Sorption of rare earth elements and uranium on biomass: a kinetic study of competition processes

The quantitative study of the adsorption of metallic ions on both organic and mineral surfaces showed that sorption is strongly dependent on chemical parameters such as pH or competing ions. An increase in pH yields to a greater amount of fixed metals whereas the competition between ions tends to decrease the relative amount of each sorbed element. Moreover, the behaviour of the adsorption sites and the binding capacity of each material (at different pH) and their selectivities have been studied for complex solutions including up to 7 cations introduced at the same starting concentration. Sorption of cations is very fast and up to 90% of the fixation is achieved in less than 10 minutes. However, fluctuation in the total of sorbed ions is observed for greater times. Results show that biomasses bound more efficiently uranium than rare earth elements, and that the final amounts of sorbed rare earth elements depends on the nature of the elements, with the following order of increasing sorbed quantities: Ce, Nd, La, Pr and Dy. The same order is found during the sorption of rare earth elements on clays. Finally, kinetics analysis of sorption were done in order to fit experimental results by Freundlich or Langmuir adsorption model which seems more appropriated.