Cadmium removal by bioclastic granules (Lithothamnium calcareum): batch and fixed-bed column systems sorption studies

摘要

The potential of Bioclastic Granules - BG (calcium-carbonate-based material) using the algae Lithothamnium calcareum as sorbent for the removal of Cd(II) from aqueous solutions by sorption was evaluated through batch and continuous systems tests using a fixed-bed column. Sorption process variables, in particular pH (2-7), particle size (38-300m), initial BG concentration (0.1-1.0gL(-1)), initial Cd(II) concentrations (5-400mgL(-1)) and contact time (5-240min), were evaluated. Adsorption isotherm profiles of Cd(II) per BG were similar to an L-type, or Langmuir type, with the adsorption forming a monolayer of approximately 0.61m, with a q(max) of 188.74mgg(-1) and k(L) of 0.710Lmg(-1). Thomas's model considers that sorption is not limited to a chemical reaction but is controlled by mass transfer at the interface. In the present study, the obtained value of k(Th) was 0.895mLh(-1)mg(-1), reaching a sorption capacity q(o) of 124.4mgg(-1). For the Yoon-Nelson model, it was possible to obtain two important parameters to describe the behavior of the column, the rate constant (k(YN)), obtaining a value of 0.09h(-1) and an of 82.12h corresponding to the time required for sorption to occur of 50% of the solute in the rupture curve. X-ray diffraction and scanning electron microscopy analyses coupled to the X-ray dispersive energy system (SEM/EDS) of the BG after the Cd(II) ion sorption tests evidenced the formation of crystals with the prevalence of a new mineral phase (otavite).