JPH08290178A - Method for wet-oxidizing cyanide-containing waste water - Google Patents

Abstract

PURPOSE: To completely decompose cyanides without need for an additional treatment by wet-oxidizing a cyanide-contg. waste water under specified temp., pressure and cyanide amt. to separate sludge, etc., adding a sulfur compd. to the obtained primary treated liq. and again wet-oxidizing the treated liq. under the same conditions. CONSTITUTION: A cyanide-contg. waste water in a waste water storage tank 1 is boosted to a specified pressure by a pump 2, mixed with an oxygen-contg. gas from a compressor 22, sent to a heat exchanger 3 and heated to <=150 deg.C. In a primary reaction tower 5, the waste water is wet-oxidized at >=150 deg.C in the presence of oxygen in the amt. less than the stoichiometry necessary to make the cyanide compd., nitrogen compd. and org. and inorg. substances harmless. The oxidized waste water is sent to a solid-liq. separator 10 to remove the sludge and metallic component. The obtained primary treated liq. is mixed with sulfuric acid from a sulfuric acid storage tank 25 and sent to a catalyst- packed reaction tower 14. The treated liq. is wet-oxidized at >=150 deg.C in the same way in the reaction tower 14. The secondary treated liq. is sent to the heat exchanger 3 and then discharged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating cyanide-containing wastewater containing free cyan, cyan complex salt, cyan complex ion, metallic cyanide (hereinafter, this wastewater may be simply referred to as cyanide-containing wastewater). .

[0002]

2. Description of the Related Art As a method for decomposing cyanide in wastewater containing cyanide, various methods such as thermal decomposition and thermal hydration are proposed in addition to a method of treating with a chemical such as chlorine-based chemicals, ozone and iron salts. Has been done.

For example, Japanese Patent Publication No. 52-45679,
"A method for treating a tetracyanonickelate / cyan waste liquid, which is characterized by performing a heat treatment at a temperature of 150 ° C or higher" is disclosed.

Japanese Examined Patent Publication No. 55-50718 discloses that "cyan waste liquid containing iron cyanide complex ions is heated to 140 ° C. or higher in the presence of 2 mol or more of alkali metal hydroxide per iron cyanide complex ion / mol of the waste liquid. A method for treating a cyan waste liquid containing iron cyanide complex ions, which is characterized by performing heat treatment at a temperature ".

Japanese Unexamined Patent Publication (Kokai) No. 1-115490 basically discloses a method of pre-heating a cyan waste liquid and then thermally hydrolyzing it by heating steam under high temperature and high pressure.

Japanese Unexamined Patent Publication (Kokai) No. 1-194997 discloses that "a thermally decomposed solution obtained by thermally decomposing cyan in a cyan-containing solution is treated with an aerobic bacterium in which a facultative anaerobic bacterium is acclimatized and modified. The method of treating the contained liquid "is disclosed.

However, the treatment with chemicals has a limit to the cyanide concentration in the waste water which can be applied from the economical point of view, and the method of adding an iron salt to form a sparingly soluble complex salt requires treatment of sludge containing cyanide. And

Further, the thermal decomposition method requires a long time for completely decomposing the cyan compound depending on the kind of the (a) cyanide complex ion.
Part of cyan remains in the sludge after treatment, (b)
Therefore, a method of further biologically treating the treated water has been proposed (see Japanese Patent Laid-Open No. 1-194997), but this method requires treatment with specific bacterial cells and also requires nitrogen removal. In some cases, ammonia stripper or biological denitrification equipment is required. (C) When the treatment method is batch type, it is not suitable for treating a large amount of wastewater,
There are problems such as.

[0009] Generally, sludge containing cyanide needs to be treated as hazardous waste. Further, according to the conventional treatment method, the treatment of wastewater containing high-concentration cyanide containing cyanide complex ions has problems that the process becomes complicated and the treatment cost becomes high.

[0010]

Therefore, the present invention provides a new technique capable of decomposing substantially completely and inexpensively cyanogen in cyanide-containing wastewater without the need for additional treatment. The main purpose is that.

[0011]

The present inventor has conducted various studies in view of the current state of the art as described above, and as a result, in the case of performing wet oxidation treatment of cyanide-containing wastewater under specific conditions, It was found that the task could be almost achieved.

That is, the present invention provides the following methods: I. When the cyanide-containing wastewater is subjected to wet oxidation treatment, the following steps are continuously carried out; (1) The cyanide-containing wastewater is preheated to a temperature of up to 150 ° C by heat exchange with the secondary treatment liquid. After that, while maintaining a temperature of 150 ° C. or higher and a pressure at which the wastewater maintains a liquid phase, oxygen of less than the theoretical oxygen amount necessary for decomposing cyanide compounds, nitrogen compounds, organic substances and inorganic substances in the wastewater is generated. Wet oxidation treatment in the presence to obtain a primary treatment liquid, (2) a step of separating and removing sludge and / or metal components from the high temperature and high pressure primary treatment liquid, and (3) a high temperature and high pressure At least one of sulfuric acid, sulfur and a sulfur compound is added to the primary treatment liquid, and a cyan compound, a nitrogen compound, an organic compound in the treatment liquid in the presence of a catalyst containing at least one of a metal and a metal compound as an active ingredient are present. In the presence of oxygen in an amount equal to or more than the theoretical oxygen amount required for decomposing the organic substance and the inorganic substance, the wet oxidation treatment is performed while maintaining the temperature at 150 ° C. or more and the pressure at which the treatment liquid maintains the liquid phase. A step of obtaining a secondary treatment liquid.

II. When the cyanide-containing wastewater is subjected to wet oxidation treatment, the following steps are continuously carried out; (1) The cyanide-containing wastewater is preheated to a temperature of up to 150 ° C by heat exchange with the secondary treatment liquid. After that, while maintaining a temperature of 150 ° C. or higher and a pressure at which the wastewater maintains a liquid phase, oxygen of less than the theoretical oxygen amount necessary for decomposing cyanide compounds, nitrogen compounds, organic substances and inorganic substances in the wastewater is generated. Wet oxidation treatment in the presence to obtain a primary treatment liquid, (2) a step of separating and removing sludge and / or metal components from the high-temperature, high-pressure primary treatment liquid, (3) primary treatment At least one of sulfuric acid, sulfur and a sulfur compound is added to the liquid, and a cyanide compound, a nitrogen compound, an organic substance and an inorganic substance in the treatment liquid in the presence of a catalyst containing at least one of a metal and a metal compound as an active ingredient are present. In the presence of oxygen in an amount equal to or higher than the theoretical oxygen amount required for decomposing the volatile substance, while maintaining the temperature of 150 ° C. or higher and the pressure at which the treatment liquid maintains a liquid phase, the wet treatment is performed to obtain a secondary treatment liquid. And (4) a step of circulating at least a part of the gas phase obtained by gas-liquid separation of the secondary treatment liquid to the step (1) and using it as an oxygen source in the step (1).

