Preparation of blast furnace burden utilizing sinter return fines: Cold-bonded pellet forming and comprehensive burden structure optimization

Abstract

The utilization of sinter return fines in preparing cold-bonded pellets (CBPs-RF) as blast furnace burden presents a promising approach. This study experimentally investigated the impact of raw material moisture content and molding pressure on pellet performance. A grading index was introduced to characterize particle size distribution. The experimental findings demonstrated that the porosity of CBPs-RF was notably reduced from 17.3 % to 11.4 % when subjected to a grading index of 0.5. This substantial decrease in porosity was primarily attributed to the iron ore concentrate effectively filling the interstitial spaces among the coarser return fines, thereby enhancing the material's compactness. Furthermore, a composite binder tailored for sinter return fines was developed; organic binder B contains abundant polar functional groups, which facilitate chemical adsorption onto the surface of iron ore compounds, thereby ameliorating the contact heterogeneity between inorganic binder A and the return fines. The crosslinking reaction between organic binder B and inorganic binder A yields an interwoven three-dimensional network structure, underpinning the enhanced binding strength of the composite binder. Compared to conventional sinters, CBPs-RF demonstrated superior performance in low-temperature reduction degradation (RDI_+3.15 > 90 %) and reduction swelling index reduction (RSI < 10 %). Its advantages stem from the dispersed arrangement of sinter return fines and their effective synergy with soft binders and porous iron fine layers, mitigating crack propagation and expansion during reduction, thus alleviating volumetric expansion. Comprehensive burden studies indicate that incorporating 5.0 % CBPs-RF exhibits favorable softening and dripping properties, providing crucial insights for the efficient utilization of sinter return fines as a blast furnace burden.