JPS5922693A - Method for removing dithionate ion from waste water of desulfurization - Google Patents

Abstract

PURPOSE:To reduce the volume of the concd. soln. of dithionate ions, by capturing the dithionate ions in the waste water of desulfurization in the froth films formed by adding a specific cationic surfactant to the waste water and separating the same as froth liquid and scum. CONSTITUTION:Waste water 1 of desulfurization added with a cationic surfactant is admitted onto the 1st stage froth sepn. tank 12, where air is supplied to the waste water from a gas supply pipe 21 to form the surfactant films adsorbed on the surfaces of the fine foam ascending in a liquid phase 13. The dithionate ions in the waste water of desulfurization are captured by the films and ascend in the froth part 14 in the upper part of the liquid phase 13. As the amt. of the froth increases, the froth is forced out to a froth collecting part 24, where the froth is separated as froth liquid and scum from the waste water of desulfurization. Part of the liquid entrained in the froth in the part 24 is recovered as liquid and is again admitted into the tank 12 by a reflux pipe 28 so as to be subjected to the treatment similar to the treatment mentioned above.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wet method flue gas desulfurization equipment or flue gas denitrification desulfurization equipment for combustion flue gas of fuel containing sulfur such as petroleum and coal, or sulfur dioxide flue gas from catalytic sulfuric acid production equipment. Discharge water from absorption treatment equipment using the wet method (hereinafter referred to as desulfurization wastewater).
2. Most of the suspended solids (SS) and metal ions cannot be discharged into public waters as they are.2 Most of the suspended solids (SS) and metal ions are removed and separated by precipitation, coagulation, etc., and in some cases, COD is removed by oxidation treatment with sodium hypochlorite, ozone, etc. After reducing the load substances, the water is discharged at an acceptable pH value.

The sources of COD contained in desulfurization wastewater are almost never organic, and the majority comes from various sulfur compounds produced as by-products during the oxidation reaction of sulfur dioxide. contains large amounts of dithionate ions, which are extremely stable substances.

Physical treatments such as coagulation and sedimentation and filtration, as well as the chemical oxidation treatment mentioned above, are hardly able to remove this substance, and activated carbon adsorption is also ineffective, so it is often contained in the effluent and discharged as is. Ta.

Dithionate ion has COD for theoretical oxygen consumption.
It is a substance that is extremely difficult to oxidize, as reported in the literature (Tsugio Sato et al., "Sulfuric Acid and Industry," April 1972 issue, p. 72) that the value measured by the M+1 method was 21.8%. Dithionate ions in wastewater differ slightly due to the influence of coexisting substances, but 100■52O6/Z is C
ODM.

In measurements, it is detected at a level of 3 to 4 qo/.

COD Mn, which is a measurement method stipulated by law,
Since the legally detected value is low, its removal has rarely been an issue until now, but in recent years, total COD amount regulations have been implemented in some regions, making it necessary to remove even smaller COD sources. In particular, in businesses such as thermal power plants that discharge large amounts of desulfurized wastewater, dithionate ions must be almost completely removed in order to meet the total amount regulation value. Removal of dithionate ions has become commonplace.

The concentration of dithionate ions and the types and concentrations of coexisting substances contained in desulfurization wastewater vary greatly depending on the type of exhaust gas absorption equipment such as flue gas desulfurization equipment and the circulation rate of water used within the system. There are also differences depending on the type of
5- Since it is difficult to express the average numerical value, in many examples at thermal power plants, it is 100 to 1. ．． Dithionate ions in the range of about 0.000% are contained in sulfuric acid acidic wastewater with a pH of about 1.5 to 2, as well as sulfur compounds such as thiosulfate ions and sulfane disulfonate ions, calcium ions, and magnesium ions. , sodium ions, etc. are included in the range of tens to hundreds of inches, and in some cases, phosphate ions and fluorine ions are also recognized.

The basic technology for conventional dithionate ion treatment is (
1) Acid hydrolysis method, (2) Alkaline hydrolysis method, (3)
The pyrolysis method is well known.

