Hydrothermal solidification of inorganic waste materials

To create an environmently friendly community, the authors have investigated the recycling technology of inorganic, wastes to make high performance building materials and the stabilization technology of toxic heavy metals by using hydrothermal treatment. The inorganic waste materials used were bottom ash and fly ash from incinerated municipal waste, incinerated ash from sewage sludge, concrete waste, and construction sludge. These waste were mixed with Ca(OH)₂ and autoclaved for 6 h at 180°C under saturated steam pressure. Except for the specimen by using incinerated ash from sewage sludge, the formation of tobermorite (Ca₅(Si₆O₁₈H ₂)·4H₂O) and hydrogarnet (Ca₃Al ₂(SiO₄)(OH)₈) were observed. The flexural strength of the specimens varied from 3.2 to 16.2 MPa with the bulk density of 1200 to 1550 kg/m³. The higher SiO₂ content and the finer particle size gave the higher strength. The amount of dissolved heavy metal (Pb) was decreased to 1/40 after autoclaving, suggesting the possibility of the heavy metal fixation by hydrothermal treatment. In addition, hydrothermally solidified specimens using incinerated ash from sewage sludge and construction sludge had 1.5 times of higher self humidity controlling property than the ordinal wood