JPH06182364A - Treatment of waste water containing heavy metal - Google Patents

Abstract

PURPOSE:To purify waste water by efficiently removing a heavy metal in the waste water by adjusting the concn. of an iron compd. in the waste water to a predetermined value or more and subsequently subjecting the waste water to a wet oxidation treatment at a predetermined temp. under a predetermined pressure while supplying an oxygen-containing gas and separating and removing a formed water-insoluble or hardly water-soluble heavy metal compd. CONSTITUTION:In the treatment of waste water containing a heavy metal, the waste water containing the heavy metal supplied from a waste water supply line 8 is subjected to a wet oxidation treatment in a wet oxidation reaction tower 1. At this time, the concn. of the water-soluble or water suspensible iron compd. in the waste water is adjusted to 100mg/l or more at first. Next, the waste water is subjected to wet oxidation treatment at 110-370 deg.C under the pressure holding the waste water to liquid phase in the wet oxidation reaction tower 1 while an oxygen-containing gas is supplied from an oxygen- containing supply line 9 through a compressor 5 and a formed water-insoluble or hardly water-soluble heavy metal compd. is separated and removed from the waste water.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention purifies waste water containing heavy metal elements discharged from various industrial plants such as chemical plants, food processing equipment, metal processing equipment, metal plating equipment, printing plate making equipment or photographic processing equipment. Regarding how to handle. More specifically, the present invention relates to a treatment method for efficiently removing these heavy metals in wastewater containing heavy metal ions, heavy metal compound ions or heavy metal elements of organometallic compounds to purify the wastewater.

[0002]

2. Description of the Related Art Wastewater from various industrial plants often contains metals dissolved or suspended in the wastewater, and dumping into rivers, the sea, sewage, etc. often poses a problem in terms of environmental pollution. In particular, heavy metal elements are severely regulated by the Water Pollution Control Act and others due to their harmfulness.

In addition, these wastewaters generally contain a large amount of BO.
Since it contains D, COD components, etc., it is often treated by biological treatment or chemical treatment. However, when this biological treatment is performed, various heavy metal elements contained in the wastewater often cause the biological treatment to hinder the treatment. For example, since the metal is harmful to living organisms, the activated sludge bacteria used for the treatment are killed, and this treatment cannot be sufficiently performed.

Further, in chemical treatments such as an oxidation method using a chlorine-based chemical agent, an electrolytic oxidation method, a hydrogen peroxide-ferrous iron salt method, an ozone oxidation method, and a wet oxidation method, the oxidation reaction by various heavy metal elements is performed. There are problems such as inhibition and scale generation.

Therefore, in the treatment of wastewater by biological treatment or chemical treatment, it is necessary to remove various heavy metal elements contained in the wastewater in advance or dilute the wastewater in large quantities to reduce the influence thereof. .

Examples of the technique for removing various heavy metal elements contained in the wastewater in advance include, for example, a coagulation separation removal method by adding an inorganic or organic coagulant, an electrolytic removal method, activated carbon, an inorganic adsorbent or an organic compound. The adsorption removal method using a polymer material, the dry solidification method in which waste water is heated and evaporated, the reverse osmosis method using a membrane, the electrodialysis method, or the ultrafiltration method has been implemented or proposed.

[0007]

When the above-mentioned methods are used, there are many problems as described below, and any of the methods needs improvement. For example, (1) the coagulation separation removal method or the like is suitable for a concentrated liquid, but is not suitable for a dilute liquid, (2) the adsorption removal method or the like, on the contrary, is suitable for a diluting liquid but for a concentrated liquid. Not suitable, (3) aggregation separation removal method, adsorption removal method, etc., it is difficult to treat the solid component after treatment,
(4) The reverse osmosis membrane method, ultrafiltration removal method, electric filtration method, etc. are difficult to remove if the wastewater contains a specific organic matter. (5) Dry solidification method by heat evaporation, coagulation separation The removal method is
The treatment method is complicated, and (6) electrolysis method, electrodialysis method, reverse osmosis membrane method, ultrafiltration removal method and the like increase the treatment cost. In particular, when COD components such as organic substances coexist in wastewater, it is difficult to remove heavy metal species,
The waste water cannot be sufficiently purified.