(1) and (2) are 120 to 1 under strong acid or strong alkali.
It is difficult to achieve 100% decomposition even if the concentration of acid or alkali is very high and the heat treatment is performed at around 95°C for several hours at atmospheric pressure for several hours at around 50°C. 3)
As a result, it is necessary to concentrate the dithionate ions to a solid state or a water content close to that of a solid state. Even if this method were adopted, it would be difficult to say that it is an economical treatment method in terms of equipment configuration, chemical cost, and operating cost of energy consumption if it is applied to desulfurization wastewater as it is, and it is difficult to say that it is an economical treatment method in terms of equipment configuration and operating cost of chemicals and energy consumption. desired. If an electrodialysis membrane or a reverse osmosis membrane is used, most of the other co-dissolved substances can be concentrated and separated at the same time as dithionate ions, and in order to make more than a few concentrated liquids, a very ingenious configuration is required. Although the method of intensively adsorbing dithionate ions using an ion exchange resin and concentrating them in the regenerant waste liquid yields several degrees of concentration and is currently widely adopted, it is still the most complete treatment technology. It can be said that it is still insufficient to adopt method (3).

The present invention is characterized in that dithionate ions are intensively collected in a foam separation tank, adsorbed onto the surface of bubbles, and recovered as foam powder and scum. The purpose is to reduce the volume significantly compared to the method, and also to facilitate immediate thermal decomposition treatment by heating means such as incineration, spray drying, and evaporative drying.

In other words, the present invention uses a quaternary ammonium salt,
By adding a cationic surfactant based on aliphatic amine salts, alkylpyridium salts, etc., and supplying air or nitrogen as fine bubbles to the desulfurization wastewater, a film of cationic surfactant is formed on the surface. to form a foamy end,
Dithionate ions in the desulfurization wastewater are captured in the film of the foam powder and separated from the desulfurization wastewater as foam powder and scum, and the foam powder that has captured the dithionate ions in the foam powder and scum is broken. The present invention relates to a method for removing dithionate ions from desulfurization wastewater, which is characterized by concentrating dithionate ions.

Furthermore, the present invention provides the method for removing dithionate ions from desulfurization wastewater as described above, including the following additional technical means:
A means for adjusting the amount of dithionate ions to be collected from desulfurization wastewater.

・Means for reducing the amount of sulfate ions contained in the desulfurization wastewater to an equivalent ratio of 80 times or less of dithionate ions before adding a cationic surfactant to the desulfurization wastewater.

- A means for reducing the amount of phosphate ions contained in the desulfurization wastewater to an equivalent ratio of 0.1 times or less of dithionate ions before adding a cationic surfactant to the desulfurization wastewater.

・Means for thermally decomposing the dithionate ion concentrate by heating to 250 to 300° C. the foam powder containing the dithionate ions has been broken.

- Means for filtering the foam-separated desulfurization wastewater from which the foam powder that has collected dithionate ions has been separated, and subjecting the filtered residue to a heat treatment in the thermal decomposition of the dithionic acid concentrate in which the foam powder has been broken.

This item -9- relates to a method for removing dithionate ions from desulfurization wastewater, which is characterized by adding.

Next, embodiments of the present invention will be described in detail with reference to the drawings.

Figure 1 is an example of the principle of a conventional desulfurization wastewater treatment method that does not remove dithionate ions.
In the adjustment tank 2, the pH is adjusted by adding a pH adjuster (acid or alkali) from the addition device 3, and then led to the coagulation-sedimentation tank 4, where a flocculant is added from the addition device 5 to precipitate and separate SS, heavy metals, etc. Subsequently, the COD-loaded substances are introduced into an oxidation tank 6 and subjected to an oxidizing treatment using an oxidizing agent (air, oxygen, primary sodium hypochlorite, ozone, etc.) from an addition device 7, and then transported to a neutralization tank 8 from an addition device 9. After neutralization by adding a neutralizing agent (acid or alkali) to a discharge standard pH value, the water is treated in a filtration tank 10 to be clarified and discharged. Reference numeral 11 denotes a solid-liquid separation tank, which temporarily stores the discharged sludge from the coagulation sedimentation tank 4 and the backwash recycled wastewater from the filtration tank 1O to precipitate solids, and returns the supernatant water to the coagulation and sedimentation treatment line again. 19 is shaped so that the solids precipitated and concentrated in the solid-liquid separation tank 11 can be easily disposed of as a sludge cake using a dehydrator. The order of each treatment step in FIG. 1 does not necessarily have to be the same as that shown in FIG. 1, so there are many different configuration methods. As mentioned above, it is almost impossible to remove .

