KR100814309B1 - Process for producing ammonium ceriumiv nitrate - Google Patents

Abstract

An object of the present invention is a method of recovering a high purity cerium compound from a solution containing cerium in a short time with high yield, specifically, recovering cerium as cerium ammonium nitrate (IV) from an acidic aqueous solution containing cerium such as an etching waste solution. To provide a way.

The present invention provides a method for producing ammonium cerium nitrate (IV) from an acidic aqueous solution containing at least trivalent cerium, tetravalent cerium, ammonium ions, and nitric acid, wherein the acidic solution has an oxidation potential of 0.7 to 1.6 at pH 2 or less. A method for producing ammonium cerium (IV), which contains a V phosphorus metal and increases the concentration of nitric acid in the acidic aqueous solution to precipitate an ammonium cerium nitrate (IV) crystal.

Description

Process for producing cerium ammonium nitrate (IV) {PROCESS FOR PRODUCING AMMONIUM CERIUM (IV) NITRATE}

The present invention is industrially important, and expensive cerium nitrate cerium (IV) (formula: (NH ₄ ) ₂ Ce (NO ₃ ) ₆ ) is obtained from an aqueous solution containing cerium (hereinafter referred to as "CAN"). To abbreviate). In particular, the present invention relates to a method for recovering cerium from waste liquid of an etchant used in the manufacturing process of a semiconductor device or a liquid crystal display device.

Cerium ions in aqueous solution change from tetravalent to trivalent if the reducing material is present in the aqueous solution. When the oxidation number of cerium is reduced from tetravalent to trivalent, the oxidation potential of cerium is very high in comparison with other metals in the acidic region. This shows that many metals can be oxidized and dissolved (ionized). Taking advantage of this property, an aqueous solution containing tetravalent cerium is widely used industrially as an etchant for metals. In particular, the effect as an etchant of a high oxidation potential metal, such as chromium, is industrially important.

In this manner, in the etching solution using the oxidation ability of cerium, the acid present in the etching solution is consumed. Therefore, acidic components, such as sulfuric acid, nitric acid, and perchloric acid, are added to such etching liquid normally.

Cerium belongs to rare earths and is relatively expensive due to its low abundance on the earth as an element. Therefore, a method of recovering and purifying cerium from an etching solution (etching waste solution) containing cerium containing has been proposed. For example, Japanese Patent Laid-Open No. 11-236217, Japanese Patent Laid-Open No. 11-236632 and the like propose a method of recovering cerium in a solution as CAN as a raw material of an etching solution. However, the method described in these methods has a problem in that a large amount of cerium can be recovered with high purity, but it takes time because it has a plurality of manufacturing processes. In addition, in order to remove impurities such as alkali metals present in the manufacturing process of CAN, there is a process of washing the precipitate (cerium hydroxide) generated during the manufacturing process with pure water, and the amount of waste water generated in the whole CAN manufacturing process is large. There was also a problem that the processing cost is increased and the load on the surrounding environment is large.

In general, it is known that the solubility of CAN in aqueous nitric acid solution decreases as the nitric acid concentration increases. Based on this knowledge, if an acidic aqueous solution containing cerium and nitric acid is concentrated by distillation or the like, the concentration of nitric acid in the solution becomes high, and as a result, CAN is crystallized, so that CAN can be easily recovered by recovering and refining it. do. In this method, however, tetravalent cerium can be recovered as CAN, but trivalent cerium contained in a large amount in an acidic aqueous solution cannot be recovered, resulting in insufficient recovery.

Disclosure of the Invention

In view of the above problems, the inventors of the present invention include a method of recovering high purity cerium in a short time and high yield from an acidic aqueous solution containing cerium, specifically, trivalent cerium and tetravalent cerium, specifically, cerium such as an etching waste liquid. The method of recovering and refining cerium as a cerium ammonium nitrate (IV) crystal | crystallization from the acidic aqueous solution which carried out was earnestly examined.

As a result, when a metal having a specific oxidation potential is present in the acidic aqueous solution containing cerium, it is found that by increasing the nitric acid concentration in the acidic aqueous solution, CAN crystals are precipitated with very high purity and the recovery of cerium is increased. The invention has been reached.

That is, the gist of the present invention is a method for producing ammonium cerium nitrate from an acidic aqueous solution containing at least trivalent cerium, tetravalent cerium, ammonium ions, and nitric acid, wherein the acidic aqueous solution is oxidized at pH 2 or lower. A method of producing ammonium cerium (IV), which contains a metal having a potential of 0.7 to 1.6 V and raises the concentration of nitric acid in the acidic aqueous solution to precipitate cerium ammonium nitrate (IV) crystals.

