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

Abstract

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 (<38-300 μm), initial BG concentration (0.1-1.0 g L), initial Cd(II) concentrations (5-400 mg L) and contact time (5-240 min), 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 0.61 μm, with a q of 188.74 mg g and k of 0.710 L mg. 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 was 0.895 mL h mg, reaching a sorption capacity q of 124.4 mg g. For the Yoon-Nelson model, it was possible to obtain two important parameters to describe the behavior of the column, the rate constant (k), obtaining a value of 0.09 h and an τ of 82.12 h 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).

Characteristics and mechanisms of cadmium adsorption onto biogenic aragonite shells-derived biosorbent: Batch and column studies

“…The finial pH solution in this study ranged from 6.13 to 7.33, confirming that the adsorption mechanism did not involve the precipitation of cadmium with hydroxide. This finding is similar to that presented by Veneu et al (2017) for Cd(II) adsorption onto algae Lithothamnium calcareum, but dissimilar to Alidoust et al (2015) for Cd(II) adsorption onto calcined oyster shells.…”

“…The amount of Cd(II) adsorption onto FMS increased when pH solution increased, with its adsorption capacity reaching plateau values at pH solutions higher than 4.0. This conclusion is well consistent with observations documented in (Veneu et al, 2017;Sdiri et al, 2012). As presented in Figure 5b, the pH PZC of FMS is 10.8, which is identical to the finding of other CaCO 3 -enriched materials, such as 11.4 for eggshells (Flores-Cano et al, 2013), 10.6 for calcined eggshells (Slimani et al, 2014), and 9.2 for mussel shells (El Haddad, 2016).…”

“…(1) certain chemical interactions with sufficient energy could overcome the surface-electrostatic repulsive force, such as ion exchange (Equation 8) or/and surface precipitation (Equations 9-10); and (2) the electrostatic attraction played an insignificant role in adsorption mechanism. The same result has been reported in other studies (Veneu et al, 2017;Sdiri et al, 2012). Notably, in strong acidic media (pH = 2.0), the reaction between abundant hydrogen (H + ) ions and HCO 3ions spontaneously occurs; as a result, carbon dioxide was formed and escaped from the solution Equation 7.…”

“…However, the precipitation of Cd(OH) 2 was ruled out in this study, which is very consistent with the XRD result (absence of diffraction peaks observed for cadmium hydroxide). Cadmium will be precipitated as Cd(OH) 2 in an alkaline medium (pH soultion > 8.5) (Veneu et al, 2017;Guo et al, 2015). The finial pH solution in this study ranged from 6.13 to 7.33, confirming that the adsorption mechanism did not involve the precipitation of cadmium with hydroxide.…”

“…Similarly, Zhao et al (2016) reported that more than 85% cadmium in the solution was adsorbed onto golden apple snail shells within 5 min. Recently, Veneu et al (2017) found that CaCO 3 -based adsorbent (algae Lithothamnium calcareum) had a strong binding ability to cadmium in solution, with approximately 58% of cadmium being removed within 5 min in the kinetic study.…”