FIG. 2 is an explanatory diagram showing an example of an embodiment of the present invention. 1' is a desulfurization solution containing dithionate ions that has been pretreated by a known method suitable for foam separation and has a cationic surfactant added thereto. In the wastewater, ] 2 is a first-stage foam separation tank, which is composed of a liquid phase portion 13 and a foam end portion 14 . 16 is a second-stage foam separation tank, which is composed of a liquid phase section 13 and a foam end section 14; the first-stage foam separation tank 12 includes a discharge pump 15 and a mixer 18 for the pH adjusting agent They are communicated with each other through a transfer pipe 17. 21 is a gas supply pipe attached to the lower part of the foam separation tanks 12 and 16, 22 is a diffuser plate attached to one side of the lower part of the tank 11, and 23 is a gas supply pipe attached to the second stage foam separation tank 16. Ionic surfactant, 24 is the foam collection part of the first stage foam separation tank 12, 25 is the second stage foam separation tank 1
A plurality of 26 Fi foam breaking plates having a built-in heating mechanism using electric heating are installed in the bubble non-collecting and breaking part 25. 27 is a foam transfer pipe that communicates the foam collecting section 24 and the foam uncollected and broken foam section 25; on the 2nd, the liquid separated in the foam collecting section 24 is returned to the first stage foam separating tank]2. In the reflux tube, # is the outlet for the concentrated liquid containing the broken foam. Next, to explain the operation and effect of the present invention, desulfurization wastewater 1 to which a cationic surfactant has been added is made to flow into the first stage foam separation tank 12.

When air is supplied from the gas supply pipe 21, a film of surfactant adsorbed on the surface of the microbubbles rising in the liquid phase 13 is formed, and dithionate ions in the desulfurization wastewater are captured by the film, and the liquid phase The foam ends rise to the foam end section 14 at the upper part of the section 13, and as the amount of foam ends increases, the foam ends are pushed to the foam end collection section 24.
12 - It is extracted and separated as foam powder and scum from the desulfurization wastewater. In addition, a part of the liquid accompanying the foam powder is collected as a liquid in the foam powder collecting section 24, and is flowed into the first stage foam powder separation tank 12 again through the reflux pipe 28 and subjected to the same treatment.

The foam end liquid and scum are gradually led to the foam uncollecting and foam breaking section 25 through the foam end communication pipe 2'7. First stage foam separation tank 12
Desulfurization wastewater treated with.

If the discharge standard value is reached, the water may be discharged from the tank 12, but if this value is not reached, the water is sent to the mixer 1 by the drainage pump 15, where it is mixed with the pH adjuster 3 and adjusted to an appropriate pH value. The dithionate ions remaining without being removed in the first stage foam separation tank 12 are supplied to the next second stage foam separation tank 16, where the cationic surfactant 23 is newly added. The foam is separated using a method. What about the uncollected bubbles and broken pond section 25? f8! When the foam powder in the liquid powder and the scum comes into contact with the bubble-breaking plate 26 having an electric heating mechanism, the gas volume in the bubbles expands and the bubbles burst, forming a surfactant liquid containing concentrated dithionate-13- ions. It is taken out from the takeout port 29. If the amount of scum is large and is not entrained with the foam powder, a mechanism may be provided to separately take out only the scum. The desulfurized wastewater 20 from the second stage foam separation tank 16 from which dithionate ions have been removed is discharged from the four tanks when it reaches the discharge standard. Note that depending on the properties of the desulfurization wastewater, one stage of foam separation treatment may be sufficient, or three or more stages of treatment may be necessary. If the amount of calcium in the desulfurization wastewater 1 is large, it may react with carbon dioxide in the supplied air and cause precipitation of calcium carbonate, which may have an adverse effect on the air diffuser plate 12. In such cases, nitrogen should not be used. good.

The method of thinning ions in water using the foam separation method shown in Figure 2 is a technique generally called ion flotation, but in principle it is similar to an ion exchange reaction, and the trapped substances The amount of surfactant added as a scavenger is theoretically required to be in a 1:1 equivalent ratio. extra is needed.