Best Mode for Carrying Out the Invention

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The acidic aqueous solution containing cerium used in the present invention contains at least trivalent cerium, tetravalent cerium, nitric acid, and ammonium ions. Preferably used etchant used for the etching of chromium, nickel, copper or the like, that is, an etching waste liquid, particularly preferably an etching waste liquid in which chromium has been etched. When the metal is etched with an etchant containing cerium ammonium nitrate (IV), part of the tetravalent cerium becomes trivalent cerium. Therefore, trivalent cerium and tetravalent cerium exist in the etching waste liquid.

Cerium contained in the acidic aqueous solution contains both trivalent cerium and tetravalent cerium. According to the present invention, trivalent cerium can also be recovered as cerium ammonium nitrate (IV). Examples of cerium sources include cerium ammonium nitrate (III), cerium ammonium nitrate (IV), cerium hydroxide (III), cerium hydroxide (IV) and the like.

In the present invention, the cerium concentration in the acidic aqueous solution is arbitrary. In general, the higher the cerium concentration is, the larger the amount of cerium ammonium nitrate (IV) crystals precipitated when the concentration of nitric acid is raised, and the slurry concentration of the acidic aqueous solution increases, which tends to lower the operability of crystal recovery. On the other hand, the higher the cerium concentration, the higher the recovery rate of cerium nitrate (IV) from the acidic aqueous solution.

Therefore, the concentration of cerium ammonium nitrate (IV) in the acidic aqueous solution is preferably 0.1 to 15% by weight, particularly 0.5 to 10% by weight, especially 1 to 8% by weight, based on the weight% of cerium.

For example, when the method of the present invention is carried out batchwise, when the cerium concentration in the acidic aqueous solution is too low, a large amount of water is evaporated to raise the nitric acid concentration, which is economically undesirable. On the contrary, when the cerium concentration is too high, the slurry concentration may increase, making it difficult to collect CAN crystals from, for example, a concentration tank, or to transfer a slurry containing a large amount of CAN crystals. Therefore, in the present invention, the cerium concentration in the acidic aqueous solution is preferably 1 to 10% by weight, especially 1.5 to 4% by weight, particularly 1.8 to 3.8% by weight.

In addition, when performing batchwise, it is preferable to carry out so that the liquid level of the acidic aqueous solution in the container which concentrates nitric acid may become substantially constant. For example, when water is evaporated from an acidic aqueous solution to increase the nitric acid concentration, the liquid level of the acidic aqueous solution is temporarily lowered as the moisture evaporates, and crystals precipitate on the container wall surface. Since this crystal may be crystallized by concentrating impurities such as chromium, it is preferable to avoid precipitation of such a crystal.

On the other hand, when the method of the present invention is carried out continuously, the precipitated ammonium cerium (IV) or the like is purged out of the reaction system, so that the crystal concentration of the ammonium cerium nitrate (IV) in the reaction system, that is, the slurry concentration is substantially constant. Nitric acid can be concentrated.

Therefore, in the case of carrying out the present invention continuously, the cerium concentration in the acidic aqueous solution may be carried out under solubility of ammonium cerium nitrate (IV) at the concentration temperature of the acidic aqueous solution of the concentrated high nitric acid concentration. In addition, since the purged acidic aqueous solution contains ammonium cerium nitrate (IV) crystals, the concentration of the slurry may be adjusted in a circulating operation method in which the purged liquid is filtered to return a part of the obtained solution to the concentration tank.

In the present invention, the nitric acid concentration in the acidic aqueous solution is arbitrary. Generally nitric acid concentration is 5-50 weight% in acidic aqueous solution before raising a concentration, especially 5-40 weight% is preferable since the load at the time of raising nitric acid concentration may be small.                 

However, in order to precipitate all cerium in an acidic aqueous solution as CAN crystals, the acidic aqueous solution should contain at least 6 mol times nitric acid with respect to cerium. Therefore, it is preferable that the nitric acid concentration in acidic aqueous solution is 6 mol times or more with respect to cerium.

The acidic aqueous solution may further contain an acidic component other than nitric acid. Examples of the acidic component contained in the acidic aqueous solution include perchloric acid and sulfuric acid. When an explosive substance such as perchloric acid is used as the acidic component, the crystals of perchlorate adhered to the container wall are dried when the acidic aqueous solution is heated and concentrated to increase the concentration of nitric acid in the acidic aqueous solution, for example. The condition creates a risk of explosion decomposition. Therefore, the explosion decomposition may be avoided by treatment such as preventing drying of the precipitated crystals.

Although the concentration of an acidic component is arbitrary, what is necessary is just to adjust so that it may become 5-40 weight% normally as the total concentration with the nitric acid mentioned above in the acidic aqueous solution before raising a nitric acid concentration. The higher the nitric acid concentration in the acidic aqueous solution, the lower the solubility of CAN. Therefore, in order to recover CAN, the higher the nitric acid concentration in the acidic aqueous solution, the lower the increase in the nitric acid concentration corresponding to the amount of precipitated cerium ammonium nitrate crystal. Since the energy at the time of concentrating an aqueous solution becomes minimum, it is efficient.

