Removal of Cadmium (II) Ions from Aqueous Phase by Biosorption on Biological Activated Dates' Pedicels (Kinetic, Equilibrium and Thermodynamic Study)

The preparation of biological activated dates’ pedicels (ADP) adsorbents and its biosorption behaviour of cadmium (II) was the topic of this study. The raw (RDP) and activated (ADP) dates’ pedicels were characterized by SEM, XRF, FTIR and surface area analysis. SEM analysis revealed a heterogeneous structure for ADP and a cellular aspect different from that of RDP, due to the deposit of the bacterial film which has been constituted during the biological treatment of the material. The XRF results show the presence of potassium, calcium in RPD, and sodium in APD which could favour the retention of heavy metals in aqueous solutions by ions exchange. The FT-IR spectra showed that there are different functional groups in adsorbents, which are able to react with metal ions in aqueous solution. Biological pretreatment was carried out in nitrate enriched solution; allowing to enhance the development of denitrifying micro-organisms already existing on the organic support without the need for biomass inoculation. Biological pretreatment allowed the appearance of a bacterial film at the surface of the date pedicel particles, which improved their biosorption capacity. Indeed, the biosorption yields of cadmium (II) ions obtained at equilibrium (60 min) were 70.4 and 57.4% for ADP and RDP, respectively. The experimental data were analyzed by the Langmuir and Freundlich isotherm models and the model constants were evaluated. The maximum biosorption capacity as calculated using the Langmuir isotherm model was 10.75 mg g-1 which is greater than that of commercial and granular activated carbon. The kinetic data obtained at different initial cadmium concentrations and different temperatures were analyzed using pseudo-second-order and intra-particle diffusion models. The biosorption kinetics followed a pseudo-second-order kinetic model. The biosorption of cadmium ion was endothermic and spontaneous. Elution efficiencies with different concentrations of CaCl2, KCl and NaCl were evaluated. The desorption studies showed the reversibility of biosorption and CaCl2 was the most efficient desorbent for elution and desorption of cadmium from the biosorbant.