Effect of ionic strength and coexisting ions on the biosorption of divalent nickel by the acorn shell of the oak quercus crassipes humb. & bonpl.

This study investigated the effect of ionic strength and background electrolytes on the biosorption of Ni²⁺ from aqueous solutions by the acorn shell of Quercus crassipes Humb. & Bonpl. (QCS). A NaCl ionic strength of 0.2 mM was established to have no effect on the Ni²⁺ biosorption and the biosorption capacity of the heavy metal decreased as the ionic strength increased from 2 to 2000 mM. The background electrolytes (KCl, NaNO₃, Na₂SO₄, CaCl₂, MgSO_4, and MgCl₂) had no adverse effects on the biosorption of Ni²⁺ at a concentration of 0.2 mM. However, at background electrolyte concentrations of 2 and 20 mM, divalent cations (Ca²⁺ and Mg²⁺) had greater negative effects on the biosorption of Ni²⁺ compared to the monovalent cations (Na⁺ and K⁺). Additionally, the SO₄²⁻ and Cl⁻ anions affected the biosorption of Ni²⁺. The fractional power, Elovich, and pseudo-second order models represented the kinetic processes of the biosorption of Ni²⁺ adequately. The results show that QCS can be a promising and low-cost biosorbent for removing Ni²⁺ ions from aqueous solutions containing various types of impurities with different concentrations.