JPS5934134B2 - Method for recovering highly concentrated chromic acid liquid from wastewater containing chromate ions - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a method for recovering a highly concentrated chromic acid solution from wastewater containing chromate ions discharged from a chromium plating process, a chromate treatment process, a chromium dyeing process, etc. using an economical and easy operation. The present invention relates to a method using the improved resin.

Conventionally, when treating wastewater containing chromate ions, a method has been adopted in which the wastewater is reduced to chromium ions (Cra+) using a reducing agent, and then an alkali is added to precipitate the chromium ions as chromium hydroxide.

This reduction and neutralization method produces a large amount of sludge, and there is a concern that secondary pollution may occur due to the disposal of the sludge.

In addition, from the perspective of effective resource utilization, it is thought that the ion exchange method will replace the reductive neutralization method in the future, but even with this ion exchange method, how will the chromate ions adsorbed on the resin be recycled? There is a question of whether to recover it as a romic acid solution if it can be used.

In other words, chromate ions discharged from the chromium plating process, chromate treatment process, chrome dyeing process, etc. are adsorbed with an ion exchange resin, and the sodium chromate obtained by desorption with an aqueous alkaline solution such as aqueous caustic soda solution is converted into a so-called closed process and recycled. When using sodium chromate or as a raw material for producing other chromic acid compounds, there remain unresolved technical problems regarding the purity and concentration of sodium chromate.

For example, conventionally commercially available amine-type or quaternary ammonium salt-type anion exchange resins easily oxidize chromic acid, but the resin deteriorates rapidly with long-term use, and also adsorbs impurities in wastewater, resulting in alkali desorption. The liquid contains many chromium ions (Cr34-) generated by oxidation of the resin, deteriorating components of the resin, and impurities in wastewater.

Furthermore, while conventional anion exchange resins have a low adsorption capacity for chromate ions, they have a large adsorption force and require a large amount of desorbent, making it impossible to increase the concentration of chromate in the desorption solution very much. .

When considering the economical use of ion exchange resins, the amount of desorbent and concentration ratio are one of the major factors.

In view of the above-mentioned circumstances, the present inventors have arrived at the present invention as a result of intensive studies on a method for recovering a reusable high-concentration chromic acid solution from wastewater containing chromate ions.

That is, the present invention involves bringing wastewater containing chromate ions into contact with a porous weakly basic anion exchange resin (hereinafter referred to as pyridine resin) which has a pyridine core structure in its main chain or side chain and has a crosslinked structure. Chromate ions are adsorbed, then desorbed with an aqueous alkaline solution, the portion of the desorption liquid with a high concentration of chromic acid is separated and collected, and the consumed alkali is added to this high concentration chromate desorption liquid to be used as the desorption liquid for the next cycle. This is a method of economically recovering a high concentration chromic acid solution by repeating the operations used one after another.

It is convenient to use vinylpyridine as the monomer for the pyridine resin used in the present invention.

For example, 4-vinylpyridine, 2-vinylpyridine, 4-vinylpyridine,
Examples include vinyl-2-methylpyridine and vinylisoquinoline.

Examples of the crosslinking agent include divinylbenzene, divinyl tucrate, and ethylene glycol diacrylate. Radical suspension polymerization is generally preferred as the method for polymerizing the vinylpyridine monomer and the crosslinking agent. Various known methods can be used.

In carrying out the present invention, the raw water to be treated is first subjected to removal of suspended matter and pH adjustment.

For example, sand filtration, filter tear filtration, etc. are used to remove suspended substances.

It is desirable to adjust the pH to a range of 2 to 5, taking into account the oxidizing properties of chromic acid and the adsorption capacity of pyridine resin.

Next, the raw water subjected to the above treatment is brought into contact with a pyridine resin, and it is better to use the pyridine resin in its salt form than in its OH form, and it is particularly desirable to use it in its sulfate form.

The reason for this is that the basicity of bepyridine resin is lower than that of normal amine-type anion exchange resins, so the OH-type has almost no adsorption capacity for chromate ions, but the chromate-exchange capacity is comparable to that of normal commercially available resins used in the hydrochloride-type. More interestingly, when used in the sulfate form, the commercially available resin has a 1.5 to 2
This is based on our experimental findings that it adsorbs about twice as much chromate ion.

Note that chromate ions can be adsorbed and removed from raw water using a pyridine resin in the same manner as with ordinary ion exchange resins.

Contains almost no impurities like chrome plating wastewater, and p
If the raw water does not require H adjustment, it can be directly contacted with the pyridine resin, and about 240.9 chromic anhydride is adsorbed per 14 parts of the pyridine resin.

