JPH05309375A - Method for repeated thermal hydrolysis treatment of cyan waste solution and apparatus therefor - Google Patents

Abstract

PURPOSE:To develop excellent effect in the lowering of the concn. of cyan by repeating operation such that a treated waste solution is discharged at every one batch of thermal hydrolysis treatment and batch treatment is performed a specific number of times during a period when the concn. of cyan is kept within a control limit value to discharge sludge. CONSTITUTION:In the thermal hydrolysis treatment of a cyan waste solution, the cyan waste solution W to be treated containing a cyan complex ion is adjusted to its pH at 10 or more, if necessary to be introduced into a pressure container 1 and heated to 140-250 deg.C under predetermined gauge pressure according to a batchwise system to be held to said temp. to decompose the cyan complex ion into ammonia and formate and the heavy metal bonded to cyan is removed as heavy metal oxide sludge. The treated waste solution is discharged out of the pressure container 1 at every one batch of thermal hydrolysis treatment and this thermal hydrolysis treatment is batchwise performed 1-5 times during a period when the concn. of cyan is kept within a predetermined control limit value and, thereafter, sludge is discharged out of the system from the bottom part of the pressure container 1.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a heavy metal cyanide such as iron, copper, nickel, zinc, cadmium, manganese, chromium, etc., which is discharged in the surface nitriding treatment of steel and liquid carburizing, surface treatment such as plating and the like. The present invention relates to a novel wastewater treatment method capable of reducing the cyanide concentration in an industrial waste liquid containing complex ions to an extremely low level by a thermal hydrolysis treatment method, and an apparatus for carrying out this treatment method. .. In the following description of the present invention, a waste liquid containing cyan ions and / or complex ions is sometimes abbreviated as a cyan-containing treated waste liquid or simply a waste liquid.

[0002]

2. Description of the Related Art As a method for treating a cyanide-containing waste liquid containing a heavy metal cyanide complex salt, there is the invention disclosed in Japanese Patent Publication No. 55-50718 (Japanese Patent Application No. 47-39405). The method of the present invention, as the title of the invention is described as “a method for treating a cyan waste liquid containing iron cyan complex ions”, provides an iron cyan waste liquid containing iron cyan complex ions such as ferrocyan ion and ferricyan ion. It is a limited invention and belongs to what is called the thermal hydrolysis treatment method at present including the method of the present invention. The invention disclosed in the above-mentioned publication heats a cyan waste liquid containing iron cyanide complex ions at a temperature of 140 ° C. or higher in the presence of 2 mol or more of alkali metal hydroxide per 1 mol of iron cyanide complex ions in the waste liquid. It is characterized in that it is treated, and it is described that the treatment time can be remarkably shortened when treated at a temperature of 150 ° C. or higher.

The decomposition of cyanide by thermally hydrolyzing a high-concentration cyanide-containing waste liquid (for example, a plating waste liquid) containing each ion such as copper, zinc, and nickel is disclosed in the technical magazine "PPM" 1977 published by Nihon Kogyo Shimbun. 58th of August issue
This is a known technique as described on page 68. The matters described in the above journals are summarized below. The principle of the thermal hydrolysis treatment is that a cyan compound is heated and held in a pressure vessel, and cyan is converted to ammonia (NH ₃ ) and formate (HCO).
It is a method of decomposing it into OK) and detoxifying it so that it can be discharged.
When applied to potassium cyanide, which is the simplest reaction formula, it is represented by the following reaction formula (1). KCN + 2H ₂ O → NH ₃ + HCOOK (1) Metal cyanide complex salts of iron (Fe), zinc (Zn), nickel (Ni), etc. require the addition of an alkali to proceed with the reaction, and react in the presence of an alkali. Progresses and is hydrolyzed to ammonia, formate and metal oxides and metal hydroxides. The reaction formula when K ₄ Fe (CN) ₆ (yellow blood salt) is used is shown in (2) below. K ₄ Fe (CN) ₆ + 12NaOH + 66H ₂ O + O ₂ = 36NH ₃ + 2Fe ₃ O ₄ + 12HCOONa + 24HCOOK (2) The above reaction formula (2) relates to a waste liquid in which the yellow blood salt as an iron-cyan complex salt is present alone. However, in a plating plant or a steel soft nitriding treatment facility, potassium is expensive, so sodium (Na) is used instead of potassium. When a cyanide complex salt of sodium and iron is used instead of the yellow blood salt as the iron cyanide complex salt, K in the above reaction formula (2) may be replaced by Na.