In addition, substances with a higher ion valence than the substance to be thinned often act as interfering ions, and those with the same ion valence may have a similar degree of ionization in the liquid or be overwhelmingly larger than the substance to be thinned. If there are many ions, the rate at which they act as interfering ions increases. Therefore, since chemical costs account for most of the processing costs, the recovery of valuable materials (e.g. uranium, vanadium) outweighs the cost of dropped chemicals.

(e.g., platinum) or harmful substances that must be removed (e.g., cadmium, arsenic, etc.).

This method was considered unsuitable from an economical point of view for purposes such as removing COD sources from wastewater, which is the object of the present invention, and was not considered. but.

For the present inventor, ') Equipment costs required for concentrating thionate ions and decomposing the concentrated liquid.

As a result of comprehensive consideration of operating costs and other factors, we found that even if this ion flotation method is adopted, as long as appropriate pretreatment and selection of surfactant as a thinning agent are not mistaken,9 Even when compared with the method described above that combines the use of an ion exchange resin and evaporation drying thermal decomposition, which is considered to be a reliable dithionate ion concentration separation and decomposition method, the operating cost is the same or less, and the equipment is available.

The main principle behind the ion flotation method's ability to thin inert ions and molecules in water is that the surfactant adsorbed to the bubble surface causes an electrostatic adsorption reaction and forms a complex compound. has been done. However, it is extremely difficult to completely elucidate this theoretically due to the difficulties in measuring the bubble diameter in the liquid phase and the zeta potential on the bubble surface. For this reason, if emphasis is placed on electrostatic adsorption reactions, it will be greatly influenced by polyvalent anions that coexist with dithionate ions, and it will not necessarily be necessary to focus on thinning dithionate ions. In addition, if the emphasis is placed on complex compound reactions, the surfactant may react directly before being adsorbed to the bubble surface, or its hydrophilicity may outweigh its hydrophobicity and it may separate from the bubble surface into water, forming precipitates or It forms a floating state in the water.

Even if such a phenomenon occurs, it is possible to remove dithionate ions by increasing the amount of surfactant used or installing a clarification device for the water treated with the foam separator at the subsequent stage, but this reduces the cost of chemicals. This will lead to an increase in the number of units and the complexity of subsequent equipment.

Dithionate ions and coexisting substances in desulfurization wastewater have large differences in concentration as mentioned above, but the types of substances are quite limited.As a result of repeated experiments in the presence of these coexisting substances, Two methods for removing dithionate ions, such as the present invention, have been completed as a treatment method that can be applied to many desulfurization wastewater treatments.

FIG. 3 is a flow sheet showing another embodiment of the present invention. 1 For example, by replacing the part after the oxidation tank 6 in FIG. 1 with the whole of FIG. This is a method that can almost completely remove it. In Figure 3, 1 is desulfurization wastewater containing dithionate ions from which SS and heavy metals have been removed; 4
2 is a precipitation separation tank that removes most of the ions that interfere with foam separation of dithionate ions, 2 is a pH adjustment tank that adjusts the pH value to be suitable for foam separation, and 3 is a pH adjuster (acid or alkali). 23 and 23' are cationic surfactant addition devices, and 12 is a foam separation device as shown in FIG.

8 is a neutralization tank, 9 is a neutralizing agent (acid or alkali) addition device, 10 is an overflow device, 30 is a heating device for foam-breaking liquid,
31 is a solid-liquid separator for recycled cleaning wastewater from the offshore filter 10;
2 is a heating device 30 for the slurry separated in the solid-liquid separator.
33 is a recovery water pipe that returns the water separated by the solid-liquid separator to the previous stage equipment, such as the coagulation sedimentation tank 4 in FIG. 1, 21
is a gas supply pipe that supplies gas to the foam separator 12. 3 shows a device for adding a pH adjuster to the foam powder separation tank 1'7 in the latter stage when the foam separation tanks 1' and 7 are arranged in series in multiple stages. The basic function, effect, and operation of the present invention will be explained.