The pyridine resin that has adsorbed a certain amount of chromate ions desorbs the chromate ions with an alkaline aqueous solution such as caustic soda.

The concentration of the alkaline aqueous solution is usually 1 to 20%, preferably 4 to 12%.

By the way, one of the major factors that influences the economic efficiency of removing chromate ions by the ion exchange method is the amount of desorbent.

Regarding this point, although pyridine resin adsorbs chromic acid in a much larger amount than commercially available resins, it is possible to desorb it almost quantitatively by using a theoretical equivalent amount of alkali to the adsorbed chromate ion. be.

For example, when caustic soda is used as a desorbent, the regeneration level of pyridine resin 17-IM is 150-200 g.
This is approximately the same amount as the regeneration level of commercially available weakly basic anion exchange resins.

Furthermore, in order to carry out the ion exchange method economically, the desorption solution must be used effectively.

In other words, if this desorption liquid is converted into a chromium hydroxide sludge by the reductive coagulation method, there is no point in implementing the ion exchange method.

Therefore, in order to effectively utilize the desorption liquid as a raw material for producing chromic acid compounds or for closed production, the purity and concentration of chromic acid are important issues.

First, regarding purity, conventional amine-type anion exchange resins are weak against the oxidation of chromic acid, and the desorption liquid is chromium ion (
Cr3+) and impurities considered to be deteriorating components of the resin.

For example, when measuring the precipitated impurities in the desorption solution using a turbidity meter, it is found that the desorption solution of commercially available resins is extremely dirty, but the desorption solution of pyridine resin contains almost no of these impurities. This is consistent with the rationale that the pyridine core structure is resistant to chromic acid oxidation.

Next, regarding the concentration, a particularly high concentration is required in order to facilitate handling when transporting, storing, etc. the desorption solution.

First of all, the chromic acid concentration in the desorption solution is greatly influenced by the chromic acid adsorption capacity of the resin and the alkali regeneration level.

For example, when a pyridine resin that has adsorbed chromic acid up to a certain flow-through exchange capacity and a commercially available resin are desorbed using an alkaline aqueous solution of the same concentration and amount, the chromic acid concentration in the desorption liquid is The concentration of chromic acid in the desorption solution of pyridine resin is proportional to the amount of adsorption, and is about 1.5 to 2 times that of commercially available resins.

However, even this desorption solution has a low chromic acid concentration and requires further concentration.

There is also a physical evaporation concentration method for this method, but considering its economic efficiency and the characteristic of pyridine resin that it is resistant to oxidation of chromic acid, a method of concentrating chromic acid by circulating an alkaline desorption liquid is considered. .

When setting the range for circulating the desorption liquid, it is better to include this area in the study, since high-concentration chromic acid also flows out at the beginning of the water washing process after the alkali desorption process.

If more detailed settings are desired, the chromic acid concentration may be determined by sampling the desorption liquid at regular intervals and measuring the alkali concentration.

In this way, alkali is added to the desorption liquid separated and collected in a certain range and used as a desorption agent in the next cycle to increase the chromic acid concentration. The amount of desorption liquid does not necessarily have to be the same.

That is, the amount of desorption liquid to be separated and collected and the amount of desorption liquid to be used in the next cycle are related to the excess desorption liquid of each cycle and the concentration rate, and these settings can be freely selected.

Next, in order to use the pyridine resin for adsorption of chromate ions in the next cycle, it must be made into a sulfate form, which requires sulfuric acid using an amount of sulfuric acid equivalent to the acid exchange capacity of the pyridine resin after the alkaline desorption and water washing steps. Make it into a mold.

The concentration of the sulfuric acid used here is preferably 1 to 15%, and the operation is the same as that for ordinary ion exchange resins, followed by washing with water, backwashing, etc., and then using it for the next cycle of adsorption of chromate ions.

In addition, the regenerated waste liquid other than the desorption liquid separated and collected in each cycle, that is, the waste liquid from alkali, pickling, water washing, and backwashing processes, is all collected, and if necessary, the pH is adjusted and treated with pyridine resin, resulting in waste water containing chromate ions. Chromate ions can be adsorbed and removed in the same way as the treatment.

As described above, by using pyridine resin, it is possible to recover a chromic acid solution having excellent purity and concentration.

Regarding the details of the method for circulating and concentrating the desorption liquid using pyridine resin, various methods can be used, and combinations with known evaporation and concentration methods are also possible, and these methods can be freely selected depending on the purpose.

The present invention will be explained in more detail below with reference to Examples, but it goes without saying that the present invention is not limited thereto.

