JPH1076249A - Treating method of waste solution containing iron chelate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method for incineration treatment of a waste soln. containing an iron chelate such as a photographic treatment waste soln. SOLUTION: Alkali is added to a waste soln. containing an iron chelate to adjust the pH of the waste soln. to 12 or more to form a precipitate and, after the formed precipitate is separated, the remaining waste soln. is sprayed into an incinerator to be subjected to incineration treatment. Further, the waste soln. is preliminarily conc. and alkali is added to the conc. waste soln. When alkali is added, it is desirable to heat the waste soln. to 60-250 deg.C. By this constitution, when the waste soln. containing the iron chelate is subjected to incineration treatment, the operation of the incinerator becomes easy and long-term operation becomes possible. Not only a waste photographic soln. but also a waste soln. mixed with various waste solns. or waste acids to contain an iron chelate as a result can be effectively treated. Further, this method can be adapted by providing iron component removing equipment corresponding to pretreatment to existing incineration equipment and is advantageous economically.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for treating a waste liquid containing iron chelates. More specifically, it is a method of incinerating waste liquid containing iron chelate such as photographic processing waste liquid. Waste liquid containing so-called iron chelates solubilized by a chelating agent together with organic and inorganic compounds, that is, waste liquid generated in the photographic processing step, waste liquid when washing ore containing iron in the refining step, and metal processing step This method is suitable for treating waste liquid generated in the above process, boiler cleaning waste liquid, waste liquid generated from the pickling process of various metals, and the like.

[0002]

2. Description of the Related Art With respect to the treatment of various kinds of waste liquids generated in association with industrial activities, it is required to reduce the burden on the environment due to the increasing awareness of the environment. Wastewater containing an inorganic compound together with an organic compound having a COD and BOD load and further containing an iron chelate has been regarded as a wastewater which is difficult to treat, and most of these wastewaters have hitherto been disposed of by ocean dumping. I was

[0003] However, with the recent strengthening of the Water Pollution Control Law and pollution control, many of the above-mentioned waste liquids including photographic processing waste liquids are prohibited from being dumped into the ocean, and must be treated on land. Hereinafter, a processing method of a photographic processing waste liquid will be described as a representative example of a waste liquid containing an iron chelate.

[0004] As a method for treating a photographic processing waste liquid, an evaporation concentration / solidification method, a chemical treatment method, an activated sludge method, an ion exchange method, a reverse osmosis method and the like have been known so far, but they are not always satisfactory. Did not. Recently, Japanese Patent Laid-Open No. 7-9
No. 1637, a method in which the molar ratio of Na / K is set in a specific range and incineration treatment is performed.
As disclosed in JP-A-185592, a method of combining wet oxidation treatment and biological treatment after pretreatment has been proposed.

[0005] The photographic processing waste liquid includes a developing solution, a fixing solution, a color developing solution, a bleaching solution, a bleach-fixing solution, and the like. And several percent of organic compounds having COD and BOD loads are present, resulting in a COD value of tens of thousands ppm and an inorganic compound of about 10% and iron of 1000 pp.
The waste liquid contains about 1 m of the iron chelate compound, and the remainder is a waste liquid having a water composition.

When such photographic processing waste liquid is incinerated, organic compounds can be almost completely decomposed, but a large amount of ash such as salts and oxides generated by decomposition of inorganic compounds and iron chelate compounds. Since it is generated and adheres or accumulates in the furnace, the condition of the furnace is often unstable, and it has been necessary to periodically remove ash adhered to the furnace. In the incineration method, waste liquid is often concentrated before being treated from the viewpoint of energy saving.
Concentration increases the proportion of inorganic compounds and the like, which in turn promotes an unstable state of the furnace conditions, which may hinder long-term operation.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to propose a new method for incinerating waste liquid containing iron chelates such as photographic processing waste liquid, which is sprayed into an incinerator and incinerated. At this time, the present invention provides a processing method that stabilizes the furnace condition and enables long-term operation.

[0008] The present invention is a method for mixing various waste liquids and waste acids which have been difficult to treat so far, and as a result, can effectively treat even waste liquids containing iron chelates. Is provided.

