Nickel is listed as a critical mineral in the United States due to its necessity for electric vehicle batteries, the aerospace industry, and for artificial intelligence. The US government has made securing the US supply chain for nickel a high-priority through both opening new mines and developing new technologies that can extract nickel from waste resources. In this study, we introduce a novel bioleaching process to extract high-purity nickel from low-grade nickel mine tailings (0.1 wt% nickel). Cattails are grown and subsequently decomposed on the surface of the tailings pond. The decomposing biomass introduces organic acids, which are primarily acetic acid with minor amounts of lactic and citric acids, into the tailings. The organic acids lower the pH to around 4.5 and solubilizes the nickel at concentrations between 10-20 ppm. The solubilized nickel is then pumped out of the tailing pond to be recovered through electrowinning. The modeled process produces 4.5 kg of high-purity nickel per acre per day over a design life of 15 years.
Through process modeling, the economic and environmental feasibility of the bioleaching process was determined to be favorable. The main cost drivers for the process are the capital costs for the electrowinning equipment and the electricity needed to continuously circulate water between the tailings pond and the electrowinning unit. Environmentally, the vast majority of GHG emissions are from electricity usage. A number of scenario analysis will be presented including the impact of using renewable electricity vs grid, the effect of changing the initial nickel concentration and solubilization rate, and the potential sequestration of CO2 through the formation of iron carbonates when iron in the tailings react with the organic acids.
