Magnesium phosphate cement prepared with electric furnace ferronickel slag: Properties and its hydration mechanism

摘要

High-magnesium electric furnace ferronickel slag (EFS) is an industrial solid waste, typically generated in nickel metallurgical production. This study presents an eco-friendly approach to prepare magnesium phosphate cement by using EFS as the substitute for magnesium oxide to react with ammonium dihydro-gen phosphate (NH4H2PO4, ADP). The effects of EFS/ADP ratio and the addition of magnesium oxide on the compressive strength and setting behaviour of EFS-based magnesium phosphate cement (EMPC) are studied. The evolutions of pH and ions (Mg2+ and PO43-) concentrations of EMPC suspensions and the hydration product are investigated through inductively coupled plasma-atomic emission spec-troscopy (ICP-AES), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and Fourier trans -form infrared spectroscopy (FTIR). Results show that the compressive strength of EMPC paste with the optimal formulations (EFS/ADP mass ratio of 4.0, MgO content of 3.2% and water-to-cement mass ratio (W/C) of 0.20) reach up to 33, 42, 52 and 62 MPa at 1, 3, 7 and 28 d, respectively, and the initial setting time is 7 min. Struvite (MgNH4PO4 center dot 6H(2)O) is identified as the principal hydration product of EMPC. The formation mechanism regarding EMPC involves the dissolution of NH4H2PO4, MgO and Mg2SiO4, the pre-cipitation of the intermediate hydrate phase and the formation of struvite as the binder phase. Moreover, EMPC paste has an excellent solidification/stabilization performance of heavy metals, and the Cr leaching concentration meets the requirement of limit value of GB 5085.3-2007 (USEPA 1311). (C) 2021 Elsevier Ltd. All rights reserved.