Heavy metals other than iron used in a plating plant or the like include nickel (Ni), zinc (Zn), copper (Cu), cadmium (Cd), gold (Au) and silver (A).
g), chromium (Cr), and several other types, of which, typically, four types of nickel, zinc, copper, and cadmium, and sodium are represented by the reaction formulas of the usual thermal hydrolysis treatment of each cyan complex salt. Examples are shown in (3) to (6) below. _{Na 2 NI (CN) 4 +} 2NaOH + 8H 2 O = 4NH 3 + Ni (OH) 2 + 4HCOONa ······ (3) Na 2 Zn (CN) 4 + 2NaOH + 8H 2 O = 4NH 3 + Zn (OH) 2 + 4HCOONa ··· _{··· (4) Na3Cu (CN)} 4 + NaOH + 8H 2 O = 4NH 3 + Cu (OH) + 4HCOONa ······· (5) Na 2 Cd (CN) 4 + 2NaOH + 8H 2 O = 4NH 3 + Cd (OH) 2 + 4HCOONa ... (6)

As is clear from comparison of the above reaction formulas, the reaction formulas (3) to (6) are very similar to each other, and the products obtained by the thermal hydrolysis treatment are ammonia and heavy metals. Hydroxide and formate. Therefore, the mixed waste liquid containing these heavy metal cyanide complex salts does not cause another reaction to proceed by mixing, and can be handled as a simple mixed liquid, and is also suitable for thermal hydrolysis of the respective cyanide complex salts of the above heavy metals. The above reaction formula can be applied. In the reaction formulas (3) to (6), it is shown that hydroxides of each heavy metal are produced. However, since the pressure vessel is under high temperature and high pressure, a dehydration reaction produces heavy metal oxides. ..

As an example, nickel (Ni) and zinc (Z
The reaction formula for n) when an oxide is formed by thermal hydrolysis is shown below. _{Na 2 Ni (CN) 4 +} 2NaOH + 7H 2 O = 4NH 3 + NiO + 4HCOONa ······· (7) Na 2 Zn (CN) 4 + 2NaOH + 7H 2 O = 4NH 3 + ZnO + 4HCOONa ······· (8) above Among the heavy metal cyanide complex salts, it is the copper cyanide complex salt that is difficult to treat by the thermal hydrolysis method, and in the case of the waste liquid mainly composed of the copper cyanide complex salt, the reaction proceeds due to the addition of the iron cyanide complex salt. When processing mixed waste liquid from various plating plants and steel soft nitriding and liquid carburizing facilities, it is usually supplied in the state that a considerable amount of iron cyanide complex salt is contained in the waste liquid. It is almost unnecessary to add an iron cyanide complex salt.