[0008]

In order to solve the above-mentioned problems, the present inventor has conducted earnest research and, as a result, carried out a wet oxidation treatment of wastewater containing heavy metal species in the wastewater.
100 mg per liter (iron equivalent weight, hereinafter "mg /
The present invention has been completed by finding a method for treating wastewater that is easy in operation and excellent in practicality and economy by adjusting the conditions for coexistence and performing wet oxidation treatment.

More specifically, when the wastewater containing heavy metal elements is subjected to the wet oxidation treatment, water-soluble or water-suspendible iron compounds are contained in the wastewater in an amount of 100 per liter of the wastewater.
It is adjusted so as to be more than mg (weight equivalent to iron), and then the waste water is subjected to wet oxidation treatment under the pressure at which the waste water retains a liquid phase at a temperature of 110 ° C. to 370 ° C. while supplying a gas containing oxygen. By so doing, the water-insoluble or sparingly water-soluble compound of the heavy metal element produced is separated and removed from the wastewater.

The heavy metal element contained in the wastewater to be treated by the method of the present invention is not particularly limited as long as it is an element generally called a heavy metal element, but it can be effectively treated by the method of the present invention. As, for example, vanadium, chromium, manganese, cobalt, nickel, copper, zinc, zirconium, molybdenum, silver, cadmium, tin,
It is at least one heavy metal element selected from the group consisting of tungsten, niobium, antimony, hafnium, tantalum, mercury, thallium, bismuth, and lead.

The form of these heavy metal elements may be in any state as long as it is dissolved or suspended in the waste water, and is not particularly limited, but is preferably a heavy metal ion, a heavy metal compound or this. An ion or an organometallic compound or this ion. More specifically, for example, heavy metal ions include copper ions, silver ions, nickel ions, cadmium ions, mercury ions, lead ions, zinc ions, chromium ions, thallium ions, manganese ions, zirconium ions, tin ions, hafnium ions, vanadium. Ions, niobium ions, antimony ions, tantalum ions, bismuth ions, ions such as tungsten ions, and heavy metal compounds or this ion, paramolybdic acid, tungstophosphoric acid, niobium acid, manganate, copper hydroxide, A compound or an ion such as nickel hydroxide, and an organometallic compound or this ion means a metal-EDTA such as a cobalt-EDTA complex.
Complexes or compounds such as copper acetate.

The concentration of the heavy metal species is not particularly limited, but it is effective when the waste water is contained in an amount of 100 g / liter or less, and more effective is 50.
It is not more than g / liter. If it exceeds 100 g / liter, the solubility of the gas containing oxygen in the waste water is drastically reduced and the reaction is hindered.

The water-soluble or water-suspendible iron compound in the waste water according to the present invention is not particularly limited as long as it is water-soluble or water-suspendable in the waste water. , An iron-containing compound or its ion, or an iron-containing organometallic compound or this ion, and specifically, the iron ion is a divalent or trivalent ion, and an iron-containing iron compound Alternatively, the ions include molybdo ferrate ion, tungsto ferrate ion, iron hydroxide and the like, and the iron-containing organic metal compound or the ion includes iron-EDTA complex, iron acetate and the like.

If the water-soluble or water-suspendable iron compound according to the present invention is contained in the waste water within the following range, the wet oxidation treatment can be carried out as it is, but usually within the following range. It is rare that it is contained in wastewater.In such a case, the object of the present invention is achieved by adding a water-soluble or water-suspendable iron-containing material to the wastewater within the following range and performing wet oxidation. it can.

The water-soluble or water-suspendible iron compound to be added may be the same as the iron compound contained in the waste water, but it is not particularly limited, but the removal efficiency of heavy metal elements is high. Considering the above, it is preferably water-soluble.

The water-soluble or water-suspendable iron-containing substance to be added may be any one as long as it can be dissolved or suspended in wastewater, but it can be added to wastewater. Considering handling, ferrous sulfate and ferric sulfate
Iron, ferric nitrate, ferric chloride, iron acetate, iron-EDTA complex and the like are preferable.