III. When the cyanide-containing wastewater is subjected to wet oxidation treatment, the following steps are continuously carried out; (1) The cyanide-containing wastewater is preheated to a temperature of up to 150 ° C by heat exchange with the secondary treatment liquid. After that, while maintaining a temperature of 150 ° C. or higher and a pressure at which the wastewater maintains a liquid phase, oxygen of less than the theoretical oxygen amount necessary for decomposing cyanide compounds, nitrogen compounds, organic substances and inorganic substances in the wastewater is generated. A step of obtaining a primary treatment liquid by performing a wet oxidation treatment in the presence, (2) a step of separating and removing sludge and / or a metal component from the high-temperature high-pressure primary treatment liquid, (3) a primary treatment liquid At least one of sulfuric acid, sulfur and a sulfur compound is added to the mixture, and in the presence of a catalyst containing at least one of a metal and a metal compound as an active ingredient and in a treatment liquid, a cyanide compound, a nitrogen compound, an organic substance and an inorganic substance. A secondary treatment liquid is obtained by performing wet oxidation treatment in the presence of oxygen at a theoretical oxygen amount or more necessary for decomposing a substance and at a temperature of 150 ° C. or higher and a pressure at which the treatment liquid maintains a liquid phase. Step, and (4) a step of circulating at least a part of the liquid phase obtained by gas-liquid separation of the secondary treatment liquid to the step (3) at a ratio of 1 to 10 times the volume of the primary treatment liquid.

IV. When the cyanide-containing wastewater is subjected to wet oxidation treatment, the following steps are continuously carried out; (1) The cyanide-containing wastewater is preheated to a temperature of up to 150 ° C by heat exchange with the secondary treatment liquid. After that, while maintaining a temperature of 150 ° C. or higher and a pressure at which the wastewater maintains a liquid phase, oxygen of less than the theoretical oxygen amount necessary for decomposing cyanide compounds, nitrogen compounds, organic substances and inorganic substances in the wastewater is generated. A step of obtaining a primary treatment liquid by performing a wet oxidation treatment in the presence, (2) a step of separating and removing sludge and / or a metal component from the high-temperature high-pressure primary treatment liquid, (3) a primary treatment liquid At least one of sulfuric acid, sulfur and a sulfur compound is added to the mixture, and in the presence of a catalyst containing at least one of a metal and a metal compound as an active ingredient and in a treatment liquid, a cyanide compound, a nitrogen compound, an organic substance and an inorganic substance. A secondary treatment liquid is obtained by performing wet oxidation treatment in the presence of oxygen at a theoretical oxygen amount or more necessary for decomposing a substance and at a temperature of 150 ° C. or higher and a pressure at which the treatment liquid maintains a liquid phase. Process,
(4) At least a part of the gas phase obtained by gas-liquid separation of the secondary treatment liquid is circulated to the step (1) to obtain the step (1).
And (5) at least a part of the liquid phase obtained by gas-liquid separation of the secondary treatment liquid at a ratio of 1 to 10 times the amount of the secondary treatment liquid (3). The process of circulating to.

In the following, the inventions I to IV will be referred to as the first invention to the fourth invention, respectively.
When all inventions are summarized, they are simply referred to as the present invention.

The cyanide-containing wastewater targeted by the present invention is not particularly limited, and is used for various cyanide-containing wastewater discharged from the plating industry, surface nitriding treatment of steels, liquid carburizing treatment, chemical conversion treatment and the like. Examples of the cyan liquid to be used, cyan waste liquid discharged from the surface treatment process, and the like.
These cyan-containing wastewaters further include various organic and inorganic substances (organic acids such as formic acid and acetic acid), various nitrogen compounds such as ammonia (in this specification, nitrogen such as ammonia other than cyan compounds). The compound may be simply referred to as a nitrogen compound), or an organic chlorine compound such as trichlorethylene may also be contained.

The present invention further provides Mg, Al, Si,
P, Ca, Ti, Cr, Mn, Fe, Co, Ni, C
It is also useful for treating wastewater or sludge containing one or more metal components such as u, Zn and Cd. As wastewater or sludge containing such metal components, kitchen waste,
Household wastewater including paper, plastics, human waste, paper mill wastewater, pharmaceutical factory wastewater, wastewater generated by coal liquefaction or gasification, wastewater generated by thermal decomposition of municipal waste,
Sludge generated by biological treatment of industrial wastewater (anaerobic treatment, aerobic treatment), sewage sludge, wastewater generated by oilification of water sludge, photographic wastewater, printing wastewater, agricultural chemicals-related wastewater, dyeing wastewater, semiconductor manufacturing Examples include various wastewaters such as factory wastewater and sludges.

The first to fourth applications of the present application will be described below with reference to the drawings.
The invention will be described in detail. In the following, in order to simplify the description, a case of targeting cyanide-containing wastewater will be described.

I. First Invention of the Present Application FIG. 1 is a flow sheet showing an outline of the first invention of the present application.

The cyan-containing waste liquid from the waste water storage tank 1 is boosted to a predetermined pressure by the pump 2 and further compressed by the compressor 22.
After being mixed with the oxygen-containing gas whose pressure has been preliminarily increased by, and then heated by the heat exchanger 3 to a temperature of 150 ° C. or lower,
It is supplied to the primary reaction column 5 (hereinafter, simply referred to as the reaction column 5 unless otherwise required to distinguish it from the secondary reaction column 14 described later). As a heat source of the heat exchanger 3,
A high-temperature treatment liquid (secondary treatment liquid) from the secondary reaction tower 14 (hereinafter, simply referred to as the reaction tower 14 unless necessary to distinguish it from the primary reaction tower 5) is circulated. You can use it. When it is not possible to maintain a predetermined reaction temperature during the reaction, such as in winter, or when it is necessary to raise the temperature to a predetermined temperature, the wastewater is heated by the heater 4, or the steam generator 6 to the reaction tower 5 are used.
It is also possible to supply steam to. Further, in order to bring the temperature in the reaction tower 5 to a predetermined temperature at the time of start-up, the steam from the steam generator 6 is directly supplied into the reaction tower 5,
Alternatively, the wastewater can be heated by the heater 4 provided between the heat exchanger 3 and the reaction tower 5.

