Soluble salt removal from MSWI fly ash and its stabilization for safer disposal and recovery as road basement material

Fly ash from municipal solid waste incinerators (MSWI) is classified as hazardous in the European Waste Catalogue. Proper stabilization processes should be required before any management option is put into practice. Due to the inorganic nature of MSWI fly ash, cementitious stabilization processes are worthy of consideration. However, the effectiveness of such processes can be severely compromised by the high content of soluble chlorides and sulphates. In this paper, a preliminary washing treatment has been optimized to remove as much as possible soluble salts by employing as little as possible water. Two different operating conditions (single-step and two-step) have been developed to this scope. Furthermore, it has been demonstrated that stabilized systems containing 20% of binder are suitable for safer disposal as well as for material recovery in the field of road basement (cement bound granular material layer). Three commercially available cements (pozzolanic, limestone and slag) have been employed as binders.