The aim of this research was to develop a novel thermal treatment technology able to transform the problematic fine fraction of incinerator bottom ash (IBA) into an inert material suitable for the production of ceramics.
In this project two different problematic fractions of fine IBA have been used. The less than 1mm fraction of processed fine IBA dust was obtained from the dry discharge system for IBA used in the Energy from Waste (EfW) plant at Monthey, Zurich. The dry discharged fine IBA dust from the Monthey plant is currently disposed of to landfill at high cost. The second fine IBA fraction was supplied by Day Group who process wet discharge IBA from the Lakeside and the Newhaven EfW facilities in the South of England. There are currently no beneficial uses for the fine fraction which is either blended back into coarser fractions or disposed of to landfill.
The conclusion from the research is that the fine fractions of IBA generated from both discharge techniques can be transformed into an inert material suitable for the production of hard, dense ceramics. Processing involves the addition of glass, wet ball milling and calcining, pressing and sintering. The addition of glass aids liquid phase sintering and improves the appearance of the ceramic body formed, milling increases sintering reactivity and calcining limits the loss of volatiles and shrinkage during firing. This transforms the major crystalline phases present in the fine IBA fraction from quartz (SiO2), calcite (CaCO3), gehlenite (Ca2Al2SiO7) and hematite (Fe2O3), to the pyroxene group minerals diopside (CaMgSi2O6) and clinoenstatite (MgSi2O6), together with some andradite (Ca3Fe2Si3O12). Processed calcined powders can be pressed and sintered to form dense (>2.5 g/cm3), hard ceramics that exhibit low firing shrinkage (<7%), zero water absorption and minimal leaching. Calcining the IBA: glass powders before processing was able to minimize the linear shrinkage observed compared to samples produced using uncalcined powders. Calcining also had the effect of reducing the leaching of metals of environmental concern present in the fine IBA fraction by over 95%. These are encapsulated within the glassy phases present in the calcined and sintered materials.