Abstract
Abstract The main objective of this work is to investigate a viable alternative for the final disposal of sewage sludge from urban wastewater treatment plants using a mixture with cement and jarosite/alunite (J/A) precipitate to develop new construction materials. J/A precipitate is a waste product of a new hydrometallurgical process, which was developed in order to treat economically low-grade nickel oxide ores. In the current study two methods were used for the hardening of the stabilized/solidified products: (1) in laboratory conditions and (2) in accelerated conditions (autoclave treatment). For this purpose, mortar prism samples of 4 × 4 × 16 cm in dimension were prepared, composed of 50% sewage sludge, 30% cement and 20% jarosite/alunite. The samples were treated in an autoclave for 3 h at a temperature of 200 °C and a pressure of 16 bar as well as in laboratory conditions for 28 and 90 days. Compressive and bending strength, while chemical, XRD, thermal analysis, as well as tests of leaching, were tested according to the standard/principal methods of toxicity characteristics leaching procedure (TCLP) and CEN/TS 14405. The results indicated that stabilized/solidified products can be produced for use in construction and that the heavy metals of sludge can be contained in the cement and jarosite/alunite mixture.
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