JPS5935842B2 - Method for recovering useful substances from chromic acid aging solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for recovering the chromic acid content in the form of chromium oxide from an aged liquid that is about to be discarded and is a concentrated chromic acid solution with accumulated impurities generated from a chromium plating factory. be.

In recent years, in addition to the implementation of pollution prevention measures, plating factories have seen a series of rapid increases in the cost of various materials and large increases in water rates, which have had a significant impact on plating costs, so the plating process has become closed. Research has begun on this, and methods have been adopted to reduce the amount of plating solution pumped out, or to proactively collect the pumped solution and return it to the plating bath.

As a result, impurities remain in the plating solution and accumulate, causing the plating solution to gradually age and become unusable.

It is strongly desired that an effective method be developed to utilize this aged chromic acid solution with accumulated impurities, and similarly, in zinc chromate treatment, large amounts of chromic acid are required to periodically renew the solution. Aging fluid is generated, and its utilization is strongly desired.

There are two ways of thinking about this usage; one is to remove impurities from the aged liquid, and the other is to extract and use useful substances in the aged liquid. .

Among the methods currently in use for removing impurities, there are two methods: an iron removal method using electrolytic treatment and a cation removal method using an ion exchange resin.

The former method involves electrolyzing the aging solution using an unglazed cylindrical diaphragm to remove accumulated iron and trivalent chromium and reusing it as a plating bath, but the electrolytic efficiency is poor, and this type of regeneration is In some cases, the plating properties of the baths were poor, so the process was not technically complete, and only a few attempts had been made.

The latter method uses a cation exchange resin to adsorb and remove the cations accumulated in the aged solution, and if fully implemented, it should theoretically be the same as the new solution, but the chromic acid concentration If concentrated, the ion exchange resin will be damaged, so it must be diluted.Also, zinc chromate solution accumulates a lot of cations, so a large amount of ion exchange resin is required. Although it has been carried out, it is not necessarily economical and the processing method is complicated, so it cannot be said that it has been put into practical use.

On the other hand, as a method for extracting and utilizing useful substances in the aged liquid, the aged liquid is neutralized with caustic soda, Fe3+, cr
3+, ZT12+, cu2+, Ni2+, etc. are precipitated as hydroxides, filtered, and the filtrate is recovered as a sodium chromate solution, which can be used as a chromate treatment agent or as an intermediate raw material at a sodium dichromate manufacturing factory. A mixed use method is being implemented.

However, this method has little demand as a chromate treatment agent, and when used to produce sodium dichromate, the shipping cost is often higher than the evaluated value because the liquid is relatively dilute. This has no choice but to be an expensive disposal method.

In addition, in the neutralization filtration method, fluoride, nitrate, hydrochloride,
Since sulfates, etc. are not removed, sodium chromate becomes contaminated with these, which has a negative impact on the quality of the product line.

As mentioned above, effective usage methods have not been established at present.
Generally, the method of disposing of the reduced and neutralized precipitate is carried out, but this method requires expensive chemicals such as sodium sulfite and caustic soda, which are used during reduction*, and there are concerns about secondary pollution. However, there were still problems, and the recycling of the sediment was a mixed sludge with a high content of impurities, so its use was limited.

The type and content of impurities in the aging chromium plating solution vary depending on the purpose of plating and the operating method of each manufacturer, and an analysis example has the following composition.

In addition, sulfuric acid is used in a certain ratio to chromic anhydride, and the standard weight ratio is 100:1, but in practice it ranges from 100:2 to 100:0.5. Contains.

It also contains fluorine compounds and other substances.

In addition, the chromic acid aging solution of the zinc chromate solution is a solution in which zinc and other substances are dissolved in the following standard solution and accumulated in large amounts.

The purpose of the present invention is to utilize such a romic acid aging solution,
By separating and removing the heavy metals and volatile substances dissolved in this chromium salt, and recovering the useful chromic acid content in the form of chromium oxide, we can produce products that are industrially useful and expensive among chromium salts. An object of the present invention is to provide an effective method for using a chromic acid aging solution.

The inventors have discovered that by neutralizing the aging liquid with ammonia, heavy metals will chemically change to hydroxides and form precipitates, chromic acid will dissolve as ammonium dichromate, and sulfuric acid will dissolve as ammonium sulfate. I found out that there is.

The precipitate is filtered out from the neutralized solution obtained in this way, and the resulting filtrate is heated, evaporated and concentrated to dryness. When heat is subsequently applied, a decomposition reaction begins and a green chromium oxide powder is produced, producing intense heat. If this decomposition product is further heated, C
r2O3 minutes improves and 8 minutes decreases.

Further washing with water or acid solution significantly reduces the time of 8 minutes.

For example, if the temperature is raised to 1000°C, a chromium oxide product equivalent to JI8 No. 2 product can be obtained, and if it is further washed with water or an acid solution, it can be used as a metallic chromium raw material that requires a particularly low content of 8. This invention was completed by discovering that a chromium oxide product having the following characteristics could be obtained.

