Pellet feed grinding by HPGR

• HPGR size reduction does improve the specific surface area of iron ore pellet feed material.
• Closed circuits with partial product recycle can be applied for adequate product qualities.
• A prediction model for product specific surface area from feed quality and recycle ratio is presented.
• A moisture range exists for optimising specific surface area, throughput and energy consumption.
• Dry HPGR and classification can provide a solution for minimize water usage and operating cost.

Apart from tertiary and quaternary crushing applications in a wide variety of ore types, High Pressure Grinding Roll (“HPGR”) technology is also applied in regrinding of iron ore pellet feed concentrate. A relatively large number of units have been or are being installed in iron ore pellet feed over the last few years throughout the world, in various circuits of single pass or closed circuit in combination with ball milling or stand-alone arrangement, and a number in a set-up involving a closed circuit of partial product recycle.Whereas the HPGR function in comminution operations obviously is the size reduction, the main purpose in pellet feed applications is a combination of fines generation with a main emphasis of creating a high specific surface area increase.This publication discusses three aspects of the features and experiences for pellet feed applications; an approach on the effect of discharge recycle ratio on the product quality and HPGR operation, a description of the effects of material moisture, and a discussion on the use HPGR for final grinding in iron ore pellet feed preparation by use of air classification.