These techniques involve mixing a siliceous ~pozzolanic! material
with other alkaline earth material such as lime or gypsum in the
presence of water to produce a concrete-like mass. This technique
generally involves pozzolanic reactions between SiO2, Al2
O3 ,
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 stabilize/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!.