It is another object of the present invention to provide a method that reduces the burden of remodeling incineration equipment such as an incinerator.

[0010]

According to the present invention, an alkali is added to a waste solution containing an iron chelate to form a precipitate at a pH of 12 or more, and the remaining waste solution after separating the formed precipitate is sprayed into an incinerator. And treating the waste liquid containing iron chelate. Furthermore, a method for treating a waste liquid in which an alkali liquid is added to the concentrated waste liquid after the waste liquid containing the iron chelate is concentrated in advance,
In any case, it is desirable to heat the waste liquid to 60 to 250 ° C. when adding the alkali.

[0011]

[Action] Most of the ash generated in the incinerator by spraying waste liquid containing iron chelate such as photographic processing waste liquid into an incinerator with the liquidity being in the alkaline region is mostly sodium ash such as sodium sulfate. And complex oxides of iron and salts mainly composed of potassium and iron, especially the complex oxide of iron has a high melting point and is difficult to melt in the furnace. And found that long-term operation becomes difficult. The present invention has been completed based on the above findings.

Therefore, in the present invention, the iron chelate in the waste liquid stabilized by a chelating agent such as EDTA is used.
It is decomposed by adding an alkali to reduce the proportion of iron contained in the waste liquid before supply to the incinerator. When incinerating waste liquid as described above, a large amount of heat energy is required to heat and evaporate a large amount of water that constitutes the waste liquid as an aqueous solution to the combustion temperature, so the waste liquid is concentrated prior to incineration. However, the present invention is effective when applied to the case where the inorganic compound and the iron chelate in the waste liquid are increased as a whole by passing through the concentration step as described above, and the iron content is also increased. .

That is, in the present invention, an alkali is added to a waste liquid containing an iron chelate to form a precipitate having a pH of 12 or more, and the remaining waste liquid after separating the formed precipitate is sprayed into an incinerator for incineration treatment. By performing incineration in a state where the proportion of iron contained in the waste liquid is reduced, the proportion of salts such as sodium sulfate that shows the fusibility of ash generated in the furnace increases. It is believed that the relative ratio of the hard-to-melt iron composite oxide will decrease, and it will not stick or accumulate in the furnace, stabilizing the furnace condition and enabling long-term operation. ing. In the present invention, from the results of observation of the furnace conditions during the incineration process and the conditions in the furnace after the incineration process, the absolute amount of the hardly fusible iron composite oxide is reduced, It is presumed that the ash content was increased and the fluidity of the ash was improved as a whole, and the ash was discharged out of the furnace by involving a hardly fusible product such as a complex oxide of iron.

In the present invention, first, an alkali is added to a waste liquid containing an iron chelate to form a precipitate at pH 12 or more. This is because iron chelates in the waste liquid stabilized by a chelating agent such as EDTA are decomposed and precipitated as hydroxide. In this step, in addition to the iron content normally contained in the photographic processing waste liquid, if there are small amounts of metal components such as heavy metals that are mixed in when various waste acids are mixed, they also almost precipitate. It is removed from the liquid in the next solid-liquid separation step. Therefore, one of the effects of this treatment is that the amount of metal oxides generated by the incineration treatment is reduced.

Preconcentration of the waste liquid containing the iron chelate in advance has the effects of saving energy, reducing the processing capacity, making the equipment compact, and is desirable. The degree of concentration of the waste liquid is twice or more, preferably three times or more. However, if the degree of concentration is too high, a precipitate may be generated in the liquid. Therefore, the upper limit is appropriately determined according to the properties of the waste liquid.

[0016] From the efficiency of iron removal from the waste liquid, the pH is 12
As described above, the reaction is preferably carried out at a pH of 13 or more, and the temperature may be room temperature. However, it is desirable to heat the mixture to 60 to 250 ° C. because heating improves the iron removal efficiency. The temperature is preferably from 60 to 150 ° C. When the reaction temperature exceeds the boiling temperature under atmospheric pressure, it is necessary to carry out the reaction under pressure as a matter of course. Increasing the temperature at which a precipitate is formed by adding an alkali not only improves the iron removal efficiency, but also improves the sedimentation of the precipitate and improves the separability. For this reason, it also affects the solid-liquid separation process for separating the generated precipitate, and contributes to cost reduction in solid-liquid separation.