To explain this invention in more detail, the method for recovering useful substances from aged liquid includes a neutralization step, a filtration step, an evaporation concentration drying step, and a decomposition and temperature raising step.

*First, the neutralization process is a process in which ammonia is added to the aged liquid to chemically change dissolved heavy metals into hydroxides and form a precipitate. Unlike using caustic soda, a common neutralizing agent, neutralization is carried out using an appropriate and narrow range of pH.
It must be done.

According to experiments conducted by the inventors, the relationship between the neutralization pH value and the concentration of heavy metals dissolved in the solution is shown in Table 1, and the appropriate neutralization pH varies depending on the type of heavy metals in the aged solution, 7, preferably 60-65.

Decorative chrome plating aging solution (chromic acid 321?/l
) is neutralized with concentrated ammonia water.In this step, if the aged liquid is extremely rich in impurities, the neutralized liquid may become mushy and the subsequent filtration may be difficult.

Furthermore, when the chromic acid concentration is too high, all of the generated ammonium dichromate may not be dissolved and a portion may precipitate.

In order to avoid such phenomena, water is added as necessary before, during, or after neutralization.

Regarding this added water, if the cake is washed with water in order to recover ammonium dichromate adhering to the cake in the next filtration step, it is preferable to replenish it with the washing water.

The conditions for dissolving the entire amount of generated ammonium dichromate are to adjust the concentration of ammonium dichromate in the filtrate to be less than the dissolved concentration of (NH4)2Cr207 shown in Table 2.

For example, at 40°C, the concentration of ammonium dichromate in the filtrate needs to be 36.9% or less.

For neutralizing ammonia, you can blow in ammonia gas or add ammonia water, but if the concentration of chromic acid or impurities in the aged liquid is low, it is better to neutralize with ammonia gas because the amount of water that evaporates during the concentration process can be reduced. This is advantageous because it reduces

On the other hand, if the concentration of chromic acid or impurities is high (if you need to add water, you can neutralize it with either), but if you use ammonia water, the amount of water you add will only decrease.

In the filtration step, filtration can be performed using a known and commonly used vacuum filter or filter press.

In order to recover as much useful content as possible, the filter cake is preferably washed with water, and the dilute solution of ammonium dichromate obtained at this time is preferably used as addition water in the next neutralization step.

The evaporation concentration drying process can be carried out using a known general dryer, but in order to carry out the process from evaporation to drying continuously, a shelf-type dryer that is placed in a suitable container for drying, or a groove-type dryer that uses indirect steam heating may be used. is even more appropriate.

In the decomposition and temperature raising step, the dry matter obtained in the previous step is ignited using an appropriate means, or if the dry matter is heated to about 240°C, it decomposes while producing intense heat, producing a green color. Chromium oxide powder forms.

This decomposition reaction is thought to be due to the decomposition of ammonium dichromate present in the filtrate according to the following reaction formula.

(NH4)2Cr207→Cr2O3+N2↑±4H2
0↑It has been found that this decomposition reaction does not completely progress to chromium oxide by the above decomposition alone, but by continuing to raise the temperature, the decomposition reaction progresses and the purity of chromium oxide increases.

Furthermore, it was found that by washing the product thus obtained with water or an acid solution, the chromium oxide purity was improved and decreased by 8 minutes.

For example, after decomposition reaction, 1000 to 1100
By heating at .degree. C. for 1 hour, it was possible to obtain a chromium oxide product equivalent to JIS No. 2 product, and by further washing with water, it was possible to obtain chromium oxide, which is suitable as a raw material for metallic chromium and has an extremely low content of 8 minutes.

Next, the present invention will be explained with reference to examples.

The analytical methods for Cr2O3 and 8 minutes of chromium oxide in these Examples were all conducted in accordance with the method of JISKI 401-1969.

Example 1 Decorative chrome plating aging solution (chromic acid 321t/l, C
r3+6.899/l, Fe 1.81? /l, 5o
41.73g/, e) 11. Ammonia gas was blown into the solution to neutralize it to pH 6.0, and vacuum suction filtration was performed using a Nutsche equipped with 5B filter paper.

The temperature of the filtrate was 50°C, and the ammonium dichromate concentration was 3.
It was 0.3%, which was below the dissolved concentration.

In order to recover useful components adhering to the cake, 200 rIL of water was poured onto the cake and similarly filtered under vacuum suction, placed in a glass beaker together with the filtrate, heated in a water pass, and evaporated to dryness.

When a small amount of ethyl alcohol was added dropwise to the dried solids obtained in this manner and ignited with a matchstick, the dry solids reacted violently and decomposed to become a green powdery decomposition product.

At this time, the temperature of the decomposed product rose to 520°C.

The analytical values of this decomposed product are shown in Table 3, and it was confirmed that the decomposed product was mainly composed of chromium oxide.

Further, the decomposition product obtained in this way was transferred to a magnetic crucible and heated in an electric heating furnace at 700°C, 800°C, 900°C for 10
Heating at each temperature of 00°C, 11,100°C for 1 hour,
Chromium oxide of 3 parts of Cr2O shown in Table 4 and 8 parts of chromium oxide shown in Table 5 were obtained.

