A new experimental approach to study the longterm behaviour of solidified/stabilized wastes

Abstract

To mimic the long term behaviour of solidified/stabilized wastes, kinetics of release of elements were measured using a water extractor similar to the soxhlet device used to study weathering mechanisms of rocks. Samples used were small bowls whose diameter was about a few centimetres and prepared according to the ECOFIX procedure. The release kinetics show that: (1) the total amount of soluble salts is eliminated from the solid phase in a few days; (2) the amount of potentially toxic elements released after 175 days is generally lower than 1%; and (3) some elements released may precipitate in the pore space to give neoformed compounds. New pores appear during weathering which correspond, in particular, to the dissolution of soluble salts. The release of elements from the solidified/stabilized waste is controlled by diffusion only during the period of the dissolution of the more soluble salts; afterwards the release is controlled by surface reactions. As has already been shown for sulfates and some other minerals the weathering of solidified/stabilized waste obeys the Bovington and Jones formalism. The similarities observed with respect to weathering mechanisms between the solidified/stabilized wastes and rocks allow the assessment of the time needed in the nature to obtain the same rate of weathering observed in the water extractor. The equivalent time is assessed dividing the amount of water which flows in the water extractor by rainfall. The solidified/stabilized waste may be characterized with respect to the release of potentially toxic elements by the flux of elements that move through the surface of individual constituents of the sample per equivalent year. The considered surface here is the specific surface area determined applying the BET formalism to the nitrogen adsorption isotherm. © 1999 Taylor and Francis Group, LLC.