JP3665918B2 - Treatment method for petroleum combustion ash - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for efficiently recovering an active ingredient (hereinafter referred to as a valuable material) contained in combustion ash by wet-treating petroleum-based combustion ash.
[0002]
[Prior art]
When burning high-S heavy oil, petroleum-based fuel or the like in a thermal power plant, a part of sulfur dioxide (SO ₂ ) in the flue gas generated by the combustion is oxidized to sulfur gas (SO ₃ ). SO ₃ becomes sulfuric acid mist when moisture is present, and corrodes metals such as dust collectors and flues. In order to prevent this, ammonia (NH ₃ ) is generally injected into the exhaust gas, and SO ₃ is reacted to form ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) or acidic ammonium sulfate (NH ₄ HSO ₄ ), and combustion ash Collect with a dust collector. Therefore, the characteristics of the collected combustion ash are mainly composed of ammonium (NH ₄ +) and sulfate radical (SO ₄ ² −). Besides this, vanadium (V), nickel (Ni), magnesium (Mg), etc. Is contained in several percent. A number of patents relating to methods for recovering the above main components from combustion ash as valuables have been filed (for example, JP-A 61-171582, JP-A 61-177153, JP-A 50-9570, JP-A 62-62). 298489, Literature: Chemical Engineering Vol.56, No.6, P391, 1992).
[0003]
For example, as a method for wet-treating combustion ash, a method of adding a reducing agent such as acid (or alkali) and hydrazine (N ₂ H ₄ ) to a water mixture of combustion ash and dissolving it, or oxidizing heat treatment A number of methods for recovering valuable materials mainly including separation and recovery of vanadium have been proposed, such as a method of crystallization separation with V being pentavalent.
[0004]
Moreover, after recovering vanadium, valuable materials in the combustion ash can be recovered by operations such as nickel recovery, ammonia recovery around pH 11 and gypsum recovery. However, the ash treatment method including the recovery of valuable materials as described above has a low purity of recovered vanadium, a low recovery rate of vanadium, or a complicated system and a problem in operability and economy. Most of them do not reach the point where they are applied to actual devices.
[0005]
As a result of earnestly proceeding with research on a method for treating combustion ash in the context of a wet desulfurization apparatus, the present inventors once precipitated vanadium as a hydroxide together with nickel, separated and recovered the precipitate, dissolved, and adjusted the vanadium concentration. The present invention recovers vanadium with high purity by increasing the temperature and heating and oxidizing it and precipitating it as ammonium metavanadate. The recovered ammonia is effectively used as an alkaline agent for pH adjustment necessary in the system, and all the sulfates in the remaining liquid from which vanadium and ammonia have been recovered are recovered as gypsum and supplied to the desulfurization tower. Is the main point of the present invention.
[0006]
[Problems to be solved by the invention]
The above-described conventional methods for recovering valuable materials, particularly recovery of vanadium, include a crystallization method as ammonium metavanadate and a precipitation method as a hydroxide. In the former, it is possible to recover high-purity vanadium, but it takes a long time and a large crystallization tank to perform crystallization by removing from 70 ° C. or more to room temperature for crystallization, In addition, there is a problem that another device is required to collect vanadium that cannot be recovered by crystallization. Further, when vanadium concentration in the slurry is low in order to oxidize vanadium with air, there is a problem that the volume of the reaction tank becomes large. The latter has a feature that the system is simple, but there is a problem in that the purity of vanadium cannot be increased because nickel or the like coprecipitates during precipitation collection as a hydroxide.
[0007]
The object of the present invention is to propose an economical process for recovering vanadium from the combustion ash of petroleum-based fuels. In addition, how to efficiently treat the remaining components from which vanadium has been recovered is a major issue for practical use.
[0008]
[Means for Solving the Problems]
The above purpose is to dissolve combustion ash by adding acid and / or a reducing agent to an aqueous solution, then raising the pH to around 6 to precipitate hydroxide, and separating vanadium and nickel from other components in the slurry. Then, the separated precipitate is concentrated, heated at pH 6 to 9 and oxidized by blowing air, and further adjusted to pH 5 to 7 (preferably 6) to precipitate ammonium metavanadate. In particular, when oxidizing using air, it is important to oxidize by supplying air for oxidation from the bottom of the tower in order to improve stirring of the concentrated slurry, and to increase the concentration of vanadium by concentrating the slurry. In addition, slaked lime is added to the liquid after recovering vanadium to raise the pH, and this is heated to recover ammonia, and then all the sulfate in the remaining solution is precipitated as gypsum, and this slurry liquid is put into the desulfurization tower. Supplying is a major feature.
