JP2017179562A - Method of recovering vanadium from denitration catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently separate tungsten and vanadium, which are valuable metal, and recover them separately.SOLUTION: A method of recovering vanadium (V) from a denitration catalyst includes the steps of: crushing a denitration catalyst comprising vanadium (V) and tungsten (W); allowing V to leach from the crushed denitration catalyst; adding Ca salt to a post-leaching liquid to allow V to be precipitated as calcium salt, and then allowing V to leach with a carboxylic acid; and recoverying V from the post-leaching liquid.SELECTED DRAWING: None

Description

  The present invention relates to a method for recovering vanadium from a denitration catalyst.

As a method for removing NO _x which is a causative substance such as photochemical smog and acid rain, a flue gas denitration method using selective catalytic reduction using ammonia (NH ₃ ) as a reducing agent is widely used mainly in thermal power plants. As this catalyst, a titanium oxide (TiO ₂ ) -based catalyst containing vanadium, molybdenum, and tungsten as active components is used, and it is the mainstream of current denitration catalysts. At present, the catalytic ammonia reduction denitration method is mainly used for purification of exhaust gas from large-capacity boilers such as power generation boilers and gas turbines, and a huge amount of catalyst of several hundred to several thousand m ³ per plant, Used for 2-10 years without replacement. Since these catalysts become new secondary pollutants when they become waste catalysts after the years of use, the reuse of waste catalysts is a very important issue for environmental protection and effective use of resources. Yes.

  Vanadium, molybdenum, and tungsten are valuable metals that are widely used as raw materials for superalloys and metal materials. Therefore, it is very important to recover these metals from the spent catalyst and reuse them from the viewpoint of effective utilization of resources. However, at present, most of the waste catalyst is disposed of in landfills, and it is costly at the time of disposal.

  Further, when the catalyst is used in an oil-fired boiler, vanadium contained in the oil is trapped by the catalyst, so that further recovery of vanadium can be expected.

  In Patent Document 1, in order to solve a problem that a desired metal component is effectively recovered from a catalyst, a superalloy, or the like, while a melting temperature is as high as 600 ° C. to 1200 ° C., a process cost for extraction is increased. In addition, a technique for separating and recovering tungsten, molybdenum, and vanadium from a catalyst at a high yield even at a low temperature is disclosed.

  Specifically, in the method for separating and recovering the metal component from the member containing at least one metal component of tungsten, molybdenum, or vanadium, the member and the first member containing an alkali metal hydroxide or an alkaline earth metal hydroxide. 1 melt and a second melt different from the first melt containing at least one of alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal salt or alkaline earth metal salt A process for producing a compound, mixing the compound and water to produce an extract of the metal component, and separating the extract and the solid content are disclosed. Has been. More specifically, for example, a metal component contained in a member by mixing and baking a mixture obtained by mixing sodium hydroxide and potassium hydroxide and a member containing a metal component, and further mixing with water. A technique is disclosed that includes extracting.

International Publication No. 2014/155547 Pamphlet

  By the way, from the viewpoint of effective use of resources, Patent Document 1 is considered to be a useful technique from the viewpoint of separating and recovering tungsten, molybdenum, and vanadium from a member containing these metal components, specifically, a catalyst component in a high yield. However, it is necessary to dissolve tungsten and vanadium together, and the use of ammonia or ammonium salt for the separation of tungsten and vanadium has a high environmental impact, and the exhaust gas and wastewater treatment processes become complicated. That is why there is still room for improvement.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor had previously made it a problem to dissolve both tungsten and vanadium and to separate them from the solution. Thus, it was found that each can be preferentially dissolved, and each of vanadium and tungsten was effectively separated and recovered.

  The present invention completed on the basis of such knowledge is as follows.

(1) A step of crushing a denitration catalyst containing tungsten (W) and vanadium (V), a first V leaching step of leaching V from the crushed denitration catalyst, and adding Ca salt to the solution after leaching to add calcium A method for recovering V from a denitration catalyst, comprising: a second V leaching step of leaching V with carboxylic acid after precipitation as a salt; and a step of recovering V from the solution after leaching.

(2) The method according to (1), wherein the size of the denitration catalyst after the step of crushing the denitration catalyst containing W and V is 5 mm to 50 mm.

(3) The leaching rate of V is 90% or more and the leaching rate of W is 25% or less in the first V leaching step of leaching V from the crushed denitration catalyst. the method of.

(4) In the first V leaching step of leaching V from the crushed denitration catalyst, leaching is performed at a temperature of 40 ° C. or less using an alkaline solution having a NaOH concentration of 5 to 10% ( The method according to any one of 1) to (3).

