Biosorption of Technologically Valuable Metal Ions on Algae Wastes: Laboratory Studies and Applicability

Abstract

In the context of a circular economy that recommends the most efficient use of wastes, algae wastes have a huge potential for valorization. In this study, algae wastes obtained after the alkaline extraction of active compounds from two types of marine algae (green algae—Ulva sp. and red algae—Callithamnion sp.) were used as biosorbents to remove metal ions from aqueous effluents. The efficiency of these biosorbents was tested for Zn(II), Cu(II), and Co(II) ions, considered technologically valuable metal ions. The batch monocomponent experiments performed under optimal conditions (pH = 5.0; 4.0 g biosorbent/L; 22 ± 1 °C) showed that more than 75% of the metal ions were removed when their initial concentration was less than 1.25 mmol/L. The experimental data were well described by the pseudo-second-order kinetic model and Langmuir isotherm model. The high values obtained for the maximum biosorption capacity (qmax: Cu(II) (0.52 mmol/g) > Zn(II) (0.41 mmol/g) > Co(II) (0.39 mmol/g) for G-AWB, and qmax: Cu(II) (1.78 mmol/g) > Zn(II) (1.72 mmol/g) > Co(II) (1.66 mmol/g) for R-AWB) show the potential use of these biosorbents to remove such technologically valuable metal ions from industrial wastewater. This possibility was tested using industrial wastewater samples obtained from the metal coating industry. The quantitative removal (>91%) of Zn(II), Cu(II), and Co(II) ions was obtained when their initial concentration was adjusted to 50 mg/L. In addition, the rapid and efficient desorption of these metal ions from loaded biosorbents by simple treatment with small volumes of HNO3 (10−1 mol/L) further emphasizes the possibility of their recovery and reuse in the technological circuit. The results included in this study indicate that algae wastes have the potential to be used in industrial effluent decontamination processes and open new perspectives for the implementation of circular economy principles.