JPS5846360B2 - Method of processing waste containing cyanide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating cyanide-containing sludge and activated carbon waste, and particularly provides a method for easily decomposing cyanide contained in sludge and activated carbon.

Potassium Cyanide Cyanide compounds, including cyanide complexes such as sodium cyanide, zinc cyanide, copper cyanide, silver cyanide, and potassium ferrocyanide, are used in large quantities in the plating industry.

As plating solutions containing cyanide compounds, zinc cyanide baths, copper cyanide baths, and copper cyanide baths are well known.

In order to remove these impurities from the plating solution and perform good plating, the solution may be treated by a method called activated carbon filtration.

Activated carbon filtration involves adding activated carbon to the plating solution, stirring it, and then
This is a process in which impurities in the plating solution are adsorbed onto activated carbon and removed from the solution by filtering or passing the plating solution through a layer filled with activated carbon.

This activated carbon filtration produces waste activated carbon containing a large amount of cyanide.

Conventionally, these waste activated carbons were mixed with waste liquid and added with substances that dissolve in water and generate hypochlorite ions, such as chlorine and hypochlorite ions, to oxidize and decompose cyanide. .

However, activated carbon has many pores, and it is difficult to decompose cyanide compounds that have entered the pores, and it takes about 10 times the processing time of a normal plating solution.

In addition, cyanide compounds in the pores cannot be detected with measuring instruments such as redox electrometers and are difficult to manage. In some cases, processing was necessary.

Additionally, substances such as anode slime may precipitate in the tank during plating, and this sludge also contains cyanide compounds, making it difficult to reliably decompose the cyanide compounds. There was a problem.

Furthermore, it has been impossible to treat activated carbon and sludge containing cyanide complexes such as iron and nickel using only the conventional method using hypochlorous acid.

In view of the above-mentioned drawbacks of the conventional methods, the present invention has been made with the object of providing a method for reliably decomposing activated carbon and cyanide in sludge in a single operation.

The present invention is characterized in that a muddy mixture in which sludge containing cyanide compounds is mixed with powdered or granular charcoal, or activated carbon containing cyanide compounds, is heated to 200°C or higher to decompose the cyanide compounds. It is.

The muddy mixture or activated carbon is dried by the heating, and then the powdered or granular carbon in the muddy mixture or the activated carbon is combusted, and the cyanide is decomposed by the heat of combustion.

In the method of the present invention, the cyanide compound is heated to a considerably high temperature because it is contained in the combusting activated carbon or the mixture of sludge and powdered or granular coal, so that it can be completely decomposed in one step.

Furthermore, activated carbon and powdered or granular carbon provide a high enough temperature to burn and decompose cyanide compounds simply by contacting them with an appropriate amount of air, so there is no need for strict control or measurement of cyanide concentration.

Furthermore, the method of the present invention has the advantage that activated carbon and sludge containing cyanide complexes such as iron and nickel can be treated in one step.

In addition to the activated carbon and sludge generated in the plating industry mentioned above, activated carbon used in the surface treatment of steel that has adsorbed hydrogen cyanide gas, that is, cyanide compounds, is mixed into the interior of the solid. This method is particularly effective in treating waste containing cyanide compounds, which requires a long treatment time and is difficult to operate reliably.

Further, the present invention also provides hydrogen cyanide gas, potassium cyanide,
Alkali metal cyanides such as sodium cyanide, metal cyanides such as zinc cyanide, copper cyanide, silver cyanide, potassium copper cyanide, alkali metal salts of metal cyanide complexes such as potassium gold cyanide, potassium ferrocyanide, potassium ferricyanide, etc. etc., any one of the cyanide compounds
Applicable to activated carbon or sludge containing seeds or more.

Furthermore, the concentration of the cyanide compound contained in the activated carbon or sludge to which the present invention is applied does not need to be particularly specified.

When the target to be treated is activated carbon, its type, shape, etc. are arbitrary.

Furthermore, when treating sludge with the method of the present invention, it is necessary to mix it with powdered or granular charcoal in advance.

As the powdered or granular charcoal used for this purpose, in the plating industry it is advantageous to use used activated carbon, but other materials such as charcoal can also be used.

The reason why it is limited to powdered or granular charcoal is that when mixed with sludge and heated, the entire sludge must be heated uniformly by the combustion heat of the charcoal, and pulverized charcoal is particularly preferred because it is inexpensive.

The particle size of the granular charcoal is preferably an average diameter of 15 mm or less, but is not particularly limited. For example, even if the method involves mixing lump charcoal with sludge and then pulverizing it, the charcoal will eventually be used as granules. Therefore, it is included in the present invention.

