Adsorption of La,Eu and Lu on raw and modified red clay

Adsorption of La, Eu, and Lu on red clay was studied in an initial concentration range of 10^?4–10^?3 mol/dm³ and a pH range of 2–10. Among the different forms of red clay: T-clay (thermally modified), R-clay (raw, unmodified), Na-clay (sodium form), H-clay (acid form), and HDTMA-clay (surfactant-modified form), T-clay was found to be the most effective adsorbent of the lanthanides studied. The adsorption/desorption isotherms, i.e. log K _d versus log c _eq dependencies, had a linear character. Among the investigated lanthanides, Eu was most strongly bound by the clay surface and, therefore, parameters a (slopes of the lines log K _d = alog c _eq + b) of Eu were the highest compared to those for La and Lu. Desorption isotherms were located above adsorption isotherms, which resulted from chemiadsorption of the investigated lanthanides. Changes in lanthanide adsorption with pH were successfully modelled based on the molar fractions of Ln³⁺, LnOH²⁺, LnCO₃ ⁺, and Ln(CO₃) ₂ ^? species in the aqueous phase Ln—lanthanide(III)].