In this study, Ca-loaded macroalga Pelvetia canaliculata was investigated as a natural cation exchanger for barium removal. A mass action law was able to fit satisfactorily the equilibrium data for the ternary mixture (Ba 2+ /H + /Ca 2+), resulting in selectivity coefficients of Ba H K = 6.88/0.41 and Ca H K = 3.08/0.03, for carboxylic/sulphonic groups. In the packed bed column, the service capacity was 237 bed-volumes (BV), treating 14.2 L of influent with a feed concentration of 2.9 mEq Ba 2+/ L, until the breakthrough point of 0.07 mEq Ba 2+ /L. Elution efficiency near to 100% was achieved using 5 BV of 1.0 M HCl in counter-flow direction. A dynamic mass transfer model, considering equilibrium given by the mass action law, linear driving force (LDF) approach to describe the intraparticle mass transfer resistance and the stagnated film resistance described well the breakthrough profiles for all species obtained in a packed bed column.