Depending on the properties of the desulfurization wastewater l, if the pH is adjusted to a neutral range by adding a pH adjuster such as calcium hydroxide from the addition device 3 in the pH adjustment tank 2, most of the sulfate ions will be in the form of H2SO4. The sulfate ions turn into calcium sulfate, and a significant portion of this becomes precipitate, making it possible to reduce the sulfate ion concentration in the wastewater. Coagulation sedimentation tank 4
When an inorganic flocculant containing aluminum or iron is added in step 1, most of the coexisting phosphate ions can also be precipitated and removed. When the above treatment is carried out, the substances coexisting with dithionate ions in the desulfurization wastewater 1 are usually not large enough to significantly interfere with the separation of dithionate ions into foam particles, so the sedimentation separation tank 4 is It can often be omitted. In addition, since the purpose of pH adjustment and coagulation and sedimentation in the conventional method is to remove suspended solids and heavy metals, it is not necessarily necessary to have the secondary effect of modifying the desulfurization wastewater to properties suitable for the present invention. In such cases, the precipitation separation tank 4 shown in Fig. 3 is installed to increase the sulfate ion concentration in the desulfurization wastewater 1 to about 80 times the dithionate ion concentration in terms of the actual ratio. Reduce the amount to less than that. Similarly, if a large amount of phosphate ions are included,
The equivalent ratio of phosphate ion concentration to 0 of dithionate ion concentration
．． Reduce the amount to about 1 degree or less. Any known technique, such as the addition of calcium hydroxide, may be used as a means of weight loss, provided that other polyvalent anions are not formed as a result of the weight loss. Normally, there are almost no anions other than phosphate ions with a valence of 3 or higher in desulfurization wastewater, and even if they do exist, the amount is extremely small, but it is possible to treat wastewater from other than desulfurization equipment as well. In the case of batch processing using an apparatus, it may be necessary to consider reducing the amount of other trivalent or higher anions.

-20 In the present invention, it is not preferable to remove thiosulfate ions and sulfane disulfonic acid ions from desulfurization wastewater because it increases the amount of surfactant used, but it is not preferable to remove thiosulfate ions and sulfane disulfonate ions from the desulfurization wastewater, but they can be removed by an economically inexpensive method. is preferably removed by a method other than the method of the present invention.

In Figure 3, the pH adjustment tank 2-#- is used to adjust the pH to the optimum level for foam separation, but the type of surfactant, concentration of dithionate ion, and type and concentration of other coexisting substances are Since the optimum pH value often differs depending on the pH value, it is better to keep the pH adjustable within a wide range of about 3 to 12. As the pH adjuster 3, when adding an acid, hydrochloric acid is preferable, but even sulfuric acid has no practical problem as long as the increase in sulfate ions due to addition is within the above range, and when adding an alkali, it is preferable to use hydrochloric acid. Sodium hydroxide is suitable. In principle, the surfactant portion and 23' are of the same type, but they may be of different types. -21- Selection of surfactant is very important, but in order to dilute dithionate ions most efficiently against the influence of coexisting substances, a desk-scale test using actual wastewater should be carried out. It is better. This has the same meaning as 1, for example, confirmation by the jar test method, which is used to select a flocculant, flocculant aid, etc. and determine the amount to be added in the coagulation-sedimentation method. A cationic surfactant is used as the surfactant. Generally, quaternary ammonium salts (e.g. stearyltrimethylammonium, distearyldimethylalmonium).

The use of chloride or bromide of hexadecyltrimethylammonium (such as hexadecyltrimethylammonium) has good thin-forming efficiency.

Aliphatic amine salts tended to have better thinning efficiency as the number of hydrogen atoms in the amine decreased.

Surfactants usually contain at least one hydrophilic group and one hydrophobic group, but increasing the number of hydrophobic groups often yields better results, and most surfactants have long chains of alkyl groups. It was available in case. In addition, when the concentration of these cationic -22- surfactants is increased, they form micelles and become difficult to be adsorbed on the bubble surface, resulting in an extremely low thin-form efficiency, so it is necessary to add them below the critical micelle concentration. The critical micelle concentration of the various surfactants mentioned above is approximately 1 mol.
/m''. The amount added is within the above-mentioned coexistence range of phosphate ions and sulfate ions.