(5) A step of crushing a denitration catalyst containing tungsten (W) and vanadium (V), a first V leaching step of leaching V from the crushed denitration catalyst, and leaching V from the crushed denitration catalyst The step of leaching W from the residue of the first V leaching step, the step of adding Ca salt to the solution after leaching, and the step of recovering W as calcium tungstate, increasing W from the denitration catalyst Recovering with purity.

(6) The residue of the first V leaching step of leaching V from the crushed denitration catalyst is leached at a temperature higher than 40 ° C. using an alkaline solution having a NaOH concentration of 10% or more. The method according to (5).

(7) At least one of the residue of the second V leaching step of leaching V with formic acid or acetic acid according to (1), and the residue of the step of calcium salt precipitation with Ca salt of the solution after leaching according to (5) Recovering calcium tungstate from the process.

  According to the present invention, it is possible to efficiently separate and recover valuable metals such as tungsten and vanadium.

It is a flowchart which shows one Embodiment of this invention.

  The present invention will be described below. In this specification, the value of% of concentration means weight percent unless otherwise specified.

  FIG. 1 is a flowchart showing an embodiment of the present invention.

  In FIG. 1, the method according to the embodiment of the present invention includes a denitration catalyst crushing step (step S10), which is a step of crushing a denitration catalyst containing tungsten (W) and vanadium (V), and from the crushed denitration catalyst. After the first V leaching step (step S12), which is a step of leaching V, and a Ca salt precipitation step (step S14) in which the solution after leaching is calcium salt precipitated with Ca salt, V is added with carboxylic acid such as formic acid or acetic acid. It has the 2nd V leaching process (step S16) which is a process to leach, and the process (step S18) which collects V from the solution after leaching.

  In step S10, the denitration catalyst containing W and V is crushed. In the specification of the present application, “crushing” is a technical term, and means that the object is crushed to obtain small-sized pieces (chunk), but not so fine (not crushed) that it becomes grains or powder. . In this crushing step, as a pretreatment for the first V leaching step described later, the purpose is to reduce the size of the denitration catalyst so that it can be easily stirred in the solution. When performing the V leaching step, hardly soluble W is easily dissolved, which is not preferable from the viewpoint of efficiently separating V and W. From such a viewpoint, the size of the denitration catalyst after crushing is 5 mm to 50 mm, preferably 10 mm to 30 mm.

  In step S12, V is leached from the denitration catalyst crushed in step S10, and solid-liquid separation is performed to obtain a first leaching residue and a first leached liquid. When leaching V from the denitration catalyst, it is preferable that the leaching rate of V is 90% or more and the leaching rate of W is 25% or less from the viewpoint of efficiently separating V and W.

  As one mode for realizing such leaching, an aqueous solution of sodium hydroxide (NaOH) is used as the leaching solution. An alkaline solution having a NaOH concentration of 1 to 10%, preferably 5 to 10% at this time is used. Use. Considering the difference in solubility between V and W in sodium hydroxide, leaching is preferably performed at a temperature of 40 ° C. or lower so that V dissolves but W is difficult to dissolve. Further, the reaction time is not particularly limited, but it is preferably performed for 1 hour or more and 3 hours or less from the viewpoint of dissolving V and not dissolving W.

In step S14, calcium (Ca) salt is added to the first leached solution obtained in step S12 to precipitate a calcium salt of valuable metals. Examples of the Ca salt used here include adding calcium ion (Ca ²⁺ ) such as calcium hydroxide Ca (OH) ₂ , calcium chloride CaCl ₂ , calcium nitrate Ca (NO ₃ ) ₂ , etc. It reacts with the above Ca salt, Na and Ca are substituted, and V and W are precipitated as calcium salts of V and W, respectively.
Na ₂ WO ₄ + CaCl ₂ → CaWO ₄ + 2NaCl
2NaVO ₃ + CaCl ₂ → Ca (VO ₃ ) ₂ + 2NaCl
2Na ₃ VO ₄ + 3CaCl ₂ → Ca ₃ (VO ₄ ) ₂ + 6NaCl

  In step S16, a carboxylic acid such as formic acid, acetic acid, citric acid, maleic acid, or its acid anhydride is added to the precipitate obtained in step S14, and V is leached. At this time, the pH of the leachate is 4-8, preferably 6-7. In addition, V enters into the liquid after leaching (second liquid after leaching), but W remains in the leaching residue (second leaching residue) in the form of calcium tungstate. In this way, W that has been leached somewhat in the first V leaching step (step S12) can be separated from V.

