the third and fourth tanks similar to the first and second tanks, introduce the electrolytic solution in the second tank into the third tank, and electrolytically oxidize ammonia and salt, It is also possible to perform electrolytic reduction in four tanks to produce nitrogen gas or the like.

FIG. 2 shows the relationship between the change in nitrate ion (19) and the amount of current (A) when a system containing no salt and having a pH of 14 and sodium nitrate of 0.04 M was electrolyzed. Under alkaline conditions, when the current is increased, nitrate ions are electrolytically reduced, and the concentration thereof decreases. However, depending on the set conditions, ammonium salt (21) and / or nitrite (23) are formed.

FIG. 3 shows an aqueous solution of sodium chloride (NaCl) = 10% and sodium nitrate (NaNO ₃ ) = 0.04 M, pH = 7.
When electrolyzing in an electrolytic cell with a diaphragm under the conditions of 1), the pH in the first cell (anode) and the second cell (cathode), and the first cell
The time-dependent change of the chlorine ion amount in a tank (anode) is shown. In the first tank (anode), chlorine ions (29) are electrolytically oxidized to generate chlorine gas and hypochlorite (31), and as a result, the chloride ion concentration (29) and pH (27) are lowered. Occur. On the other hand, as a result of electrolytic reduction at the cathode, the pH becomes alkaline (25), and basically, the reduction of nitric acid similar to the tendency shown in FIG. 2 occurs.

FIG. 4 shows that ammonia (NH ₄ OH) = 0.
The time course of ammonium ions in the first tank (anode) when a system containing 03M and sodium carbonate = 0.25M is electrolyzed in an electrolytic tank having a diaphragm is shown. It has been shown that as a result of electrolytic oxidation at the anode, ammonium ions (33) are oxidized to nitrates (35). The degree of oxidation changes depending on the set conditions.

FIG. 5 shows that pH = 5 and sodium nitrate 100
In a system containing mg / l, manganese (41), subsalt (3
9) shows the change with time of nitrate ion when metal powder of aluminum (37) was added and stirred. As shown in this figure, in the case of adding manganese, almost 100% of nitrate is reduced by contact for about 15 minutes, but the nitrate reduction rate of aluminum is low. Thus, the nitric acid reduction rate differs depending on the metal even under the same conditions. Although not shown, the concentrations of nitrogen gas, nitrous acid, and ammonia produced as a result of nitric acid reduction also differ depending on the metal, so it is necessary to set conditions such as the metal, pH, and contact time depending on the purpose of treatment.
In any case, the metal and its salt reduce nitric acid to nitrogen gas, nitrous acid, ammonia, etc., so that it is possible to form nitrogen gas, chloramine, etc. in combination with the electrolytic treatment.

As described above, the electrolytic oxidation / reduction causes the oxidation of chlorine ions and ammonia at the anode and the reduction of nitric acid at the cathode under alkaline conditions to generate chlorine gas, chloramine, nitrogen gas, etc. Iso-reactions will be available for processing and recycling purposes.

[0041]

The "method and apparatus for decomposing / utilizing a solution containing a salt and an inorganic nitrogen compound" of the present invention has the above-described effects, and therefore (1) salt and / or nitric acid, ammonia and the like are simultaneously added. And, it has a function of decomposing into harmless nitrogen gas etc. in a short time, and (2) as a result of electrolysis, hypochlorite or chloramine having a bactericidal effect is produced, and this can be used as a bactericide Since (3) is an electrolytic reaction, it has an effect of enabling automation of processing and labor saving.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of “a method and apparatus for decomposing / utilizing a solution containing salt and an inorganic nitrogen compound” of the present invention.

FIG. 2 shows the relationship between the change in nitrate ion concentration and the amount of current (A) when electrolyzing in a single electrolytic cell.

FIG. 3 shows the changes with time of pH in the first tank (anode) and the second tank (cathode) when electrolyzing in an electrolytic cell having a diaphragm.
It is a change over time in the amount of chlorine ions in the tank (anode).

FIG. 4 is a time-dependent change of ammonia in the first tank (anode) when electrolyzing in an electrolytic cell having a diaphragm.

FIG. 5 is a change with time of nitrate ions when metal powders of manganese, subsalt, and aluminum are added and stirred.

