Comparison of Microwave and Conventional Roasting in the Leaching of Rare Earth Elements, V, Ni, and Li from Polymetallic Black Shale

Polymetallic black shale from the Buckton deposit in Alberta, Canada, is an undeveloped resource for V, rare earth elements (REEs), Ni, Li, and a few other metals. In this work, the valuable elements are extracted from the shale using a low-temperature sulfation roasting-water leaching method. Sulfation roasting enables the destruction of mineral phases releasing V ions as well as REEs, Li and Ni. We compare microwave and conventional roasting under varying temperature, sulfuric acid dosage, and time, followed by water leaching, to determine the optimum leaching efficiencies of metals. Microwave roasting consumes less energy than conventional roasting for similar release % of metals in laboratory-scale as well as scaled-up process (5 times larger) with a significant reduction in roasting temperature (by 40 °C) and time (by 30 min). A maximum leaching efficiency of 100% of gadolinium, 85% of ytterbium, 84% of Ce, 76% of Ni, 74% of V, 59% of Li, 34% of neodymium, 21% of yttrium, and 13% of La was achieved. We have identified the host minerals of several of the valuable elements using detailed mineralogical analyses which can be useful in formulating more efficient metal release strategies.