Optimizing 1-hydroxyethylidene-1,1-diphosphonic acid and mechanically-activated iron ore tailings to prepare low-cost and retarded magnesium oxysulfate cement

Industrial solid waste, known as iron ore tailings (IOT) is often generated in mineral processing. Precariously, the output of tailing byproducts is quite large while its utilization is very low, and this has become a vital issue to China's economic and social development. This study is aimed at developing a sustainable composite using IOT. In this paper, the impact of IOT and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) on the magnesium oxysulfate (MOS) cement attributes were studied from the micro and macro aspects. Retardation, high-strength, low-cost MOS cement samples were prepared. The compressive strength, setting time and water resistance of MOS cement were explored by replacing light-burned magnesia powder with activated IOT (by 10%, 20%, and 30% respectively). In this paper, the mechanical properties, water resistance, and retardation mechanism of adding HEDP to MOS cement were thoroughly investigated by XRD, TG-DTA, SEM, MIP and other test methods. HEDP forms a stable chelate with [Mg(OH)(H2O)]+ produced during the hydration of MgO, slowing down the hydrolysis of active MgO to Mg(OH)2, thereby delaying the setting time of MOS cement. The addition of HEDP provides feasibility for the application of MOS cement in practical engineering. Experimental results reveal an optimal HEDP dosage of 0.75% and the addition of 10% of mechanically activated IOT for 1.0 h does not reduce the compressive strength of MOS cement, and the purpose of solid waste treatment can be achieved.