Percolation Segregation in Binary Size Mixtures of Spherical and Angular-Shaped Particles of Different Densities

Abstract

Percolation segregation in binary size mixtures for two particulate types, urea (spherical) and potash (angular), were studied. Materials chosen are major raw ingredients of blended fertilizer that represent two extremes based on shape and density. In this study, the coarse and fine particles were classified using particle sizes larger and smaller than 2,000 μm, respectively. Three coarse mean sizes (3,675 μm, 3,075 μm, and 2,580 μm) for both spherical and angular particles and three fines mean sizes (2,180 μm, 1,850 μm, and 1,550 μm) for angular particles and two fines mean sizes (2,180 μm and 1,850 μm) for spherical particles were selected for tests. Size ratio for binary size mixture is defined as the ratio of mean size of coarse to fine particles. Binary mixed samples of coarse and fine particles were placed into the shear box of the primary segregation shear cell (PSSC-II) very gently to avoid segregation. Percolation segregation was quantified using PSSC-II. Based on experimental results, the segregated fines mass, normalized segregation rate (NSR), and segregation rate of fines for binary mixtures were higher for larger size ratios as expected (2.4 > 2.0 > 1.7). The NSR is defined as the amount of fines percolated from initial fines present in the binary mixture based on total time of PSSC-II operation (kg/kg-h). Segregation rate was the highest and lowest for mixing ratios 33:67 and 67:33, respectively, when coarse mean size was 3,675 μm, where mixing ratio for binary mixtures is the ratio of the mass of coarse particles to the mass of fine particles. For the same size ratio, segregated fines mass for coarse-fine size combinations in the binary mixtures of urea and potash were significantly different (p < 0.05). Segregated fines mass of potash and urea particles was significantly different for the same size ratio and the same coarse sizes (p < 0.05). Percent segregated fines of angular particles (59%) was higher than that of spherical particles (45%) for the size ratio 2.0 and coarse mean size of 3,675 μm.