The concentration of iron compounds in the waste water of the method according to the present invention (weight in terms of iron) is not particularly limited as long as it is 100 mg / liter or more, but preferably 300.
It is effective that the content is in the range of mg / liter to 100 g / liter, and more preferably in the range of 500 mg / liter to 50 g / liter.

If it exceeds 100 g / liter, the solubility of the gas containing oxygen in the waste water is drastically reduced, the reaction is inhibited, and the amount of solid matter after the treatment increases.
If the iron concentration is 100 mg / liter or less, the removal rate of heavy metals decreases.

Further, the amount of the iron compound has a correlation with the amount of the heavy metal element in the wastewater, and in order to carry out the method of the present invention more efficiently, the amount of the iron compound (converted into the atomic weight of iron is calculated. Weight): The total amount of heavy metal elements in the wastewater (weight converted into atomic weight of each metal, excluding iron) is 1: 1 to 10
00: 1, preferably 2: 1 to 100: 1, more preferably 5: 1 to 50: 1. The amount of iron compound is 10
When it exceeds 00: 1, iron is excessively supplied, the amount of solid matter after the treatment increases, which is not preferable, and when the amount of heavy metal element is less than 1: 1, the removal efficiency decreases.

The concentration of COD in the waste water is not particularly limited, but is 1.0 g / liter to 250 g / liter.
It is effective when the water content is 1 liter (content per 1 liter of wastewater), and more effective is 5.
It is 0 g / liter to 200 g / liter. When the COD concentration exceeds 250 g / liter, the heat of oxidation of the COD component becomes very large, which makes it difficult to control the treatment equipment. When the COD concentration is less than 1.0 g / liter,
There is little merit in removing heavy metal species from wastewater using this method, and heavy metal species can be removed using other conventional techniques. Further, when the amount is less than 5.0 g / liter, the heat of oxidation of the COD component is small, and in such a case, even if heat is recovered using a heat exchange device as an auxiliary equipment, the heat of the wet oxidation treatment device using this heat is reduced. This is because autonomous driving becomes difficult. Further, in such a case, although there is no problem in the wet oxidation itself, a separate heat supply device is required for the treatment, and the merit of the device is reduced, which is not preferable in operation.

The COD component includes various organic substances, organometallic compounds, inorganic substances, and the like, and is not particularly limited as long as they belong to these. For example, the organic substances are formic acid, acetic acid, P-toluene. Organic acids such as sulfonic acid, nitrogen-containing compounds such as ethanolamine and DMF,
DMSO, sulfur-containing compounds such as thiophene, hydrocarbons such as benzene and hexane, organometallic compounds are complexes such as EDTA and compounds such as copper acetate, and inorganic substances include sulfur and sodium sulfide. , Sodium thiosulfate, etc.

The wet oxidation apparatus used in the present invention may be of a commonly used type, and may be of a single tube type or a multi-tube type, and may be of a horizontal type, a vertical type or the like. Although it can be used, it is preferably a single tube vertical type. The inside of the reactor of this device may be empty,
A filler or a catalyst may be filled.

When a catalyst is used, the catalyst is
Any catalyst may be used as long as it is a solid catalyst and has both activity and durability under the conditions of liquid phase oxidation, and for example, contains titania, iron, alumina, silica, zirconium or activated carbon. The above-mentioned components (hereinafter referred to as the A component) and the second
Ingredients can be added. Of these, the solid catalyst is preferably a catalyst containing an oxide or a composite oxide containing titania as a main component.

As the second component, manganese, iron, cobalt, nickel, tungsten, copper, cerium, silver,
It is possible to use a catalyst containing at least one metal such as platinum, palladium, rhodium, gold, iridium or ruthenium, or a component (hereinafter referred to as component B) made of a metal compound of these. This catalyst is A component 75
It is preferable that the proportion of the component B is 25 to 0.05% by weight with respect to 99.95% by weight.