The mixing ratio of powdered or granular charcoal and sludge varies depending on the moisture content of the sludge, the cyanide compounds in the sludge, etc., but for example, when using sludge with a moisture content of 75%, 1 part of sludge is mixed with 0.0% of powdered or granulated charcoal. Adding 5 or more can easily maintain a high enough temperature to decompose the cyanide.

If activated carbon or sludge has a high moisture content, it will take a long time to dry it to a combustible level when heated, so it is preferable to lower the moisture content in advance using a filter press or the like.

The moisture content of activated carbon or a mixture of powdered or granular carbon and sludge is preferably 80% or less.

Further, in order to further reduce the water content and reduce the time required for drying, preliminary drying may be performed at a temperature of less than 200°C.

When activated carbon containing cyanide compounds or a mixture of sludge and powdered or granular carbon is heated, a small amount of ammonia gas is generated.

To prevent the bad odor of ammonia gas, a deodorizing device is required.

On the other hand, activated carbon requires oxygen from the atmosphere to burn.

Therefore, the atmosphere is introduced through the vent, and the exhaust gas containing ammonia gas is discharged into the atmosphere through the deodorizing device through the exhaust port.

Although a small amount of hydrogen cyanide gas is contained in the exhaust gas, it can be easily removed by a treatment such as contact absorption with an alkaline solution such as an aqueous sodium hydroxide solution.

The main purpose of a deodorizing device is to remove ammonia gas, and this purpose can be achieved simply by passing the exhaust gas through water or an acidic aqueous solution such as sulfuric acid or hydrochloric acid.

Many devices are commercially available that satisfy this purpose.

As a heat source for heating, electricity, gas, heavy oil, etc. can be used.

The heating method may be to heat the container from the outside, heat the container internally, or heat the air introduced into the container.

The reason why the heating temperature is limited to 200° C. or higher is that if the heating temperature is lower than this, it is difficult to start burning the activated carbon or the mixture of sludge and charcoal, and the decomposition of the cyanide compound becomes extremely slow.

However, once the activated carbon or the mixture of sludge and charcoal burns and begins to glow red, the external heating may be stopped or reduced.

In addition, when processing a large amount of activated carbon or a mixture of sludge and charcoal, it is necessary to stir the activated carbon or sludge and charcoal mixture to ensure uniform combustion and complete decomposition of cyanide. It is valid.

Containers containing activated carbon or a mixture of sludge and charcoal directly are heated by combustion of the activated carbon or charcoal, which is much more expensive than heating with an external heating device alone; The temperature when heated with only 5
The temperature never exceeds 00°C, and even an iron container can withstand use several dozen times, so the equipment is inexpensive.

Example 1 10 m3 of a copper cyanide plating solution was filtered through activated carbon from 50 kg of powdered palm.

The activated carbon after filtration has a moisture content of approximately 75% and a total cyanide concentration of 12
00 ppm, there were 9 out of 200 in total.

This is height 40CrrL, width 50cm, depth 40cy
Place the container in a stainless steel container with a temperature of 30℃.
The temperature was reduced to 0° C., and the mixture was heated for 4 hours while blowing air at 101/min.

After being left to cool, total cyanide was analyzed and found to be 0.0.
It was 1 ppm or less.

Example 2 A blackish brown muddy precipitate was formed in the copper cyanide plating tank.

Analysis of this revealed that its main component was cuprous oxide, with 1
It contained 8000 ppm total cyanide.

1 kg of this precipitate and 1 kg of powdered charcoal were mixed, placed in a constant temperature bath, and heated at an ambient temperature of 400° C. for 2 hours.

At this time, air was introduced at 51/min, and the gas coming out of the exhaust port was passed through 500 cc of 0.5 N sodium hydroxide solution to collect cyan gas.

The total cyanide in the waste is less than 0.01 ppm, and the cyanide concentration in the exhaust gas is 20 ppm before collection.

It was not detected after collection.

As described above, in the method of the present invention, by heating a mixture of cyanide-containing sludge mixed with powdered or granular carbon, or cyanide-containing activated carbon to 200°C or higher, Drying, combustion, and decomposition of cyanide compounds are performed in one step, and expensive chemicals are not required, so there is an advantage that waste containing cyanide compounds can be easily treated at a very low cost.

Furthermore, according to the present invention, cyanide compounds are completely decomposed, there is almost no residue left, and gases such as ammonia that are generated in small amounts can be easily removed, so cyanide waste can be disposed of safely and reliably. , provides a very effective way to solve pollution problems.

Claims (1)

[Claims] 1. A method for treating waste containing cyanide compounds, which comprises heating activated carbon containing cyanide compounds to a temperature of 200° C. or higher to decompose the cyanide compounds.