[0009]
The first means of the present invention for achieving the above object is to dissolve the combustion ash collected by a dust collector installed in an exhaust gas flow path such as a boiler using petroleum-based fuel into an aqueous solution to make a slurry. In accordance with the method for treating petroleum-based combustion ash in which acid and / or a reducing agent is added to dissolve the combustion ash and the insoluble matter is separated and removed from the solution after separating the vanadium, the insoluble matter is separated and removed. After adding the alkali to the solution, the pH is adjusted to 6 or more to precipitate vanadium and nickel as hydroxides, the precipitate is separated and recovered and redissolved, and the solution is heated and oxidized. To separate and recover vanadium as a precipitate of ammonium metavanadate . Moreover, an insoluble matter is supplied to a desulfurization apparatus.
[0010]
A second means of the present invention for achieving the above object is that in the first means, an alkali is added to the solution after the insoluble matter is separated and removed to adjust the pH to 6 to 8 to add vanadium and nickel. A vanadium concentrate, which is a high-concentration slurry liquid that is precipitated as a hydroxide and concentrated and separated, is heated to 60 ° C. or higher, and oxidized to pH 6-9 in the presence of ammonia to convert vanadium to ammonium metavanadate. It is characterized by collect | recovering as.
[0011]
A third means of the present invention for achieving the above object is characterized in that, in the second means, the vanadium concentrate is oxidized by blowing air into the vanadium concentrate as a slurry when oxidizing the vanadium concentrate. To do.
[0012]
The fourth means of the present invention for achieving the above object is that in the second or third means, an acid is added to the solution after the oxidation treatment to adjust the pH to 5 to 7, and the ammonium metavanadate compound is precipitated and precipitated. It is characterized by being separated from the solution.
[0013]
A fifth means of the present invention for achieving the above object is characterized in that, in the above fourth means, the solution after precipitation separation with vanadium as an ammonium metavanadate compound is returned to an ash dissolution tank for dissolving combustion ash. .
[0014]
According to a sixth means of the present invention for achieving the above object, a flocculant is added to a precipitate obtained by precipitating vanadium and nickel as a hydroxide in order to produce the high-concentration slurry liquid. The precipitate is aggregated to make the vanadium hydroxide concentration 5,000 ppm or more.
[0015]
A seventh means of the present invention for achieving the above object is the method according to any one of the above first to sixth aspects, wherein slaked lime is added to the solution after recovering vanadium, and sulfate is precipitated as gypsum and heated. After the ammonia is separated and recovered by the above, the slurry liquid containing the remaining gypsum is supplied to the desulfurization apparatus.
[0016]
The eighth means of the present invention for achieving the above object is that in the first means, the solution after separating and removing the insoluble matter is adjusted to pH 6 to 11 by adding alkali to vanadium and nickel. Is precipitated as a hydroxide, separated, the separated precipitate is redissolved, pH is adjusted to 4-6, only vanadium is precipitated, and vanadium is recovered.
[0017]
A ninth means of the present invention for achieving the above object is characterized in that, in the above eighth means, the solution after recovering vanadium is circulated to an ash dissolution tank for dissolving combustion ash.
[0018]
A tenth means of the present invention for achieving the above object is characterized in that, in any one of the above first to ninth means, the recovered ammonia is used as an alkaline liquid for pH adjustment necessary in the system.
[0019]
The eleventh means of the present invention for achieving the above object is the method of adding a reducing agent to the aqueous solution of combustion ash in any one of the above first to eighth means, containing sulfurous acid generated from sulfur oxides in exhaust gas. A liquid is added. That is, it is characterized in that sulfur oxides in exhaust gas are absorbed under the condition of pH 5 or higher using an alkaline liquid, and sulfite water is generated and used.
