Microbial leaching of rare earth elements from fluorescent phosphor

Rare Earth Elements (REE) are used in mostly all new technologies and until now, there is no environmentally friendly recycling-process for fluorescent phosphor. Furthermore, China has with a worldwide market share of 94 % (2011) [1] a virtual monopoly in the production of REE. Therefore, there is increasing demand for novel recycling technologies to secure the supply of REE. During recycling of energy-saving bulbs fluorescent phosphor containing rare earth elements (REE) is collected as a distinct fraction. In this study hydrometallurgical techniques were investigated to recycle REE from spent technological products. Due to electrochemical restrictions, leaching with organic acids and metal binding molecules is more promising, than oxidation or reduction reactions [2, 3]. On this basis, different hetero- and autotroph aerobe microorganism pure and mixed cultures are selected. Among them are “classical” leaching organisms like Acidithiobacillus ferrooxidans and A. thiooxidans, as well as the organic acid producing Corynebacterium collunae (glutamic acid), the yeast Yarrowia lipolytica (citric acid) and the tea fungus kombucha. The investigations regarding their ability to leach the REE from fluorescent phosphor, originating from recycling processes, were performed in fed-batch experiments.
It could be shown that complexation of the REE by organic acids produced by the microorganisms lead to considerable higher concentrations of REE in the supernatant than in the control. These results show that the usage of microbial processes for the recovery of REE is possible and could be an eco-friendly alternative to the currently employed methods.

1. Roskill, Rare Earths & Yttrium: Market Outlook to 2015. 14th Edition ed. 2011, London. 534.
2. Evans, C.H., Biochemistry of the Lanthanides. Biochemistry of the Elements, ed. E. Frieden. Vol. 1. 1990, New York, London: Plenum Press. 444.
3. Morss, L.R., Yttrium, Lanthanum, and the Lanthanide Elements, in Standard Potentials in Aqueous Solution, A.J. Bard, R. Parsons, and J. Jordan, Editors. 1985, Marcel Dekker, Ink.: New York, Basel. p. 587-629.