A concrete processing method of this prior art is shown in FIG. Automatic valve 1 from the stock solution tank 11 in the horizontal pressure vessel 31
About half of the waste liquid is introduced via 2 and raw steam is directly blown into the waste liquid from a boiler (not shown) via the steam valve 14, and the temperature inside the pressure vessel 31 is raised to a predetermined temperature of 140 ° C. or higher. The temperature is controlled by opening and closing the steam valve 14 according to a command from the temperature sensor 13 installed in the pressure vessel 31. In addition, after a certain time after the target temperature is reached by the function of the timer provided in the control mechanism (not shown), the decomposition of cyan is completed, and it is in a state in which it has been processed and can be discharged (called a processed liquid). There is. At this point, the automatic discharge valve 15 installed in the pressure vessel automatically opens,
The treated liquid is discharged to the next cooling tank 16 by the pressure inside the pressure vessel 31 of the discharge pipe of FIG. In the conventional method, the processes from the introduction of the waste liquid to the subsequent thermal hydrolysis treatment and discharge of the treated liquid are regarded as one batch of the decomposition treatment, and when the discharge is completed, the waste liquid is moved to the next batch and put into the pressure vessel. The same process was repeated. In this case, most of the oxides and hydroxides such as iron oxide produced by the thermal hydrolysis reaction shown in the above reaction formulas are discharged to the cooling step together with the treatment liquid, but some remain. , It gradually accumulates in the container as the number of treatments is increased. In the conventional apparatus of this type, these sludges may be difficult to discharge due to the structure of the above-mentioned container, and it is not possible to discharge them in each processing batch or in a small number of batches. At the time of the legal inspection, a cleaning worker entered inside and discharged from the pressure vessel to the outside.

[0008]

In the conventional thermal hydrolysis treatment, as shown in the above formula, sludge mainly composed of heavy metal oxides is produced from the waste liquid containing heavy metal ions, or the waste liquid is discharged. Depending on the type and reaction conditions of
When sludge with hydroxides of heavy metals is generated and a new waste liquid is added while some sludge remains in the pressure vessel and thermal hydrolysis is repeated, thermal hydrolysis of the metal cyanide complex salt is performed. There was a tendency for the efficiency to decrease, the cyan concentration in the treated liquid to fluctuate, and the concentration to increase further, and sometimes to exceed the regulation value. In addition, as described above, the treated liquid passes through the discharge valve 15 under the pressure in the pressure vessel 31 along with sludge and passes through the cooling tank 16 of the next step.
However, since the flow velocity is considerably high, the discharge valve 15 is likely to be damaged by erosion due to sludge in the discharged liquid, and needs to be replaced in many cases. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for solving the above-mentioned various problems in such a cyan waste liquid treatment method and an apparatus used therefor.

[0009]

As a first step for solving the above-mentioned problems, when the cyan waste liquid is thermally hydrolyzed in a batch system, the reason why the above problems occur when the batch treatment is repeated is Clarified. The thermal hydrolysis efficiency of the metal cyanide complex salt decreases and the cyan concentration in the treated liquid changes,
The reason for the higher cyan concentration is that heavy metal oxides or hydroxides are deposited as decomposition products in the discharged liquid, and some of them remain in the pressure vessel, and the next waste liquid treatment is repeated. As a result, it was predicted that the amount of sludge remaining in the pressure vessel gradually increased. Therefore, the inventors examined the relationship between the cyan concentration after the reaction and the residual sludge, that is, the relationship between the cyan decomposition efficiency and the number of treatments, based on the above prediction. During the initial period when the number of treatments is small after operating the waste liquid treatment equipment, there is little variation (fluctuation) in the cyan concentration in the treated liquid, and the concentration value is less than the regulation value of 1.0 ppm, but as the number of treatments progresses The cyan concentration in the treatment liquid varied and had a high value, often exceeding 1.0 ppm, and the cyan decomposition efficiency decreased. At this point, a considerable amount of sludge was mixed in the waste liquid, and as the sludge remained in a certain amount or more in the pressure vessel, it was judged that this had a sharp adverse effect on the thermal hydrolysis of cyanide. Was done.

