Exploration of indium in sulfidic mine waste and acid mine drainage environments

Indium (In) is a critical metal essential for the transition to a low-carbon economy including its use in solar panels. However, there is a significant knowledge gap regarding cycling of indium in mine waste environments. This study aims to understand the mobility of indium in two different geological mine waste environments as an essential first step toward designing a remining process. Core, waste rock, acid mine drainage (AMD)-impacted waters and sediment samples were collected from Mt Morgan (Au-Cu VHMS) and Baal Gammon (Sn granite-related) historic/abandoned mines and subjected to geochemical and mineralogical investigations. Preliminary results suggest that core and waste rock from Baal Gammon contain above 500 ppm In, with sphalerite the main endowed In-bearing mineral (up to 3,776 ppm In). High concentrations, up to 73 mu m/L In, were measured in AMD waters along with fluoride (38 to 120 mg/L). In contrast, waste rock and AMD water samples from Mt Morgan reported a maximum of 3.53 ppm and up to 5 mu m/L In (with elevated chloride) respectively. This study found that indium is significantly enriched in the sampled Sn-granite mine waste and that pH and fluoride can potentially control indium mobility in AMD waters.