Correlation between the parameters of material transfer and granulation indexes in mixtures with varying ratios of concentrate to iron ore fines

Abstract

The production of high-grade fine material or concentrate continues to increase due to the depletion of high-grade ore deposits. In iron ore granulation, fine materials are involved in producing granules through the coalescence process and auto-layering around coarse particles. The effectiveness of granulation depends on the role of each size fraction of the ore mixture and the level of material transfer between size fractions, and it is measured by different granulation indexes, including maximum permeability, granulation effectiveness (x0.5) and mass fraction of fine material or concentrate. This study focused on the correlation between the level of material transfer between size fractions in granulated mixtures and different granulation indexes. Regular iron ore fines were replaced with 10%, 20%, 30% and 40% concentrate, respectively, to produce granules with an optimum moisture content, determined by the maximum permeability from a pilot-scale JPU (Japanese Permeability Unit) pot. The results indicated that the level of material transfer between size fractions can be used as an alternative index to evaluate the granulation effectiveness of ore mixtures. Adding more concentrate increased the formation of mini-granules that grow slowly, which is associated with a sluggish level of material transfer between size fractions. The growth of large granules was also delayed, leading to a small mean size of granules, low bed permeability and low granulation effectiveness or partition coefficient, x0.5. The coefficients of variance for the material transfer level and maximum permeability were comparable, providing an opportunity to replace the commonly maximum permeability with the level of material transfer in the measurement of the granulation effectiveness.