The alkali may be a strong alkali such as sodium hydroxide, sodium carbonate, potassium hydroxide or the like, as long as the pH of the waste liquid can be adjusted to 12 or more. However, the alkali to be added remains on the liquid side after solid-liquid separation, and forms ash by incineration.If potassium in the ash becomes too large, it tends to easily adhere to the furnace wall. It is desirable to use a sodium compound that contributes to improvement in fluidity, and among them, sodium hydroxide is particularly preferred. Further, it is desirable to use the alkali as a high-concentration liquid in order to reduce the increase in moisture. The addition of the alkali in the present invention reduces the pH of the waste liquid to 1
Since it is two or more, if a waste alkali is available, it may be used. For example, in a photographic processing waste solution, a fixing system and a bleaching system waste solution contain a large amount of iron and are weakly acidic, but since the developing solution is alkaline, this developing solution is used as a part of the alkali, and the insufficient alkali is replaced with water. What is necessary is just to supplement with sodium oxide etc.

The reaction time for forming a precipitate by adding an alkali is not particularly limited.
It is about 30 to 60 minutes when the temperature is lower than 100 ° C., and about 15 minutes when the temperature is 100 ° C. or higher.

As described above, when the alkali of the photographic processing waste liquid is added, the ammonia originally contained in the waste liquid is diffused, and when the temperature is increased, the ammonia diffusion becomes remarkable. It is necessary to. The released ammonia may be recovered by contacting with an absorbing solution such as sulfuric acid, or may be treated by catalytic oxidation or incineration using a catalyst. Alternatively, the ammonia can be guided to an incinerator described below and incinerated together with the waste liquid. In this case, ammonia is effective in reducing NOx in the exhaust gas.

As the solid-liquid separation process for separating the waste liquid and the precipitate, a known method can be applied. For example, a filtration method, a centrifugation method, or the like can be used. When the reaction temperature for forming the precipitate is low, the separability of the precipitate is slightly inferior. When the concentration is high, it is desirable to use a centrifugal separation method. In the present invention, the remaining waste liquid after separating the generated precipitate is sprayed into an incinerator to be incinerated, so that the suspension in the waste liquid is also removed in the step of separating the precipitate, This is also effective for avoiding troubles such as nozzle clogging when spraying waste liquid. In particular, the precipitate formed in the present invention is mainly composed of iron hydroxide, and iron hydroxide is well-known as a coagulant, and also has an advantageous effect in solid-liquid separation such as filtration. I do. When separating the precipitate, a known filter aid such as diatomaceous earth may be used as necessary.

Next, the remaining waste liquid after separating the precipitate is
The method of incineration will be described. The incinerator used in the present invention is a heat-resistant furnace or the like lined with a refractory, and is sprayed as fine droplets into a furnace heated to a high temperature by burning a fuel such as LPG, city gas, light oil from a burner. It is only required that the supplied waste liquid can be decomposed by combustion, and the shape may be vertical or horizontal.

An example of a facility mainly for an incinerator for incinerating waste liquid will be described with reference to the drawings. FIG. 1 shows an example of an incinerator that can be used in the method of the present invention. In the incinerator main body 1 in the figure, the outside is covered with a metal plate and the inside is formed of a refractory, and a burner 2 having a fuel inlet and an air inlet is provided at the upper part of the furnace. As the burner, it is preferable to use a high-load, short-flame burner in order to make the incinerator small and achieve a stable combustion state at a high temperature. It is desirable to use LPG or kerosene, which is a clean fuel that can be completely burned and does not generate acid gas and dust components required for post-treatment.

