Excellent adsorption performance of sulfated yeast for heavy metal ions: High capacity and selectivity for rare earth elements.

The aim of this study is to provide valuable knowledge for developing a biological material effective in recovering and removing metals from solutions. Yeast was used as the base material. Yeast, a homogeneous material with a rigid cell wall, is inexpensive, readily available (it can even be obtained from brewer's waste), and amenable to chemical and genetic modification. Since native yeast exhibits low adsorption capacity, yeast with numerous sulfate groups to enhance metal binding was prepared through chemical modification in this study, and the heavy metal adsorption properties of the resulting S-yeast were analyzed. The modification increased the sulfur content of the yeast to over 10 %, and S-yeast prepared using HNSO exhibited a high adsorption capacity exceeding 2 mmol/g dry weight for Cu, Zn, and Cd. Additionally, Cu was rapidly adsorbed upon addition, could be desorbed with HCl, and readsorbed onto the desorbed yeast. Rare earth elements were also adsorbed at levels exceeding 1 mmol/g dry weight, with these values surpassing those achieved by previously developed phosphorylated yeast. The effect of HCl addition on adsorption differed between rare earth elements and divalent heavy metals, with rare earths selectively adsorbed at 0.3 M HCl. Furthermore, light rare earth elements were selectively adsorbed over heavy rare earths, suggesting that rare earths with larger ionic radii are more readily adsorbed. Sulfated yeast thus shows promise as a material for removing and recovering heavy metals from solution. These findings offer valuable insights into the development of new environmental materials.