Performance of alkali-activated slag binder in immobilizing heavy metals

It is commonly known that Portland cement production causes tremendous environmental impacts. In this context, sustainable binders are desired.

Alkali-activated materials (AAMs) have attracted increasing attention due to their lower embodied energy and 25-60% less CO2 emission.

The most widely used precursors to synthesise AAMs are ground granulated blast furnace slag (GGBFS), fly ash and metakaolin. Among these, alkali-activated GGBFS (AAS) is the dominant class of AAMs in large-scale production.

However, the availability of GGBFS is becoming limited due to the policy changes related to green transition of the iron and steel industry, which consequently impedes the commercial scale production and use of AAS.

To deal with this issue, researchers are searching for alternative metallurgical slags, such as ferronickel slag, copper slag, lead-zinc slag and electrolytic manganese residue.

Although many efforts have been made, the current utilization of these metallurgical slags as precursors is still restricted. One of the biggest obstacles is the considerable amounts of heavy metals (HMs) in these metallurgical slags. Effective immobilization of HMs within AAS has become a critical issue for utilizing these metallurgical slags.

Against this background, we aim to determine the performance of AAS binder in immobilizing HMs under in-service conditions.

The effects of slag chemistry and alkaline activator on solidification as well as ions leaching, cracking and redox condition in slag on stabilization of HMs in AAS will be elucidated.

Moreover, a novel reactive-transport model considering the binder chemistry and shrinkage-induced cracking will be established for the first time to predict solidification/stabilization of HMs in AAS.

The results of this project will provide a solid foundation for assessing the performance of AAS in immobilizing HMs, which is essential for the sustainable development of AAS and efficient treatment of hazardous wastes by using AAS binder.