In view of the above, the present inventors did not discharge sludge containing a heavy metal oxide as a main component out of the pressure vessel system for each batch of treatment in the conventional thermal hydrolysis treatment method. The equipment was modified so that the sludge was discharged out of the system for each batch of treatment, and the thermal hydrolysis treatment could be started in a state where the sludge hardly remained in the pressure vessel. As a result, no matter how many times the waste liquid is treated,
It was found that cyanide can always be efficiently hydrolyzed without reducing the decomposition efficiency, and the cyan concentration in the treated liquid can be stably reduced to around 0.1 ppm, which is one tenth of the regulation value. It was When a certain amount of sludge is mixed in the waste liquid, the reason why the thermal hydrolyzability of cyan contained in the waste liquid is deteriorated is not theoretically clear at the present time, but the present inventors confirmed the cause. However, the present invention has been accomplished as a means for coping with this. The requirements for the implementation method of the present invention are described below. That is, in the present invention, the pH of the cyan complex ion-containing cyan waste liquid supplied is preferably 10 or more. If the pH is 10 or more, treat it as it is,
When the pH is 10 or less, alkali is added to adjust the pH to 10 or more with the alkali. Next, 2.7 × 10 ⁵ P
Thermal hydrolysis treatment is performed at a pressure of about a and a temperature of 140 ° C. or higher. Then, after the completion of thermal hydrolysis, the mixture is left to stand to settle the sludge mainly composed of heavy metal oxides precipitated from the waste liquid, the supernatant liquid is discharged, and the sludge is discharged to the outside of the system while washing the inside of the container with water. To let

The temperature range of the thermal hydrolysis treatment is 140 to 25.
0 degreeC is preferable and 150-210 degreeC is more preferable. The reason for selecting such a temperature range is that the reaction is less likely to occur at 140 ° C. or lower in the thermal hydrolysis treatment of the cyan waste liquid, and even if the reaction occurs at 140 ° C., the reaction becomes active by setting the temperature to 150 ° C. is there. Especially in the case of a cyanide complex salt of nickel or copper, it is necessary to set the temperature to 170 ° C. or higher. The upper limit of the temperature is set to 250 ° C. because of the regulation value for the pressure vessel.

An important point in the present invention is that the sludge containing decomposition products such as heavy metal oxides as the main component is washed with water and discharged out of the pressure vessel as carefully as possible without remaining in the pressure vessel. It is in. It is not always necessary to carefully discharge the sludge in each batch as long as the cyan wastewater regulation value (1 ppm) or less is cleared, but in order to improve the cyanide decomposition efficiency, the sludge in each batch must be carefully discharged. Must be discharged.

Next, an apparatus for carrying out the method of the present invention will be described. At the bottom of the pressure vessel for decomposing treatment, a recess for sedimenting sludge mainly composed of heavy metal oxides and hydroxides deposited from the waste liquid, and a water wash for discharging sludge remaining in the pressure vessel It is the point that the means and the discharging device having a structure that easily discharges the sludge are provided. Specifically, as shown in FIG. 1, the pressure vessel has a vertical shape, the bottom of the pressure vessel has a concave surface, and a water washing spray device is provided as a water washing means for effectively discharging sludge remaining in the pressure vessel. It is preferable that the discharge port has a structure that allows sludge to be easily discharged, and that the discharge port is provided at the center of the concave portion of the bottom of the pressure vessel. Vertical type is suitable as a pressure vessel,
As shown in FIG. 2, a suitable recess 21a is formed on the bottom of the pressure vessel 21.
If it is provided, it may be a horizontal type. Description of other parts is omitted. As a heating method, there is a method of directly heating the pressure vessel from the outside, but in a factory of a certain size or more, it is preferable to directly blow high-pressure live steam from the viewpoint of work efficiency and equipment.

