Clays tailings flocculation using bio-based flocculants from Nannochloropsis gaditana

In copper mining water recirculation is a crucial aspect, with approximately 70% used during the ore processing stage being recirculated. After extraction, the process water has a high concentration of clays, which exert a deleterious effect on mineral concentration, so the industry employs flocculation processes to remove them using chemical flocculants derived from polyacrylamide, which are toxic and persistent in the environment. The development of bio-based flocculants derived from microalgae represents a sustainable alternative for clay removal. Therefore, sedimentation tests were performed using the Jar-test method with Nannochloropsis gaditana to remove kaolinite-type clay. The sedimented flocs were subjected to various analyses, including zeta potential, Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). The zeta potential of N. gaditana is negative in deionized water across a pH ranging between 2 and 11, whereas in seawater only at pH between 7 and 9. Nannochloropsis gaditana was evaluated under different conditions (live cells, boiled cells, wet biomass, and freeze-dried biomass). Live and boiled cells were the most effective in kaolinite removal, as they instantly reduced turbidity to 76 FNU, achieving a sedimentation efficiency close to 97% at pH 7, which favored seawater clarification. Sedimentation efficiency was higher when using 10 g L−1 of live N. gaditana cells compared to the chemical flocculant used as a control. Finally, FT-IR was used to determine the degree of kaolinite absorption on the surface of microalgae, and showed that the presence of carboxylic functional groups and polysaccharide amides on the cell surface favors this interaction.