Production of monolithic ceramics fr om incinerated municipal sewage sludge, paper mill sludge and steelworks slag

A municipal sewage sludge (MSS) from a traditional wastewater treatment plant and a paper mill sludge (PS) were incinerated and transformed into powders which were blended in different proportions to give powders with different composition. Blendings were performed by attrition milling in order to reduce the milling time with respect to the traditional wet milling process. Powders were then pressed into specimens which were submitted to thermodilatometric tests to evaluate their shrinkage and their softening temperatures on heating up to 1350°C. Samples were then air sintered by means of a muffle furnace and characterized by density, strength, hardness, fracture toughness measurements and XRD and SEM investigations. The mechanical properties of the sintered specimens are satisfactory for all compositions and this may be due to the formation of small grains that, in some cases, are surrounded by a vitreous phase. One binary composition (75% MSS and PS 25%) showed a strength over 150 MPa. A mixture containing 33 % wt MSS, 33 % wt PS and 33 % wt steelworks slag (SS) was also prepared, processed and characterized like the other blends. All sintered samples were finally aged in an acidic (HCI) water solution to evaluate the elution of the components. It was observed that it is possible to limit the release of many of the most hazardous metals contained in the starting powders by an appropriate sintering schedule.