[0014]

EXAMPLES The apparatus used for carrying out the first example of the present invention, the specific method for the thermal hydrolysis treatment, and the results obtained thereby will be described below with reference to FIG. As shown in FIG. 1, the pressure vessel 1 has a vertical shape and a bottom portion 1a has a concave curved surface, and a water washing spray 2 as a means for discharging sludge therein and a discharge port 3 as a sludge discharging means. And an automatic valve 4 for discharging is provided. The sludge settled inside the pressure vessel is effectively discharged by spraying water from the spray 2 with an appropriate water pressure. Next, a thermal hydrolysis treatment method using the apparatus shown in FIG. 1 will be described. First, the cyan complex ion-containing waste liquid W is introduced into the pressure vessel 1 from the stock solution tank 11 by using the submersible pump 17 or the like. Then, in order to bring the container to a predetermined temperature and pressure for thermal hydrolysis (usually, the saturated vapor pressure of water at approximately that temperature), high-pressure raw steam S was blown directly from a boiler (not shown). In the process, the cyan complex ion is decomposed into sludge such as ammonia, heavy metal oxides and formate as shown in the above reaction formula. Here, a part of the generated sludge such as heavy metal oxides is accumulated in the container.

Example 1 In the pressure-resistant container shown in FIG.
A waste liquid having a pH of 10.3 to 10.8 at 000 ppm was introduced by the submersible pump 17. Next, in order to bring the container to a predetermined temperature and pressure for thermal hydrolysis, high-pressure live steam is directly blown into the container, the heating temperature is set to 170 ° C. ± 1 ° C., and the temperature is maintained for 3 hours for thermal hydrolysis treatment, Subsequently, the treated liquid is allowed to stand, the sludge containing heavy metal oxide as the main component is allowed to settle, and the operation of gently discharging the supernatant liquid is defined as one batch, and further one batch of the decomposition treatment is carried out. The operation of washing the inside of the container each time with water and carefully discharging the sludge was repeated as one cycle, and the operation after starting a new thermal hydrolysis treatment was the next cycle. The thermal lysis of the waste liquid was carried out for 27 cycles, and the total cyan concentration after the decomposition treatment was measured. As a result, the average value was 0.09 ppm (maximum value 0.13 ppm, minimum value 0.04 pm), which was extremely low. Results were obtained.

Comparative Example 1 The same waste liquid as in Example 1 was used in the horizontal pressure vessel 1 shown in FIG. 3, and treatment was performed 23 times in one month without washing operation as in the conventional method, and treatment was performed each time. The total cyan concentration of the finished solution was measured. As a result, as an average value, 2.14 ppm
(Maximum value is 2.8 ppm, minimum value is 0.83 ppm), and a considerably large number of batches (batch) of the treated liquid exceeds the regulation value of 1.0 ppm, which is an unfavorable result.

Comparative Example 2 From Comparative Example 1, it was confirmed that the accumulation of sludge containing a heavy metal oxide as a main component remaining in the pressure vessel after the treatment had a bad influence on the thermal hydrolysis treatment. This is shown in Example 1.
In order to confirm the case of using the device of the present invention used for, the same waste liquid as the same device as in Example 1 was used, and the sludge discharge operation of washing with water for each batch of treatment was not performed in the container. The measurement was performed so that a part of the sludge remained and accumulated. The total cyanide concentration of the treated water after the batch treatment of 10 times has an average value of 0.82 ppm and a maximum value of 1.9.
ppm, the minimum value was 0.09 ppm, clearly showing a bad result as compared with Example 1. The reason for this is considered as follows. That is, the pressure vessel 1 in the apparatus of FIG. 1 used for carrying out the present invention is of a vertical type and the bottom portion 1a is formed as a concave curved surface for allowing sludge to settle.
Therefore, if sludge is not discharged every time batch processing is performed, sludge tends to remain as in the conventional pressure vessel (horizontal type), and sludge such as heavy metal oxides remains as a residue in the thermal hydrolysis reaction. Is considered to have decreased.

