Understanding the effect of metamictization on the efficiency of zircon milling

Six commercially available zircon sands were characterised by XRD, SEM, BET and helium pycnometry to determine their degree of metamictization. These sands were categorized into pairs denoted as high, medium or low levels of metamictization. The six samples were subsequently dry milled under identical conditions and their milling behaviour was tracked by measuring the particle size distribution at regular intervals. Samples with low levels of metamictization were found to achieve a marginally smaller particle size than samples with high levels of metamictization after prolonged milling. This was attributed to two potential mechanisms during breakdown – brittle fracture in the former due to retained hardness, in comparison to a more ductile resistance to fracture in the latter due to reduced hardness. However, no clear trend between specific metamictization characteristics and milling behaviour was found. The results reveal a poorer overall milling efficiency for high metamict samples, which has implications such as increased energy costs, poor quality product and a need for further processing of samples exhibiting high levels of metamictization. This study creates a novel link between the milling behaviour of zircon and its level of metamictization. The knowledge gained holds strong importance for industrial entities wishing to carry out and maintain an efficient milling process, with feed material quality likely to become more variable in future years.