Reference example 1 Synthesis of pyridine resin In a 21 separable flask equipped with a stirring bar and a cooler, add ion-exchanged water (448 g), salt (186,!i+), and Na
N0□ (2,3g), hydroxyethyl cellulose (3
, 4g), divinylbenzene (10'l), isooctane (47g), 4-vinylpyridine (16:l) and benzoyl peroxide (1,6,9) and gradually heated to 80°C over 3 hours with stirring. The mixture was heated and then stirred at 95°C for 5 hours.

After cooling and filtration, methanol washing and hot water washing were repeated several times to obtain 700 ml of white opaque granular material.

Example 1 (1st cycle) Chromate ion was set as hexavalent chromium, and chromium plating wastewater (pH = 2.4) containing 707p1) In was injected into the 804 type of pyridine resin (11) obtained in Reference Example 1 for 1 hour. ri1O
1 (SV=10 h-1).

After 17 hours, the concentration of hexavalent ROM in the treated water was 0.5 Tl.
The amount of hexavalent ROM adsorbed was 120.29 (CrO2) per 11 pyridine resins.
231g).

Desorption and regeneration conditions are 8% NaOH aqueous solution 31, water washing 61.5
%H2SO4 aqueous solution 31, water washing 31 in order, all 5V=
The test was carried out with a downflow of 10 h-1.

This desorption regeneration solution was sampled in liters and numbered in the order of collection, and the hexavalent ROM concentration and NaOH concentration were measured for each sample.

The results are shown in the first cycle of Table 1.

(A1 to 3 in the table are alkaline desorption liquids, !4 to 9 are washing liquids,
AIO-12 is a pickling solution, A13-15 is a washing solution) A2-5 with a hexavalent ROM concentration of 110,000 pp or more
The sample was separated and mixed uniformly.

The hexavalent ROM concentration and NaOH concentration of this separated sample are the second
It is shown in the first cycle of the table.

(Second cycle) The pyridine resin desorbed and regenerated in the first cycle is approximately 2
1 water was used for backwashing with an upflow of S■=2h-1, and used for adsorption in the second cycle.

The concentration of hexavalent ROM in the stock solution in the second cycle was 774 pI.
) In, the conditions for passing the liquid were the same as in the first cycle, and the liquid was passed for 16 hours.

Hexavalent ROM adsorption amount is 123.89 per 14 pyridine resin.
(238 g as CrO2).

The alkaline desorption liquid used for this desorption is the separation collection liquid of the first cycle (total of 52 to Arashi 5, 25,4 as hexavalent chromium).
00 ppm) to which 214 g of NaOH was added so that the NaOH concentration was 8%.

The subsequent water washing, pickling, and water washing steps were performed in the same manner as in the first cycle.

This desorption regeneration solution was also sampled in 1 liter portions, and the hexavalent ROM concentration and NaOH concentration were measured and shown in the second cycle of Table 1.

In addition, the separated and sampled portions are A2 to A2 as in the first cycle.
5 was also mixed uniformly, and the hexavalent ROM concentration and NaOH concentration were measured and shown in the second cycle of Table 2.

(3rd cycle to 6th cycle) The operations described in the second cycle were sequentially performed up to 6 cycles.

The range to be separated and sampled was all 41 of A2 to A5, and 31 of them were added with NaOH to make up for the shortage and used for desorption in the next cycle.

Hexavalent ROM concentration and NaOH in the desorption regeneration solution of each cycle
The concentration is shown in Table 1, and the hexavalent ROM concentration and Na
The OH concentration and the amount of NaOH added are shown in Table 2.

Table 3 shows the concentration of hexavalent ROM in the stock solution used in each cycle and the passage time.

By circulating the desorption solution for the above 6 cycles, the concentration of hexavalent ROM was 83,700p (26% as Na2Cr04).
1%) high concentration liquid 41 and a desorption surplus liquid 51 which was not used in the next cycle were obtained in each cycle.

In addition, the regenerated liquid that was not separated and sampled in each cycle, that is, the first
The total of Arashi 1 and A6-15 and backwash liquid in the table is approximately 801, which is 6
It had a valent chromium content of 719 ppI+@ and a pH of 11.2.

Therefore, sulfuric acid was added to adjust the pH to 2.3, and pyridine resin (S
When treated with O4 type), hexavalent chromium could be removed in the same way as chromium plating wastewater.

Example 2 (1st cycle) Chromium plating wastewater (pH = -2,4) containing 637 p of chromate ions as hexavalent chromium was added to the SO4 type of pyridine resin (11) obtained in Reference Example 1 for 1 hour. 101(
The solution was passed at SV=10h').

After 18 hours, the concentration of hexavalent ROM in the treated water was 0.5111.
) m or more, so the flow of liquid was stopped.