The temperature during the reaction is usually about 150 ° C. or higher,
More preferably, it is about 150 to 370 ° C. The higher the temperature during the reaction, the higher the rate of decomposition and removal of cyanide compounds, and the shorter the retention time of wastewater in the reaction tower, but on the other hand, the equipment cost increases, so the concentration of cyanide compounds in wastewater,
It may be determined by comprehensively considering the required degree of processing, operating cost, construction cost, and the like. The pressure during the reaction may be equal to or higher than the pressure at which the waste water can maintain the liquid phase at a predetermined temperature.

The amount of oxygen added to the cyan-containing wastewater is less than the theoretical amount of oxygen required to decompose cyanide compounds, nitrogen compounds, organic and inorganic substances into harmless products,
More preferably, it is about 0.01 to 0.5 times the theoretical oxygen amount. When the amount of oxygen is less than 0.01 times the theoretical amount of oxygen, the decomposition of cyanide compounds will be insufficient, while even if it exceeds 0.5 times, the further improvement of the decomposition efficiency is recognized. I can't. As an oxygen source, air, oxygen-enriched air, oxygen, and oxygen containing one or more of hydrogen cyanide, hydrogen sulfide, ammonia, sulfur oxides, organic sulfur compounds, nitrogen oxides, hydrocarbons, etc. as impurities Waste gas etc. are illustrated.

The reaction can be promoted by providing a plurality of trays inside the reaction tower 5.

Alternatively, the decomposition reaction can be promoted by filling the inside of the reaction tower 5 with a filler made of metal oxide, metal or the like. As such a packing, a known catalyst carrier can be used as it is. More specifically, alumina, silica, zirconia, titania, composite metal oxides containing these metal oxides (alumina-silica, alumina-silica-zirconia, titania-zirconia, etc.), these metal oxides or composites Examples thereof include metal oxide-based fillers containing a metal oxide as a main component and metal-based fillers such as iron and aluminum. Among these, zirconia, titania, and titania-zirconia, which have excellent durability, are more preferable. The shape of the filling body is not particularly limited, and may be any shape such as spherical shape, pellet shape, cylindrical shape, crushed piece shape, powder shape, and honeycomb shape.

Sludge (eg, black Fe ₃ O ₄ as a main component when the wastewater is iron cyanide complex ion-containing wastewater) may be accumulated in the reaction tower 5 with the passage of time. . In such a case, for example, the inside of the reaction tower 5 is cleaned or washed with air, water, steam, chemicals, etc.,
It is preferable to periodically remove the accumulated sludge.
Alternatively, the accumulated sludge can be
It is also possible to continuously withdraw from the lower part of the reaction tower 5. Similar cleaning or washing can be performed on other devices such as the heat exchanger 3 if necessary.

Cyan-containing waste water tends to form sludge at temperatures of about 150 ° C. or above, especially because the decomposition reaction of cyan is promoted. Therefore, in order to suppress the accumulation of sludge in the heat exchanger 3, a part of the cooled final treatment liquid 20 is supplied to the pump 21 with respect to the secondary treatment liquid 30 from the reaction tower 14 used for heat exchange. It is preferable to circulate and mix via line 33 to suppress the temperature of the cyanide-containing waste water in heat exchanger 3 to about 150 ° C. or lower.

Treatment liquid from the reaction tower 5 (primary treatment liquid)
Enters the gas-liquid separator 7 and is separated into a gas phase component 8 and a liquid phase component 9. The liquid phase component 9 is sent to the solid-liquid separator 10,
Solid-liquid separation is performed into a liquid phase 11 and a solid content (sludge) 12 under high temperature and high pressure. Solid-liquid separation can be performed by methods such as a carrier filling method, a filter filtration method, a magnetic separation method, a cyclone method, and a gravity sedimentation method. The solid-liquid separation can be continuously performed by configuring the solid-liquid separator 10 with two towers and alternately switching the separation operation and the washing operation.
Alternatively, the removal of sludge from the solid-liquid separator 10 can be performed periodically by a lock hopper method after a predetermined period.

The primary treatment liquid 11 after the solid-liquid separation is mixed with the gas phase component 8 separated as described above, sulfuric acid is added from the sulfuric acid storage tank 25, and the oxygen-containing gas whose pressure is previously increased by the compressor 22 is added. Are mixed and then supplied to a reaction tower 14 filled with a catalyst. Although not shown, the oxygen-containing gas may be heat-exchanged with the primary treatment liquid 11 or the liquid phase 32 from the heat exchanger 3 prior to the supply to the reaction tower 14, if necessary. The primary treatment liquid may contain a considerably large amount of alkali metal compound derived from wastewater. Therefore,
0.2 per 1 mol of total amount of alkali metal in the primary treatment liquid
The pH is adjusted by adding 5 to 0.55 times the amount of sulfuric acid. Further, the addition of this sulfuric acid can also suppress the production of nitrogen compounds (particularly NO ₂ -state nitrogen and NO ₃ -state nitrogen) in the reaction tower 14. Note that instead of or together with sulfuric acid, a substance capable of producing sulfuric acid under the reaction conditions in the reaction tower 14 (for example, sulfur, a sulfur compound such as ammonium thiosulfate) may be added to the first treatment liquid 11. In the present invention, unless otherwise specified,
The expression "sulfuric acid" is intended to also include these substances.

When the predetermined reaction temperature cannot be maintained during the reaction, such as in winter, the second treatment liquid is heated by the heater 13 or steam is supplied to the reaction tower 14 from a steam generator (not shown). You can also do it. Further, in order to bring the inside of the reaction tower 14 to a predetermined temperature at the time of start-up, heating can be performed by the heater 13, or steam can be directly fed into the reaction tower 14 to raise the temperature.