In the present invention, the pH of the acidic aqueous solution is usually pH 2 or less, preferably pH 1 or less. When pH 2 is exceeded, cerium tetravalent, chromium hexavalent and chromium trivalent may precipitate.

Ammonium ion contained in an acidic aqueous solution is normally supplied to an acidic aqueous solution by using cerium ammonium nitrate as a cerium source at the time of preparing an acidic aqueous solution. When a cerium source other than cerium ammonium nitrate is used, ammonia water, ammonium nitrate or the like may be used as the ammonia source.

Ammonium ion concentration in an acidic aqueous solution is arbitrary. In general, the ammonium ion concentration is preferably 0.1 to 5% by weight, particularly 0.2 to 1.6% by weight, based on the acidic aqueous solution. However, in order to precipitate all cerium in an acidic aqueous solution as CAN, at least 2 mol times or more of ammonium ion should be contained in an acidic aqueous solution. Therefore, the ammonium ion concentration in the acidic aqueous solution is preferably 2 mole times or more with respect to cerium. However, when the ammonium ion concentration is too high, ammonium nitrate crystals may precipitate when the nitric acid concentration is increased. Among these, about 2-2.5 times mole is preferable.

Increasing the nitric acid concentration of the acidic aqueous solution precipitates CAN. This is because the higher the nitric acid concentration of the acidic aqueous solution containing CAN, the smaller the solubility of CAN. The method of raising nitric acid concentration is arbitrary. Specifically, for example, distillation, distillation under reduced pressure, stripping, and the like can be cited. Among them, raising the nitric acid concentration by distillation, distillation under reduced pressure, especially distillation under reduced pressure, can lower the crystallization temperature of CAN in the concentration tank. It is preferable because the impurity content of the crystal can be reduced and the CAN crystal with high purity can be recovered.

As distillation conditions at this time, the lower the distillation temperature is preferable in order to obtain high purity CAN crystals. Generally, it is preferable to carry out at 100 degrees C or less, especially 70 degrees C or less. Specifically, it is preferable that they are room temperature-100 degreeC, especially 40-70 degreeC, especially 45-70 degreeC. The distillation pressure is usually 466.6 [hPa] (about 350 mmHg) or less, preferably 133.3 [hPa] (about 100 mmHg) or less, particularly preferably 40 to 133.3 [hPa] (about 30 to about 100 mmHg). ) to be. If the distillation pressure is too low, the condensate liquid temperature of the evaporated content is low, and condensation at normal water temperature may be difficult. In this case, what is necessary is just to perform condenser cooling by a refrigerator (chiller) or the like.

In atmospheric distillation, the distillation temperature is usually 100 ° C. or higher, and the precipitation of CAN crystals is performed at a high temperature of 100 ° C. or higher, so that impurities may be increased into the CAN crystals. On the other hand, in vacuum distillation, since the distillation temperature is low, the precipitation of CAN crystal is carried out at low temperature, so that impurities with little impurities are introduced into the crystal and high purity CAN is easily obtained. Therefore, distillation under reduced pressure is preferably used.

The nitric acid concentration is usually raised to at least 50% by weight, preferably at least 60% by weight relative to the acidic aqueous solution. For example, when the solution is concentrated by distillation or the like, it is particularly preferable to increase the nitric acid concentration to the upper limit of the azeotropic concentration of nitric acid and water (67%). When the nitric acid concentration after raising is too low, the solubility of CAN crystal | crystallization in a mother liquid becomes high, and the recovery amount and recovery rate of cerium fall.

When the nitric acid concentration is increased by heating such as distillation, the acidic aqueous solution is usually cooled to room temperature, and precipitates CAN as much as it cannot be dissolved due to the temperature drop.

The present invention is characterized in that, when the nitric acid concentration of the acidic aqueous solution is increased, the acidic aqueous solution contains a metal having an oxidation potential of 0.7 to 1.6 V or below pH 2.

As a metal whose oxidation potential in pH 2 or less is 0.7-1.6V, a chromium, nickel, cobalt, etc. can be mentioned specifically, For example, chromium is used preferably. In the case of chromium, the valence is between hexavalent and trivalent, and the effect of the present invention is remarkable. What is necessary is just to select the density | concentration of the metal whose oxidation potential is 0.7-1.6V in pH 2 or less in acidic aqueous solution suitably by composition, such as cerium, ammonium ion, nitric acid concentration, etc. in the acidic aqueous solution which recovers CAN.

Generally 0.3 wt% or less may be used, and in order to recover cerium as cerium ammonium nitrate efficiently from an acidic aqueous solution, it is 0.001 wt% or more, especially 0.005 wt% or more, Furthermore, 0.01 wt% or more, Especially preferably, It is preferable that it is 0.05 weight% or more. Moreover, it is preferable that this metal exists as an ion in acidic aqueous solution.

