Abandoned historical gold mining wastes often exist as geographically extensive, unremediated, and poorly contained deposits that contain elevated levels of As and other potentially toxic elements (PTEs). One of the key variables governing human exposure to PTEs in mine waste is particle size. By applying a size-resolved approach to mine waste characterisation, this study reports on the proportions of mine waste relevant to human exposure and mobility, as well as their corresponding PTE concentrations, in four distinct historical mine wastes from the gold province in Central Victoria, Australia. To the best of our knowledge, such a detailed investigation and comparison of historical mining wastes has not been conducted in this mining-affected region. Mass distribution analysis revealed notable proportions of waste material in the readily ingestible size fraction (aecurrency sign250 A mu m; 36.1-75.6 %) and the dust size fraction (aecurrency sign100 A mu m; 5.9-45.6 %), suggesting a high potential for human exposure and dust mobilisation. Common to all mine waste types were statistically significant inverse trends between particle size and levels of As and Zn. Enrichment of As in the finest investigated size fraction (aecurrency sign53 A mu m) is of particular concern as these particles are highly susceptible to long-distance atmospheric transport. Human populations that reside in the prevailing wind direction from a mine waste deposit may be at risk of As exposure via inhalation and/or ingestion pathways. Enrichment of PTEs in the finer size fractions indicates that human health risk assessments based on bulk contaminant concentrations may underestimate potential exposure intensities.
Particle size distribution (PSD) analysis of the Gregory mine coal rejects, over a period of time is presented. The PSD has important implications on several processes contributing to the acid mine drainage. In this paper, correlation between the particle breakdown in the coal rejects and the rate of oxidation of sulphides is presented. Difference between the initial and the subsequent values of particle size distribution coefficient over a period of time indicated a change in particle breakdown mechanisms. An initial physical breakdown due to structural breakdown/rearrangement caused by wetting of the sample, and subsequent breakdown caused by the combined effects of physical and chemical weathering are proposed. Total number of particles increased with time, as the mean size of the distribution decreased. Increase in surface area calculated form the PSD analysis followed a power law with respect to time. The pyrite oxidation rate is dominated by diffusion and mass transfer processes initially, and as the total surface area is increased, contributed by breakdown of larger particles, a phase boundary control dominates the oxidation process.