Comparison of different comminution flowsheets in terms of minerals liberation and separation properties

Abstract

Comparative mineral liberation and separation tests of hematite ores were conducted for three comminution flowsheet options to produce relatively fine products at the 70% and 90% passing 74 µm: Option A uses a high pressure grinding roll (HPGR) with screening and subsequent ball milling, Option B uses an HPGR with an air classification, and Option C uses a jaw crusher with screening and subsequent ball milling.Cracks growing inwards are relatively flat along the direction of applied force during conventional crushing. However, cracks surround the weak interface during HPGR crushing, generating a large number of “mosaic-type” locked-particles. Mineral liberation was only affected after the final grinding mode, not by the crushing method before grinding. “Mosaic-type” locked-particles produced via the particle-bed breakage have no better way to liberate in downstream ball-mill grinding.Fine mineral grains are then detached from the ore under the high compressive stress, which leads to a significant and clean liberation of the mineral phases in HPGR coarse grinding. Overall, HPGR grinding is more beneficial to the quartz liberation, while ball mill grinding is more beneficial to oxidised iron minerals at a coarse grinding fineness; these advantages disappeared after the further fine grinding.The coarse-sized liberated quartz, although well-liberated, raised rejection of coarse gangue in magnetic separation during HPGR grinding. Finally, recovery of the HPGR grinding process increased by 4.4–5.2 percentage points higher than that of the ball milling process.