Immobilization is a technical treatment of a
waste material. The immobilization treatment changes the
physical and/or
chemical properties of the
material. This is done to ensure that the risk of
dispersion of
environmentally dangerous matter by
leaching,
erosion or
diffusion is diminished, for the short as well as the long time range.
Immobilization serves a number of purposes, such as:
The aim of the immobilization of waste materials is to treat waste in such a manner that it can be used as building material, or that it can be used as landfill when before treatment it was too toxic for that.
Re-use as building material is to be preferred because of economical reasons (no cost of landfill) and because it diminishes the use of primary raw materials.
Immobilisation can be achieved in a number of ways, that can be divided into four main categories:
- Inorganic binders. Waste materials are immobilised with the use of inorganic binders like cement. Cement is often used in combination with other materials like modified clay, active carbon, silica fume or lime.
- Organic binders, like bitumen and polymers, and organic complex formers that bind specific elements. Bitumen, because of their water repellent properties, are suitable for the encapsulation of inorganic impurities and waste materials containig salts. Thermoset polymers don't have a continuous pore structure and are thus inaccesible to water. The disadvantage of organic binders is that the immobilisation processes often occur at high temperatures, so that volatile matter can escape.
- Thermal methods, like sintering, vitrification and crystallization after melting. These processes take place at temperatures of 1000 degrees C or more, which causes a great amount of volatile matter to escape (bad thing). The advantage is that organic matter or impurities are completely decomposed. Vitrified materials have no extended pore structure, which is a good thing.
- Chemical fixation, which diminishes the solubility of a waste matter. Chemical fixation only changes the chemical behaviour of a material, not the external features like grain size.