The catalyst shape is pellet, spherical,
Various types such as a ring-shaped, crushed type, and an integral structure such as a honeycomb can be adopted, but the honeycomb is preferable. The method for producing these catalyst-shaped products is a method in which the catalyst components are mixed according to a usual procedure and molded into the above-mentioned shape, and dried or calcined to form a catalyst, which is usually used as a carrier for the catalyst. Pellet, spherical, ring-shaped, honeycomb-shaped carrier, spraying or impregnating the slurry of the catalyst or its precursor,
There is a method of drying or calcining to use as a catalyst.

The treatment temperature of the waste liquid is 110 ° C to 370 ° C, preferably 130 ° C to 300 ° C. 370
This is because the waste liquid cannot hold the liquid phase when the temperature is higher than or equal to ° C. On the other hand, if the temperature is lower than 110 ° C., the treatment efficiency will decrease.

The pressure of the waste water is appropriately selected according to the correlation with the temperature of the waste water, and the pressure of the waste water is such that the liquid phase is maintained.

The treated amount of waste water is 20 in terms of space velocity.
hr- ^{1 to} 0.1 hr- ¹ and preferably 10 hr- ^{1 to} 0.
It is 25 hr ~ ¹ . When it exceeds 20 hr to ¹ , the treatment efficiency decreases, and when it is less than 0.1 hr to ¹ , the treatment amount of wastewater decreases and the equipment becomes huge, which is not preferable.

The oxygen-containing gas used in the reaction is a gas containing oxygen, air, or ozone. When a gas such as ozone or oxygen is used, it should be diluted appropriately with an inert gas before use. Can be done. In addition to these gases, oxygen-containing waste gas generated from other plants can also be used as appropriate.

The amount of this gas used depends on the concentration of wastewater.
Although it can be appropriately selected, CO of the wastewater is preferable.
10 of the amount of oxygen (total oxygen demand: TOD) required to completely convert the D component, etc. to water, carbon dioxide, inorganic salts, and other ash
Double to 0.4 times (hereinafter also referred to as “O ₂ / TOD”), preferably 5 to 0.7 times. When it exceeds 10 times, the treatment efficiency does not improve, but rather the temperature of the wastewater is lowered. On the other hand, if it is less than 0.4 times, the amount of oxygen is not sufficient and the removal of heavy metal components is incomplete.

Further, the range of 0.4 times to 1.0 times is not sufficient as the amount of oxygen necessary for completely converting the COD component of the wastewater into water, carbon dioxide gas, inorganic salts, and other ash, The reason is (1) In addition to the oxygen gas that supplies the amount of oxygen required to supply COD for oxidative decomposition, substances that have an oxidizing effect, such as those contained in the wastewater, may be oxidatively decomposed and heavy metals may be generated. Contribution to insolubilization, (2) Heavy metals can be insolubilized or hardly soluble in water even without decomposing COD components with high efficiency, (3) Chelate compound or organometallic compound When heavy metals and organic substances are bound to each other and heavy metals are dissolved in wastewater, such as
It is sufficient to partially destroy the structure without completely oxidizing and decomposing the organic metal component bound to the heavy metal. (4) When the treatment efficiency of COD is not 100%, this treatment efficiency Even if the supply amount is reduced to the required oxygen amount, or even if the supplied oxygen amount is further reduced from the required oxygen amount, the COD treatment efficiency may not change so much, and the COD component is decomposed 100%. This is because the heavy metal species can be sufficiently removed without supplying oxygen necessary for the above.

Further, in the treatment method of the present invention, it is preferable to wet-oxidize the wastewater, and then use a solid-liquid separation treatment apparatus to remove the generated heavy metal element precipitates and the like by wet-oxidation. As the solid-liquid separation treatment device, various devices such as a sedimentation separation treatment device, a centrifugal separation treatment device or a filtration separation treatment device can be adopted.

Further, the heavy metal element removing technique by the wet oxidation treatment method of the present invention can be adopted without any problem even if it is used in combination with a conventional existing wastewater treatment technique.

In order to further improve the treatment efficiency of wastewater depending on the type of wastewater, or when treating corrosive wastewater, in the present invention, in wet oxidation treatment,
NaOH, H ₂ SO ₄ , and NaNO are used for the treatment before the treatment.
₃ , alkali such as Na ₂ CO ₃ , acid, inorganic salt, etc. may be added. In addition, the pH is appropriately adjusted as a treatment after the wet oxidation treatment.