[0020]
According to a twelfth means of the present invention for achieving the above object, in the first means, a floc is formed by adding a flocculant to a solution containing a precipitate of vanadium and nickel hydroxide to form a hydroxide. It is characterized by sedimentation.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
The existence state of the compound of the metal component in the petroleum combustion ash is not clear, but is estimated as follows. That is, most of them exist as sulfates (VOSO ₄ , NiSO ₄ , MgSO _4, etc.), and some are oxides (V ₂ O ₅ , NiO, MgO, etc.). Further, it is presumed that a part is a metal oxide composite (for example, V ₂ O ₅ .MgO). Therefore, even if water is simply added to the combustion ash, it is not completely solubilized and some kind of pretreatment operation is required. When dilute sulfuric acid is added to the combustion ash, dissolution of the metal oxide proceeds. When recovering vanadium as a hydroxide, pentavalent vanazine contained in ash is reduced to tetravalent vanadate ion (VO ^2- ) by adding a reducing agent such as sulfurous acid, hydrazine or hydroxylamine. There is a need to.
[0022]
FIG. 2 shows a precipitation curve as vanadium, nickel, and magnesium hydroxide of this solution after the combustion ash is dissolved and reduced. Curve 1 shows a vanadium precipitation curve, curve 2 shows a nickel precipitation curve, and curve 3 shows a magnesium precipitation curve. Magnesium in curve 3 does not precipitate until pH 7, but tetravalent vanadium ions begin to precipitate as hydroxide from around pH 4, and can be recovered almost quantitatively as hydroxide at pH 6 or higher.
[0023]
On the other hand, nickel ions start to precipitate at pH 7 or higher when nickel is precipitated as a hydroxide from a solution containing only pure nickel ions, whereas EP ash solution containing other metal ions starts from around pH 5 Start precipitation. When the EP ash solution is adjusted to pH 6 or more, vanadium is precipitated and separated by 99% or more, but the precipitation amount of nickel also increases. The precipitate recovered as a hydroxide at pH 5 or higher contains nickel, and high-purity vanadium cannot be obtained.
[0024]
In addition, since the precipitate generated at pH 6 has a high water content and poor filter separation, a flocculant is added and the mixture is settled and recovered (slurry). When a floc of vanadium hydroxide is formed and collected using a flocculant, the vanadium concentration in the obtained solution is easily concentrated twice or more, and the vanadium concentration in the solution becomes 5,000 ppm or more. Ammonia is added to this concentrated solution and heated in the range of pH 6-9, and further air for oxidation is supplied from the lower part of the bubble column to change tetravalent vanadium to pentavalent to produce ammonium metavanadate.
[0025]
As shown in FIG. 3, the saturation concentration of the ammonium metavanadate solution in the solution decreases most around pH 6, that is, the solubility decreases most near pH 6. Therefore, the separation of ammonium metavanadate is most efficient when it is performed at around pH 6 (pH 5 to 7) where the vanadium concentration in the liquid is the lowest, from the solubility curve of FIG. Addition of a large amount of ammonium salt (for example, (NH ₄ ) ₂ SO ₄ , NH ₄ Cl, etc.) decreased the solubility of ammonium metavanadate and improved the recovery rate of vanadium, but a recovery operation was required. Undesirably, the process becomes complicated. Since nickel in the precipitate is dissolved by adjusting the pH to 6, the recovered ammonium metavanadate has a purity of 98% or more.
[0026]
In the present invention, since vanadium is recovered from the concentrated solution, a high recovery rate of 95% or more can be obtained without performing a crystallization operation that requires a long time for cooling, and a large crystallization tank is not required. In addition, since ammonium metavanadate has a larger particle size than the hydroxide, the sedimentation rate is large and it is easily separated and easily recovered. Furthermore, the solution from which ammonium metavanadate has been separated is returned to the hydroxide precipitation tank and repeatedly collected, whereby the vanadium can be completely treated.
[0027]
The present invention is illustrated in more detail by the following examples, but is not limited by the following examples.
