(366e) Using Agricultural Wastes to Recover Rare Earth Elements from End-of-Life Materials

An economical and eco-friendly bench-scale process that relies on microbial production of organic acids has been developed to solubilize and release rare earth elements (REE) from solid recyclable materials (Reed, Hydrometallurgy, 2016, 166:34-40). Techno-economic analysis (TEA) and life cycle analysis (LCA) for bioleaching of REE from fluid catalytic cracking (FCC) catalysts suggested that a bioleaching plant could be profitable, but could be even more profitable if the cost of the sugar (glucose) used for growing the microbes was reduced (Thompson, ACS Sustainable Chemistry & Engineering, 2017, 6:1602-1609). This presentation will focus on our efforts to improve the economics of REE bioleaching using alternative carbon and energy sources as microbial growth substrates.

In our previous work examining the potential for several organic acid producing microorganisms to leach REE from end-of-life waste materials we identified Gluconobacter oxydans B58 as a promising industrial strain. Lixiviant produced by G. oxydans, containing predominantly gluconic acid, could recover ~50% of the total REE content of FCC catalyst. The biologically produced lixiviant was more effective than an abiotically prepared solution containing a similar concentration of gluconic acid. TEA and LCA showed that bioleaching could be more profitable and environmentally friendly than industrial standard chemical leaching processes, suggesting commercial viability. However, substantial reductions in operating costs could be achieved by replacing the refined glucose used in the original growth medium with a lower cost substrate. Consequently corn stover and potato wastewater were tested as growth substrates for G. oxydans. The initial lixiviants generated were tested against FCC and yielded a leaching efficiency 50-90% of the best case leaching efficiency of glucose-derived biolixiviant. Work is ongoing to optimize biolixiviant production from agricultural wastes. The conditions for improving bioleaching using waste-derived biolixiviants, including TEA and LCA evaluations, will be discussed.