JPS61136913A - Purifying method of salt water for electrolysis - Google Patents

Abstract

PURPOSE:To absorb only the hard components such as Ca and Mg without absorbing mercury on a chelate resin by regulating the salt water for electrolysis contg. mercury to the specified pH and thereafter bringing it into contact with the chelate resin. CONSTITUTION:After regulating the pH of salt water for electrolysis contg. mercury to 7-9, it is brought into contact with a chelate resin in the conditions of 2-5 SV flow velocity and 10-80 deg.C temp. to purify the salt water for electrolysis. By this method, the high-degree treatment stable for a long period can be performed without absorbing mercury on the chelate resin and without decreasing the absorption capacity of Ca and Mg or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying salt water for electrolysis, particularly by using an ion exchange membrane method.

It is well known that chlorine and caustic soda are produced by electrolyzing salt water, but raw salt water often contains impurities such as heavy metals and hard components such as calcium, magnesium, strontium, and barium.

In conventional electrolysis using the mercury method or diaphragm method, the presence of such impurities on the order of several wt/l did not pose a particular problem to operation, but in recent electrolysis using ion exchange membranes, there are many impurities. This may cause various troubles such as a decrease in current efficiency, an increase in electrolytic voltage, or an effect on the membrane life due to membrane blistering. In addition, strict purification of the raw salt water is required, especially when the hardness component, ie, the force p, Si and magnesium ions must be removed to at least 0.05 vq/rnl or less.

Conventionally, as an industrial purification method for salt water, a method has often been adopted in which acid salt is added to the salt water, and hard components are precipitated and removed as carbonates. However, in this method, partly because the solubility product of the carbonate produced is relatively large, it was inevitable that a hardness component of ~/l remained.

Therefore, in addition to primary purification using the conventional coagulation-precipitation method, secondary purification using an adsorption method using a chelate resin is attracting attention as a method for removing hardness components as much as possible.

Adsorption resins that have been used include chelate resins that have iminodiacetic acid as a functional group and chelate resins that have an aminophosphoric acid group as a functional group, and the leakage of calcium and magnesium must be kept below 0.05 #/l. was possible.

However, in the conventional method, the pH of salt water is strongly alkaline, exceeding 9, so when electrolytic salt water containing mercury is processed by passing it through a chelate resin layer, a small amount of mercury is also adsorbed on these chelate resins, resulting in a reduction in the number of cycles. It was found that with repeated regeneration, mercury was not easily desorbed during normal regeneration, and the adsorption capacity for calcium and magnesium gradually decreased.

Therefore, when treating mercury-containing electrolytic brine with a chelate resin, as a result of intensive study on a treatment method that would prevent mercury from being adsorbed to the chelate resin, we found that the pH of the electrolytic brine was adjusted to 7 to 9 and brought into contact with the chelate resin. For example, we discovered the fact that mercury is not adsorbed to chelate resins, but only hard components such as calcium and magnesium, leading to the present invention.

That is, the present invention is a method for purifying electrolytic brine containing mercury using a chelate resin, which comprises adjusting the pH of the brine to 7 to 9 and bringing it into contact with the chelate resin. be.

The present invention will be explained in more detail.

The chelate resin used in the present invention is a typical chelate resin for salt water purification, that is, a chelate resin having iminoniacetic acid as a functional group, such as Diaion CR-10 (manufactured by Mitsubishi Chemical Corporation), Revacit OC-1048 (Pai Nip), etc. Examples include Numichelate MC-80 (manufactured by Sumitomo Chemical Co., Ltd.), and chelate resins having aminophosphoric acid as a functional group, such as Duolite GS-467 (manufactured by Diamond Jamrock Co., Ltd.).

The method of contacting the salt water with the chelate resin is not limited in any way and may be carried out in an upward flow or a downward flow. The flow rate of the salt water is 5V = 2 to 50 (Hr'), preferably S
V=10 to 40 (Hr-') is preferable both economically and in order to keep the force μsium leak extremely low.

The pH of the brine that is passed through is preferably in the range of 7 to 9.