[Explanation of symbols]

 1 Salt and / or Inorganic Nitrogen Compound-Containing Aqueous Solution 3 Anode 5 Cathode 7 First Tank 9 Heating Water Tank 11 Second Tank 13 Mixing Water Tank (Reaction Tank) 15 Chlorine Gas 17 Hydrogen Gas 19 Nitrate Ion 21 Ammonium 23 Nitrite Ion 25 Cathode PH 27 Anode pH 29 Chlorine ion 31 Chloramine 33 Ammonia 35 Nitrate ion 37 Reduction with aluminum 39 Reduction with subsulfite 41 Reduction with manganese

Claims (3)

[Claims] 1. (a) Introducing water containing salt and / or an inorganic nitrogen compound into one electrolytic water tank provided with an anode and a cathode, and performing electrolytic oxidation and electrolytic reduction under conditions of pH = 1 to 14. , Chloramine, sodium hypochlorite, nitrogen gas or the like, or (b) in the electrolytic cell in which the first tank and the second tank are separated by an ion exchange membrane or a diaphragm, the first tank has an anode. Is installed, and water containing salt and / or inorganic nitrogen compound is continuously introduced therein, and p
Under the condition of H = 1 to 14, electrolytically oxidize ammonia and salt to produce chloramine, nitric acid, nitrogen gas, chlorine gas, etc. The first step and (c) the solution that has passed through the first step is introduced to a heating water tank, The solution that has undergone the second step of (d) the first or second step of thermally decomposing ammonium nitrate or ammonium nitrite that has been partially formed into nitrogen gas is introduced into a second tank equipped with a cathode, and electrolysis is performed. In an aqueous solution that is alkaline due to the resulting OH ^- ions, or p
Under conditions of H = 1 to 14, in the third step of electrolytically reducing nitric acid to nitrogen gas and (e) the third step, if ammonia or the like remains, it is returned to the first tank again. And oxidize it to form nitric acid, and then lead it to the second tank again, and electrolytically reduce the generated nitric acid into nitrogen gas, or use an ion exchange membrane or a diaphragm between the third tank and the fourth tank in the same manner. Separately, the ammonia-containing solution from the second tank is introduced into a third tank with an anode for electrolytic oxidation, and a fourth tank with a cathode is electrolytically reduced to produce nitrogen gas. Chlorine gas produced in one tank (or first tank and fourth tank) and second tank (or second tank)
Tank and fourth tank) to mix the alkaline solution in the fifth tank to form hypochlorite, and (g) hypochlorite formed in the fifth step and (g) And / or containing chloramine (2) A sixth step of storing an aqueous solution or injecting it into treated water of an adjacent treatment facility to sterilize bacteria, and if necessary, And a device for decomposing a solution containing salt and nitric acid, nitrous acid, ammonia, etc., characterized by comprising a reaction promoting device such as stirring installed in stages 2. An aqueous solution containing ammonium, if necessary, in order to improve the conductivity and decomposability, carbonate, sulfate,
A salt and / or nitric acid, nitrous acid, or the like according to claim 1, wherein an electrolyte such as salt is added, and electrolytically oxidized and electrolytically reduced by the method according to "claim 1" to produce nitrogen gas or the like. Method and apparatus for decomposing solution containing ammonia etc. 3. (a) In the preceding stage of the steps (a) and (b) of claim 1, aluminum, iron, zinc, manganese, vanadium, palladium, powders of other metals, metal salts and metals. Oxide is added under the specified pH condition (p
H1-9), stir for 1-120 minutes, reduce nitric acid in raw water, and pass through the mixed solution of the first step (b) the first step such as nitrogen gas, nitrous acid, ammonia, etc. Etc. to separate unreacted metals and electrolyze the filtered solution of the second step and (c) second step in a single electrolysis tank, or lead to the first tank and ammonia, nitrous acid at the anode And / or salt is electrolyzed and decomposed into chloramine, hypochlorite, nitrogen gas, nitric acid, etc., and the eluted metal is further oxidized (partial metal, pH is adjusted further. ) Insolubilize and introduce the filtered liquid of the third step (d) the third step, which is recovered by solid-liquid separation method such as filtration, into the second tank equipped with a cathode, and electrolytically reduce the remaining nitric acid. The metal recovered in the fourth step (e) the second and third steps using nitrogen gas or the like is used for the nitric acid reduction in the first step. Fifth claims 1 and 2 salt and / or (3) according to; and a step of nitric acid, nitrous acid decomposition method and apparatus of the solution containing the Anmoniya like