Impact of high-pressure grinding roll on ironsand pellets preparation:mechanical activation mechanism and energy efficiency assessment

The utilization of ironsand for preparing oxidized pellets poses challenges, including slow oxidation and low consolidation strength. The effects and function mechanisms of high-pressure grinding roll (HPGR) pretreatment on the oxidation and consolidation of ironsand pellets were investigated, and the energy utilization efficiency of HPGR with different roller pressure intensities was evaluated. The results indicate that HPGR pretreatment at 8 MPa improves the ironsand properties, with the specific surface area increasing by 740 cm² g^-1 and mechanical energy storage increasing by 2.5 kJ mol^-1, which is conducive to oxidation and crystalline connection of particles. As roller pressure intensity increases to 16 MPa, more mechanical energy of HPGR is applied for crystal activation, with mechanical energy storage further rising by 18.1 kJ mol^-1. The apparent activation energy for pellet oxidation initially decreases and then increases, reaching a minimum at 12 MPa. Simultaneously, the roasted pellets porosity decreases by 2.8%, while the compressive strength increases by 789 N. At higher roller pressure intensity, the densely connected structure between particles impedes gas diffusion within the pellets, diminishing the beneficial effects of HPGR on pellet oxidation. Moreover, excessive roller pressure intensity decreases the HPGR energy utilization efficiency. The optimal HPGR roller pressure intensity for ironsand is 12 MPa, at which the specific surface area increases by 790 cm² g^-1, mechanical energy storage increases by 10.6 kJ mol^-1, the compressive strength of roasted pellets rises to 2816 N, and the appropriate preheating and roasting temperatures decrease by 250 and 125 °C, respectively.