Relationship between particle size distribution and the PFD80 transportable moisture limit of iron ore fines.

Abstract

Since 2011, mineral cargoes shippers shall comply with a regulatory framework established by the United Nation’s International Maritime Organization (IMO): the International Maritime Solid Bulk Cargoes (IMSBC) Code. Some wet mineral cargoes, including some types of iron ore fines, may liquefy during ocean transport, i.e., the cargo can shift and lead the vessel to sink. According to the IMSBC Code, for safe shipping, the moisture content of these cargoes shall be lower than a regulatory limit: the Transportable Moisture Limit (TML). Iron ore fines TML can be obtained through the Modified Proctor/Fagerberg Test for Iron Ore Fines (PFD80), a dynamic compaction test which consists in compacting ore samples at different moisture contents, the TML being the moisture content at which the material reaches 80% saturation. TML has become a relevant parameter for the mining industry, firstly due to the crew and ship safety aspect, and because failure to comply with the TML can legally interrupt an ore shipment or even an entire mining/shipping operation. Therefore, knowledge related to the TML and the understanding of how it varies with ore characteristics are essential. Despite that, research works on this topic are still scarce. In this study, the relationship between particle size distribution and the TML of iron ore fines was experimentally investigated. The results have shown that the TML is highly related to the particle size distribution of the tested material, and that the TML variations can be explained by structural packing effects caused by particle interactions during compaction for different types of size distribution. It was also found that the coefficient of uniformity can be used for numerically representing the particle size distribution in order to establish relationships with the TML. Another relevant conclusion is that the TML of a mixture of different iron ore fines may not be the result of the weighted average of the individual components’ TML. This knowledge is of utmost importance for the industry, as blends of different ore products are common practice, and this finding is relevant for other cargoes that are susceptible to liquefaction.