JPS6036833B2 - How to treat chrome peck wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating chrome plating wastewater discharged from a chrome plating process.

Conventionally, when treating chromium plating wastewater, the method is to reduce chromate ions (C) to chromium ions (Cr) using a reducing agent, and then add alkali to precipitate the chromium ions as chromium hydroxide. It is taken. This reduction-neutralization method produces a large amount of sludge, and there is concern that secondary pollution may occur due to its disposal, and the treated water contains many undesirable ions and cannot be reused. On the other hand, various treatment methods using ion exchange resins have been investigated for the purpose of recovering chromate ions and obtaining treated water with high purity, but none have yet been satisfactory. For example, when adsorbing chromate ions with the conventional method '1) Strong base anion exchange≠sword resin, the exchange capacity of chromate ions is low, but the regeneration efficiency is poor. For example, when regenerating with a caustic soda aqueous solution, the regeneration level is 300. This method is uneconomical as it requires NaOH/1-resin, but today weakly basic anion exchange resins are generally used because they are easy to regenerate.

[2- When adsorbing chromate ions with OH-type weakly basic anioso-doken resin (hereinafter simply referred to as "OH-type"), the regeneration efficiency of the resin is good, but chromate ions tend to leak out during liquid passage. In addition, the exchange capacity of chromate ions is drastically reduced compared to when the salt type is used.

'3} When chromate ions are adsorbed using salt-type weakly basic anion exchange resins (hereinafter simply referred to as "salt-type"), the regeneration efficiency and chromate ion exchange capacity of the resin are satisfactory; CI- or S042- substituted with ions leaks out and the treated water becomes acidic.

As mentioned above, today, when chromate ions are to be efficiently recovered, salt type is used, and the treated water is pH-adjusted and discharged. Although the exchange capacity is not good, I am using the OH type. In addition, chromium plating wastewater contains trivalent chromium,
Strongly acidic cation exchange resins are generally used along with the above anion exchange resins because they contain harmful cations such as iron. However, with regard to trivalent chromium, it is not possible to completely adsorb and remove it using the strongly acidic cation exchange resin alone, and the current situation is that it leaks out at around pm (total chromium), which is the wastewater regulation value.
As described above, the subordinate treatment method has various drawbacks. For this reason, the present inventors have conducted various research into treatment methods using ion exchange resin in order to efficiently recover chromate ions from wastewater discharged from the chromium plating process and to obtain high-purity treated water. They discovered that the combination of ion exchange resins to be used and the order of flow are very important in order to advantageously treat the wastewater, and have completed the present invention.

That is, the present invention includes a first step in which chromium plating wastewater discharged from the chrome plating process is treated with a wind-salt type weakly basic anionic resin; Process (O day type strongly acidic cation exchange ≠ treated with sword resin and then treated with OH type strong basic anion exchange resin or mixture consisting of H type strongly acidic cation exchange resin and OH type strongly basic anion exchange resin This is a method for treating chromium plating wastewater, which is characterized by sequentially passing the liquid through a third step in which it is treated with a resin.

In the present invention, the combination of ion exchange resins and the order in which the wastewater flows are very important, and if the above conditions are not met, sufficient effects will not be obtained. The present invention will be explained below based on the drawings. Wind Chrome plating wastewater is first collected in A. The liquid is passed through the column, but here the chromate ions are exchanged with "salt type" CI- or S042-, and instead of the chromate ions being adsorbed and removed, CI- or SQ2- leaks from the column. .

In other words, when the salt type is used in the CI type, CI- and S042- are leaked from the resin in an amount equivalent to the adsorbed chromate ions when used in the S04 type. The S042- (containing about 1% based on 3 of C) passes through the column A and leaks out. 'B} Next, A containing CI- or S042-
The water treated by the tower is passed through a tower filled with "OH type", and most of the CI- or S042- is adsorbed and removed.

{C' Continuing, since the A2 tower treated water contains cations such as trivalent chromium and some anions, a mixed tower of H-type strongly acidic cation exchange resin and OH-type strongly basic anion exchange resin is used. (hereinafter referred to as M column), or by treatment with an H-type strongly acidic cation exchange resin and then with an OH-type strongly basic anion exchange resin, highly purified treated water can be obtained. Next, the A column and the A2 column, which are the main parts of the present invention, will be explained in detail. As shown in Figure 1, when chromium plating wastewater is passed through the tower A, chromate ions will eventually leak out, but if the flow continues until the chromate ion adsorption chamber in the tower is almost completely exhausted.
CI in the salt form or S042 replaces most of the chromate ions, and the column is substantially saturated with the chromate ions.

