JPS58205501A - Depositing method of electrolyte salts - Google Patents

Abstract

PURPOSE:To deposit electrolyte salts efficiently from a soln. of electrolyte salts by maintaining the degree of supersaturation necessary for depositing the electrolyte salts from said soln. continuously with an electrodialysis device. CONSTITUTION:The waste washing water 1' which is passed through a filter A so as to be removed of suspended solids is mixed with the desalted water 5 from an electrodialysis device D and the mixture is fed to a reverse osmosis device B. The nonpermeated liquid 4 wherein electrolyte salts are concentrated to a certain extent is fed into an intermediate vessel C. The liquid 4 in the vessel C is desalted in the device D and the treated water 5 is circulated to the inlet of the device B. On the other hand, the concentrated soln. 6 of the device D is circulated through a concentrate vessel E to the device D. The concentrated soln. 7 in the vessel E is fed to a crystallization vessel F, where the soln. 7 is cooled indirectly with the cooling water 8 produced in a refrigerator I to supersaturate the dissolved salts and the salts corresponding to the supersaturation in the soln. 7 are deposited by crystal growth.

Description

[Detailed Description of the Invention] Conventionally, the method of precipitating electrolyte salts as a solid from an electrolyte salt solution has been the evaporation concentration method.

Examples include precipitation separation methods.

The evaporative concentration method requires latent heat required for evaporation in addition to sensible heat up to the evaporation temperature, so if the amount of the target solution is large, an enormous amount of thermal energy is required. Therefore, in order to reduce the thermal energy required for evaporation, a step of concentrating the target solution is provided before the evaporation operation5, for example, reverse osmosis.

The volume of the target solution is reduced in advance using electrodialysis or ion exchange resin methods.

On the other hand, the precipitation separation method is an operation in which dissolved solid substances or electrolyte salts are precipitated from a solvent by taking advantage of differences in solubility caused by temperature differences.In particular, in crystallization operations, precipitation and separation are performed by crystal growth of seed crystals or naturally occurring nuclei. There is. Since these precipitation operations utilize the solubility of the solute, in order to perform them continuously, it is necessary to sequentially provide a degree of supersaturation relative to the operating temperature by some method.

Generally, supersaturation is achieved by evaporation or cooling of the solvent.

However, when a solute is precipitated by a cooling operation, the liquid concentration decreases by an amount corresponding to the precipitated solute, and in order to continue the precipitation operation, it is necessary to evaporate the solvent in the solution and give a degree of supersaturation. . Therefore, in the past, an evaporation operation was always required in the operation of precipitating electrolyte salts as a solid from an electrolyte salt solution.

The purpose of the present invention is to efficiently precipitate electrolyte salts from an electrolyte salt solution without performing an evaporation step. It is characterized by giving. That is, in concentrating an electrolyte salt solution to precipitate the electrolyte salt as a solid, the present invention includes a first step of concentrating the electrolyte salt solution using an electrodialysis device, and cooling the concentrated electrolyte salt concentrated solution to a temperature below the dissolution saturation temperature. It consists of a second step in which a part of the electrolyte salts are precipitated, and a third step in which the precipitated electrolyte salts are separated from the electrolyte salt concentrated solution. This is a method for depositing electrolyte salts, which is characterized in that electrolyte salts are deposited without performing the first and second steps again through circulation.

The present invention will be explained in detail below.

Electrodialysis is an operation in which ions are transferred through an ion-exchange membrane, but by using both a cation membrane and an anion membrane, it is possible to desalinate and concentrate solute salts in a solution. Generally, the concentration ratio on the concentration side can be set to about 17,100. Furthermore, the concentration on the concentrated side can be easily controlled by adjusting the volume of the concentrated liquid. The present invention focuses on the large concentration ratio of this electrodialysis method and the ease of adjusting the concentration of the concentrated solution. It has been discovered that electrolyte salts can be sequentially precipitated as a solid without evaporation of the solvent by precipitating the electrolyte by a cooling operation, then separating the salts, and then concentrating the remaining electrolyte solution again using an electrodialysis device. It is in.

Next, an embodiment of the method of the present invention will be described below with reference to the drawings, taking as an example a case where the method is used in a process for treating cleaning wastewater generated from a metal surface treatment factory.

The drawing is a flow sheet of the method of the present invention.

A is a filter, B' is a reverse osmosis device, and C is an intermediate tank.

D is an electrodialysis device, E is a concentrated water tank, F is a crystallization tank, G is a centrifugal separator, H is a heat exchanger, and ■ is a refrigerator.

