An investigation of the leaching behavior of trace elements from Spreader Stoker Coal Fly Ashes-based systems

• Valorization of Spreader Stoker Coal Fly Ashes (SSCFA).
• Stabilization of SSCFA with various binders and chemical activators.
• Study of leaching behavior and compressive strength of SSCFA-based systems.
• Improvement of SSCFA pozzolanic reactivity by correct activating systems.
• Decrease in the leachability of some elements by correct activating systems.

Spreader Stoker Coal Fly Ashes (SSCFA) are not considered as standard by-products equivalent to Pulverized Coal Fly Ashes (PCFA) and are currently sent to landfill. From economical and environmental points of view, the landfill of these ashes is a serious concern and an alternative solution consisting in reusing them appears to be essential. For example, they could be incorporated in hydraulic binders for the manufacturing of nonstructural blocks. A previous study showed that SSCFA had interesting pozzolanic properties with specific characteristics approaching those of PCFA and reported encouraging leaching results for blended cements with SSCFA and slag. However, some leachate concentrations were still too high. The aim of this study is to assess the stabilization of SSCFA by using alternative binders (slag, cement, clinker, portlandite) and chemical activators (water glass, calcium sulfate, sodium sulfate, potassium sulfate, calcium chloride), which could be more interesting to activate SSCFA and reduce the leachability of trace elements. Results show that some alternative binders and chemical activators can increase the pozzolanic reactivity of SSCFA and the early strength of SSCFA-based systems. Adding sodium and potassium sulfate to systems composed of SSCFA and portlandite greatly improves the compressive strength value. The value is even increased when a part of portlandite is replaced by cement, clinker or slag. Moreover, the leachability of some trace elements can be reduced. This study points out the fact that alternative solutions to landfill of SSCFA might exist and reminds the need for more research work on waste stabilization.