ORANGE PEEL WASTE AS SUSTAINABLE MATERIALS FOR POLLUTANTS REMOVAL FROM AQUEOUS SOLUTIONS

World production of oranges is estimated at 75 million tons per year, and it is approximated that about 15 million tons of orange peel waste (OP) were generated in the world increasing every year. Heavy metal ions are among the most released contaminants, and for this reason they are of particular concern. Organic dyes, in addition, are coloured substances that tend to be very stable and hardly biodegradable, contributing significantly to water pollution. The widespread presence of heavy metals and synthetic dyes in water bodies, their bioaccumulation, potential toxicity and negative health effects have made the study of their environmental fate very important. The chemical compounds composing orange peel (OP) waste contain different functional groups, such as carboxyl and hydroxyl, making OP a potential adsorbent material for the removal of heavy metals and dyes from aqueous solutions. In this study, Citrus sinensis peel wastes were valorised, to obtain materials usable for the adsorption of heavy metal ions and organic dyes, showing promising results. For this purpose, OPs were cut up into small pieces, washed with water and dried in the oven at 40°C. OPs were successively saponified with NaOH to cleave ester bonds on the surface of peels to generate more hydroxyl groups, followed by thorough washing with deionized water to remove excess base. Washed peels were sonicated in 2-propanol to extract soluble organic compounds and then filtered, washed with water, dried, and chemically/morphologically characterized. This contribution reports preliminary results on the application of the OP as new absorbent materials in water samples containing a mix of heavy metal ions showing a selective sequestration of lead ions; OP materials were also applied for the absorption of several cationic dyes. The equilibrium and kinetic properties were explored for the absorption of both types of pollutants. Owing to the multifunctional characteristics of biopeels, adsorption of these pollutants is facilitated by a combination of processes, involving ion exchange, complexation, and electrostatic interaction.