If the pH exceeds 9, mercury in the salt water will be adsorbed to the chelate resin, and mercury will be difficult to desorb during normal regeneration, and the adsorption capacity for carunium, magnesium, etc. will gradually decrease, which is not preferable.

On the other hand, if the pH is less than 7, mercury will not be adsorbed, but the adsorption capacity for important calcium, magnesium, etc. will be extremely reduced, which is not preferable.

In addition, the temperature of the salt water to be passed is preferably in the range of 10 to 80°C, preferably 20 to 70°C from the viewpoint of adsorption rate and resin deterioration.1) After purification by passing salt water, the chelate resin is regenerated.

In the chelate resin regeneration process, the salt water replacement process that is performed prior to the backwashing process uses soft water, and it may be in the same direction or in the opposite direction as the liquid flow, but the flow rate is s v =
Replace with 1o (ur-1) or less. The flow velocity is S V=
If it is larger than 10 (Hr-'), the salt water in the resin will not be completely replaced, and hydrochloric acid, which is a regenerant, will be passed through the system with chlorate present, resulting in decomposition of chlorate and generation of free chlorine. .

In addition, between the end of the regeneration process and the start of brine passage, brine is passed through to replace the inside of the resin column with brine, but the flow rate of brine is S V =
10 (Hz) or less.

If the flow rate is higher than SV = 10 (Hr-''), the soft water in the resin will not be completely replaced.Also, if salt water is passed rapidly, the resin will suddenly shrink, which is undesirable as it will lead to the resin being crushed. The dilute brine generated in the two substitution processes can be recycled as a raw salt solution. Also, in the regeneration process, the functional group of the chelate resin can be changed from H type to N type.
The step of converting to type A uses hydrochloric acid and a caustic alkali such as caustic soda, respectively.The concentration of the hydrochloric acid and the caustic alkali is preferably about 2 to 25 degrees Celsius, and the temperature can be about 10 to 80 degrees Celsius. However, it is usually carried out at room temperature. Further, the method of passing the drug may be either downward flow or upward flow. Further, the flow rate of the drug, extrusion, water washing, etc. is usually about 5V=2 to 7 hr-'.

When purifying brine for electrolysis using the method of the present invention, the raw brine should be purified! However, there is no problem in applying the method of the present invention to salt water that has been previously treated by a known method such as the above-mentioned coagulation-sedimentation method; rather, such subsequent treatment has a purification effect, etc. It is more preferable in this respect.

Thus, according to the method of the present invention, even when purifying electrolytic brine containing mercury, mercury is hardly adsorbed to the chelate resin, and a highly stable and highly efficient solution can be obtained for a long time without reducing the adsorption capacity of calcium, magnesium, etc. processing is now possible.

The present invention will be explained below using examples.

Example-1 Teniolite ES-467 was packed in a 200 ml glass column (inner diameter 25 m, height 10,100 O), regenerated with 7 chloride hydrochloric acid at a regeneration level of 185? Level/L/74?/J-R to convert to Na type, wash with water, adjust mercury method electrolyzed brine to pH = 7, and then pass through at 5V = 20hr'. Calcium leakage was 1. -q/l was reached, the fluid flow was stopped, and regeneration was performed under the same regeneration conditions as above, and this operation was repeated 20 times. During these 20 fluid flows, the constant leakage of calcium was always 0.Q 5・It is less than or equal to q/l,
There were no problems at all.

Further, the amount of mercury adsorbed in the resin after 20 passes was 0.29 y/g-H.

Comparative Example-1 Example except that the pH of the mercury method electrolyzed brine was adjusted to 11-
The liquid was passed under exactly the same conditions as in 1. After 20 times of liquid passage, the constant leakage of calcium was always 0.05~/J or less and there was no problem, but the calcium adsorption capacity decreased by 20%. Also, the amount of mercury adsorbed in the resin after 20 passes was 11.4? /IB.

Claims (1)

[Claims] A method for purifying electrolytic brine containing mercury using a chelate resin, which comprises adjusting the pH of the brine to 7 to 9 and then bringing it into contact with the chelate resin.