For example, when chromium is used as a metal having an oxidation potential of 0.7 to 1.6 V at a pH of 2 or less, the chromium concentration is 1/2 to 1/10 times the molar concentration, particularly 1/4 to 1/7 times the molar concentration of cerium trivalent. It is preferable that the concentration is in the vicinity of 1/6 times molar concentration, particularly within this range. If the amount of chromium in the acidic aqueous solution is too high, chromium may adhere to the CAN crystals, which may lower the purity, which is undesirable.

In the present invention, cerium can be recovered in high yield as cerium ammonium nitrate (IV) by containing a metal having an oxidation potential of 0.7 to 1.6 V at pH 2 or less in the acidic aqueous solution, and increasing the nitric acid concentration. This reason is estimated as follows.                 

As the nitric acid concentration in the acidic aqueous solution increases, the solubility of CAN decreases, and tetravalent cerium precipitates first as CAN crystals. When tetravalent cerium in the solution is removed as a CAN crystal, the total oxidation potential is lowered. On the contrary, a metal having an oxidation potential of 0.7 to 1.6 V at a pH of 2 or less becomes an ion having the highest oxidation potential. Therefore, this metal ion acts as an oxidizing agent to oxidize trivalent cerium to tetravalent cerium. And this metal ion itself is reduced and becomes a low valence ion.

The tetravalent cerium produced is precipitated as CAN crystals again because of its low solubility in acidic aqueous solution with high nitric acid concentration. In this way, in the present application, trivalent cerium, which was conventionally not recovered as CAN, can be precipitated and recovered as CAN, and the yield is dramatically increased.

In the present invention, a metal having an oxidation potential lower than tetravalent cerium (1.6 V when pH = 1) but higher than the trivalent cerium itself (0.7 V when pH = 1) is contained in an acidic aqueous solution, thereby providing pH 2 It was found and completed that trivalent cerium can be effectively oxidized to tetravalent cerium in the following acidic aqueous solution.

The precipitated CAN crystals are separated from the mother liquor by filtration. The obtained CAN crystals are usually washed with high purity concentrated nitric acid to remove the mother liquor attached to the crystals.

Increasing the number of cleanings by high-purity nitric acid can elute impurities present on the surface of the CAN crystals, further increasing the purity of the CAN, but reducing the recovery of the CAN. The number of cleanings is determined appropriately depending on the purpose of the recovered CAN. As the high purity nitric acid, concentrated nitric acid having a nitric acid concentration of at least 60% by weight, preferably at least 65% by weight is used. At this time, it is preferable that the total metal impurity concentration in high purity concentrated nitric acid is low, and usually 5 ppm or less, Preferably it is 1 ppm or less.

Furthermore, after washing with such high purity concentrated nitric acid, the CAN crystals are washed with a small amount of high purity dilute nitric acid to improve the purity and suppress the nitrate odor and the like. Although the nitric acid concentration of the high purity dilute nitric acid used at this time is arbitrary, it is generally 1 to 20 weight%, and it is especially preferable that it is 10 weight% or less, especially 5 weight% or less. Moreover, it is preferable that the total metal impurity concentration in high purity dilute nitric acid is also low, and 5 ppm or less normally, Preferably 1 ppm or less is used.

Trivalent cerium and trace amounts of tetravalent cerium are usually dissolved in the filtrate after increasing the nitric acid concentration in the acidic aqueous solution to precipitate and filter CAN.

Below, the example which used the etching waste liquid as acidic aqueous solution is demonstrated concretely. This etching waste liquid contains cerium, ammonium ions, and nitric acid, and also contains chromium as "a metal having an oxidation potential of 0.7 V to 1.6 V at a pH of 2 or less."

When the metal chromium is etched with an etching solution composed of an acidic aqueous solution containing cerium, ammonium ions, and nitric acid, the metal chromium (zero-valent) is oxidized by tetravalent cerium to form hexavalent chromium ions, and eluted with an acidic solution. Tetravalent cerium is reduced to trivalent cerium. The etching solution (etching waste liquid, ie, acidic aqueous solution) after the completion of etching is, while a large amount of tetravalent cerium ions is present, the oxidation potential of tetravalent cerium is maintained higher than that of chromium in the acidic aqueous solution. It can stably be present in an acidic aqueous solution.

However, when the nitric acid concentration is increased by, for example, concentration operation under reduced pressure, tetravalent cerium becomes crystallization of cerium ammonium nitrate (IV) due to its low solubility. Then, since tetravalent cerium which maintained the high oxidation potential decreases in the acidic aqueous solution, hexavalent chromium having a high oxidation potential gradually becomes dominant. Thus, the hexavalent chromium ion acts as an oxidant and the dissolved trivalent cerium is oxidized to become tetravalent cerium. This tetravalent cerium is precipitated again as CAN because of its low solubility under high nitric acid concentration. The presence of hexavalent chromium makes it possible to precipitate, produce and recover cerium in an acidic aqueous solution as cerium ammonium nitrate (IV) regardless of the valence.

