Use of alkali-activated concrete binders for toxic waste immobilization

The increasingly urgent need for the use of industrial inorganic waste as raw material for new materials poses geopolymers as an alternative to the traditional Portland cement /concrete. These alkali activated materials can, in fact, be considered a resource in a sustainable waste management as it is possible to formulate them starting from waste, mostly aluminosilicates, not dangerous. Nevertheless it is also possible to design and use alumina and silica bearing wastes as matrices for inertization of hazardous compounds which might be contained in the waste itself or that can be added on with the purpose to reach solidification/stabilization. In this sense we can define the geopolymerization of waste materials the technique that combines the alkaline activation of the aluminosilicatic and/or phosphatic component to act as matrix and the dissolution/activation/hydrolization of the surface of the particles of waste. The surface reactivity is in fact responsible for the bond that is formed between the waste particles and the aluminosilicatic matrix immobilizing the heavy metal ions. The nature of the waste, in terms of mineralogy, alumina and silica contents, particle size, surface area and morphology, significantly affect the reactivity of the waste itself. Single heavy metals cations as well as more complex hazardous wastes of industrial or urban origin have been successfully treated with the geopolymeration technique over the past few years.