Characterisation of airborne dust in a South African opencast iron ore mine : a pilot study

The iron ore mining industry makes use of various processes to produce a final product that results in the release of airborne dust into the surrounding atmosphere where workers are exposed. The deposition and toxicological influences of airborne dust can be determined by their physicaland chemical characteristics. The Occupational Health and Safety Act (OHSA) regulations for hazardous chemicals have no current system of how the physicaland chemical properties of particulates originating from specific areas will have an influence on worker exposure and health, especially for ultrafine particles (UFP). It is therefore imperative to characterize airborne dust containing micrometer and UFP size particles originating from specific areas to determine the influence that the physicaland chemical properties will have on the workers‘ health. Aim: This pilot study was aimed at the physical and chemical characterisation of the airborne iron ore dust generated at the process areas of a South African opencast iron ore mine. Method: Sampled areas include the Primary-secondary crusher, Tertiary crusher, Quaternary crusher and Sifting house. Gravimetric sampling was conducted through the use of static inhalableand respirable samplers in conjunction with opticaland condensation particle counters that were placed near airborne dustemitting sources. Physicaland chemical characterisation was done through the use of scanning electron microscopy (SEM) and energy dispersive X-ray (EDS) spectroscopy. Results: The results found in the study indicate high mass concentration levels of inhalable dust at all four process areas, as well as high levels of respirable dust found at the Primary-secondary crusher area. Particle size distribution optical particle counter (OPC) results indicate that the majority of particles at all four process areas were 0.3 μm in size. Condensation particle 30 counter (CPC) results integrated with OPC results indicate that at the primarysecondaryand Tertiary crushers the majority of particles were found to be in the size fraction <0.3 μm. SEM analysis indicates that particle agglomeration largely occurs in the airborne iron ore dust. Particle splinters originating from larger particle collisions and breakages are present in the airborne dust . EDS analysis indicates that the elemental majority of the airborne iron ore dust consists of iron, oxygen, carbon, aluminium, silicon, potassium and calcium. The elemental percentages differ from each process area, where an increase in iron and decrease in impurities can be seen as the ore moves through the beneficiation process from the primarysecondary crusher to the Sifting house. Conclusion: The results obtained from the physicaland chemical properties of the airborne iron ore dust, indicate a high risk of overexposure to the respiratory system, as well as possible ultrafine particle systemic exposure that may overwhelm the physiological defense mechanisms of the human body and lead to reactive oxygen species (ROS) formation and the development of pathologies such as siderosis, silicasiderosis and lung cancer.