A small amount of hexavalent chromium, a large amount of trivalent chromium, trivalent cerium, and a small amount of tetravalent cerium are dissolved in the acidic aqueous solution at the time when the precipitation of ammonium cerium (IV) crystals by increasing the nitric acid concentration is finished. It is thought to be.

The acidic aqueous solution after removing CAN contains trivalent cerium and a trace amount of tetravalent cerium as mentioned above. Therefore, in order to recover these ceriums as cerium ammonium nitrate, it can be precipitated as CAN crystals by adding hydrogen peroxide to the acidic aqueous solution after CAN removal. Hydrogen peroxide is usually added as hydrogen peroxide water. At this time, it is preferable that the acidic aqueous solution is substantially free of metal ions whose oxidation potential at pH 2 or lower is higher than hydrogen peroxide, specifically, metals having an oxidation potential of 1.5 V or higher at pH 2 or lower. The reason why CAN is precipitated by adding hydrogen peroxide to an acidic aqueous solution that is substantially free of such metals is not clear.However, when a large amount of metal ions having an oxidation potential below pH 2 is higher than hydrogen peroxide, hydrogen peroxide is added to this ion. In the case where metal ions having a higher oxidation potential at pH 2 or less than hydrogen peroxide are substantially present, the hydrogen peroxide acts as an oxidizing agent on trivalent cerium ions.

The metal whose oxidation potential in pH 2 or less is 1.5 V or more is a metal whose oxidation potential in pH 2 or less is 1.6 V or more specifically, tetravalent cerium, hexavalent manganese, tetravalent lead etc. are mentioned.

The amount of hydrogen peroxide added is usually an amount necessary for the tetravalent cerium to precipitate as the cerium (IV) nitrate crystal and to raise the valence of the trivalent cerium remaining in the solution to tetravalent cerium. It is 1/5 times mole or more normally, Preferably it is 1/3 times mole or more, and is usually equimolar or less, Preferably it is 2/3 times mole or less. Among these ranges, the vicinity of 1/2 double mole is preferable. Moreover, when hexavalent chromium etc. exist in an acidic aqueous solution, the addition amount of hydrogen peroxide becomes smaller than the range mentioned above.

The fact that the metal whose oxidation potential at pH 2 or less is higher than hydrogen peroxide is not substantially present in the acidic aqueous solution can be confirmed that no gas (oxygen gas) is generated when hydrogen peroxide is added to the acidic aqueous solution. That is, when such a metal is present, hydrogen peroxide acts as a reducing agent and hydrogen peroxide itself is oxidized to generate oxygen gas. On the contrary, when hydrogen peroxide acts as an oxidizing agent, oxygen of hydrogen peroxide itself is used for oxidation, so no oxygen gas is generated.

In addition, the fact that the metal ion whose oxidation potential in pH 2 or less is higher than hydrogen peroxide does not exist substantially shows that the content of these metal ions is several ten ppm or less normally.

Since CAN crystal obtained by the method of this invention is high purity, it can be used as a raw material at the time of adjusting the etching liquid of chromium as mentioned above as it is.

An Example is shown to the following and this invention is demonstrated to it further more concretely. In addition, in the following Examples and Comparative Examples, "%" represents "weight%" unless there is particular notice.

<Method of analyzing cerium>

The total amount of tetravalent cerium and trivalent cerium (total cerium) and the total amount of hexavalent chromium and trivalent chromium (total chromium) were measured by ICP (luminescence analysis), and measured by tetravalent cerium redox titration, Trivalent cerium was subtracted from to yield trivalent cerium. In addition, about crystal | crystallization, aqueous solution was manufactured by the conventional method, and this was made into the analysis sample.

(Example 1)

Short distillation was carried out using 1000 ml of glass third chamber colben equipped with a water-cooled condenser in the distillation extraction line from the top of the column. In addition, a pressure reducing pump is attached to the rear portion of the water-cooled condenser to allow for reduced pressure distillation. And Colben was equipped with the thermometer for measuring kiln liquid temperature.

600 g of chromium etching waste liquids having the composition shown below were injected into Colben, and heated to 53.3 [hPa] (40 mmHg) under reduced pressure.

Tetravalent cerium: 1.96% (7.67% in terms of cerium ammonium nitrate)

Trivalent cerium: 1.00% (3.48% in terms of cerium ammonium nitrate)

Total Chromium: 0.07%

Nitrate: 35%

Balance: water

As distillation extraction started at the kiln temperature of 40 ° C, fine crystals were precipitated in the kiln liquid, and the kiln liquid was dark black. This black color is inferred from the generation and dissolution of trivalent chromium. Distillation was carried out until the amount of the condensed liquid was distilled from the top of the column to 400 g, that is, the cauldron liquid became 200 g and the cauldron liquid was concentrated three times. The kiln temperature at the end of distillation was about 50 ° C.