Example 2 Using the same vertical apparatus as in Example 1 (FIG. 1) and the same waste liquid,
Instead of rinsing with water for each batch of treatment as in Example 1, sludge is discharged once with two batches of water, for a total of 20 batches and 10 times of sludge discharge. A test was conducted, and the total cyan concentration of the discharged liquid was measured at each discharge. As a result, the average value of all cyan densities was 0.42 ppm, the maximum value was 0.82 ppm, and the minimum value was 0.06 ppm. The sample group including the maximum value is the value immediately after repeating the thermal hydrolysis twice after discharging the sludge, and the sample group including the minimum value is the result after the thermal hydrolysis immediately after discharging the sludge.

[0019]

EFFECTS OF THE INVENTION By the thermal hydrolysis treatment method of the present invention, sludge is discharged for each batch of the thermal hydrolysis treatment to effectively decompose the total cyanide concentration of the cyan complex ion-containing waste liquid, and the total cyanide concentration of about 0. Since it can be reduced to 1 ppm, it exhibits an excellent effect of lowering the cyan density as compared with the conventional processing method. The apparatus for carrying out the present invention includes a recess for sludge settling at the bottom of a pressure vessel, a spray for washing and discharging the settled sludge, a discharge port and a discharge valve having a structure for easily discharging sludge. By providing and, the above effect can be achieved.

[Brief description of drawings]

FIG. 1 is a system diagram of a thermal hydrolysis treatment apparatus using a vertical pressure vessel to carry out the present invention.

FIG. 2 is a systematic diagram of a thermal hydrolysis treatment apparatus using a horizontal pressure vessel to carry out the present invention.

FIG. 3 is a system diagram of a conventional thermal hydrolysis treatment apparatus using a horizontal pressure vessel.

[Explanation of symbols]

 1, 21, pressure vessel 1a, 21a bottom of pressure vessel 2 water washing spray tank 3, 23 sludge discharge port 4 sludge discharge valve 11 stock solution tank 12, 14, 15 automatic valve 13 temperature sensor 16 cooling tank 17 submersible pump S vapor W waste liquid

Claims (4)

[Claims] 1. A treated cyan waste liquid containing a cyan complex ion is adjusted to pH 10 or higher, if necessary, and introduced into a pressure vessel, and the waste liquid is batch-processed at a predetermined gauge pressure at 140 to 250 ° C. In the thermal hydrolysis treatment method of the cyan waste liquid, which is heated and maintained at a temperature of 10 to decompose cyan and complex cyan into ammonia and formate, and the heavy metal bound to cyan is mainly removed as heavy metal oxide sludge, Discharging the treated effluent out of the pressure vessel for each batch of thermal hydrolysis treatment, and while maintaining the cyan concentration of the treated effluent within a predetermined control limit value,
Repeating the thermal hydrolysis treatment batch 1 to 5 times, and then discharging the sludge from the bottom of the pressure-resistant container to the outside of the system. Repeated thermal hydrolysis treatment of a cyan waste liquid. Method. 2. The method for iterative thermal hydrolysis treatment of cyan waste liquid according to claim 1, wherein the inside of the pressure vessel is washed with water when the sludge is discharged to the outside of the pressure vessel. 3. A stock solution tank for storing a treated cyan waste liquid containing cyan complex ions, and a pressure for receiving the treated cyan waste liquid, holding the same at a predetermined temperature for a predetermined time, and performing thermal hydrolysis treatment by a batch method. A cyan waste liquid treatment device having a container and a discharge device for discharging the treatment liquid from the pressure container, wherein the pressure container is deposited on the bottom portion of the cyan waste liquid by the thermal hydrolysis treatment. A recess for facilitating the collection of sludge such as heavy metal oxides, a washing device provided above the recess for washing the settled sludge with water, and a structure for easily discharging the washed sludge out of the system And a discharge device, and a repeated thermal hydrolysis treatment device for a cyan waste liquid. 4. The repeated cyan waste liquid according to claim 3, wherein the pressure vessel is a vertical type, the concave portion is formed as a concave curved surface, and the water washing device is a spray device using pressurized water. Thermal hydrolysis treatment equipment.