Single and binary equilibrium studies for Ni²⁺ and Zn²⁺ biosorption onto lemna gibba from aqueous solutions

The biosorption ability of Lemna gibba for removing Ni²⁺ and Zn²⁺ ions in aqueous batch systems, both individually and simultaneously, was examined. The influences of solution pH and initial single and binary metal concentrations on equilibrium Ni²⁺ and Zn²⁺ biosorption was explored. The optimal solution pH for Ni²⁺ and Zn²⁺ biosorption was 6.0, for both the single and binary metal systems. Ni²⁺ and Zn²⁺ biosorption capacities increased with increasing initial metal concentrations. The presence of Zn²⁺ ions more adversely affected the biosorption of Ni²⁺ ions in the binary metal systems than vice versa. The single and binary biosorption isotherms of Ni²⁺ and Zn²⁺ revealed that L. gibba's affinity for Zn²⁺ ions was higher than that for Ni²⁺ ions. The Redlich-Peterson and Freundlich isotherm models fit well to the experimental equilibrium data of Ni²⁺ ions, whereas Redlich-Peterson and Langmuir models better described the equilibrium data of Zn²⁺ ions in single metal systems. The modified Sips isotherm model best fit the competitive biosorption data of Ni²⁺-Zn²⁺ on L. gibba. FTIR analyses suggest the involvement of hemicellulose and cellulose in the biosorption of Ni²⁺ and Zn²⁺. The presence of Ni²⁺ and Zn²⁺ on the L. gibba surface was validated by SEM-EDX.