The impact of iron sulfide on lead recovery at the giant Navan Zn-Pb orebody, Ireland

It has been proposed that blending of Navan Conglomerate Group Ore (CGO) with Pale Beds Ore (PBO), the latter which floats well in isolation, results in sub-optimal Pb recovery with increased abundance of pyrite reporting to the concentrate and increased abundance of galena reporting to the tails. QEMSCAN data indicate that poor liberation of galena particles is not the primary cause of sub-optimal recovery of galena. Rather, principal component analysis (PCA) of time of flight secondary ion mass spectrometry (ToF-SIMS) reveals that chemically altered surface species interfere with the selectivity and recovery of froth flotation indicating that there is some poisoning of galena mineral surfaces particularly with Fe-containing species possibly leading to loss of recovery. Analysis of the Pb-circuit cleaner tails indicates Pb-species association with sphalerite surfaces, as was observed for the flotation feed and rougher tails but with insufficient induced hydrophobicity by Pb–collector interaction for flotation. A small population of relatively clean galena surfaces is also observed which may result from low bubble–particle collision efficiency or insufficient liberation. Fine-grained framboidal pyrite is the main diluting phase in the cleaner concentrate and is likely present due to entrainment. The presence of framboidal pyrite in CGO is of particular significance as its large surface area increases the rate of galvanic interaction with other metal sulfide minerals. We propose that increased abundance of refractory framboidal pyrite in CGO is the critical factor affecting the performance of the Navan Pb flotation circuit rather than purely high pyrite abundance.