Treatment liquid from the reaction tower 14 (secondary treatment liquid)
As described above, after being used as a heat source in the heat exchanger 3 via the lines 30 and 31, it is sent to the cooler 15 and further to the gas-liquid separator 16, where the gas phase 17 and the liquid phase 18 And separated.

The liquid phase 18 obtained from the secondary treatment liquid is sent to the solid-liquid separator 19 and contains metal and / or metal contained in the liquid phase.
Alternatively, after the sludge component is removed, the final treatment liquid 20 is obtained. As a separation method in the solid-liquid separator 19, a known method such as a method using gravity settling, a method using a magnet, a method using a filter press, and a method using coagulating sedimentation can be adopted.

The difference between the primary reaction tower 5 and the secondary reaction tower 14 is that the latter is filled with the catalyst supported on the carrier.

Examples of the catalytically active component include iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and water-insoluble or sparingly water-soluble compounds of these metals. More specific examples of such compounds include oxides (cobalt oxide, iron oxide, etc.), chlorides (ruthenium dichloride,
Platinum dichloride, etc.), sulfides (ruthenium sulfide, rhodium sulfide, etc.) and the like. These metals and their compounds may be used alone or in combination of two or more kinds. These catalytically active components are used in a state of being supported on known metal oxide carriers and metal carrier carriers according to a conventional method. The metal oxide carrier and the metal carrier are not particularly limited, and those known as catalyst carriers can be used. Examples of the metal oxide carrier include alumina, silica, zirconia, titania, composite metal oxides containing these metal oxides (alumina-silica, alumina-silica-zirconia, titania-zirconia, etc.), these metal oxides or composite metal oxides. Examples of the metal carrier include a metal oxide-based carrier containing a substance as a main component, and examples of the metal carrier include iron and aluminum. Among these carriers, zirconia, titania and titania-zirconia, which have excellent durability, are more preferable.

The shape of the supported catalyst is not particularly limited, and examples thereof include sphere, pellet, column, crushed piece, powder, and honeycomb. In the case of using a fixed bed, the reaction tower volume in the case of using such a supported catalyst packed is such that the space velocity of the liquid is about 0.5 to 10 Hr ⁻¹ , more preferably ¹ to 5 Hr.
^It is good to set it to about ^-1 . The size of the supported catalyst used in the fixed bed is usually about 3 to 50 mm, more preferably about 5 to 25 mm in the case of a spherical shape, a pellet shape, a cylindrical shape, a crushed piece shape, a powder shape, or the like. Further, as the honeycomb structure when the catalyst is supported on the honeycomb-shaped carrier and used, an opening having any shape such as a quadrangle, a hexagon and a circle is used. The area per unit volume, the aperture ratio, etc. are not particularly limited, but usually the area per unit volume is 200 to 800 m ² / m ³ , and the aperture ratio is 40.
Use about 80%. Examples of the material for the honeycomb structure include the same metal oxides and metals as those described above, and zirconia, titania, and titania-zirconia having excellent durability are more preferable.

When a fluidized bed is formed in the reaction tower 14, the amount of the supported catalyst capable of forming a fluidized bed in the reaction tower 14, that is, usually 0.01 to 2 based on the weight of cyanide-containing wastewater is used.
About 0%, more preferably about 0.05 to 10% is used by suspending it in a slurry in the primary treatment liquid. When a fluidized bed is used, the supported catalyst is supplied to the reaction tower 14 in a state of being suspended in a slurry in the primary treatment liquid, and the catalyst is removed from the treated liquid discharged outside the tower after the completion of the reaction. It is separated and collected by an appropriate method such as sedimentation or centrifugation and used again.
Therefore, considering the ease of separation and recovery of the catalyst from the treated liquid, the particle size of the supported catalyst used in the fluidized bed is
More preferably, it is about 0.15 to 0.5 mm.
The amount of the catalytically active metal supported is not particularly limited, but is usually in the range of about 0.01 to 25% by weight of the carrier, more preferably about 0.1 to 3%.

II. Second Invention of the Present Application FIG. 2 is a flow sheet showing an outline of the second invention of the present application.

In the second invention of the present application, the gas-liquid mixture from the reaction tower 14 is separated into a gas phase and a liquid phase by the gas-liquid separator 23, and at least a part of the gas phase containing residual oxygen that has not been used in the reaction. Except that it is circulated to the reaction column 5 via line 24 and used as its oxygen source, and that the remainder of the gas phase is circulated to the reaction column 14 via line 27 branching from line 24. There is no difference from the first invention of the present application.

That is, in the second invention of the present application, at least the gas phase obtained in the gas-liquid separator 23 is adjusted so that the amount of oxygen in the reaction column 5 becomes 0.01 to 0.5 times the theoretical amount of oxygen. A part is circulated to the reaction tower 5 via the line 24. At this time, the liquid phase is sent to the heat exchanger 3 via lines 30 and 31.
Therefore, oxygen cannot be supplied from the compressor 22 to the cyan-containing wastewater supplied to the reaction tower 5, but only to the primary treatment liquid supplied to the reaction tower 14.

As a result, the practical effect of reducing the amount of oxygen used is achieved.

III. Third Invention of the Present Application FIG. 3 is a flow sheet showing an outline of the third invention of the present application.

In the third invention of the present application, a part of the secondary treatment liquid separated by the gas-liquid separator 23 is circulated to the reaction tower 14 via a line 29 branching from a line 30 and a pump 26, and the reaction is performed. Except for the fact that at least a part of the unused oxygen-containing gas phase is circulated to the reaction column 14 via the lines 24 and 27 and is used as a part of the oxygen source, it is substantially the present invention. 1 There is no difference from the invention.

Due to the partial circulation of the secondary treatment liquid, the liquid linear velocity in the reaction tower 14 is increased, and the adhesion of the metal component remaining in the primary treatment liquid to the catalyst surface is reduced.
Due to the increase in the flow rate in the reaction tower 14 and the uniform temperature distribution in the reaction tower 14, excellent catalytic activity is maintained for a long period of time.

The circulation amount of the secondary treatment liquid is appropriately determined according to the degree of progress of the decrease in catalyst activity, but is usually the reaction tower 14.
The amount is about 1 to 20 times, and more preferably about 1 to 10 times the amount of the primary treatment liquid supplied to the.

