Preparing a binder for cemented paste backfill using low-aluminum slag and hazardous oil shale residue and the heavy metals immobilization effects

Abstract

The high cost and carbon emission of ordinary Portland cement (OPC) increase the burden of mining industry and aggravate environmental pollution. In this study, a cheaper and greener binder was prepared using low-aluminum slag and calcined oil shale residue (COSR) as main precursors to provide an alternative cementing material for cemented paste backfill (CPB). The influence of COSR content on the properties of the CPB sample was investigated, including rheological properties, setting time, mechanical strength, and pore structure. Characterization of binder sample was then conducted via isothermal calorimetric analysis, X-ray diffraction (XRD), thermogravimetry (TG), and scanning electron microscope (SEM). The optimal mix proportion of binder was 56 wt% slag, 24 wt% COSR, 15 wt% flue gas desulfurization gypsum (FGDG), and 5 wt% OPC. The solid waste utilization rate in the binder production reached 95%, considered an eco-friendly binder. Besides, the best performance of the binder was mainly due to the optimal Al2O3 and CaO content, leading to large amounts of precipitated ettringite. It then contributed to a denser structure with high mechanical strength. Furthermore, the sequential extraction test showed that the heavy metal in the solidified CPB sample existed mainly as a residual fraction, contributing to the superior immobilization effects.