10 - Alkali activation of water and wastewater sludges: Solidification/stabilization and potential aluminosilicate precursors

Abstract

Alkali-activated materials (AAMs) are alternative cementitious or ceramic-like binders, and their use as alternative construction materials and for the solidification/stabilization (S/S) of various waste streams has been extensively studied. Their preparation requires an aluminosilicate precursor (e.g., clay minerals, metallurgical slags, or fly ashes) and an alkali activator (typically an aqueous solution of alkali silicate or hydroxide), which are allowed to react under (near) ambient conditions. The main binder pHases in AAMs consist of an amorphous alkali-aluminosilicate-hydrate framework or partly cross-linked tobermorite-like chains. In addition, various secondary phases can form, such as zeolites, ettringite, or layered double hydroxides. The relevance of using alkali-activation technology for sludge management is twofold: (1) Al- and/or Si-rich sludges represent a potential aluminosilicate precursor for AAMs and (2) the S/S of sludges containing hazardous components in AAMs is possible. This chapter provides an overview of the alkali activation of different water and wastewater treatment sludges, including the pre-treatments required for sludge, the development of the mix design, and the leaching of pollutants after treatment.