When the temperature inside the tower becomes too high due to the heat generated by the decomposition reaction in the reaction tower 14, a heat exchanger (not shown) is arranged between the gas-liquid separator 23 and the pump 26. By performing heat recovery by performing the heat recovery, the temperature of the secondary treatment liquid in the reaction tower 14 and in the circulation can be adjusted.

IV. Fourth Invention of the Present Application FIG. 4 is a flow sheet showing an outline of the fourth invention of the present application.

The fourth invention of the present application is a line 2 for branching a part of the liquid phase separated by the gas-liquid separator 23 from the line 30.
9 is substantially the same as the second invention of the present application except that it is circulated to the reaction tower 14 via the pump 9 and the pump 26.

By partially circulating the liquid phase to the reaction tower 14, the same effect as the third invention of the present application is achieved. Further, the same effect as that of the second invention of the present application is achieved by partially circulating the gas phase to the reaction tower 5.

[0049]

EFFECTS OF THE INVENTION According to the method of the present invention, the cyanide complex ions and cyanide in the wastewater are substantially completely decomposed, and they are hardly contained in the final treatment liquid and the sludge produced. Further, nitrogen oxides, organic substances and inorganic substances in the waste water are also substantially completely decomposed, so that a stable waste water treatment effect is achieved. .

Substantially no harmful components are found in either the gas phase or the liquid phase after the final gas-liquid separation. When an oxygen-containing waste gas is used as an oxygen source, the presence of harmful components derived from the waste gas is substantially not recognized in either the gas phase or the liquid phase. Moreover, the sludge formed is excellent in sedimentation and easy to handle.

Furthermore, according to the method of the present invention, since the processing flow is extremely simple, the processing cost (equipment cost, operating cost, etc.) is significantly reduced, and the process control is facilitated.

[0052]

EXAMPLES Examples and comparative examples will be shown below to further clarify the features of the present invention.

Example 1 A cyan complex ion-containing waste liquid having the composition shown in Table 1 was treated according to the first invention of the present application according to the flow shown in FIG.

[0054]

[Table 1]

Cyan-containing wastewater having a pH of 10.6 was subjected to a space velocity of 1.0 Hr ^-1 (based on empty column) and a mass velocity of 14.15 m.
Air was supplied at a space velocity of 3.4 Hr ^-1 (empty tower standard, standard state conversion) while supplying ³ m- ² Hr ^-1 to the reaction tower 5. The air supply amount is the theoretical oxygen amount (82.5 Nm ³ / k
It was an amount corresponding to 0.0103 times the amount of 1).

In the reaction, waste water and air are introduced into the inlet side of the heat exchanger 3, and the temperature of the gas-liquid mixture at the outlet side of the heat exchanger 3 (the inlet side of the reaction tower 5) is 150 ° C.
As described above, a part of the final treatment liquid 20 was circulated and mixed with the treatment liquid from the reaction tower 14 flowing through the line 30 by the pump 21 through the line 33 to control the temperature. Also,
By supplying steam from the steam generator 6 to the reaction tower 5, the temperature inside the reaction tower 5 is 220 ° C. and the pressure is 30 kg · cm.
^Held at ^-2 . The reaction tower 5 was equipped with trays every 70 cm.

In the primary treatment liquid having a pH of 10.6 from the reaction tower 5, the metal components in the initial waste water are contained in the lower part of the reaction tower 5 and the high pressure type solid-liquid separator 10 (in this embodiment, titanium burning). It was pulled out from the lower part (using a metal filter).
Primary treatment liquid 1 obtained at the outlet of solid-liquid separator 10
Table 2 shows the composition of 1 and the like.

[0058]

[Table 2]

Subsequently, the content of alkali metal in the first treatment liquid 11 (Na = 0.0909 mol·l ⁻¹ and K = 0.3)
22 mol · l ⁻¹ total 1.231 mol · l ⁻¹ ) 1/2
0.62 mol·l ⁻¹ sulfuric acid equivalent to double amount is added to the sulfuric acid storage tank 2
5 to the first treatment solution, and then add it to a space velocity of 0.7.
5Hr ^-1 (empty tower standard) and mass velocity 14.15m ³ ·
While supplying m ⁻² · Hr ⁻¹ to the reaction tower 14, air was supplied at a space velocity of 90.4 Hr ⁻¹ (empty tower standard, standard state conversion). The air supply amount was an amount equivalent to 1.1 times the theoretical oxygen amount. In addition, a spherical catalyst (diameter 4 to 6 mm) in which 2% of the weight of the carrier was supported on ruthenium was loaded in the reaction tower 14, and the temperature and the pressure were maintained almost the same as in the reaction tower 5.

Table 3 shows the composition of the secondary treatment liquid from the reaction tower 14 and the like.

[0061]

[Table 3]

Next, the secondary treatment liquid was subjected to coagulation-precipitation treatment at a temperature of 25 ° C. under normal pressure.

The composition of the final treatment liquid 20 thus obtained is shown in Table 4.
Shown in

[0064]

[Table 4]

Note: In addition, cadmium and its compounds, total chromium, lead, mercury, etc. were not detected as metal components.

As is clear from the comparison between Tables 1 and 4, according to the method of the present invention, the cyan component is decomposed substantially completely, and the ammonia and formic acid produced from cyan during the reaction are also decomposed. In the end, it was almost decomposed. Most of the metal components were removed by the lower part of the reaction tower 5 and the solid-liquid separator (titanium sintered metal filter) 10.
Further, the gas phase 17 does not contain cyan and ammonia,
It consisted essentially of O ₂ , N ₂ and CO ₂ .

The sludge withdrawn from the reaction tower 5 and the solid-liquid separator 10 has a black color and contains Fe ₂ O ₃ and Fe ₃ O ₄ as main components, and P ₂ O ₅ and N as other components.
a ₂ O, ZnO, and the like SiO _2, CN content 1 mg · kg
^{When it was -1} or less, the precipitate had good sedimentation property.

Comparative Example 1 Cyan-containing wastewater having the composition shown in Table 1 was treated in the same manner as in Example 1 except that air was not supplied to the reaction tower 5.

The properties of the primary treatment liquid, the secondary treatment liquid and the liquid after the coagulation-sedimentation treatment (final treatment liquid) are shown in Table 5, Table 6 and Table 7, respectively.

