Lanthanum biosorption by different Saccharomyces cerevisiae strains

Biosorption can be a promising technology in rare earth metal separation and recovery due to the low costs of waste biomasses (used as biosorbents) and the high selectivity exploiting specific interaction between metals and biological active sites. In this work, Saccharomyces cerevisiae biomass was used to recover lanthanum. Biosorption properties of two S. cerevisiae strains, wild type and rim20. mutant, have been tested. Potentiometric titrations were carried out for rim20. mutant strain and compared with wild type. Nature of the main active sites and their concentration were determined by implementing mechanistic models. Carboxylic, amino and phosphoric sites are the main groups present. Higher concentration of negatively charged sites was found in rim20. (0.0024 mol/g) than in wild type (0.0022 mol/g). The rate of lanthanum biosorption process is very fast requiring only 10-20 minutes to reach equilibrium condition for both strains. Then biosorption equilibrium tests were done for both biomasses by testing two equilibrium pH (4.0 and 6.0). Maximum uptake capacities (qmax) were: 70 mg/g and 40 mg/g at pH 4.0 for rim20. and wild type, respectively, and 67 mg/g and 80 mg/g at pH 6.0 for wild type and rim20., respectively. These data evidenced that: rim20. mutant had a higher maximum biosorption capacity with respect to wild type counterpart, and that pH had a relevant effect on lanthanum removal. S. cerevisiae yeast denoted good lanthanum biosorption properties and, between tested strains, rim20. was found to be the most promising for such aim.