When treating wastewater containing solids or suspensions, it is preferable to remove the solids and the like before the wet oxidation treatment. As this solid-liquid separation treatment device, the solid-liquid separation device after the above-mentioned wet oxidation treatment can be used.

[0036]

[Effect] Does this treatment method change the water-soluble or water-suspendible heavy metal elements in wastewater into water-insoluble or sparingly soluble substances such as oxides, inorganic salts, and other compounds?
Alternatively, a heavy metal element is removed by being adsorbed or coprecipitated by an iron compound that has become a compound that is insoluble or hardly soluble in water and is precipitated and solid-liquid separated and removed from the wastewater.

In addition, other pollutants in this wastewater,
For example, it is possible to purify waste water by efficiently oxidizing and oxidatively decomposing organic substances and inorganic COD components and converting them into inorganic salts, carbon dioxide gas, water and ash. Therefore, when the heavy metal element forms a compound with the organic matter in the wastewater and is water-soluble or water-suspendable in the wastewater, the present invention can also decompose the organic matter in the wastewater at the same time. , It is very effective in removing heavy metal elements from wastewater.

The wastewater after this treatment can be discharged directly or subjected to biological treatment or chemical treatment as a post treatment. Even in this case, since the heavy metal element is removed from the wastewater in advance, the burden on the biological treatment equipment or the chemical treatment equipment becomes very small.

Further, even if the organic components in the wastewater are not completely decomposed by the treatment method of the present invention, high-molecular weight organic substances can be oxidatively decomposed into low-molecular weight ones. Therefore, after performing the treatment method of the present invention, The combined use of biological treatments is sufficiently possible, and the present invention is effective even in this case.

During the treatment of the present invention, the hardly biodegradable inorganic component is also oxidatively decomposed and becomes a component having improved biodegradability. Therefore, as described above, the biological treatment is used in combination with the treatment of the present invention. Doing so will also be effective.

Further, the precipitate after the solid-liquid separation has an organic matter content, particularly a high molecular weight organic matter content, which is determined by the coagulation separation removal method,
Compared with the adsorption separation removal method, the amount is much smaller, and the treatment of the precipitate after separation is easy.

Further, in the present invention, since the site is small and the apparatus is compact, the processing equipment is very small as compared with the conventional processing equipment, the processing process is simplified, the capital investment and running are reduced. It is also advantageous in terms of cost.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0044]

【Example】

(Example 1) To the wet oxidation treatment apparatus for a reaction tube made of stainless steel shown in FIG. 1, was introduced preheat-mixed waste water and air from the lower part of the reaction tube, and continuously wet-oxidized for 500 hours.
After that, the liquid is collected at the outlet of the treated water discharge line 13,
After filtering with a 0.2 μm membrane filter, the removal rates were determined by measuring the amounts of chromium and iron in the filtrate by inductively coupled high frequency plasma emission spectroscopy. Similarly, TOC and COD (Cr) were measured to determine the treatment efficiency.

The components of the wastewater used for the treatment were chromium of 30 mg / liter, iron of 1 mg / liter or less, TO
C was 0.8 g / liter, COD (Cr) was 2.5 g / liter, TOD was 2.7 g / liter, and the pH was 6.5. Therefore, before performing the wet oxidation treatment, ferrous sulfate was added to the wastewater so that the concentration of iron was 0.80 g / liter.

A detailed method of using this treatment apparatus is as follows. The waste water sent from the waste water supply line 8 is pressurized to 75 kg / cm ² G at a flow rate of 1 liter / Hr by the waste water supply pump 3, while the oxygen-containing gas supply line is used. The air supplied from No. 9 was pressurized by the compressor 5, and then mixed into the waste water at a ratio of O ₂ / TOD (oxygen amount in air / total oxygen consumption amount) = 1.0. This gas-liquid mixture is supplied to the gas-liquid mixture supply line 1
After heating to 260 ° C. in the heat exchanger 2 via 0,
It is introduced into the wet oxidation reaction tower 1, subjected to wet oxidation treatment, and the treated water is cooled in the heat exchanger 2 through the treated water line 11,
It flowed to the gas-liquid separator 4. The space velocity of the waste water in the wet oxidation reaction tower was 1.0 hr to ¹ , and the linear velocity of the waste water was 10 m / hr. In the gas-liquid separator 4, the liquid level controller (L
The liquid level is detected by C), the liquid level control valve 6 is operated to maintain a constant liquid level, and the pressure controller (P
According to C), the pressure is detected and the pressure control valve 7 is operated to maintain a constant pressure.