[0070]

[Table 5]

[0071]

[Table 6]

[0072]

[Table 7]

T-CN in the primary treatment liquid was 0.48 m
g · ^1-1 , cyan is not completely processed.
Further, NH ₃ -N of the primary treatment solution is, 6690mg ·
The l ^-1 and TOD were 24800 mg · l ^-1 .

The sludge withdrawn from the lower part of the reaction tower 5 and the solid-liquid separator 10 has a black color and contains Fe ₃ O ₄ as a main component and P ₂ O ₅ , Na ₂ O and Z as other components.
Containing nO, SiO _2, etc., the CN content is 179 mg.
The precipitation was kg ^-1 , and the sedimentation was low.

The water quality after the secondary treatment was substantially the same as in Example 1.

Comparative Example 2 The cyanide-containing wastewater having the composition shown in Table 1 was treated in the same manner as in Example 1 except that sulfuric acid was not supplied to the primary treated water supplied to the reaction tower 14.

The properties of the secondary treatment liquid and the liquid after the aggregation and precipitation (final treatment liquid) are shown in Tables 8 and 9, respectively.

[0078]

[Table 8]

[0079]

[Table 9]

As is clear from the comparison between Example 1 and this comparative example, the addition of sulfuric acid to the secondary treatment liquid suppresses the production of all nitrogen components, especially NO ₂ and NO ₃ nitrogen. The effect is achieved.

Example 2 and Comparative Examples 2 to 8 According to the flow shown in FIG. 2, the cyan complex ion-containing waste liquid having the composition shown in Table 1 was treated by the second invention of the present application.

More specifically, the gas-liquid mixed phase from the reaction tower 14 is separated into a gas phase and a liquid phase by the gas-liquid separator 23, and a part of the gas phase is increased to 0.25 times the theoretical oxygen amount. It is circulated to the reaction tower 5 through the line 24 at a corresponding ratio, and the line 3
As shown in Table 10, by controlling the circulation amount of the secondary treatment liquid to the reaction tower 5 via 0 and the line 33,
Wet oxidative decomposition of cyanide-containing wastewater was performed in the same manner as in Example 1 except that the temperature of the gas-liquid mixture on the outlet side of the heat exchanger 3 (the inlet side of the reaction tower 5) was adjusted variously.

[0083]

[Table 10]

The amount of sludge produced in the heat exchanger, the heater and the pipes thereof due to the decomposition of the cyan complex component is based on the amount produced in Example 1 (the outlet side temperature of the heat exchanger 3 is 150 ° C.) (100). Are shown in Table 11.

[0085]

[Table 11]

When the cyanide-containing wastewater is heated so that the temperature at the outlet of the heat exchanger 3 (the inlet of the reaction tower 5) exceeds 150 ° C., the sludge in the heat exchanger, the heater and these pipes Since the production amount increases, the pressure loss increases. Therefore, it is necessary to regularly remove the generated sludge from these devices by jet cleaning, chemical cleaning or the like.

That is, the time during which stable operation can be continuously performed is only about 1/30 in Comparative Example 8 as compared with Example 1. In other words, the outlet side temperature of the heat exchanger 3 is set to 15
By adjusting the temperature to 0 ° C. or less, the operation of the entire apparatus can be stably performed for a long period while suppressing the generation of sludge.

Comparative Example 9 and Examples 3 to 6 According to the flow shown in FIG.
The gas phase obtained by gas-liquid separation of the gas-liquid mixed phase from 4 is line 2
The wet oxidation treatment of the cyanide-containing wastewater is performed in the same manner as in Example 1 except that the amount of oxygen supplied to the reaction column 5 (relative oxygen amount when the theoretical oxygen amount is 1) is circulated from 4 to be variously changed. It was Table 12 also shows the results of Example 2.

[0089]

[Table 12]

In the case of Comparative Example 9 in which the air supply amount was less than 0.01 times the theoretical oxygen amount, 0.40 mg · l ⁻¹ of T-CN was detected in the primary treatment liquid. , T-CN was detected in the sludge 12 at 112 mg · kg ⁻¹ .

On the other hand, in Examples 1 to 6, T-CN in the primary treatment liquid was 0.1 mg · l ⁻¹ or less, and T-CN in the sludge 12 was ¹ mg · l ^−1. It was below kg ^-1 .

Even when air is supplied in an amount equal to or more than 0.5 times the theoretical oxygen amount, T-CN in the treated liquid is also supplied.
Was 0.1 mg · l ^-1 or less, but it is not preferable because it has disadvantages such as an increase in compression power cost and an increase in heating fuel (or vapor amount) due to an increase in liquid evaporation amount in the system. .

Regarding the properties of the secondary treatment liquid and the waste gas, in both Comparative Example 9 and Examples 2 to 6,
It was almost the same as in Example 1.

Example 7 The cyan complex ion-containing waste liquid having the composition shown in Table 1 was treated according to the third invention of the present application according to the flow shown in FIG.

That is, the reaction tower 5 was filled with titania spheres having a diameter of 5 mm, and the secondary treatment liquid was added to the gas-liquid separator 23.
Wet oxidation of the cyanide-containing waste liquid in the same manner as in Example 1 except that the liquid phase was separated into the gas phase and the liquid phase by 1. Processed.

The components contained in the primary treatment liquid from the reaction tower 5 and the sludge 12 obtained in the solid-liquid separator 10 were analyzed as in Example 1.
Same as those of (treated solution T-CN = 0.1 mg · l
^-1 or less, CN content in sludge = 1 mg · kg ^-1 or less), the residence time in the reaction tower 5 is
It was shortened by about 15% as compared with Example 1. Further, the black sludge 12 obtained by the solid-liquid separator 10 was a sediment having a good sedimentation property.

Similar effects were achieved when zirconia spheres or titania-zirconia spheres were used instead of the above titania spheres.

By circulating the liquid phase of the secondary treatment liquid obtained in the reaction tower 14 after gas-liquid separation through the line 29, the time until NH ₃ -N is detected in the final treatment liquid is reached. Was extended about 4 times as compared with the case of Example 1.

Examples 8 to 11 Example 1 except that the treatment temperature in the reaction tower 5 is variously changed.
In the same manner as in Example 1, the cyan complex ion-containing waste liquid having the composition shown in Table 1 was treated so that the same water quality as shown in Table 2 of Example 1 was obtained. Table 13 shows the results when the residence time in the reaction tower 5 in Example 1 was 100.

