Optimization of the Ni tailings flocculation process by applying central composite design and mathematical modeling using chitosan and humic acid

This study optimizes the flocculation process of a nickel tailings sample using chitosan and humic acid (HA) as natural flocculants. A central composite design was used, together with mathematical modeling, to identify the most efficient and sustainable conditions for turbidity removal. The optimal dosages of chitosan and HA were 24.9 g/t and 6.3 g/t, respectively, achieving efficient removal at solids concentrations of up to 2.15%. Flocculant adsorption was evaluated at pH 7, with limited adsorption capacity at higher solids concentrations. Surface charge analysis for particles smaller than 20 μm revealed a net negative charge, favoring flocculation, with distinct zero-charge (isoelectric) points for chitosan and HA across different experimental conditions. Mathematical models indicated that variables such as surface charge, stirring speed, solids concentration, and the presence of cations (Ca, Mg, Na, K) significantly influenced the efficiency of the process, achieving a turbidity reduction of less than 40 NTU in accordance with Brazilian environmental standards.