Influence of the Cd 2+ Ions on the Crystal Violet Dye Adsorption from Aqueous Solutions by Activated Charcoal Obtained from Pine Cones

Aiming to obtain low-cost adsorbents for dyes and metallic ions from wastewaters, this study proposed cheap techniques such as carbonization of pine cones, coming from Romanian forests, using low temperature (500 ℃) in an auto-generated atmosphere and then, activation by using three types of chemicals: NaOH, KOH and H3PO4, respectively and low temperature for thermal treatment (700 ℃). The resulted adsorbents were characterized (by AFM, SEM, EDX, XRD, BET specific surface, porosity, FTIR and surface charge) and tested for removal of crystal violet dye (CV) and cadmium ions (Cd2+) from synthetic mono- or di-solute aqueous solutions. The effects of independent variables such as contact time, adsorbent dosage (0.1–0.2 g/L), initial dye concentration (2.5–20.0 mg/L) on the adsorption capacity of the proposed adsorbents were investigated and discussed correlated with the surface properties. The highest adsorption capacity was evidenced by the sorbent activated with NaOH (71.94 mg . g−1 CV adsorbed from single solute solution). In solutions with (Cd2+: CV)w ratio = 1:1, the presence of Cd2+ ions strongly diminished the CV adsorption with aprox. 28%. Cd2+ seems to be a redoubtable competitor for CV in the adsorption process. In case of adsorption from di-solute systems with (Cd2+: CV)w ratio = 540:5, the qmax for CV was 24.8 mg . g−1, while for Cd2+ cations, was 370.37 mg . g−1, for the same adsorbent, activated with NaOH. The adsorption processes follow the Langmuir model for all the tested species and the process kinetic is well described by the pseudo-second-order reaction model. Considerations on the sorption mechanism were made based on the experimental data.