After leaving the kiln to stand at room temperature and cooling, the filtrate was separated by filtrate and crystals. As a result, 60 g of a crystal having a total content of 5.9% of nitric acid and water was obtained. The composition of the filtrate and the wet crystals (fines) were analyzed by the above method. The composition in this wet crystal (fine product) was as follows.

Tetravalent cerium concentration: 21.78% (85.17% in terms of cerium ammonium nitrate (IV))                 

Trivalent cerium concentration: 2.56% (8.88% in terms of cerium ammonium nitrate)

Total Chromium Concentration: 0.05%

Balance: aqueous nitric acid solution

The total cerium concentration of the filtrate was 2.66%, the total chromium concentration was 0.26%, and the balance was water, nitric acid, and metallic impurities. In addition, the majority of chromium in the filtrate was trivalent chromium and dissolved in the filtrate.

Subsequently, in order to remove the mother liquor attached to the crystals, 52.5 g of crystals (one-time cleaning product) were suspended and washed with high purity concentrated nitric acid (total amount of impurity metal of 1 ppm or less) of 69.5% of this crystal and the same weight. )

The composition in the obtained wet crystal (one time wash | cleaned product) was as follows, and it was confirmed that trivalent cerium is not process.

Tetravalent cerium: 24.06% (94.11% in terms of cerium ammonium nitrate (IV))

Trivalent cerium: 0% (0% in terms of cerium ammonium nitrate)

Total Chromium: 0.007%

Balance: aqueous nitric acid solution

The recovery rate of total cerium was 71.1% by the following equation.

[(52.5g × (0.2406 + 0)) / (600g × (0.0196 + 0.0100))] × 100 = 71.1%

Moreover, the recovery rate of tetravalent cerium with respect to tetravalent cerium in injection liquid was 107.4% by the following formula | equation.

[(52.5g × 0.2406) / (600g × 0.0196)] × 100 = 107.4%                 

This indicates that in addition to tetravalent cerium present in the waste liquid, part of the cerium present as trivalent cerium was also recovered as cerium ammonium nitrate (IV).

Furthermore, the wet crystal obtained by washing this crystal | crystallization (once washing | cleaning product) three times using crystal | crystallization and nitric acid (total amount of impurity metals of 1 ppm or less) of the same weight concentration 69.5%, wash | cleaned four times in total (4 Ash cleaning product) was an ammonium cerium nitrate (IV) crystal having a content of 1 ppm or less of metal impurities such as chromium and iron, and the amount thereof was 30 g. Moreover, the composition in this wet crystal was as follows, and it was confirmed that trivalent cerium is not processed and almost no chromium is contained.

Tetravalent cerium: 24.10% (94.29% in terms of cerium ammonium nitrate (IV))

Trivalent cerium: 0% (0% in terms of cerium ammonium nitrate)

Total chromium: 0.0001% or less

Balance: aqueous nitric acid solution

The recovery rate of tetravalent cerium at this point was 61.5% by the following equation.

[(30g × 0.241) / (600g × 0.0196)] × 100 = 61.5%

Moreover, the recovery rate of total cerium was 40.7% by the following formula.

[(30g × (0.241 + 0)) / (600g × (0.0196 + 0.0100))] × 100 = 40.7%

The number of days from the start of distillation to the end of the four washes was one day. Moreover, the removal rate of chromium by 4 washes was 99.9%.

(Example 2)

The same procedure as in Example 1 was repeated except that the reduced pressure distillation was changed to atmospheric distillation.

Boiling started at the kiln liquid temperature of 110 degreeC, and the kiln liquid temperature at the end of distillation was about 118 degreeC. The obtained wet crystal (fine product) was 60 g. The composition in this wet crystal (fine product) was as follows.

Tetravalent cerium: 18.66% (73.00% in terms of cerium ammonium nitrate (IV))

Trivalent cerium: 5.48% (19.00% in terms of cerium ammonium nitrate)

Total Chromium: 0.09%

Balance: aqueous nitric acid solution

The recovery rate of total cerium was 81.6% by the following equation.

[(60 g × (0.1866 + 0.0548)) / (600 g × (0.0196 + 0.01))] × 100 = 81.6%

Moreover, the recovery rate of tetravalent cerium with respect to tetravalent cerium in injection liquid was 95.2% by the following formula | equation.

[(60g × 0.1866) / (600g × 0.0196)] × 100 = 95.2%

In addition, this wet crystal (fine product) was washed once with high purity concentrated nitric acid having a nitric acid concentration of 69.5% in the same manner as in Example 1.

The obtained wet crystal (one time wash product) was 52 g. Moreover, the composition was as follows.

Tetravalent cerium: 20.12% (78.76% in terms of cerium ammonium nitrate)

Trivalent cerium: 3.81% (13.21% in terms of cerium (III) ammonium nitrate)

Total Chromium: 0.02%                 

Balance: aqueous nitric acid solution

The recovery rate of total cerium was 70.0% by the following formula.

