Competitive adsorption of silver and copper ions on bentonite clay

Author(s)

Emanuelle Dantas de Freitas

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Química
• Defense date: 2016-12-02

Examining board members

Melissa Gurgel Adeodato Vieira; Edson Antonio da Silva; Maria Regina Wolf Maciel

• Advisor: Melissa Gurgel Adeodato Vieira; Ambrósio Florêncio de Almeida Neto

Abstract

The removal and recovery of heavy metals from aqueous effluents have attracted increasing attention from researchers. One alternative is the adsorption process, which generates the need of new adsorbents evaluation. In this study, binary solutions of silver and copper were investigated under adsorption process over Verde-lodo bentonite clay. To fulfill this purpose, the kinetic study was performed using solutions with different metals concentrations (mmol/L) and molar fractions of each metal, at environmental pressure and temperature. The adjustment of the kinetic curves over the data obtained was made by the following models: pseudo first order, pseudo second order, intra-particle diffusion, Boyd and mass transfer by external film model. The results showed the highest adsorption capacity of copper, when in presence of silver. Besides, the high ions quantity in solution presented some interference as a high competition for the active sites. Equilibrium study was conducted through adsorption isotherms assays, which confirmed the higher copper adsorption in binary solution with silver and showed different behaviors. Copper adsorption presented low temperature influence, tending to the highest adsorption at high temperatures and silver adsorption was favored at low temperatures. The highest adsorption capacities obtained in assays were 0.110 mmol/g for copper at 60 ºC and 0.090 mmol/g for silver at 20 ºC. Experimental data were adjusted by the following models: competitive Langmuir, modified competitive Langmuir, non-competitive Langmuir and Langmuir-Freundlich. The last one presented the best results. Fixed bed dynamic assays were performed to evaluate the flow rate influence over the efficiency parameters MTZ and %Rem, and the best results were obtained at 3 mL/min. At this flow rate, initial concentration and molar fraction changes were evaluated. The best results were achieved at the highest initial concentration (total initial concentration 2 mmol/L). The profiles obtained showed the highest selectivity of Verde-lodo clay for copper. The maximum removal obtained in the fixed bed was 46.65 % of silver and 48.20 % of copper, considering both metals simultaneously. Furthermore, some assays presented overshoot in case of silver, indicating its ions were replaced by copper ions. Adsorption and desorption cycles were performed using HNO3 as eluent, which proved to be efficient in this purpose. Removal of 89.18 % of silver and 76.10 % of copper were obtained in the first desorption and 67.65 % of copper in the second desorption. The second cycle of adsorption presented overshoot of silver. To evaluate the clay behavior in face of the adsorption process, the adsorbent after adsorption process was characterized and compared to the natural calcined clay characterization. The techniques employed were the X-ray diffraction (DRX), scanning electron microscopy (MEV), mercury porosimetry, helium gas picnometry, nitrogen physisorption through the BET method, thermogravimetry (TG), differential thermal analysis (DTA), spectroscopy in the infrared region (FT-IR) and surface charge determination (pHzpc). The absence of strong changes in structural characteristics of the Verde-lodo clay, before and after the adsorption was verified. Besides, the regenerated clay characterization was accomplished by the techniques DRX, MEV, FT-IR and TG/DTA, which showed imperfections in morphology due to the HNO3, but no changes in crystal structure, functional groups and thermal stability (AU)

• FAPESP's process: 13/25212-0 - Competitive adsorption of silver and copper ions in bentonite clay
• Grantee: Emanuelle Dantas de Freitas
• Support Opportunities: Scholarships in Brazil - Master