Abstract
The valorization of algal biomass and bi-valve shells allows synthesizing, in the presence of urea, a sorbent highly efficient for methylene blue (MB) sorption (sorption capacity: 1.5 mmol MB g(-1) at pH 5.8). The dyefunctionalized sorbent shows enhanced sorption properties for Cr(VI) recovery at pH 3. The sorption isotherm is fitted by the Langmuir equation: maximum sorption capacity reaches 8.53 mmol Cr g(-1) (for MB-loading: 1.5 mmol g(-1)). Different mechanisms may be involved such as the electrostatic attraction of anionic species, chelation on reactive groups, reduction of Cr(VI) into Cr(III). Under selected experimental conditions, the sorption is achieved within less than 60 m. The kinetic profiles are controlled by the pseudo-second order rate equation. Alkaline NaCl solutions effciently desorb chromate while maintaining a good stability of the dye (negligible release). Therefore, the sorption and desorption performances are maintained remarkably stable for at least 5 sorption/desorption cycles. The sorbent is successfully applied for chromate recovery from Cr(VI)-spiked solutions (tap water and wastewater from petrochemical unit) with limited loss in sorption performances. The sorbent is characterized by BET, TGA, FTIR, SEM, EDX and zetametry to help in the understanding of binding mechanisms and sorption performances.