Adsorção dos íons de cobre usando pó da palha da carnaúba e bentonita: estudo cinético, termodinâmico e de equilíbrio

Abstract

The toxicity, non-biodegradability and bioaccumulation presented by industrial effluents containing heavy metals has become a deep environmental concern. Given this fact, there are already several treatment techniques to remove heavy metals from industrial effluents, but they have some disadvantages, such as inefficiency in treatment, high cost, use of chemicals in the treatment and problems with the disposal of waste. sludge formed. From this finding, there has been research with materials that can be used to overcome these deficiencies, presenting satisfactory results in the removal of heavy metals in the treatment of industrial effluents. Carnauba straw dust and bentonite in their natural and modified forms were used as adsorbents to remove copper in aqueous solution. The experiments were performed from the evaluation of the influence of the variables pH, contact time, adsorbent mass, initial metal concentration, effects of binders and co-ions on the metal removal efficiency and adsorbent regeneration capacity. From the experimental data, it was possible the kinetic, thermodynamic and equilibrium study of the adsorption process. FTIR, BET, FRX, XRD and Zeta Potential analyzes were also performed to characterize the materials used in the adsorption process and to ensure the efficiency of their modifications. In the kinetic study, all adsorbents adjusted to the pseudo second order kinetic model and it was observed that, in general, the adsorbents used presented a fast kinetics, in which carnauba straw powder (CSP), bentonite treated carnauba straw powder (BTCSP), natural bentonite (NB), sodium bentonite (SB) reached equilibrium time. 5, 25, 100 and 100 minutes, respectively. The equilibrium study showed that the experimental data of the adsorbents studied supported the Langmuir model. The maximum adsorption capacity of CSP, BTCSP, NB, SB were 8.48, 21.97, 12.92 and 24.51 mg/g, respectively. Studies showed that although the materials had a low surface area, they had other positive characteristics, such as CSP and BTCSP with functional groups (hydroxyl and carbonyl) with good interaction capacity, and NB and SB with good exchange capacity cationic. The thermodynamic parameters obtained in the adsorption experiments showed that for BTCSP, NB, SB the process was non-spontaneous and endothermic, whereas for CSP the process was spontaneous and exothermic. In the desorption and regeneration study of natural and sodium bentonites, 4 cycles of dsorption and desorption were required. The desorption efficiency of copper ions using sodium and natural clay decreased from the first to the last cycle from 69.47% to 41.33% and from 48.36% to 22.46%, respectively.