Biosorption of Pb (II) on the epidermis of Agave atrovirens by means of microscopy, spectroscopy and image analysis

Agro-industrial waste has been used as heavy metals adsorbent; their effectiveness depends mainly on the functional groups, especially lignocellulosic compounds that provide properties as biosorbents. The aim was to characterize the microstructure and functional groups on the surface of the Agave atrovirens epidermis available to biosorption of Pb (II) in solution and the semi-quantitative evaluation of metal distribution using microscopy and image analysis. The Agave atrovirens epidermis that was used as biosorbent was dried and then crushed. The particle size was 710 μm, with different doses: 0.5, 3.5 and 5.0 g/L; the material was placed in flasks with solution of 100 ppm of Pb (II) at pH 4.0, stirred at 200 rpm at 30 °C for 1 hour. Every 10 minutes, solution samples were taken as follow: the biosorption process, the percentage of Pb (II) adsorbed (determined by Atomic Absorption Spectrophotometer), the characterization of functional groups (performed by Fourier Transform Infrared Spectroscopy), the microstructure (was evaluated by Environmental Scanning Electron Microscopy) and a semi-quantitative analysis of Pb (II) (was made using an Energy Dispersive X-ray Spectroscopy). The percentage of Pb (II) adsorption varied from 3 to 65 %, according to the adsorbent dosification, when the biosorbent dose was higher provided a greater amount of functional groups capable to adsorb Pb (II). Carbonyl groups (about 1670 cm ^-1) and hydroxyl (about 3400 cm-1) were found, which may be responsible for metal biosorption. Agroindustrial waste as Agave is an interesting material to biosorption for removing heavy metal contaminants in effluents and offers the possibility of metal recovery.