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
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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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