The obtained results are that the chromium removal rate is 99% or more, the TOC treatment efficiency is 93%, and the COD (Cr) treatment efficiency is 95%.
%, The pH of the treatment liquid was 2.7, and the concentration of residual iron was 1 mg / liter or less. In addition, the process 500
After the time, no particular deposit was found on the side surface of the reaction tube.

(Example 2) In Example 1, the waste water composition and treatment conditions were changed to the following waste water composition and treatment conditions, and air was replaced with O ₂ / TOD (oxygen amount in gas / theoretical oxygen demand). The amount of silver and iron was measured in the same manner as in Example 1 except that the oxygen-containing gas was changed to 3.0 to determine the removal rate. Also, similarly, TOC, COD (C
r) was measured to determine the treatment efficiency.

The component of the wastewater used for the treatment is 200 m of silver.
g / liter, iron 1 mg / liter or less, TOC 25 g
/ Liter, COD (Cr) 87g / liter, TOD9
The pH was 3.1 at 0 g / liter. Therefore, before the wet oxidation treatment, ferric nitrate was added to the wastewater so that the iron concentration was 1.1 g. The treatment conditions were a reaction temperature of 150 ° C., a reaction pressure of 9 kg / cm ² G, a space velocity of waste water in the wet oxidation reaction tower of 0.5 hr to ¹ and a waste water linear velocity of 5 m / hr. The obtained result is 99% of silver removal rate.
%, The TOC treatment efficiency was 34%, the COD (Cr) treatment efficiency was 38%, the pH of the treatment liquid was 5.7, and the concentration of residual iron was 3 mg / liter. In addition, the process 500
After the time, no particular deposit was found on the side surface of the reaction tube.

(Example 3) Nickel was prepared in the same procedure as in Example 1 except that gas, wastewater composition and treatment conditions of the following oxygen concentration were used in place of air, wastewater composition and treatment conditions. And the amount of iron was measured and the removal rate was calculated. Similarly, TOC and COD
(Cr) was measured and the treatment efficiency was calculated.

The composition of the wastewater used for the treatment is nickel 45
mg / liter, iron 2.0 g / liter, TOC15.
7 g / liter, COD (Cr) 51 g / liter, TO
The pH was 13.1 at D53 g / liter.

Preheated waste water and an oxygen-containing gas having an oxygen concentration of 8% were mixed and introduced from the lower part of the reaction tube.

The treatment conditions are a reaction temperature of 200 ° C., a reaction pressure of 40 kg / cm ² G, a space velocity of waste water of 1.0 hr to ¹ in the wet oxidation reaction tower, and a linear velocity of waste water of 10 m / h.
It was r. The oxygen-containing gas was introduced into the reaction tube at O ₂ / TOD (oxygen amount in gas / theoretical oxygen demand amount) = 1.2.

The result obtained is that the nickel removal rate is 99%.
Above, TOC removal rate 65%, COD (Cr) treatment efficiency 68
%, The pH of the treatment liquid was 10.2, and the concentration of residual iron was 2 mg / liter. Further, after the treatment was carried out for 500 hours, no particular deposit was found on the side surface of the reaction tube.

Example 4 The procedure of Example 1 was repeated except that the following waste water composition, treatment conditions and catalyst were used instead of the waste water composition and treatment conditions in Example 1, and the amounts of cobalt and iron were changed. The removal rate was measured. Further, in the same manner, TOC and COD (Cr) were measured, and the treatment efficiency was obtained.

