Geochemical cycles of arsenic in historic tin tailings from multiple ore sources : an example from Australia

In this work, we studied a geochemically unique abandoned tin mining tailings facility in tropical north Queensland, Australia. Tin mining residues from local operations were reprocessed and left without proper remediation, after which native plant species colonised this site over time. The aim of this study was to characterize the mine tailings to understand the geochemistry and predict the potential mobility and bioavailability of major contaminants, arsenic and tin. Major and trace minerals were identified with X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Acid digestion and sequential extraction procedures were used to quantify elemental concentrations and potential mobility. We found that the highly oxidized tailing cells were dominated by quartz with limited buffering capacity to prevent acid mine drainage formation, consequently creating an acidic environment (pH 4). Arsenic (As) and tin (Sn) were identified as the main contaminants in the tailings with concentrations of up to 2980 μg g−1 and 2910 μg g−1, respectively. Tin was mainly bound to the residual fraction (52% of total Sn) and crystalline Fe-oxide fraction (33% of total Sn), limiting its release and mobility. The bulk of As (~77% of total As) was present in the crystalline Fe-oxide fraction, while ~19% in the amorphous/poorly crystalline Fe-oxide fraction. The bioavailable As fraction was negligible (~1%), and this was confirmed by limited As accumulation in terrestrial and aquatic plants (Cyperaceae sp., Eleocharis equisetina, and Poaceae sp.) sampled at the site. This interdisciplinary study reveals biogeochemical properties of Sn tailings, the fate of As, and how native plants can thrive in this unfavourable environment. This information can potentially guide further phytostabilization efforts at this site