This paper describes the leaching and stabilization of oxyanion forming elements, mainly As, Se and Sb from solid wastes (sludge, fly ash, bottom ash). It is argued that knowledge of the leaching behaviour of oxyanions from waste is of high importance relative to wastewater treatment. Experiments and modelling demonstrate that immobilization of the oxyanions is mainly due to precipitation with Ca and to adsorption and solid solution formation with minerals such as calcite, gypsum, ettringite, HFO and AAM.