[(52g × (0.2012 + 0.0381)) / (600g × (0.0196 + 0.01))] × 100 = 70.0%

Moreover, the recovery rate of tetravalent cerium with respect to tetravalent cerium in an injection liquid was 89.0% by the following formula | equation.

[(52g × 0.2012) / (600g × 0.0196)] × 100 = 89.0%

When distillation is carried out at atmospheric pressure, crystal precipitation occurs at high temperature, and thus, it is estimated that cerium nitrate (III) nitrate crystals are precipitated in steps, resulting in a lower cerium tetravalent amount than in Example 1.

(Comparative Example 1)

The experiment was conducted in the same manner as in Example 1 except that 600 g of an aqueous solution having the following composition containing cerium ammonium nitrate (IV) and (III) not containing chromium instead of the chromium etching waste solution was used.

Tetravalent cerium: 3% (11.74% in terms of cerium ammonium nitrate)

Trivalent cerium: 1% (3.48% in terms of cerium ammonium nitrate)

Nitrate: 35%

Balance: water

The precipitated crystals were analyzed in the same manner as in Example 1. In addition, since it does not contain chromium etc., nitrate washing was not performed.

The obtained wet crystal (fine product) was 71.3 g. The composition was as follows.

Tetravalent cerium: 24.25% (94.88% in terms of cerium ammonium nitrate (IV))

Trivalent cerium: 0.0008% (0% in terms of cerium ammonium nitrate)

Balance: aqueous nitric acid solution

The recovery rate of total cerium was 72.0% by the following formula.

[(71.3g × 0.2425) / (600g × (0.03 + 0.01))] × 100 = 72.0%

Moreover, the recovery rate of tetravalent cerium with respect to tetravalent cerium in injection liquid was 96.1% by the following formula | equation.

[(71.3g × 0.2425) / (600g × 0.03)] × 100 = 96.1%

As a result, the amount of the tetravalent cerium recovered is not increasing than that of the tetravalent cerium in the cerium-containing solution, so that the amount of cerium nitrate (IV) can be increased across the trivalent cerium as in the present invention. I could see that there was no.

The above results are summarized in the following table.

Total Ce Recovery (wt%) Tetravalent Cerium Recovery (wt%) Example 1 Pressure gauge 0 washes 82.0 111 1 time cleaning 71.1 107 4 washes 40.7 61.4 Example 2 Atmospheric pressure gauge 0 washes 81.6 95.2 1 time cleaning 70 89 Comparative Example 1 Pressure gauge 0 washes 72 96

(Example 3)

Short distillation was carried out using a 500L glass lining tank (with a stirrer and jacket attached) fitted with a water-cooled condenser made of a lining in the distillation extraction line from the top of the tower. Further, a water-sealed pressure reducing pump is attached to the rear portion of the glass-lined water-cooled condenser, so that reduced-pressure distillation is possible.

The glass lining tank is equipped with a temperature sensor for measuring the liquid temperature and the jacket temperature of the kiln, and a pressure sensor for measuring and controlling the internal pressure of the kiln.

400 kg (about 388 L) of chromium etching waste liquid of the composition shown below was inject | poured into the glass lining tank, and it heated at 53.3 [hPs] (40 mmHg) and the temperature in a jacket at 70 degreeC under reduced pressure.

Tetravalent cerium concentration: 2.16% (8.45% in terms of cerium ammonium nitrate (IV))

Trivalent cerium concentration: 1.54% (5.36% in terms of cerium ammonium nitrate)

Total Chromium Concentration: 0.10%

Nitrate: 14%

Balance: water

Distillation extraction is started at a temperature of about 40 DEG C in the kiln, and the chromium etching waste liquid having the same capacity as the distillation extraction rate from the top of the column is continuously supplied to a glass lining tank (hereinafter, simply referred to as a "kiln"). Distillation was continued to keep the liquid level almost constant. And it distilled until the liquid volume obtained by condensation became 800 kg. That is, the residual liquid in the kiln at the end of distillation was 400 kg, and the chromium etching waste liquid in the kiln was tripled (concentrated 1200 kg of chromium etching waste liquid to 400 kg). .                 

After returning the pressure in the kiln to atmospheric pressure, water was allowed to pass through the jacket, and cooled until the temperature in the kiln became a room temperature. Subsequently, the concentrate in the kiln was separated into crystal and filtrate using a fluororesin lined centrifuge. This obtained wet crystal (fine product) was 106.6 kg, and the composition was as follows.

Tetravalent cerium concentration: 25.1% (98.20% in terms of cerium ammonium nitrate (IV))

Trivalent Cerium Concentration: 0%

Total Chromium Concentration: 0.012%

Balance: aqueous nitric acid solution

The total cerium concentration in the separated filtrate was 5.7%, the total chromium concentration was 0.39%, and the balance was water, nitric acid, metallic impurities, and the like.