Washing wastewater 1 containing electrolyte salts is first passed through a filter A to remove suspended substances, and washing wastewater 1' from which 2M turbid substances have been removed is mixed with desalinated water 5 from the electrodialysis equipment, and this mixed water is 2
is sent to reverse osmosis equipment B. In the reverse osmosis device B, an amount of the mixed water 2 that is approximately the same volume as the cleaning waste water 1' is recovered as permeated water 3, and a non-permeated liquid 4 in which electrolyte salts are concentrated to some extent is sent to the intermediate tank C. Next, the non-permeate liquid 4 in the intermediate tank C is desalted using an electrodialysis device, and the desalted water 5 is circulated to the inlet of the reverse osmosis device B as described above. On the other hand, the concentrated solution 6 flowing to the concentration side of the electrodialysis apparatus is circulated through the electrodialysis apparatus via the concentration water tank E, and the salts in the non-permeated liquid are sequentially transferred to the concentrated solution 6.

Concentrate salts. Next, the concentrated solution 7 in the concentrated water tank E is sent to the crystallization tank F, and the concentrated solution 7 is indirectly cooled with the cooling water 8 generated by the refrigerator I, so that the dissolved salts are supersaturated, and the concentrated solution 7 An amount of salts corresponding to the supersaturation in the solution is precipitated by crystal growth.

The slurry 9 containing the salts precipitated in this way is then sent to a centrifuge G, where the solid content 10 is recovered and the separated liquid 1
1 is indirectly heated in a heat exchanger H using heated waste water 12 discharged from the refrigeration equipment, and returned to the concentrated water tank E as a separated liquid 11' at room temperature.

As explained above, by using the method of the present invention, electrolyte salts contained in washing wastewater, etc. can be precipitated as a solid without performing evaporation operations, and by installing a reverse osmosis device before the electrodialysis device, the separated liquid can be separated. It can be discharged as treated water with extremely low salt concentration.

Furthermore, in the present invention, by treating the separated liquid in which electrolyte salts have been precipitated in a crystallization tank or the like with an electrodialysis device, it is possible to concentrate the solution to the concentration of the concentrated solution before the precipitation operation or to a concentration that can be precipitated. It is possible to continuously deposit electrolyte salts as a solid.

Furthermore, the present invention does not require a huge amount of thermal energy to evaporate the solvent because there is no phase transformation between gas and liquid phases, and the main energy consumption is the electrical energy of the ions transferred through the ion exchange membrane. This is an energy-saving invention that requires 1,150 to 1/200 times less energy cost than conventional solid-liquid separation methods that include evaporation operations.

In the embodiment shown in the drawings, a reverse osmosis device was installed before the electrodialysis device.

This is a case where it is desired to obtain treated water with a low salt concentration as well as solid salts. For example, if it is not necessary to obtain such treated water, the reverse osmosis device can be omitted.

The method of the present invention will be explained below according to examples.

Example 1 Na2SO4 contained in neutralized sulfuric acid wastewater generated from a metal surface treatment factory was treated by the method of the present invention.

Is the amount of neutralized water 1cerr? The average amount of N a2 S 04 contained in the neutralized water in 7 days is 6', ooa q
/t. This neutralized water (zi/n) is 0.7
The mixture was sent to an electrodialysis machine in which 70 pairs of cation exchange membranes and anion exchange membranes of 5 m2 were stacked, and partially demineralized circulating water was added (
10,5ty//H), applying a voltage of 140V
, 800 μ/l. The power consumption required for desalination is 4
．． At 7Kw/H, desalinated water (z??1'/) ()
The water was recycled and used as process water. On the other hand, 140,000 m of concentrated solution was passed through the concentration side of the electrodialyzer.
g'/l (10,5 m/H) increased to a concentration of 140,800 .mu./l due to the transfer of ions from the desalting side. Next, the concentrated solution (17-5℃) in the concentrated water tank is sent to a completely mixed crystallization tank and cooled to 16℃ with cooling water from the refrigerator.
Crystals of Na2SO4 were grown, and the crystal slurry was centrifuged to precipitate and collect Na2SO4 as a solid.

The amount recovered was 202 kg/day. The separated liquid was heated to 17.5°C using a heat exchanger using heated waste water from the refrigerator, and was heated to a concentration of 131,600μ/l (1.0m"/l).
H) was returned to the concentration water tank.

This treatment reduces Na2S contained in the neutralized water.
O4 can be precipitated and recovered as a solid, and the power consumption (4,'iKw/
H-nl) is approximately 1/1/2 of the thermal energy when the neutralized water is directly passed through an evaporator and recovered as a solid.
It only cost 200 energy.