[0028]
FIG. 1 shows a first embodiment according to the present invention. The outline of the present embodiment is as follows. The combustion ash is mixed with water to make a slurry in an ash dissolution tank, and is solubilized by adding an acid and a reducing agent. This is sent to the separation tank 2, and solids such as end-burning fuel and metal oxide that are not dissolved are separated. The solid matter is supplied to the desulfurization tower and processed. The solid material after separation is sent to the settling tank 3. In the precipitation tank 3, NH ₃ is added to adjust the pH to 6 to 8, and a hydroxide mainly composed of vanadium (V) and nickel (Ni) is generated and precipitated. Next, only the supernatant liquid is separated from the V and Ni slurry liquids in the separation tank 4. The V and Ni hydroxides precipitated and separated in the separation tank 4 are concentrated as a concentrated slurry, and the V concentration in the solution is concentrated to 5,000 ppm or more and stored in the concentrated slurry tank 7. The concentrated slurry stored in the concentrated slurry tank 7 is further transferred to the oxidation treatment tank 8, and NH ₃ is added to the oxidation treatment tank 8 to adjust the pH to 6 to 9, and air is supplied while maintaining the temperature at 60 ° C. or higher to obtain a tetravalent value. The vanadium is oxidized to pentavalent. The oxidized concentrated slurry is sent to the precipitation tank 9 and acid is added in the precipitation tank 9 to adjust the pH to around 5 to ₇ to precipitate ammonium metavanadate NH ₄ VO ₃ . This is transferred to the separation tank 10 where the precipitate (ammonium metavanadate) is recovered, and the recovered liquid is recycled to the ash dissolution tank 1. Note that. The solution after separating the V and Ni precipitates in the separation tank 4 is sent to the treatment tank 5 and adjusted to pH 11 or higher using, for example, slaked lime (Ca (OH) ₂ ) and then heated to ammonia (NH ₃ ). Is separated and recovered, and the sulfate radical is precipitated as gypsum. All the slurry liquid containing this gypsum is supplied to the desulfurization absorption tower 6.
[0029]
Since the vanadium precipitate has a very small particle size, it is difficult to separate it by a normal mechanical method. In the separation tank 4, a flocculant is added to form a floc and can be easily separated by sedimentation. By this method, a concentrated slurry having a vanadium hydroxide concentration of 5,000 ppm or more can be easily produced.
[0030]
In the oxidation treatment tank 8, ammonia is added to the vanadium-enriched slurry liquid to adjust the pH, and oxidation is performed by air supplied from the lower part of the tower, so that ammonium metavanadate (NH ₄ VO ₃ ) is finally generated. Since the solubility of NH ₄ VO ₃ is high under a high pH of 8 or more, sulfuric acid is added in the precipitation tank 9 to lower the pH. When the pH is adjusted to around 5 to 7, the solubility (saturated solution concentration) is lowered and the vanadium concentration in the solution is lowered as shown in FIG. 3, so that the NH ₄ VO ₃ recovery rate can easily achieve 90% or more.
[0031]
In the treatment tank 5, slaked lime is added to the liquid after the vanadium is separated to raise the pH to about 11, and the ammonia that has become free by heating it is separated and recovered. This ammonia is circulated as a necessary pH adjuster in the system. Slurry liquid containing gypsum and magnesium from which ammonia has been separated is collectively supplied to the desulfurization absorption tower 6. Such a method eliminates the need for waste liquid treatment in the combustion ash treatment system. Further, since this slurry liquid contains unrecovered ammonia and magnesium, when this slurry liquid is supplied to the desulfurization absorption tower 6, the desulfurization performance is improved and the purity of the recovered gypsum does not supply the slurry liquid. It also has characteristics that do not change.
[0032]
FIG. 4 shows the relationship between the vanadium concentration in the slurry and the oxidation time under the conditions of pH 8 and temperature 80 ° C. when a small bubble column is used. Comparison of oxidation time with oxidation time under the condition of V concentration: 3,000 ppm as 1. The oxidation time is shortened when the V concentration is increased, and the oxidation time is reduced to about 1/3 when it is concentrated to 20,000 ppm. Shortened. Therefore, if the vanadium concentration is increased, the processing apparatus is miniaturized and the vanadium recovery rate is further improved, so that vanadium can be recovered with high efficiency.
[0033]
FIG. 5 shows the relationship between the temperature of the slurry and the oxidation time. The oxidation time is compared with the oxidation time under the condition that the temperature of the slurry is 45 ° C. being 1. However, when the temperature is raised, the oxidation time is shortened. It can be seen that if the V concentration of the slurry is concentrated to 10,000 ppm and the oxidation temperature is set to 80 ° C. or higher, the oxidation time can be greatly reduced.
[0034]
In this way, it is possible to recover the vanadium hydroxide as ammonium metavanadate.
[0035]
FIG. 6 shows a desulfurization test in which a simulated liquid having the same components as the liquid from which vanadium and ammonia were recovered was supplied to a small absorption tower. The obtained liquid gas ratio: L / G (L / m ³ ) and desulfurization rate The relationship is shown. As limestone, the same limestone that is usually used in Japan was used. However, in order to obtain a desulfurization rate of 90% under the present experimental conditions, a simulation solution was added (in the added figure, (b) Mg : Equivalent to 5000 ppm), the desulfurization performance becomes high, and it is expected that L / G can be reduced by about 20% compared to the case where conventional addition is not performed.