If the amount is 0.9 to 1.1 equivalent per equivalent of dithionate ion, more than 90% of the dithionate ion can be made thin, but
If a certain amount of dithionate ion is allowed to flow out within the COD regulation value, a small amount can be added. It is one of the features of the present invention that the amount of leaked dithionate ions can be selected quite freely.
For example, in the removal method using ion exchange resin or membrane separation technology, it is carried out by mixing appropriate amounts of the material that has bypassed the removal device and the material that has undergone removal treatment. No bypass amount adjustment device is required.

-23- If the dithionate ion concentration to be treated exceeds the critical micelle concentration of the cationic surfactant to be added, multiple foam separation tanks may be installed in series, each with a In such cases, a surfactant is added at a concentration below the critical micelle concentration.

Because dithionate ions are removed sequentially.

Since the coexistence ratio of sulfate ions to dithionate ions increases toward the later stage of the foam separation tank, it is necessary to adjust the pH in that case quite strictly.

The placement positions of the neutralization tank 8 and the filter 10 in Fig. 3 can often be reversed, but as a result of neutralization, suspended solids that are thought to be caused by hydroxides may be generated. - Therefore, it is safer to place the neutralization tank 8 before the filter 10. A rotary cylindrical or filter press type filter 10 reduces the amount of water that accompanies the filtration residue during regeneration.

Any device may be used as long as it is easy to process afterward and can function as a filter. The purpose of installing this filter 10 is that the weight of substances adsorbed on the surface of the bubbles in the foam separation tank J2 exceeds the upward force of the bubbles and separates into the liquid phase. The purpose is to separate by filtration the floc-like surfactant that mainly captures dithionate ions that have become contained suspended substances.

Although it is extremely difficult to completely eliminate the amount of suspended solids, it is important to select the type of surfactant in the foam separation tank 12, maintain a good adsorption reaction with the bubbles, and adjust the size of the bubbles. It can be significantly reduced by making it appropriate.

The heating device 30 in FIG. 3 may be of any type as long as it can provide the 250 to 300° C. heating required for thermal decomposition of dithionate ions for about 10 minutes.
For continuous treatment, a spray dryer is suitable, and a sludge incinerator may also be used. Furthermore, filter 1
The solid-liquid separator 31 for the filtration residue during the regeneration of 0 is as follows:
A filter such as a belt press type is suitable, but it is not necessary if a filter with a compressor is used. Any of the known techniques may be adopted as appropriate.

The cost of removing dithionate ions from desulfurization wastewater by conventional methods is quite high regardless of which method is employed.

The treatment cost according to the present invention depends on the price of the cationic surfactant used, but it can be said that it is proportional to the content of dithionate ions in the desulfurization wastewater. If the amount of dithionate ions is to be allowed to flow out, it will be proportional to the amount of dithionate ions to be captured and removed. Price differences due to different types of surfactants must be compared in terms of 2/mol rather than simple weight unit prices when used in applications such as the present invention.

Desulfurization wastewater 1? ? / When the amount of dithionate ions to be removed from the inside is 100 to 1201, in addition to the surfactant cost and the heating fuel cost for thermal decomposition, the desulfurization wastewater 1-
Not only are various costs such as pH adjuster and power costs lower than conventional methods, but costs such as equipment installation costs and maintenance costs can be reduced, and the advantage is that it can also be used when the amount of removal increases. There is also.

Next, the present invention will be explained in detail.

Example 1 Treated wastewater from oxidation tank of desulfurization wastewater treatment equipment] Otr? /h
The water to be treated was divided into two streams and used as water to be treated in the method for removing dithionate ions according to the present invention.The properties of the water to be treated are as shown in Table 1.

