Influence of hydrolysis mechanisms on molybdate sorption isotherms using chitosan

Molybdate sorption using chitosan sorbents has proved to be strictly contro lled by the pH of the solution. Sorption isotherms exhibit a sigmoid trend, which has been correlated to the appearance of polynuclear hydrolyzed spec ies, the most favorable species for sorption on chitosan. Sorption capacity exceeds 7 mmol.g(-1), which corresponds to a molar ratio between Mo and th e amine group significantly higher than 1. The formation of complexes in a pendant fashion and/or the ion-exchange mechanism of polynuclear metal ions are suspected to occur between polynuclear molybdate species and protonate d amine groups, though several amine groups can interact with the same poly nuclear molybdate group.