  In step S18, V is recovered by a conventionally known method from the second post-leaching solution obtained in step S16.

Specifically, for example, after the second leaching solution is acidified, for example, sulfuric acid acidity to pH 2.0 to 2.5, and Ca ²⁺ is precipitated and removed as CaSO ₄ , ammonia or ammonium salt, For example, ammonium hydroxide and ammonium chloride can be added to adjust the pH to 6 to 8, and V can be precipitated as ammonium metavanadate and recovered by solid-liquid separation.

  By collecting V as described above, it becomes possible to collect V preferentially (selectively) based on the difference in solubility with W. In addition, since the second leaching solution has a high V concentration and a small amount of liquid, the amount of ammonia and ammonium salt used can be reduced and the environmental load can be reduced. Furthermore, the amount of impurities mixed into V can be reduced in view of the distribution law.

  On the other hand, W is leached from the first leaching residue obtained in step S12 (step S20).

In step S20, the first leaching residue is leached at a temperature higher than 40 ° C. using an alkaline solution having a NaOH concentration of 10% or more.
WO ₃ + 2NaOH → Na ₂ WO ₄ + H ₂ O

In step S22, a calcium (Ca) salt is added to the post-leaching solution obtained in step S20 to precipitate W calcium salt. Examples of the Ca salt used herein include those containing calcium ions (Ca ²⁺ ) such as calcium hydroxide Ca (OH) ₂ , calcium chloride CaCl ₂ , calcium nitrate Ca (NO ₃ ) ₂ , and the like. Here, as described above, W is precipitated as a calcium salt of W.
Na ₂ WO ₄ + CaCl ₂ → CaWO ₄ + 2NaCl

In step S24, to collect the resulting precipitate in step S22, to obtain a CaWO _4. Since that similarly performed by precipitation with Ca salts of tungstic acid also in step S14, and recovered in accordance with the second leach residue obtained in step S16, may be obtained CaWO _4.

In step S26, W from CaWO ₄ recovered in step S24 is recovered by a conventionally known method.

Specifically, for example, recovered CaWO ₄ is leached with hydrochloric acid at, for example, 80 ° C. to obtain tungstic acid (monohydrate: H ₂ WO ₄ ). At this time, calcium remains in the liquid as calcium ions (Ca ²⁺ ). Subsequently, the pH is controlled to about 4 to keep tungsten as W ⁶⁺ to prevent recrystallization of tungstate. Thereto, excess ammonium hydroxide is added to keep H ₂ WO ₄ in a saturated ammonium solution (pH> 11.0) and precipitate and remove calcium and other impurities. The ammonium solution from which impurities have been removed is evaporated to dryness, and ammonium paratungstate (APT) is obtained by crystallization.
CaWO ₄ + 2HCl → H ₂ WO ₄ + CaCl _{2
H2WO 4 + 2NH 3 · H 2} O → (NH 4) 2 WO 4 + 2H 2 O
12 (NH ₄ ) ₂ WO ₄ → 5 (NH ₄ ) ₂ O · 12 WO ₃ · 5H ₂ O (APT) + 14NH ₃ + 2H ₂ O

  By recovering W from the two-stage leaching residue as described above, it is possible to obtain an effect that W can be obtained with high purity as a reaction to recovering V preferentially.

  Examples of the present invention are shown below, but the present invention is not intended to be limited to the following examples.

(Example 1) Vanadium leaching (first V leaching step)
Square honeycomb honeycomb denitration catalyst (vanadium pentoxide: 0.5% by mass, tungsten trioxide: 10 ± 5% by mass, titanium dioxide: 89.5 ± 5% by mass, acidic clay: 3 ± 3% by mass, glass fiber : 7 ± 3 mass%) was crushed to a size of about 10 mm to 30 mm.

  Subsequently, 30 g of the crushed material was added to 300 ml of 5%, 10% and 25% sodium hydroxide aqueous solution and stirred. The leaching treatment using each concentration of sodium hydroxide aqueous solution was performed at both room temperature (about 23 ° C.) and warmed state (about 54 ° C.). Sampling was performed 30 ml after 24 hours (and 48 hours for samples at room temperature), and the contents of tungsten (W) and vanadium (V) were measured by inductively coupled plasma (ICP) emission spectrometry. . The results are shown in Tables 1 and 2.

  According to Tables 1 and 2, vanadium exhibited a high leaching rate of almost 100% regardless of the concentration of sodium hydroxide aqueous solution and the leaching temperature. On the other hand, with respect to tungsten, when the concentration of the aqueous sodium hydroxide solution is 5% and 10%, the leaching rate is about 30% at both room temperature and 54 ° C. Further, when the concentration of the aqueous sodium hydroxide solution is 25%, The leaching rate was about 40% at 54 ° C.