Example-2 Cleaning wastewater containing CuSO4 generated from a metal surface treatment factory was treated according to the flowchart in the drawing, and the amount of cleaning wastewater was 115.
0. ,'/day, the average amount of CuS O4 contained in the wastewater was 1,0 OC1% I/l.

This wastewater (6.2m"/H) was first treated with a 10μ precision filter to remove suspended solids, and then treated with an electrodialysis device (
Desalinated water (concentration 2,000
W/l, flow rate 2.1? ? 1'/H),
This mixed water (8.3 tt?/H) was passed through a cellulose acetate hollow fiber type reverse osmosis device. This reverse osmosis device was operated at a pressure of 28 kg/crl, and the concentrate was concentrated to 5,0001 ng/t.
! /H treated water was obtained, and the treated water was recycled as it was as process water. Next, the above 5 from the reverse osmosis device
．． 000 tng/l of concentrated water (2,1,//H). "75m" (500m+uX1,5-05-0O
When desalinated to 2,000 k/l using an electrodialysis machine consisting of 50 stacked pairs of cation exchange membranes and anion exchange membranes, some desalinated circulating water was added and a voltage of 100 V was applied to desalinate the membrane to 2,000 k/l, which required a current of 74 A. did. On the other hand, on the concentration side of the electrodialysis machine, 160.000'Nj/l (7-8m
I/H) is 160. The concentration increased to Boo 189/1. Next, the concentrated solution at 17.5°C in the concentrated water tank is sent to a completely mixed crystallization tank and heated to 15.0°C with cooling water from the refrigerator.
The slurry was cooled to a temperature of 50°C to grow crystals of CuSO4, and the crystal slurry was centrifuged to precipitate and collect CuSO4 as a solid. The amount recovered was 15oky7 days. The separated liquid was heated to 17.5℃ using a heat exchanger using heated waste water from a refrigerator.
The mixture was heated to a temperature of 157,000 μl/l and returned to the concentration water tank.

Through such treatment, CuS contained in process wastewater is reduced.
O4 can be precipitated and recovered as a solid without any evaporation operation, and the power consumption in the electrodialysis device in one process is approximately 1.2*wH per m of wastewater, and the entire amount of concentrated water in the reverse osmosis device can be recovered. The energy cost is approximately 1/200 of the thermal energy required for an evaporator.

Operating costs were also reduced to approximately 1,150 yen.

[Brief explanation of the drawing]

The drawing shows an example of an embodiment of the present invention, and is a flow explanatory diagram of a method for depositing electrolyte salts. A... Filter device B... Reverse osmosis device C...
・Intermediate tank D...Electrodialysis equipment...Concentration water tank F...Crystallization tank G...Centrifugal separator
H... Heat exchanger ■... Freezer 1... Washing waste water 2... Mixed water 3... Permeated water 4... Non-permeated liquid 5... Desalinated water 6... Concentrated solution 7...Concentrated solution
Death...Cooling water 9...Slurry 10...Solid content 11...Separated liquid 12...Amendment for warm water drainage procedures (voluntary) August 77, 1980 Commissioner of the Japan Patent Office Kazuo Wakasugi 1 , Indication of the case 1982 Patent Application No. 87995λ Name of the invention Method for precipitation of electrolyte salts 3, Person making the amendment Relationship to the case Patent applicant address 5-5-16 Hongo, Bunkyo-ku, Tokyo Name (
440) Organo Co., Ltd. Representative Nagai
Kunio 4, Agent 〒113 5, Column a for detailed explanation of the invention in the specification subject to amendment Contents of the amendment As shown in the attached sheet, we have 3 negative points regarding the following matters in the specification. In the 80th bottom line of Z, the text "f' (Jo, 5@/II) J" is corrected to "f (10,5ml/++) 1" 11th, 6° or more I

Claims (1)

[Claims] After concentrating the electrolyte salt solution to precipitate the electrolyte salts, a first step of concentrating the electrolyte salt solution using an electrodialysis device and lowering the concentrated electrolyte salt concentrate solution to a temperature below the dissolution saturation temperature are performed. and a second step of cooling to precipitate a portion of the electrolyte salts. The third step consists of separating the precipitated electrolyte salts from the electrolyte salt concentrated solution, and the electrolyte salt concentrated solution from which the electrolyte salts have been separated is circulated through the concentration side of the electrodialysis device, and then the first step is repeated. 1. A method for depositing electrolyte salts, which comprises performing a second step and a third step in order to deposit electrolyte salts without performing an evaporation step.