The crystals were then washed using crystals and high purity concentrated nitric acid (total impurity metal concentration of 1 ppm or less) with a concentration of 69.5% of the same weight. This washing was performed by continuously supplying the crystal layer in the centrifuge while rotating the inside of the centrifuge.

The weight of the wet crystal (four times washed product) obtained by carrying out this washing method four times was 79.3 kg. The crystal composition was as follows. As a result, it was found that this crystal (four times cleansing product) was a very high purity ammonium cerium (IV) crystal in which trivalent cerium and chromium were removed.

Tetravalent cerium: 25.1% (98.2% in terms of cerium ammonium nitrate (IV))

Trivalent Cerium: 0%

Total chromium: 0.0001% or less                 

Balance: aqueous nitric acid solution

In this example, the recovery rate of cerium in the wet crystal (four times washed product) was determined in the same manner as in Example 1.

Total Cerium Recovery = 44.8% ((79.3 × 0.251) / (1200 × 0.037) × 100)

Recovery of tetravalent cerium = 76.8% ((79.3 × 0.251) / (1200 × 0.0216) × 100)

In addition, the concentrated nitric acid filtrate obtained when the fine crystal wet crystal is washed with high purity concentrated nitric acid is returned to the kiln as a concentrated raw material, whereby cerium can be recovered more efficiently.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

This application is based on the JP Patent application 2001-175181 of an application on June 11, 2001, The content is taken in here as a reference.

According to this invention, the following effects are exhibited.

(1) Cerium can be recovered at a high recovery rate.

(2) Cerium can be recovered as cerium ammonium nitrate (IV), which is useful as a raw material for etching liquid.

(3) The etching waste liquid which etched chromium contains hexavalent chromium which is a poison. Usually, the waste liquid containing hexavalent chromium is processed after reducing hexavalent chromium to trivalent chromium with low toxicity by adding a reducing agent. When the chromium etching waste solution is used as the acid solution of the present invention, since most of the hexavalent chromium in the acidic aqueous solution is reduced to trivalent chromium, the amount of the reducing agent used at the time of the waste liquid treatment is reduced, and the waste liquid treatment can be carried out at low cost. have.

(4) Since cerium hydroxide as an intermediate product is not produced, the washing process of cerium hydroxide is unnecessary, and the amount of wastewater treatment is reduced, so that the manufacturing cost of the whole process and the environmental load can be reduced.

(5) Compared with the conventional method, the process can be simplified and the recovery can be completed in a short time.

Claims (16)

A method for producing ammonium cerium nitrate from an acidic aqueous solution containing at least trivalent cerium, tetravalent cerium, ammonium ions, and nitric acid, wherein the acidic aqueous solution has a oxidation potential of 0.7 to 1.6 V at a pH of 2 or less. And increasing the concentration of nitric acid in the acidic aqueous solution to precipitate cerium ammonium nitrate (IV) crystals. The method according to claim 1, wherein the ammonium ion content in the acidic aqueous solution is at least 2 mol times the cerium concentration. The method according to claim 1 or 2, wherein the concentration of nitric acid in the acidic aqueous solution is raised to 50% by weight or more. The production method according to claim 1 or 2, further comprising an acidic component other than nitric acid. The method for producing ammonium cerium nitrate (IV) crystals obtained by the process according to claim 1 or 2, which is washed with a concentrated aqueous solution of nitric acid having a nitric acid concentration of 60% by weight or more and a total metal impurity content of 1 ppm or less. . The method according to claim 5, wherein after washing with a concentrated nitric acid solution, the nitric acid concentration is further washed with a dilute nitric acid solution of 10 wt% or less. The production method according to claim 1 or 2, wherein the metal having an oxidation potential of 0.7 to 1.6 V at a pH of 2 or less is hexavalent chromium. The production method according to claim 1 or 2, wherein the nitric acid concentration is increased at a temperature of 100 ° C or lower. The method according to claim 1 or 2, wherein the nitric acid concentration is increased by distillation under reduced pressure in an acidic aqueous solution. The method according to claim 9, wherein the reduced pressure distillation is carried out under a reduced pressure of 100 mmHg or less. The method according to claim 1 or 2, wherein the concentration of nitric acid in the acidic aqueous solution is increased to precipitate cerium ammonium nitrate crystals, and then hydrogen peroxide is added to the acidic aqueous solution to precipitate cerium ammonium nitrate crystals. Characterized in the manufacturing method. 12. The production method according to claim 11, wherein the acidic aqueous solution to which hydrogen peroxide is added contains substantially no ions of metals having an oxidation potential of 1.5 V or more at pH 2. The production method according to claim 1 or 2, wherein the acidic aqueous solution is an etching solution after being used in an etching step. The manufacturing method of Claim 13 which is an etching liquid after being used for the chrome etching process. delete delete