Adsorption of rare earth ions from synthetic seawater and hot spring water using phosphorylated yeast

In a previous study, a metal-adsorbing yeast with chemically modified phosphate groups (referred to as P-yeast) was developed. The adsorption performance of P-yeast was evaluated using synthetic seawater and hot spring water for extracting rare earth elements (REEs) from nature. In the case of synthetic seawater containing Dy3+, 90% of the ions were adsorbed while the adsorption of Na+ and Mg2+ present at high concentrations was suppressed. Furthermore, the performance of P-yeast was examined using strongly acidic hot spring water (from Tamagawa hot spring, Japan) containing several tens of ppb of REEs (Ce3+, La3+, Dy3+, and Gd3+). A part of Al3＋ and Fe2＋ present at high concentrations in hot spring water was removed as a precipitate after pH adjustment while 60%–80% of REEs remained in the solution. Ce3+, the most abundant REE, was contained at 37 ppb. P-yeast could adsorb REEs from the solution after the treatment and, in combination with a desorption phase using acid, these elements could be concentrated 10–19 times with a recovery of 20%–37%. It was strongly suggested that P-yeast is a practical microbial adsorbent, as selective adsorption and concentration were achieved even in environmental water, which has a low concentration of target substances and many contaminants. In the future, P-yeast made from industrial waste such as surplus yeast is expected to be applied to recover rare earth ions.