RESUMO
In this study, four Brazilian clays (Bofe, Verde-lodo, commercial Fluidgel, and expanded commercial vermiculite) were evaluated for their adsorptive capacity and removal percentage in relation to different toxic metals (Ni2+, Cd2+, Zn2+, and Cu2+). The best results were obtained by expanded vermiculite, with cadmium removal reaching values of 95%. The most promising clay was modified by the sodification process, and the metal cadmium was used to evaluate the ion exchange process. The clays expanded vermiculite (EV) and VNa-sodified vermiculite were evaluated by equilibrium study at 25, 35, and 45 °C. At 25 °C, EV obtained a maximum adsorption capacity of 0.368 mmol/g and sodified vermiculite 0.480 mmol/g, which represents an improvement of 30.4% in modified clay capacity. At 45 °C, the sodified vermiculite reached 0.970 mmol/g adsorption capacity. The Langmuir, Redlich-Peterson Freundlich, and Dubinin-Raduskevich models were adjusted to the results. Langmuir provided the best fit among the models. The thermodynamic quantities (ΔS, ΔH, and ΔG) demonstrated that the process is spontaneous and endothermic and the metal is captured by physisorption and chemisorption in the studied temperature range. For the ion exchange equilibrium, the binary Langmuir and binary Langmuir-Freundlich models were adjusted to the expanded vermiculite and sodified vermiculite isotherms, respectively. Both models were predictive. Thermal analysis indicated good heat resistance even after material modification. The apparent and real densities demonstrated that after each treatment or contamination, the clayey material undergoes contraction in its structure. An improved efficiency of the adsorbent was found after sodification.
Assuntos
Silicatos de Alumínio , Argila , Termodinâmica , Adsorção , Argila/química , Brasil , Troca Iônica , Silicatos de Alumínio/química , Poluentes Químicos da Água/química , Metais/químicaRESUMO
Critical metals such as rare earths are essential for important industrial applications and for producing high-tech materials. Currently, the development of alternative and non-conventional biomaterials has gained significant interest. This work investigated the use of crosslinked sericin-alginate-based natural polymeric particles for the removal of rare earths from water. Affinity tests showed that sericin-alginate/polyethylene glycol diglycidyl ether had the highest potential for capturing europium (0.258 mmol/g and 94.33%) and erbium (0.259 mmol/g and 94.55%). Next, erbium was selected based on the affinity with sericin-alginate/polyethylene glycol diglycidyl to investigate the effect of dose/pH, biosorption kinetics, isothermal equilibrium, desorption/reuse, and selectivity. The effect of dose and pH showed that 8.0 g/L (95.91%) and pH 5.0 (97.53%) were more efficient in capturing erbium. The biosorption kinetics showed that the equilibration time was reached within 210 min. The PSO and EMTR models effectively represented the kinetics data. The isothermal equilibrium revealed that the maximum uptake capacity for erbium was 0.641 mmol/g. The isothermal curves better fit the Dubinin-Radushkevich (55 °C) and Langmuir (25 and 40 °C) models. Thermodynamic quantitates indicated that erbium uptake was spontaneous, governed by entropic changes, and endothermic. The recovery of Er3+ was greater than 98% and the reuse of the eluent in the cycles enriched the Er3+ load 10-times (1.0 to 9.91 mmol/L). The beads also showed better performance for capturing Er3+ and Eu3+ with other coexisting ions. Characterization analyzes revealed the ion exchange mechanism between Ca2+/Er3+ prevailed in the Er3+ removal. Thus, the results pointed out that crosslinked sericin-alginate can be used as an alternative and promising biosorbent to remove and recover rare earths.
RESUMO
The use of mineral clays as alternative adsorbent has received attention due to their physicochemical characteristics, superficial negative charge, abundance of vermiculite (especially in Brazil), low cost, and chemical composition, which allows the material modification to increase the adsorptive capacity. This manuscript evaluated the use of expanded vermiculite (EV) and sodium-modified vermiculite (VNa) in the adsorption and ion exchange of Cd2+ ions. The sodification was successfully carried out making the ion exchange capacity greater in the modified clay, confirmed by EDX, cation exchange capacity (CEC), DRX, and FTIR analysis. The CEC was 210 and 233 mEq/100 g for the EV and VNa, respectively, with 97.8% exchangeable ion (Na+) in the VNa. FTIR spectra showed small variations in the groups related to ion exchange and XRD analysis indicated changes in the distance of the layers with loss of crystallinity after clay modification, which was recovered after cadmium adsorption. The kinetics became faster with an equilibrium time of 10 min for VNa and 45 min for EV. Cd2+ removal by vermiculite above 99% was achieved. Pseudo-second order model best described the kinetics, in which the resistance to mass transfer in external film is the limiting step of the process and, once this resistance is overcome, the ion exchange happens quickly. Despite the decrease in surface area after sodification, the adsorptive capacity increased 158% in the sodified adsorbent, from 0.107 mmol/g for EV to 0.276 mmol/g for VNa, under the evaluated conditions.