A waste liquid supply device such as a spray nozzle 3 for supplying waste liquid into the furnace is provided at the shoulder portion of the furnace that widens from the burner section. In general, the installation locations and the numbers thereof can be appropriately selected as needed. The waste liquid is sprayed from a spray nozzle 3 through a pipe 4 toward a high-temperature portion in the furnace, whereby rapid evaporation of water, decomposition of waste liquid components, and combustion of organic substances are performed. At the time of incineration of the waste liquid, the position of the spray nozzle 3 for supplying the waste liquid is arranged symmetrically with respect to the central axis of the furnace so that the waste liquid ejected into the furnace is dispersed well in the center of the furnace. It is desirable to take measures such as:

In the present invention, in order to completely incinerate the organic matter and ensure the fluidity of the generated ash, the incineration temperature needs to be 850 ° C. or higher. As the maximum temperature of the area where the waste liquid is incinerated, the higher the temperature, the higher the NO
The temperature is preferably set to 1100 ° C. or less from the viewpoint of increasing the generation of x, saving fuel, and problems with the furnace material.

Combustion exhaust gas 6 generated by incineration
Is discharged out of the furnace through the outlet 5 of the furnace, and then cooled and, if necessary, subjected to a treatment for detoxification, and then released into the atmosphere. In the figure, reference numeral 7 denotes ash, and most of the ash generated by the incineration process is taken out of the furnace along with the flue gas 6, but the ash of the ash that has partially adhered to the furnace wall or the like has a low fluidity. If it is good, it will gradually be discharged out of the furnace. In the actual operation, as shown in FIG.
The combustion exhaust gas 6 may be discharged into the system 3 after cooling and dust removal by blowing combustion exhaust gas into the exhaust gas 3.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a photographic processing waste liquid after desilvering processing, a fixing waste liquid, a mixed waste liquid of a fixing waste liquid and a developing waste liquid, and a concentrated waste liquid obtained by concentrating the mixed waste liquid about three times are used.
A precipitate was formed by adding 48% by weight of sodium hydroxide as an alkali, and the precipitate was centrifuged at 3000 G.
The iron content in the waste liquid after separation by centrifugal force was measured. The reaction temperature was room temperature (25 ° C), 60 ° C, and 100 ° C and 150 ° C using an autoclave.

PH and density of the used fixing waste liquid, a mixed waste liquid of the fixing waste liquid and the developing waste liquid, and a concentrated waste liquid of the mixed waste liquid,
The iron content was as follows: In addition, a large amount of organic compounds were contained, the COD was tens of thousands ppm, and a chelating agent such as EDTA was present. Item Fixing waste liquid Mixed waste liquid Concentrated waste liquid pH 6.5 8.2 7.6 Density (ρ) 1.09 1.08 1.33 Iron (mg / kg) 1600 2000 5300

The results of measuring the iron content in the three kinds of waste liquids were as follows:
This is shown in FIGS. The concentration of iron in the waste liquid in the figure is based on the initial waste liquid. In any case, the iron content in the waste liquid gradually starts decreasing at pH 12 or higher, and sharply decreases at pH 13 or higher.
In addition, as for the reaction temperature, the higher the temperature, the lower the iron content tends to be, and it can be seen that the tendency becomes remarkable in a high pH region. The generated precipitate had better sedimentation properties when the reaction temperature was higher than room temperature (25 ° C.).

Using the concentrated waste liquid obtained by concentrating the above-mentioned fixing waste liquid and mixed waste liquid about three times, adding 48% by weight of sodium hydroxide to adjust the pH to 13, and forming a precipitate at a temperature of 60 ° C. . After the sediment was separated by a centrifugal separator at a centrifugal force of 3000 G, the obtained waste liquid having a reduced iron content was supplied to the incinerator shown in FIG. Air was sent from the air line 11 provided with the control valve 14 to heat the inside of the furnace, and the waste liquid was sprayed into the furnace by compressed air (not shown) from the spray nozzle 3 and incinerated at 950 ° C.

The iron content of the fixing waste liquid and the concentrated waste liquid after the separation of the precipitate was 480 mg / L and 900 mg / L, respectively, based on the initial waste liquid, and the waste liquid was separately and continuously incinerated. In this case, the furnace condition was stable and continuous operation for two weeks was possible. The COD in the cooling water was several ppm, and the organic matter in the waste liquid was almost completely decomposed. After the operation was completed, the inside of the furnace was observed. In the case of the fixing waste liquid, only a small amount of ash was observed at the bottom of the furnace. A small amount of the light brown iron complex oxide mixed with the ash having good flowability was present, but it was observed that the ash flowed out toward the outlet of the furnace as a whole.