[0100]

[Table 13]

Examples 12 to 22 Cyan-containing wastewater having the composition shown in Table 1 was wet-oxidized by the fourth invention of the present application according to the flow chart shown in FIG.

That is, after the gas-liquid mixed phase from the reaction tower 14 is gas-liquid separated, the gas phase containing oxygen equivalent to 0.02 times the theoretical oxygen quantity is circulated to the reaction tower 5 as an oxygen source. A gas phase corresponding to three times the amount of the primary treatment liquid was circulated in the reaction tower 14. Other than that the composition of the catalyst was changed, the procedure of Example 1 was repeated.

Table 1 shows the properties of the catalyst and the secondary treatment liquid used.
4 shows.

[0104]

[Table 14]

Example 23 The cyan complex ion-containing waste liquid having the composition shown in Table 1 was treated according to the second invention of the present application according to the flow shown in FIG.

Cyan-containing wastewater having a pH of 10.6 was subjected to a space velocity of 1.0 Hr ^-1 (based on empty column) and a mass velocity of 14.15 m.
^While supplying the reaction tower 5 with ³ · m ⁻² · Hr ⁻¹ , the reaction tower 14
The gas phase obtained from
It was circulated and supplied to the reaction tower 5 at r ⁻¹ (empty tower standard, standard state conversion). The gas-phase circulation supply amount is the theoretical oxygen amount (82.5 Nm
³ / kl) and the amount corresponding to 0.0103 times.

The treatment of the primary treatment liquid in the reaction tower 14 and the gas-liquid separation were carried out in the same manner as in Example 1.

The results for the primary treatment liquid, the secondary treatment liquid and the final treatment liquid were almost the same as in Example 1.

Example 24 The cyan complex ion-containing waste liquid having the composition shown in Table 1 was treated according to the third invention of the present application according to the flow shown in FIG.

The cyan complex ion-containing waste liquid was treated in the reaction tower 5 in the same manner as in Example 1, then sulfuric acid was added to the primary treatment liquid, and then treated in the reaction tower 14. However, the reaction tower 14
After the gas-liquid separator 23 was used for gas-liquid separation of the treatment liquid from Example 1, the obtained liquid phase was circulated and mixed with the primary treatment liquid. At this time, the mixed liquid of the primary treatment liquid and the circulating liquid phase was introduced into the reaction tower 14 at a space velocity of 3.6 Hr ^-1 (empty column standard) and a mass velocity of 42.5 m ^3.
-Supplied with m ^-2 and Hr ^-1 .

In this method, the water quality of the treatment liquid from the reaction tower 5 and the water quality of the final treatment liquid were almost the same as those of Example 1, but the water quality of the treatment liquid from the reaction tower 14 was the same as that of Example 1. It was further improved compared to the case.

In this method, in particular, the increase in the liquid linear velocity in the reaction tower 14 reduces the adhesion of the metal component to the catalyst surface, and it is presumed that the liquid film resistance on the catalyst surface decreases. Further, due to the uniform temperature distribution in the reaction tower 14, a high degree of catalytic activity was maintained for a long time. More specifically, the time until NH ₃ —N was detected in the final treatment liquid was extended by about 4.5 times as compared with the case of Example 1.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an outline of the first invention of the present application.

FIG. 2 is a flow sheet showing an outline of the second invention of the present application.

FIG. 3 is a flow sheet showing an outline of a third invention of the present application.

FIG. 4 is a flow sheet showing an outline of a fourth invention of the present application.

[Explanation of symbols]

 1 ... Waste water storage tank 2 ... Pump 3 ... Heat exchanger 4 ... Heating device 5 ... Primary reaction tower 6 ... Steam generator 7 ... Gas-liquid separator 8 ... Gas-phase component 9 ... Liquid-phase component 10 ... Solid-liquid separator 11 ... Primary treatment liquid 12 ... Sludge 13 ... Heater 14 ... Secondary reaction tower 15 ... Cooler 16 ... Gas-liquid separator 17 ... Gas phase 18 ... Liquid phase 19 ... Solid-liquid separator 20 ... Final treatment liquid 21 ... Pump 22 ... Compressor 23 ... Gas-liquid separator 24 ... Gas phase circulation line 25 ... Sulfuric acid storage tank 26 ... Pump 27 ... Gas phase circulation line 29 ... Liquid phase circulation line 30 ... Liquid phase circulation line 31 ... Liquid phase circulation line 32 ... Liquid phase circulation line 33 ... Final treatment liquid circulation line

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/38 B01J 23/38 M 23/42 23/42 M 23/44 23/44 M 23 / 46 23/46 M 301 301M 311 311M 23/52 23/52 M 23/70 23/70 M 23/72 23/72 M 23/745 C02F 1/58 CDCN 23/75 B01J 23/74 301M 23/755 311M C02F 1/58 CDC 321M

Claims (16)

