Alkanolamines-activated steel slag for stabilization/solidification of heavy metal contaminated soil

Abstract

Steel slag (SS) is a byproduct discharged from steel-making industry with less than 25% utilization rate in China. The low utilisation rate of SS is associated with its low hydration activity in cement and concrete. In this study, four different alkanolamines (TEA, TIPA, EDIPA and DEIPA) were used to activate SS to improve its cementitious properties and metal binding performance, and hence its capacity on treating heavy metal-contaminated soils containing Cd, Cu, Ni, Pb and Zn. Compared with the reference SS without activators, concentrations of leached Cd, Cu, Ni, Pb, and Zn have reduced by 87.2%, 78.8%, 62.4%, 73.6% and 64.5% by using 0.1% TIPA-activated SS after 28 days, and they were all below their respective regulatory limits by Standard for Pollution Control on the Hazardous Waste Landfill (GB 18598–2019) in China, and the unconfined compressive strength (UCS) of the treated soil at 28 days was enhanced by 237.7% using 0.1% TIPA-activated SS. To elucidate the activation mechanism, the hydration process of SS was thoroughly followed via isothermal calorimetry (IC) and conductivity analysis, and the nature of hydration products was studied by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). It was concluded that alkanolamines facilitated the dissolution of minerals in SS and formation of hydration products (e.g., C-S-H, C-A-H, C-F-H and Mc), and hence significantly enhanced the microstructural development and engineering properties of SS. This work demonstrated a promising way of upcycling SS as an effective and sustainable S/S agent for handling complex heavy metal contaminated soil, with the potential of enhancing the SS utilization significantly.