From these results, it is possible to reduce the amount of iron as in the present invention and to reduce the ratio of iron oxide in the ash, even if the iron in the waste liquid is not reduced until it is thoroughly removed. Thus, it can be seen that improving the fluidity of the ash is effective.

The concentrated waste liquid obtained by concentrating the above-mentioned fixing waste liquid and mixed waste liquid about three times is directly supplied to the incinerator shown in FIG.
It was sprayed into a furnace and incinerated at 950 ° C. In the case of the fixing waste liquid, brown ash was found to adhere to the lower part of the furnace, and the flowability of the ash was low, so that it was expected that long-term operation would be hindered. In the case of the concentrated waste liquid, the operation was stopped in a week because the pressure inside the furnace was increased due to the sound of the small lumps generated by the separation of the ash in the cooling water during operation. When the inside of the furnace was observed after the operation, a large amount of brown ash remained in the vicinity of the outlet at the bottom of the furnace in a solidified state.

As described above, the method of the present invention for incinerating the waste liquid containing iron chelate from the waste liquid containing the iron chelate by reducing the iron content in advance using an alkali is not only a photographic processing waste liquid but also an organic compound and an inorganic compound. Obviously, it is applicable to waste liquids containing iron chelates.

[0034]

According to the present invention, the incinerator can be easily operated for long-term operation when waste liquid containing iron chelate such as photographic processing waste liquid is incinerated. Also,
Organic substances in the waste liquid for incineration can be treated at a high decomposition rate.

According to the present invention, not only photographic processing waste liquid but also photographic processing waste liquid can be removed by removing 70 to 90% of iron in waste liquid, which has been a problem during incineration treatment, and reducing the relative proportion to other components. By mixing various waste liquids and waste acids which have been difficult to treat so far, it is possible to effectively treat even waste liquids containing iron chelates.

Further, the present invention is a method that requires a facility for removing iron from waste liquid, but can be implemented with a small burden such as modifying incineration equipment such as an incinerator. Therefore, it can be applied to existing incinerators by installing equipment that removes iron equivalent to pretreatment, and is considered to be economically advantageous.

[Brief description of the drawings]

FIG. 1 is an example of an incinerator that can be used in the present invention.

FIG. 2 is an example of an incinerator that can be used in the present invention;
It is equipped with a cooling system for incineration exhaust gas.

FIG. 3 shows a measurement result of iron content in a solution after adding an alkali to a fixing waste solution and separating a generated precipitate.

FIG. 4 shows a measurement result of iron content in a mixed waste liquid such as a fixing waste liquid and a development waste liquid after adding a base to separate a generated precipitate.

FIG. 5 shows the measurement results of iron content in a liquid obtained by adding an alkali to a concentrated waste liquid of a mixed waste liquid of a fixing waste liquid and a developing waste liquid, and separating a generated precipitate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incinerator main body 2 Burner 3 Spray nozzle 4 Pipe 5 Furnace outlet 6 Combustion exhaust gas 7 Ash content 10 Fuel line 11 Air line 12 Downcomer 13 Cooling water 14 Flow control valve

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiroshi Obayashi 4-26-3 Shimoishikami, Nerima-ku, Tokyo

Claims (3)

[Claims] 1. An alkali is added to a waste liquid containing an iron chelate to form a precipitate having a pH of 12 or more, and the remaining waste liquid after separating the formed precipitate is sprayed into an incinerator for incineration. Of waste water containing iron chelate. 2. The method for treating a waste liquid containing an iron chelate according to claim 1, wherein the waste liquid containing the iron chelate is concentrated in advance, and then an alkali is added to the concentrated waste liquid. 3. The waste liquid is added to the mixture in an amount of 60 to 250 when adding an alkali.
The method for treating a waste liquid containing an iron chelate according to claim 1 or 2, wherein the waste liquid is heated to a temperature of ℃.