[Claims] 1. A method characterized in that the following steps are continuously carried out when wet treating cyanide-containing wastewater: (1) The cyanide-containing wastewater is preheated to 150 ° C. by heat exchange with a secondary treatment liquid. Theoretical oxygen necessary to decompose cyanide compounds, nitrogen compounds, organic substances and inorganic substances in the wastewater while maintaining the liquid phase of the wastewater at a temperature of 150 ° C or higher after heating A step of obtaining a primary treatment liquid by performing a wet oxidation treatment in the presence of less than an amount of oxygen, (2) a step of separating and removing sludge and / or metal components from the high-temperature and high-pressure primary treatment liquid, and ( 3) At least one of sulfuric acid, sulfur and a sulfur compound is added to a high temperature and high pressure primary treatment liquid, and in the presence of a catalyst containing at least one of a metal and a metal compound as an active ingredient and a cyanide and nitrogen in the treatment liquid. Wet oxidation treatment in the presence of oxygen at a theoretical oxygen amount or more necessary for decomposing compounds, organic substances and inorganic substances, while maintaining a temperature of 150 ° C. or higher and a pressure at which the treatment liquid maintains a liquid phase. The step of obtaining the secondary treatment liquid by. 2. The method for treating cyanide-containing wastewater according to claim 1, wherein steam is fed into the reaction vessel of step (1) to raise the temperature. 3. The addition amount of sulfuric acid in the step (3) is 0.25 per 1 mol of the total amount of alkali metal in the primary treatment liquid.
The method for treating cyanide-containing wastewater according to claim 1, wherein the amount is ˜0.55 times. 4. The catalytically active component in step (3) is iron,
The cyan according to claim 1, which is at least one selected from the group consisting of cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and compounds of these metals which are insoluble or sparingly soluble in water. Treatment method of wastewater containing. 5. A method characterized in that the following steps are continuously carried out during wet oxidation treatment of cyanide-containing wastewater; (1) The cyanide-containing wastewater is preheated to 150 ° C. by heat exchange with a secondary treatment liquid. Theoretical oxygen necessary to decompose cyanide compounds, nitrogen compounds, organic substances and inorganic substances in the wastewater while maintaining the liquid phase of the wastewater at a temperature of 150 ° C or higher after heating A step of obtaining a primary treatment liquid by performing a wet oxidation treatment in the presence of less than an amount of oxygen, (2) a step of separating and removing sludge and / or a metal component from the high temperature / high pressure primary treatment liquid, (3) ) At least one of sulfuric acid, sulfur and a sulfur compound is added to the primary treatment liquid, and in the presence of a catalyst containing at least one of a metal and a metal compound as an active ingredient and in the treatment liquid, a cyanide compound, a nitrogen compound and an organic compound. Stuff Quality and inorganic substances in the presence of more than the theoretical amount of oxygen required to decompose oxygen in the presence of a temperature of 150 ℃ or more and the pressure of the treatment liquid to maintain a liquid phase, by wet oxidation treatment Step (4) of obtaining the treatment liquid, and (4) at least a part of the gas phase obtained by gas-liquid separation of the secondary treatment liquid is circulated to the above-mentioned step (1) and used as an oxygen source in the step (1). Process. 6. The method for treating cyanide-containing wastewater according to claim 5, wherein steam is fed into the reaction vessel of step (1) to raise the temperature. 7. The addition amount of sulfuric acid in the step (3) is 0.25 per 1 mol of the total amount of alkali metal in the primary treatment liquid.
The method for treating cyanide-containing wastewater according to claim 5, wherein the amount is ˜0.55 times. 8. The catalytically active component in step (3) is iron,
The cyan according to claim 5, which is at least one selected from the group consisting of cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and compounds of these metals which are insoluble or sparingly soluble in water. Treatment method of wastewater containing. 9. A method characterized in that the following steps are continuously carried out when performing wet oxidation treatment of cyanide-containing wastewater; (1) The cyanide-containing wastewater is preheated to 150 ° C. by heat exchange with the secondary treatment liquid. Theoretical oxygen required to decompose cyanide compounds, nitrogen compounds, organic substances and inorganic substances in the wastewater while maintaining the liquid phase of the wastewater at a temperature of 150 ° C or higher after heating to A step of obtaining a primary treatment liquid by performing a wet oxidation treatment in the presence of less than an amount of oxygen, (2) a step of separating and removing sludge and / or a metal component from the high temperature and high pressure primary treatment liquid, (3) At least one of sulfuric acid, sulfur and a sulfur compound is added to the primary treatment liquid, and a cyanide compound, a nitrogen compound and an organic substance are present in the treatment liquid in the presence of a catalyst containing at least one metal and a metal compound as an active ingredient. And a secondary treatment by performing a wet oxidation treatment in the presence of oxygen at a theoretical oxygen amount or more necessary for decomposing the inorganic substance while maintaining a temperature of 150 ° C. or more and a pressure at which the treatment liquid maintains a liquid phase. A step of obtaining a liquid, and (4) at least a part of the liquid phase obtained by gas-liquid separation of the secondary treatment liquid is circulated to the step (3) at a ratio of 1 to 10 times that of the primary treatment liquid. Process. 10. The method for treating cyanide-containing wastewater according to claim 9, wherein steam is fed into the reaction vessel of step (1) to raise the temperature. 11. The amount of sulfuric acid added in step (3) is 0.2 per mol of the total amount of alkali metals in the primary treatment liquid.
The method for treating cyanide-containing wastewater according to claim 9, wherein the amount is 5 to 0.55 times. 12. The catalytically active component in step (3) is
10. At least one selected from the group consisting of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and compounds of these metals which are insoluble or sparingly soluble in water. Method for treating wastewater containing cyanide. 13. A method characterized in that the following steps are continuously carried out when wet treating cyanide-containing wastewater: (1) The cyanide-containing wastewater is preheated to 150 ° C. by heat exchange with a secondary treatment liquid. Theoretical oxygen required to decompose cyanide compounds, nitrogen compounds, organic substances and inorganic substances in the wastewater while maintaining the liquid phase of the wastewater at a temperature of 150 ° C or higher after heating to A step of obtaining a primary treatment liquid by performing a wet oxidation treatment in the presence of less than an amount of oxygen, (2) a step of separating and removing sludge and / or a metal component from the high temperature and high pressure primary treatment liquid, (3) At least one of sulfuric acid, sulfur and a sulfur compound is added to the primary treatment liquid, and a cyanide compound, a nitrogen compound and an organic substance are present in the treatment liquid in the presence of a catalyst containing at least one metal and a metal compound as an active ingredient. Quality and inorganic substances in the presence of more than the theoretical amount of oxygen required to decompose oxygen in the presence of a temperature of 150 ℃ or more and the pressure of the treatment liquid to maintain a liquid phase, by wet oxidation treatment A step of obtaining a treatment liquid,
(4) At least a part of the gas phase obtained by gas-liquid separation of the secondary treatment liquid is circulated to the step (1) to obtain the step (1).
And (5) at least a part of the liquid phase obtained by gas-liquid separation of the secondary treatment liquid at a ratio of 1 to 10 times the amount of the secondary treatment liquid (3). The process of circulating to. 14. The method for treating cyanide-containing wastewater according to claim 13, wherein steam is fed into the reaction vessel of step (1) to raise the temperature. 15. The amount of sulfuric acid added in step (3) is 0.2 per 1 mol of the total amount of alkali metals in the primary treatment liquid.
The method for treating cyanide-containing wastewater according to claim 13, wherein the amount is 5 to 0.55 times. 16. The catalytically active component in step (3) is
14. At least one selected from the group consisting of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum, copper, gold and tungsten, and compounds of these metals which are insoluble or sparingly soluble in water.
The method for treating wastewater according to.