[0036]
FIG. 7 is a graph showing the relationship between the ratio of the coexisting components contained in the gypsum obtained in the test based on FIG. 6 and the pH of the absorbing solution. The ratio of the coexisting component (metal component) contained in the generated gypsum by changing the pH to 4 to 6 is shown for each pH value. At any pH value, each metal content in the gypsum is 0.2% or less, and it can be seen that the pH value hardly affects the gypsum purity. Therefore, it has been clarified that even if the slurry liquid containing gypsum is supplied to the desulfurization tower, there is no substantial influence on the purity of the gypsum product.
[0037]
FIG. 8 shows an embodiment in which sulfurous acid gas in exhaust gas is used as a reducing agent necessary for ash dissolution as a second embodiment of the present invention. First, the exhaust gas is led to the SO ₃ generation tower 11 where sulfurous acid gas in the exhaust gas is absorbed by water to generate sulfurous acid. This sulfurous acid can be used as a reducing agent added to the ash dissolution tank 1. However, when sulfurous acid is produced, the pH is lowered, which is undesirable because it is oxidized by oxygen in the exhaust gas to become sulfuric acid. For this reason, when an alkaline liquid, preferably ammonia water, is used as the absorbing liquid and absorption is performed under a condition where the pH is 5 or more, the produced sulfurous acid is not oxidized by oxygen in the exhaust gas. Such a method has the advantage that it is not necessary to purchase a new reducing agent. The steps after the ash dissolution tank 1 are the same as those in the first embodiment, and a description thereof will be omitted.
[0038]
FIG. 9 shows a third embodiment of the present invention. In this embodiment, the combustion ash is dissolved in the ash dissolution tank 1 and sent to the separation tank 2, and the insoluble matter is separated in the separation tank 2 and then sent to the precipitation tank 3. In the precipitation tank 3, an alkaline solution is added to adjust the pH to 4 to 11 (preferably 6 to 11) to precipitate all vanadium and nickel. Next, vanadium and nickel of the precipitate are introduced into the dissolution tank 12, and for example, sulfuric acid is added to dissolve the precipitate. Furthermore, if the solution which melt | dissolved vanadium and nickel is guide | induced to the precipitation tank 9, and an alkali liquid, for example, sodium hydroxide, is added and pH is adjusted to 4-6, only vanadium can be collect | recovered independently. The solution containing nickel after recovering vanadium can be circulated in the ash dissolution tank 1 for use.
[0039]
By treating the combustion ash generated from petroleum-based fuel with the above method, vanadium and ammonia, which are the active ingredients, can be efficiently recovered, and the sulfate in the remaining liquid is precipitated as gypsum to desulfurize this slurry liquid. By supplying to the tower, waste water treatment in this system can be omitted. At the same time, the desulfurization rate is improved.
[0040]
【The invention's effect】
According to the method of the present invention, the recovery of valuable materials from petroleum fuel ash, in particular, the operation of recovering vanadium is simplified. Moreover, it has a great feature in that highly pure vanadium can be recovered with high efficiency.
[Brief description of the drawings]
FIG. 1 is a basic flowchart of a first embodiment of the present invention.
FIG. 2 is a graph showing the precipitation recovery rate of vanadium, nickel and magnesium from the ash solution corresponding to the pH of the ash solution.
FIG. 3 is a graph showing the solubility (saturated solution concentration) of ammonium metavanadate corresponding to pH.
FIG. 4 is a graph showing the relationship between V concentration and oxidation time.
FIG. 5 is a graph showing the relationship between temperature and oxidation time.
FIG. 6 is a graph showing the relationship between the liquid gas ratio and the desulfurization rate.
FIG. 7 is a graph showing the relationship between the metal component of gypsum obtained in the desulfurization absorption tower and the pH of the absorbing solution using a simulated solution having the same components as the solution after recovering vanadium and ammonia as the absorbing solution.
FIG. 8 is a flowchart showing a second embodiment of the present invention.
FIG. 9 is a flowchart showing a third embodiment of the present invention.