As the apparatus for carrying out the method of the present invention, the apparatus configuration shown in Fig. 3 but with the sedimentation separation tank 2 omitted is used, and the foam separation tank is based on the structure shown in Fig. 2, and is a cylinder with an inner diameter of 2 m. Two units of this shape were used in series. The depth of the liquid phase was 1 m, the air diffuser plate had a bubble diameter of 0.8 mm, and air was supplied from a turbo blower as a bubble source to the bottom of each foam separation tank at a rate of 4 ON m'/h. 0, 2 ky f/cd
Supplied by. Stearyltrimethylammonium chloride was used as the cationic surfactant, and the pH was adjusted using gold sodium hydroxide and sulfuric acid to adjust the optimum value to 8°9±0 for the first stage foam separation tank. .3, 9.4± for the second stage foam separation tank
0.2. In addition, the amount of surfactant to be added is approximately 1:1 in equivalence ratio with dithionate ion, divided into two parts and added to each foam separation tank for foam separation and foam breaking treatment (foam breaking using an electric heating plate). ) The average values of the results are shown in Table 2, and 90.8% of the dithionate ions could be removed only by such foam separation and foam breaking treatments.

Example 2 Under the operating conditions of Example 1, the amount of surfactant added was
As a result of operation with the equivalent ratio of dithionate ion reduced to l j O,5, the dithionate ion after foam separation and foam breaking treatment was tri 39 WSzOa/l, and the removal rate was 4.
It was 8%. This can be said to be a removal rate that depends on the amount of surfactant added, and therefore, the leakage amount of dithionate ions can be adjusted by -28- depending on the degree to which the amount of surfactant added is reduced.

Example 3 In an experimental apparatus, the removal rate of dithionate ions was measured by changing the coexistence conditions of sulfate ions and phosphate ions with respect to the concentration of dithionate ions.

The equipment used was a glass cylinder with an inner diameter of 7mm and a height of 5401111mm, and a diffuser plate was installed at the bottom of the two cylinders.As the liquid to be treated, dithionic acid was added to ion-exchanged water in the proportion shown in Table 1. Prepare a solution in which sodium, sulfuric acid, and trivalent phosphoric acid are dissolved, and add the two types of surfactants listed in Table 1 to this coexisting solution in an amount equivalent to the dithionate ion while feeding the solution from the top of the cylinder. At the same time, compressed air was supplied from the lower part of the cylinder at a rate of 0.05 Ntl/h, and the treated liquid was taken out from the lower part. In addition, to adjust the pH of the liquid to be treated, hydrochloric acid and IJium hydroxide were added to the liquid before feeding it into one cylinder. The residence time of the liquid to be treated in the cylinder is 20 minutes.

-29- Figure 4 shows the relationship between the pH value and the dithionate ion removal rate for the liquid to be treated having the composition shown in Table 1.

The equivalent ratio as sulfate ion is less than 80 times that of dithionate ion, and as phosphate ion, the equivalent ratio is 0 times that of dithionate ion.
．． If the equivalent ratio is 1:1 or less, if stearyltrimethylammonium chloride is used as a surfactant, 90%
% or more, 'Also. This shows that when laurylamine acetate is used as a surfactant, about 70 ions of dithionate ions are removed.

Example 4 The foam-separated water subjected to the dithionate ion removal treatment described in Example 1 contained suspended solids at a temperature of about 10 degrees as measured by a turbidity meter, and the pH of the foam-separated water was 9.4. After adding sulfuric acid to neutralize the pH to 7.5, we filtered it using a filter press type filter.
The turbidity of the discharged water, which is filtered water, was 5 or less -30-, and the removal rate of dithionate ions was 95%.

The foam liquid and scum containing dithionate ions formed in the foam separation tank are approximately o, os tt? /h, and the average dithionate ion concentration was 6etny/l.One portion of the dithionate ion was heated in a spray dryer at a temperature of about 280°C for 10 minutes to thermally decompose the dithionate ion. Where I went.

The amount of dithionate ions in the dry solid after the thermal decomposition treatment was 420q. Since the amount of dithionate ions before spray drying was calculated to be about 681F, the dithionate decomposition rate in the thermal decomposition treatment was 99.38%.

Also, when heating foam powder and scum containing dithionate ions in a spray dryer.

When a mixed solution to which 0.1 volume of the filtration residue slurry from the filter press type p-filter was added was thermally decomposed under the same conditions, the amount of dithionate ions in the dry solid after the thermal decomposition process was as follows. It was 451q. Since the dithionate ion concentration in the filtration residue slurry was approximately 8.1 ■/l, the amount was 810 q, and the amount of dithionate ion before spray drying was calculated to be 68.81 F. The dithionic acid decomposition rate in the thermal decomposition treatment was 99.3'i'%, and almost complete thermal decomposition was achieved in all cases.