At this time, the flow of liquid is stopped, but the timing is A2. It can be freely set in consideration of the exchange capacity of the column and the M column. When the flow of liquid is stopped, the column is A, CI- or S04 discharged from the column.
2- converts most of the ``OH type'' to the ``salt type'', and it also adsorbs chromate ions leaked from the A column. Next, regeneration is performed, but A. The tower is regenerated with an alkaline aqueous solution such as caustic soda, and a highly pure sodium chromate aqueous solution is recovered. It is then washed with water to make it into an "OH type" and used as the second tower in the next cycle. (Second
(see figure). In addition, the A2 column is mostly in the "salt type", but if necessary, the amount of mineral acid such as hydrochloric acid or sulfuric acid used when converting the OH type of a normal weakly basic anion exchange resin to the salt type is 1/10. About 1/3 may be used to completely convert into the "salt form". This A2 column will be used as the first column in the next cycle (see Figure 2). Thereafter, the same operation is repeated and the order of passing the liquid through the A, column and A2 column is reversed for each cycle, but basically the chromium plating wastewater is passed through the "salt type" and "OH type" in that order. Process. The regeneration cycle of the M tower varies depending on the total thione concentration in the raw water and the slight anion concentration leaked from the second tower, but the regeneration is carried out by a known operating method. Examples of the weakly basic anion exchange resin used in the present invention include Duolite E
S-308 A weakly basic anion exchange resin represented by Duolite ES-368 (both manufactured by Diamond Shamrock Chemical Co.) is used, but it is particularly desirable that it has strong oxidation resistance to chromic acid, and that it It is a porous, weakly basic anion exchange resin that has a pyridine skeleton structure in the main chain or side chain in that it has a very large exchange capacity (adsorbs 240 units of C per resin). However, it is Sumikylate CR-2 (manufactured by Sumitomo Chemical Co., Ltd.). Examples of the H-type strongly acidic cation crosslinking resin include Duolite C-20, Duolite C-250, and Duolite ES-26 (all manufactured by Diamond Shamrock Chemical Co.). Examples of strong basic anion exchange resins include Duolite A-101D, Duolite A-1020, and Duolite A-161 (all manufactured by Diamond Shamrock Chemical Co.).

The method of the present invention is carried out using the above-mentioned resin composition, and the "salt type" in the first column is easy to regenerate and has a large exchange capacity for chromate ions, and can be used up to the limit of its exchange capacity. Use the points to further check the second tower's
In the "type", CI- in the acidic liquid discharged from the first column
Alternatively, most of the S042- can be adsorbed and automatically converted to the salt form, which can be used as the first column in the next cycle, and the load of water purification in the third column can be greatly reduced. This is a very effective method because it can be processed economically and with simple equipment. In addition, the conventional methods of sequentially passing a strong acidic cation exchange resin and then a weakly basic anion cross-sizing resin, or the method of subsequently using a strongly basic anion exchange resin, are not completely effective. Trivalent chromium, which could not be removed by adsorption, can be easily removed using this method, and the treated water can be of high purity.Moreover, the sodium chromate recovered from the first column can also be of high purity. This is also a major feature of the present invention. Next, the present invention will be explained in more detail with reference to Examples, but it goes without saying that the present invention is not limited thereto. Example 1 In a liquid passing device as shown in Fig. 1, A and the tower are equipped with
Filled with 1 piece of "salt type" Sumikylate CR-2, 5% ratio S
It was adjusted to type S04 using three aqueous solutions of 04.

The A2 column was filled with 1.5 OH type sumichlate CR-2, and the M column was filled with 0.5 of the strongly acidic cation exchange resin (
A mixed resin tower was prepared using Duolite ES-26) and IZ's strongly basic anion cross sword resin (Duolite A-101D). 6 as raw water passing through such treatment equipment.
Chromium plating washing water with a pH of 2.4 containing 50 pm of valent chromium, 15.8 ppm of sulfate ions, 25 ppm of trivalent chromium, 8.5 ppm of chlorine ions, 4.6 ppm of fluorine ions, etc. was used for 10 evenings/h. At flow rate A, tower, A2 tower,
The liquid was passed through the M tower in this order. When the amount of liquid passed was 210, hexavalent chromium started to leak from the column A. Adsorption in the column started, but the liquid continued to flow, and when 250 chromium was processed, hexavalent chromium was leaked from the column A. Since 70 ppm of water was leaking, the flow of liquid was stopped. During this period, the quality and specific resistance of the treated water were both satisfactory. Analytical values regarding the quality of treated water are shown in Table 1. Table 1 Example 2 The first column (A, column) used in Example 1 desorbs chromate ions using 4% NaOH aqueous solution 5 and then 15
It is washed with that water to form an "OH type", which is used as the second tower in this example.