[Explanation of symbols]
1 ash dissolving tank 2 separating tank 3 sedimentation tank 4 separation tank 5 treatment tank 6 desulfurization absorption tower 7 thickened slurry tank 8 oxidation treatment tank 9 sedimentation tank 10 separation vessel 11 SO ₃ generation column 12 dissolving tank

Claims (13)

Combustion ash collected by a dust collector installed in an exhaust gas flow path of a boiler or the like using petroleum-based fuel is dissolved in an aqueous solution to form a slurry. If necessary, acid and / or a reducing agent is added to form combustion ash In the method for treating petroleum-based combustion ash, in which vanadium is separated from the solution after dissolution treatment and separation and removal of insoluble matter,
Wherein the solution after separating and removing insolubles, by adding an alkali was adjusted to 6 or more pH vanadium and nickel precipitated as hydroxide, and re-dissolved by separating and recovering the precipitate, the dissolution A method for treating petroleum combustion ash, wherein the vanadium is separated and recovered as a precipitate of ammonium metavanadate by heating and oxidizing the liquid .   2. The method for treating petroleum combustion ash according to claim 1, wherein alkali is added to the solution after the insoluble matter is separated and removed to adjust the pH to 6 to 8 to precipitate vanadium and nickel as hydroxides. The vanadium concentrate, which is a high-concentration slurry obtained by concentrating and separating the precipitate, is heated to 60 ° C. or more, and oxidized to pH 6-9 in the presence of ammonia to recover vanadium as ammonium metavanadate. A method for treating petroleum combustion ash.   3. The method for treating petroleum combustion ash according to claim 2, wherein when the vanadium concentrate is oxidized, the vanadium concentrate is oxidized by blowing air into the vanadium concentrate that is a slurry. Processing method. In the processing method of the petroleum-based combustion ash according to claim 2 or 3, wherein the pH5~7 an acid is added to the solution after the oxidation treatment to precipitate ammonium metavanadate compound, to separate from the solution as a precipitate A method for treating petroleum-based combustion ash characterized by In the processing method of the petroleum-based combustion ash of claim 4, the solution was precipitated separated vanadium as ammonium metavanadate compounds, petroleum combustion ash and returning the ash dissolution tank to dissolve the ash Processing method.   2. The method for treating petroleum-based combustion ash according to claim 1, wherein a flocculant is added to a precipitate obtained by precipitating vanadium and nickel as a hydroxide to produce the high-concentration slurry liquid, thereby aggregating the precipitate. A method for treating petroleum combustion ash, characterized in that the vanadium hydroxide concentration is 5,000 ppm or more.   The method for treating petroleum-based combustion ash according to any one of claims 1 to 6, wherein ammonia is separated and recovered by adding slaked lime to precipitate the sulfate as gypsum and heating the solution after recovering vanadium. Then, the processing method of the petroleum-type combustion ash characterized by supplying the slurry liquid containing the remaining gypsum to a desulfurization apparatus.   2. The method for treating petroleum-based combustion ash according to claim 1, wherein the solution after separating and removing the insoluble matter is adjusted to pH 6 to 11 by adding alkali to precipitate vanadium and nickel as hydroxides. And separating the separated precipitate, adjusting the pH to 4-6 to precipitate only vanadium, and recovering vanadium. In the processing method of the petroleum-based combustion ash of claim 8, the processing method of the petroleum-based combustion ash, characterized in that the solution after the recovery of vanadium, causes circulatory ash dissolution tank for dissolution treatment of the combustion ash.   The method for treating petroleum-based combustion ash according to any one of claims 1 to 9, wherein the recovered ammonia is used as an alkaline liquid for pH adjustment necessary in the system. .   The method for treating petroleum combustion ash according to any one of claims 1 to 8, wherein as a method of adding a reducing agent to the aqueous solution of combustion ash, a sulfurous acid-containing liquid generated from sulfur oxides in exhaust gas is added. A method for treating petroleum-based combustion ash.   The method for treating petroleum combustion ash according to claim 1, wherein flocs are added to a solution containing precipitates of hydroxides of vanadium and nickel to form flocs, and the hydroxides are precipitated and separated. A method for treating petroleum combustion ash.   12. The method for treating petroleum-based combustion ash according to claim 11, wherein sulfur oxides in the exhaust gas are absorbed with an alkaline liquid, preferably ammonia water under a pH of 5 or more, and sulfite water is generated and used. A method for treating petroleum combustion ash, characterized in that:

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