Table 1 Table 2 -32- Table 3 □

[Brief explanation of drawings]

Figure 1 is a flow sheet diagram of a conventional desulfurization wastewater treatment method that does not remove dithionate ions, Figures 2 to 4 show embodiments of the present invention, and Figure 2 shows the method of the present invention implemented. 3 is a flow sheet diagram showing another embodiment of the method of the present invention, and FIG. 4 is an explanatory diagram of an apparatus having two stages of foam separation tanks. FIG. 4 is a flow sheet diagram showing another embodiment of the method of the present invention. By changing the coexistence conditions of acid ions,
It is a graph in which the removal rate of dithionate ions was measured by adding different types of surfactants in equivalent amounts to dithionate ions. ■...Desulfurization wastewater 16...Second stage foam separation tank 2,...pH adjustment tank 17...Transfer pipe 3
,... Addition device 18... Mixer 4... Coagulation sedimentation tank 19... Outlet 5... Addition device 20... Desulfurization wastewater 601. Oxidation tank
21... Gas supply pipe 7... Addition device
22... Diffusion plate 8... Neutralization device 2
3... Cationic surfactant 9... Addition device
24... Foam dust collecting section 10... Filtration device
25... Foam uncollected/bubble broken section 11... Solid-liquid separation tank
26... Broken foam plate 12... First stage foam separation tank 27... Foam powder transfer pipe 13... Liquid phase part
2B... Reflux pipe 14... Foam end 15... Discharge pump -34- Procedural amendment (voluntary) 1. Display of the case 1982 Patent Application No. 130468 2 Name of the invention Method for removing dithionate ions from desulfurization wastewater 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 for detailed explanation of the invention in the specification to be amended and drawing a Contents of the amendment I would like to request correction of the following matters in the description as shown in the attached sheet. /Page 11, line 10, ``1 is for foam separation'' is 1
1' is corrected to 1 for foam separation. 12, lines 13 to 14, [Desulfurization wastewater]] is corrected to ``Desulfurization wastewater 1' is 1. 3. Page 14, lines 1 to 2, 1 outlet 29 ” has been corrected to read [Exit port 19]. Figure 4 of the original drawing is corrected as shown in the attached sheet. that's all

Claims (1)

[Claims] (1) A cationic surfactant based on a quaternary ammonium salt, an aliphatic amine salt, an alkylpyridium salt, etc. is added to desulfurization wastewater. By supplying air or nitrogen as microbubbles to the desulfurization wastewater, a foam powder whose surface is a film of cationic surfactant is formed, and the dithionate ions in the desulfurization wastewater are captured in the foam film. Desulfurization wastewater is separated from the desulfurization wastewater as foam powder and scum, and the foam powder that has captured dithionate ions in the foam powder and scum is broken to concentrate the dithionate ions. A method to remove more dithionate ions. (2) From the desulfurization wastewater according to claim 1, wherein the amount of the cationic surfactant added to the desulfurization wastewater is adjusted depending on the amount of dithionate ions to be collected from the desulfurization wastewater. Method for removing dithionate ions. (3) Before adding the cationic surfactant to the desulfurization wastewater, the sulfate ions contained in the desulfurization wastewater are reduced to an equivalent ratio of 80 times or less of dithionate ions. A method for removing cydithionate ions from desulfurization wastewater according to claims 1 and 2. (4) Before adding a cationic surfactant to the desulfurization wastewater, it is recommended to reduce the amount of phosphate ions contained in the desulfurization wastewater to an equivalent ratio of 0.1 times or less of dithionate ions. A method for removing dithionate ions from desulfurization wastewater according to claims 1 and 2. (5) Claims 1 and 2, characterized in that the dithionate ion concentrate, which is obtained by breaking the foam containing the dithionate ions, is thermally decomposed by heating to 250 to 300°C. A method for removing dithionate ions from desulfurization wastewater according to items 3 and 4. (6) Filter the foam-separated desulfurization wastewater that has collected dithionate ions and separated the f'C foam powder, and heat-treat the filtration residue in thermal decomposition of the dithionic acid concentrate with the foam powder broken. A method for removing dithionate ions from desulfurization wastewater according to claim 5.