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Stabilization/Solidification - 5.0 Important Considerations

 

5.0 Important Considerations

5.1 Compatibility of Wastes and Treatment Process

Waste characteristics are the most important concern when selecting a S/S technology. Table 5.1 is a summary of compatibility of different wastes with different S/S technologies provided by USEPA (1986). For example, cement-based treatment is very effective for inorganic acid wastes, because cement can neutralize acids. However, if thermoplastic microencapsulation is used to treat the inorganic acid wastes, the wastes need to be neutralized before treatment (Sharma, 1994). 

Table 5.1: Compatibility of Selected Waste Categories with Different Stabilization/Solidification Technicues

Waste Component

Treatment Type

Cement-Based

Pozzolan-Based

Thermoplastic

Microencapsulation

Surface

Encapsulation

ORGANICS

 

 

 

 

Organic solvents and oils

May impede setting, may escape as vapor

May impede setting, may escape as vapor

Organics may vaporize on heating

Must first be absorbed on solid matrix

Solid organics (e.g., plastics, resins, tars)

Good-often increases durability

Good-often increases durability

Possible use as binding agent in this system

Compatible-many encapsulation materials are plastic

INORGANICS

 

 

 

 

Acid wastes

Cement will neutralize acids

Compatible, will neutralize acids

Can be neutralized before incorporation

Can be neutralized before incorporation

Sulfates

May retard setting and cause spalling unless special cement is used

Compatible

May dehydrate and rehydrate causing splitting

Compatible

Halides

Easily leached from cement, may retard setting

May retard set, most are easily leached

May dehydrate and rehydrate

Compatible

Heavy metals

Compatible

Compatible

Compatible

Compatible

Radioactive materials

Compatible

Compatible

Compatible

Compatible

Reproduced from: USEPA, 1986

5.2 Pre-treatment Process

Numerous pre-treatment techniques can be used to render stabilization/solidification more effective. These include:

  1. Destruction of materials that interfere with solidification reagents, such as acids or oxidizers.
  2. Reduction of total volume of waste to be treated, using processes such as dewatering or settling.
  3. Chemical binding of certain toxic waste constituents to solid phases, removing them from solution.
  4. Improving the scale of waste processing, i.e. bulking and homogenizing waste so that the number of waste forms to be treated is reduced.

Compatibility problems can be addressed by pretreatment of wastes. Pretreatment methods serve to bring the chemical waste into an inert or less soluble form. This process improves the efficiency of S/S and reduces the cost.

Generally, the most widely used pretreatment methods are (Sharma, 1994):

  • Neutralization
  • Oxidation-reduction
  • Chemical scavenging
  • Other pretreatment methods, such as dewatering and consolidation, removal of volatile organics, etc.  

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