The composition of the wastewater used for this treatment is as follows: cobalt 120 mg / liter, iron 1 mg / liter or less, TO
C 9.8 g / liter, COD (Cr) 32 g / liter, TOD 35 g / liter, and pH 10.6. Therefore, before performing the wet oxidation treatment, the Fe-ED was adjusted so that the concentration of iron in the waste water was 2.0 g / liter.
The TA complex was added. As the catalyst, a catalyst composed of a titania-zirconia composite oxide and platinum (0.4% by weight of platinum) was used.

The treatment conditions are a reaction temperature of 240 ° C., a reaction pressure of 70 kg / cm ² G, a space velocity of waste water in the wet oxidation reaction tower of 3.0 hr to ¹ (empty tower standard), and a linear velocity of waste water of 30 m / m. It was hr. Also, the air is O ₂ / TOD
(Amount of oxygen in air / theoretical oxygen demand) = 2.0 and introduced into the reaction tube.

The result obtained is that the removal rate of cobalt is 99%.
Above, TOC processing efficiency 75%, COD (Cr) processing efficiency 7
8%, the pH of the treatment liquid was 8.8, and the concentration of residual iron was 1 mg / liter or less. In addition, the process 500
After the time, no particular deposit was found on the side surface of the reaction tube.

(Comparative Example 1) In Example 1, the amount of chromium was measured and the removal rate was obtained in the same manner as in Example 1 except that iron was not added to the wastewater. Similarly, TOC and CO
The processing efficiency was obtained by measuring D (Cr).

The obtained results are that the removal rate of chromium is 30%,
TOC processing efficiency 91%, COD (Cr) processing efficiency 93%
Then, the pH of the treatment liquid was 3.1. In addition, processing 50
After 0 hour, a small amount of black deposit adhered to the side surface of the reaction tube. As a result of analysis with an electron probe microanalyzer, it was found that chromium was an adhering substance whose main component was chromium.

(Comparative Example 2) A wet oxidation treatment was conducted in the same manner as in Example 1 except that the air was replaced with nitrogen gas, and the amounts of chromium and iron were measured to obtain the removal rate. Similarly, TOC and COD (Cr) were measured to determine the treatment efficiency.

The results obtained are as follows: chromium removal rate 0%, T
The OC treatment efficiency was 3%, the COD (Cr) treatment efficiency was 4%, the pH of the treatment liquid was 6.2, and the concentration of residual iron was 3.0 g /
It was liter. Further, after the treatment was carried out for 500 hours, no particular deposit was found on the side surface of the reaction tube.

[Brief description of drawings]

FIG. 1 is one of embodiments of a processing apparatus according to the present invention.

[Explanation of symbols]

 1. Wet oxidation reaction tower 2. Heat exchanger 3. Waste water supply pump 4. Gas-liquid separator 5. Compressor 6. Liquid level control valve 7. Pressure control valve 8. Waste water supply line 9. Oxygen-containing gas supply line 10. Gas-liquid mixture supply line 11. Treated water line 12. Gas discharge line 13. Treated water discharge line

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kunio Sano Inventor, Kunio Sano 1 992 Nishikioki, Kamahama, Aboshi-ku, Himeji-shi, Hyogo, Japan Catalysis Research Institute, Inc.

Claims (2)

[Claims] 1. When wet-oxidizing wastewater containing heavy metal elements, the concentration of the water-soluble or water-suspending iron compound in the wastewater is adjusted to be 100 mg (weight equivalent to iron) or more per liter of wastewater. Then, a water-insoluble or sparingly soluble compound of the heavy metal element produced by subjecting the wastewater to a wet oxidation treatment under a pressure at which the wastewater maintains a liquid phase at a temperature of 110 ° C. to 370 ° C. under the supply of a gas containing oxygen. A method for treating wastewater, which comprises separating and removing water from the wastewater. 2. The heavy metal element is vanadium, chromium, manganese, cobalt, nickel, copper, zinc, zirconium, molybdenum, silver, cadmium, tin, tungsten,
The method according to claim 1, wherein the method is at least one element selected from the group consisting of niobium, antimony, hafnium, tantalum, mercury, thallium, bismuth, and lead.