Characterization of adsorption processes for the removal of metal ions from waste effluents using biosorbents and graphene-based sorbents. Studies in Batch and in fixed-bed column

Ben Amar, Marwa
Wastewater discharged from industrial and agricultural activities contains relatively large amounts of toxic metal ions, especially including Cd(II), Cu(II), Pb (II), and Cr(VI). The removal of these pollutants is of great interest from both health and environmental perspectives. Arsenic contamination, generally associated with the geochemical environment, is a global threat due to its acute toxicity and carcinogenicity. The oxidation of different mineral species due to the redox conditions causes arsenic to become soluble and enter into the surrounding environment through drainage water. Conventional technologies for wastewater treatment and water purification such as precipitation, coagulation-flocculation, membrane processes, electrodialysis and ion-exchange are of limited utility due to their high cost, inefficiency in removing low metal concentrations, and sometimes also because they can generate large volumes of sludge. Adsorption is an attractive alternative due to its simplicity, its ability to remove trace amounts of metal ions, low cost, short operation time, and for the capacity for the material to be reused. Sorption processes are based on physical adsorption, chemical adsorption and ion exchange mechanisms. Among the different sorbent materials, activated carbon is the most widely used despite its high initial cost together with its regeneration costs. In the search for highly efficient, eco-friendly and economic adsorbents, agricultural waste and by-products from forest industries, including tea waste, coffee, hulls and shells from different nuts, sawdust, barks, cellulosic and lignocellulosic waste, corncobs, rice hulls, olive cake, fruit peels, sugar beet pulp, palm fruit bunch, maize leaves, among others, have been evaluated as biosorbents. They all typically have a good capacity to adsorb metal ions due to their porous structure and the fact that they have having carboxyl, hydroxyl, and other functional groups on their surface. The type of functional groups and chemical components of lignocellulosic materials makes them a good alternative adsorbent to treat contaminated effluents. The costs of these treatments will be low if the most suitable locally available biosorbents are used. Hence, in our case, we have evaluated lignocellulosic agroindustrial waste that is available in the Mediterranean region, such as olive stones and pine cones, as efficient biosorbents for the removal of toxic metal ions such as Pb(II), Cu(II), Cd(II) and Cr(VI) ​
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