Evaluation of a lime-mediated sewage sludge stabilisation process. Product characterisation and technological validation for its use in the cement industry

摘要

This paper describes an industrial process for stabilising sewage sludge (SS) with lime and evaluates theudviability of the stabilised product, denominated Neutral, as a raw material for the cement industry. Limeudnot only stabilised the sludge, raised the temperature of the mix to 80–100 C, furthering water evaporation,udportlandite formation and the partial oxidation of the organic matter present in the sludge.udProcess mass and energy balances were determined. Neutral, a white powder consisting of portlanditeud(49.8%), calcite (16.6%), inorganic oxides (13.4%) and organic matter and moisture (20.2%), proved to beudtechnologically apt for inclusion as a component in cement raw mixes. In this study, it was used insteadudof limestone in raw mixes clinkerised at 1400, 1450 and 1500 C. These raw meals exhibited greater reactivityudat high temperatures than the limestone product and their calcination at 1500 C yielded clinkerudcontaining over 75% calcium silicates, the key phases in Portland clinker. Finally, the two types of rawudmeal (Neutral and limestone) were observed to exhibit similar mineralogy and crystal size anduddistribution.