(Example 2) Calcium salt precipitation with Ca salt Subsequently, with respect to a solution obtained by adding 40 mL of water to 60 mL of the post-leaching solution obtained in Example 1, calcium chloride is 1 equivalent to W, 10 equivalents, 54 Equivalent amount was added and stirred at room temperature for 3 hours. Vanadium and tungsten contained in the solution after leaching are precipitated as calcium vanadate and calcium tungstate, which are salts, respectively, and the precipitate is collected, and the filtrate is obtained by inductively coupled plasma (ICP) emission spectrometry. ) And vanadium (V) content.

  Each content of W and V and the residual ratio in the filtrate were measured, and the results are shown in Table 3.

(Example 3) Vanadium leaching (second V leaching step) to V recovery Two solutions were prepared by adding 10 g of a sample corresponding to the salt obtained in Example 2 to 100 ml of pure water. Formic acid was added dropwise to Solution 2 and acetic acid was adjusted to pH 6. When the acid dropping is started and the pH is lowered, the liquid turns yellow, and then the pH starts to rise and the liquid becomes white. Therefore, the acid was dropped while maintaining the pH at 6 while stirring for 2 hours. Both solution 1 and solution 2 were 6.3. Furthermore, it left still for 1 hour, it filtered, the residue was dried, and the 2nd leaching residue was collect | recovered.

  In order to grasp the difference between leaching with formic acid and leaching with acetic acid, the content of tungsten (W) in the second leached solution was measured by inductively coupled plasma (ICP) emission spectrometry. The results are shown in Table 5.

(Example 4) Tungsten leaching-precipitation with Ca salt (W leaching step)
To the first leaching residue obtained in Example 1, 300 ml of an aqueous sodium hydroxide solution having a concentration of 10% or more, for example, 10% or 25% is added and stirred. The liquid temperature at this time is 40 ° C. or higher, for example, about 50 ° C., and tungsten (W) is leached.
Subsequently, calcium chloride is added to the liquid after leaching in W so as to be 10 equivalents or more, and the mixture is stirred at room temperature for 3 hours. Tungsten contained in the liquid after leaching is precipitated as calcium tungstate, and this precipitate is collected.

(Example 5) Recovery of W Calcium tungstate (CaWO4) is recovered from at least one of the residue obtained by the second V leaching of Example 3 (second leaching residue) and the precipitate obtained in Example 4 Acidified with hydrochloric acid and leached at 80 ° C. to obtain tungstic acid monohydrate. Thereafter, the pH is maintained at about 4, excess ammonium hydroxide is added, and the resulting precipitate is removed by filtration. The ammonium solution from which the precipitate has been removed is evaporated to dryness to crystallize and recover ammonium paratungstate (APT).

Claims (7)

Crushing a denitration catalyst containing tungsten (W) and vanadium (V);
A first V leaching step of leaching V from the crushed denitration catalyst;
A second V leaching step of leaching V with carboxylic acid after adding Ca salt to the solution after leaching to precipitate V as a calcium salt;
And a step of recovering V from the liquid after leaching, and a method of preferentially recovering V from the denitration catalyst.   The method according to claim 1, wherein the size of the denitration catalyst after the step of crushing the denitration catalyst containing W and V is 5 mm to 50 mm.   2. The method according to claim 1, wherein a leaching rate of V is 90% or more and a leaching rate of W is 25% or less in the first V leaching step of leaching V from the crushed denitration catalyst.   The first V leaching step of leaching V from the crushed denitration catalyst is leached at a temperature of 40 ° C or lower using an alkaline solution having a NaOH concentration of 5 to 10%. 4. The method according to any one of 3. Crushing a denitration catalyst containing tungsten (W) and vanadium (V);
A first V leaching step of leaching V from the crushed denitration catalyst;
Leaching W from the residue of the first V leaching step of leaching V from the crushed denitration catalyst;
Adding Ca salt to the liquid after leaching;
A process for recovering W with high purity from a denitration catalyst, comprising the step of recovering W as calcium tungstate.   The residue of the first V leaching step of leaching V from the crushed denitration catalyst is leached at a temperature higher than 40 ° C. using an alkaline solution having a NaOH concentration of 10% or more. Item 6. The method according to Item 5.   The tungstic acid from at least one of the residue of the second V leaching step of leaching V with formic acid or acetic acid according to claim 1 and the residue of the step of calcium salt precipitation of the post-leaching solution with Ca salt according to claim 5 A method characterized by recovering calcium.