The concentration of hexavalent chromium in this regeneration solution 20 is It was 5785 ppm.

In addition, the second tower (futo tower) used in Example 1 adsorbs a small amount of chromate ions, but most of them are converted to salt form, and this is backwashed using approximately 30% of the water. In Example 2, it is used as the first column. More mixed trees*
* Strongly acidic cationic resin (ES-26) of 8th column (M column)
was regenerated into H type using 5% aqueous solution of 2S04 and 5% water, and strong basic anion resin (A-101D) was regenerated with 4% Na.
It is regenerated into an OH type using 5 parts of an OH aqueous solution and 5 parts of water, and the two are mixed and used as a mixed resin tower. As shown in FIG. 2, the liquid is passed through the A2 tower and the A. Do this in order of tower and M tower. The raw water and the rate of liquid passage were the same as in Example 1, and the quality of the treated water after passing through the first column, second column, and M column, which were passed for 25 hours, is as shown in Table 2. Table 2 Example 3 In Example 2, after the two-stage time treatment, the residual fluid was stopped and regenerated.

The first column (column) in Example 2 desorbs chromate ions using a 4% NaOH aqueous solution and washes it with water to form an OH type, which is used as the second column in Example 3. do.

The concentration of 6 chromium in this regenerated solution is 5980 ppm.
Met. In addition, the second column (A, column) used in Example 2 was completely made into a salt form with a 5% ratio S04 aqueous solution, and then washed and backwashed with that water three times. use. The mixed resin column was regenerated in the same manner as in Example 2. As shown in FIG. 1, the liquid was passed in the order of A, tower, ~ tower, and M tower. The raw water and the rate of liquid passing were the same as in Example 1, and the liquid was passed for 25 hours. The quality of the treated water after passing through the first tower, second tower and M tower is as shown in Table 3. Reference example in Table 3 1. Chromium plating wastewater containing 450 ppm of hexavalent chromium and 18 ppm of trivalent chromium was mixed with 1. S04 type weakly basic anion exchange resin (Sumichelate CR-2) and 1. H type strongly acidic cation exchange resin. The trivalent chromium concentration in the treated water that was sequentially passed through (Duolite ES-26) at a flow rate of 10 mm/h was measured.

The results are shown in Table 4, but trivalent chromium cannot be completely adsorbed and removed by omitting the strongly basic anion exchange resin and passing only the weakly basic anion exchange resin and the strongly acidic cation exchange resin. It turns out it can't be done. Reference Example 2 Model wastewater containing 100 ppm of trivalent chromium and pH = 2.5 was passed through two types of H-type strongly acidic cation exchange resins (Duolite C-20 and Diaion SKIB) at a rate of 10 m/h each. The trivalent chromium concentration in the treated water was measured.

The results are shown in Table 5. Although the concentration of trivalent chromium in actual chromium plating washing water is not this high, this result shows that complete adsorption removal is not possible with a strongly acidic cation exchange resin alone. Table 4

[Brief explanation of the drawing]

The drawings are system diagrams schematically illustrating the liquid passing operation for carrying out the method of the present invention, in which FIG. 1 shows the liquid passing operation in the first cycle, and FIG. 2 shows the liquid passing operation in the second cycle. shows. In the figure, A.・・・・・・Weakly basic anion exchange resin tower,
~... Weakly basic anion exchange resin tower, M... A mixed resin tower of a strong acidic cation resin and a strong basic anion resin, respectively. Diamond 1 Leopard 2

Claims (1)

[Claims] 1. A first method of treating chrome plating wastewater discharged from the chrome plating process with (A) a salt-type weakly basic anion exchange resin.
Step (B) Treatment with an OH type weakly basic anion exchange resin Second step (C) Treatment with an H type strongly acidic cation exchange resin,
Then, it is treated with an OH type strong basic anion exchange resin, or
Alternatively, a method for treating chrome plating wastewater, characterized in that the liquid is sequentially passed through a third step of treatment with a mixed resin consisting of an H-type strongly acidic cation exchange resin and an OH-type strongly basic anion exchange resin. 2. The treatment method according to claim 1, wherein the weakly basic anion exchange resin has a pyridine skeleton structure in its main chain or side chain and is porous.