Properties, microstructure and leaching of sintered sewage sludge ash

Sewage sludge incinerator ash has been compacted and fired at different temperatures to produce a range of sintered ceramic materials. The effects of sintering temperature and pressing pressure on density, water adsorption and shrinkage have been determined and the microstructure of material sintered at 1040degreesC for 1 h characterised by X-ray diffraction (XRD) and scanning electron microscopy. Sintering produces potentially useful ceramic materials with maximum densities resulting from firing between 1000 and 1020degreesC. Density decreases as the firing temperature is further increased, due to a bloating effect associated with the formation of high volumes of approximately spherical pores. The major crystalline phases present in both as-received and sintered sewage sludge ash (SSA) ceramics are quartz (SiO2), the calcium magnesium phosphate mineral, whitlockite (Ca7Mg2P6O24) and hematite (Fe2O3). The as-received and sintered SSAs have low acid neutralisation capacities and leach significant fractions of Cu, Mn and Zn under acid conditions. Sintering SSA was found to reduce metal leaching for all metals analysed. (C) 2003 Elsevier B.V All rights reserved.