JPS586551B2 - How to detoxify harmful substances - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detoxifying harmful substances, and in particular, to a method for detoxifying harmful substances.
The present invention relates to a method for detoxifying harmful pollutants containing heavy metals such as , Pb, etc.

Generally, in order to dispose of hazardous pollutants containing heavy metals such as Cd and Pd from incineration ash generated from waste incineration equipment, collected ash from reduction kilns related to steel manufacturing, and plating sludge, asphalt, It is necessary to cover and fix the surface of particles containing harmful pollutants with plastic or the like to render them harmless.

This takes advantage of the water impermeability and water resistance properties of asphalt and plastics, but if the coating is not completely done, harmful substances may come into contact with water after being landfilled or dumped in the ocean.
It may dissolve and contaminate the environment.

For this reason, a method has been adopted in which harmful substances are insolubilized in advance and then covered with asphalt or the like.

That is, Cd, Pb, etc. are converted into hydroxides and then covered and fixed with asphalt or the like.

However, when dust ash and plating sludge contain harmful metals Cd and Pb at the same time, it is not possible to render them harmless by simply converting them into hydroxide.

This is because Pb is an amphoteric metal, so on the acidic side, Pb
Since Pb dissolves as HPbO2- on the alkali side, the range of pH values that can make Pb poorly soluble becomes very narrow.

In other words, what is shown in Fig. 1 shows the solubility of Cd and Pb in the collected ash from the garbage incinerator with respect to the pH value, but Pb and Cd are set at the standard value of 3 ppm and 0.
．． In order to make it harmless to 3 ppm or less, the pH value must be 10~10.
12. If you look at safety, you will find that you have to adjust it to a range of 10.5 to 11.5.

Therefore, in actual operation of the equipment, if it is attempted to maintain this range, problems with stability remain and equipment costs become large.

An object of the present invention is to provide a method for detoxifying hazardous substances that can make waste containing both heavy metals, Cd and Pb, difficult to solubilize in an extremely easily controlled manner.

The details of the method of the present invention will be explained below.

The material used in the experiment was collected ash from a garbage incinerator, and its physical properties are shown in Tables 1 to 4.

First, slaked lime, which is an alkaline substance, was mixed with the above compounds such as Cd and Pb in order to convert them into hydroxides in order to make them insolubilized.

That is, first, 3 to 10% by weight of slaked lime was added to and mixed with 100 pieces of collected dust ash having the above composition, and then an elution test was conducted.

As a result, the relationship with pH value was as shown in FIG.

As is clear from Figure 2, in order to suppress the elution amount below the standard value, the pH of Cd must be ≧8, and the pH of Pb must be 9.5<8.
It is sufficient to make it poorly soluble at pH<10.5.

Therefore, in order to keep the elution amount of both Cd and Pb below the standard value, the pH value of the mixture must be adjusted within the range of 9.5 to 10.5.

However, as it is, the adjustment range is only 1 in terms of pH value.
The adjustment range is extremely narrow due to the nature of Pb as an amphoteric metal.

Therefore, we conducted an experiment in which Pb was precipitated in the form of sulfide.

That is, 3 to 10% of slaked lime to 100 parts of collected dust ash,
Further, magnesium sulfate was added in an amount of 3 to 15% by weight, and after mixing, an elution test was conducted in the same manner.

FIG. 3 shows the relationship between the elution amount and the pH value, and FIG. 4 shows the relationship between the pH values obtained when the amounts of slaked lime and magnesium sulfate (MgSO4) added were varied.

As a result of the above experiment, as is clear from the elution curve shown in Figure 3, in order to suppress the elution amount of Cd and Pb below the standard value, Cd should be kept at pH≧8 and Pb at pH≦10.5. It has become clear that it is sufficient to make it less soluble.

In other words, by precipitating Pb in the form of sulfide, the pH range at which both Cd and Pb elution can be reduced to below the standard is 8 to 10.5, and the range of application is wider than when only slaked lime is used. It is clear that it will become wider.

As is clear from the above description, according to the present invention, Cd,
Before covering and fixing waste particles containing harmful pollutants such as Pb with asphalt or plastic, alkaline substances that can make harmful heavy metals such as Cd and Pb hardly soluble in the form of hydroxides and sulfides are added as a pretreatment process. Because we use the addition method, we can widen the range of pH values when adjusting harmful heavy metals to below the elution standard, making it easier to control the operation of treatment equipment, and preventing waste from being landfilled or dumped as final disposal. This provides an excellent effect of ensuring stability.

[Brief explanation of the drawing]

Figure 1 is a diagram explaining the relationship between pH value and elution amount of Cd and Pb when hydroxide is used, and Figure 2 is a diagram explaining the relationship between pH value and elution amount when slaked lime is used. Figure 3 is a diagram explaining the relationship between pH value and elution amount when slaked lime and magnesium sulfate are used, and Figure 4 is a diagram showing the relationship between pH value and elution amount when the mixed amount of magnesium sulfate and slaked lime is changed. It is a line diagram explaining the relationship.

Claims (1)

[Claims] In a hazardous substance detoxification treatment method that covers and fixes waste containing ICd and Pb with asphalt or plastic, slaked lime and Adding 3 to 15% magnesium sulfate by weight,
A method for detoxifying harmful substances, which comprises performing a pretreatment step of converting Cd and Pb into hydroxides and sulfides.