There was a tendency that the higher the temperature, the higher the Cr2O3 content and the lower the 8 minute content, and it was possible to obtain chromium oxide equivalent to JIS No. 2 product by heating at 1000°C.

Furthermore, the decomposition products obtained in the above operation and 1 at each temperature
The products obtained by heating for a period of time are allowed to cool and then repulped with about 10 times the weight of 15°C water, 40°C water, IN hydrochloric acid water, or IN nitric acid water, 5
Vacuum suction filtration was carried out using a nutsche equipped with B filter paper to separate the washing liquid, and the cake was repulped again with the same amount of fresh water at room temperature, and the washing liquid was separated in the same manner.

The thus washed cake was transferred to a stainless steel container and dried in a box type dryer at a temperature of 110° C. until a constant weight was obtained, thereby obtaining 3 minutes of Cr2O shown in Table 4 and 8 minutes of chromium oxide shown in Table 5.

In either case, cleaning improves Cr2O3 and decreases 8.

In particular, the chromium oxide that was washed at 1000° C. after 8 minutes was 0.00%, which is preferable as a raw material for metallic chromium.

(In the above, in the case of hydrochloric acid water and nitric acid water, the decomposition product and 10
The temperature was limited to 00°C.

) Example 2 Decorative chrome plating aging solution (chromic acid 321?/, e
, Cr3+6.89 fl/L Fe 1.81
? /l.

5o41.73? /l: ) Add 267rrLl of 28% aqueous ammonia to 1l, neutralize to pH 6.3, and
Vacuum suction filtration was performed using a Nutsche equipped with 5B filter paper.

The temperature of the filtrate was 40°C, and the ammonium dichromate concentration was 2.
It was 7.1%, which was below the dissolved concentration.

In order to recover the useful components attached to the cake, 200 ml of water was poured onto the cake, filtered with vacuum suction in the same way, placed in a glass beaker together with the filtrate, and heated on a sand bath at about 240'C. When it was evaporated and concentrated to dryness, it immediately reacted violently and decomposed to become a green powdery decomposition product.

The analytical values of this decomposed product and the analytical values obtained when the thus obtained decomposed product was transferred to a magnetic crucible and heated at 1000° C. for 1 hour in an electric heating furnace are shown in Table 6, and it was confirmed that it was chromium oxide.

Example 3 Aging solution for hard chrome plating (chromic acid 183?/L C
r3+19.8? /L Fe 7.71? / l,
5o43.36 ff/l) 11VC77 Moni7 gas was blown into the solution to neutralize it to pH=6.5, and vacuum suction filtration was carried out using a Nutsche equipped with flat 5B filter paper.

The temperature of the filtrate was 42°C, and the ammonium dichromate concentration was 1.
It was 5.6%, which was below the dissolved concentration.

In order to recover the useful components attached to the cake, pour 200 g of water onto the cake, vacuum filtrate it in the same way, put it in a glass beaker together with the filtrate, and heat it in a water bath to evaporate and concentrate to dryness. Ta.

A small amount of ethyl alcohol was added dropwise to the dried solids thus obtained, and when ignited with a matchstick, the dry solids reacted violently and decomposed to become a green powdery decomposition product.

The analysis value of this decomposed product and the decomposed product thus obtained were transferred to a magnetic crucible and heated to 800°C110 in an electric heating furnace.
Table 7 shows the analytical values when heated at 00°C and 1100°C for 1 hour.

Example 4 Aging solution of zinc chromate solution (chromic acid 82.3?/l,
Cr3+9.94? /L Zn 28.1? /l
5o422.5g/1) Ammonia gas was blown into 11 to neutralize it to pH=6.4', and vacuum suction filtration was performed using a Nutsche equipped with A5B filter paper.

The temperature of the filtrate was 44°C and the ammonium dichromate concentration was 7.
%, which was below the dissolved concentration.

In order to recover the useful components attached to the cake, 200 ml of water was poured onto the cake, filtered with vacuum suction in the same manner, and placed in a glass beaker together with the filtrate, heated in a water bath to evaporate and concentrate to dryness. Ta.

A small amount of ethyl alcohol was added dropwise to the dried solids thus obtained, and when ignited with a matchstick, the dry solids reacted violently and decomposed to become a green powdery decomposition product.

The analysis value of this decomposition product and the decomposition product thus obtained were transferred to a magnetic crucible and heated at 800℃ and 1000℃ in an electric heating furnace.
Table 8 shows the analytical values when heated for 1 hour at temperatures of 1100°C and 1100°C.

Claims (1)

[Claims] 1. The pH of the chromic acid aged solution is adjusted so that the neutralized solution produced has appropriate fluidity and the ammonium dichromate produced is sufficiently dissolved.
It is characterized by neutralizing with ammonia to a range of 6 to 7, separating the precipitate from the obtained slurry solution, heating the solution to evaporate and concentrate it to dryness, and then decomposing it by heating to obtain chromium oxide. A method for recovering useful substances from chromic acid aged liquid.