Hydrothermal solidification of wastes with formation of zeolites

In order to use waste materials effectively, a possibility of simultaneous solidification of inorganic waste materials and fixation of alkaline ions a nd heavy metal through formation of zeolite by using hydrothermal processin g, was investigated. Fly ash, cinder of sewage sludge, and cinder of rubbis h were used as the starting materials. Ca/Si and 2Na/Si molar ratios of the specimens were changed by the addition of CaO and Na,CO,. These mixtures w ere formed and hydrothermally processed at 200 degreesC. Various zeolites, such as analcime, Linde B-1 zeolite, cancrinite, zeolite P-C, and hauyne, w ere formed at Ca/Si = 0.3 or 0.5 and 2Na/Si = 0.1-1.0. In the case of the f ly ash system, although only the zeolite minerals were formed, the flexural strength reached up to 17 MPa when Ca/Si = 0.3 and 2Na/Si = 0.1, and the f ixing ratio of Na+ ion reached a maximum value of 85% by the formation of z eolites. When cinder of rubbish was used, dissolution of heavy metals from the solidified specimen was scarcely observed. The microstructure and the v ariation of pore size distribution were also discussed.