The adsorption amount of hexavalent rom is 114.69 per 11 pyridine resin.
(220,!i+ as CrO2).

Desorption and regeneration conditions are 4% NaOH aqueous solution 51, water washing 61.5
%H2SO aqueous solution 31, water washing 31, all 5v=i
I did it with the down flow of oh'.

This desorption regeneration solution was sampled 11 times at a time, and the hexavalent ROM concentration and Na
The OH concentration was measured and the results are shown in the first cycle of Table 4.

Here, 2 to 8 where the hexavalent ROM concentration is 10009% or more
A range of 1 was separated and collected and mixed uniformly.

The hexavalent ROM concentration and NaOH concentration of this separated sample are the 5th
It is shown in the first cycle of the table.

(Second cycle) The pyridine resin desorbed and regenerated in the first cycle is approximately 2
1 water was used for the second cycle of adsorption, which was reversed with an upflow of 5 V = 2 h-1.

The concentration of hexavalent ROM in the stock solution used in the second cycle was 65
51) In INII, the liquid passing conditions were the same as in the first cycle, and the liquid was passed for 17 hours.

The adsorption amount of hexavalent rom is 111.3 per 11 pyridine resin.
,! i' (214 g as Cr03).

The alkaline desorption liquid used for this desorption is 5 of the separation collection liquid (1440pp111 as hexavalent chromium) of the first cycle.
1, add 196 g of NaO so that the NaOH concentration is 4%.
The one to which H was added was used.

The subsequent water washing, pickling, and water washing steps were performed in the same manner as in the first cycle.

Eleven samples of this desorption regeneration solution were also sampled, and the hexavalent ROM concentration and NaOH concentration were measured and shown in the second cycle of Table 4.

Also, the separated and sampled range is A2-8, same as in the first cycle.
This was also mixed uniformly and the hexavalent ROM concentration and NaOH concentration were measured and shown in the second cycle of Table 5.

(3rd cycle to 4th cycle) The operations described in the 2nd cycle were performed sequentially up to 4 cycles, and the range to be separated and collected was all 71 from &2 to 8.
NaOH was added to 51 of them to make up for the shortage and used for desorption in the next cycle.

Hexavalent ROM concentration and NaOH in the desorption regeneration solution of each cycle
The concentration is shown in Table 4, and the hexavalent ROM concentration and Na
The OH concentration and the amount of NaOH added are shown in Table 5.

The concentration of hexavalent chromium in the stock solution used in each cycle and the time for passing the solution are shown in Table 6.

Through the above four cycles of circulating the desorption solution, a desorption solution with a hexavalent ROM concentration of 39,000 ppm was obtained.

Compared to Example 1, the concentration of hexavalent ROM is lower in NaOH.
This is because the concentration is low and the range of separation and collection is wide.

In addition, the regenerated liquid that was not separated and sampled in each cycle, that is, the fourth
Total 501 of table 51 and A9-17 and backwashing liquid is 6
It contained 11 Q ppm of valent chromium and had a pH of 3.1.

When this was treated with pyridine resin (S04 type), hexavalent chromium could be adsorbed and removed in the same way as chromium plating wastewater.

No deterioration of the pyridine resin was observed in Examples 1 and 2.

Example 3 Chromium plating wastewater (pH = 25) containing 300 pp [0 as hexavalent chromate ion] was mixed with commercially available styrene-based weakly basic anion exchange resin (SO4 type) 11 and pyridine resin (S04 type) [ 5v=ioh-x each
The liquid was passed through.

When the flow-through point was set to 0.5 ppm (hexavalent chromium), the commercially available resin broke through in 19.4 hours, and the pyridine resin broke through in 39.0 hours.

The flow-through exchange capacity is 58.29 (C
112.9 as r03) and 117'i (Cr
03 was 225g).

Next, desorption was performed using 4% NaOH aqueous solution 51, and
The test was carried out with a downflow of V=10h-1.

The precipitated impurities in this desorption solution are measured using a turbidity meter (kaolin calibration curve).
When measured using a commercially available resin, the temperature was 126 degrees, and the temperature of the pyridine resin was 25 degrees.

Claims (1)

[Claims] 1 Wastewater containing chromate ions is brought into contact with a porous weakly basic anion exchange resin having a pyridine skeleton structure in its main chain or side chain and a crosslinked structure to adsorb chromate ions, and then treated with an aqueous alkaline solution. The process is repeated sequentially to separate and collect the part with a high concentration of chromic acid in the desorption liquid, add the consumed alkali to this high concentration chromic acid desorption liquid, and use it as the desorption liquid for the next cycle. How to recover high concentration chromic acid solution.