Use of centaurea benedicta root powder as green adsorbent for Ni(II) and Cd(II) removal from aqueous solutions

This study investigated the potential of Centaurea benedicta root (CBR) as a natural adsorbent for removing nickel (Ni) and cadmium (Cd) from aqueous solutions. Known for its rich phytochemical composition, including polyphenols and cnicin, Centaurea benedicta has been little explored beyond medicinal uses. It is widespread in the Mediterranean area. In the present work, we collected Centaurea benedicta plants from the northern region of Algeria and the extracted root was used to remove Ni and Cd from aqueous solution. The adsorption capacity was tested as function of contact time, pH, and initial metal concentration in both single-ion and binary systems. Adsorption kinetics were modeled using pseudo-first-order (PFO) and pseudo-second-order (PSO) equations, while equilibrium data were fitted with Langmuir and Freundlich isotherms. Statistical and residual analyses were used to evaluate model adequacy. The PFO model best described Cd adsorption, whereas Ni adsorption data were not well fitted by either kinetic model. Equilibrium data followed the Langmuir model more closely, with some deviation toward the Freundlich model, indicating surface heterogeneity. The Langmuir-derived maximum adsorption capacities were 15.6 mg/g for Cd and 8.72 mg/g for Ni. Adsorption increased with increasing pH, with the highest adsorption capacity observed at pH 7 for both metals. FTIR analysis highlighted the role of oxygen-containing functional groups on the CBR surface in the adsorption process, particularly for Cd. Electrostatic interactions may also contribute to metal ions adsorption. In binary systems, the adsorption capacity of both Cd and Ni was noticeably reduced. This competition may be attributed to the combined influence of the intrinsic physicochemical properties of the metal ions and the heterogeneous nature of the CBR surface. Overall, the CBR showed promising potential capacity to absorb potentially toxic metals from contaminated water.