This technique generally involves pozzolanic reactions between SiO2, Al2O3, Fe2O3, and available calcium in lime. The results of these reactions are very stable, and strong calcium silicates and aluminates can be considered as the equivalent of Portland cement in initiating the cementation process. The most common pozzolanic materials used in the stabilization/solidification of wastes are fly ash, ground blast-furnace slag, and cement-kiln dust. The use of these materials, themselves considered by-products with little commercial value, to stabiliza/solidify another waste may offer economical advantages to the process. The vulnerability of the final product to acid leaching is the major disadvantage of this technique. Combined cement-pozzolanic processes can be used to give a better and more economic final waste product (USEPA 1989).